Physiological Psychology Cell Fundamentals

Cell Fundamentals
• All cells share common features-They have DNA as
genetic material, have a cellular boundary (plasma
membrane) use the same processes to make proteins
(have cytoplasm) and follow the same basic
metabolic principles as other cells (proteins built at
ribosomes) but still cells are very varied (size, role
they serve)
• Eukaryotic have a separate nucleus with DNA and
organelles in enclosed structures vs. Prokaryotic cells
with no nucleus, organelles not contained in a
membrane and smaller than eukaryotic cells
Proteins are the main workers of
the cell and all cells need to make them

Programmed cell death• Cell death can occur either by injury due to toxic exposure, by
mechanical damage, or by an orderly process called programmed cell
death or apoptosis. Programmed cell death occurs during development
as the organism is pruning away unwanted, excess cells. It also occurs
during infections with viruses, cancer therapy, or in the immune
response to illness. The process of programmed cell death is another
function of mitochondria.
• Normally, ATP production is coupled to oxygen consumption. During
abnormal states such as fever, cancer, or stroke, or when dysfunction
occurs within the mitochondria, more oxygen is consumed or required
than is actually used to make ATP. The mitochondria become partially
“uncoupled” and produce highly reactive oxygen species called free
radicals. When the production of free radicals overwhelms the
mitochondria’s ability to “detoxify” them, the excess free radicals
damage mitochondrial function by changing the mitochondrial DNA,
proteins, and membranes. As this process continues, it can induce the
cell to undergo apoptosis. Abnormal cell death due to mitochondrial

Fluid Mosaic Model• The fluid-mosaic model describes the
plasma membrane of animal cells. The
plasma membrane that surrounds these
cells has two layers (a bilayer) of
phospholipids
(fats with phosphorous attached)
• Each phospholipid molecule has a head that is attracted to
water (hydrophilic: hydro = water; philic = loving) and a tail
that repels water (hydrophobic: hydro = water; phobic =
fearing). Both layers of the plasma membrane have the
hydrophilic heads pointing toward the outside; the
hydrophobic tails form the inside of the bilayer
• Proteins and substances such as cholesterol become
embedded in the bilayer, giving the membrane the look of
a mosaic. Because the plasma membrane has the consistency
of vegetable oil at body temperature, the proteins and other substances are able to
move across it. That’s why the plasma membrane is described using the fluid-mosaic

Fluid Mosaic Model
The molecules that are
embedded in the plasma
membrane also serve a
purpose. For example,
the cholesterol that is
stuck in there makes
the membrane more stable
and prevents it from
solidifying when your
your body temperature is low
Carbohydrate Polymers may attach to parts of the membrane, forming
Glycolipids when attach to Phospholipid Molecules and
Glycoproteins when they attach to proteins. Both
Glycolipids and Glycoproteins can act as Cell Receptor
Sites. Hormones may bind to them, as may drugs, to
instigate a response within the cell. They may also be involved in
Cell Signalling in the Immune System. Phospholipid

Membrane Components
• Some Intrinsic Proteins are Channel Proteins. These are Transport Proteins that allow the
movement of molecules that are normally too large or too Hydrophilic to pass through the
membrane by forming a tube-like structure that goes through the whole membrane.
• Other Transport Proteins are Carrier Proteins. These use energy in the form of ATP to actively
move substances across the membrane. (For example, ions in the soil are actively transported in
the root hair cells of plants).
• Enzymes and Coenzymes may be attached to part of the membrane in order to carry out
Metabolic Reactions. Mitochondria have infoldings of the membrane (called Cristae) containing
Enzymes which are partly responsible for Aerobic Respiration.
• The Steroid Molecule Cholesterol gives the Plasma Membrane in some Eukaryotic Cells stability
by reducing the fluidity and making the Bilayer more complete.

Cell Membranes
The membrane that surrounds a cell is made up of proteins and lipids.
Depending on the membrane’s location and role in the body, lipids can
make up anywhere from 20 to 80 percent of the membrane, with the
remainder being proteins. Cholesterol, which is not found in plant cells,
is a type of lipid that helps stiffen the membrane. Image Credit: National
Institute of General Medical Sciences

The effect of Omega-3 fatty acids on cell membrane
Part of the break down products for
omega-3 fatty acids are taken up into
the cell membrane and since these are
PUFA (polyunsaturated fats) they
have a double bond at every
third carbon (omega-3) which
kinks the long
hydrocarbon chain
(saturated fats have no double bonds
and the tail is straight) The kinked tail
increases membrane fluidity improving cell communication
Unsaturated fats assume a particular geometry that prevents the
molecules from packing as efficiently as they do in saturated molecules.

Membrane lipids: where they are and how they behave Nat Rev Mol Cell Biol. 2008
Feb; 9(2): 112–124 Van Meer et al.
Lipids fulfil three general functions. First, because of their relatively reduced
state, lipids are used for energy storage, (principally as triacylglycerol esters and steryl esters,
in lipid droplets. These function primarily as anhydrous reservoirs for the efficient storage of caloric reserves
and as caches of fatty acid and sterol components that are needed for membrane biogenesis). Second, the
matrix of cellular membranes is formed by polar lipids, which consist of a
hydrophobic and a hydrophilic portion. The propensity of the hydrophobic
moieties to self-associate (entropically driven by water), and the tendency of the
hydrophilic moieties to interact with aqueous environments and with each other,
is the physical basis of the spontaneous formation of membranes. This same
principle is recapitulated within the cell to produce discrete organelles. This
compartmentalization enables segregation of specific chemical reactions for the
purposes of increased biochemical efficiency and restricted dissemination of
reaction products. In addition to the barrier function, lipids provide membranes
with the potential for budding, tubulation, fission and fusion, characteristics
that are essential for cell division, biological reproduction and intracellular
membrane trafficking. Lipids also allow particular proteins in membranes to
aggregate, and others to disperse. Finally, lipids can act as first and second
messengers in signal transduction and molecular recognition processes.In
addition, some lipids function to define membrane domains, which recruit proteins from the cytosol that
subsequently organize secondary signalling or effector complexes

Energy Production
• The main function of the mitochondrion is
the production of energy, in the form of
adenosine triphosphate (ATP). The cell uses
this energy to perform the specific work
necessary for cell survival and function.
https://www.youtube.com/watch?v=XI8m6o0gXDY

Energy Production
• The raw materials used to generate ATP are the foods that we eat,
or tissues within the body that are broken down in a process
called catabolism. The breaking down of food into simpler
molecules such as carbohydrates, fats, and protein is called
metabolism. These molecules are then transferred into the
mitochondria, where further processing occurs. The reactions
within the mitochondria produce specific molecules that can have
their electrical charges separated within the inner mitochondrial
membrane. These charged molecules are processed within the
five electron transport chain complexes to finally combine with
oxygen to make ATP. The process of the charged substances
combining with oxygen is called oxidation, while the chemical
reaction making ATP is called phosphorylation. The overall
process is called oxidative phosphorylation. The product
produced by this process is ATP.

Cell-specific functions
• Other functions of mitochondria are related to the cell
type in which they are found. Mitochondria are
involved in building, breaking down, and recycling
products needed for proper cell functioning. For
example, some of the building blocks of DNA and RNA
occur within the mitochondria. Mitochondria are also
involved in making parts of blood and hormones such
as estrogen and testosterone. They are required for
cholesterol metabolism, neurotransmitter metabolism,
and detoxification of ammonia in the urea cycle. Thus,
if mitochondria do not function properly, not only
energy production but also cell-specific products needed
for normal cell functioning will be affected.

Cell Types
• Neurons communication-receive transmit
messages Many dendrites One axon
• Glia cells- remove waste materials, build
myelin sheaths, guide the growth of axons
and dendrites

Nerve Cells -Neurons
Resting Potential The sodium-potassium pump in the
neuron cell membrane uses the energy of ATP to pump Na+
out of the cell and, at the same time, to pump K+ in. This
ongoing process maintains resting potential

Resting Potential
Resting membrane potential needs to be maintained by the Na+/K+
pump that is constantly pumping Na+ out and K+ in
Resting Potential The sodium-potassium pump in the neuron cell
membrane uses the energy of ATP to pump Na+ out of the cell and, at
the same time, to pump K+ in. This ongoing process maintains resting
potential

Passive vs. Active Transport
Simple diffusion moves molecules from an area of higher concentration to
an area of lower concentration without an input of energy. Facilitated
diffusion follows the same rules as regular diffusion (higher to lower
concentration and no energy input), but uses protein carrier molecules to
allow substances that are fat soluble to diffuse through the cell membrane.

Scale of Measurement milli-micron-
nano-angstrom

Two Causes of Resting Potential
• The sodium/potassium ATPase. This pump pushes
only two potassium ions (K+) into the cell for
every three sodium ions (Na+) it pumps out of the
cell so its activity results in a net loss of positive
charges within the cell.
• Some potassium channels in the plasma membrane
are "leaky" allowing a slow facilitated diffusion of
K+ out of the cell (red arrow).

Generating an Action Potential
• The first step in the generation of an action potential is to
depolarize the cell by injecting current into the axon. This will
partially depolarize the cell membrane, causing it to become less
negative and this change in membrane potential triggers voltage
gated Na+ to open. Na+ ions are now free to pass through this
channel, resulting in a relatively massive influx of Na+ inside
the axon. Since the membrane is now overwhelmingly
permeable to Na+ the membrane potential at the top of the spike
will be driven close to the Na+ Nernst potential of 55+mV.
Voltage gated K+ channels also open as a response to
depolarization but they only do so after the opening of the Na+
channels allowing a relatively large amount of K+ to leave the
axon. As the voltage gated K+ channels open, the voltage gated
Na+ channels now close preventing additional Na+ from
entering the axon. So much positive charged K+ leaves the axon
under these conditions that the membrane potential temporarily
becomes hyperpolarized at a value of -64mV. Voltage gated
channels are now closed and the membrane potential had
returned to its normal resting potential.

Transmission
• When a nerve signal is sent by the nervous system, the
dendrites receive the signal. The axon then transmits the
nerve signal to the axon terminals which synapse with
dendrites or other tissues such as a muscle. (Refer to the
Figure below)
There are two types of axons, myelinated and
unmyelinated. Unlike unmyelinated axons, myelinated
axons have a sheath of fatty tissue called myelin wrapped
around them. There are breaks in the myelin called Nodes
of Ranviers which allow the nerve signal to jump from
node to node. This causes the nerve signal to be
transmitted faster.

Sodium Ions ( ) are at different concentrations outside (top) and inside
(bottom) of the nerve cell. This maintains the resting voltage at -90
millivolts (mV). The inside is negative relative to the outside because
sodium ions are positively charged and there's more of the positive
charges on the outside. Please note that this is a simplified version of the
events that lead to an action potential. Other ions and processes are
involved, but this explanation covers most of the effect.

Types of Reactions
• Graded Potential- IPSPs, EPSP
• Action Potentials
http://www.stolaf.edu/people/giannini/flashanimat/transport/second
ary%20active%20transport.swf

Excitation
Excitable Cells
Conduct action potentials along entire cell membrane
In humans, nerves, skeletal and cardiac muscle cells
All possess voltage-gated ion channels
Channels that change between open/closed states as Vm changes
Voltage-gated ion channels:
Open <---> Closed states determined by voltage difference across
membrane (Vm)
Threshold: Closed state often referred to as channel inactivation
Has a voltage sensor region
Inactivation region

Graded Potential
Review Graded Potential
• Variable amplitude
• Variable duration
• Can be summed
• Hyper- or depolarization
• Decremental; not propagated; decreased amplitude as it passes
along a membrane

Action Potential
• propagation

Action Potential
• Action Potential
• All or None (threshold)
• One direction (dendrites to terminal)
• Refractory period
• Propagated (non-decremental)

Chemical Transmission
• The greater the surface area of the dendrites the
more information it can receive
• Neurons differ from other cells based on their
shape (which is related to their function)

Pre-Post Synaptic Transmission

Ionic vs. Metabotropic Transmission
• Ionic transmission- Flow of ions effects change by
direct action on receptor proteins (fast action)
• Metabotropic Transmission Second messengers
exert their effects directly and indirectly by
attaching themselves to proteins and causing a
conformational change. An example of a direct
effect is the protein conformational change due to
calcium in muscle which leads to muscle
contraction.
• Neurons often release several neurotransmitters and
may respond to many neurotransmitters

Ligand ionotropic vs metabotropic receptors
• G protein-coupled receptors (GPCRs),
constitute a large protein family of
receptors that sense molecules outside
the cell and activate inside signal
transduction pathways and, ultimately,
cellular responses. When a ligand binds
to the GPCR it causes a conformational
change in the GPCR. The GPCR can then activate an
associated G-protein by exchanging its bound GDP for a GTP. The G-
protein's α subunit, together with the bound GTP,
can then dissociate
from the β and γ subunits
to further
affect
intracellular signaling
proteins or target
functional proteins
directly

First vs. Second Messengers
• The term second messenger refers to a molecule in a cell
that communicates information or change throughout the
cell. A first messenger would be a molecule (usually) that
communicates information or change from one cell or cell
group to another, like a hormone or neurotransmitter.
• First messengers are outside the cell, whereas second
messengers are inside the cell. First messengers attach
themselves to receptors on the outside of cell membranes
and begin a "cascade" of events that lead to the release of
second messengers inside of cells.

Second Messenger Systems
• The second messenger cyclic Adenosine MonoPhosphate
(cAMP) is formed from Adenosine TriPhosphate (ATP) by the
enzyme adenylate cyclase. ATP is the molecule that provides
cells with the energy they require to function. Adenylate cyclase
serves to amplify the signal from the first messenger, because
once activated it can convert many ATP molecules into cAMP
second-messenger molecules.
• The other prominent second messengers are cyclic Guanosine
TriPhosphate (cGTP), inositol triphosphate, DiAcylGlycerol
(DAG) and calcium ion. cGMP acts as a second messenger in
the retina and in the Purkinje cells of the cerebellum. Calcium
usually acts as a second messenger when its ion is attached to
the protein calmodulin.
• http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3579514/

Distinct modes of dopamine and GABA release in a dual transmitter neuron-
Maria Borisovska et al. J Neurosci. Jan 30, 2013; 33(5): 1790–1796.
• We now know of a surprising number of cases where single neurons contain
multiple neurotransmitters. Neurons that contain a fast-acting
neurotransmitter such as glutamate or GABA, and a modulatory transmitter
such as dopamine are a particularly interesting case because they presumably
serve dual signaling functions. The olfactory bulb contains a large population
of GABA and dopamine-containing neurons, which have been implicated in
normal olfaction as well as in Parkinson’s disease. Yet, they have been
classified as non-exocytotic catecholamine neurons because of the apparent
lack of vesicular monoamine transporters. Thus we examined how dopamine
is stored and released from tyrosine-hydroxylase-positive-GFP (TH+-GFP)
mouse periglomerular neurons in vitro. TH+ cells expressed both VMAT2
and VGAT, consistent with vesicular storage of both dopamine and GABA.
Carbon fiber amperometry revealed that release of dopamine was quantal and
calcium-dependent, but quantal size was much less than expected for large
dense core vesicles, suggesting that release originated from EM-identified
small clear vesicles. A single action potential in a TH+ neuron evoked a brief
GABA synaptic current whereas evoked dopamine release was asynchronous,
lasting for tens of seconds. Our data suggests that dopamine and GABA serve
temporally distinct roles in these dual transmitter neurons

Blood Brain Barrier
• Glucose crosses the BBB and therefore is
the primary source of energy
• Glucose does not need insulin to enter the
BBB (as it does in other cells)
• Other sugars are not primary energy sources
(e.g. Fructose)

Regulation of Cerebral Blood Flow
• Three aspects of CBF regulation
• Cerebral autoregulation- refers to process by which
cerebral arterioles maintain a constant blood flow
during changing cerebral perfusion pressure (CPP)
• Flow-metabolism coupling- refers to the brains
ability to vary blood flow to match metabolic
activity.
• Neurogenic regulation-refers to extrinsic factors
(nerves and neurotransmitters outside of the brain
parenchyma-comprises the functional parts of an
organ and in plants) and intrinsic factors (nerves and
neurotransmitters deep within the brain

Descriptive Terminology of Nervous System
• DORSAL VENTRAL
• ANTERIOR POSTERIOR
• SUPERIOR INFERIOR
• LATERAL MEDIAL
• PROXIMAL DISTAL
• IPSILATERAL CONTRALATERAL
• PLANES
• CORONAL SAGITTAL HORIZONTAL
• GYRUS SULCUS FISSURE

Descriptive Terminology of Nervous System
• Tract a set of neurons within the CNS (AKA
projection)
• GANGLION-cluster of neuron cell bodies (usually
outside of CNS
• Gray matter cell bodies + dendrites
• White matter myelinated axons
•

CNS and PNS
• The nervous system In most animals the nervous system consists of
two parts, central and peripheral. The central nervous system of
vertebrates (such as humans) contains the brain, spinal cord, and
retina.
• The peripheral nervous system consists of sensory neurons, clusters of
neurons called ganglia, and nerves connecting them to each other and
to the central nervous system. These regions are all interconnected by
means of complex neural pathways
• The spinal cord (within the CNS) a segmented structure which
communicates with all the sense organs and muscles except those of
the head The cell bodies of the sensory neurons are in clusters of
neurons outside the spinal cord (dorsal root ganglion)
• Bell-Magendie (1822) Law the commonly accepted principle that the
dorsal roots of spinal nerves contain only afferent or sensory fibers
and that the ventral roots carry only efferent or motor ones. The law is

Autonomic Nervous System
• The autonomic nervous system, or ANS, is responsible for
controlling several body responses which are under the
conscious level and which are mostly involuntary, like
breathing, digestion, sexual arousal, beating of the heart,
and many other biochemical processes. There are two
distinguishable divisions: the parasympathetic and the
sympathetic nervous systems
• Sympathetic axons prepare the organs for fight or flight
(increasing breathing and heart rate, decreasing digestion)
Because the sympathetic ganglia are closely linked they
often act as a single system (in sympathy) with one another
• Sweat glands, adrenal glands, certain muscles that constrict
blood vessels or that erect the hairs of the skin have only
sympathetic not parasympathetic input

Sympathetic -Parasympathetic

ANS-Autonomic Nervous system
Sympathetic - Parasympathetic

• Sympathetic nervous system is a network of nerves
that prepare the organs for vigorous activity (fight or
flight) thoracic-lumbar
• Ganglia are often acting synchronously or together
(in sympathy)
• Sweat glands, adrenal glands, muscles that constrict
blood vessels and muscles that erect the hair on the skin
have only sympathetic not parasympathetic input
• Parasympathetic system facilities vegetative,
nonemergency responses (para- beside) craniosacral

• Parasympathetic system postganglionic axons
release ACh
• Most of the postganglionic synapses of the
Sympathetic nervous system release NE
(norepinephrine)
• Because the two systems use different transmitters
certain drugs excite or inhibit one system or the
other

Lower brain structures
• Hindbrain-posterior part of brain –medulla, just
above the spinal cord could be considered as an
enlarged extension of the cord controls vital
reflexes Damage to the medulla frequently life
threatening. Medulla and pons also contain
Reticular Formation (ascending input arousal
descending motor)
• Pons Most of it appears as a broad anterior bulge
rostral to the medulla. Posteriorly, it consists
mainly of two pairs of thick stalks called cerebellar
peduncles. They connect the cerebellum to the pons
and midbrain

Midbrain Forebrain Structures
• Midbrain Superior and inferior colliculi
• Forebrain most anterior and prominent part of the
mammalian brain. Two hemispheres with outer
portion known as the cerebral cortex- includes
various structures such as
basal ganglia, thalamus,
hypothalamus, hippocampus
pituitary gland (endocrine or
hormone producing) limbic
system (interlinked structures)
ventricle system

Sensation/Proprioception from spinal cord to brain
• Located in the medulla oblongata, the
gracile nucleus is one of the dorsal
column nuclei that participate in the
sensation of fine touch and
proprioception of the lower body (legs
and trunk). It contains second-order
neurons of the dorsal column-medial
lemniscus system, which receive inputs
from sensory neurons of the dorsal root
ganglia and send axons that synapse in
the thalamus. Internal arcuate
fibers are the axons of second order
neurons contained within the gracile and
cuneate nuclei of the medulla oblongata
The medial lemniscus is a pathway in
the brainstem that carries sensory
information from the gracile and

gracile fasiculus
and fasciculus
cuneatus are
ascending tracts,
which carry
received sensory
information up the
spinal cord as part
of the posterior
column-medial
lemniscus
pathwayAdditional
functions of the
fasciculus gracilis
include carrying
deep touch,
vibrational, and
visceral pain
information to the
brain stem

Brain Structures Cerebral Cortex

Cerebral Cortex
• In most mammals the cerebral cortex contains up to
6 separate horizontal layers (laminae) of cell bodies
that are parallel to the surface of the cortex The first
neurons to differentiate migrate to what will become
Layer VI

Ventricular System CSF
• The cerebral ventricles are a series of
interconnected, fluid-filled spaces that lie in the
core of the forebrain and brainstem The presence of
ventricular spaces in the various subdivisions of the
brain reflects the fact that the ventricles are the
adult derivatives of the open space or lumen of the
embryonic neural tube
• The ventricles are filled with cerebrospinal fluid,
and the lateral, third, and fourth ventricles are the
site of the choroid plexus, which produces this fluid

Cerebral Spinal Fluid
• The cerebrospinal fluid percolates through
the ventricular system and flows into the
subarachnoid space through perforations in
the thin covering of the fourth ventricle; it is
eventually absorbed by specialized
structures called arachnoid villi or
granulations and returned to the venous
circulation

Meninges
• Membranes - covering the brain and spinal cord and
consist of 3 connective tissue layers collectively called
the meninges. Consisting of the pia mater (closest to the
CNS structures), the arachnoid and the dura mater
(farthest from the CNS), the meninges also support
blood vessels and contain cerebrospinal fluid. These are
the structures involved in meningitis, an inflammation
of the meninges, which, if severe,
may become encephalitis,
an inflammation of the brain.
The subarachnoid space is the
space that normally exists between
the arachnoid and the pia mater,
which is filled with cerebrospinal fluid.

Meninges
• There are no pain receptors in the brain
itself. The meninges (coverings around the
brain), periosteum (coverings on the bones),
and the scalp all have pain receptors,
though.
• In the rest of the body, pain receptors send
signals to the brain, and that is where pain
is "felt".

Forebrain Structures
• Most sensory information goes first to the thalamus
(exception olfactory)-The cortex sends information
back to the thalamus elaborating or focusing on
certain kinds of input
• Hypothalamus involved in feeding, drinking
temperature regulation sexual behavior, activity
level fighting
• Pituitary an endocrine grand (hormone producing)
attached to base of hypothalamus releases hormones
in response to hypothalamus (master gland)

Basal Ganglia• A group of subcortical structures lateral to the
thalamus including the caudate nucleus, putamen
and globus pallidus (structure similar in mammals and amphibians)
• Strongest connections with frontal areas of cortex
responsible for planning and sequencing behavior as
well as certain types of memory and emotion
• In conditions such as Parkinson’s and Huntington’s
with BG deterioration there
is impaired movement but
also difficulties in memory,
attention (depression)
GP-medial-Putamen Lateral

Cortical Structures and function

Limbic System
• limbic system (or paleomammalian brain) is a
complex set of brain structures that lies on both
sides of the thalamus, right under the cerebrum. It is
not a separate system, but a collection of structures
The components of the limbic system located in the cerebral cortex
generally have fewer layers than the classical 6-layered neocortexion of structures
• Limbic system structures are involved in many of our
emotions and motivations, particularly those that are related
to survival. Such emotions include fear, anger, and emotions
related to sexual behavior. The limbic system is also
involved in feelings of pleasure that are related to our
survival, such as those experienced from eating and sex

Structure of the Vertebrate
Nervous System
• Hindbrain Midbrain Forebrain
• Thalamus, Hypothalamus, Pituitary, Basal
Ganglia, Hippocampus
• Ventricles-CSF
• Organization of the cerebral cortex

Brainstem and Cerebellum
• Brainstem consists of the 1) medulla- just above the
spinal cord controls vital functions such as
respiration, blood pressure HR, vomiting, salivation
via cranial nerves
• 2) Pons-axons from each half of the brain cross to
the opposite side of the spinal cord (left hemisphere
controls muscles on right side) Nuclei for certain
cranial nerves also found in Pons
• Reticular Formation –Descending
Tract controls motor areas of spinal
cord while ascending tract sends
info to cortex for arousal/attention

Cranial Nerves
It is through the cranial nerves that the brain receives
information from, and issues controls of functions of
various structures, primarily of the head and neck
•Since spinal nerves reach only to the level of the first
cervical vertebra, thus the cranial nerves fill the same
role above this level, as spinal nerves do below the
head and neck
•http://www.gwc.maricopa.edu/class/bio201/cn/cranial

Cerebellum• Region of the brain that plays an important role in motor control. Involved
in some cognitive functions (see Richard Thompson) but its movement-
related functions are the most solidly established. The cerebellum does not
initiate movement, but it contributes to coordination, precision, and accurate
timing. It receives input from sensory systems of the spinal cord and from
other parts of the brain, and integrates these inputs to fine tune motor
activity.
• Because of this fine-tuning function, damage to the cerebellum does not
cause paralysis, but instead produces disorders in fine movement,
equilibrium, posture, and motor learning.

Cerebellar Organization
• The cerebellum is organized into three main parts: 1) the cerebro
cerebellum, 2) the vestibulo cerebellum, and 3) the spinocerebellum.
• The cerebrocerebellum is the largest subdivision of the cerebellum, as it
occupies most of the lateral cerebellar hemisphere. The cerebrocerebellum
has the role of regulating highly skilled movements, so it plans and executes
complex spatial and temporal movement sequences.
• The vestibulocerebellum is the oldest part of the cerebellum from a
phylogenetical point of view. (The vestibulocerebellum includes the
flocculus and the nodulus). The role of this cerebellum section is to regulate
movements regarding posture and equilibrium after receiving input from the
vestibular nuclei in the brainstem.
• The spinocerebellum is the cerebellum part which is located in its median
and paramedian zone. This is the only section to receive input directly from
the spinal cord, being of major importance for movements of distal muscles.
From another organizational perspective, the cerebellum can also be divided
into two lateral hemispheres. These hemispheres are connected by a medial
part, which is the vermis.

Development of the Brain
•Brain development continues for an extended period
postnatally. The brain increases in size by four-fold
during the preschool period, reaching approximately
90% of adult volume by age 6
•https://www.youtube.com/watch?v=e5pRdb5F7tg

02/23/15 110
Developmental Disabilites
Abnormality of CNS during developmental period
resulting in lifelong impairment in any combination of
physical, cognitive, sensory, speech, language or
neuropsychological functions
Development- Birth of the nervous system
(gastrulation) until ~ 5 years of age
Disorder of mental development- Impairment in
acquisition of one or more complex skills not caused
by acquired brain lesion, sensory or motor impairment
or lack of opportunity to learn
Menkes & Sarnat Child Neurology (6th edition)

02/23/15 111
Development and Disorder
• Development- Birth of the nervous system
(gastrulation) until ~ 5 years of age
• Disorder of mental development- Impairment in
acquisition of one or more complex skills not
caused by acquired brain lesion, sensory or
motor impairment or lack of opportunity to
learn
Menkes & Sarnat Child Neurology
(6th
edition)

Eight Phases in Embryonic and Fetal
Development at a Cellular Level
1. Mitosis/Proliferation
2. Migration
3. Differentiation
4. Aggregation
5. Myelination
6. Synaptogenesis
7.Neuron Death/Apoptosis
8. Synapse Rearrangement
8 stages are sequential
for a given neuron, but
all are occurring
simultaneously
throughout fetal
development

Development and Plasticity
• New neurons probably do not form in the adult cerebral
cortex (*hippocampus)
• A growing axon follows a path of cell-surface
molecules being attracted by some and repelled by
others
• Sympathetic nervous system forms many more neurons
than needed but when one muscle and neuron form a
synapse the muscle delivers a protein NGF (nerve
growth factor-a neurotrophin) to promote survival of
that axon- NGF cancels the program of apoptosis
• BDNF most abundant neurotrophin in nervous system

Developing Brain
• Developing brain highly vulnerable to malnutrition
toxic chemicals, infection
• Immature neurons transplanted to different parts of
cortex develop characteristics of new location while
slightly older neurons may retain some of their old
properties as well
• Axons and dendrites continue to modify their structure
throughout life (dendritic spines and environmental
effects) –rewiring in blind or deaf individuals
• https://www.youtube.com/watch?v=mMDPP-Wy3sI
developing neurons from conception to birth

Migration-Differentiation
• After the proliferation phase, the neuron
precursor cells leave the ventricular zone of
the neural tube and migrate to their final
locations in the brain. Once each neuron
reaches its final destination, its cell body
develops the axon and dendrites that will
enable it to make connections with other
neurons

Determinants of Neuronal Survival
• The sympathetic nervous system forms many more
neurons than it needs. When one of its neurons
forms a synapse onto a muscle that muscle delivers
a protein NGF (nerve growth factor)
• Axons that do not receive NGF die off via apoptosis
-NGF cancels apoptosis (programmed cell death)
• Bcl-2 (B-cell lymphoma 2), encoded in humans by
the BCL2 gene, is the founding member of the Bcl-2
family of regulator proteins that regulate cell death
(apoptosis), by either inducing (pro-apoptotic) it or
inhibiting it (anti-apoptotic). Bcl-2 is specifically
considered as an important anti-apoptotic protein

Plasticity after brain injury
• Ischemia(common type of stroke)-results from a
blood clot or artery obstruction There is a restriction
in blood supply to tissues, causing a shortage of
oxygen and glucose needed for cellular metabolism
(to keep tissue alive).
• Ischemia and hemorrhage (ruptured artery) cause
edema (accumulation of fluid-swelling) and both
impair the sodium-potassium pump and sodium
accumulates inside neurons. The combination of
edema and excess sodium provokes excess release
of glutamate

• The influx of calcium and sodium from glutamate
receptor stimulation results in membrane
depolarization, which can also activate voltage-
dependent calcium channels. These other calcium
channels then allow further calcium influx,
aggravating the intracellular calcium overload
initiated by overstimulation of the glutamate
receptors and opening of the associated ion
channels.

• Neuronal glutamate that is released into the synaptic
space (The key process that triggers the entire excitotoxic cascade is the
excessive accumulation of glutamate in the synaptic space) is normally
removed from the synaptic space by adjacent glial cells,
in which the glutamate is converted to the closely
related glutamine, which can then readily diffuse back
into the neuron. Glutamine is converted back to
glutamate in the neuron.
• Trauma is a blunt mechanism that massively elevates the
extracellular glutamate levels
• Glutamate excitotoxicity is the final common pathway resulting
in neuronal injury for many seemingly unrelated disorders,
including ischemia, trauma, seizures, hypoglycemia, hypoxia,
and even some neural degenerative disorders

Treatment of Brain Injury
• Tissue plasminogen activator (tPA) is a protein
involved in the breakdown of blood clots. It is a serine
protease (enzymes that cleave peptide bonds in proteins)
found on endothelial cells, the cells that line the blood
vessels. As an enzyme, it catalyzes the conversion of
plasminogen to plasmin, the major enzyme responsible
for clot breakdown. treat embolic or thrombotic stroke.
Use is contraindicated in hemorrhagic stroke
• Clinical trials of drugs that block the NMDA receptor in
acute ischaemic stroke have been disappointing. No
improvement in clinical outcome of stroke has been
seen with competitive NMDA antagonists Curr Med
Res Opin 2002 Akins,P et al.

• Axon regeneration after injury is limited in mamals A cut
causes scar tissue Fuirther when glia in the CNS react to
brain damage they release Nogo
• The membrane protein Nogo-A was initially characterized
as a CNS-specific inhibitor of axonal regeneration.
• The function of Nogo in the adult CNS is now understood
to be that of a negative regulator of neuronal growth,
leading to stabilization of the CNS wiring at the expense of
extensive plastic rearrangements and regeneration after
injury. In addition, Nogo proteins interact with various
intracellular components-Nat Rev Neurosci. Schwab,M 12/11/2010

• Axon sprouting After loss of axons the cells that lost
their source of innervation react by secreting
neurotrophins to induce other axons to form new
branches or collateral sprouts- Sprouting may occur in
similar neurons (hippocampal damage may lead to
entorhinal sprouting and may even cross hemispheres)
Sprouting may occur in unrelated neurons which may
be useful ,neutral or harmful

• Denervation supersensitivity-Heightened
sensitivity to a
neurotransmitter after
destruction of incoming axon-Denervation
supersensitivity may help someone recover partial
function. However may cause problems in that if
there is spinal injury and postsynaptic neurons
develop increased sensitivity to remaining axons and
may enhance sensations such as pain-
• phantom limb- continuing sensation
of an amputated body part (somatosensory)
cortex (face) reorganizes and
m may activate areas previously

Occipital lobe
• Lateral surface shows no clear landmarks
• Medial view shows Calcarine, Lingual sulcus &
fusiform gyrus- Distinct Stripes-Striate Cortex
• Occipital cortex shows at least 9 visual areas- V1-V5 DP
V 1 has many more than 6 layers (first processing level). V1
Anatomically homogenous (functionally
heterogeneous) but stains for enzyme necessary to
make energy available for cells involved in
color/form/motion perception
• Formerly believed that color perception not
involved in processing motion, structure, depth or
position Tanaka, 2001

Occipital (continued)
• Theory of late ‘60s visual info hierarchically
processed 17 >18>19 with each area elaborating
prior
• More recent views include a hierarchical process
with multiple parallel and interconnecting levels
• V1 (Striate) projects 1) Dorsal Stream(visual guidance of movement)
2)Ventral Stream-object recognition/perception 3) STS superior temporal sulcus
stream (convergence of dorsal and ventral system) “probably important in
visualspatial functions” K & W--”. . . More cortex is concerned with vision than with
any other function in the primate cortex”-Occipital structures are merely the
beginning of visual processing
Vision used for action/motion (e.g. catching a ball) part of parietal
visual area: Vision used for facial recognition temporal
Egocentric vs. Allocentric Space (objects/locations relative to one another)

Parietal Lobe
• Principal Areas Brodman’s 1,2,3 (postcentral gyrus) afferent
paresis- finger movement clumsy due to impaired
feedback 5&7 (superior parietal lobule) , 43 (p. operculum)
40 (supramarginal gyrus) 39 (angular gyrus) The parietal cortex
integrates somatosensory and visual information
• especially with regard to controlling movement
• Anterior zone is somatosensory cortex
Angular gyrus & supramarginal gyrus
Compose the inferior parietal lobe
Rats and cats have much smaller parietal
Areas (‘lobes’)
Posterior Zone specialized in integrating
information

Von Economo’s map
von Economo’s map (PE,PF, PG) pg347
PE (BA5) - somatosensory from primary areas
PG (BA 7 & visual areas)-somatosensory and visual input
PG-(TPO) receives input from visual, somatosensory,
proprioceptive (internal stimuli) auditory, vestibular (balance)
oculomotor, cingulate-PG part of Dorsal Stream -Area of significant
expansion in human evolution
Difficulties in sterognosis- inability to recognize object by touch

Parietal Lobe continued
• Close relationship and connection between
Posterior Parietal > Prefrontal (46) -Both project to
same paralimbic, temporal & subcortical and
hippocampus- critical in spatially guided behavior- This area
critical for detecting stimuli in space and in directing movements pg347
• Parietal- Anterior processes somatic sensations, posterior
integrates sensory, somatic & visual info mostly to control
movement most neurons in posterior parietal region are
active during sensory input and movement pg350top
• Some cells posterior parietal respond to object features (size, orientation) when object manipulated pg350
• Posterior Parietal directs movements in space and detects stimuli in space. Lesions impair
guided movements
• Mental manipulation (object manipulation-ROTATED FIGURES example pg352-352
TPO hypothesized

Parietal Lobe-Spatial Properties
• Three symptoms not obvious as parietal lobe
symptoms
• Arithmetic (acalculia)- (52 minus 25)-numbers in
different positions have different meanings ‘borrowing’ requires pg352-353
understanding of spatial relationships while 846-32=? Does not
• Language- spatial organization of same letters in different
words (pat vs. tap) - Spatial organization of same words in phrases my
son’s wife vs my wife’s son
• Movement- Pts. with parietal lobe injuries have difficulty copying
movements of others pg354

Parietal Syndromes
• Diversity of Symptoms
• Astereognosis- Inability to recognize object by touching it
• Simultaneous extinction-Different objects in both visual fields detected but the
Same objects in both fields results in only one being identified pg355
• Asymatognosia-Loss of knowledge or sense of one’s
own body or condition- generally following rt side lesion
A) anosognosia (denial of illness) B) anosodiaphoria
(indifference to illness) C) asymbolia for pain (absence of
normal reactions to pain)
• Finger agnosia pt. unable to point to or show fingers on request
a common type of autopagnosia (inability to localize body parts)
• Spina bifida commonly have finger agnosia (acalculia)

Parietal Symptoms Continued
• Contralateral Neglect- Neglect occurs in visual, auditory and
somatosensory stimulation opposite lesion –neglect may be accompanied
by denial pg 358
• While a common area involves the Right Inferior Parietal Lobule Neglect may be
seen subsequent to damage to the frontal lobe and cingulate gyrus
• Pts. may not complete one side (lt) drawing. Right inferior parietal
lobule common area for lesions- Hypothesis of cause- Parietal lobe
lesions disrupt integration of sensory information. While stimulus
perceived, its location is uncertain and ignored (alt hyp- neglect
results from defect in attention/orientation pg359
• Object Recognition- unfamiliar views (rotated) of objects disturbed
due to inability to correctly categorize-results from right parietal injury
• Apraxia-movement disorder not caused by weakness,difficulties in
movement, tone or intellect- 1) Ideomotor -unable to copy
movements/gestures e.g. wave ‘hello’(more common left hem damage)
(2)Constructional Apraxia-difficulties in assembling puzzles, drawing, copying facial
movements (may occur from damage in either lobe ? Question is debated)
However,posterior parietal damage common cause

Parietal symptoms
• A function of parietal lobe may be Selective attention (disengagement)
Disengage from one task/object to reset visual guidance system to next
target- This may also explain mental manipulation which may require
disengaging from or shifting or resetting our perceptionpg 362
• Summary
• Behaviors are often complex In drawing a design Left hemisphere
damage may result in poor details of drawing while right damage my omit details from left
side of page or show poor orientation
• Both hemispheres show effects in spatial cognition tests-
• Mental rotation requires an image and then the rotation of that image pg363
• Lesions of either hemisphere produce some overlapping
symptoms(see table pg 363) Unlike temporal + Frontal lobe, parietal rarely epileptogenic
• Factor of cognitive mode as an explanation of overlapping symptons-
verbal people will solve a task (spatial) by talking through it vs a
spatial approach to a spatial task (directions)

Temporal lobe
Comprises all tissue below Sylvian fissure
and anterior to occiptal lobe Contains insula
(gustatory cortex)limbic cortex, amygdala &
hippocampus auditory association cortex

Temporal Lobe
• Cortex of superior temporal multimodal, input from
auditory, visual, somatic regions & two other polymodal
areas (frontal & parietal) and the paralimbic cortex pg372
• Left & right temporal lobes connected by corpus callosum medial
temporal cortex by amygdala (emotion) and ant. Commissure
• Primary and secondary auditory visual areas project to temporal pole
ALSO- visual/auditory association areas project to perirhinal
>entorhinal cortex>hippocampus MEMORY (LTM?)

Three basic sensory functions of
temporal lobe
• 1) VISUAL OBJECT RECOGNITION ventral visual pathway
• 2)PROCESS AUDITORY INPUT parallel ventral stream of auditory processing (stimulus
recognition or ‘what’) and travelling from auditory areas to posterior parietal cortex is a dorsal auditory stream (involved in directing
movements related to auditory information) pg 372-373
• 3) MEMORY long term storage of sensory info
• Medial temporal projection – Auditory and visual association areas
project to medial temporal cortex (perirhinal-> entorhinal-> hippocampus
& amygdala (perforant pathway)
• Frontal lobe projections – from association areas

Temporal Lobe continued
• Temporal lobe shows Cross modal matching-
integrating visual & auditory info Damage to temporal cortex
leads to deficits in identifying and categorizing stimuli (locating stimulus involves posterior parietal
and identifying if stimulus present involves primary sensory areas) pg374
• Affective responses Amygdala regulates association of stimuli with consequences
(positive, negative or neutral) which modifies behavior (see Kluver-Bucy syndrome) pg375
• Superior Temporal Sulcus likely area involved
interpreting complex social info -integrates and
interprets social meaning of face/body movements pg375
• “. . .If people have temporal lobe injuries that lead to impairments in biological motion,
there is likely a deficit in social awareness” pg 376
• Asymmetry of Temporal lobe function- Although left and right
temporal lobes are specialized there is a great deal of functional overlap pg 376

Disorders of the Temporal Lobe I
• Auditory Perception- lesions may result in distorted
speech perception (pt has difficulty in discriminating sounds
presented quickly- as in ‘normal’ learning a new language- and also in
judging temporal order of sounds (500ms vs 50ms in normals) These
deficits appear related more to left than right temporal lobe lesions
i.e. speech pg 377 bottom-pg379 “It is likely that the special mechanism for speech perception is
in the left temporal lobe” temporal lobe deficits seen in other animal’ vocalization perceptions
• Right Temporal (primary auditory cortex) process pitch
discrimination (related to frequency)which also contributes to
prosody (tone of voice) pg 380 bottom
• Characteristics of both language and music likely analyzed selectively by
both temporal hemispheres. Humans are likely born with predisposition for
analyzing both speech and music

Disorders of the temporal lobe• Visual Perception-Visual field function generally intact in temporal
lobe lesions but discrimination of complex patterns impaired (closure or
anomalous details missed) pg 382 top
• Facial Recognition- Right temporal lobe lesions show impairment
of recognition/recall of faces or pictures of faces – warrington pg 382Middle
• Visual Recognition of objects- inferior temporal lobe lesions
result in deficits of visual recognition of objects pg382 bottom Also Tanaka-
1) stimulus specificity of neurons altered by experience. When
presented with new complex stimuli more cells become involved and
fire on subsequent discrimination tasks (i.e. plasticity/learning seen even in adults) &
2) Inferior temporal neurons fire after stimulus is removed apparently
providing basis of memory or ‘imagery’ pg384
• Selective Attention & Recall of Visual/Auditory Input impaired with
temporal lobe damage right temporal lesions show bilateral deficits in recall of
simultaneous visual info Lt temporal lesions show unilateral recall deficits (in rt
visual field) Therefore The right temporal lobe may have greater role
than left in selective attention to visual input pg385 bottom

Temporal Lobe Disorders
• Organization of sensory input appears to be a function
of Temporal lobes - Left Temporal lobectomies –impair ability
to categorize even single words, pictures of familiar objects. Also
automatic categorization impaired (when asked to recall members of
category -e.g. if Asked to recall animals, unable to give examples such as dog, cat etc. )
• Also posterior left temporal damage -impairs semantic hierarchical
categories- broader categories recognized e.g. duck recognized as
animal but not bird, waterfowl pg 385
• Using Contextual Information- “fall” tumble or season based on
context. Seeing person out of usual context; We interpret events
based on context (are we with friends or family when an event takes place?) pg386
• Memory- Left Temporal involved with verbal recall (visually or
aurally presented stimuli –word lists or short stories) Anna Thompson 386 Bottom
Right Temporal –involved with nonverbal recall (faces, song
melodies)

Temporal Lobe (summary)- Four
functional Zones
• Auditory processes –Superior Temporal Gyrus
• Visual Processes- Inferior temporal cortex
• Emotion- Amygdala
• Spatial Navigation and spatial and object memory-
Hippocampus (and associated cortex) The parietal
• e lobe uses analyzes spatial location in relation to
• movement while temporal lobe uses space as
• part of object identificion

Temporal lobe cortical anatomy

Cramped Synchronized General Movements in Preterm
Infants as an Early Marker for Cerebral Palsy Ferrari,F
Arch Pediatr Adolesc Med. 2002
• Objective To ascertain whether specific abnormalities(ie,
cramped synchronized general movements [GMs]) can
predictcerebral palsy and the severity of later motor
impairment inpreterm infants affected by brain lesions.
• Design Traditional neurological examination was
performed,and GMs were serially videotaped and blindly
observed for 84preterm infants with ultrasound
abnormalities from birth until56 to 60 weeks' postmenstrual
age. The developmental courseof GM abnormalities was
compared with brain ultrasound findingsalone and with
findings from neurological examination, in relationto the
patient's outcome at age 2 to 3 years.

Cramped Synchronized General Movements in Preterm Infants as
an Early Marker for Cerebral Palsy
• An early prediction of cerebral palsy will lead to earlier enrollmentin
rehabilitation programs. Unfortunately, reliable identificationof cerebral
palsy in very young infants is extremely difficult.10
It is generally
reported that cerebral palsy cannot be diagnosedbefore several months
after birth11-15
or even before the ageof 2 years.16
• A so-called silent period, lasting 4 to 5 monthsor more, and a period of
uncertainty until the turning pointat 8 months of corrected age have also
been identified.12-13
The neurological symptoms observed in the first few
months afterbirth in preterm infants who will develop cerebral palsy are
neither sensitive nor specific enough to ensure reliable prognoses.
• Irritability, abnormal finger posture, spontaneous Babinskireflex,17-18
weakness of the lower limbs,19
transient abnormalityof tone,12-13,20-24
and
delay in achieving motor milestones11
are some of the neurological signs
that have been describedin these high-risk preterm infants

Early Marker for Cerebral Palsy continued
• Results Infants with consistent or predominant (33 cases)cramped
synchronized GMs developed cerebral palsy. The earliercramped
synchronized GMs were observed, the worse was the neurological
outcome. Transient cramped synchronized character GMs (8 cases)
were followed by mild cerebral palsy (fidgety movements were
absent) or normal development (fidgety movements were present).
Consistently normal GMs (13 cases) and poor repertoire GMs (30
cases) either lead to normal outcomes (84%) or cerebral palsywith
mild motor impairment (16%). Observation of GMs was 100%
sensitive, and the specificity of the cramped synchronized GMswas
92.5% to 100% throughout the age range, which is much higherthan
the specificity of neurological examination.
• Conclusions Consistent and predominant cramped synchronizedGMs
specifically predict cerebral palsy. The earlier this characteristic
appears, the worse is the later impairment

Babinski Reflex
• Babinski reflex is very common among extremely
young children and is considered as a problem if it
occurs in children above age the age of 2 years

Brain Recovery/Reorganization
• Lysosomes are specialized organelles for protein recycling and as
such are involved in the terminal steps of autophagy. However, it has
become evident that lysosomes also play an important role in the
progression of apoptosis. This latter function seems to be dependent
on lysosomal proteases, which need to be released into the cytosol
for apoptosis to be efficient. Among the lysosomal proteases, the
most abundant are the cysteine cathepsins and the aspartic protease
cathepsin D, which seem to be the major apoptosis mediators. This
chapter reviews the methods used to study lysosomes and lysosomal
proteases. Lysosomes in apoptosis. Ivanova S
Methods Enzymology 2008
• http://the-scientist.com/2012/05/31/active-brains-
help-heal-paralysis/

Endocannabinoids Prevent β-Amyloid-mediated Lysosomal Destabilization in Cultured Neurons
*JanisNoonan J.BiolChem 2010
Neuronal cell loss underlies the pathological decline in cognition and memory
associated with Alzheimer disease (AD). Recently, targeting the endocannabinoid
system in AD has emerged as a promising new approach to treatment. Studies have
identified neuroprotective roles for endocannabinoids against key pathological events
in the AD brain, including cell death by apoptosis. Elucidation of the apoptotic
pathway evoked by β-amyloid (Aβ) is thus important for the development of
therapeutic strategies that can thwart Aβ toxicity and preserve cell viability. We have
previously reported that lysosomal membrane permeabilization plays a distinct role
in the apoptotic pathway initiated by Aβ. In the present study, we provide evidence
that the endocannabinoid system can stabilize lysosomes against Aβ-induced
permeabilization and in turn sustain cell survival. We report that endocannabinoids
stabilize lysosomes by preventing the Aβ-induced up-regulation of the tumor
suppressor protein, p53, and its interaction with the lysosomal membrane. We also
provide evidence that intracellular cannabinoid type 1 receptors play a role in
stabilizing lysosomes against Aβ toxicity and thus highlight the functionality of these
receptors. Given the deleterious effect of lysosomal membrane permeabilization on
cell viability, stabilization of lysosomes with endocannabinoids may represent a
novel mechanism by which these lipid modulators confer neuroprotection.

Laminae of Cortex
Cerebral cortex has six layers and
contains between 10 and 14 billion
neurons. The six layers of this part of the
cortex are numbered with Roman
numerals from superficial to deep. Layer I
is the molecular layer, which contains very
few neurons; layer II the external granular
layer; layer III the external pyramidal
layer; layer IV the internal granular layer;
layer V the internal pyramidal layer; and
layer VI the multiform, or fusiform layer.
Each cortical layer contains different
neuronal shapes, sizes and density as well
as different organizations of nerve fibers

Layers of the cerebral cortex
• Functionally, the layers of the cerebral cortex can be divided into three parts. The
supragranular layers consist of layers I to III. The supragranular layers are the
primary origin and termination of intracortical connections, which are either
associational (i.e., with other areas of the same hemisphere), or commissural (i.e.,
connections to the opposite hemisphere, primarily through the corpus callosum).
The supragranular portion of the cortex is highly developed in humans and
permits communication between one portion of the cortex and other regions
• The internal granular layer, layer IV, receives thalamocortical connections,
especially from the specific thalamic nuclei. This is most prominent in the
primary sensory cortices
The infragranular layers, layers V and VI, primarily connect the cerebral cortex with
subcortical regions. These layers are most developed in motor cortical areas. The motor
areas have extremely small or non-existent granular layers and are often called
"agranular cortex". Layer V gives rise to all of the principal cortical efferent projections
to basal ganglia, brain stem and spinal cord. Layer VI, the multiform or fusiform layer,
projects primarily to the thalamus

Layers of the Cortex continued
• There are several identifiable cell types in the cerebral cortex.
The pyramidal cells are the main cell type within layers III and
V. These cells can be extremely large in layer V of the motor
cortex, giving rise to most corticobulbar and corticospinal fibers.
The largest of these neurons are called "Betz cells". These cells
are pyramidal in shape, with an apical dendrite that extends all
the way to layer I of the cortex. There are also several basal
dendrites projecting laterally from the base of these neurons.
• Dendrites of cortical neurons have many spines that are sites of
synapse. The thin axon that arises from the base of the pyramidal
cell has collaterals and a long process that leaves the cortex. This
is the process that connects with other brain regions by extending
through the white matter deep to the cortex
Stellate or granule cells are most prominent in layer IV. Their axons remain
in the cortex

Cortical tracts
• The corticobulbar tract is composed of the upper
motor neurons of the cranial nerves. The muscles of
the face, head and neck are controlled by the
corticobulbar system, which terminates on motor
neurons within brainstem motor nuclei. This is in
contrast to the corticospinal tract in which the
cerebral cortex connects to spinal motor neurons,
and thereby controls movement of the torso, upper
and lower limbs.

Pyramidal tracts include
Corticobulbar, Corticospinal tracts

Upper and lower motor neurons
Upper motor neurons (UMN) are a type of first
order neuron. They are unable to leave the central
nervous system. The pyramidal tract is a very
important upper motor neuron tract. The
extrapyramidal tract also consists of upper motor
neurons.
Upper motor neurons remain inside the neuraxis, they
synapse with neurons of another type called lower
motor neurons which can carry messages to the
muscles of the rest of the body. When children have
neuromuscular problems due to UMN lesions that
occur before, during, and shortly after birth they are
said to have cerebral palsy.
Lower motor neurons, or second order neurons are
cranial and spinal nerves. Thee cell bodies of these
neurons are located in the brain stem, but their axons
can leave the central nervous system and synapse
with the muscles of the body.

Pyramidal tracts
• The pyramidal tracts refers to both the corticospinal and corticobulbar
tracts.
• The corticospinal tract conducts impulses from the brain to the spinal cord.
It contains mostly motor axons. The corticospinal tract is made up of two
separate tracts in the spinal cord: the lateral corticospinal tract and the
anterior corticospinal tract. The corticospinal tract also contains the Betz
Cell (the largest pyramidal cells) that are not found in any other region of the
body. An understanding of these tracts leads to an understanding of why one
side of the body is controlled by the opposite side of the brain. The
corticospinal tract is concerned specifically with discrete voluntary skilled
movements, such as precise movement of the fingers and toes. The brain
sends impulses to the spinal cord relaying the message. This is imperative in
understanding that the left hemisphere of the brain controls the RIGHT side
of the body, while the right hemisphere of the brain controls the LEFT side
of the body. The signals cross in the medulla oblongata, this process is also
known as decussation.
• The corticobulbar tract carries information to motor neurons of the cranial
nerve nuclei, rather than the spinal cord

Movement Central Pattern Generators
Central pattern generators. (a) Early work
suggested two hypotheses for the generation
of rhythmic and alternating movements. In
the reflex chain model (left) sensory neurons
innervating a muscle fire and excite
interneurons that activate motor neurons to
the antagonist muscle. Right, in a central
pattern generator (CPG) model a central
circuit generates rhythmic patterns of
activity in the motor neurons to antagonist
muscles lobster with electromyographic
recording (EMG) wires implanted to
measure stomach motor patterns in the
behaving animal. Top right, EMG recording
showing that triphasic motor pattern
generated by the LP, PY, and PD neurons

• Central pattern generators are capable of
producing rhythmic activity without
receiving extrinsic phasic timing
information, but as discussed below,
neuromodulators, supplied by descending
pathways, are often required to activate
central pattern generating circuits.

Transduction and visible light
• Muller’s law of specific nerve energies –whatever
excites a particular nerve establishes a particular kind
of energy unique to that nerve –Light stimulates one
set of receptors, sound another set etc.

Visual System
• Transduction of energy-Law of specific energies
Muller (1838)
• PupilRetina
• Rods Cones-(bipolar horizontal amacrine cells)
Ganglion cells
• Center Fovea Cones dominate –Details Color, Bright
light (1 to 1 ganglion cells: bipolar cells to Cones-
Each ganglion cell (midget ganglion cell) responds to one
cone-each cone in fovea has a direct line to brain
• Periphery Rods dominate Movement dim light
Toward periphery more receptors converge on
bipolar and ganglion cells

Visual System
• Both rods and cones contain photopigments
(chemicals) that release energy when struck by light
• Light converts this photopigment (one type of
Vitamin A) to another type which activates second
messengers within the cell

Anatomy of Retina
As light enters the eyes, retinal photoreceptors
transforms the energy into electrical signals.
The information is transferred by interneurons
(bipolar, horizontal, and amacrine cells) to the
ganglion cells, in which the axons of the
ganglion cells leave the eye at the optic disk
through the optic nerve.

Anatomy of Retina continued
• Rods:Cones 20:1 but

Pathways to LGN and Cortex
• In the fovea each cone attaches to just one
bipolar cell which in turn connects to a single
ganglion cell
• Three categories of Primate ganglion cells
Parvocellular neurons small cell bodies and
receptive fields around fovea Magnocellular
neurons larger cell bodies and receptive fields
throughout retina Koniocelluar neurons small
cell bodies throughout retina
• Parvocellular neurons sensitive to detail and
color (ventral stream) Magnocellular neurons
more sensitive to movement (dorsal stream)

Vision - continued
The pathway continues to the optic chiasm, where fibers from the
median half of the retina split and join uncrossed fibers from the
lateral half of the other retina to form the optic tract. A great
majority of the fibers from the optic tract terminate in the lateral
geniculate nucleus which is the thalamic relay nucleus for vision

Visual System
• Lateral Inhibition- the capacity of an
excited neuron to reduce the activity of its
neighbors. Lateral inhibition sharpens the
spatial profile of excitation in response to a
localized stimulus.

A stimulus affecting all three neurons, but which
affects B strongest or first, can be sharpened if B
sends lateral signals to neighbors A and C not to fire,
thereby inhibiting them. Lateral inhibition is used in
vision to sharpen signals to the brain (pink arrow).

Lateral Inhibition
• Lateral inhibition occurs when the activity of one
cell suppresses the activity of a nearby cell. lateral
inhibition illustrates that vision is not a passive
process of seeing merely what is objectively there.
Different photoreceptors in the eye respond to
varying degrees of light. When one cell activates in
response to light, its activity impairs or prevents
neighboring cells from activating. This causes the
edges between light and dark areas to appear more
prominent than they would be otherwise.

Lateral Inhibition
• Horizontal cells activity
spreads by graded
potential or depolarization
decays over distance While
one cell shows net excitation
which outweighs the effect
of the horizontal cell’s
inhibition the cells lateral
are less directly excited and
the horizontal cell inhibits
them

Retinal Organization
• Retinal organization
• There are five types of neurons in the retina distributed in five
layers. The photoreceptors are in the outer nuclear layer, the
horizontal, amacrine and bipolar cells are in the inner nuclear
layer, and the ganglion cells are in the ganglion cell layer.
• The outer plexiform layer contains the processes and cell
contacts of the photoreceptors, horizontal and bipolar cells.
• The inner plexiform layer contains those of the bipolar,
amacrine, and ganglion cells.
• A direct three-neuron chain – from photoreceptor to bipolar to
ganglion cell – is the major route of information flow from the
light source to the optic nerve.
• The horizontal and amacrine cells are primary responsible for
lateral interactions.

Visual Pathway
• ConesParvocellular ganglion Inferior Temporal
(what pathway) ; Shape object recognition Ventral
Stream
• Rods Magnocellular ganglion Posterior Parietal
(where pathway) Navigation, spatial orientation
Dorsal Stream

Parvocellular Magnocellular Pathways
• V
• visual information being organised into basic
channels

Visual Pathways
• •Different ganglion cells exist and are organized so that they
feed into one of two channels entering the optic nerve.
• The two channels are the 1) Parvocellular channel which
- dominate central visual area Carry information about color
and detail (spatial form) to the brain (ventral stream)
• •Magnocellular channel to be found in the peripheral retina
(distributed throughout retina) (dorsal stream)
- Carry information about movement and location to the brain
- Contributions from the magno and parvo channels then feed
into the ventral 'what' stream and the dorsal 'where' stream
The dorsal stream helps the motor system find and use
objects while the ventral stream identifies/recognizes objects

Thalamus LGN
• The top four layers are parvocellular layers
• The bottom two layers are magnocellular layers
• All 6 layers of LGN project to area V1 in cortex

Simple Cell responding receptive
field primary visual cortex

Primary Visual Cortex
• Simple Cell receptive field with a fixed excitatory
and inhibitory zones The more the light shines in
the excitatory zone the more the cell responds
(receptive field a bar) V1
• Complex cells in V1 and V2 do not respond to
exact location of a stimulus but to a particular
orientation
• A cell that responds to a stimulus in only one
location is a simple cell while one that responds
equally throughout a large area is a complex cell

Unlike Simple cells(top), complex cells (bottom) are not fussy about
the position of the stimulus, as along as it falls somewhere inside the
receptive field (left and middle-left examples above). Many complex
cells are also direction-selective, in the sense that they respond only
when the stimulus moves in one direction and not when it moves in the
opposite direction. Complex cells will respond to patterns of light in a
certain orientation within a large receptive field (V1,V2 BA 19)

Theories of Color Perception
• Trichromatic (Young-Helmholtz Theory)
• We perceive color through the relative rates of responding
by three kinds of cones, each kind maximally sensitive to a
different set of wavelengths (short, medium and long
wavelength types) by the ratio of activity across the three types of cones

Trichromatic Theory (Young-Helmholtz)
• We discriminate among wavelengths by the ratio of
activity across the types of cones The nervous system
compares responses of different types of cones Light at 550nm
excites medium and long wavelength receptors but very little short
wavelength –We do not have a separate color receptor for each color

Opponent Process Theory of
Color Perception
• We perceive color in terms of
opposites A bipolar cell excited
by short wavelength (blue) is
inhibited inhibited by longer
wavelengths. If the blue
wavelength is stimulated long
enough the (bipolar) cell
becomes fatigued and will be
inhibited so that you will see a
different color (yellow)
• Stare at the cross-hair in the
parrot while you count slowly
to 20, then look immediately at
one spot in the empty bird cage.
A faint, ghostly image of the
bird will appear in the cage.
Notice the blue-green color

Cerebral Cortex
Brodmann published his maps of cortical areas in
humans, monkeys, and other species in 1909Many of
the areas Brodmann defined based solely on their
neuronal organization have since been correlated
closely to diverse cortical functions. For example,
Brodmann areas 1, 2 and 3 are the primary
somatosensory cortex; area 4 is the primary motor
cortex; area 17 is the primary visual cortex; and areas
41 and 42 correspond closely to primary auditory
cortex.
Higher order functions of the association cortical
areas are also consistently localized to the same
Brodmann areas by neurophysiological, functional
imaging, and other methods (e.g., the consistent
localization of Broca's speech and language area to
the left Brodmann areas 44 and 45). However,
functional imaging can only identify the approximate
localization of brain activations in terms of
Brodmann areas since their actual boundaries in any
individual brain requires its histological examination.

Opponent Process Theory of
Color Perception
• We perceive color in terms of
opposites A bipolar cell excited
by short wavelength (blue) is
inhibited inhibited by longer
wavelengths. If the blue
wavelength is stimulated long
enough the (bipolar) cell
becomes fatigued and will be
inhibited so that you will see a
different color
• Stare at the cross-hair in the
parrot while you count slowly
to 20, then look immediately at
one spot in the empty bird cage.
A faint, ghostly image of the
bird will appear in the cage.
Notice the blue-green color

Visual Pathway Occipital cortex
• V 1 V 2
• V1 Primary visual cortex
(striate cortex)

Dorsal Stream
• The dorsal stream begins with V1, goes
through Visual area V2, then to the
dorsomedial area and Visual area MT (also
known as V5) and to the posterior parietal
cortex. The dorsal stream, sometimes called
the "Where Pathway" or "How Pathway", is
associated with motion, representation of
object locations, and control of the eyes and
arms, especially when visual information is
used to guide saccades or reaching

Ventral Stream
• The ventral stream begins with V1, goes
through visual area V2, then through visual area
V4, and to the inferior temporal cortex. The
ventral stream, sometimes called the "What
Pathway", is associated with form recognition
and object representation. It is also associated
with storage of long-term memory
• Damage to this pathway may lead to visual
agnosia Person may point to object (may even
with difficulty describe it) but fail to recognize it
or name it

Pattern Recognition
• Simple cells –receptive field with fixed
excitatory and inhibitory zones. Light
shining in the excitatory zones increases
cell responding-cells respond to stimulus in
one location (V1)
• Complex cells- responds to pattern in a
particular orientation (V1 and V2)
• Visual Agnosia ________Stream?
• ventral stream

Facial and Motion Detection
• Prosopagnosia –Fusiform gyrus
• Motion detection MT (V5) medial superior temporal
cortex (cells respond when something moves at a particular speed in a particular direction
• Responds to movement (even in photographs that
imply movement)
• Perceiving biological motion activates MT areas
• Damage to MT may result in motion blindness- See
objects but impaired at whether they are moving and
what is their direction

Biological Motion
• Viewing a complex moving pattern activates many
brain areas spread among all four lobes of the cortex
• Most cells in MT respond selectively when
something moves at a particular speed and in a
particular direction, sensitive to acceleration and
deceleration as well as absolute speed-Area MT
responds to photographs of movement (people
running) MT involved with biological motion
• Neurons in the ventral part of MST (medial superior
temporal) respond to objects moving relative to its
background (but are silent during eye movement this enables
you to distinguish between eye movement and object

Motion Sensitivity
• Functionally active areas during viewing of moving
images compared to a static image. The alternating
green and yellow spots highlight significant activity
in the middle-temporal (V5/MT) regions.
• For each aspect of (visual) experience a
sensitive (critical) period can be
identified when experiences have a very
strong and enduring influence
• Critical period for some visual functions can be
longer or shorter depending if some changes require
local rearrangements of axons or greater growth of
axons over longer distances

Article write up
• Introduction
• Stimulants are an effective treatment for ADHD
but lowers threshold for seizures and may cause
non-epileptic children to have seizures
• Methods
• Two hundred and thirty four non-epileptic children
with ADHD were selected from a child neurology
database and examined with follow-up using EEGs
with 205 receiving stimulant treatment. Thirty-six
children demonstrated EEG abnormalities

• Results
• Only four patients in the stimulant group
experienced seizures with one patient demonstrating
a normal EEG. Prevalence of seizures in the
stimulant group did not differ from the untreated
group among the three patients with abnormal EEGs
• Discussion
• The data reviewed does not support increased
seizure risk due to stimulant use. Children with an
epileptiform EEG are at a higher risk to eventually
get seizures
• Methodological Consideration

Auditory System
• Outer Ear – Pinna
• Middle Ear Eardrum 1)
Hammer 2) Anvil 3) Stirrup
• Inner Ear-Cochlea
Sensory Receptors
• Afferent neurons innervate cochlear inner hair cells, at
synapses where the neurotransmitter glutamate
communicates signals from the hair cells to the dendrites of
the primary auditory neurons
• This sound information, now re-encoded, travels down the
vestibulocochlear (VIII) through intermediate stations such
as the cochlear nuclei and superior olivary complex of the
brainstem and the inferior colliculus of the midbrain being
further processed at each waypoint. The information
eventually reaches the thalamus , and from there it is
relayed to the cortex. In the human brain , the primary
auditory cortex is located in the temporal lobe

Dimensions of sound
• Amplitude of sound wave (Intensity) = Loudness
the sensation associated with Amplitude
• Frequency of sound wave=Pitch sensation related to
frequency cps or Hz
• Timbre= Quality of sound

Current Theory of Audition
• For low frequency sounds the basilar membrane
vibrates in synchrony with the sound waves
• (Frequency Theory)
• and auditory nerve axons generate one action potential per wave (sound
wave of 50Hz generates 50 action potentials/sec in VIII nerve)For higher
frequency sounds action potentials are phase locked to the

Hair Cells in Basilar Membrane
• Place theory Higher frequency sounds vibrate the hair cells
near the base of the basilar membrane and for lower frequency
sounds the hair cells farther along the basilar membrane
vibrate
• Frequency Theory-basilar membrane vibrates in synchrony with sound
Due to refractory period (1/1000 sec) maximum firing rate ~1,000Hz
well below highest frequencies heard 20,000Hz(dogs40 Hz to 60 kHz cats 55 Hz up to 79 kHz)

• Auditory information leaves cochlear passes through
subcortical areas, crosses over in the midbrain and
passes through the inferior colliculus and then to
Primary auditory cortex(Area A1)-Auditory Cortex

Auditory Cortex
• Information travels to Primary Auditory Cortex or A1
(similar to V1 for Vision)
• Similar to Visual system Auditory cortex has a “what”
pathway (anterior temporal cortex) sensitive to
identifying sounds and a “where”
pathway sensitive to sound
localization (posterior auditory cortex)
• Superior temporal cortex detects movement of sound
(similar to MT cortex for visual movement) Damage to
superior temporal cortex does not affect hearing sounds
but person cannot detect source of a moving sound

Audition
• In alert waking animals each cell in area A1 gives a
prolonged response to its preferred sound and little or no
response to other sounds.
• While damage to area V1 results in blindness damage to
A1 (assuming damage that is not extensive) able to hear
simple sounds but not recognize combinations or
sequences of sound as in music or speech
• Areas outside of A1 have cells which respond to changes
in sound rather than to any prolonged sound
• Cells outside of A1 respond best to “auditory objects”
identification of sounds such as animal, machinery
noises or music etc.(some of these cells respond so slowly that are
probably not part of the initial perception of sound)

Auditory Cortex continued
• Similar to visual system the auditory system
requires experience for full development
• Difference in organization between systems-
While damage to V1 results in blindness (cortical
blindness) damage to A1 does not result in
deafness but in the difficulty to recognize
combinations or sequences of sounds
• Like visual system that starts with simple
recognition and proceeds to more complex
processing but unlike the visual system the cortex
is not necessary for all hearing but for advanced
processing of it

Hearing Loss
• Conductive deafness- damage to middle ear with
cochlear and auditory nerve left intact. Possible to
correct with amplification (hearing aids)
• Nerve deafness-damage to cochlea, hair cells or
auditory nerve-cannot compensate for extensive
damage with hearing aids

Cochlear Implant
• With a cochlear implant, the damaged hair cells are
bypassed, and the auditory nerve is stimulated directly
• The cochlear implant does not result in “restored” or
“cured” hearing. It does, however, allow for the perception
of the sensation of sound
• Cochlear implants have external (outside) parts and internal
(surgically implanted) parts that work together to allow the
user to perceive sound

Early Nerve deafness
• Maternal exposure to Rubella virus sensorineural
loss. Prenatal
• Infections
• Rh factor complications- mom's blood creates anitbodies to
baby's blood
• Fetal Alcohol Syndrome
• Anoxia- lack of sufficient oxygen
• Maternal diabetes
– Perinatal
• Anoxia
• Cochlea damage with forceps (this is quite rare)
http://www.youtube.com/watch?v=PvvDf4RUtc8
Sound and fury

Postnatal
Ototoxic drugs- some life-saving antibiotics can cause damage to
the cochlea (aspirin)*
High fever
Influenza, meningitis, measles, mumps, rubella, encephalitis
Genetics
50% of congenital hearing loss in children is thought to be due to
genetics
In 25% of cases, the causes are unknown
90% of children with severe to profound hearing loss have
parents with normal hearing
Source- Pubmed Health NIH
*Reye's (Ryes) syndrome is a rare but serious condition that causes swelling in the liver and
brain. Reye's syndrome most often affects children and teenagers recovering from a viral
infection and who may also have a metabolic disorder. Signs and symptoms such as
confusion, seizures and loss of consciousness require emergency treatment. Early diagnosis
and treatment of Reye's syndrome can save a child's life.
Aspirin has been linked with Reye's syndrome, so use caution when giving aspirin to
children or teenagers. Though aspirin is approved for use in children older than age 2,
children and teenagers recovering from chickenpox or flu-like symptoms should never take

Sound Localization
• Difference in intensity and arrival time of sound
reaching the two ears For high frequency sounds with a wave
length shorter than the width of the head, the head creates a sound
shadow

Sound Localization continued
• Phase difference between the ears. If a sound
wave originate to the side of the head the
sound wave strikes the two ears out of phase

Mechanical Senses
• Mechanical senses respond to pressure, bending or other
distortions of a receptor (Audition is also a mechanical sense as
hair cells are modified touch receptors)
• Vestibular organ adjacent to the cochlear monitors movement –
three semicircular canals with hair cells Project to the VIII cranial
nerve (both auditory and vestibular)-Like hearing receptors the
vestibular receptors are modified touch receptors
• The three semicircular canals (in perpendicular planes) are filled
with a viscous (jellylike) substance and
lined with hair cells. Acceleration of the
head at any angle causes the fluid
(a gelatinous fluid, called the cupula)
which surrounds the hair cells in a
canal to push against hair cells (action
potentials are produced and travel to

Standing Walking Balance
• Equilibrioception or sense of balance is one of the physiological
senses. It helps prevent humans and animals from falling over
when walking or standing still. Balance is the result of a number
of body systems working together: the eyes (visual system),
ears (vestibular system) and the body's sense of where it is in
space (proprioception) ideally need to be intact. The vestibular
system, the region of the inner ear where three semicircular
canals converge, works with the visual system to keep objects in
focus when the head is moving. This is called the vestibulo-
ocular reflex (VOR). The balance system works with the visual
and skeletal systems (the muscles and joints and their sensors)
to maintain orientation or balance. Visual signals sent to the
brain about the body's position in relation to its surroundings are
processed by the brain and compared to information from the
vestibular, visual and skeletal systems

Standing Walking Balance• Romberg's test is a test used in an exam of neurological function, and also
as a test for drunken driving. The exam is based on the premise that a
person requires at least two of the three following senses to maintain
balance while standing: proprioception (the ability to know one's body in
space); vestibular function (the ability to know one's head position in
space); and vision (which can be used to monitor [and adjust for] changes in body position).
• A patient who has a problem with proprioception can still maintain balance
by using vestibular function and vision. In the Romberg test, the standing
patient is asked to close his or her eyes. A loss of balance is interpreted as a
positive Romberg's test.
• The Romberg test is a test of the body's sense of positioning
(proprioception), which requires healthy functioning of the dorsal columns
of the spinal cord.
• The Romberg test is used to investigate the cause of loss of motor
coordination (ataxia). A positive Romberg test suggests that the ataxia is
sensory in nature, that is, depending on loss of proprioception. If a patient
is ataxic and Romberg's test is not positive, it suggests that ataxia is
cerebellar in nature, that is, depending on localized cerebellar dysfunction instead

Mechanical Senses continued
• Somatosensory system includes touch, pressure, cold,
warmth, pain, position and movement of joints
• Most receptors respond to more than one type of stimulus
(e.g. touch and pain responses for a simple bare nerve ending)
• Pacinian corpuscle-detects sudden displacements or high
frequency vibrations on the skin Any deformation in the
corpuscle causes action potentials to be generated by
opening pressure-sensitive sodium ion channels in the axon
membrane. This allows sodium ions to influx, creating a
receptor potential
• Similar to conscious vision and hearing which depend on
primary visual and auditory cortex the primary
somatosensory cortex is essential for conscious touch
experiences

Pacinian corpuscle responds best
to sudden displacement of the skin
or high frequency vibration only
briefly to steady pressure
Information from touch receptors
in the head enter the CNS through
the cranial nerves while receptors
below the head send information
into the spinal cord to the brain
(via 31 spinal nerves)

Mechanoreceptors
• Meissner's corpuscles (or tactile corpuscles) are a
type of mechanoreceptor. They are a type of nerve
ending in the skin that is responsible for sensitivity to
light touch
• Various areas of the (somatosensory)
thalamus send impulses to different
areas of the primary somatosensory
cortex (parietal lobe). Some areas
respond to touch,
others to deep
pressure on the
muscles and joints

Sensation in the CNS
• Sensory information traveling through
the spinal cord follows well-defined
pathways to the brain(the touch pathway
in the spinal cord is separate from the
pain pathway)
• Different areas in the thalamus send impulses to different
areas of the primary somatosensory cortex (parietal lobe)
with some areas responding mostly to touch on the skin
and others to deep pressure and joint/muscle movement
• Information from touch receptors in the head enter the
CNS through the cranial nerves and below the head it
enters the spinal cord through the 31 spinal nerves which
innervate (connect) to a defined region Dermatomes

Pain Temperature and Touch
• sensory Information travels through the spinal cord
along well defined pathways to the brain

Sensation
• A-beta fibers to spinal cord-2 ascending tracts
• Fasciculus gracilis (lower part of body)
• Fasciculus cuneatus (upper body)

Rapidly adapting and slow
adapting fibers
• Rapidly adapting fibers- fire only initially
• Slowly adapting, They continue to trigger nerve impulses as long as the stimulus
persists.
• Take two sheets of sandpaper of slightly different grades.
• By rubbing your fingertips over the surface you can easily distinguish which is
rougher. The rubbing is necessary to activate the RA1 receptor.
• Rubbing produces vibrations as grains repeatedly pass over each receptor. RA1
receptors have small receptive fields and thus fine spatial discrimination.
• Now place your fingertips steadily on each sheet. Note that it hard to say which is
rougher.
• This is because the RA1 receptors rapidly adapt to steady pressure.
• If you do not have sand paper, rub your fingertips over a table top. Try to find a
small scratch. Compare this sensation to that produced by just placing your finger
tips on the table.
• Whay are pressure receptors deeper in tissues?
• Pressure is a sustained sensation that is felt over a larger area than touch. It occurs
with deformation of deeper tissues than does touch.

Discrimination of touch on surfaces
• Spatial Resolution
• - the minimum physical distance between stimuli that results
in a two point stimulus being perceived as a two point
stimulus is a function of: Receptor density and Sensory
“fields” - convergence of receptor neurons on one brain
pathway Spatial resolution smallest for tongue: 2 mm
• Spatial resolution for finger tips: 4 mm Spatial resolution
largest for back:40 mm
The Receptive Field size determines spatial resolution--small
receptive field-high resolution large receptive field-lower
resolution
(the number of points that can be detected in a given skin area)
http://sriechman.tamu.edu/427%202%20Sensory%20pain%20inflammation%20&
%20hemostasis%20%5BCompatibility%20Mode%5D.pdf

Pain
• Associations
– No association with one particular stimulation
– All pain has the potential to cause tissue damage
– Often have emotional reactions
– Pain centers
• No single center in the brain for pain
• Up to 35% of patients with pathological pain get relief
from placebos
24 of 49

Pain Involved brain areas
• Reticular formation
Spinoreticular tract Arousal
• Limbic system
• Spinomescencephalic tract -Emotional
• Thalamus
• Posterior nuclear group Dull, burning pain
• Ventrobasal complex Sharp, prickling pain
• Cortical area
• Cingulate gyrus
• http://www.youtube.com/watch?v=uCFtvmlOZTs

Pain and Touch pathways
• Medial lemniscus pathway sensory pathway
responsible for transmitting fine touch, vibration and
conscious proprioceptive information from the body
to the cerebral cortex
• Spinalthalamic tract transmits information to
the thalamus about pain and temperature ( itch and crude touch).
The pathway decussates at the level of the spinal
cord, rather than in the brainstem like the posterior
column-medial lemniscus pathway
(and corticospinal tract)

Intensity is coded by the frequency of action potentials (frequency
coding) and the number of receptors activated (population coding).
Stronger stimuli produce a higher frequency of actions potentials

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