2. – Neuron circuits – a single neuron cannot fully
perform its function, thus its optimal performance
has to be within a circuit
– Plasticity- allows the brain to change from circuit
to circuit depending on sensory input and past
experience
9. Neural Tissue: Metabolic Needs
• Oxygen
– Passes freely across blood-brain barrier
– Brain receives 15% of blood pumped by heart
• Glucose
– Brain responsible for about half of body’s glucose
consumption
– Membrane transporters move glucose from
plasma into the brain interstitial fluid
– Hypoglycemia leads to confusion,
unconsciousness, and death
10. Spinal Cord: Overview
Central nervous system,
posterior view
Figure 9-4a
The spinal cord has
two enlargements
and ends in the
lumbar region.
Spinal nerves are
part of the PNS and
carry both sensory
and motor neuron
fibers.
12. Spinal Cord: Anatomy
Figure 9-7b
Propriospinal
tracts remain
within
the cord
Tracts carry
information in
only one
direction along
a specified
path of
interneuron
connections.
14. Spinal Cord: Integrating Center
Figure 9-8
Simple reflexes
can be
integrated by the
spinal cord
without input
from the brain
15. Figure 9-9d
Anatomy of the Brain
Oldest and
most
primitive
region of
the brain.
Ascending
and
descending
tracts pass
through the
brain stem.
16. The Brain: The Brain Stem
• Divided into three regions- medulla oblongota, pons,
and midbrain
• Each region contains cranial nerves & nuclei that
control autonomic function
• Many nuclei are associated with reticular formation-
white fibers that interconnect different areas
throughout the brain.
• Medulla Oblongata- controls involuntary funtions and
connects to spinal cord.
– Somatosensory (ascending) and corticospinal (descending)
tracts in white matter
– Pyramids- area where the fibers cross over thus the many
functions are controlled by the opposite side of the brain.
17. 2. Reticular formation-
These are clusters of
neurons (white matter)
that run through the
core of the brainstem.
Involved in maintaining
the brain alert, arousal,
and sleep. It also
control visceral
functions like heart rate
& vomiting. A motor
tract goes down the
spinal cord and is
involved in movement.
Reticular Formation
20. The Brain: Diencephalon
Figure 9-10
Thalamus is a relay
and integrating station
Hypothalamus is the
homeostasis center
and also controls
behavior related to
homeostasis
Two endocrine
structures: pineal and
pituitary gland.
22. The Brain: Cerebellum
Lateral view of brain
The cerebellum coordinates movement- also processes
sensory information and motor input from the cerebrum; it
smoothes and coordinates movement.
Figure 9-9b
23. Figure 9-9c
Cerebral Mid-Sagittal View
Corpus
Callosum is
white matter
that connects
the two
hemispheres
Sulci= grooves
Gyri=
convolutions
24. White Matter in the cerebrum contains fibers that connect
various brain areas
25. Gray Matter of the Cerebrum
Figure 9-11
Cerebral cortex is
30 layers thick and
it’s the site of
higher brain
function.
The level of
processing is
directly related to
the surface area
Basal ganglia-
neural calculators
that control
movement
26. The Brain: The Limbic System
• Emotion, memory,
learning, and visceral
responses
• Links higher cognitive
functions and
primitive emotional
responses
• Incorporates sensory
areas, basal ganglia,
and the diencephalon
(hypothalamus)
relates state of mind
to physiological
functions
Figure 9-13
27. Brain Function: complex processing
and responses
• The brain may generate
information and output
signals in the absence of
external input
• Motor output is influenced
by sensory information,
cognition, and behavior.
Thus cognitive input may
influence the motor output
sent without sensory input.
28. Brain Function: Functional Areas of the Cerebral Cortex
Figure 9-15
Specialized sensations have separate designated
areas on the cortex
29. Brain Function: Cerebral Cortex
• Three specializations – Sensory, Motor, and Association (cognition
and behavior).
– Sensory areas - stimulus activates sensory receptors, info travels in
ascending pathways and stops at the cerebellum or sensory areas of
cerebrum
• Sensory input translated into perception – brain’s interpretation of
various input regions
– Motor areas – info travels in descending pathways, cross-over at
brainstem or spinal cord, and reaches muscles
Direct skeletal muscle movement – initiated by cognitive system
based on input from cerebral motoer ares, cerebellum, & basal
ganglia
– Association areas -
• Integrate information from sensory and motor areas -
• Can direct voluntary behaviors – control over conscious actions
32. Brain Function: Sensory Information
• Primary somatic sensory cortex- found on the
post-central gyrus (parietal lobe)
– Skin, musculoskeletal system, and viscera-
components that send information to this region
when a stimulus activates a sensory receptor
– Somatosensory pathways – carry information of
senses in conscious awareness of general somatic
sense, damaged brain area causes reduced
sensitivity in opposite side
• Touch
• Temperature
• Pain
• Itch
• Body position
33. Brain Function: Sensory Information
• Special senses have devoted regions -
– Visual cortex –Occipital lobe (Visual
Assosiaction area and Visual cortex)
– Auditory cortex – Temporal lobe
(Auditory association area and
Audiotory Cortex
– Olfactory cortex- Temporal lobe
(uncus)
– Gustatory cortex – Frontal lobe
• Processed into perception – allows the
stimulus to be translated into a different
aspect (photons=colors) and “fills-in”
missing information. Perception is the
brains interpretation of sensory input
and it is not directly dictated by the input
34. Brain Function: Motor Output
• Three major types
– Skeletal muscle movement
• Somatic motor division, involves voluntary actions processed at
cerebrum or reflexes processed at the spinal cord
– Neuroendocrine signals
• Hypothalamus and adrenal medulla- secrete neurohormones that
influence motor output
– Visceral responses
• Autonomic division- brains stem and diecephalon stimulate
involuntary muscle and glands to maintain involuntary actions
needed for function of internal organs and homeostasis
• Voluntary movement
– Primary motor cortex and motor association- contralateral control, also
influenced by behavioral and cognitive systems
35. Brain Function: Cerebral Lateralization
Each lobe has special functions- these are not equally
shared by the opposite lobe. Right handed people tend
to have left hemisphere dominance.
Figure 9-16
36. Brain Function Influenced by Behavioral State
• Modulator of sensory and cognitive processes – incorporates the
reticular formation, hypothalamus, limbic system, and regions of
the cerebral cortex
• Neurons known as diffuse modulatory systems- regulate brain
function by affecting attention, motivation, wakefulness, memory,
motor control, mood, and metabolic homeostasis
– In reticular formation in brain stem- most originate at brain stem and
innervate areas of the cerebrum and diencephalon, classified by
neurotransmitters used
• Four modulatory systems
– Adrenergic – secretes norepinephrine, originate at pons, modulate:
attention, arousal, sleep-wake cycles, learning, memory, anxiety, pain,
and mood.
– Serotonergic – secretes serotonin, originate at brain stem midline,
modulate pain, movement, sleep-wake cycles, mood, emotion
– Dopaminergic – secretes domamine, originate at midbrain, modulate
motor control and addictive behaviors
– Cholinergic – secrete acetylcholine, originate at cerebrum and brain
stem, modulate sensory information pathways through thalamus,
arousal, sleep-wake cycles, learning, memory
38. Behavioral State System: Arousal and Sleep-Wake Cycles
• Consciousness- a state of arousal in which the brain is aware of
self and environment
– Reticular formation- actively interacting through ascending tracts
– Anesthetics- block signals from reaching the reticular formation
• Electroencephalograms (EGG)
– Dectect level of activity of cerebral cortex neurons used electrodes
• Awake State- various stage of awareness
– Uncoordinate firing of cortical neurons due to ascending signals in
reticular formation results in low-amplitude high-frequency waves
– As awareness declines signals the frequency of waves declines and
amplitute increases
• Sleep- major rest period for the body, no external interaction,
easily reversible, brain is as active as when awake
39. Behavioral State System: States of Arousal
Electroencephalograms
(EEGs) and the sleep
cycle
Wave frequency
lessens and
amplitude increaes
as arousal
diminshes
During sleep the brain
cycles multiple
types between all
stages
Delta waves are high
amplitude, low
frequency
Figure 9-20a
40. Behavioral State System: States of Arousal
• Four stages with two major phases
– Slow-wave sleep – delta waves,
• Adjust body without conscious commands
– REM sleep
• Brain activity inhibits motor neurons to skeletal muscle,
paralyzing them –also reducing homeostasis responses
• Dreaming takes place
• Circadian rhythm
– Suprachiasmatic nucleus- location of neurons that
signal light-dark cycle phases and responses
42. Brain Function: Language
Cerebral processing of spoken and visual language
Damage to Wernicke’s causes receptive aphasia- unable to understand
spoken or visual information
Damage to Broca’s area causes expressive aphasia- can understand information
but cannot speak or write in proper order, are aware of mistakes
Figure 9-23a
43. Cerebrospinal Fluid (CSF)
CSF fills ventricles and subarachnoid space.
- Volume = 150 ml
- Rate of production =550 ml/d, so it turns 3.7 times/day.
- Lumbar CSF pressure = 70-180 mm CSF
- Absorption of CSF occurs by bulk flow is proportionate to CSF
pressure.:
- At pressure of 112 mm (normal average): filtration and absorption
are equal.
- Below pressure of 68 mm CSF, absorption stops.
- Hydrocephallus:
1. External hydrocephallus: Large amounts of CSF accumulates when
the reabsorptive capacity of arachnoid villi decreases.
2. Internal hydrocephallus: occurs when foramina of Luschka &
Magendie are blocked or obstruction within ventricular system,
resulting in distention of the ventricles.
44. - CSF is formed in:
1. Choroid plexus.
2. Around blood vessels.
3. Along ventricular walls.
• CSF is absorbed by:
• Arachnoid villi
45. Composition of the CSF
• The composition of CSF is essentially the same
as brain ECF
Substance CSF Plasma
Na+ 147 150
K+ 2.9 4.6
HCO3- 25 24.8
PCO2 50 39.5
pH 7.33 7.4
Osmolality
Glucose
289
64
289
100
46. Functions of the CSF
1. Protective function: The brain is supported within
the arachnoid by the blood vessels , nerve roots and
the arcahnoid trabiculae. In air brain weight =1400 g,
but in its water bath of CSF , brain weight = 50 g,
making it suspended effectively. When the head
receives a blow, the arachnoid slides on the dura and
the brain moves, but its motion is gently checked by
the CSF cushion and by the arachnoid trabiculae.
Removal of CSF during lumbar puncture can cause
severe headache
47. Functions of CSF, continued,…
2. Facilitation of pulsatile cerebral blood flow,
3. Distribution of peptides, hormones, neuroendocrine factors
and other nutrients and essential substances to cells of the
body,
4. Wash away waste products.
5. Cardiovascular dynamics are also affected by CSF pressure, as
the flow of blood must be tightly regulated within the brain
to assure consistent brain oxygenation .
48. Blood brain Barrier (BBB)
It is formed by the tight junctions between
capillary endothelial cells of the brain and
between epithelial cells in the choroid plexus.
This effectively prevents proteins from
entering the brain in adults and slow the
penetration of smaller molecules.
Mechanisms of transport:
- Bulk flow.
- Carrier mediated transfer
- Vesicular transport.
49. Penetration of substances into the
brain
• Molecules pass easily:H2O, CO2, O2, lipid-
soluble free forms of steroid hormones.
• Molecules not pass: proteins, polypeptides.
• Slow penetration: H+, HCO3-
• Glucose : its passive penetration is slow, but is
transported across brain capillaries by GLUT1
50. Functions of BBB
• Maintanins the constancy of the environment
of the neurons in the CNS.
• Protection of the brain from endogenous and
exogenous toxins.
• Prevent escape of the neurotransmitters into
the general circulation.
