The nervous system has three main functions: sensory, integration, and motor. It is divided into the central nervous system (CNS; brain and spinal cord) and peripheral nervous system (PNS). The CNS contains neurons and neuroglia. Neuroglia provide support and protection for neurons. There are two types of neurons - sensory neurons transmit sensory information to the CNS, and motor neurons transmit signals from the CNS to effectors like muscles. Neurons communicate via electrical or chemical synapses using neurotransmitters like acetylcholine, GABA, glutamate, and catecholamines.

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ChapterChapter :8:8
NervousNervous SystemSystem
PartPart :1:1
Presented by: Prof.Mirza Anwar BaigPresented by: Prof.Mirza Anwar Baig
Anjuman-I-Islam's Kalsekar Technical CampusAnjuman-I-Islam's Kalsekar Technical Campus
School of Pharmacy,New Pavel,NaviSchool of Pharmacy,New Pavel,Navi
Mumbai,MaharashtraMumbai,Maharashtra
11

2. 2
The Nervous system has three major
functions:
 Sensory – monitors internal & external
environment through presence of receptors
 Integration – interpretation of sensory
information (information processing);
complex (higher order) functions
 Motor – response to information processed
through stimulation of effectors
 muscle contraction
 glandular secretion

3. 3
Basic Organization
• Sensory Input triggered
by stimuli
– conduction of signals to
processing center
• Integration
– interpretation of sensory
signals within processing
centers
• Motor output
– conduction of signals to
effector cells (i.e.
muscles, gland cells)
sensory receptor (sensory input)  integration  (motor output)
 effector

4. 4
• Brain
WHAT PARTS DO YOU KNOW THAT
ARE IN THE NERVOUS SYSTEM?
• Spinal Cord
• Peripheral
Nerves

5. 5
Two Anatomical Divisions
 Central nervous system (CNS)
 Brain
 Spinal cord
 Peripheral nervous system (PNS)
 All the neural tissue outside CNS
 Afferent division (sensory input)
 Efferent division (motor output)
 Somatic nervous system
 Autonomic nervous system
General Organization of the nervous system

6. 6
General Organization of the nervous system
Brain & spinal
cord

7. 7
Histology of neural tissue
Two types of neural cells in the nervous
system:
 Neurons - For processing, transfer, and
storage of information
 Neuroglia – For support, regulation &
protection of neurons

8. 8
Neuroglia (glial cells)
CNS neuroglia:
Astrocytes: Induces blood-brain barrier
Oligodendrocytes: Produce myelin
Microglia : Phagocytes in CNS
Ependymal cells : Line brain ventricles and
central canal of spinal cord
also part of structure that
makes CSF
PNS neuroglia:
Schwann cells : Produce myelin
Satellite cells : Support neurons in PNS

9. 9

10. 10

11. 11

12. 12
Astrocytes
• create supportive
framework for neurons
• create “blood-brain
barrier”
• monitor & regulate
interstitial fluid
surrounding neurons
• secrete chemicals for
embryological neuron
formation
• stimulate the
formation of scar tissue
secondary to CNS injury

13. 13
Oligodendrocytes
• create myelin sheath
around axons of
neurons in the CNS.
Myelinated axons
transmit impulses
faster than
unmyelinated axons
Microglia
• “brain macrophages”
• phagocytize cellular
wastes & pathogens

14. 14
Ependymal cells
• line ventricles of brain
& central canal of spinal
cord
• produce, monitor &
help circulate CSF
(cerebrospinal fluid)

15. 15
Schwann cells
• surround all axons of
neurons in the PNS creating
a neurilemma around them.
Neurilemma allows for
potential regeneration of
damaged axons
• creates myelin sheath
around most axons of PNS
Satellite cells
• support groups of cell
bodies of neurons within
ganglia of the PNS

16. 16
Neuron structure

17. 17
•Most axons of the nervous
system are surrounded by a
myelin sheath (myelinated axons)
•The presence of myelin speeds
up the transmission of action
potentials along the axon
•Myelin will get laid down in
segments (internodes) along the
axon, leaving unmyelinated gaps
known as “nodes of Ranvier”
•Regions of the nervous system
containing groupings of
myelinated axons make up the
“white matter”
•“gray matter” is mainly
comprised of groups of neuron
cell bodies, dendrites & synapses
(connections between neurons)
of Ranvier

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Classification of neurons
1. Structural classification based on number of
processes coming off of the cell body:

19. 19
Anaxonic neurons
• no anatomical clues to
determine axons from
dendrites
• functions unknown
Multipolar neuron
multiple dendrites &
single axon
most common type

20. 20
Bipolar neuron
• two processes coming
off cell body – one
dendrite & one axon
• only found in eye, ear
& nose
Unipolar
(pseudounipolar)
neuron
• single process
coming off cell body,
giving rise to
dendrites (at one end)
& axon (making up
rest of process)

21. 21
2. Functional classification based on type of
information & direction of information transmission:
Sensory (afferent) neurons –
•transmit sensory information from receptors of PNS towards the CNS
•most sensory neurons are unipolar, a few are bipolar
Motor (efferent) neurons –
transmit motor information from the CNS to effectors
(muscles/glands/adipose tissue) in the periphery of the body
all are multipolar
Association (interneurons) –
transmit information between neurons within the CNS; analyze inputs,
coordinate outputs
are the most common type of neuron (20 billion)
are all multipolar

22. 22
Conduction across synapses
Most synapses within the nervous system are chemical
synapses, & involve the release of a neurotransmitter
In order for neural control to occur, “information”
must not only be conducted along nerve cells, but
must also be transferred from one nerve cell to
another across a synapse.

23. 23
Neuronal Pools

24. 24
Anatomical organization of neurons
Neurons of the nervous system tend to group together
into organized bundles
The axons of neurons are bundled together to form
nerves in the PNS & tracts/pathways in the CNS.
Most axons are myelinated so these structures will be
part of “white matter”
The cell bodies of neurons are clustered together into
ganglia in the PNS & nuclei/centers in the CNS.
These are unmyelinated structures and will be part of
“gray matter”

25. 25
Anatomical structure of Nerves
Fig. 14.6

26. 26
Generation - Conduction of Neural Impulses
• Dependent on concentration
gradients of Na+ & K+
– Na+ 14x greater outside
– K+ 28x greater inside
• Membrane permeability
– lipid bilayer bars passage of K+
& Na+ ions
– protein channels and pumps
regulate passage of K+ & Na+
• at rest more K+ move out than
Na+ move in
• K+ ions diffuse out leave
behind excess negative charge
• Sodium-potassium pump
– Na+ out - K+ in (more Na+ out
than K+ in
– contributes to loss of (+)

27. 27
Overview of Neural Impulse

28. 28
• Maintenance of negative charge within neuron
– resting membrane potential about -70 millivolts
• Dissolved organic molecules [negative charge]
kept inside
• Na+ - K+ balance

29. 29

30. 30
Neurotransmissions:

31. 31
• Stimulus causes opening of
Na+ gates & closing of K+
gates -
• Threshold [~ +30 mV]
– all - or - nothing response
• Action potential localized
electrical event
• Changes permeability of
region immediately ahead
– changes in K+ & Na+ gates
– domino effect
– propagation of signal
• Intensity of stimuli (i.e. pinch
vs. punch) = number of
neurons firing
• Speed on impulse based on
diameter of axon & amount
of myelination

32. 32
Neurons Communicate at Synapses
Electrical [no synapse]
– common in heart & digestive tract - maintains steady,
rhythmic contraction
– All cells in effector contain receptor proteins for
neurotransmitters
Chemical - skeletal muscles & CNS
– presence of gap (SYNAPTIC CLEFT) which prevents action
potential from moving directly to receiving neuron
– ACTION POTENTIAL (electrical) converted to CHEMICAL
SIGNAL at synapse (molecules of neurotransmitter) then
generate ACTION POTENTIAL (electrical) in receiving neuron

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Overview of Transmission of Nerve Impulse
Action potential
1.synaptic knob
2.opening of Ca+ channels
3.neurotransmitter vesicles fuse with membrane
4.release of neurotransmitter into synaptic cleft
5.binding of neurotransmitter to protein receptor
molecules on receiving neuron membrane
6.opening of ion channels
7.triggering of new action potential
• Neurotransmitter is broken down by
enzymes & ion channels close -- effect
brief and precise

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Nerve Impulse
• Presynaptic neuron
• Vesicles
• [Calcium channels]
• Synaptic cleft
• Postsynaptic neuron
• Neurotransmitter
receptor

35. 35
Nerve Impulse
• Action potential
1.synaptic knob
2. opening of Ca+
channels
3.neurotransmitter
vesicles fuse with
membrane
4.release of
neurotransmitter
into synaptic cleft
Ca2+

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Nerve Impulse
• Action potential
neurotransmitter
vesicles fuse with
membrane
release of
neurotransmitter
into synaptic cleft

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• Action potential
binding of
neurotransmitter to
protein receptor
molecules on
receiving neuron
membrane
opening of sodium
channels
triggering of new
action potential

38. 38
Classification of Nerve Fibers
• Axons can be classified into three major groups based on the amount of
myelination, their diameters, and their propagation speeds:
1. A fibers :
The largest-diameter axons (5 – 20 mm) and are myelinated. A fibers
have a brief absolute refractory period. and conduct nerve impulses
(action potentials) at speeds of 12 to 130 m/sec (27–280 mi/hr). Example:
axons of sensory neurons for touch ,pressure etc
2. B fibers:
having axons with diameters of 2 – 3 mm. Like A fibers,B fibers are
myelinated and exhibit saltatory conduction at speeds up to 15 m/sec
(32 mi/hr). B fibers have a somewhat longer absolute refractory period
than A fibers. B fibers con- duct sensory nerve impulses from the
viscera to the brain and spinal cord.
3. C fibres: Smallest-diameter axons (0.5–1.5 mm) and unmyelinated. Nerve
impulse propagation 0.5 to 2 m/sec (1 – 4 mi/hr),longest absolute
refractory periods. These unmyeli- nated axons conduct some sensory
impulses for pain, touch,pressure, heat, and cold from the skin, and pain
impulses from the viscera.

39. 39
Neurotransmitters
• Catecholamine Neurotransmitters
– Derived from amino acid tyrosine
• Dopamine [Parkinson’s], norepinephrine,
epinephrine
• Amine Neurotransmitters
– acetylcholine, histamine, serotonin
• Amino Acids
– aspartic acid, GABA, glutamic acid, glycine
• Polypeptides
– Include many which also function as
hormones
– endorphins

40. 40
Neurotransmitters:
• About 100 substances are either known or suspected
neurotrans-mitters.
• Some neurotransmitters bind to their receptors and act quickly
,Others act more slowly via second-messenger systems to
influence chemical reactions inside cells.
• The result of either process can be excitation or inhibition of
postsynaptic neurons. Many neuro- transmitters are also
hormones released into the bloodstream by endocrine cells in
organs throughout the body.
• Within the brain, certain neurons, called neurosecretory cells,
also secrete hormones.
• Neurotransmitters can be divided into two classes based on size:
small-molecule neurotransmitters and neuropeptides
• The small-molecule neurotransmitters include acetylcholine,
amino acids, biogenic amines, ATP and other purines, and nitric
oxide.

41. 41
Ion channels for neurotransmitters

42. 42
1. Acetylcholine:
• The acetylcholine (ACh) is released by many PNS
neurons and by some CNS neu-rons.
• ACh is an excitatory neurotransmitter at some
synapses,such as the neuromuscular junction, where the
binding of ACh to ionotropic receptors opens cation
channels.
• It is also an inhibitory neurotransmitter at other synapses,
where it binds to metabotropic receptors coupled to G
proteins that open K channels.
• For example, ACh slows heart rate at inhibitory synapses
made by parasympathetic neu-rons of the vagus (X)
nerve.
• The enzyme acetylcholinesterase (AChE) inactivates
ACh by splitting it into acetate and choline fragments.

43. 43
2. Amino Acids:
• These neurotransmitters are present in the CNS.
• Glutamate (glutamic acid) and aspartate (aspartic
acid) have powerful excitatory effects.
• Most excitatory neurons in the CNS and perhaps half
of the synapses in the brain communicate via
glutamate.
• At some glutamate synapses, binding of the neuro-
transmitter to ionotropic receptors opens cation
channels.
• The consequent inflow of cations (mainly Na ions)
produces an EPSP. Inactivation of glutamate occurs
via reuptake.
• Glutamate transporters actively transport glutamate
back into the synaptic end bulbs and neighboring
neuroglia

44. 44
Excitotoxicity:
• A high level of glutamate in the interstitial fluid of the CNS
causes excitotoxicity—destruction of neurons through
prolonged activation of excitatory synaptic transmission.
• The most common cause of excitotoxicity is oxygen
deprivation of the brain due to ischemia (inadequate blood
flow), as happens during a stroke.
• Lack of oxygen causes the glu-tamate transporters to fail,
and glutamate accumulates in the interstitial spaces
between neurons and glia, literally stimulating the neurons
to death.
• Clinical trials are underway to see if antiglutamate drugs
administered after a stroke can offer some protection from
excitotoxicity.

45. 45
Gamma aminobutyric acid:
• GABA and glycine are important inhibitory neurotransmitters.
• At many synapses, the binding of GABA to ionotropic receptors
opens Cl ion channels.
• GABA is found only in the CNS, where it is the most common
inhibitory neurotransmitter.
• As many as one-third of all brain synapses use GABA.
• Antianxiety drugs such as diazepam enhance the action of
GABA.
• Like GABA, the binding of glycine to ionotropic receptors opens
Cl channels.
• About half of the inhibitory synapses in the spinal cord use the
amino acid glycine; the rest use GABA.

46. 46
3. Catecholeamine (Biogenic Amines)
• Norepinephrine, dopamine, and epinephrine are classified
Catecholamines, are synthesized from the amino acid tyrosine.
• Inactivation of catecholamines occurs via reuptake into
synaptic end bulbs.
• Then they are either recycled back into the synaptic vesicles or
destroyed by the enzymes.
• The two enzymes that break down catecholamines are catechol-
O-methyltrans- ferase or COMT, and monoamine oxidase or
MAO.

47. 47
• Certain amino acids are modified and decarboxylated to
produce biogenic amines.
• Those that are prevalent in the nervous system include
norepinephrine, epineph-rine, dopamine, and serotonin.
• Most biogenic amines bind to metabotropic receptors
• Biogenic amines may cause either excitation or inhibition.
a. Norepinephrine (NE) :
NE plays roles in arousal (awakening from deep sleep),
dreaming, and regulating mood.
• A smaller number of neurons in the brain use epinephrine as a
neurotransmitter.
• Both epinephrine and norepinephrine also serve as hormones.
• Cells of the adrenal medulla, the inner portion of the adrenal
gland, release them into the blood.

48. 48
b. Dopamine:
• Brain neurons containing the neurotransmitter dopamine
(DA) are active during emotional responses, addictive
behaviors, and pleasurable experiences.
• In addition, dopamine-releasing neurons help regulate
skeletal muscle tone and some aspects of movement due to
contraction of skeletal muscles.
• The muscular stiffness that occurs in Parkinson disease is
due to degeneration of neurons that release dopamine. One
form of schizophrenia is due to accumulation of excess
dopamine.
c.Serotonin:
• Also known as 5-hydroxytryptamine (5-HT).
• Concentrated in the neurons in a part of the brain called the
raphe nucleus.
• It is thought to be involved in sensory
perception,temperature regulation, control of mood,
appetite, and the induc-tion of sleep.

49. 49
ATP and Other Purines:
• It is an excitatory neurotransmitter in both the CNS and the
PNS.
• Most of the synaptic vesicles that contain ATP also contain
another neurotransmitter.
• In the PNS, ATP and norepinephrine are released together
from some sympathetic neurons; some parasympathetic
neurons release ATP and acetyl-choline in the same vesicles.
Nitric Oxide:
• The simple gas nitric oxide (NO) is an important
neurotransmitter that has widespread effects throughout the
body.
• NO contains a single nitrogen atom, in contrast to nitrous
oxide (N 2 O), or laughing gas, which has two nitrogen atoms.
• N 2 O is sometimes used as an anesthetic during dental
procedures.

50. 50
Neuropeptides:
• Neurotransmitters consisting of 3 to 40 amino
acids linked by peptide bonds called
neuropeptides , are numerous and widespread in
both the CNS and the PNS.
• Neuropeptides bind to metabotropic receptors
and have excita-tory or inhibitory actions,
depending on the type of metabotropic receptor
at the synapse.
• Neuropeptides are formed in the neuron cell
body, packaged into vesicles, and transported to
axon terminals.
• Besides their role as neurotransmitters, many
neuropeptides serve as hormones that regulate
physiological responses.

51. 51
Role of Neuropeptides:

52. 52
Modifying the effect of neurotransmitters:
Substances naturally present in the body as well as drugs and
toxins can modify the effects of neurotransmitters in several
ways:
1. Neurotransmitter synthesis can be stimulated or inhibited. For
in-stance, many patients with Parkinson disease receive
benefit from the drug L -dopa because it is a precursor of
dopamine. It boosts dopamine production in affected brain
areas.
2. Neurotransmitter release can be enhanced or blocked.
Amphetamines promote release of dopamine and
norepinephrine. & Botulinum toxin causes paralysis by
blocking release of acetylcholine from somatic motor neurons.
3. The neurotransmitter receptors can be activated or blocked.
Isoproterenol (Isuprel ® ) is a powerful agonist of epinephrine
and norepinephrine.

53. 53
Regeneration & repair of nervous
tissue:
Throughout your life, nervous system exhibits plasticity.
At the level of individual neurons, the changes that can occur
include the germination of new dendrites, synthesis of new
proteins, and changes in synaptic contacts with other
neurons.
Despite plasticity, mammalian neurons have very limited
powers of regeneration, the capability to replicate or repair
themselves.
In the PNS, damage to dendrites and myelinated axons may
be repaired if the cell body remains intact and if the
Schwann cells that produce myelination remain active.
In the CNS, little or no repair of damage to neurons occurs.
Even when the cell body remains intact, a severed axon
cannot be repaired or regrown.

54. 54
Neurogenesis in CNS:
• Neurogenesis—the birth of new neurons from undifferenti-
• ated stem cells—occurs regularly in some animals. For example,
new neurons appear and disappear every year in some
songbirds. Until recently, the dogma in humans and other
primates was “no new neurons” in the adult brain.
• Epidermal growth factor (EGF) stimulated cells taken from the
brains of adult mice to proliferate into both neurons and
astrocytes.
• In 1998, scientists dis-covered that significant numbers of new
neurons do arise in the adult human hippocampus only , an
area of the brain that is crucial for learning .

55. 55
Reasons for lack of regenration of neurons in
CNS:
Factors responsible for lack of regenration:
1) inhibitory influences from neuroglia, particularly oligoden-
drocytes.
2) absence of growth-stimulating signals during fetal
development.
3) Axons in the CNS are myeli-nated by oligodendrocytes rather
than Schwann cells, and this CNS myelin is one of the factors
inhibiting regeneration of neurons.
4) Also, after axonal damage, nearby astrocytes proliferate
rapidly, forming a type of scar tissue that acts as a physical
barrier to regeneration.
Thus, injury of the brain or spinal cord usually is
permanent.

56. 56
ANATOMY OF CENTRAL
NERVOUS SYSTEM

57. 57
Parts of Brain:
1. Cerebrum-largest
part of brain.
responsible for
reasoning,
thought, memory,
speech,
sensation, etc.
• Divided into two
halves.
• Further divided
into lobes;
occipital, parietal,
temporal and
frontal.

58. 58
2. Cerebellum-
responsible for
muscle coordination
3. Brain stem- most
basic functions;
respiration,
swallowing, blood
pressure.
4.Lower part (medulla
oblongata) is
continuous with
spinal cord

59. 59
5. Spinal cord-
begins at foramen
magnum and ends
at second lumbar
vertebrae
Contains both
afferent (to the
brain) and efferent
(motor neurons-
away from the
brain)

60. 60
Coverings:
Both the brain and spinal cord are covered by a
membrane system called the meninges,lying between
the skull and the brain and between the vertebrae
and the spinal cord.
• Named from outside inwards they are:
1)Dura mater
2)Arachnoid mater
3)Pia mater
The dura and arachnoid maters are separated by a
potential space, the subdural space.
The arachnoid and pia maters are separated by the
subarachnoid space, containing cerebrospinal fluid.

61. 61
Coverings and Blood Brain Barrier:

62. 62
Cerebrospinal fluid (CSF)
• Ependymal cells form cerebrospinal fluid from blood
plasma by filtration and secretion.
• Secreted into each ventricle of the brain by choroid
plexuses (vascular areas where there is a proliferation
of blood vessels surrounded by ependymal cells in the
lining of ventricle walls.)
• CSF is a clear, slightly alkaline fluid with a specific
gravity of 1.005, consisting of:
– water
– mineral salts
– glucose
– plasma proteins: small amounts of albumin and globulin
– creatinine
– urea
– a few leukocytes.

63. 63
Formation of CSF:

64. 64
Flow of CSF:

65. 65
Ventricles
1.Filled with CSF (cerebrospinal fluid)
2.Lined by ependymal cells (these cells
lining the choroid plexus make the CSF)
3.Continuous with each other and central
canal of spinal cord

66. 66
Functions of cerebrospinal fluid
1. It supports and protects the brain and spinal cord.
2. It maintains a uniform pressure around these delicate
structures.
3. It acts as a cushion and shock absorber between the
brain and the cranial bones.
4. It keeps the brain and spinal cord moist and there may
be interchange of substances between CSF and nerve
cells, such as nutrients and waste products.

67. 67
Peripheral nervous system
• Somatic system
– 12 pairs cranial
nerves
– 31 pairs spinal
nerves
• Autonomic
– Sympathetic
• Fight or flight
– Parasympathetic

68. 68
Brain:
The brain constitutes about one-
fiftieth of the body weight and lies
within the cranial cavity.
The parts are
1. cerebrum
2. midbrain
3. pons
4. medulla oblongata
5. cerebellum.
6. the brain stem

69. 69
Blood supply to the brain:
• The circulus arteriosus and its
contributing arteries play a
vital role in maintaining a
constant supply of oxygen
and glucose.
• The brain receives about 15%
of the cardiac output, approx
750 ml of blood/minute.
• Autoregulation maintain blood
flow to the brain constant by
adjusting the diameter (about
65-140 mmHg) with changes
occurring only outside these
limits.

70. 70
Cerebrum
This is the largest part of the brain
and it occupies the anterior and
middle cranial fossae.
It is divided by a deep cleft, the
longitudinal cerebral fis-sure, into
right and left cerebral
hemispheres, each containing one
of the lateral ventricles.
Deep within the brain the
hemispheres are connected by a
mass of white matter (nerve
fibres) called the corpus
callosum.
The superficial (peripheral) part of
the cerebrum is composed of
nerve cell bodies or grey matter,
forming the cerebral cortex, and
the deeper layers consist of nerve
fibres or white matter.

71. 71
Surface anatomy
Gyri (plural of gyrus)
Elevated ridges
Entire surface
Grooves separate gyri
A sulcus is a
shallow groove
(plural, sulci)
Deeper grooves are
fissures

72. 72
Gyri (plural of gyrus)
Elevated ridges
Entire surface
Grooves separate gyri
A sulcus is a shallow groove (plural, sulci)
Deeper grooves are fissures

73. 73
 Lateral sulcus separates temporal lobe from
parietal lobe
 Parieto-occipital sulcus divides occipital and
parietal lobes (not seen from outside)
 Transverse cerebral fissure separates cerebral
hemispheres from cerebellum

74. 74
Cerberal cortex:
The cerebral cortex shows many infoldings or furrows
of varying depth. The exposed areas of the folds are the
gyri or convolutions and these are separated by sulci or
fissures.
These convolutions greatly increase the surface area of the
cerebrum.
For descriptive purposes each hemisphere of the cerebrum is
divided into lobes which take the names of the bones of the
cranium under which they lie:
frontal, parietal,temporal and occipital.
The boundaries of the lobes are marked by deep sulci
(fissures). These are the central, lateral and parieto-occipital
sulci .

75. 75
Interior of the cerebrum:
The surface of the cerebral cortex
is composed of grey matter
(nerve cell bodies).
Within the cerebrum the lobes
are connected by masses of
nerve fibres, or tracts, which
make up the white matter of the
brain.
The afferent and efferent fibres
linking the different parts of the
brain and spinal cord are as
follows.
• Association (arcuate) fibres
• Commissural fibres
• Projection fibres

76. 76
Afferent and efferent fibres:
• Association (arcuate) fibres connect different parts of a
cerebral hemisphere by extending from one gyrus to another,
some of which are adjacent and some distant.
• Commissural fibres connect corresponding areas of the two
cerebral hemispheres; the largest and most important
commissure is the corpus callosum.
• Projection fibres connect the cerebral cortex with grey matter of
lower parts of the brain and with the spinal cord, e.g. the
internal capsule ( lies deep within the brain between the basal
nuclei (ganglia) and the thalamus.
Many nerve impulses passing to and from the cerebral cerebral cortex
are carried by fibres that form the internal capsule.
Motor fibres within the internal capsule form the pyramidal tracts
(corticospinal tracts) that cross over (decussate) at the medulla
oblongata.

77. 77
Functions of cerbrum (simplified)
Back of brain: perception
Top of brain: movement
Front of brain: thinking

78. 78
Functional areas of the cerebrum
1. Motor areas of the cerebrum
a.The premotor area. This lies in the frontal
lobe immediately anterior to the motor area.
Motor speech (Broca's) area which controls the
movements necessary for speech. It is dominant
in the left hemisphere in right-handed people and
vice versa.
b.The frontal area. This extends anteriorly from
the premotor area to include the remainder of the
frontal lobe.

79. 79

80. 80
Sensory areas of the cerebrum
The postcentral (sensory) area.
Ø This is the area behind the central sulcus.
Ø Sensations of pain, temperature, pressure and
touch, knowledge of muscular movement and the
position of joints are perceived.
The sensory area of the right hemisphere
receives impulses from the left side of the body
and vice versa.

81. 81
The auditory (hearing) area. This lies immediately below
the lateral sulcus within the temporal lobe. (8th cranial
nerves).
The olfactory (smell) area. This lies deep within the
temporal lobe where impulses from the nose via the
olfactory nerves (1st cranial nerves) are received and
interpreted.
The taste area. This is thought to lie just above the lateral
sulcus in the deep layers of the sensory area. (8th cranial
nerves)
The visual area. This lies behind the parieto-occipital
sulcus and includes the greater part of the occipital lobe.
(2nd cranial nerves)

82. 82
Association Areas
 Tie together different kinds of sensory input
 Associate new input with memories
 Is to be renamed “higher-order processing“
areas
Different areas
1. Premotor area:
2. Prefrontal area:
3. Wernicke’s area (speech area):
4. Pareito-occipital temporal area:

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Motor areas of cerebrum

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Other areas of the cerebrum
Deep within the cerebral
hemispheres there are groups of
cell bodies called nuclei
(called ganglia) which act as
relay stations where impulses
are passed from one neurone to
the next in a chain.
Important masses of grey matter
include:
• basal nuclei
• thalamus
• hypothalamus.

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Basal nuclei.
These are areas of grey matter, lying deep within the
cerebral hemispheres, with connections to the cerebral
cortex and thalamus.
The basal nuclei form part of the extrapyramidal tracts and
are thought to be involved in initiating muscle tone in slow
and coordi-nated activities.
If control is inadequate or absent, move-ments are jerky,
clumsy and uncoordinated.

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Thalamus.
The thalamus consists of two masses of nerve cells and fibres
situated within the cerebral hemispheres just below the corpus
callosum, one on each side of the third ventricle.
Sensory input from the skin, viscera and special sense organs is
transmitted to the thalamus before redistribution to the cerebrum.
Hypothalamus.
• The hypothalamus is composed of a number of groups of nerve
cells. It is situated below and in front of the thalamus, immediately
above the pituitary gland.
• The hypothalamus is linked to the posterior lobe of the pituitary
gland by nerve fibres and to the anterior lobe by a complex
system of blood vessels.
• Through these connections, the hypothalamus controls the output
of hormones from both lobes of the gland.

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Other functions of hypothalamus:
autonomic nervous system
appetite and satiety
thirst and water balance
body temperature
emotional reactions, e.g. pleasure, fear, rage
sexual behaviour including mating and child rearing
biological clocks or circadian rhythms, e.g. sleeping
and waking cycles, body temperature and secretion of
some hormones.

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Brain stem
1. Midbrain:
The midbrain is the area of the
brain situated around the
cerebral aqueduct between the
cerebrum above and the pons
below.
It consists of groups of cell
bodies and nerve fibres (tracts)
which connect the cerebrum with
lower parts of the brain and with
the spinal cord.
The cell bod-ies act as relay
stations for the ascending and
descending nerve fibres.

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2. Pons
The pons is situated in front of the cerebellum, below the
midbrain and above the medulla oblongata.
It consists mainly of nerve fibres which form a bridge
between the two hemispheres of the cerebellum, and of
fibres passing between the higher levels of the brain and
the spinal cord.
There are groups of cells within the pons which act as relay
stations and some of these are associated with the cranial
nerves.
The anatomical structure of the pons differs from that
of the cerebrum in that the cell bodies (grey matter) lie
deeply and the nerve fibres are on the surface.

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3.Medulla oblongata
The medulla oblongata extends from the pons above and is
continuous with the spinal cord below.
It is about 2.5 cm long and it lies just within the cranium
above the foramen magnum.
Its anterior and posterior surfaces are marked by central
fissures. The outer aspect is composed of white matter
which passes between the brain and the spinal cord, and
grey matter lies centrally.
Some cells con-stitute relay stations for sensory nerves
passing from the spinal cord to the cerebrum.
The vital centres, consisting of groups of cells associated
with autonomic reflex activity, lie in its deeper structure.
These are the:
cardiac centre
respiratory centre
vasomotor centre
reflex centres of vomiting, coughing, sneezing and
swallowing.

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Other functions of medulla oblongata:
1. Decussation (crossing) of the pyramids. In the medulla
motor nerves descending from the motor area in the
cerebrum to the spinal cord in the pyramidal (corticospinal)
tracts cross from one side to the other.
These tracts are the main pathway for impulses to skeletal
(voluntary) muscles.
2. Sensory decussation. Some of the sensory nerves ascending
to the cerebrum from the spinal cord cross from one side to
the other in the medulla.
3. Others decussate at lower levels, i.e. in the spinal cord.

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4. The cardiovascular centre :
controls the rate and force of cardiac contraction. sympathetic
and parasympathetic nerve fibres originating in the medulla
pass to the heart. Sympathetic stimulation increases the rate
and force of the heartbeat and parasympathetic stimulation has
the opposite effect.
5. The respiratory centre:
controls the rate and depth of respiration. From this centre,
nerve impulses pass to the phrenic and intercostal nerves
which stimulate contraction of the diaphragm and intercostal
muscles,thus initiating inspiration.
The respiratory centre is stimulated by excess carbon dioxide
and, to a lesser extent, by deficiency of oxygen in its blood
supply and by nerve impulses

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6. The vasomotor centre:
It controls the diameter of the blood vessels, especially the
small arteries and arterioles which have a large proportion
of smooth muscle fibres in their walls.
Vasomotor impulses reach the blood vessels through the
autonomic nervous system.
Stimulation may cause either constriction or dilatation of
blood vessels depending on the site.
The sources of stimulation of the vasomotor centre are the
arterial baroreceptors, body temperature and emotions
such as sexual excitement and anger.
Pain usually causes vasoconstriction although severe pain
may cause vasodilatation, a fall in blood pressure and
fainting.

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7. Reflex centres:
• When irritating substances are present in the
stomach or respiratory tract, nerve impulses pass
to the medulla oblongata, stimulating the reflex
centres which initiate the reflex actions of vomiting,
coughing and sneezing to expel the irritant.

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Reticular formation:
The reticular formation is involved in:
Coordination of skeletal muscle activity associated with
voluntary motor movement and the maintenance of
balance
Coordination of activity controlled by the autonomic
nervous system, e.g. cardiovascular, respiratory and
gastrointestinal activity.
Selective awareness that functions through the reticular
activating system (RAS) which selectively blocks or passes
sensory information to the cerebral cortex, e.g. the slight
sound made by a sick child moving in bed may arouse his
mother but the noise of regularly passing trains may be
suppressed.

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Cerebellum:
• The cerebellum is situated behind the pons and
immediately below the posterior portion of the cerebrum
occupying the posterior cranial fossa.
• It is ovoid in shape and has two hemispheres, separated by
a narrow median strip called the vermis.
• Grey matter forms the surface of the cerebellum, and the
white matter lies deeply.

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CerebellumTwo major hemispheres: three
lobes each
Anterior
Posterior
Floculonodular
Vermis: midline lobe connecting
hemispheres
Outer cortex of gray
Inner branching white matter,
called “arbor vitae”
Separated from brain stem by 4th ventricle

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Functions:
• The cerebellum is concerned with the coordination of
voluntary muscular movement, posture and balance.
• Cerebellar activities are not under voluntary control.
• The sensory input for these functions is derived from the
muscles and joints, the eyes and the ears.
• Proprioceptor impulses from the muscles and joints indicate
their position in relation to the body as a whole and those
impulses from the eyes and the semicircular canals in the
ears provide information about the position of the head in
space.
• Impulses from the cerebellum influence the contraction of
skeletal muscle so that balance and posture are maintained.
• Damage to the cerebellum results in clumsy uncoordinated
muscular movement, staggering gait and inability to carry out
smooth, steady, precise movements.

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SPINAL CODE:

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SPINAL CORD:
It is the elongated, almost cylindrical part of the central nervous
system, which is suspended in the vertebral canal surrounded
by the meninges and cerebrospinal fluid.
It is continuous above with the medulla oblongata and extends
from the upper border of the atlas to the lower border of the 1st
lumbar vertebra.
It is approximately 45 cm long in an adult Caucasian male, and
is about the thickness of the little finger.
When a specimen of cerebrospinal fluid is required it is taken
from a point below the end of the cord, i.e. below the level of
the 2nd lumbar vertebra (lumbar puncture).
Nerves conveying impulses from the brain to the various organs
and tissues descend through the spinal cord.

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Some activities of the spinal cord are independent of the
brain, i.e. spinal reflexes (through extensive neurone
connections between sensory and motor neurones ).
The spinal cord is incompletely divided into two equal parts,
anteriorly by a short, shallow median fissure and posteriorly
by a deep narrow septum, the posterior median septum.
A cross-section of the spinal cord shows that it is composed
of grey matter in the centre surrounded by white matter
supported by neuroglia.

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Grey matter:
• The arrangement of grey matter in the spinal cord resembles the shape
of the letter H, having two posterior, two anterior and two lateral
columns.
• The area of grey matter lying transversely is the transverse commissure
and it is pierced by the central canal, an extension from the fourth
ventricle, containing cerebrospinal fluid.
• The cell bodies may be:
• Sensory cells: which receive impulses from the periphery of the body
• Lower motor neurones: which transmit impulses to the skeletal
muscles
•Connector neurones: linking sensory and motor neurones, at the same
or different levels, which form spinal reflex arcs.
• At each point where nerve impulses are passed from one neurone to
another there is a synaptic cleft and a neurotransmitter

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Posterior columns of grey matter:
These are composed of cell bodies which are stimulated by
sensory impulses from the periphery of the body.
The nerve fibres of these cells contribute to the formation of the
white matter of the cord and transmit the sensory impulses
upwards to the brain.
Anterior columns of grey matter
These are composed of the cell bodies of the lower motor
neurones which are stimulated by the axons of the upper
motor neurones or by the cell bodies of connector neurones
linking the anterior and posterior columns to form reflex
arcs.
The posterior root (spinal) ganglia are composed of
cell bodies which lie just outside the spinal cord on the pathway
of the sensory nerves.
• All sensory nerve fibres pass through these ganglia. The only
function of the cells is to promote the onward movement of
nerve impulses.

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White matter:
It is arranged in three columns or tracts
1. anterior
2.posterior
3.lateral.
These tracts are formed by sensory nerve fibres ascending to
the brain, motor nerve fibres descending from the brain and
fibres of connector neurones.
Tracts are often named according to their points of origin and
destination, e.g. spinothalamic, corticospinal.

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Sensory nerve tracts (afferent or ascending) &
motor nerve tracts (efferent or descending)
in the spinal cord

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Reflex arc:

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The Stretch Reflex
• A stretch reflex causes contraction of a skeletal muscle (the
effector) in response to stretching of the muscle.
• This type of reflex occurs via a monosynaptic reflex arc. The reflex
can occur by activation of a single sensory neuron that forms one
synapse in the CNS with a single motor neuron.

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Tendon refelx:

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Functions
1.Sensory and motor innervation of
entire body inferior to the head
through the spinal nerves
2.Two-way conduction pathway
between the body and the brain
3.Major center for reflexes