Anatom and physiology for the cental nervous system.

2.  The central nervous system
- The brain
- Spinal cord
 Peripheral nervous system
- spinal nerves – 31 pairs
- cranial nerves – 12 pairs
- autonomic nervous system

8.  DEFINITION
It is a cell that transmits nerve impulses
 STRUCTURE
 Cell body – form the grey matter
 Dendrites – processes which carry
impulses towards nerve cells (several)
 Axon – a long slender process that carry
nerve impulses away from the cell (only
one)

9.  Structure-cont’d
 Myelin sheath surrounds most
axons(gives a white appearance)
- it protects axon from injury and speed
the flow of nerve impulses tho’ axon
 Nodes of Ranvier(breaks in myelin
sheath)
- help in rapid transmission of impulses

10.  Structure-cont’d
 Neurilemma – a delicate membrane
that encases the axons, they consist
of Schwann cells
 Each axon ends in numerous
branches(synaptic knobs) which
contain chemical transmitters

12. 1. Sensory or afferent
- Transmit impulses from skin and other
organs toward the CNS
2. Motor or efferent
- Transmit impulses from the CNS toward
cells e.g voluntary muscles, sweat glands,
exocrine glands
3. Mixed nerves
- Sensory and motor nerves which are
enclosed within the same sheath of
connective tissue

13. 1. Irritability
The ability to initiate nerve impulses
in response to stimuli from:
- outside the body e.g touch , temp
- inside the body e.g a change in the
concentration of CO2 in blood alters
respiration

14. 2. Conductivity
Means the ability to transmit an impulse
from:
• One part of the brain to another
• The brain to V. muscles
• The brain to organs of the body-results
in contraction of muscles or secretion of
glands
• The outside world to the brain tho’ the
eyes, ears, nose and tongue

15.  Acetylcholine – produced at
neuromuscular junctions where it
causes muscle contraction
 Adrenaline
 Nor-adrenaline
 Serotonin
 GABA
 Dopamine

16.  There is always more than 1 neurone
involved in the transmission of a
nerve impulse from its origin to its
destination, whether sensory or
motor
 The point at which the nerve
impulse passes from one to another
is the synapse

17.  At its free end, the P.synaptic
knobs(boutons) are in close proximity
to the dendrites and cell body of the
next neurone. The boutons contain
vesicles which contain N.T
 The space between them is the synaptic
cleft
 The Neurotransmitter carry impulses
across synaptic clefts
 Once the action is over, the N.T are
neutralised by enzymes

20. Neuroglias (glial cells) are cells that
support and protect neurones
 TYPES
1. Astrocytes
- star-shaped
- found adjacent to blood vessels and
control the exchange of materials between
blood vessels and neurones(BBB)

22. 2. Oligodendrocytes
- Form the myelin sheath
3. Microglia
- Phagocytic macrophages which
engulf germs

24. These are coverings of the brain and
S.C
1. The Dura Mater
- The tough outer meninx lying just
inside the skull and vertebrae
2. The Arachnoid Mater
- The middle meninx
- The subarachnoid space - space
found between the arachnoid and Pia
Mater – it contains C.S.F

25. 3. The Pia Mater
- The innermost meninx – it tightly
covers the brain and S.C

29. 1. They are 4 cavities within the brain,
filled with CSF
2. STRUCTURE
 Right and left lateral Ventricles
 The 3rd ventricle – found below the
L.V
 The 4th ………… - found below the
3rd ventricle

32.  The ventricles communicate with the
S.A.S by foramina(openings)
 And also connects to the central
canal of the S.C

33.  It is secreted by the choroid plexus(network of
capillaries) in each ventricles
 The CSF circulates from the lateral Vent.to the
3rd and 4th Vent.
 From the 4th Vent. CSF passes into the Sub
Arachnoid Space , surrounding the brain and
Spinal Cord and the central canal
 CSF is reabsorbed tho’ the arachnoid villi
(B.Cap) and returned to the blood

35.  Clear, slightly alkaline fluid( PH 7.28-7.32)
 Consists of :
1. Water
2. Mineral salts
3. Glucose
4. Plasma proteins
5. Small amount of albumin & globulins
6. Creatinine (very small amount)
7. Urea (very small amount)

36.  FUNCTIONS OF CSF
1. Supports and protects the CNS
2. Acts as a cushion and shock
absorber to the brain
3. Distributes nutritive materials to
and remove wastes from
nervous tissues

37. The brain consists of the :
1.Cerebrum
2.Brain stem – midbrain
- pons varolli
- medulla oblongata
3.Cerebellum

38. 1.THE CEREBRUM
 STRUCTURE
 The largest part of the brain
 Appears as folded ridges and
grooves(convolutions)
 The convolutions are separated by
fissures or sulci

39. CEREBRUM- STRUCTURE(CONT’D)
 Consists of RT and LT cerebral
hemispheres
 Superficial part – grey
matter(cerebral cortex)
 Deeper layers – white matter

41.  LOBES
 Frontal
 Temporal
 Parietal
 occipital

43.  FUNCTIONS OF CEREBRUM
 Carries out mental activities
involved in memory, intelligence,
thinking, reasoning and learning
 Involves sensory perceptions e.g
pain, temp. touch, sight, taste, smell
etc
 Initiates and control voluntary
muscle contraction

44.  Above functions are carried out by :
- Motor area - Sensory area
- Auditory area - Taste area
- Speech area - Olfactory area
- Visual area

45.  INTERIOR OF CEREBRUM
Consists of groups of nerve cells
 Basal nuclei – influences skeletal tone
 Thalamus – involved with perception of
pain, temp. and sensory perception from
viscera and special sense organs
 The hypothalamus :
- Controls the ANS – e.g emotion, behaviour,
hunger, thirst, body temp.
- Controls the output of hormones from the
pituitary gland

47. 2.THE BRAIN STEM
 The midbrain
It connects the cerebrum to the lower part
of the brain and SC
Cranial nerves 3 and 4 originate from it
 The pons V
It is the bulging region in the middle of the
brain stem
It controls respiration
4 pairs of C.N

48.  The medulla oblongata
The lower portion of the brainstem which
merges with S.C
Consists of Vital centres:
- Respiratory centre - Coughing centre
- Vasomotor centre - Sneezing centre
- Reflex centre - Swallowing centre
- Vomiting centre
Decussation of pyramids(crossing over of
motor nerves)

49. 3. THE CEREBELLUM
 Position: behind pons and below
posterior cerebrum
 Shape : ovoid and has 2 wing-like lobes
 Functions:
-For coordination of voluntary muscular
movement
-For posture and balance(equilibrium)

50.  STRUCTURE
 It is an extension of the brain stem that
begins at the foramen magnum down to
L1
 It is elongated(cylindrical) and lies in the
vertebral canal
 The S.C ends by the filum terminale that
attaches to the coccyx
 Spinal nerves emerge in pairs, one from
each side of the cord(31 pairs)

53.  CROSS SECTION OF THE S.C
Composed of grey matter in the
centre(letter-H) and surrounded by white
matter
Nerve tracts
 Sensory nerve tract(ascending)
Transmit sensory information from various
parts of the body to the brain
 Motor nerve tract(descending)
Transmit impulses from the brain to
muscles and glands

57.  FUNCTION OF SC
- For transmission of nerve impulses
- For spinal reflexes

58.  REFLEX ARC
- A rapid involuntary response to a stimulus
E.g touching a very hot surface with the
fingers
- Most reflexes are spinal reflexes with
pathways that pass only tho’ the SC
- Components are :
Stimulus nerve endings→ sensory nerve→
connector nerve→ motor nerve→ muscle

59.  A rapid automatic response to a stimulus by an
organ or system of organs, which does not
involve the brain for its initiation.
Stimulus activation of receptor CNS,Spinal
Cord or Brain Motor Neurone Effector
(muscle or gland)

60. The Reflex Arc
 Reflex – rapid, predictable, and
involuntary responses to stimuli
 Reflex arc – direct route from a sensory
neuron, to an interneuron, to an effector

61. Simple Reflex Arc
Figure 7.11b, c

62. Types of Reflexes and Regulation
 Autonomic reflexes
1. Smooth muscle regulation
2. Heart and blood pressure regulation
3. Regulation of glands
4. Digestive system regulation
 Somatic reflexes
1. Activation of skeletal muscles

63.  Contraction or dilatation of pupil of the eye
due to changes in light intensity (cranial reflex
action)
 Blinking of the eye when a foreign particle
touches the cornea.(cranial reflex action)
 Knee jerk ( spinal reflex action)
 Contraction of the biceps muscles to remove
the hands from a hot object ( spinal reflex
action)

65. 1. THE SPINAL NERVES
 Number
- 31 pairs
- They leave the SC tho’ the
intervertebral foramina

67.  NAMES
According to the vertebrae with which
they are associated
 8 cervical
 12 thoracic
 5 lumbar
 5 sacral
 1 coccygeal

68.  Outside the VC the spinal nerves
divide into branches
 In some regions the spinal nerves
unite to form large masses of nerves
known as plexuses

69.  there are 12 pairs of CN
 They originate from nuclei in the
inferior surface of the brain
 They consist of :
- Sensory nerves
- Motor ……...
- Mixed ……..

70.  12 pairs of Cranial nerves
1. Olfactory nerve for sense of smell.
2. Optic nerve for sense of sight .
3. Occulomotor Nerve for moving the eye
ball, focussing and regulating the size of
the pupil.
4. Trochlear Nerve Movement of eyeball.
5. Trigeminal Nerve for Chewing and
sensation from the face.

71. 6.Abducent Nerve for movement of eyes.
7.Facial Nerve sense of taste and movements of
facial expressions.
8.Vestibulocochlear Nerve for maintainance of
balance and sense of hearing.

72. 9.Glossopharyngeal Nerve for secretion of saliva,
sense of taste and movement of pharynx.
10.Vagus Nerve for movements and secretion.
11.Accessory Nerve for movements of head,
shoulders .
12. Hypoglossal Nerve for movement of tongue.

75.  DEFINITION
It is the involuntary part of the
nervous system which controls
functions of the body carried out
automatically

77.  FUNCTIONS OF THE ANS
 Maintains homeostasis
 Controls the rate and force of the of the
heart
 Controls secretion of the glands of the
GIT
 Causes contraction and relaxation of
involuntary muscles
 E.g vasoconstriction or vasodilatation
 Controls the size of the pupils of the eyes

78.  Consists of the :
1. Sympathetic nervous system
2. Parasympathetic ……………
 Majority of organs are supplied by
both SNS and the PNS
 The 2 systems have opposite effects
that are finely balanced

79.  Prepares the body to deal with
excitement and stressful situations
 It mobilises the body for <fight and
flight>

81.  It has a tendency to slow down body
processes
Exceptions are:
-Digestion and absorption of food
-Functions of the genito-urinary system
 Its general effect is that of a
<Peacemaker>, allowing relaxation and
rest(restoration process)

84.  An impulse is initiated by stimulation of:
- Sensory nerve endings or
- By the passage of an impulse from
another nerve
 Transmission of the impulse (action
potential) is due to movement of ions
across the nerve cell membrane
1. Polarization
2. Depolarization
3. Repolarization

86. 1.Polarization(resting membrane potential)
At rest the charge:
- outside is +ve(due to Na+)
- inside is –ve (due to K+)
2. Depolarisation
When there is a stimulation:
- Na+ move inside the cell(+ve inside)
- K+ move outside the cell(-ve outside)
This creates a nerve impulse
3. Repolarization

87.  Synapse is a specialised junction between
two neurones where the nerve impulse is
passed from one neuron to another.
 In a chemical synapse, a nerve impulse
from the pre-synaptic neurone triggers
chemical transmitter substance which is
bind to the postsynaptic neurone.
 Nerve impulse reaches the terminal end
of the pre-synaptic neurone.

88.  This triggers the influx of Calcium ions
into the pre-synaptic neurone.
 Synaptic vesicles carrying the
neurotransmitters move to the membrane
of pre-synaptic neurone and fuse.
 Neurotransmitter (acetylcholine) stored
into the synaptic vesicle diffuse across the
synaptic cleft.
 Neurotransmitter bind to receptor in the
next post-synaptic neurone causing ion
channels

89. to open into the postsynaptic neurone
which then open certain ion channels in
the post-synaptic membrane.
 The movement of ions in and out of the
post-synaptic neurone results in the
generation of a post-synaptic potential
which allow the transmission of impulse
from one neurone to another.

91.  CNS influence the activity of skeletal muscle
through two sets of neuron which are the
1. Upper motor neuron
2. Lower motor neuron

92.  Upper motor neurons (UMN) are responsible
for conveying impulses for voluntary motor
activity through descending motor pathways
that make up the upper motor neurons.
 UMN send fibers to the LMN, and that exert
direct or indirect supranuclear control over the
LMN of the cranial and spinal nerves..

93.  Upper motor neuron control lower motor
neuron through two different pathways:
1. Pyramidal tract
2. Extra pyramidal tract

94.  All voluntary movement depend upon
excitation of lower motor neuron by upper
motor neuron.
 These are the only neurons that innervate the
skeletal muscle fibers, they function as the final
common pathway, the final link between the
CNS and skeletal muscles.

95.  Motor Neuron in spinal cord
 Motor component of cranial nerve nuclei in
brain stem.
 Those in cranial nerves innervate the skeletal
muscles associated with the movements of the
eyes, tongue, chewing, swallowing, vocalizing.

98.  It is the blood flow in the brain.
 Supplies oxygen, nutrients & glucose to the
brain.
 Remove carbon-dioxide, lactic acid &
metabolites from the brain.
 Cerebral Vasculature has unique anatomy &
physiology.
 Brain is highly vulnerable to disruption in
blood flow.

99.  Brain is supplied by 4 main arteries:
1. 2 Internal Carotid Arteries
2. 2 Vertebral Arteries
 The vessels are interconnected in brain to form
an arterial circle known as the Circle of Willis
below the hypothalamus.
 6 large arteries originate from the Circle of
Willis which supply the cerebral cortex.

100.  Non-fenestrated capillaries with tight junctions
between endothelial cells. (Capillaries in
choroid plexus are fenestrated)
 Few vesicles in endothelial cells.
 Limited diffusion & vesicular transport.
 Surrounded by end feet of astrocytes, induce
tight junctions in endothelial cells.
 Anatomic basis of Blood Brain Barriers.