CNS physiology general description and introduction Brain and spinal cord Brain is covered by meninges, CSF is fluid present in subarachnoid space It has a protective function Peripheral nervous system consists of cranial nerves and spinal nerves There are 12 pairs of cranial and 31 pairs of spinal nerves Spinal cord is present in the vertebral canal of vertebral column, surrounded by the meninges and there is CSF present in subarachnoid space. - It is almost cylindrical but in cervical and lower thoracic and lumbar regions it contains fusiform shaped enlargements called cervical enlargements and lumbar enlargements. In the cervical segments there is more gray matter and also there is more gray matter in the lower thoracic and lumbar region. Cervical segments supply the upper limb i.e. it supplies more muscles, so more gray matter is present. Similarly the lumbar region supplies the lower limb so more gray matter is present in this region. Just below the lumbar enlargements, spinal cord abruptly tapers, this tapering part is called conus medularis, and it gives attachment to a fibrous thread called filum terminale, which is attached to the back of coccvx. In the spinal cord on the anterior surface there is anterior median fissure and on the posterior surface is posterior median sulcus. Fissure is much deeper than the sulcus. Spinal nerves arise from the spinal cord and each spinal nerve has two roots. 1. Ventral (anterior root); which is motor and it contains both somatic and autonomic fibers. 2. Dorsal (Posterior root); is sensory and in the dorsal root there is dorsal root ganglia. It contains sensory neurons which give rise to cell fibers.

1. Organization and Cells of the
Nervous System
Dr saima zareen

2. Nervous system
• It is a communication and control system
• Its function involves conduction of impulses
• Impulses go to the brain---- processing occurs in brain ----
brain give direction to effectors
• Nervous system is anatomically divided into:
1. Central nervous system
2. Peripheral nervous system

3. Functional division of CNS
• 1. Somatic nervous system
• 2. Autonomic nervous system
• Somatic nervous system consists of nervous system which
supplies the general structures of the body, skeletal muscle
and skin
• Autonomic nervous system supplies viscera’s or you say
involuntary effectors i.e. Cardiac muscles, Smooth muscle
and Glands
• Autonomic nervous system is represented in CNS and also a
component of peripheral nervous system

5. Central Nervous System
• Consist of brain and spinal cord
• formed by neurons and
supporting cells (neuroglia)
• Structures of brain and spinal
cord are arranged in two layers,
gray matter and white matter
• Brain is situated in the skull.
• It is continued as spinal cord in
the vertebral canal through the
foramen magnum of the skull
bone.

6. • In the nervous system there are
neurons and neuroglia
• Nervous system is organized into
Gray matter and white matter
• Outer layer Gray matter consists of
cell bodies and the proximal portions
of their nerve fibers embedded in
the neuroglia.
• Inner White matter consists of nerve
fibers(axons)embedded in the
neuroglia.

7. Protective coverings of CNS
• Brain and spinal cord are surrounded
by three layers of meninges
• outer dura mater,
• middle arachnoid mater
• inner pia mater
• The space between arachnoid mater
and pia mater is known as
subarachnoid space
• This space is filled with cerebrospinal
fluid. Brain and spinal cord are
actually suspended in the
cerebrospinal fluid

8. Parts of brain
• 1.Brain stem consist of
Mid brain
Pons
Medulla
• 2. Cerebellum
• 3. Forebrain
a. Diencephalon
(1) Hypothalamus (2) Thalamus
b. Cerebrum
(1) Basal nuclei (2) Cerebral cortex

10. Peripheral nervous system
• Consists of nerves that arise
from the CNS and go to
periphery. i.e. 12 pair of
cranial nerves and 31 pair of
spinal nerves

11. There are 12 pair of cranial nerves
• 1. Olfactory nerve
• 2. Optic nerve
• 3. Oculomotor nerve
• 4. Trochlear nerve
• 5. Trigeminal nerve
• 6. Abducent nerve
• 7. Facial nerve
• 8. Vestibulocochlear nerve
• 9. Glossopharyngeal nerve
• 10. Vagus nerve
• 11. Accessory spinal nerve
• 12. Hypoglossal nerve
Out of 12 cranial nerves only 4 nerves contain Parasympathetic
fibers. These are 3rd (Oculomotor), 7th (Facial), 9th
(Glossopharyngeal) and 10th (Vagus).

12. There are 31 pair of spinal nerves
• 8 pair of cervical
• Thoracic; 12
• Lumbar; 5
• Sacral; 5
• And Coccygeal; 1
• A nerve may contain both somatic
and autonomic nerve fibers. A
nerve may also contain both
motor and sensory fibers

13. Spinal cord
• present in the vertebral canal of vertebral
column, surrounded by the meninges and
CSF present in subarachnoid space
• Just below the lumbar region spinal cord
abruptly tapers, this tapering part is
called conus medullaris, and it gives
attachment to a fibrous thread called
filum terminal, which is attached to the
back of coccyx
• Spinal cord ends at the lower border of
first lumbar vertebrae ,nerves which
arise from the lower lumbar and sacral
region, descends in the vertebral canal as
Cauda Equina (meaning: Horse-tail)

14. Spinal nerves
• Spinal nerves arise from the spinal
cord and each spinal nerve has
two roots
• 1. Ventral (anterior root); which is
motor and it contains both
somatic and autonomic fibers
• 2. Dorsal (Posterior root); is
sensory and in the dorsal root
there is dorsal root ganglia. It
contains sensory neurons which
give rise to cell fibers

15. • The two roots of spinal
nerve join to from the spinal
nerve either within the
spinal canal or in the
Intervertebral foramen.
• Spinal nerve emerges
through the intervertebral
foramen

16. • Generally spinal nerves are
labelled or identified according to
the vertebrae at the lower border
of which it emerges out. But there
is exception in the cervical region.
In case of cervical nerves, they are
labelled according to the upper
border of which vertebrae they
arise. C1 nerve arise from the
upper border of C1 vertebrae and
C8 arise from the upper border of
T1 (between the C7 and T1 spinal
vertebrae)

17. • When spinal nerve emerges out it
divides into two branches or rami
• Posterior ramus is smaller and the
anterior ramus is larger.
• Posterior ramus passes posteriorly
to supply the skin and muscles of
the back
• Anterior ramus passes anteriorly to
supply the anterolateral parts of
the body and limbs

18. Grey matter of spinal cord
• In the spinal cord white matter is on the
surface while inner core is formed by the
gray mater.
• Gray matter is present on the form of H
shaped structure. It consists of two ventral
horns and two dorsal horns which are
united by a thin transverse commissure
containing the central canal of spinal cord.
In the central canal there is CSF present.
• gray matter is divided into three types of
gray columns. Anterior gray columns
(ventral Horn) and Posterior gray column
(Dorsal horn)
• In some segments T1 to L2 there is also
lateral horn (lateral gray column). In these
gray columns different neurons are present

19. Neurons in ventral horn or anterior gray column
• 1. Alpha motor neurons
They are large and multipolar
neurons. There nerve fibers are
called Alpha efferent or alpha
motor nerve fibers. They
innervates the skeletal muscles
• 2. Gamma-motor neurons
These are small and multipolar.
They give rise to gamma efferent
or gamma motor nerve fibers.
They supply intrafusal muscle
fibers in the muscle spindles

20. Neurons in Dorsal horn (Posterior gray column)
• 1. Substantia gelatinosa receives
sensory impulses about pain,
temperature and touch
• 2. Nucleus Proprius receives impulses
about proprioception, Two-point tactile
discrimination
• 3 Clarke’s column These are present
from T1 to L2 or L3 They receive
impulses from proprioceptors
• 4. Visceral afferent nucleus receives
impulses form the viscera
• Present in segments from T1 to L2 or L3

21. Neurons in lateral horn (lateral gray column)
• In segment of spinal cord T1 to
12 neurons are sympathetic
preganglionic.
• in sacral segments S2 to S5,
these neurons are
parasympathetic preganglionic.
• These neurons give rise to these
nerve fibers

22. White matter of spinal cord
• On outer side of gray matter is
white mater, divided into
columns
• Anterior white column between
the anterior root and median
fissure and
• posterior white column between
posterior root and median sulcus.
• Lateral column between anterior
and posterior roots
• These white columns contains
ascending and descending tracts

23. Dermatomes
• The area of skin supplied by a single spinal
nerve or single segment of spinal cord
• Say you take 1 spinal segment T1 so area of
skin supplies by T1 is its dermatome.
• There is systematic distribution of spinal
nerves to the skin. Map of dermatomes are
available and they help clinicians to
determine the level and extent of damage
to spinal cord
• Systemic distribution of spinal nerves to the
skeletal muscles is not so perfect as skin
E.g. Diaphragm supplied by Phrenic nerve
(C3-C5) [its in thoracic region]

24. Neurons
Structural and functional unit of nervous system
Cells within the nervous system that
• receive stimuli,
• generate nerve impulse
• transmit information to effectors(nerve cells, muscle, or
gland cells)

25. Parts of a neuron
• Soma i.e. nerve cell body
• Dendrites
• Axon

26. Nerve cell body / Soma/ perikaryon
• Neuroplasm covered by cell membrane
Large central nucleus (1 or 2 nucleoli, no
centrosome, no division)
Membranous organelles with ribosomes
causes protein synthesis
• Nissl bodies (small basophilic granules,
present in soma except in axon hillock
• Fatigue / nerve injury  Nissl bodies
fragment & disappear  chromatolysis
• Reappear after recovery / regeneration

27. • Neurofibrils (bundles of
neurofilaments & microtubules in
soma, dendrites & axons and provide
internal support to them.
• Mitochondria (produce ATP in soma
& axon)
• Golgi apparatus (packs proteins into
granules)

28. Dendrites
Short tree like branched tapering
process of nerve cell
• Nerve impulse travel from dendrite
towards cell body
• Dendritic spines .... knob like
projections, form functional
contacts with axons
• Have Nissl granules & neurofibrils

29. Dendrites
• Function:
To receive chemical signals from axon termini
To convert them into small electric impulses
Transmit them towards the cell body (spread to the axon
hillock)

30. Axon
• Axon always conduct impulses
away from cell body
• Emerge at axon hillock
• Initial segment have no myelin
even in myelinated nerves
• Lack Nissl granules.
• Axoplasm: cytoplasm of axon
• Axolemma: plasma membrane
• Schwann cells & myelin sheath
encloses axon