Notes about peripheral nerve

1. NERVOUS SYSTEM= system comprising of organs and structures
made up of specialised tissue called Nervous tissue : Neurons + Neuroglia

2. •The Nervous System is the body’s
main processing system for
information
•It is the most complex product of
biological evolution ( complexity
comes by the number of cells and
not types)

3. NERVOUS
SYSTEM
Central Nervous
System(CNS)
Brain
Spinal cord
Peripheral Nervous
System(PNS)
Somatic Nervous
System(SNS)
Autonomic
Nervous
system(ANS)
Afferent & Efferent :Voluntary
control over the skeletal muscle
contraction
Afferent & Efferent: Supply
involuntary structures like heart,
smooth muscle and glands
Nervous tissue organised as
:Brain, Spinal cord, Ganglia,
Nerves
Functionally :Afferent(Sensory)
& Efferent system(Motor)
Central Nervous System (CNS) –
centres of nervous system, wide degree of
effect if damaged
Present at the centre of the body
Sympathetic & Parasympathetic
Peripheral Nervous System (PNS)
connect the CNS to the limbs and organs – Cranial(12
pairs) & spinal nerves(31 pairs
2 components: (Somatic- supply skeletal muscles &
Autonomic)

4. Functions of CNS:
• Integration, processing, co-
ordinating sensory data and giving
appropriate motor commands
• Seat of higher functions such as
intelligence, memory, learning and
emotions
Functions of PNS:
• Provides sensory information to the CNS and carries its
motor commands to the peripheral tissues and systems

5. AUTONOMIC NERVOUS SYSTEM: controls involuntary activities of the body, like sweating, salivation,
peristalsis etc.
• SYMPATHETIC(THORACO-LUMBAR OUTFLOW) & PARASYMPATHETIC(CRANIOSACRAL OUTFLOW)

6. • PRE- GANGLIONIC
• POST GANGLIONIC

7. • 2 classes of cells:
– Neurons or nerve cells
– Glialcells(glia)
• Glia surround neurons – from the
Greek for ‘glue’
NERVOUS TISSUE:

8. PERIPHERAL NERVOUS
SYSTEM
• Peripheral nerves- Cranial, Spinal
• Ganglia

9. Glial Cells:
• There are about 1 trillion glial cells in the brain
– 10 - 50 x more than these are neurons
• Types :
IN THE CNS---
• Oligodendrocytes
• Astrocytes
• Ependymal cells
• Microglia
IN THE PNS ---
• Satellite cells
• Schwann cells

10. Types of Glial Cells:
• Astrocytes:
– Star shaped cells
- Most numerous
– Fill spaces between neurons
– Form Blood-brain barrier
• Oligodendroglia:
– Wrap axons with myelin sheath in brain and
spinal cord (Not all axons are myelinated)
– Each oligodendrocyte wraps several axons in

11. • Microglia:
- act as Phagocytes - clean debrisneur
Satellite cells:
• Capsular cells
• Surround the neurons of sensory and
autonomic ganglia
FUNCTIONS:
• supply nutrients to the surrounding
neurons and also have some structural
function
• protective, cushioning cells

12. • Schwann Cells:
– Wrap axons with myelin sheath outside the
brain and spinal cord
– Each Schwann cell wraps only one axon
• Ependymal Cells:
– Line the ventricles
– Involved with secretion and absorption of
cerebral spinal fluid
– Also play a role in routing embryonic cells
during development

13. Important functions of glial cells:
– Act like a glue- hold the nervous tissue
– Surround & support neurons
– separate & insulate groups of neurons
– some produce myelin ( Oligodendrocyte- CNS, Schwann cells- PNS)
– some are scavengers- Microglia
– some take up & remove chemical transmitters
– some guide migration of neurons during development
– some help form an impermeable lining in capillaries & venules, creating the blood-brain
barrier:Astrocytes

14. Neurons:
• Basic cells(functional units) of the nervous system
• There are about 100 billion neurons in the brain
– more in the spinal cord, peripheral nervous system
and sensory organs
• Neurons derive form the neural tube during
development
• 4 morphologically distinct regions:
• Cell Body (soma)
• Dendrites-carry impulses towards the cell body
• Axon-single, carry impulses away from the cell body
Axon divides into collateral branches and end in
Axon Terminals with bulbous endings/ terminal
buotons

15. IMPORTANT TERMINOLOGIES IN
NEUROANATOMY:
• NERVE CELL- Neuron
• NERVE FIBER- Axon of a neuron
• NEURO-TRANSMITTER: chemical messengers
released at the nerve endings to effector organs like
another nerve cell, a muscle cell or a gland
• NERVE---Bundle of nerve fibers outside the CNS
• TRACT--- A bundle of nerve fibres[axons]
connecting neighbouring and distant nuclei of the CNS
• NUCLEUS--- Collection of nerve cell bodies in the
CNS
• GANGLIA --- collection of cell bodies outside the
CNS
• The interior of the central nervous system is organized
into gray and white matter
• GRAY MATTER – Nerve cells embedded in
neuroglia.
• WHITE MATTER- nerve fibers (axons) embedded
in neuroglia.

16. • UPPER MOTOR NEURON- cell
bodies of neurons inside the
cerebral/motor cortex
• LOWER MOTOR NEURON-
cell bodies of neurons in the spinal
cord/ brain stem
Upper motor neuron controls/
regulates the activity of lower motor
neuron
Lower motor neuron is in contact
with the muscle and glands

17. PERIPHERAL NERVE

18. Peripheral Nerve :
• Nerves in the Peripheral
Nervous system
• solid white cords composed
of bundles of nerve fibers
• Cranial nerves(12 pairs) &
Spinal nerves(31 pairs)

19. • Each peripheral nerve consists of a large number
of fine filaments- nerve fibers- arranged in the
form of bundles/ fasciculi and surrounded by
fibrous connective tissue:
• Structure of of peripheral nerve(Cross section):
3 protective coverings of connective tissue:
 Endoneurium – loose, surrounds individual
nerve fibers
 Perineurium – surrounds bundle of nerve fibers
Epineurium – encloses the bundle of nerve fibers
forming a trunk
Importance – provide mechanical strength to the
nerve fibers
• Nerve fibers- Motor, sensory

20. • Non-myelinated - simply enveloped by
the cytoplasm of Schwann cells
• Myelinated - wrapped by concentric
layers of schwann cell plasma
membrane( Neurilemma)
All peripheral nerves are enveloped by the schwann
cells- some are myelinated and non-myelinated

21. CRANIAL NERVES: 12 pairs

22. SPINAL NERVES:
• Nerves arise from the
spinal cord and pass
through the
intervertebral foramina
in the vertebral column
• 31 pairs
8-cervical
12-thoracic
5-lumbar
5-sacral
1-coccygeal
Spinal nerves emerging from the
spinal cord by means of 2 roots Spinal nerves passing through the
intervertebral foramina

23. SPINAL SEGMENT: A section of the spinal cord that gives rise to one
pair of spinal nerve
31 pairs of spinal nerves

25. TYPICAL SPINAL NERVE (THORACIC) :

26. • Roots- anterior &
Posterior
• Trunk of spinal nerve
• Ramus- Anterior &
Posterior:
Anterior ramus- divides
into Anterior & Lateral
cutaneous branches,
connected to sympathetic
ganglion by grey & white
rami communicantes
Posterior Ramus – small,
divides into medial &
lateral branches

27. • Spinal nerves (anterior primary ramii)
----- Except for T3 to T11 thoracic
nerves, all form plexus(network of
nerves)----branches from the plexuses
Cervical plexus : C1 to C4 nerves
Brachial plexus : C5 to T1 nerves
Lumbosacral plexus : L1 to S5 nerves
Importance of Plexus formation: Redistribution
of the nerve fibers

28. DERMATOME: Area of skin
supplied/innervated by a single
segment of spinal cord giving
origins to one pair of spinal nerves

29. MYOTOME: group of muscles which is innervated by
single spinal nerve root
Each muscle in the body is supplied by one or more levels or segments of
the spinal cord and by their corresponding spinal nerves. A group of
muscles innervated by the motor fibres of a single nerve root is known as a
myotome

30. • important diagnostic tool to localize neurologic levels
• Symptoms that follow a dermatome (e.g. like pain or a rash) may indicate a pathology that involves the
related nerve root.
• Herpes Zoster( Shingles)- follow one or two adjacent
dermatomes
DERMATOME TESTING

31. • Testing of myotomes, in the form
of isometric resisted muscle
testing, provides the clinician with
information about the level in the
spine where a lesion may be
present.
• During myotome testing, the
clinician is looking for muscle
weakness of a particular group of
muscles. Results may indicate
lesion to the spinal cord nerve
root, or intervertebral
disc herniation pressing on
the spinal nerve roots.

33. GANGLIA:
• Collection of nerve cell bodies
outside the central nervous system –
ganglion
• Sensory ganglia - Dorsal root
ganglia of spinal & on the trunks of
cranial nerves
• Autonomic ganglia- Sympathetic &
Parasympathetic
DORSAL ROOT GANGLION

34. CENTRAL NERVOUS SYSTEM
• Brain & Spinal cord
• Delicate CNS is well protected as it is enclosed by the skull and vertebral canal and
meninges and is bathed in cerebrospinal fluid

35. • Sections through the CNS
presents
grey matter: nerve cell bodies,
dendrites
white matter: Predominantly
made up of myelinated nerve
fibers
Sub-cortical grey matter- brain(
basal nuclei)

36. BRAIN:
• Lies within the
cranial cavity
• 6 major parts :
a) Cerebrum
b)Diencephalon
c)Midbrain
d) Pons
e) Medulla oblongata
f) Cerebellum
BRAINSTEM