Here are the answers to your questions: 1. Glial cells are the connective tissue of the CNS. There are three main types of glial cells: astrocytes, oligodendrocytes, and microglia. Astrocytes help form the blood-brain barrier and provide nutrients. Oligodendrocytes create myelin sheaths around axons. Microglia are immune cells that remove cellular debris. 2. The main classifications of nerve fibers are: - Erlanger and Gasser classification (Aα, Aβ, Aγ, Aδ, B, C, etc.) based on diameter and conduction velocity. - Numerical classification (Ia, Ib

1. By:
Dr. Yogesh Kumar
Additional Professor
AIIMS Patna
Introduction to Nerve and
Muscle

2. At the end of the session
you should be able to:-
1. Name the parts of a neuron and their
functions.
2. Name the various types of glia and their
functions.
3. Classify the nerve fibres and tell its
functions.
4. Classify the different types of muscles.

3. Neuron
 Basic structural & functional unit of the
nervous system.
 Neuron is used to describe the nerve cell and
it’s processes, the dendrite and the axon.
 5μm to 120μm in diameter.
 100 billion neurons in the human nervous
system.

4. Glial Cells
 Glial cells (or glia) are CNS connective tissue
 Microglia are scavenger cells that resemble tissue
macrophages and remove debris resulting from
injury, infection, and disease .
 There are three types of Macroglia:
1. Oligodendrocytes,
2. Schwann cells,
3. Astrocytes
1. Fibrous astrocytes.
2. Protoplasmic astrocytes.

6. Structure of Neuron
 Three main parts of a neuron :
1. Dendrite
2. Body
3. Axon

8. Dendrite
 Outward extensions from the cell body.
 Five to seven in number.
 Aroborize extensively.
 Have small knobby projections called
dendritic spines especially in cerebral &
cerebellar cortex.

9. Neuronal Body
 Also called soma.
 It contain nucleus, nissl granules & cell organelles
except centriole so the neuron can’t divide.
 Cell body synthesize proteins which are
transported to the axonal ending by axoplasmic
flow.
 Cell body maintains the functional & anatomical
integrity of the axon.
 Wallerian degeneration: If axon is cut, the part
distal to the cut degenerates.

10. Axon
 Long fibrous structure.
 Originates from axonal hillock.
 First portion is called initial segment.
 Terminal end divides to form synaptic knobs /
terminal buttons / axonal telodendria.
 Synaptic knobs contain vesicles which stores
neurotransmitter.

11. Types of axons
1. Myelinated – surrounded by myelin sheath.
2. Unmyelinated – myelin sheath absent.

13. Myelin
 Produced by schwann cells outside the CNS &
oligodendrocytes in CNS.
 Myelin sheath is multiple layers of cell membrane of
schwann cell / oligodendrocyts containing protein-
lipid complex sphingomyelin.
 Myelin sheath is absent at the initial portion of axon,
at the ending & node of ranvier.
 Function:
 Electrical insulation of axon.
 To increase the velocity of impulse transmission.

15. Nerve
 An enclosed, cable-like bundle of peripheral axons.
 Provides a common pathway for the electrochemical
nerve impulses carried by individual nerve fiber.
 Found only in the peripheral nervous system.
 covered externally by epineurium.
 Underlying this is a layer of flat cells, the
perineurium.
 Surrounding each fibre is the endoneurium.
 Endoneurium consists of an inner sleeve of glycocalyx
and an outer meshwork of collagen fibers.

16.  Within the endoneurium, the individual nerve
fibers are surrounded by a low protein liquid
called endoneurial fluid.
 The endoneurium prevents certain molecules
from crossing from the blood into the endoneurial
fluid.
 Applied physiology:
During the development of nerve edema from
nerve irritation or injury, the amount of
endoneurial fluid may increase at the site of
irritation.

19. Classification of Nerve Fibers
 Three classifications:
1. Erlanger & Gasser Classification
2. Numerical Classification
3. Physio-clinical classification

20. Erlanger & Gasser
Classification
Fiber Type Function Diameter
(µm)
Velocity
(ms)
A
α Proprioception,
somatic motor
12-20 70-120
β Touch, pressure,
motor
5-12 30-70
γ Motor to muscle
spindle
3-6 15-30
δ Pain, cold, touch 2-5 12-30

21. B Preganglionic
autonomic
<3 3-15
C
Dorsal root Pain,
temperature,
touch,
pressure
0.4-1.2 0.5-2
Sympathetic Preganglionic
sympathetic
0.3-1.3 0.7-2.3

22. Numerical Classification
No. Origin Fiber Type
Ia
Ib
Muscle spindle, annulospiral
ending.
Golgi tendon organ.
Aα
Aα
II Muscle spindle, flower spray
ending; touch, pressure.
Aβ
III Pain & cold receptors; some
touch receptors.
Aδ
IV Pain, temperature,& other
receptors.
Dorsal root C

23. Clinical Physio- Classification
Suseptibilit
y
Most Intermediat
e
Least
Hypoxia B A C
Pressure A B C
Local
Anaesthesia
C B A

24. Types of Muscles
 Three major types of muscles:
Skeletal
Smooth
Cardiac

25. Skeletal Muscle
 Voluntary muscles, attach to bones of skeletal
system
 Fibers appear striped, so sometimes called
striated muscle
 Allow external movement and are developed
through exercise

26.  Smooth muscles
Involuntary muscles, called smooth
because don’t have striped appearance of
skeletal muscles
Found within certain organs, blood
vessels, and airways, and allow for
internal movement
Change in blood vessel diameter is one
example

27.  Cardiac muscle
Completely involuntary; specialized
muscle with striated appearance
Found solely in heart
Contraction of muscle causes heart beat,
internal movement

29. Answer the following:-
1. What are Glial cells? Innumerate its type.
2. Classification of nerve fibers.