The document provides a comprehensive overview of nerve physiology, focusing on the structure and functions of neurons and neuroglia, as well as the roles of nerve growth factors. It details various classifications of neurons, their parts, and functions, including axon types and myelinogenesis. Additionally, the document discusses the central and peripheral nervous systems, the importance of neuroglia, and concludes with multiple-choice questions and assignments for further understanding.

1. NERVE PHYSIOLOGY
Dr. Nabeel Beeran
Assistant Professor
Department of Physiology
Yenepoya Medical College

2. Competency
PY3.1: Describe the structure and functions
of a neuron and neuroglia. Discuss nerve
growth factors.

3. Specific Learning Objectives
At the end of class, you should be able to:
1. Draw the labeled diagram of a neuron.
2. Name the different parts of a neuron and give
their functions.
3. Classify types of axons and give examples for
each.
4. Understand the process of myelinogenesis.
5. Enumerate nerve growth factors.
6. Classify neurons and give examples for each type
of neuron.
7. Name different types of neuroglia and mention
their functions.

4. Central Nervous System
The Brain + Spinal cord
The center of integration and control
Peripheral Nervous System
 The nervous system outside of the
brain and spinal cord
 Consists of:
– Spinal nerves
– Cranial nerves
 Responsible for communication between
the CNS and the rest of the body.
Organization of the Nervous System

6. Peripheral Nervous System
 Somatic nervous system
 Autonomic nervous system
Sympathetic division Parasympathetic division

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.  The structural and functional unit of the nervous
system.
 Its primary function is to receive the various stimuli
and transmit the signals to other neurons and tissues.
 An excitable cell where message transmission occurs
in the form of action potentials.
 About 1011
neurons are present in the human central
nervous system (CNS).
 Supporting cells called glial cells are 10 to 30 times
more in number than the neural cells.
NEURON (NERVE CELL)

10. CLASSIFICATON
OF
NEURONS

11. DEPENDING UPON THEIR FUNCTION
DEPENDING UPON THE NUMBER OF
POLES
DEPENDING UPON THE LENGTH OF
THE AXONS

12. DEPENDING UPON THEIR FUNCTION
Sensory (afferent) neurons
 Carry impulses from the sensory receptors
TOWARDS the CNS
Motor (efferent) neurons
 send information AWAY from the central
nervous system to muscles or glands.
Interneurons
send information BETWEEN sensory
neurons and motor neurons.

13. By function (connections)
Interneuron
Sensory Motor

15. DEPENDING UPON THE NUMBER OF POLES
i) Unipolar neurons
Have a single pole from which both the process
of axon and dendrite arise (embryonic stage in
human being)

16. ii) Bipolar neurons
Have two poles one for axon and other for
dendrite (Vestibular, cochlear ganglia,
bipolar cells of the retina)

17. iii) Multipolar neurons
Have many processes that extend from the
cell body. However, each neuron has only one
axon (Eg: Spinal motor neurons, pyramidal
neurons, Purkinje cells).

19. Types of neurons based on arrangement of axon.
(A) Unipolar neuron; (B) Pseudounipolar neuron; (C) Bipolar neuron; (D) Multipolar Neuron

20. DEPENDING UPON THE LENGTH
OF THE AXON
Golgi Type I neuron:
- Have long axons
- The cell body of these neurons is in
central nervous system and their axons
reach the peripheral organs
Golgi Type II neuron:
- Have short axons
- Present in cerebral cortex
and spinal cord

21. STRUCTURE
OF
NEURON

22. Parts:
1. a cell body
2. dendrites
3. an axon that ends at axon terminal
 Neurite: Any projection from the cell body is
called a neurite.
STRUCTURE OF A NEURON

23. Structure of an unmyelinated neuron

25. Cell body (Soma / Perikaryon)
i) Nucleus- pale, large, spherical, central
ii) Neuroplasm- has neurofibrils, Nissl
granules, mitochondria, golgi apparatus,
neurosecretory material
Absence of centrosome - Indicates that the
neuron has lost the ability for division

26. Dendrite
i) multiple & short
ii) contain Nissl granules
iii) carry impulses towards soma

27.  Numerous short extensions from the
cell body
 Increase the cell surface area many
folds.
 Small knobby projections called
dendritic spines further increase the
surface area (cerebral and cerebellar
cortex).
 RECEIVE the incoming signals from
other cells and transmit it to the cell
body.
 Can cause protein synthesis, also
generate and conduct the action
potentials.
 About 10,000 dendrites per neuron in
the CNS.
THE DENDRITES

28. Axon
i) generally long
ii) arises from axon hillock
iii) axis cylinder has axoplasm, neurofibrils &
mitochondria
iv) axons end in terminal buttons
v) carry impulses away from cell body

29. Axon arises from the conical extension of the cell
body – AXON HILLOCK

30.  Axon or the axis cylinder of the neuron forms the
nerve fiber.
 A long tubular process that extends away from
the cell body to transmit output signals to
target organs.
 Arises from a thickened, tapered area of the cell
body called the axon hillock or the initial
segment of the axon.
 The action potential is generated at the
- INITIAL SEGMENT area in motor neurons and
- FIRST NODE OF RANVIER in sensory
neurons.
 Axoplasm contains mitochondria, Golgi
apparatus, and cytoskeletal proteins.
 Axolemma is the plasma membrane of the axon.
THE AXON

31. Types of Axon
 Myelinated Axons
 Unmyelinated Axons

32.  Myelinated axons have a covering around their
axons, called myelin sheath.
1.Myelin sheath is formed by the Schwann cells.
2. In the CNS of mammals, myelination is carried out
by oligodendrocytes. Each oligodendrocyte
projects several processes that wrap around many
axons.
MYELINATED AXONS

33. Do not have myelin sheath
 Somatic nerve fibers of small diameter.
 Postganglionic fibers of the autonomic nervous
system.
 Dorsal nerve roots.
 Nerve fibers in the CNS.
 Most of the fibers in invertebrates.
 Speed of conduction of impulse is slower.
UNMYELINATED AXONS

34.  Transfer of substances between cell body and
axon terminal is called axoplasmic transport.
 Various proteins, organelles and other cellular
substances required for the development, growth
and maintenance of the neuron are transported
mainly along the length of the axon.
AXOPLASMIC TRANSPORT

35. 1. Anterograde (Orthograde) transport
2. Retrograde transport
3. Transneuronal transport
TYPES OF AXOPLASMIC TRANSPORT

36.  Transport of materials from the cell body towards
the axon terminal
 Eg: Neurotransmitters
 Types: Fast & Slow
 Brought about by: Kinesins
ANTEROGRADE TRANSPORT

37.  Transport of substances from the axon terminal
to the cell body
 Speed: 200mm/day
 Brought about by: Dynein
RETROGRADE TRANSPORT

38.  Trophic substances like nerve growth factors are
transported across the synapse to the
presynaptic membrane of another neuron.
 This is called transneuronal transport.
 Helps in maintenance of the synaptic contacts.
TRANSNEURONAL TRANSPORT

40. FUNCTIONS
OF
NEURON

41.  Cell body
1. Maintains functional and anatomical integrity of
the axon.
2. Neurotrophins, proteins for neurotransmitters are
synthesized in the endoplasmic reticulum of the
cell body.
3. Stored in the synaptic knob by axoplasmic flow.
 Dendrites
1. Receptive process of the neuron.
2. Transmits impulses towards cell body.
3. Local potentials are developed.

42. Axon
1. Axon arises from axon hillock.
2. Long processes.
3. Forms an envelope called myelin sheath.
4. Initial segment of axon is the origin for action
potential.
5. Axon terminal form terminal knobs which store
neurotransmitters.
6. Axonal process
-Transmits propagated impulses away from cell
body to the nerve endings.
 Synaptic knobs
- Neurotransmitters are stored in the nerve endings.
which get released due to the arrival of action potential.

43. Fig. 26.7: Functions of different parts of the neuron.

44.  The adjacent layers of the Schwann cell stick to each
other tightly with the help of a protein called protein
zero (P0) present in the Schwann cell membrane.
 Mutation of P0 cause defective myelination.
 In multiple sclerosis, an autoimmune disease,
patchy destruction of myelin causes decreased
conduction velocity in both motor and sensory
neurons.
 Myelin contains protein, lipids and water. The main
lipids present include cholesterol, phospholipid
and glycosphingolipids.
MYELIN SHEATH

45.  The axon invaginates into the cytoplasm of an
adjacent Schwann cell.
 The axon remains suspended by a fold of the
Schwann cell membrane called mesaxon.
 The mesaxon becomes greatly elongated and
spirally wraps around the axon several times.
 Lipids get deposited between adjacent layers of
the membrane.
 A thin layer of Schwann cell cytoplasm form an
additional sheath called neurilemma.
MYELINOGENESIS

47. 1. Increases the speed of conduction.
2. Reduces energy expenditure by the cell.
3. Provides a protective covering to the axon.
4. Responsible for the colour of the white matter of
the brain and spinal cord.
OBJECTIVES OF MYELINATION

48.  The gaps between the Schwann cells are called
the nodes of Ranvier, where the axolemma is
exposed to the ECF.
 Each node is 0.5-1.0 µm in length.
 The action potential travels from node to node
(saltatory conduction) and thus the conduction
is faster in myelinated axon.
 Internodal distance is 1-2 mm.
NODES OF RANVIER

49. ARRANGEMENT OF NEURONS
 The neuronal structures are present in
endoneurium, perineurium and epineurium.

50.  Various factors affect neuronal development,
growth and survival.
I. Neurotrophins:
II. Other Growth factors:
- Cilliary NTF
- Glial cell-line derived NTF
- Leukemia inhibitory factor
- FGF, PDGF, TGF, IGF-1
GROWTH OF NEURONS

51.  They are trophic proteins to the neurons, as they
promote nerve growth and survival.
 They are produced by the nerves, muscles, glands
and astrocytes.
Known neurotrophins are:
1. Nerve growth factor (NGF)
2. Brain-derived neurotrophic factor (BDNF)
3. Neurotrophin - 3 (NT-3)
4. Neurotrophin 4/5
NEUROTROPHINS

52.  First neurotrophin to be identified.
 Promotes the growth and survival of sympathetic
nerves and some sensory nerves.
 An autocrine survival factor for memory B
lymphocytes.
 Found in high concentration in the saliva of male
mice.
 Decreases apoptosis of neurons by acting through
tyrosine kinase A receptor.
NERVE GROWTH FACTOR

53. NEUROGLIA

54.  Specialized form of connective tissue cells
found in association with nervous system.
 They are not excitable and they cannot conduct
impulses.
 Number of neuroglia is much more than
neurons.
 Unlike the neurons they retain the ability to
divide and multiply throughout life.

55. Functions:
 Responsible for the fixation of the neurons
within the nervous system.
 Phagocytosis.
 Nutrition.
 Myelin sheath formation in CNS.
 They acts as a “set point” for regulation of
various neural control mechanisms because of
their fixed metabolism.

57. Neuroglia: Supporting Cells
Ependymal cell
Microglia
Oligodendrocyte
Astrocyte

58. Neuroglia of CNS
• Astrocytes
– Regulate extracellular brain fluid composition
– Promote tight junctions to form blood-brain barrier
• Ependymal Cells
– Line brain ventricles and spinal cord central canal
– Help form choroid plexuses that secrete cerebrospinal fluid (CSF)

59. Neuroglia of CNS
• Microglia
– Specialized macrophages
• Oligodendrocytes
– Form myelin sheaths if surround axon

60. Neuroglia of PNS
• Schwann cells or neurolemmocytes
– Wrap around portion of only one axon to form myelin sheath
• Satellite cells
– Surround neuron cell bodies in ganglia, provide support and
nutrients

61. Microglia
 Specialized macrophages.
 Shows phagocytic action.
 Found in the grey matter of the CNS.

62. Astrocytes
Found scattered throughout the CNS.
Both in grey and white matters.
Two types:
 Protoplasmic Astrocytes.
 Fibrous Astrocytes.

63. Functions:
 Provides nutrition and remove the waste products.
 Support the neuron.
 Anatomical basis of blood brain barrier.
 They act as a electrical insulator.

64. Ependymal cells
They resemble epithelial cells and line the
ventricles of the brain and central canal of
spinal cord.
Function: Secretion of CSF.

65. Oligodendrocytes
Present both in grey and white matter.
Function: To lay down myelin sheath around
the nerve fiber within the brain.

66. Satellite cells
 Encapsulate the dorsal and cranial nerve
ganglion cells.
 Function: Regulate their micro environment
(Barrier formation).

68. Schwann cells
 They help in the formation of myelin sheath
around the peripheral neurons.

69. Summary

70. MCQs
1. The structural and functional unit of nervous system
is:
a. Neuroglia b. Renshaw cell
c. Synaptic cell d. Neuron
2. Material responsible for maintaining integrity of the
axon is:
a. RNA b. DNA
c. Neurotrophins d. Lipoprotein complexes

71. MCQs
3. Which among the following is not a glial cell of CNS?
a. Microglia b. Astrocyte
c. Schwann cell d. Oligodendroglia
4. Which part of a neuron has the highest
concentration of Na+ channel:
a. Dendrites b. Cell body
c. Axon hillock d. Synaptic knob

72. MCQs
5. Thickness of myelin sheath is determined by:
a. Thickness of unit membrane
b. Thickness of the axon
c. Number of unit membrane layers wrapped around
the axon
d. Number of Schwann cells

73. Assignment
1. Classify neurons and give examples for
each type of neuron.
2. Name different types of neuroglia and
mention their functions.
3. Write a note on myelin sheath.
4. Enumerate nerve growth factors.

74. References
1. Ganong’s Review of Medical Physiology - 26th
Edition.
2. Guyton and Hall Textbook of Medical Physiology - 13th
Edition.
3. Textbook of Medical Physiology, G K Pal - 4th
Edition.
4. Textbook of Medical Physiology, A K Jain - 10th
Edition
(Volume 1).
5. Essentials of Medical Physiology, K Sembulingam - 6th
Edition.

75. Validation committee has
validated this presentation.

76. THANK YOU