PHYSIOLOGY OF NEURON, STRUCTURE AND FUNCTIONS OF NEURON, NERVE GROWTH FACTORS, CYTOKININES, Zones Of The Neuron 1. Receptor Zone 2. Site Of Origin Of Conducted Impulse 3. Zone Of All Or None Transmission 4. Zone Of Secretion Of Transmitter Functions Of Neuron Transport system in neuron Neurotrophins – Neurotrophic Factors Nerve Growth Factor Other Neurotrophins

1. STRUCTURE AND FUNCTIONS OF NEURON,
NERVE GROWTH FACTORS, CYTOKININES
AND OTHER GROWTH FACTOR
PRESENTED BY-
DR.PRIYANKA VERMA
PG RESIDENT 3RD YEAR
DEPT. OF PHYSIOLOGY
MGM MEDICAL COLLEGE INDORE M.P.
UNDER GUIDENCE OF-
DR . R. WADHWANI
PROF. & HEAD
DEPT. OF PHYSIOLOGY
MGM MEDICAL COLLEGE INDORE M.P.
DEPARTMENT OF PHYSIOLOGY
MGM MEDICAL COLLEGE INDORE M.P.
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2. • Introduction
• Structure
 Nerve Cell Body
 Dendrite
 Axon
 Myelin Sheath
 Neurilemma
• Classification
 Depending Upon The Number Of
Poles
 Depending Upon The Function
 Depending Upon The Length Of
Axon
• Zones Of The Neuron
1. Receptor Zone
2. Site Of Origin Of Conducted
Impulse
3. Zone Of All Or None Transmission
4. Zone Of Secretion Of Transmitter
• Functions Of Neuron
• Transport system in
neuron
• Metabolism And Growth Of
Neurons
• Neurotrophins –
Neurotrophic Factors
 Nerve Growth Factor
 Other Neurotrophins
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3. Introduction
• The nerve and muscle cells are excitable, that is, capable of generation of electrical
impulses at their membranes.
• The electrical impulses generated, can be used to transmit signals along the
membranes.
• A neuron is the basic unit of nervous tissue. It is specialized for the function of
reception, integration and transmission of information in the body.
• Muscles - mechanical contraction follows an action potential.
• To understand the physiological aspects, it is imperative to have knowledge about
the functional anatomy and physiological properties of the nerve, the muscle and the
neuromuscular junction.
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4. NEURON
 Neuron, or the nerve cell, is the structural and functional unit of the nervous
system.
 Neuron is similar to any other cell in the body, having nucleus and all the organelles
in cytoplasm. However, it is different from other cells by two ways:
1.Neuron has branches or processes called axon and dendrites
2.Neuron does not have centrosome.
So, it cannot undergo division.
 The nervous system of human is made up of innumerable neurons. The total
number of estimated neurons in the human brain is more than 10¹².
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6. • Structure
 Nerve Cell Body
 Neuritis
• Dendrite
• Axon
 Myelin Sheath
 Neurilemma
 Node of ranvier
 Terminal buttons
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7. STRUCTURE
• Neurons vary considerably in size, shape and other features. However,
most of them have some major features in common.
• The basic structure of a neuron is best studied in a spinal motor
neuron.
• A neuron primarily consists of the cell body and processes called
neuritis ,which are of two kinds, the dendrites and the axon.
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8. Cell body
• The cell body of a neuron is also called the soma or perikaryon and
may be round, stellate, pyramidal or fusiform in shape. Like any other cell
it consists of a mass of cytoplasm with all its principal constituents
surrounded by a cell membrane.
• The cell body contains a large nucleus with one or two nucleoli but
there is no centrosome.
Note. The absence of centrosome indicates that the neuron has lost
ability for division. Thus, neurons once destroyed are replaced by
neuroglia only.
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10. Nissl granules/bodies.
• Small basophilic granules found in cytoplasm of neurons.
• Also called tigroid substances, since these bodies are responsible for tigroid or
spotted appearance of soma after suitable staining.
• They are present in soma and dendrite but not in axon and axon hillock. Dendrites are
distinguished from axons by the presence of Nissl granules under microscope.
• Nissl bodies are membranous organelles containing ribosomes. (therefore concerned
with proteins synthesis).
• During fatigue or injury of the neuron, these bodies fragment and disappear by a
process called chromatolysis. Granules reappear after recovery from fatigue or after
regeneration of nerve fibers.
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11. Neurofibrillae - Consist of microfilaments and microtubules. ( In certain
degenerative disease like Alzheimer’s disease, the neurofilament protein gets altered,
resulting in the formation of neurofibrillary tangles.) [MCQ]
Pigment granules are seen in some neurons. For example, neuromelanin is
present in the neurons of substantia nigra. Aging neurons contain a pigment
lipofuscin. [MCQ]
Dendrites - The dendrites are multiple small branched processes which contain
Nissl bodies and neurofibres. Dendrites are the receptive processes of the
neuron receiving signals from other neurons via their synapses with axon
terminals.
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12. Axon
• The axon is the single longer process of the nerve cell.(Length- few microns to one
meter).
• Arises from - conical extension of the cell body called axon hillock,(devoid of the Nissl
bodies). [MCQ]
• Initial segment The part between the axon hillock and the beginning of myelin sheath.
• Its cell membrane continues as axolemma and the cytoplasm as axoplasm.
• The axon terminates by dividing into a number of branches, each ending in a number of
synaptic knobs also known as terminal buttons or axon telodendria.
• Synaptic knobs contain microvesicles in which chemical neurotransmitters are
stored.
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14.  Types of Axon
Axons are of two types:
• Myelinated And
• Unmyelinated.
 Myelinated Axons
• In the peripheral nervous system (PNS), myelinated axons have a sheath
around, called myelin sheath.
• Myelin sheath is formed by the Schwann cells in peripheral nerves and by the
oligodendroglia in the central nervous system. [MCQ]
• Both Schwann cell and oligodendroglia are grouped under glial cells.
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15. • Myelin contains protein, lipids (cholesterol, phospholipid and
glycosphingolipids ) and water.
• Myelin sheath is present around the axon in the so-called myelinated
nerve fibres.
• There are some axons which are devoid of myelin sheath (Non-myelinated
Nerve Fiber )
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16.  Formation of Myelin Sheath – Myelinogenesis
• Formation of myelin sheath around the axon is called the myelinogenesis.
It is formed by Schwann cells in neurilemma.
• In the peripheral nerve - it starts at 4th month of IUL.
- It is completed in the 2nd year after birth.
• Before myelinogenesis, Schwann cells of the neurilemma are very close to
axolemma, as in the case of unmyelinated nerve fiber.
• The membrane of the Schwann cell is double layered. Schwann cells
wrap up and rotate around the axis cylinder in many concentric layers.
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17. • The concentric layers fuse to produce myelin sheath but cytoplasm of the
cells is not deposited. Outside the myelin sheath a thin layer of Schwann
cell cytoplasm form an additional sheath called neurilemma
• The gaps between the Schwann cells are called the nodes of Ranvier ,
where the plasma membrane is exposed to the ECF. Each node is 0.5–
1.0 μm in length and the internodal distance is 1–2 mm.(short gap, i.e.
periodic 1 μm constrictions at about 1 mm distance)
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18. Segmentation of myelin sheath. One Schwann cell forms a small segment.
Gap between the segment is called node of Ranvier.
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19. • Myelinogenesis
• 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. These layers of the mesaxon, along with the lipids, form the
myelin sheath
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20. • 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.
• Myelin protein zero {P0 and a hydrophobic protein PMP22 }are
components of the myelin sheath in the peripheral nervous system.
• Autoimmune reactions to these proteins cause Guillain–Barré syndrome, a
peripheral demyelinating neuropathy. [MCQ]
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21. • Mutations in myelin protein genes cause peripheral neuropathies that
disrupt myelin and cause axonal degeneration (eg, Charcot-Marie-
Tooth disease). [MCQ]
• In MS, patchy destruction of myelin occurs in the CNS.
• The loss of myelin is associated with delayed or blocked conduction in
the demyelinated axons. [MCQ]
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22. Myelin sheath, shown in transverse section (A) and longitudinal section
(B) of the axon.
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23. Stages of formation of myelin sheath by Schwann cell.
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24. Functions of Myelin Sheath
1. Faster conduction
Myelin sheath is responsible for faster conduction of impulse. In myelinated
nerve fibres, the impulses jump from one node to another node. This type
of transmission of impulses is called saltatory conduction.
2. Insulating capacity
Myelin sheath has a high insulating capacity. Because of this quality,
myelin sheath restricts the nerve impulse within single nerve fiber and
prevents the stimulation of neighbouring nerve fibres.
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25. FUNCTIONS OF NEURONS
• Reception of information
• Consolidation and transference of information in the body
[MCQ]
• The cell body and dendrites serve as the receptor zone to receive the
information.
• Axon hillock and initial segment for generation of action potential.
• Axon for transmission of nerve impulse, axon terminal for discharge of
neurotransmitters.
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26. • Classification
 Depending Upon The Number Of Poles
 Depending Upon The Function
 Depending Upon The Length Of Axon
Depending Upon The Number Of Poles
Based on the number of poles from which the nerve fibers arise, neurons are divided
into three types:
1. Unipolar neurons
2. Bipolar neurons
3. Multipolar neurons.
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27. 1.Unipolar neurons
• Only one pole.
• From a single pole, both axon and dendrite arise .
• Present only in embryonic stage in human beings.
2. Bipolar neurons
• Two poles.
• Axon arises from one pole and dendrites arise from the other pole.
• Example: Retina, olfactory epithelium, sensory ganglia of cochlear and vestibular
nerves.
3. Multipolar neurons
• Have many poles.
• One of the poles gives rise to axon and all other poles give rise to dendrites.
• Example: Motor neurons, hippocampal pyramidal cells and cerebellar Purkinje cells.
• Most vertebrate neurons, especially in the central nervous system (CNS) are multipolar.
The dendrites branch profusely to form the dendritic tree.
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28. FIGURE 1: Types of neuron
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29.  DEPENDING UPON THE FUNCTION
On the basis of function, nerve cells are classified into two types:
1. Motor or Efferent Neurons
 Carry motor impulses from central nervous system to peripheral
effector organs like muscles, glands, blood vessels, etc.
 Generally, each motor neuron has a long axon and short dendrites.
2. Sensory or Afferent Neurons
 Carry the sensory impulses from periphery to central nervous system.
 Generally, each sensory neuron has a short axon and long dendrites.
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30. Figure- 2, Motor (effector) neuron and sensory (receptor) neuron. Arrows indicate direction of impulse
conduction.
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31. DEPENDING UPON THE LENGTH OF AXON
Depending upon the length of axon, neurons are divided into two types:
1. Golgi Type I Neurons
Golgi type I neurons have long axons. Cell body of these neurons is in
different parts of central nervous system and their axons reach the
remote peripheral organs.
2. Golgi Type II Neurons
Neurons of this type have short axons. These neurons are present in
cerebral cortex and spinal cord. [MCQ]
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32.  Axoplasmic transport
• Transfer of substances between cell body and axon terminal is called
axoplasmic transport.
• Axoplasm, the cytoplasm of the neurons is in constant motion. The
axoplasmic transport is vital to nerve cell functions, since movement of
various materials occur through it.
• Various proteins, organelles and other cellular substances required for the
development, growth and maintenance of the neuron .
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33. • The axoplasmic transport is of two types: rapid and slow.
1. Rapid transport
• Some materials travel 100–400 mm a day along the axoplasm and
constitute the rapid transport.
• Microtubules play an important role in this form of transport.
• Rapid transport is bidirectional, i.e. both away from (anterograde)
and towards the cell body (retrograde).
• by Kinesin . [MCQ]

34. 2. Slow transport
• The materials travelling slowly (0.1–2 mm in a day) in the axoplasm
constitute the slow transport. Slow transport is only unidirectional, away
from the cell body (anterograde).
• It is responsible for flow of axoplasm containing protein subunits of
neurofilaments, tubulins of the microtubules and soluble enzymes.
• Anterograde transport: occurs along microtubules that run along the length
of the axon.
• Retrograde transport: in the opposite direction (from the nerve ending to
the cell body). Brought about by: Dynein. [MCQ]

35. • Examples of Retrograde transport [MCQ]
1. Transport of viruses:
• Chickenpox virus reaches cell body from nerve terminals in the skin by retrograde
transport.
• The rabies virus travels from the axonal ending of motor neuron to the spinal cord
and then to brain where it multiplies.
2. Transport of toxins: Tetanus toxin at motor neuron ending is transported to the cell
body.
3. Transfer of nerve growth factor: Nerve growth factor is taken up by presynaptic
terminal and transferred to soma.
4. Reuptake of synaptic transmitters: Norepinephrine (NE) released at the nerve
terminals are rapidly removed from the synaptic cleft by reuptake into the presynaptic
neuron.
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36. Transneuronal Transport
• Trophic substances like nerve growth factors are transported across the
synapse to the presynaptic membrane of another neuron. This is called
transneuronal transport. This helps in maintenance of the synaptic
contacts.
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37. Axonal transport along microtubules by dynein and kinesin.
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38. ZONES OF THE NEURON
From the functional point each neuron is divided into four zones :
1. Receptor zone (dendritic zone) - local potential changes are
generated by integration of the synaptic connections.
2. Site of origin of conducted impulse - propagated action potentials are
generated.
In case of spinal motor neuron, initial segment and in cutaneous
sensory neurons first node of Ranvier is the site of origin of conducted
impulses.
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39. Functional zones of the neuron
3. Zone of all or none
transmission in the neuron
is the axon.
4. Zone of secretion of
transmitter (nerve endings).
The propagated impulses
(action potential) to nerve
endings cause the release of
neurotransmitter.
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40. NEUROGLIA
• The word glia is Greek for glue. For many years neuroglia cells were
viewed as connective tissue.
• Today these cells are recognized for their role in communication within
the central nervous system.
• Unlike most neurons, glia continue to undergo cell division in adulthood
and their ability to proliferate is noticeable after brain injury (eg. Stroke).
• They are the supporting cells present within the brain and spinal cord.
They are numerous, about 10 times more than the neurons.
• Two major categories :-
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41. 1. Macroglia
• Large glial cells are ectodermal in origin.
• These are of two types:
 Astrocytes (subdivided into fibrous and protoplasmic astrocytes )
 Oligodendrocytes
2. Microglia
• Small glial cells
• Mesodermal in origin.
• Flattened cell body and short processes.
• More numerous in grey matter .
• Act as phagocytes and
• Become active after damage to nervous tissue by trauma or disease.
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42. The principal types of glial cells in the nervous system.
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43. METABOLISM AND GROWTH OF NEURONS
• Neurons are metabolically active cells as mitochondria are present in
adequate numbers.
• Neurons are always active as the membrane potentials and neuronal
cytosolic activities are continuous phenomena.
• About 70% of total energy required is used to maintain polarization of
the membrane by the action of Na+ -K+ pump.
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44. • Special features of neuronal metabolism are:
1. The excitability, conductivity and recovery process - can happen in a nerve for a
considerable period in the absence of oxygen.
2. Chemical changes in the nerve are similar to that in muscles, i.e. pyruvic acid is
formed and if O2 supply is insufficient, lactic acid accumulates.
3. Energy requirement of the resting membrane potential (polarization) is supplied
primarily by combustion of sugar and phospholipids.
4. During activity, hydrolysis of ATP and creatine phosphate supply energy for
the propagation of the nerve impulse.
5. The nerve cells are rich in K+ and vitamin B1 that further assist in metabolism.
Vitamin B1 is essential for oxidation of pyruvic and lactic acids in the
neurons.
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45. NEUROTROPHINS –NEUROTROPHIC FACTORS
• These are the protein substances, which play an important role in growth
and functioning of nervous tissue.
Source of Secretion
• Secreted by many tissues in the body, particularly muscles, neuroglial cells
called astrocytes and neurons.
Functions Neurotrophins:
1. Facilitate initial growth and development of nerve cells.
2. Promote survival and repair of the nerve cells.
3. Maintenance of nervous tissue and neural transmission.
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46. Mode of Action
• Act via neurotrophin receptors, which are situated at the nerve terminals and nerve cell
body.
• They bind with receptors and initiate the phosphorylation of tyrosine kinase.
Types
Nerve growth factor (NGF) was the first protein substance identified as neurotrophin.
• Recently, it is found that neurotrophins are capable of making the damaged
neurons regrow.
• This indicates the possibilities of reversing the devastating symptoms of
nervous disorders like Parkinson disease and Alzheimer disease.
• Commercial preparations of neurotrophins are used for the treatment of
some neural diseases.
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47. NERVE GROWTH FACTOR
Nerve growth factor (NGF) is a neurotrophin found in many peripheral tissues.
Chemistry
 Peptide with 118 amino acids.
 NGF is made up of 2α, 2β and 2γ subunits.
• The α subunits have trypsin-like activity.
• The β subunits are similar in structure to insulin and possess all the nerve
growth promoting activities.
• The γ subunits are serine proteases. Their functions are unknown.
 Receptor of NGF is Trk A (tyrosine kinase activity A).
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48. Functions
1. Promotes early growth and development of neurons.
2. Major action is on sympathetic and sensory neurons, (particularly with pain)
therefore also called sympathetic NGF.
3. Also promotes the growth of cholinergic neurons in cerebral hemispheres.
4. Commercial preparation of NGF extracted from snake venom and
submaxillary glands of male mouse is used to treat sympathetic neuron
diseases
5. Important role in treating many nervous disorders such as Alzheimer
disease, neuron degeneration in aging and neuron regeneration in
spinal cord injury.
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49.  OTHER NEUROTROPHINS
1. Brain-derived Neurotrophic Growth Factor
• (BDGF) was first discovered in the brain of pig. Now it is found in human brain and
human sperm.
• promotes the survival of sensory and motor neurons, arising from embryonic neural
crest.
• also protects the sensory neurons and motor neurons.
• It enhances the growth of cholinergic, dopaminergic and optic nerves.
• Receptor for BDNF is Trk B.
• It is suggested that BDGF may regulate synaptic transmission. Commercial
preparation is used to treat motor neuron diseases.
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50. 2. Ciliary Neurotrophic Factor (CNTF)
• CNTF is secreted in peripheral nerves, ocular muscles and cardiac muscle.
• It protects neurons of ciliary ganglion and motor neurons.
3. Glial Cell Line-derived Neurotrophic Factor (GNDF)
• GDNF is found in neuroglial cells.
• It has a potent protective action on dopaminergic neurons.
• It is used for the treatment of Parkinson disease.
4. Fibroblast Growth Factor (FGF) FGF was first discovered as growth factor
promoting the fibroblastic growth. It is also known to protect the neurons.
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51. 5. Neurotrophin-3 (NT-3)
• Neurotrophin-3 (NT-3) acts on γ-motor neurons, sympathetic neurons and
neurons from sensory organs.
• Regulates the release of neurotransmitter from neuromuscular junction.
• Useful for the treatment of motor axonal neuropathy and diabetic
neuropathy.
• Recently, few more substances belonging to the neurotrophin family such as
NT-4, NT-5 and leukemia inhibiting factor are identified. NT-4 and NT-5 act on
sympathetic neurons, sensory neurons and motor neurons.
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52. CYTOKINES AND OTHER GROWTH PROMOTING FACTORS
Cytokines are critical controllers of cell, and hence tissue, growth,
migration, development and differentiation.
The family includes the inflammatory cytokines such as the interleukins
and interferons, growth factors such as epidermal and hepatocyte growth
factor and chemokines such as the macrophage inflammatory proteins, MIP-
1α and MIP-1β.
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53.  Cytokines play an important role in neuronal development as well as in
inflammation that is, they are equally immunoregulators and
modulators of neural functions and neuronal survival.
 In “normal” healthy brain the pro-inflammatory cytokine expression is
low and the homeostasis is maintained by the counter regulatory effect
of anti-inflammatory cytokines.
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54. Regulatory factors of the cytokine balance that affect the CNS functions.
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55. OTHER GROWTH PROMOTING FACTORS
- Factors, other than neurotrophins, which promote nerve growth include:
 Ciliary neurotrophic factor
 Leukaemia inhibitory factor
 Insulin-like growth factor-I
 Transforming growth factor
 Fibroblast growth factor
 Platelet-derived growth factor
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56. Summary
• Structure
• Nerve Cell Body
• Dendrite
• Axon
• Myelin Sheath
• Neurilemma
• Classification
 Depending Upon The Number Of
Poles
 Depending Upon The Function
 Depending Upon The Length Of
Axon
• Zones Of The Neuron
1. Receptor Zone
2. Site Of Origin Of Conducted
Impulse
3. Zone Of All Or None
Transmission
4. Zone Of Secretion Of
Transmitter
• Functions Of Neuron
• Transport system in neuron
• Neurotrophins –
Neurotrophic Factors
 Nerve Growth Factor
 Other Neurotrophins
04-01-2024 56

57. Neurons are built to better remember
the incompleted , the unfinished, the
uninvited & the unwanted!
- Vishwanath Ji
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