A 25-year-old lady comes to OPD with chief complaints of weakness and fatigability. Generally, during the morning she does not feel any significant weakness but, as day passes and she get involved in routine household works, weakness gradually starts to increase. The condition improves by some rest or sleep. She also reports double vision and difficulty in swallowing. Physical examination – Ptosis, diplopia, proximal muscle weakness, normal deep tendon reflex, no sensory impairment. What is the diagnosis? Why does rest improve the symptoms? How to manage the condition? What is the physiological basis of the management?

1. Structure and
functions of neurons
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
NRIIMS
Email: dr.goothy@gmail.com

2. Case study
A 25-year-old lady comes to OPD with chief complaints of
weakness and fatigability. Generally, during the morning she does
not feel any significant weakness but, as day passes and she get
involved in routine household works, weakness gradually starts to
increase. The condition improves by some rest or sleep. She also
reports double vision and difficulty in swallowing.

3. Case study
Physical examination – Ptosis, diplopia, proximal muscle
weakness, normal deep tendon reflex, no sensory impairment.
What is the diagnosis?
Why does rest improve the symptoms?
How to manage the condition?
What is the physiological basis of the management?

4. Introduction
A neuron is the structural and functional unit of the nervous system
What do u mean by structural and functional unit????
Primary function is to receive the stimuli and transmit it to other neuron
or tissue
Neuron is excitable cell
What do you mean by excitable cell???

5. Structure of neuron
Three parts
Cell body
Dendrites
Axon that ends at axon terminals

7. Cell body
Also called as soma/perikaryon
Contains nucleus and cytoplasm
Nucleus has one nucleolus
 Sometimes maybe two nucleoli
Centrioles are absent ( Neuron can not regenerate)

8. Cell body
Cytoplasm has cell organelles like Nissl granules, mitochondria, Golgi
complex, lysosomes and cytoskeletal proteins
Soma contain genetic information
Soma is capable of protein synthesis
Soma at one end gives small branching processes called dendrites
At other end a long process called axon

9. Dendrites
Numerous short extensions from Soma
Increase cell surface area by many folds for receiving information
Receive incoming signals from other cells and transmit to the cell body
At some areas of the brain they cause protein synthesis
10,000 dendrites per neuron approximately

10. Axon
Axon forms the nerve fiber
What is the difference between neurons and nerve fibers???
Long tubular process that extends away from the cell body to transmit
output signals to target organs.
Axons carry impulses away from the cell body

11. Axon
Cytoplasm – Axoplasm
Contains mitochondria, Golgi apparatus, cytoskeletal proteins
Axon raises from area called axon hillock or initial segment
AP is generated in a motor neuron at the axon hillock
AP is generated in a sensory neuron at the first node of the Ranvier

12. Axon
The plasma membrane of axon is called axolemma
The terminal part of axon loses myelin and divides into several
branches – Telodendria
The endings of telodendria form bulb like enlargements called terminal
buttons or synaptic knobs
The synaptic knobs contain the vesicles filled with neuro transmitters

13. Axon
There are two type of axons
Myelinated axons
Unmyelinated axons
Myelin sheath in the peripheral nervous system is formed by Schwann
cells
In CNS, myelination is done by oligodendrocytes

14. Myelinogenesis
The axon remains suspended by a fold of Schwann cell membrane
called mesaxon
Mesaxon greatly elongated and spirally wraps around the axon several
times
Lipids get deposited between the adjacent layers of membrane and
the myelin sheath is formed

15. Myelinogenesis
Outside the myelin sheath, a thin layer of Schwann cell cytoplasm persist
This forms an additional sheath called neurilemma
Sensory fibers of the dorsal column tract first get myelinated in 4th to 5th
months of intra-uterine life
Corticospinal tract starts myelination at 2 months of age and completes
about 2nd year of life

17. Composition of myelin sheath
Proteins
Lipids
Water
Main lipids – cholesterol, phospholipids, glycosphingolipids

18. Uses of myelin sheath
It increases the speed of conduction
It reduces energy expenditure by the cell
Provides protective covering to axon
Responsible for color of the white matter of brain and spinal cord

19. Multiple sclerosis
Autoimmune disease
Patchy destruction of myelin
Decreased conduction velocity
Effects on both sensory and motor neurons
It affects females twice as much as males

20. Multiple sclerosis
Weakness in lower limbs
Spasticity
Numbness
Urinary incontinence
Blurring of vision
Difficulty in speech and deglutition

21. Multiple sclerosis – Treatment
Use of corticosteroids to reduce inflammation
Administration of drugs
Immuno supression
Preventing the attack of the immune system on the myelin sheath
Depleting B lymphocytes

22. Unmyelinated axons
Do not have a myelin sheath
Nerve impulses travels uniformly along the axolemma
Conduction is slow
Consumes more energy
All post-ganglionic fibers of ANS

23. Transport in the Axon
The axon does not have the ability to synthesize proteins
Hence, the proteins formed in the cell body are transported through the
axon by the axoplasmic flow
Movement from the cell body to axon terminal – orthograde transport
Movement from axon terminal to the cell body – retrograde transport
Growth factors, tetanus toxin, herpes virus, poliovirus – retrograde transport

24. Transport in the Axon
Slow axonal transport – materials move at a rate of 1-5 mm per day
Movement is from axoplasm to axon terminal
Fast axonal transport – materials move at a rate of 200-400 mm per
day
Movement in both directions

25. Trans neuronal transport
Trophic substances like NGF are transported across the synapse to
the presynaptic membrane of another neuron
Helps in maintenance of synaptic contacts

26. Functions of the neurons
The cell body and dendrites serve as receptor zones to receive the
information
Axon hillock/ initial segment is for generation of action potential
Axon for transmission of nerve impulse
Axon terminal for discharge of NT

27. Cell body
It maintains the functional and anatomical integrity of the axon
The proteins associated with synaptic transmitters are synthesized in
Nissil granules of the cell body
Transported to axon terminal by axonal flow

28. Dendrites
They receive impulses and transmit the impulse towards the cell body

29. Axon
The axon hillock/ initial segment is the site where the action potential
is generated
The long axonal process propagates action potentials from the cell
body to the axon terminal

30. Axon terminal
It contain the neuro transmitters in the vesicles
The arrival of action potentials at membrane of axon terminal results in
the release of NT

31. Factors affecting the growth of neurons
Neurotrophins
Trophic proteins to the neurons
They promote nerve growth and survival
Produced by nerves, muscles, glands and astrocytes
Nerve growth factor, Neurotrophin-3, 4, 5
Brain derived neurotrophic factor (BDNF)

32. Factors affecting the growth of neurons
Nerve growth factors
First neurotrophins to be identified
Promotes growth and survival of sympathetic nerves and some sensory
nerves
Decreases apoptosis of neurons acting through tyrosine kinase A receptors
Made up of 2 alpha, 2 beta and 2 gamma units

33. Types of neurons
According to the arrangement of axons
Unipolar neurons: have single processes.
Found in ANS and cerebellum
Pseudounipolar neurons: axon after originating from soma, splits into
central and peripheral processes
DRG

35. Types of neurons
According to the arrangement of axons
Multipolar neurons: have many processes.
Spinal motor neuron

36. Types of neurons
According to the length of axons
Golgi type 1
Long axons
Cortical motor neurons

37. Types of neurons
According to the length of axons
Golgi type 2
Short axons
Cortical inhibitory neurons

38. Types of neurons
According to the function
Sensory neurons
Carry impulses from receptors to the CNS
Also called afferent neurons

39. Types of neurons
According to the function
Motor neurons
Carry impulses from CNS to the target organs
Also called efferent neurons

40. Types of neurons
According to the dendritic pattern
Pyramidal cells
These cells spread like pyramids
Hippocampal pyramidal neurons

42. Types of neurons
According to the dendritic pattern
Stellate cells
 Radial-shaped spread of dendrites occurs in these cells
Cortical stellate cells

44. Neuroglia
The nervous system contains several types of supporting cells
called neuroglia
Astrocytes
Oligodendrocytes
Microglia
Ependymal cells

45. Lambert –Eaton Syndrome
Autoimmune disease
Antibodies formed against voltage gated calcium channels
Decreased calcium influx
Decreased Ach release
EPP not sufficient to cause AP
Muscle weakness

47. THANK YOU