Objective of the study:- Structure of a typical Neuron, Classification of Neuron based on Polarity, on conduction direction, on neurotransmitters released, on their shape, Glial cells, major type of Glial cells present in CNS and PNS and their functions.

1. Neuron & Glial
cells
(Paper-2 Unit-4)
Asst Prof. Abhijeet Bhattacharya
KSD’s Model College

2. Neuron
Introduction
➢A neuron ( also known as nerve cell) is an
electrically excitable cell that processes and
transmits information by electrical and chemical
signaling.
➢ Neurons are the core components of the nervous
system, which includes the brain, spinal cord, and
peripheral ganglia.
➢ Human brain comprises tens of billions of
neurons, each linked to thousands of other
neurons via the chemical channels called
synapse.

4. Parts of a Neuron
➢There are many types of neuron but a
typical neuron has some common
structural and functional characteristics.
➢A neuron consists of three main parts
➢The Cell body or Perikaryon or Soma,
➢Dendrites, the receiving processes.
➢Axons, the transmitting fiber.

5. SOMA

6. SOMA or CELL BODY
➢The cell body is the central region which
is the most important part of the neuron
containing the nucleus of the cell.
➢The soma is, the site of major metabolic
activity in the neuron.
➢ The size of neuronal somas range
widely from 0.005 mm to 0.1 mm in
mammals.
➢Collections of cell bodies (somas) give
the greyish appearance to the gray
matter of the brain.

7. SOMA or CELL BODY
contd…
➢The protoplasm of cell body contains
peculiar angular granules, which stain
deeply with basic dyes, such as
methylene blue; these are known as
Nissl’s granules.
➢These granules disappear
(chromatolysis) during fatigue or after
prolonged stimulation of the nerve
fibers connected with the cells.
➢ Thought to be involved in the synthesis
of neurotransmitters such as
acetylcholine

8. Dendrites
➢Dendrites are extensions that carry
impulses toward the cell body and
are referred to as being afferent
fibers.
➢ They increase the surface area of a
neuron by the presence of rough
structure on their surface called
dendritic spines, to increase its ability
to communicate with other neurons.

9. Axon
➢An axon is a type of protoplasmic
protrusions that extrude from the cell
body of a neuron .
➢Unlike dendrites axons are long, slender
projection of a neuron, that conducts
electrical impulses away from the
neuron's cell body or soma.
➢Axons are distinguished from dendrites
by several features, including shape,
length , and function.
➢The point where the axon arises from a
cell body is termed as Axon Hillock.
➢Axoplasm is the cytoplasm within the
axon.

10. Axon diagram

11. Axon contd…..
➢The axolemma is the cell membrane
surrounding an axon.
➢It is responsible for maintaining the membrane
potential of the neuron, and it contains ion
channels through which ions can flow.
➢The axons of many neurons are sheathed in
myelin, which is formed by either of two types
of glial cells: Schwann cells myelinate peripheral
neurons and oligodendrocytes myelinate the
central nervous system
➢ The Myelin sheath functions to: – Protects the
axon and increases the rate of Action Potential
transmission (saltation)
➢Along myelinated nerve fibers, gaps at intervals
in the sheath known as Nodes of Ranvier.

12. Axon contd….
➢Terminally the Axon forms synaptic knob, which contains synaptic
vesicles, containing Neurotransmitter.
➢Axons contact with other cells via the synaptic knob on dendrites of
other neurons but sometimes muscle or gland cells—at junctions
called synapses.
➢The region between the two connecting neurons is known as the
Synaptic gap or Snaptic cleft or neural junction.

13. Classification of
neurons
BASED ON POLARITY
➢ Unipolar : type of neuron in which only
one protoplasmic process (neurite)
extends from the cell body. – Found
mostly in inverterbrate – In humans
mostly found in dorsal root ganglia
➢Bipolar: An axon and a single dendrite
on opposite ends of the Soma are
abundant in sensory pathways for smell,
sight, taste, hearing and vestibular
functions.
➢Multipolar: An Axon along with more
than two dendrites –Includes motor
neurons and interneurons.

14. Classification of Neuron Based on Polarity

15. Classification of neurons
BASED ON CONDUCTION DIRECTION
➢Afferent neurons also called sensory neurons. Convey information from
tissues and organs into the central nervous system.
➢Efferent neurons also called as motor neurons. Carry nerve impulses away
from the central nervous system to effectors such as muscles or glands.
➢ Interneuron also called as relay neuron or local circuit neuron connects
afferent neurons and efferent neurons in neural pathways

16. Classification of neurons
BASED ON NEUROTRANSMITTER PRODUCTION
➢Cholinergic neurons —secreting acetylcholine
➢GABAergic neurons — secreting gamma aminobutyric acid.
➢Glutamatergic neuron — secreting glutamate
➢Dopaminergic neurons — secreting dopamine .
➢ Serotonergic neurons — secreting serotonin.

17. Classification of neurons
BASED ON UNIQUE SHAPE AND FUNCTION
➢Betz cells – Large motor neurons located within the fifth layer of the
grey matter in the primary motor cortex.
➢Purkinje cells - Some of the largest neurons in the human brain, found
within the Purkinje layer in the cerebellum.
➢Renshaw cells - Neurons with both ends linked to alpha motor
neurons.
➢Pyramidal cells- Type of neurons with triangular soma found in areas of
the brain including cerebral cortex, the hippocampus, and in the
amygdala.
➢Basket cells - Inhibitory GABAergic interneurons found in several brain
regions: the molecular layer of the cerebellum, the hippocampus, and
the cortex.

18. Glial Cells.
➢Glia, also called glial
cells or neuroglia, are non-
neuronal cells in the central nervous
system (brain and spinal cord) and
the peripheral nervous system.
➢Do not produce electrical impulses.
➢They maintain homeostasis
➢Produces myelin
➢ Provide support and protection for
neurons.
➢In CNS Glial cells outnumber
neurons 10:01

19. Types of Glial Cells & Radial Glial Cells

20. Neuroglia in the CNS
There are four types of neuroglia found within the central
nervous system:
➢Astrocytes – maintain the blood brain barrier and preserve
the chemical environment by recycling ions and
neurotransmitters
➢Oligodendrocytes – myelinate axons in the central nervous
system and provide an overall structural framework
➢Ependymal cells – line ventricles (brain) and central canal
(spine) and are involved in the production of cerebrospinal
fluid
➢Microglia – remove cell debris, wastes and pathogens via
phagocytosis

21. Neuroglia in the
PNS
There are two types of neuroglia
found within the peripheral
nervous system:
➢Schwann cells – myelinate
axons in the peripheral nervous
system
➢Satellite cells – regulate
nutrient and neurotransmitter
levels around neurons in
ganglia