This document provides an overview of neurons and neuroglia in the nervous system. It describes the structure and function of neurons, including their cell body, nucleus, cytoplasm, and processes. It discusses how neurons conduct nerve impulses and communicate at synapses. It also summarizes the different types of neuroglia that support neurons, including astrocytes, oligodendrocytes, microglia, and ependyma.

1. Neurobiology of the
Neuron And Neuroglia
Presented By
Dr. Md. Shafiqul Islam Dewan
Resident (Pulmonology), Phase-A
Dhaka Medical College Hospital

2. Neuron
Definition: Neuron is the name given to the nerve
cell & all its processes.
 It is also called structural and functional unit of
the brain.
Function: They are excitable cells that are
specialized for reception of stimuli & conduction of
the nerve impulse.

3. Size of a neuron:
 Cell body of a neuron may be as small as 5µm or
as large as 135 µm in diameter.
 The process may extend more than 1m.
Number:
 Each mature brain is composed of 100 billion
neurons.

4. Parts of neuron
Neuron
Neurites/
Processes
Axon Dendrites
Cell body

6. Nerve cell body
 It consists of a mass of cytoplasm in which there is a
nucleus is embedded and is bounded externally by a
plasma membrane.
Plasma membrane
 This forms the external boundary of the cell body and
its processes.
 It is the site for initiation and conduction of nerve
impulse.
 It is 8nm thick and composed of an inner and an outer
layer of very loosely arranged protein molecules and a
middle lipid layer.

7. Nucleus
 It is usually centrally located within the cell body
and is typically large and rounded.
 The nucleus envelop is double layered and has
fine nuclear pores.
 There is a single prominent nucleolus which is
concerned with rRNA synthesis.

8. Cytoplasm
 The cytoplasm is rich in granular and agranular
endoplasmic reticulum and contains the following
organelles and inclusions:
 Nissl substance
 Golgi complex
 Mitochondria
 Microfilaments, Microtubules
 Lysosomes, Centrioles
 Lipofuscin, Melanin, Glycogen, Lipid

9. Nissl substance
 Consists of granules and distributed throughout the
cytoplasm of the cell body except axon hillock.
 Extend into the proximal parts of the dendrites but
is not present in the axons.
 It is responsible for synthesizing proteins.
 Fatigue and neuronal damage causes the Nissl
substance to move and become concentrated at the
periphery of the cytoplasm.

10. Golgi complex
 It is made up of smooth endoplasmic reticulum.
 It appears as clusters of flattened cisternae and
vesicles.
 Each cisternae of the golgi complex is specialized for
different types of enzymatic reaction.
 It is also involved in lysosome production and
formation of synaptic vesicles at the axon terminal.

11. Mitochondria
 They are spherical or rod shaped double membrane
structures.
 Scattered throughout the cell body, axon and
dendrites.
 Enzymes that take part in TCA cycle and
cytochromes chains of respiration are located on
the inner membrane and are important for the
production of energy.

12. Lysosomes
 Are membrane bound vesicles containing hydrolytic
enzymes and are formed by budding off of the golgi
apparatus.
 They act as intracelluler scavengers.
 There are three forms of lysosomes. Primary lysosome,
Secondary lysosome and Residual bodies.

13. Centrioles
 Small paired structures found in immature dividing
nerve cells.
 Each Centrioles is made up of bundles of
microtubules.
 They are associated with formation of spindle
during cell division.
 In mature nerve cells they maintain the
microtubules

14. Neurofibrils and Neurofilaments
 The cell body of a neuron is supported by a
complex meshwork of structural proteins called
neurofilaments.
 which are assembled into larger Neurofibrils.

15. Microtubules
 25nm in diameter.
 They are interspersed among the neurofilaments
and extend throughout the cell body and it’s
processes.
 They play a key role in formation of new cell
processes, retraction of old ones, axon
transport.

16. Microfilaments
 Made up of actin.
 3-5nm in diameter.
 They are concentrated at the periphery of the
cytoplasm just beneath the plasma membrane
where they form a dense network.

20. Action potential
 When the nerve cell is stimulated, a rapid change in membrane
permeability to Na ions takes place.
 Na ions diffuse through the plasma membrane into the cell
cytoplasm from the tissue fluid.
 This results in the membrane becoming progressively
depolarized.
 The sudden influx of Na ions followed by the altered polarity
produces the so-called action potential, which is approximately
40 mV. This potential is very brief, lasting about 5 msec.
 The increased membrane permeability for Na ions quickly
ceases, and membrane permeability for K ions increases.
 K ions start to flow from the cell cytoplasm and return the
localized area of the cell to the resting state.

22. Synapse
 Where two neurons come into close proximity
and functional interneuronal communication
occurs, the site of communication is referred to
as a synapse.
 Most neurons may make synaptic connections to
a 1,000 or more other neurons.
 may receive up to 10,000 connections from
other neurons.
 Communication at a synapse,under physiologic
conditions, takes place in one direction only.

23. Types of Synapse
Synapse
Chemical
Axoaxonic
Axodendritic
AxosomaticElectrical

25. Neurotransmitter
 There are several neurotransmitters in the nervous system; such as
 Acetylcholine
 GABA
 Glycine
 Dopamine
 Glutamate
 Serotonin
 Non-epinephrine
 Bradykinin
 Among them ,GABA and Glycine are inhibitory neurotransmitters.

26. Action of neurotransmitter
 The receptor protein on the postsynaptic
membrane bind with the neurotransmitter and
undergo conformational change.
 that opens the ion channels generating an
immediate, brief excitatory postsynaptic
potential(EPSP) or inhibitory postsynaptic
potential(IPSP).
 The overall effect is depolarization and propagation
of the impulse if EPSP is generated and that of IPSP
is hyperpolarization and inhibition of the neuron.

27. Fate of Neurotransmitter
 They are either destroyed by enzymes in the
synaptic cleft, eg: Acetylcholinesterase
 Or reabsorbed by the presynaptic membrane,
eg: Catecholamine.

28. Neuroglia
The neurons of the central nervous system are
supported by several varieties of non-excitable
cells, which together are called neuroglia.

29. Characteristics
 Generally smaller than neurons,
 Outnumber them 5 to 10 times,
 They comprise about half the total volume of
the brain and spinal cord.

30. Types of neuroglial
1. Astrocytes
2. Oligodendrocytes
3. Microglia
4. Ependyma

31. Astrocytes
 Astrocytes have small cell bodies with branching
processes that extend in all directions.
 There are two types of astrocytes: fibrous and
protoplasmic.

32. Fibrous astrocytes
 They are found mainly in the white matter,
where their processes pass between the nerve
fibers.
 Each process is long, slender, smooth, and not
much branched.
 The cell bodies and processes contain many
filaments in their cytoplasm.

33. Protoplasmic astrocytes
 They are found mainly in the gray matter, where
their processes pass between the nerve cell
bodies.
 The processes are shorter, thicker, and more
branched than those of the fibrous astrocyte.
 The cytoplasm of these cells contains fewer
filaments than that of the fibrous astrocyte.

34. Function of astrocytes
 Provide supporting framework,
 are electrical insulators,
 limit spread of neurotransmitters,
 take up K ions
 Store glycogen,
 have a phagocytic function,
 take place of dead neurons,
 are a conduit for metabolites or raw materials
 produce trophic substances

35. Oligodendrocytes
 Oligodendrocytes have small cell bodies and a few
delicate processes.
 there are no filaments in their cytoplasm.
 Oligodendrocytes are frequently found in rows
along myelinated nerve fibers and surround nerve
cell bodies.
 Form myelin in CNS and influence biochemistry of
neurons

36. Microglia
 Derived from macrophages outside the nervous
system.
 They migrate into the nervous system during
fetal life.
 They are the smallest of the neuroglial cells and
are found scattered throughout the central
nervous system.
 Are inactive in normal CNS, Proliferate in disease
and phagocytosis, joined by blood monocytes.

37. Ependyma
 Ependymal cells line the cavities of the brain and the
central canal of the spinal cord.
 Ependymal cells may be divided into three groups:
1. Ependymocytes - which line the ventricles of the brain
and the central canal of the spinal cord and are in
contact with the cerebrospinal fluid. Circulate and
absorb CSF.
2. Tanycytes - which line the floor of the third ventricle.
Transport substances from CSF to hypophyseal-portal
system.
3. Choroidal epithelial cells - which cover the surfaces of
the choroid plexuses. Produce and secrete CSF.