Neuroanatomy

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.