2. Objectives
By the end of the lecture students
should be able to;
1. Define nerve tissues
2. Discuss nerve tissue
3. Describe the components of a
neuron
4. State the types of neurons
5. Clinical application
3. Definition
Nerve tissue is distributed throughout the
body as an integrated communications
network
It is a complex tissue which picks up
stimuli both external and internal and
transmits these stimuli in form of an
impulse to a central region of integration
and analysis.
Then an appropriate response is
transmitted from the central region
4. Composition of nerve tissue
Cells in both central and peripheral
nerve tissue are of two kinds:
nerve cells , or neurons , which
usually show numerous long
processes; and
glial cells, are non excitable cells and
have short processes, function to;
◦ support and protect neurons
◦ participate in many neural activities,
◦ provide neural nutrition, and
◦ defense of cells in the CNS
5. Cont…
Each neuron has hundreds of
interconnections with other neurons,
forming a very complex system for
processing information and
generating responses.
6. Development of nerve tissue
nervous system develops from the
outermost of the three early embryonic
layers, the ectoderm,
beginning in the third week of development.
With signals from the underlying axial
structure, the notochord, ectoderm on the
mid-dorsal side of the embryo thickens to
form the epithelial neural plate .
The lateral sides of this plate fold upward,
bend and grow toward each other medially,
and within a few days fuse to form the
neural tube .
Cells of this tube give rise to the entire
7.
8. Cont..
As the folds fuse and the neural tube
separates from the now overlying
surface ectoderm that will form
epidermis, a large population of
developmentally important cells, the
neural crest, separates from the
neuroepithelium and becomes
mesenchymal.
Neural crest cells migrate extensively
and differentiate as all the cells of the
PNS, as well as a number of other non
9. Anatomical divisions
Central Nervous System (CNS)
consists of;
◦ Brain and spinal cord
Peripheral Nervous System
composed of;
◦ Cranial nerves
◦ Spinal nerves and
◦ autonomic nerves
10.
11. Cont..
Peripheral Nervous System
◦ Somatic ; motor and sensory
Autonomic ;
◦ visceral motor,
◦ visceral sensory
12. General features
Basic functional unit is a neuron (nerve
cell)
Has 3 parts;
◦ cell body (perikaryon), dendrites and
axon
Supporting tissues,
◦ For CNS:
glial cells
◦ peripheral nervous tissue:
Schwann cells,
Satellite cells and connective tissue
Development from ectoderm
13. Neuron
have long processes, extend from the
part of the cell body around the nucleus,
The processes can be divided into two
functionally and morphologically different
groups, dendrites and axons.
Dendrites are part of the receptive
surface
A neuron has one to several primary
dendrites, which emerge from the cell
body.
Primary dendrites may divide into
15. Axon
Each neuron has only
one axon,
◦ emerging from the
perikaryon or
◦ close to the trunks of one of
the primary dendrites.
The point of origin of the
axon from the perikaryon
is the axon hillock.
It may be branched
is the "transmitting"
process of the neuron
16. Cont….
The axon forms small, bulb-shaped
swellings called boutons at the ends
(terminal boutons)
or along the course (boutons en
passant) of its branches.
Synapses are morphologically
specialised contacts between a
bouton formed by one neuron, the
presynaptic neuron, and the cell
surface of another neuron, the
postsynaptic neuron.
18. Cont…
Synaptic vesicles contain the
neurotransmitters.
typically accumulate close to the site of
contact between the bouton and the
postsynaptic neuron.
The release of the neurotransmitter from the
synaptic vesicles into the synaptic cleft,
◦ mediates the transfer of information from the pre-
to the postsynaptic neuron.
the synaptic cleft is the space between the
bouton and the postsynaptic neuron
19.
20. Types of Neurons
classified according to the number of
processes extending from the cell body
Multipolar neurons,
◦ which have one axon and two or more
dendrites
◦ E.g, all motor neurons and CNS interneurons
Bipolar neurons,
◦ with one dendrite and one axon
◦ E.g, sensory neurons of the retina, olfactory
mucosa, and inner ear
serve the senses of sight, smell, and
balance, respectively
22. Cont..
Unipolar or pseudounipolar neurons,
◦ which have a single process that bifurcates close
to the perikaryon, with the longer branch
extending to a peripheral ending and the other
toward the CNS.
◦ E.g, in the spinal ganglia (the sensory ganglia
found with the spinal nerves)
◦ most cranial ganglia
Anaxonic neurons,
◦ with many dendrites but no true axon,
◦ do not produce action potentials,
◦ but regulate electrical changes of adjacent
neurons
23. Supporting cells of the CNS
Macroglia are;
Astocytes
Oligodendocytes
Ependymal
Microglial
24. Supporting cells of the CNS
Astrocytes
◦ Structural and
metabolic support of
neurons;
◦ are in contact with
blood vessels
◦ form Blood Brain
Barrier (BBB);
◦ repair processes-
scar forming in CNS
2 types
◦ Fibrous astrocytes
◦ Protoplasmic astrocytes
26. Cont..
Ependymal cells
Line ventricles of the brain and the central canal of the
spinal cord
◦ Aid production and movement of CSF
Microglia
can proliferate and differentiate into phagocytic cells.
◦ Defense and immune-related activities
27. Peripheral Nervous System
The PNS comprises all nervous
tissue outside the brain and spinal
cord.
It consists of;
◦ groups of neurons (ganglion
cells), called ganglia,
◦ networks of nerve fibres, called
plexuses
bundles of parallel nerve fibres that
form the nerves and nerve roots.
28. Cont…
efferent or motor fibres carry
impulses from the CNS to effector
organs commanded by these centers.
afferent or sensory nerve fibres
carry information from internal body
regions and the environment to the
CNS
Principal neurotransmitters in the
PNS are acetylcholine and
noradrenalin.
29. Cont…
Afferent, sensory fibres enter the spinal cord
via the dorsal roots,
while efferent, motor fibres leave the spinal
cord via the ventral roots.
Dorsal and ventral roots merge to form the
spinal nerves, which consequently contain
both sensory and motor fibres.
As the spinal nerves travel into the periphery
they split into branches
31. Cont..
Nerves possessing only sensory fibers
are called sensory nerves;
those composed only of fibers carrying
impulses to the effectors are called
motor nerves.
Most nerves have both sensory and
motor fibers and are called mixed
nerves,
usually also with both myelinated and
unmyelinated axons
32. Nerve Organization
Peripheral nerves contain a considerable
amount of connective tissue.
The entire nerve is surrounded by a thick
layer of dense connective tissue, the
epineurium.
Nerve fibres are frequently grouped into
distinct bundles, fascicles, within the nerve.
The layer of connective tissue surrounding
the individual bundles is called perineurium.
The space between individual nerve fibres is
filled by loose connective tissue, the
33.
34.
35. Fibrocytes, macrophages and mast
cells are present in the
endoneurium.
Nerves are richly supplied by
intraneural blood vessels, which
form numerous anastomoses.
Arteries pass into the epineurium,
form arteriolar networks beneath the
perineurium and give off capillaries to
the endoneurium.
36. Nerve fiber
One nerve fiber consists of an axon and its
nerve sheath.
Each axon in the PNS is surrounded by a
sheath of Schwann cells.
An individual Schwann cell may surround the
axon for several hundred micrometers,
it may, in the case of unmyelinated nerve
fibers, surround up to 30 separate axons.
The axons are housed within infoldings of
the Schwann cell cytoplasm and cell
membrane, the fused membrane (mesaxon)
39. Cont…
In the case of myelinated nerve fibres,
Schwann cells form a sheath around one
axon and surround this axon with several
double layers (up to hundreds) of cell
membrane.
The myelin sheath formed by the
Schwann cell
◦ insulates the axon,
◦ improves its ability to conduct
◦ provides the basis for the fast saltatory
transmission of impulses.
40. Cont…
Each Schwann cell forms a myelin
segment, in which the cell nucleus is
located approximately in the middle of
the segment.
The node of Ranvier is the place
along the course of the axon where
two myelin segments abut
42. Ganglia
Ganglia are structures containing neuronal
cell bodies and their surrounding glial
satellite cells
Supported by delicate connective tissue
and surrounded by a denser capsule
serve as relay stations to transmit nerve
impulses
ganglion will be a;
◦ Sensory ganglia
◦ Autonomic ganglia
◦ sympathetic
◦ parasympathetic
43. Sensory ganglion
Associated with;
◦ Dorsal root ganglion
◦ Cranial nerves ganglions
Large cells, with nucleus and nucleolus.
Nissl bodies,
are pseudounipolar
Satellites cells
Cell bodies in groups
Myelinated nerves
44. Autonomic ganglion
nerves effect the activity of smooth muscle,
the secretion of some glands, heart rate,
and many other involuntary activities of the
body
◦ Multipolar cells
◦ Scattered
◦ Nucleolus and Nissl bodies
◦ Few satellite cells
◦ Unmyelinated nerve
has two divisions :
◦ sympathetic
◦ parasympathetic
45. Parasympathetic ganglion
Neuronal bodies of preganglionic
sympathetic nerves are located in the
thoracic and lumbar segments of the spinal
cord
the parasympathetic division are in the
medulla and midbrain and in the sacral
portion of the spinal cord.
Found close or within the wall of organ
Intramural
Multipolar cells
Satellite cells
