1. NERVES TISSUE
MUTALIFE F. MWEEMBA

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

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

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

14. Dendrites

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.

17. Synaptic knobs (boutons)

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

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

21. Types cont..

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

25. Cont…
Oligodendrocytes
 produce the myelin
sheaths around
axons
 that provide the
electrical
insulation for
neurons in the
CNS

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

30. Spinal nerve

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

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)

37. Myelination

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

41. Nodes of Ranvier

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

46. Clinical anatomy
 Neuropraxia
 Paralysis

47.  Thank you