Upload
others
View
8
Download
0
Embed Size (px)
Citation preview
Faculty of Dental Medicine and Surgery
Sem 2
Man and his environment
Nervous tissue
Dr. Nafisa Bakri Idris
Content
• Neuron
• Synapses
• Neuroglia
• Nerve fiber
Objectives
By the end of this lecture the students should be able
to:
• Understand the microstructure of neuron and its
classification
• Master the microstructure of the synapses
• Know the micrograph and function of glia
• Familiar the microstructure of nerve fiber
Nervous tissue is composed of nerve cells
and neuroglia. The specialized cells that
constitute the functional units of the
nervous system are called neurons.
The function of neuron:generate nerve
impulses in response to stimuli and
transmit them along cellular processes.
Neuroglia or glia: neurons are supported by
a special kind of connective tissue within
the brain and spinal cord, that is called
neuroglia,it also located in the PNS.
Function: support, protect, connect
Central nervous system
Peripheral nervous system
Brain and spinal cord
The nerves and their associated ganglia.
Nervous system
1.Microstructure of neuron
Cell body
Axon
Dendrites
Microstructure
LM:
EM:
Function
Classification
Neuron
Neurons
Cell body
Processes or neurites
Dendrites
Axon
Nucleus
Cytoplasm
Cell membrane
The cell body,soma, is the part of neuron that
contains nucleus and surrounding cytoplasm,
also called perikaryon. It is the trophic center
of the neuron. The protein and enzymes
synthesis in this area.
Cell body: Perikaryon
Where is cell body
Cell body: Perikaryon
• Position: only in grey matter in CNS which
also contains dendrites and axons starting
from or ending on the cell bodies,ganglia in
PNS
• Shape:They can be pyramidal, spherical,
ovoid or pear-shaped.
• Size: Measuring 5-150 um in diameter.
Microscopic examination
(1)Cell membrane: the structure is as the same
as the normal cell. It functions in getting
the stimuli and integration and conducting
the nerve impulse.
(2) The nucleus is large and pale with H-E
stain,prominent nucleoli are very clear.
Cell body: Perikaryon
nucleus
nucleolus
(3)Cytoplasm: the cytoplasm has some
distinctive characteristics not seen in other
cells. The cytoplasm is basophilic and full
of neurofibrils.
Cell body: Perikaryon
Nissl body
Neurofibril
H-E stains Silver nitrate
Nissl bodies: The cytoplasm shows the
presence of a granular material that stains
intensely with basic dyes; this material is the
Nissl substance (also called Nissl bodies or
granules).
Cell body: Perikaryon
细颗粒样的尼氏体
Nissil body
axon hilllock
Neurofibrils
• Neurofibrils are thin black fibers
observed in LM with silver nitrate slides,
which is composed of microtubule and
filaments in EM.
Cell body: Perikaryon
EM
RER
ribosome
pigment
synapse
microtubemitochondria
EM: rough surfaced endoplasmic reticulum.
The presence of abundant granular endoplasmic
reticulum is an indication of the high level of
protein synthesis in neurons. Mitochondria,
SER,lysosomes,Golgi complexes,ribosome etc.
The proteins are needed for maintenance and
repair, and for production of neurotransmitters
and enzymes.
The processes arising from the cell body of
a neuron are called neurites.Most neurons
give off a number of short branching
processes called dendrites and one longer
process called an axon.
Neurites or processes
Cell body
Axon
Dendrites
collaterals
Nissl bodyNeurofibril
H-E stains Silver nitrate
不同形态
Axon
Dendrites
The dendrites are characterized by the fact
that they terminate near the cell body. They
are irregular in thickness, and Nissl granules
extend into them. They bear numerous small
spines which are of variable shape.
Dendrites
• Every neuron has only one long thin process
or axon which arises from a special region
or axon hillock, which is devoid of Nissl
bodies. It carries the impulse received by
the neuron to distant region.
Axon
axon hilllock
An axon may have not much branches than
that of dendrites. If branches, that arise near
the cell body and lie at right angles to the
axon are called collaterals. At its
termination the axon breaks up into a
number of fine branches called telodendria
which may end in small swellings (terminal
boutons.
The axon is identified according to the
axon hillock with LM.The part of the
axon just beyond the axon hillock is called
the initial segment.
Neurites or processes
Dendrites Axons
many one
short long
irregular in thickness uniform in diameter
Nissl granules No Nissl substance
spines axon hillock
impulse towards the soma away from the cell body
2. Classification of neuron
Cell body
Axon
Dendrites
• 1)According to the number of the processes
unipolar,or pseudounipolar neuron
bipolar neuron
multipolar neuron
multipolar neuron
bipolar neuron
Unipolar neuron
According to the size of cell body and the
length of axon: According to Cajal (1889):
Golgi type I neurons: long axon
Golgi type II neurons: short axon
Sense ( afferent )neurons:
Interneurons
Motor( efferent ) neurons
•According to their function:
• The classification of neurons:
• According to the number of process
The shape of the cell body is dependent on
the number of processes arising from it. The
most common type of neuron gives off several
processes from the cell body is, therefore,
multipolar. Some neurons have only one
axon and one dendrite and are bipolar.
Another type of neuron has a single process
(which is highly convoluted). After a very
short course this process divides into two.
One of the divisions represents the axon; the
other is functionally a dendrite, but its
structure is indistinguishable from that of an
axon. This neuron is described as unipolar,
but from a functional point of view it is to be
regarded as bipolar. (To avoid confusion on
this account this kind of neuron has been
referred to, in the past, as a pseudounipolar
neuron.
Depending on the shapes of their cell bodies some neurons are referred to as stellate (star shaped) or pyramidal.
• According to the neurotransmitter they release
• Cholinergic neurons: acetylcholine
• Aminergic neurons: adrenaline, non
• Peptidergic neurons: neuropeptids
The Synapse :
Concept: Synapses are highly specialized
intercellular junctions which link the
neurons of each nervous pathway.
Similar intercellular junctions link neurons
and their effector cells such as muscle
fibers;where neurons synapse with skeletal
muscle they are referred to as
neuromuscular junction or motor end plate.
synapse
Processes
Cell body
• Classification of synapses:
According the constitution:
axodendritic synapse
axosomatic synapse
axoaxonal synapse
dendro-axonic
dendro-dendritic
somato-somatic synapse
somato-dendritic synapse
Structures of the synapse
(1) The axon may terminate in a single bulb-like end called a presynapse bouton (or synaptic bag).
(2) synapse cleft
(3)postsynaptic cleft
presynaptic elements
postsynaptic elements
synaptic cleft
presynpatic membrane
visicle
mitochondria
postsynaptic membrane
presynaptic elemen
Synaptic cleft
Neuroglia
• Neuroglia:
Within the central nerve system:
Oligodendrocytes
astrocytes
microglia
ependymal cells
• Peripheral neuroglia:
Schwann cells are active in the formation
and maintenance of myelin in the PNS.
Satellite cells:The neuronal cell bodies of
ganglia are surrounded by a layer of small
cuboidal cells called satellite cells. (spinal
and autonomic ganglia)
• Myelinated and non-myelinated nerve fibers
In the peripheral nervous system, all axon are
enveloped by highly specialized cells called
Schwann cells which provide both structure and
metabolic support. In general, small diameter
axon (e.g. those of the autonomic nervous
system and small pain fibers) are simply
enveloped by the cytoplasm of Schwann cells.
• These nerve fibers are said to be non-
myelinated. Large diameter fibers are
wrapped by a variable number of concentric
layers of the Schwann cell plasma membrane
forming a myelin sheath; such nerve fibers
are said to be myelinated.
• Within the central nerve system, myelination
is similar to that tin the peripheral nervous
system except that the myelin sheaths are
formed by cells called oligodendrocytes.
• Nerve fibers:
These are process of neurons and are
collected to form nerve trunk.
In longitudinal section: The nerve fiber
is seen to consist of the central axis cylinder
or axon arising from the neuron. It is
surrounding by layer myelin which consist
of phospholipids which acts as an insulator.
• It is interrupted at places. At these points,
the points are called nodes of Ranvier.
Outside the myelin sheath is a thin cell of
Schwann, which are neurilemma.The cells
of neurilemma are also known as cells of
Schwann, which are neuroectodermal in
origin. These cells are responsible for laying
down the myelin sheath of the peripheral
nerves.
Myelin sheath
Nodes of Ranvier
Axon
internode
• Transverse section
• epineurium: nerve truck
• perineurium: Each of fascicles
endoneurium:each nerve fibers.
Thank you