Transcript Function

Nervous tissue
Shiping Ding
Zhejiang University
General characteristics:
---Components:
• nerve cell: neuron, receive the stimulation,
conduct the nerve impulse
• glial cell: neuroglia, support, protect,
insulate and nourish neurons
---Function:
• Transmit impulses and thus communicate
with different parts of the body through
these impulses.
• Works closely with endocrine system in
communication within the body.
Neuron: The structural and functional
cellular unit of nerve system
Morphology of neuron:
consists of cell body, dendrite and axon
---cell body: spherical, pyramidal fusiform or
satellite in shape, 5um-150um,
---dendrite: arise from the cell body and
branched like trees, usually shorter and
thinker than axon
---axon: most neuron only have one, long thin
cord-liked, arise from the axon hillock
structure of neuron
cell body: perikaryon
---cell membrane:
• unit
membrane-irritability,
receive
stimuli, initiate and conduct nerve
impulse
• membrane proteins-ions channel and
receptor
• --- cell nucleus:
• large and round, centrally- located,
less heterochromatin, pale stained and
appears empty, with a large, clear
nucleolus
• ---cytoplasm:
a. Nissl body:
Present throughout the cytoplasm of the cell
body and dendrites, but absent from the axon
hillock and axon
LM: basophilic spot-liked or granule-liked
structure
EM: parallel-arranged RER and free ribosome
The number of Nissl bodies varies according
to neuronal type and functional state.
function: synthesis of proteins:
structural protein
enzymes related to the production of
neurotransmitters
b. Neurofibril:
LM:
silver impregnation methods (silver
preparation)
thread-liked dark brown color
fibril
forming a network
abundant in cell body, dendrites
and axon
EM:
• neurofilament: 10 nm in diameter
• microtubule: 25 nm in diameter
function:
• Support neurons as a cell
skeleton
• involving
in
intracellular
transportation
c. other organelle
• Golgi complex: well-developed
• Mitochondria: scattered throughout the cytoplasm
• pigment
• Lipid droplets
dendrites:
---short branches
---structure: similar to cell body
---dendritic spine :numerous fine projections
(places for formation of synapse)
---function: receive the information from other
nerve cells
axon:
---longer and thinner process,
have a uniform diameter
---structure: no Nissl body, but have microtubule,
neurofilament, microfilament, mitochondria,
SER and vesicle
• axon hillock: the beginning part of axon (no
Nissl body)
• axolemma
• axoplasm
---function: initiate an impulse and conduct the
impulses away from the parent cell body to
other neurons or effector structures
Structure and function of neuron
axonal transports:
•
•
A cellular process responsible for movement of
mitochondria, lipids, synaptic vesicles, proteins
and other cell parts( organelles) to and from a
neuron’s cell body, through the cytoplasm of its
axon.
slow anterograde:
cytoskeletal protein: microtubule,
microfilament and neurofilament (0.1-0.4mm/d)
•
•
fast anterograde:
synaptic vesicles, enzymes and proteins( 100400mm/d)
•
•
fast retrograde:
products of metabolism, intaking materials
including protein or neurotrophic factors (100400mm/d)
Classification of neuron
---According to number of processes
• multipolar neuron
• bipolar neuron
• pseudounipolar neuron
---According to function
• sensory neuron:
receive exogenous and endogenous
stimuli
• motor neuron: conduct impulses to
effector organs and control their
function
• interneuron: connect other neurons to
form complex functional chains
synapse
Synapse
•neuron
nerve fiber
neuroglia
nerve efferent
receptor
neuron
Synapse
---definition: the junctions between neurons or
neuron and non-nerve cells
---classification:
• chemical synapse: taking neurotransmitter as
communicating medium
• electrical
synapse:
exchange
ions
for
communication, gap junction
---structure of chemical synapse:
L/M:
The axon terminate in the form of a rounded
enlargement, called axonal terminal or
terminal button
E/M:
presynaptic element: axonal terminal
• presynaptic
membrane:
axon
plasmalemma
• synaptic vesicle: store neurotransmitters
• mitochondria
synaptic cleft: the extracellular space between
the presynaptic membrane and the
postsynaptic membrane, 15-30nm
postsynaptic element:
• postsynaptic membrane:
the plasmalemma at the contract
point of the receiving neurons,
-specific receptor molecules
•
The nerve impulse reaches the
presynaptic element
•
The synaptic vesicle fuses with the
presynaptic
membrane
and
discharges the neurotransmitters
into the synaptic cleft by
exocytosis
•
The neurotransmitters diffuses
across the cleft and combines with
specific
receptors
in
the
postsynaptic membrane
•
This reaction induces an increase
in the permeability of the
postsynaptic membrane and cause
a change in the membrane
potential of the postsynaptic
neurons, then conduct the stimuli
from one neuron to other neuron
Glial cell
(neuroglia)
Form a framework to
support
neurons
and
influence their activities and
metabolism
Glial cell in central nervous
system
Astrocyte:
•
large star-shaped
•
ovoid nucleus, large and pale
•
end feet: to form glia
limitans or vascular feet constitute
blood
brain
barrier
•
Two forms:
protoplasmic astrocyte
fibrous astrocyte
---function
•
•
•
supporting, insulating and
repairing
regulate the environment and
movement of neuron
secret neurotrophic factor:
nerve growth factor and glial
cell line-derived neurotrophic
factor
protoplasmic astrocyte
fibrous astrocyte
blood brain barrier
Functional barrier:
• The continuous endothelium of
capillaries and the tight junctions
between endothelial cell
• a continuous basal membrane
around the endothelium
• The vascular foot processes of
astrocytes
surrounding
the
capillaries
----Function:
• Regulates the diffusion of many
substances between the blood and
brain, such as antibiotics, chemical
and bacterial toxic matter.
Oligodendrocyte:
---structure:
smaller, fewer process with a small round and dark stained nuclei
---function:
their processes form myelin-sheath of nerve fibers in central
nervous system (CNS)
Microglia:
---structure: smallest neuroglial cells, with a
small dark irregular nucleus
---function: phagocytosis - mononuclear
phagocyte system
Ependymal cell:
---structure:
• simple columnar epithelium
• apical: microvilli and cilia
• basal: long processes
---function:
• produce cerebrospinal fluid
---distribution: ventricle of brain and
central canal of spinal cord
Glial cell in peripheral nervous system (PNS)
Schwann cell:
envelop the axon end to end to form myelin-sheath in PNS
Satellite cell (capsular cell):
• one layer of flattened or cuboidal cell, with round, ovoid and dark
nucleus
• surrounding the Neuron in ganglion for form a kind of cellular
capsule
Nerve fiber
---definition: a structure formed by
axon and glial cell which can
conduct the impulse to certain
direction
---classification:
• myelinated nerve fiber
• unmyelinated nerve fiber
myelinated nerve fiber (MNF)
1) MNF in PNS
L/M:
• Axon
• myelin-sheath: tubular sheath encloses the axon
• neurolemma: cell membrane of Schwann cell and basement membrane
Myelin is a complex of lipids
and protein.
• Ranvier node: narrow part, no myelin-sheath
• internode: the segment of NF between two Ranvier nodes, 0.3-1.5 mm,
represent a single Schwann cell
E/M:
The myelin sheath is seen as a series of concentrically arranged light and
dack lamellae---Schwann cell plasmalemma
Schmidt-Lanterman cleft (incisure): area where the cytoplasm of the
Schwann cells is present within the myelin sheath.
Schmidt-Lanterman cleft
2) MNF in CNS
---structure:
• similar to that in PNS
• myelin-sheath formed by flattened
ending of oligodendrocyte’s processes
• one oligodendrocyte can envelop many
axons
• no incisure and basement membrane
The function of the myelin sheath:
•to provide an insulation layer around
the axon
•to speed up impulse conduction:
nerve impulses jump from node to
node across the intervening
internodal segment of myelin sheath
( the axon directly exposed to the
extracelluar fluidal ions at nodes of
Ranvier, where depolarisation occurs)
The thicker the myelin sheath, the
greater the internodal distance and
conduction speed.
unmyelinated nerve fiber (N-MNF)
N-MNF in PNS
---structure:
• thin axon and Schwann cell which connect
end to end
• no myelin-sheath and Ranvier node
• one Schwann cell envelops many axons
N-MNF in CNS
• naked axon , nothing to envelop the axon
Nerve (Study by yourself!)
---the aggregation of nerve fiber
• efferent nerve
• afferent nerve
• mixed nerve
---connective tissue
• epineurium
• perineurium
• endoneurium
Perineurium
Nerve bundle
Individual
Axon surrounded
By myelin sheath
Nerve Ending
Study by yourself!
1) Sensory nerve ending
Afferent ending
①free nerve ending
---structure: NF→lose myelinsheath → branch → distribute
in epidermis, cornea, hair
follicle epithelial cell and CT
---function: feel cold, hot, pain and
slight touch
② Encapsulated nerve ending
---have CT capsule
a. tactile corpuscle:
• encapsulated unmyelinated nerve endings, which consist of flattened
supportive cells arranged as horizontal lamellae surrounded by a
connective tissue capsule. The corpuscle is between 30-140 μm in
length and 40-60 μm in diameter.
•
A single nerve fiber meanders between the lamellae and throughout
the corpuscle.
b. lamellar corpuscle
---structure:
• large , oval or spherical
• capsule: several layers of flattened
cell concentrically-arranged
• bulb- cylindrical
• NF →lost MS→enter the bulb
---distribution: subcutaneous tissue,
mesentery, ligament
---function: feel deep or heavy pressure
c:Muscular spindles:
---structure:
•
fusiform
•
CT capsule
•
a few small muscle fibers- intrafusal
muscle fiber
•
NF: roll up the muscle fiber
---distribution: skeletal muscle
---function: detect muscle length and
change in muscle length
Muscular spindles
d: Motor nerve ending:
Efferent nerve ending
LM:
Plate-like mass with the terminal
swelling of a nerve fiber
---structure: EM
• muscle F: rich in cytoplasm, nuclei
and mito
• presynaptic membrane: - synaptic
vesicles- acetylcholine
• synaptic cleft:
• postsynaptic membrane:
-acetylcholine receptor
function:
control the contraction of skeletal
muscle fiber
Thank you for your attention!