Transcript Chapter 7 Nervous tissue

Chapter 7
Nervous tissue
1. General description:
---Components:
nerve cell: neuron
Glial cell: neuroglial
---Function:
Neurons : receive the stimulation, conduct the
nerve impulse
Glial cell: support, protect and insulate,
nourish neurons
2.
Neuron
The structural and functional cellular unit
1) shape of neuron:
consists of cell body, dendrite and axon
---cell body: spherical, pyramidal fusiform or
stellate in shape, 5um-150um
---dendrite: like branches of tree
---axon: long thin cord-liked
2) structure of
neuron
① cell body:
---cell membrane:
unit membrane-irritability, receive stimuli,
initiate and conduct nerve impulse
membrane
proteins-ions
channel
and
receptor
---cell nucleus: large and round, centrallylocated, less heterochromatin, so pale
stained, with a large, clear nucleolus
---cytoplasm: perikaryon
a.
Nissl body:
LM: basophilic spot-liked or granule-liked structure
EM: parallelly-arranged RER and free ribosome
function: synthesis of proteins
structural protein
enzymes related to the production of
neurotransmitters
b. Neurofibril:
LM: in silver
impregnation
methods(silver
preparation),
there are many
thread-liked dark
brown
color
structure to form
a network.
EM:
neurofilament: 10 nm in diameter
microtubule: 25 nm in diameter
function:
supporting
involving in intracellular transportation
c.
other organelle
Golgi apparatus
mitochondria
pigment
② dendrite:
---many, short and more branches
---structure: similar to cell body
---dendritic spine( places for formation of
synapse) and spine apparatus(structure
formed by 2-3 layers SER)
---function: receive the information
③ axon:
---thin, less branch
---structure: no Nissl body, but have microtubule,
neurofilament, microfilament, mitochondria,
SER and vesicle
axon hillock: the beginning part of axon
axolemma
axoplasm
---function: initiate an impulse and conduct the
impulse
* axonal transports:
slow anterograde: cytoskeletal
protein:
microtubule,
microfilament and neurofilament
(0.1-0.4mm/d)
fast
anterograde:
synaptic
vesicles,
enzymes
and
proteins( 100-400mm/d)
fast retrograde: products of
metabolism, intaking materials
including protein or neurotrophic
factors(100-400/d)
3) classification:
---According to number of processes
multipolar neuron
bipolar neuron
pseudounipolar neuron
---According to length of axon
Golgi type I neuron: long axon and large
Golgi type II neuron: short axon
---According to function
sensory neuron
motor neuron
interneuron
---According to the neurotransmitter
neuromodulator release by the neuron
cholinergic neuron
aminergic neuron
peptidergic neuron
aminoacidergic neuron
or
3. synapse
---definition: is the junctions between
neurons or neuron and non-nerve cells
---classification:
chemical
synapse:
taking
neurotransmitter as communicating
medium
electrical synapse: gap junction
---structure of chemical synapse:
LM: in silver preparation, there are many
button-liked structures on the surface of
dendrites and cell body, called synaptic
button
EM:
/presynaptic element: axonal terminal
presynaptic membrane
synapse vesicle:
-round or flattened, 40-60nm
-clear or with electron dense core
-contain neurotransmitters:
acetylcholine, Ach
norepinephrine, NE
dopamine, DA
-neuromodulator: peptides- change the reaction of
neuron
to
neurotransmitter,
modulate
neurotransmitter
substance P
enkephalin
vasoactive intestinal polypeptide, VIP
there are synapsin I
mito, SER, microtubule and microfilament
/synaptic cleft: 15-30nm
/postsynaptic element:
--postsynaptic membrane
--receptors
Classification of chemical synapse:
/According to function:
excitatory synapse
inhibitory synapse
/According to structure:
type I: postsynaptic membrane is
thicker than presynaptic membrane,
with wide synaptic cleft(excitatory
synapse)
type II: there are less electron dense
material
attached
on
synaptic
membrane,
the
thickness
of
postsynaptic membrane is same to
presynaptic
membrane(symmetrical
synapse)
4. Glial cell(neuroglia)
1) Glial cell in CNS
(central nervous system)
a. Astrocyte:
/large stellate
/round or ovoid nucleus, large and pale
(euchromatin)
/gliafilament: intermediate filament
/end feet: to form glia limitans or vascular
feet-constitute blood brain barrier
/classification
fibrous astrocytes:
-white matter, have long, thin and
smooth processes
-more glial filament- glial fibrillary acidic
protein, GFAP
protoplasmic astrocyte:
-gray matter, short, thick processes with
more branch
-less glial filament
/function:
ⅰ.supporting, insulating and repairing
ii. regulate the environment and
movement of neuron
iii. secret neurotrophic factor: nerve
growth factor, NGF, ciliary neurotrophic
factor, CNTP and glial cell line-drived
neurotrophic factor, GDNF
b. Oligodendrocyte:
---structure: smaller, fewer process with a small
round and dark stained N
---function:
i. their processes form myelin-sheath of NF
in CNS
ii. inhibite growth of processes of
neuron( secrete inhibiting factor- NI-35,NI250 myelin-associated glycoprotein)
c. Microglia:
---structure: smallest, elongate shape or
ovoid, with a small dark irregular N
---function:
phagocytosis-mononuclear
phagocyte system
d. Ependymal cell:
---structure:
simple cuboidal or columnar epi
apical: microvilli and cilia
basal: long processes-tanycyte
---function:
produce cerebrospinal fluid
nerve stem cell in or under ependyma
---distribution: ventricle of brain and central
canal of spinal cord
2) glial cell in PNS( peripheral nervous
system)
a.
Schwann cell:
/envelop the axon end to end to form
myelin-sheath in PNS and
/produce NGF, CNTF and BDNF(brain
derived neurotrophic factor)
b.
Satellite cell (capsular cell):
/one layer of flattened or cuboidal cell,
with round, ovoid and dark N
/surrounding the Neuron in ganglion
5. Nerve fiber and Nerve
---definition: a structure formed by axon
and glial cell can conduct the impulse to
certain direction
---classification: according to myelinsheath
myelinated nerve fiber
unmyelinated nerve fiber
1)
MNF
① MNF in PNS
LM:
Axon
myelin-sheath: HE: net-liked; OsO4(osmium
tetroside) fixation and stain: black with
Schmidt-Lantermann incisure
neurilemma: cell membrane of Schwann and
basement membrane
* Ranvier node: narrow part, no myelinsheath-saltatory conduction
* internode: the segment of NF between two
Ranvier nodes
EM: Schwann cell (neurilemmal cell) :
Schwann cell →invagination and envelop
the axon →form mesaxon → mesaxon
become longer and longer →spiral around
the fiber →to force the N and cytoplasm go to
two side, inner and out edges connecting with
incisure
②MNF in CNS
---structure:
similar to in PNS
myelin-sheath formed by flattened
ending of oligodendrocyte’s processes
one oligodendrocyte can envelop many
axons
no incisure and basement membrane
2)
N-MNF
①N-MNF in PNS
---structure:
thin axon and Schwann cell connect end to
end
no myelin-sheath and Ranvier node
one Schwann cell envelops more axons
②N-MNF in CNS
* nothing to envelop the axon-naked axon
3)
Nerve
---Nerve fiber gets together to form nerve
efferent N
afferent N
mixed N
---structure:
epineurium: DCT
perineurium:
-two layers: /outer layer- CT
/inner layer-several layers of
SSE- perineural epithelium(tight junction and
basement membrane)
endoneurium: thin layer of LCT
6. Nerve Ending
1) Sensory nerve ending
---peripheral processes of pseudounipolar
neuron + other structure to form sensory
receptor
①free nerve ending
---structure: NF→lose myelin-sheath → branch
→ distribute in epidermis, cornea, hair follicle
epithelial cell and CT
---function: feel cold, hot, pain and slight touch
② Encapsulated N ending
---have CT capsule
a.
tactile corpuscle
---structure:
oval
CT capsule
flattened cell-transverse arranged
NF→lost myelin-sheath→spiral flattened
cells
---distribution: dermal papillae, especially in tip
of finger or toe, palms, soles and lips
---function: touch receptors
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 T, 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 F
---distribution:
skeletal
muscle
---function: detect muscle
length and change in
muscle length
2)
Motor nerve ending: muscular T
and gland
①Somatic MNE: motor end plate,
neuromuscular junction
---structure: EM
muscle F: rich in cytoplasm, nuclei and mito
presynaptic membrane: - synaptic vesiclesachtylcholine
synaptic cleft:
postsynaptic membrane:
-synaptic gatter
-junctional folds
-type N receptor
* motor unit: axon of one neuron and all
skeletal muscle fiber controlled by it
② Visceral MNE
---lateral horn neuron→axon(preganglionic fiber)
→ganglia neuron or nerve plexus→axon
(postganglionic fiber)
---structure: NF are thin, no MS →form
varicosity( round granules-liked vesicles)
*vesicles: acetylcholine- round, Clear
norepinephrine, NE- granules-liked
glycine- flattened, clear
---distribution: smooth M, Cardiac M and gland