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Nervous system I
Wei yuanyuan
Nervous system
 Organization : over
100 billion neuron
 Central nervous system
 Brain + spinal cord
 Peripheral nervous system：
somatic nervous system+vegetal nervous system
 The rest of the nervous system(12 cranial nerve and 31
spinal nerve)
 Carry information between the CNS and other parts
of the body
Nervous system
31
Enteric nerve
Nervous system- glial cells
 The nervous tissue is
composed of two main cells
 Neuron: 1011
 Glial cell (in CNS): 1012
 Astrocytes
 Oligodendrocytes
 Microglia
 Ependymal cells
Nervous system- glial cells
 Function of the glial cells in CNS
 Astrocytes
 Physically support neurons
 Scaffold during fetal brain development
 constitute BBB
 Help maintaining the proper brain ion concentration and normal
neural excitability by taking up excess K+ from ECF ( epileptic
seizures)
Starlike shape of astrocytes
Nervous system- glial cells
 Function of the glial cells in CNS
 Oligodendrocytes :
 form myelin sheaths
 Microglia :
 serve as phagocyte
 Ependymal cells :
 the thin epithelial membrane lining the ventricular system of
the brain and the spinal cord. It is involved in the production
of cerebrospinal fluid (CSF).
 Glial cell (in CNS): Astrocytes ;Oligodendrocytes;
Microglia Ependymal cell
Nervous system- glial cells
 Function and type of the glial cells in PNS
 Schwann cell
 Serve as myelin sheaths
 Satellite cell
 Serve as phagocyte
Nervous system- neuron
 Basic function unit
 Definition : individual nerve cell carrying the impulse
throughout the body
Nervous system- neuron
 Soma
 Axon
 Dendrite
 Presynaptic terminals
Structure of neuron
Nervous system- neuron
Function of neuron
 Processing of information
 Soma : integrate the message
 Axon : carry the impulse away from the cell body,
transportation of nutrient to the effector
 Axon hillock: the place of AP occur
 Dendrite : receive the neuron impulse
 Presynaptic terminals : associate with another
neurons
Nervous system- neuron
Classification of neuron
 Sensory neuron : from receptor
 Interneuron: CNS
 Motor neuron: to effectors
Neuron
Nervous system- neuron
Nerve fiber (axon and dendrites)
 Function
 Conducting AP
 Nerve impulse
Nervous system- neuron
Characters of AP conduction on a nerve fiber
 The anatomic and physiological integrity
 Not easy to fatigue
 Conduct in a non-decremental fashion
Conduction velocity
 Influential factors
 Diameter
 Myelinate or not
 temperature
Classification of nerve fibers
Classification of nerve fibers
Classification of Sensory fiber
Classification of nerve fibers
 The former classification method used for
efferent fiber
 The latter classification method used for
afferent fiber
Axoplasmic transportation
 Anterograde axoplasmic transportation
 Retrograde axoplasmic transportation
Organelle:
Mitochondrial
synaptic vesicle
secretory granules
Axoplasmic transportation
 Anterograde axoplasmic transportation
 Retrograde axoplasmic transportation
growth factors
certain harmful substances:
tetanus toxin
Herpes
rabies virus
synapse
Greek "syn-" ("together")
"haptein" ("to clasp").
Transmission of the information
between the neuron
 Chemical transmission
 Classic synapse
 Non- synapse chemical transmission
 Electrical transmission
 Gap junction (Astrocytes)
Chemical Synapse
 Definition of synapse:
 the special site between the two neuron where
the information transmit
 Structure
 pre-synaptic membrane:
 Calcium channel , synaptic vesicle (neurotransmitter
storage)
 Synaptic cleft
 Transmitter diffusion
 Post- synaptic membrane
 K+ , Na+ Channel , receptor
Pre-synaptic
membrane
Synaptic
cleft
Pre-synaptic
membrane
Non- synapse chemical transmission
One neuron innervate
many effector cells
by means of varicosity
 Heart
 the terminal of
sympathetic nerve
Electrical transmission
 Gap junction (channel): electric current
movement (quickly and not easy to fatigue)
Electrical synapse
Chemical synapse
Which one is best for transmission ?
one-way conduction
Synaptic transmission
Synaptic transmission
 The process of synaptic transmission
1. Action potential propagation in presynaptic
neuron
2. Ca 2+ entry into synaptic knob
3. Release of neurotransmitter by exocytosis
4. Binding of neurotransmitter to postsynaptic
receptor
5. Opening of specific ion channels in post synaptic membrane
Neurotransmitter
 Definition: a chemical substance secreted by
presynaptic neuron
 Excitatory transmitter :
 Inhibitory transmitter:
 Binding with receptor protein
 Agonists and antagonists
Postsynaptic potential
(graded potential)
 Type :
 Excitatory postsynaptic potential (EPSP)
 Inhibitory postsynaptic potential (IPSP)
EPSP
 Postsynaptic membrane
 Mainly permeability to sodium
 EPSP: depolarization
 Characters (EPSP) :
 No threshold: local potential or gradient potential
 Decreases resting membrane potential.
 Closer to threshold.
 Graded in magnitude.
 No refractory period.
 Summation ( temporal summation and spatial summation )
Na in>Kout ，why？
IPSP
 Postsynaptic membrane
 Cl- influx and K+ efflux
 IPSP : hyperpolarization
 Characters





No threshold.
Hyperpolarize postsynaptic membrane.
Increase membrane potential( far from TP)
No refractory period
Summation
Summation of EPSP or IPSP
Integrative
function of
neuron
(0.5-1 mSec)
Nervous system- neuron
Characters of AP conduction on a nerve fiber
 The anatomic and physiological integrity
 Not easy to fatigue
 Conduct in a non-decremental fashion
Synaptic inhibition
Postsynaptic inhibition
Afferent collateral inhibiton
（reciprocal inhibition）
Afferent collateral inhibiton
（reciprocal inhibition）
 Significance：coordination activity of
different nerve centre.
Recurrent inhibition
 Neurons may also inhibit themselves in a negative
feedback fashion.
 Interneuron：
Renshaw cells
 Neurotransmitter :.
glycine
Recurrent inhibition
 significance:terminate activity of motor neuron
in time.
Presynaptic inhibition
Neuron A : inhibitory neuron
Neuron B: excitatory neuron
Neuron C : postsynaptic neuron
A
(+) Neuron B only → Neuron C
depolarization 10 mV
B
(+) Neuron A firstly then
(+) Neuron B → Neuron C depolarization
5 mV
Reason: Neuron A release inhibitory
transmitter which reduce the Neuron B
release excitatory transmitter, so ,on
Neuron C the EPSP↓
GABA（gammalon）
C
summary
 Axoplasmic transportation
 Synaptic transmission
 post-synaptic potential
 IPSP
 EPSP
 Central inhibition
 Post-synaptic inhibition
 Pre-synaptic inhibition