Wei yuanyuan Nervous system I. Nervous system Organization : over 100 billion neuron Central nervous...

Wei yuanyuan

Nervous system I

Nervous systemOrganization : over 100 billion neuron

Central nervous systemBrain + 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

The nervous tissue is composed of two main cellsNeuron: 1011

Glial cell (in CNS): 1012

AstrocytesOligodendrocytes Microglia Ependymal cells

Nervous system- glial cells

Nervous system- glial cells

Function of the glial cells in CNS

AstrocytesPhysically support neuronsScaffold during fetal brain developmentconstitute BBBHelp 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 CNSOligodendrocytes :

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

Function and type of the glial cells in PNSSchwann cell

Serve as myelin sheathsSatellite cell

Serve as phagocyte

Nervous system- glial cells

Basic function unit

Definition : individual nerve cell carrying the impulse throughout the body

Nervous system- neuron

Soma Axon DendritePresynaptic terminals

Nervous system- neuron

Structure of neuron

Function of neuronProcessing of information

Soma : integrate the messageAxon : carry the impulse away from the cell

body, transportation of nutrient to the effectorAxon hillock: the place of AP occur

Dendrite : receive the neuron impulsePresynaptic terminals : associate with

another neurons

Nervous system- neuron

Classification of neuronSensory neuron : from receptorInterneuron: CNS Motor neuron: to effectors

Nervous system- neuron

Neuron

Nerve fiber (axon and dendrites) Function

Conducting APNerve impulse

Nervous system- neuron

Characters of AP conduction on a nerve fiber

The anatomic and physiological integrityNot easy to fatigueConduct in a non-decremental fashion

Nervous system- neuron

Conduction velocityInfluential factors

DiameterMyelinate or not temperature

Classification of nerve fibers

Classification of nerve fibers

Classification of Sensory fiber

The former classification method used for efferent fiber

The latter classification method used for afferent fiber

Classification of nerve fibers

Axoplasmic transportationAnterograde axoplasmic transportationRetrograde axoplasmic transportation

Organelle:Mitochondrial synaptic vesiclesecretory granules

Axoplasmic transportationAnterograde axoplasmic transportationRetrograde axoplasmic transportation

growth factors certain harmful substances: tetanus toxinHerpesrabies virus

synapse

Greek "syn-" ("together")

"haptein" ("to clasp").

Transmission of the information between the neuron

Chemical transmissionClassic synapseNon- synapse chemical transmission

Electrical transmissionGap 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 cleftTransmitter diffusion

Post- synaptic membraneK+ , Na+ Channel , receptor

Pre-synaptic membrane

Pre-synaptic membrane

Synaptic cleft

Non- synapse chemical transmission

One neuron innervate many effector cells by means of varicosity

Heart the terminal of

sympathetic nerve

Electrical transmissionGap 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 transmissionThe process of synaptic transmission

1. Action potential propagation in presynaptic neuron

2. Ca 2+ entry into synaptic knob3. Release of neurotransmitter by exocytosis4. Binding of neurotransmitter to postsynaptic

receptor5. Opening of specific ion channels in post -

synaptic membrane

Neurotransmitter

Definition: a chemical substance secreted by presynaptic neuronExcitatory transmitter : Inhibitory transmitter:

Binding with receptor proteinAgonists and antagonists

Postsynaptic potential (graded potential)Type :

Excitatory postsynaptic potential (EPSP)Inhibitory postsynaptic potential (IPSP)

EPSP

Postsynaptic membraneMainly permeability to sodiumEPSP: depolarization

Characters (EPSP) :No threshold: local potential or gradient potentialDecreases resting membrane potential.

Closer to threshold.Graded in magnitude.No refractory period.Summation ( temporal summation and spatial summation

)

Na in>Kout ， why ？

IPSPPostsynaptic membrane

Cl- influx and K+ efflux IPSP : hyperpolarization

CharactersNo threshold.Hyperpolarize postsynaptic membrane.Increase membrane potential( far from TP)No refractory periodSummation

Summation of EPSP or IPSP

Integrative function of neuron

(0.5-1 mSec)

Characters of AP conduction on a nerve fiber

The anatomic and physiological integrityNot easy to fatigueConduct in a non-decremental fashion

Nervous system- neuron

Synaptic inhibition

Postsynaptic inhibition

Afferent collateral inhibiton（ reciprocal inhibition）

Afferent collateral inhibiton（ reciprocal inhibition）Significance ： coordination activity of

different nerve centre.

Recurrent inhibitionNeurons may also inhibit themselves in a negative

feedback fashion.

Interneuron ： Renshaw cellsNeurotransmitter :. glycine

Recurrent inhibition

significance:terminate activity of motor neuron in time.

Presynaptic inhibition

A

B

C

Neuron A : inhibitory neuron

Neuron B: excitatory neuron

Neuron C : postsynaptic neuron

(+) Neuron B only → Neuron C depolarization 10 mV

(+) Neuron A firstly then

(+) Neuron B → Neuron C depolarization 5 mVReason: Neuron A release inhibitory transmitter which reduce the Neuron B release excitatory transmitter, so ,on Neuron C the EPSP↓

GABA （ gammalon ）

summaryAxoplasmic transportationSynaptic transmissionpost-synaptic potential

IPSPEPSP

Central inhibitionPost-synaptic inhibitionPre-synaptic inhibition