Wei yuanyuan Nervous system I

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

The nervous tissue is composed of two main cells Neuron: Glial cell (in CNS): 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

Function and type of the glial cells in PNS Schwann cell Serve as myelin sheaths Satellite 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 Dendrite Presynaptic terminals Nervous system - neuron

Structure of 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 Nervous system - neuron

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 Nervous system - neuron

Conduction velocity Influential factors Diameter Myelinate or not temperature

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 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

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

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 >K out ， 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)

Characters of AP conduction on a nerve fiber The anatomic and physiological integrity Not easy to fatigue Conduct in a non-decremental fashion Nervous system - neuron

Synaptic inhibition

Postsynaptic 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 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 mV Reason: Neuron A release inhibitory transmitter which reduce the Neuron B release excitatory transmitter, so,on Neuron C the EPSP ↓ GABA （ gammalon ）

summary Axoplasmic transportation Synaptic transmission post-synaptic potential IPSP EPSP Central inhibition Post-synaptic inhibition Pre-synaptic inhibition