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[WG21:p]

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[WG21:p51]

Outside CNS, myelin is produced by Schwann cells

In CNS, myelin is produced by oligodendrogliocytes
--> A single oligodendrogliocyte forms myelin on multiple nearby axons

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[WG21:p55]

RMP in nerves = -70mV

Threshold potential in nerves ~ -55mV

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[WG21:p57]

Saltatory conduction - depolarisation in myelinated axons jumps from one node of Ranvier to the next

Current at the active node serves to electrotonically depolarise the next nodes ahead of the AP

[p59] Voltage-gated Na+ channels are highly concentrated in the nodes of Ranvier
* Cell body ~ 50-75 per square micrometer
* Initial segment ~ 350-500
* Myelin ~ <25
* Nodes of Ranvier ~ 2000-12000
* Axon terminal ~ 20-75

On unmyelinated neurons
* Axons of unmyelinated neurons ~ 110

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[WG21:p59]

In an AP, repolarization occur because

1. Increase in Na+ conduction is short-lived
   --> It very quickly inactivates
2. Opening of voltage-gated K+ channels
   * Slower and more prolonged than Na+ channel
   * Also explains the after-hypoerpolarization

Changes in ECF Na+ influence the size of AP, but not RMP

Changes in ECF [K+] influence the RMP

Decrease in ECF [Ca2+] increase excitabilities of nerve and muscles by decreasing the amount of depolarisation necessary to initiate the changes in the Na+ and K+ conductance that produce the AP

Increase in ECF [Ca2+] stabilize the membrane by reducing excitability

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[WG21:p60]

The greater the diameter of a nerve fibre, the greater its speed.

Large axons = proprioceptive sensation, somatic motor function, conscious touch, pressure

Smaller axons = pain, temperature, autonomic functions

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[WG21:p61]

A alpha - proprioception

A beta - Touch, pressure, motor

A gamma - Motor to muscle spindles

A delta - Pain, cold, touch

B - preganglionic autonomic

C dorsal root - Pain, temperature, some mechanoreception, reflex responses

C sympathetic - postganglionic sympathetics

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[WG21:p63]

Schwann cells = myelin (PNS)

Microglia = scavenger cells resembling tissue macrophages

Oligodendrogliocytes = myelin (in CNS)

Astrocytes
* Fibrous = "connective tissues" in white matter
* Protoplasmic = "connective tissues" in gray matter

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[WG21:p67]

Each thick filament is surrounded by 6 thin filaments

M line is where the myosins attach to

[WG21:p68]

Muscle RMP = -90mV

AP last 2-4 ms

Conduction speed about 5 m/s

ARP = 1-3 ms

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[WG21:p88]

3 kinds of synaptic vesicles

1. Small, clear vesicles that contains acetylcholine, glycine, GABA, or glutamate
2. Small vesicle with a dense core that contains catecholamine
3. Large vesicles with a dense core that contain neuropeptides

NB:

The small vesicles (clear one and the one with dense core) recycle in the nerve ending

Small vesicles are located near the synaptic cleft at areas of membrane thickening (active zones)

Large vesicles are evenly distributed in the terminal

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[WG21:p88]

Ca2+ influx through voltage-gated Ca2+ channel triggers release of vesicle contents

Intracellular Ca2+ is then sequestrated, primarily by a Na-Ca antiport

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[WG21:p88]

Tetanus toxin causes spastic paralysis by blocking presynaptic transmitter release of acetylcholine at the NM junction.

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[WG21:p91]

Synaptic delay = the delay (of at least 0.5ms) between an impulse reaching the presynaptic terminal, and a response is obtained in the postsynaptic neurons
--> Due to time it takes for mediators to be released and to act on the membrane of the postsynaptic cell

Inhibitoary postsynaptic potential can be due to
* Opening of Cl channel
* Opening of K+ channel
* Closing of Na+ or Ca2+ channels

In a neuron, the portion with the lowest threshold potential is the initial segment, the portion of axon next to the axon hillock.

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[WG21:p94]

Presynaptic facilitation and inhibition = at axo-axonal synapses, one neuron influence the production of AP of another neuron

Mechanism of presynaptic inhibition (e.g. by GABA)

1. Increase Cl conductance
   * Via impairing Ca2+ influx
2. Increase K conductance
   * By impairing Ca2+ influx
3. Direct inhibition of transmitter release
   * Independent of Ca2+ influx

Example of presynatic facilitation = serotonin

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[WG21:p94]

Renshaw cell - inhibitory interneurons which synapse with a collateral of a neuron and feedback on that neuron's cell body and other neurons.

[WG21:p95]

Subliminial fringe = when a cell is not discharged by an afferent impulse (not in the discharge zone) but do have their excitability increased

Neuromodulation = a nonsynaptic action of a substance on neurons that alters their sensitivity to synaptic stimulation or inhibition

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[WG21:p115]

The stimulatory effect of coffee and tea are due to blockade of adenosine receptors by caffeine and theophylline

 

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[WG21:p129]

Bell-Magendie Law = in the spinal cord, the dorsal roots are sensory and the ventral roots are motor