Glial cells

Packed between neurones to form neuroglia tissue:

a) provides mechanical support and electrical insulation

b) Schwann cells are specialised glial cells, forming myelin sheaths

c) control nutrient and ionic balance. Break down neurotransmitters

Nissl tissues

Contained in neurones:

a) generate enzymes involved in impulse transmission and synthesis of trophic factors

b) regulate growth and differentiation of nervous tissue

When impulse is not transmitted: - charge (resting potential) across axon membrane = -70mV

When impulse is transmitted: - action potential is a brief reversal of resting potential

All-or-None rule: - stimulus needs the minimum intensity to initiate an action potential. Below this, there is no impulse

Impulse takes place over: - temporal or spatial summation

Synapses

- are gaps between neurones to control impulses chemically

- release neurotransmitters that diffuse across synaptic cleft and trigger action potential in membrane

- once it reaches post-synaptic neurone, enzymes break it down and it diffuses back across synapse

Neurotransmitters used in the human body are:

- acetylcholine (motor neurones)

- noradrenaline (sympathetic synapses)

- serotonin, dopamine (in brain)

Synapses: - are effected by drugs: Hallucinogens (LSD) mimic actions of other neurotransmitters Nicotine is addictive

Curare and atropine block acetylcholine

Muscarine mimics acetylcholine