Biology Revision Notes - Synapses

AQA Biology, Energy and Continuity - Synapses

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Biology Revision Notes ­ Synapses:
Synapses are the point where two neurones meet
They also occur between, receptor and sensory neurones and motor
neurones and their effectors
Synapses are close together but do not ­ touch
The gap in between is called ­ SYNAPTIC CLEFT
The membrane of the neurone in which the impulse arrives at the
synapse is called ­ PRE-SYNAPTIC MEMBRANE
Membrane on the other side if the synapse ­ POST ­ SYNAPTIC
MEMBRANE
Where are neurotransmitters produced ­ GOLGI BODY
Sequence of events at a synapse:
o An action potential arrives at the pre-synaptic membrane
o Calcium ions diffuse into pre-synaptic membrane
o Vesicles move towards the pre-synaptic membrane
o Neurotransmitter is released by exocytosis into synaptic cleft
o Neurotransmitter diffuse across synaptic cleft
o Neurotransmitter binds to receptor molecules on the
post-synaptic membrane
o Influx of sodium ions causes depolarisation in post synaptic
membrane
o Neurotransmitter is rapidly hydrolysed after binding to the
post-synaptic membrane
Neurotransmitters:
o Acetylcholine ­ used at all types of synapses, synapses using
acetylcholine are described as CHOLINERGIC
o Noradrenaline ­ used at synapses between SYMPATHETIC
NERVES an their effectors, synapses using NORADRENALINE are
described as being ADRENERGIC
o Acetylcholine is hydrolysed by ­ ACETYLCHOLINESTERASE
o Noradrenaline is hydrolysed by ­ MONOAMINO OXIDASE
SPATIAL SUMMATION:
o Neurotransmitter from MORE THAN ONE synaptic knob
stimulates the post-synaptic membrane at THE SAME TIME a
nerve impulse may be generated even though each synaptic
knob releases SUB-THRESHOLD LEVEL of neurotransmitter
TEMPORAL SUMMATION:
o REPEATED stimulation of a post-synaptic membrane by the
SAME SYNAPTIC KNOB, within a SHORT SPACE OF TIME may
generate a nerve impulse even if each distinct release if
neurotransmitter is of sub-threshold level
NEUROMUSCULAR JUNCTIONS ­ where a MOTOR NEURONE meets
with the surface of a MUSCLE FIBRE.
o Once the threshold potential of the post-synaptic membrane is
reached, muscle contraction is stimulated by the release of

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CALCIUM IONS from the SARCOPLASMIC RETICULUM of the
muscle…read more

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