the junction between a neurone and another neurone or between a neurone and an effector cell
an action potential arrives at the synaptic knob of the presynaptic neurone which stimulates voltage-gated Ca2+ channels to open so Ca2+diffuses in
the influx of Ca2+ into the synaptic knob causes the synaptic vesicles to move to the presynaptic membrane where they fuse to it releasing ACh into the synaptic cleft by exocytosis
ACh diffuses across the synaptic cleft and binds to specific cholinergic receptors on the postsynaptic membrane causing Na+ channels to open.
the influx of Na+ into the postsynaptic neurone causes depolarisation and if a threshold is reached an action potential is generated.
ACh is broken down by acetylcholinesterase (AChE) so the response doesn't keep happening and the products are re-absorbed by the presynaptic neurone and used to make more ACh
synaptic convergence
Many presynaptic neurones connect to one postsynaptic neurone so information is amplified
Synaptic divergence
When one neurone synapses to many neurones so information can be dispersed to different parts of the body
spatial summation
Two or more presynaptic neurones meet and release as their neurotransmitters at the same time onto the same postsynaptic neurone. the threshold can be reached and trigger an action potential from a small amount of neurotransmitter from each neurone.
Spatial summation allows signals from multiple stimuli to be coordinated into one response
Temporal summation
Two or more nerve impulses arrive in quick successions from the same presynaptic neurone. it makes an action potential more likely as their will be a build up of neurotransmitters in the synaptic cleft
Why are nerve impulse transmission unidirectional
Neurotransmitters are only released from the presynaptic neurones and receptors are only on the postsynaptic membranes
