summation
occurs when effects of several excitatory post-synaptic potentials added together
excitatory post-synaptic potential (EPSP)
-1 action potential passes down axon to synapses & causes few vesicles to move to/fuse with pre-synaptic membrane
- relatively small number of acetylcholine molecules diffuse across cleft
- causes small depolarisation
- not enough to cause action potential in post-synaptic neurone
combined effect of several EPSPs
= summation
- several EPSPs to reach threshold & cause action potential
- increase membrane depolarisation until reaches threshold
temporal summation
summation results from several action potentials in same pre-synaptic neurone
spatial summation
summation occurs as result of several action potentials arriving from several different pre-synaptic neurones
inhibitory post-synaptic potentials (IPSPs)
- produced by some pre-synaptic neurones
- reduce effect of summation & prevent action potential in post-synaptic neurone
how do synapses control communication passed along nervous system:
1) several pre-synaptic neurones may converge into 1 post-synaptic neurone
- allow action potentials from different parts of nervous system to contribute to generating action potential in 1 post-synaptic neurone
- creates particular response
= spatial summation - useful where several stimuli warning of danger
how do synapses control communication passed along nervous system:
2) combo of several EPSPs prevented
by producing action potential of 1 IPSP
how do synapses control communication passed along nervous system:
3) one pre-synaptic neurone may diverge to several post-synaptic neurones
- allow 1 action potential to be transmitted to several parts of nervous system
- useful in reflex arc
- eg. 1 post-synaptic neurone elicits response while another informs the brain
how do synapses control communication passed along nervous system:
4) synapses ensure action potentials transmitted in correct direction
- only pre-synaptic bulb contains acetylcholine
- if action potential occurs halfway along neurone & ends at post synaptic membrane = not cause response in next cell
how do synapses control communication passed along nervous system:
5) synapses can filter out unwanted low-level signals
- if low-level stimulus creates action potential in pre-synaptic neurone, it is unlikely to pass across synapse
- this is because several vesicles of acetylcholine must be released to create action potential in post-synaptic membrane
how do synapses control communication passed along nervous system:
6) low-level action potentials can be amplified by summation
- if low-level stimulus is persistent, it will generate several successive action potentials in pre-synaptic neurone
- release of many vesicles of acetylcholine over short period of time will enable post synaptic EPSPs to combine to produce action potential
how do synapses control communication passed along nervous system:
7) after repeated stimulation, a synapse may run out of vesicles containing neurotransmitter
- synapse = fatigued
- nervous system no longer responds to stimulus = habituated
- eg. used to smell, background noise
- help avoid overstimulation of effector, which could cause damage
how do synapses control communication passed along nervous system:
8) creation & strengthening of specific pathways in nervous system = basis of conscious thought & memory
- synaptic membranes are adaptable
- in particular, post-synaptic membrane made more sensitive to acetylcholine by addition of more receptors
- this means particular post-synaptic neurone is more likely to fire action potential, creating specific pathway in response to stimulus
