15.5+15.6: Synapses Flashcards
Synapse
the point where one neurone communicates with another or an effector
How do synapses transmit information
by means of chemicals called neurotransmitters
Synaptic cleft
small gap (20-30nm wide) that separates neurones
Presynaptic neurone
The neurone that releases neurotransmitter
Synaptic knob
The axon of the presynaptic neurone ends in a swollen portion.
What does the synaptic knob contain
lots of mitochondria and ER which required for manufacturing the neurotransmitter which occurs in the axon
Synaptic vesicles
store the neurotransmitter
What happens once the neurotransmitter is released from the vesicles
it diffuses across to the postsynaptic neurone, which possesses specific receptor proteins on its membrane to receive it
Two features of synapses
unidirectionality
summation
Unidirectionality
Can only pass information in one direction from the presynaptic neurone to the postsynaptic neurone
What feature of synapses means that they act like valves?
unidirectionality
Summation
Rapid build up of neurotransmitter in the synapse
What process allows low frequency action potentials to trigger an action potential in the postsynaptic neurone
summation
Why are low frequency action potentials unable to trigger a new action potential in the postsynaptic neurone
they lead to the release of insufficient concentrations of neurotransmitter to trigger a new action potential
Two types of summation
spatial and temporal
Spatial summation
A number of different presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone, triggering an action potential.
Temporal summation
A single presynaptic neurone releases neurotransmitter many times over a short period, if the concentration of neurotransmitter exceeds the postsynaptic neurone’s threshold value, an action potential will be triggered
Inhibitory synapses
Synapses that make it less likely that a new action potential will be created on the postsynaptic neurone.
Which two ion channels are involved in the process of operation of inhibitory synapses
Cl- and K+
What do synapses act as
junctions
Functions of synapses
2
- a single impulse along one neurone to initiate new impulses in a number of different neurones at a synapse-number of simultaneous responses
- a number of impulses to be combined at a synapse (allows nerve impulses from receptors reacting to diff. stimuli to contribute one response
Where are neurotransmitters made
only in the presynaptic neurone
Where is the neurotransmitter stored
stored in synaptic vesicles
How is neurotransmitter released from the synaptic vesicles
when an action potential reaches the synaptic knob, the synaptic vesicles fuse with the pre-synaptic membrane to release the neurotransmitter
What happens when neurotransmitter is release from the synaptic vesicles and fuses with the pre-synaptic membrane
the neurotransmitter diffuses across the synaptic cleft to bind to specific receptor proteins which are found only on the postsynaptic neurone
What happens when the neurotransmitter binds with receptors on the postsynaptic neurone
it leads to a new action potential in the postsynaptic neurone, synapses that produce action potentials in this way = excitatory synapses
Cholinergic synapse
One in which the neurotransmitter is a chemical called acetylcholine
What is acetylcholine made up of?
acetyl and choline
Where are cholinergic synapses found
common in vertebrates where they occur in the CNS and at neuromuscular junctions
Neuromuscular junctions
junctions between neurones and muscles
