Synapses Flashcards
What is a synapse?
A physical gap between neurones
Impulses can only cross synapses in one direction. Explain why
Neurotransmitter only released from pre-synaptic knob
Receptors for neurotransmitter only present on post-synaptic membrane
What is a cholinergic synapse?
Synapses that use acetylcholine
What happens to the neurotransmitter once attached to the receptors on the post-synaptic membrane?
Hydrolysed by an acetylcholinesterase
Forms acetyl and choline which diffuse back to pre-synaptic membrane.
What stimulates the synaptic vesicles to move towards the pre-synaptic membrane?
When action potential arrives at pre-synaptic membrane
Calcium ion channel proteins open
Calcium ions (facilitated) diffuse into the synaptic knob
Calcium ions cause vesicles to move towards membrane
What happens when the acetylcholine binds with receptors on the
post-synaptic membrane
Sodium ion channels open
Sodium ions diffuse into the post-synaptic knob
If threshold is reached an action potential is generated
What is temporal summation?
Two or more nerve impulses arrive in quick succession from the same pre-synaptic membrane.
More neurotransmitter released
More sodium ions channels open on post synaptic membrane
Threshold more likely to be achieved.
What is spatial summation?
Many neurones connect to one neurone at a synapse
Each neurone releases small amounts of neurotransmitter
More sodium ions channels open on post synaptic membrane
Threshold more likely to be achieved
Describe how calcium ions are involved in synaptic transmission.
High concentration of calcium ions maintained in the synaptic cleft
Arrival of an action potential opens the calcium ion channels
Calcium ions enter pre-synaptic knob
Influx of calcium ions causes vesicles to move to pre-synaptic membrane and release acetylcholine into the synapse
GABA causes negatively charged chloride ions to enter the post synaptic neurone. How does this inhibit the propagation of an nerve impulse?
Neurone becomes more negatively/charged
More sodium ions need to diffuse into post synaptic knob to reach threshold
Depolarisation less likely to happen
How might drugs decrease synaptic transmission?
Decrease synthesis of neurotransmitter
Inhibit release of neurotransmitter
Decrease permeability of post synaptic membrane to ions
Increased activity of acetylcholinesterase
Block receptor sites on postsynaptic membrane
Hyperpolarise post synaptic membrane
How might drugs increase synaptic transmission?
Increased synthesis of neurotransmitter
Increases release of neurotransmitter f
Inhibit acetylcholinesterase
Mimic shape of neurotransmitter
How does the neurotransmitter cross the synaptic cleft?
Simple diffusion
