Synaptic transmission Flashcards
What is saltatory conduction?
In myelinated neurones, depolarisation can only occur at the nodes of Ranvier, so the impulse ‘jumps’ from node to node.
What is a synapse?
The junction between a neurone and the next neurone.
What ensures that impulses cross the synapse in one direction only?
The neurotransmitter is released from the presynaptic knob. Also, receptors for the neurotransmitter are only found on the postsynaptic membrane.
What happens to the neurotransmitter once they have attached to the receptors on the post synaptic membrane?
They are broken down by enzymes and their products are taken back into the neurone.
What stimulates the synaptic vesicles to move towards the presynaptic membrane in a cholinergic synapse?
Calcium ions diffuse into the synaptic knob causing the synaptic vesicles to move towards the presynaptic membrane.
What is the space in between two neurones called?
The synaptic cleft.
After the neurotransmitter acetyl choline is released into the synaptic cleft what happens to produce next action potential?
The ACh molecules diffuse across the synaptic cleft and temporarily bind to ligand-gated sodium ion channels (receptor proteins) in the postsynaptic membrane. This causes a conformational change in the receptor proteins, which then open, allowing sodium ions to diffuse down an electrochemical gradient into the cytoplasm of the postsynaptic neurone. The sodium ions cause depolarisation of the postsynaptic membrane, re-starting the electrical impulse (that can now continue down the axon of the postsynaptic neurone).
What prevents the acetyl choline molecules constantly opening the sodium ion channels?
To prevent the sodium ion channels staying permanently open and to stop permanent depolarisation of the postsynaptic membrane, the ACh molecules are broken down and recycled
The enzyme acetylcholinesterase catalyses the hydrolysis of the ACh molecules into acetate and choline.
How is acetyl choline recycled?
The choline is absorbed back into the presynaptic membrane and reacts with acetyl coenzyme A to form ACh, which is then packaged into presynaptic vesicles ready to be used when another action potential arrives.
What is temporal and spatial summation?
Temporal summation - If multiple impulses arrive within quick succession the effect of the impulses can be added together to generate an action potential
Spatial summation - Multiple impulses arriving simultaneously at different synaptic knobs stimulating the same cell body can also generate an action potential through spatial summation
