synapses and synaptic transmission

Question 1

what is a synapse and its function?

Answer 1

junction between the terminal button of an axon and the membrane of another axon.
Its function is to allow information transmitted from one neuron to the other (in one direction only)

Question 2

Explain the process of synaptic transmission

Answer 2

1. AP arrives at axon terminal
2. this triggers ca2+ to move into cell
3. these calcium ions cause the migration of vesicles (which contain NT) to the pre synaptic membrane
4. Vesicles fuse to presynaptic membrane emptying NT into synaptic cleft
5. NT diffuse across synaptic cleft to post synaptic membrane
6. NT binds to receptor sites on the post synaptic membrane (Lock and key- specific NT to specific receptor)
7. This binding opens NT dependent ion channels
8. This opening of ion channels changes the excitability of the post synaptic cell
9. this response will be excitatory or inhibitory
10. NT is then reuptake and recycled

Question 3

What are the 2 types of postsynaptic receptor

Answer 3

1= ionotropic (direct)- molecule of appropriate NT directly attaches to channel and ion channels open when NT binds.

2= metabotropic )indirect)- Activates enzymes which leads to a series of chemical events causing ion channels to open elsewhere

Question 4

what are 2 types of postsynaptic potential (when membrane potential is altered)

Answer 4

Depolarising (excitatory)- increases likelihood of AP

Hyperpolarizing (inhibitory)- decreases likelihood of AP

Question 5

what is the threshold for depolarisation

Answer 5

-55mV

this means an action potential is triggered and has successfully converted NT (chemical) into an electrical signal

Question 6

what does depolarisation/ hyperpolarisation depend on?

Answer 6

depends on which type of ion channel in the postsynaptic membrane is opened by NTs.

Question 7

what occurs for sodium channels? NA+

Answer 7

sodium channels open- sodium moves into neuron= depolarisation due to an increase in charge/polarisation

so sodium channels produce an excitatory postsynaptic potential

Question 8

what occurs for potassium channels? k+

Answer 8

potassium channels open- potassium leaves neurone due to efflux of K+= hyperpolarisation

so produces an inhibitory postsynaptic potential

Question 9

what occurs for chloride ions?

Answer 9

when they open at REST- NOTHING as forces balanced

when Chloride channels open when membrane has been depolarised- chloride ions enter neurone= stabilisation (reduce likelihood of AP)

Question 10

Explain the removal of NT from synapses (3 ways)

Answer 10

1- REUPTAKE= NT quickly pumped back into nearby glia or the axon terminal that released it. (via active transport)

2- DEACTIVATION- NT destroyed by enzymes near receptors so its not recognised by receptor due it now being inactive

3- REMOVAL- NT diffuses into surrounding area e.g. blood