lecture 19

Question 1

action potentials can be described as _ _ _, as they?

Answer 1

all or none, they don’t vary in size, they either do or do not occur.

Question 2

what are electrical junctions joined by

Answer 2

gap junctions

Question 3

difference between Nerve-Nerve and Nerve-muscle synapses in respect to size and quantity

Answer 3

the nerve-nerve synapses are very tiny with thousands of them occurring on the postsynaptic dendrite. Nerve-muscle synapses are comparatively huge with each muscle cell being innervated by only one neuron.

Question 4

difference between Nerve-Nerve and Nerve-muscle synapses in respect to neurotransmitter used and the nature of the signal

Answer 4

Nerve-Nerve uses many different Neurotransmitters in either excitiatory or inhibitory events. Nerve-muscle will only use ACh and will only be excititory events in the muscle cell.

Question 5

difference between Nerve-Nerve and Nerve-muscle synapses in respect to threshold

Answer 5

the nerve-muscle interaction will almost always bring muscle fibre to threshold. where as neurons will rarely bring the postsynaptic neuron to threshold, and to do so requires summation, temporally and spatially, of signals

Question 6

how quickly is ACh broken down upon arrival on the chemically gated Na+ channel

Answer 6

within 20 miliseconds

Question 7

depolarisation ends at the dendrite when

Answer 7

Depolarisation ends when ACh is broken down, into choline and acetate.

Question 8

what does the excitatory nature of the postsynaptic event depend on

Answer 8

it depends on the neurotransmitter used at the synapse. ACh and NE for excitatory and GABA for inhibitory.

Question 9

step one of synaptic transmission

Answer 9

the action potential is propagated down the axon triggering the opening of calcium gated ion channels

Question 10

step two of synaptic transmission

Answer 10

the calcium ions enter the axon and bind to the vesicles containing ACh, this triggers the exocytosis of the neurotransmitter into the synaptic cleft

Question 11

step three of synaptic transmission

Answer 11

the ACh diffuses across the synaptic cleft binding to the chemically gated ion channels on the dendrites of the post-synaptic neuron, this causes a graded depolarisation event, as Na+ enters the cell

Question 12

step four of synaptic transmission

Answer 12

the depolarisation event ends as an enzyme AChE breaks down the Ach into acetate and choline

Question 13

step 5 of synaptic transmission

Answer 13

the axon terminal reabsorbs the choline from the synaptic cleft and recycles it to make more ACh