3.4 - B Neurotransmitters at Synapses

Question 1

What happens at the synaptic cleft.

Answer 1

Neurons connect with other neurons or
muscle fibres at a synaptic cleft.

Question 2

Describe the 3 stages of A Impulse at a Synapse.

Answer 2

1. Neurotransmitters are stored in vesicles in the axon endings of the presynaptic neuron.
2. They are released into the cleft on arrival of
   an impulse.
3. They diffuse across the cleft and
   bind to receptors on the membrane of the
   postsynaptic neuron.

Question 3

How are neurotransmitters removed.

Answer 3

enzymes and reuptake

Question 4

Why do neurotransmitters need to be removed

Answer 4

to prevent continuous
stimulation of postsynaptic neurons.

Question 5

What determines if a signal is excitatory or inhibitory?

Answer 5

The receptors

Question 6

What must occur at the postsynaptic membrane for a nerve impulse to be transmitted?

Answer 6

A minimum number of neurotransmitters must attach to receptors in order to reach the threshold on the postsynaptic membrane to transmit the impulse.

Question 7

How do synapses prevent the transmission of weak or insignificant stimuli?

Answer 7

Synapses can filter out weak stimuli arising from insufficient secretion of neurotransmitters.

Question 8

How can a nerve impulse be triggered if individual stimuli are too weak on their own?

Answer 8

Summation of a series of weak stimuli can release enough neurotransmitter to trigger an impulse.

Question 9

What can a converrgent neural pathway do?

Answer 9

can release enough neurotransmitter molecules to reach threshold and trigger an impulse.