Mod 3-Obj11: Synapse

Question 1

Synapses

Answer 1

A synapse is a junction that mediates information transfer from one neuron to:

1. ) Another neuron
2. ) A muscle = neuromuscular junction
3. ) A gland = neuroglandular junction

Question 2

The neuron transmitting the signal

Answer 2

Presynaptic neuron

Question 3

The cell receiving the signal

Answer 3

Postsynaptic neuron

Question 4

Chemical synapses

Answer 4

Most abundant type of synapse

• Presynaptic and postsynaptic membranes are separated by a synaptic cleft
• Signal transmission involves chemical neurotransmitters

Question 5

Binding of neurotransmitter opens chemically-gated ion channels…

Answer 5

Graded potential produced

Question 6

If graded potential depolarises the postsynaptic cell to threshold…

Answer 6

New action potential generated & signal transmitted

Question 7

Signal transmission across a chemical synapse: Step 1

Answer 7

Action potential arrives at the presynaptic axon terminal

and depolarises the membrane

Question 8

Signal transmission across a chemical synapse: Step 2

Answer 8

Voltage-gated Ca2+ channels open & Ca2+ enters the axon

terminal

Question 9

Signal transmission across a chemical synapse: Step 3

Answer 9

Ca2+ surge triggers synaptic vesicles to release their stored
neurotransmitter (e.g. ACh) into the synaptic clef

Question 10

Signal transmission across a chemical synapse: Step 4

Answer 10

Neurotransmitter diffuses across synaptic cleft and binds to
receptors (chemically-gated ion channels) on the
postsynaptic membrane

Question 11

Signal transmission across a chemical synapse: Step 5

Answer 11

Chemically-gated ion channels open and a graded

potential is produced

Question 12

Signal transmission across a chemical synapse: Step 6

Answer 12

to threshold, voltage-gated Na+ channels open, a new action potential is generated and the signal is transmitted

Question 13

Termination of signal transmitter…

Answer 13

Within a few milliseconds the neurotransmitter

• Is degraded by enzymes
• Re-enters axon terminal
• Diffuses away from synaptic cleft

Question 14

In response to a stimulus a graded potential is generated…

Answer 14

When a stimulus triggers the opening of chemically or mechanically gated channels, present along the plasma membrane of the dendrites

Question 15

In response to a stimulus an action potential is generated…

Answer 15

If the graded potential depolarises the initial segment to threshold -55mV
-An action potential is generated down the length of the axon to the axon terminals

Question 16

In response to a stimulus an action potential is transmitted…

Answer 16

From the axon terminals across a synapse via a chemical neurotransmitter to another neuron or effector muscle or gland