Synapses Structure and Function

Question 1

Synapses location

Answer 1

-Synapses are found in the junctions between cells in the nervous system
-E.g the gap between the sensory receptor cell and the sensory neurone

Question 2

synapse structure

Answer 2

-The gap between the neurones is known as the synaptic cleft
-The post synaptic neurone has a rounded end called the synaptic knob

Question 3

How are impulses passed across the synaptic cleft

Answer 3

-Once the action potential reaches the end of the axon of the presynaptic neurone, the membrane becomes depolarised
–This means that voltage gated calcium ion channels are open, leading to calcium ions diffusing into the synaptic knob
-The calcium ions push the vesicles containing neurotransmitters towards the presynaptic neurone membrane
-The vesicles then fuse with this membrane, releasing the neurotransmitters into the synaptic cleft via excocytosis
-The neurotransmitters then bind to receptors on the post synaptic membrane
-If enough neurotransmitter molecules are binded to the post synaptic membrane, then an action potential is generated
-This action potential moves down the axon of the post synaptic neurone

Question 4

Whether an action potential is generated at the postsynaptic membrane depends on…

Answer 4

-If the threshold potential is reached
-This in turn also depends on the number of action potentials arriving at the pre synaptic knob

Question 5

How does having a large number of action potentials arriving at the pre synaptic knob matter

Answer 5

-Many action potentials will cause the release of more neurotransmitters into the synaptic cleft
-A larger number of neurotransmitters binding to the postsynaptic membrane will cause more voltage-gated sodium ion channels to open
-The large influx of sodium ions due to the opening of more sodium ion channels increases the likelihood of reaching the threshold potential

Question 6

What happens to the neurotransmitters after the action potential has been generated

Answer 6

After an action potential has been generated, neurotransmitters are broken down to prevent further stimulation of the postsynaptic neurone

Question 7

Additional features of synapses

Answer 7

-Synapses ensure the one way transmission of nerve impulses
-This is because at the synapse the neurotransmitter is released on one side and their receptors are on the other side
-This means the nerve impulse cannot travel in the opposite direction
-DIVERGENCE OF IMPULSES
-One neurone can connect to many other neurones at the synapse
-This means that one neurone can send signals in many different directions
SUMMATION
-When the threshold potential is not reached due to only a small amount of neurotransmitters being released into synaptic cleft- small number of sodium ion channels opened- too small a number of sodium ions released
-this can be overcome by summation
-Summation is when several pre synaptic neurones converge to meet one post synaptic neurone
-This results in many action potentials arriving at the post synaptic knob in succession