Neurons (further)

Question 1

What are action potentials?

Answer 1

• When a neuron is sending a ‘message’ it is actually firing an electrical impulse.
• These electrical impulses are called action potentials.
• Action potentials are caused by changes in electrical charge in the neuron.

Question 2

Electrical transmission

Answer 2

• Neurons change from a negative charge to a positive charge (this change in charge is called the action potential).
• When the action potential reaches the end of the neuron (the axon terminal) it cannot go any further so instructs chemical transmission of the message at the synapse (synaptic transmission).

Question 3

Where does synaptic transmission take place?

Answer 3

• Neurons do not physically connect with other neurons.
• There is a microscopic gap between each neuron- called the synaptic cleft.
• Chemical transmission of a message takes place at the synapse.

Question 4

What happens when the action potential reaches the axon terminal?

Answer 4

• When an action potential reaches the axon terminal the vesicles move and then fuse with the presynaptic membrane.
• This causes the neurotransmitters to be released into the synaptic cleft.

Question 5

What happens at the synaptic cleft during synaptic transmission?

Answer 5

• The neurotransmitters diffuse across the synaptic cleft and attach to the receptors on the membrane of the postsynaptic neuron.
• This binding then sets off an action potential (electrical impulse) in this neuron (summation).

Question 6

Neurotransmitters and charge….

Answer 6

• Neurotransmitters can have an excitatory or inhibitory effect on the next neuron.

Question 7

Excitatory neurotransmitters

Answer 7

• Excitatory neurotransmitters like adrenaline increase the neuron’s positive charge and make it more likely to fire ( readies the membrane).

Question 8

Inhibitory neurotransmitters

Answer 8

• Inhibitory neurotransmitters like serotonin increase the neuron’s negative charge and make it less likely to fire (creates resistance/ harder to find the tipping point).

Question 9

So how does summation occur?

Answer 9

• A neuron can receive thousands of excitatory and inhibitory signals at any one time. If there are enough excitatory signals then summation occurs.
• Summation is needed for the action potential to fire (mark scheme answer).
• Summative effect must be excitatory for AP to fire (better answer).

Question 10

Random facts…

Answer 10

• Action potential is an all or nothing effect.
• Threshold must be crossed for the neuron to become positive (e.g. the net effect needs to be excitatory).
• Summative effect determines the likelihood of the AP firing.