Biopsychology - Neurons

Question 1

What is the function of neurons?

Answer 1

There are 100 billion nerve cells (neurons) in the human nervous system, 80% of which are located in the brain.

By transmitting signals electrically and chemically, these provide the nervous system with its primary means of communication.

Question 2

What are the different types of neurons?

Answer 2

• motor neurons
• sensory neurons
• relay neurons

Question 3

What are motor neurons?

Answer 3

Motor neurons connect the CNS to effectors such as muscles and glands. They have short dendrites and long axons.

Question 4

What are sensory neurons?

Answer 4

Sensory neurons carry messages from the PNS to the CNS. They have long dendrites and short axons.

Question 5

What are relay neurons?

Answer 5

Relay neurons connect sensory neurons to motor or other relay neurons. They have short dendrites and short axons.

Question 6

What are the different structures of a neuron?

Answer 6

• cell body (or soma)
• dendrites
• axon
• terminal buttons/axon terminal

Question 7

What is a cell body (or soma)?

Answer 7

Includes a nucleus which contains the genetic material of the cell.

Question 8

What are the dendrites?

Answer 8

Branch-like structures that protrude from the cell body. These carry nerve impulses from neighbouring neurons towards the cell body.

Question 9

What is the axon?

Answer 9

Carries the electrical impulse away from the cell body down the length of the neuron.

• It is covered in a fatty layer of myelin sheath that protects the axon.
• Gaps in the axon called ‘nodes of Ranvier’ speed up the transmission of the impulse.

Question 10

What is the terminal button?

Answer 10

Terminal buttons at the end of the axon communicate with the next neuron in the chain across a gap called the synapse.

Question 11

What is electric transmission?

Answer 11

When a neuron is in a resting state, the inside of the cell is negatively charged compared to the outside.

When a neuron is activated, the inside of the cell becomes positively charged for a split second, causing an action potential to occur.

This creates an electrical impulse that travels down the axon towards the end of the neuron.

Question 12

What is a synapse?

Answer 12

Each neuron is separated from the next by a tiny gap called the synapse.

Question 13

What is chemical transmission?

Answer 13

Signals within neurons are transmitted electrically; however, signals between neurons are transmitted chemically across the synapse.

When the electrical impulse reaches the end of the neuron (the presynaptic terminal) it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles.

Once the neurotransmitter crosses the gap, it is taken up by the postsynaptic receptor site on the next neuron.

The chemical message is converted back into an electrical impulse and the process of electric transmission begins.

Question 14

What are neurotransmitters?

Answer 14

Neurotransmitters are chemicals that diffuse across the synapse to the next neuron in the chain.

Several dozen neurotransmitters have been identified. Each has its own specific molecular structure that fits perfectly into a post-synaptic receptor site, like a lock and key.

Question 15

What is the function of acetylcholine?

Answer 15

Acetylcholine found where a motor neuron meets a muscle, causing muscles to contract.

Question 16

What is the function of serotonin?

Answer 16

Serotonin affects mood and social behaviour (among other things) which is why it has been implicated as a cause of depression.

Question 17

Is adrenaline excitatory or inhibitory?

Answer 17

Generally excitatory, increasing the positive charge of the postsynaptic neuron, making it more likely the neuron will fire.

Question 18

Is serotonin excitatory or inhibitory?

Answer 18

Generally inhibitory, increasing the negative charge of the postsynaptic neuron, making it less likely the neuron will fire.

Question 19

Is dopamine excitatory or inhibitory?

Answer 19

Dopamine is an unusual neurotransmitter as it is equally likely to have excitatory or inhibitory effects on the next neuron in the chain.

Question 20

What is summation?

Answer 20

Excitatory and inhibitory influences are summed and must reach a certain threshold in order for the action potential of the postsynaptic neuron to be triggered.

If the net effect of the neurotransmitters is inhibitory then the postsynaptic neuron is less likely to fire. It is more likely to fire if the net effect is excitatory.