Biopsychology: The Structure and Function of Neurons

Question 1

What are the 3 types of neurone?

Answer 1

• sensory
• relay
• motor

Question 2

Describe the role of a sensory neurone

Answer 2

Carry messages from the PNS to the CNS.

Hence, they only transmit messages and are known as unipolar.
They tell the brain about the external & internal environment by processing information from one of the five sets of sensory receptors (e.g., eyes and ears) which are quickly converted into neural impulses.
In the brain, these impulses are translated into sensations so we can react appropriately.
They have long dendrites and short axons.

Question 3

Describe the role of a relay neurone

Answer 3

These are the most common type of neuron in the CNS.
They allow sensory and motor neurons to communicate and connect with each other - i.e., they carry nerve impulses between neurons.
They are multipolar as they send and receive information from many sources.
As they only carry messages from one part of the CNS to the other, they are not found in other part of the nervous system (just the brain, spinal cord and visual system).
They have short and stubby dendrites and axons.

Question 4

Describe the role of a motor neurone

Answer 4

These connect the CNS to effectors such as muscles and glands.
They are multipolar as they send and receive information from many sources.
They project their axons outside the CNS to directly or indirectly control muscles and glands.
They form synapses with muscles and when stimulated release neurotransmitters to trigger a response in the muscle. This makes the muscle contract. The strength of this contraction depends on the rate of nerve impulses. Inhibition of these neurons causes muscle relaxation.
They have short dendrites and long axons.

Question 5

Describe synaptic transmission step by step

Answer 5

1. When the dendrite picks up the message (the NT) it sends an impulse (action potential) through the cell body and along the axon to the terminal buttons.
2. Once an action potential has arrived at the terminal buttons at the end of the axon, it needs to be transferred to another neuron. To achieve this it must cross the synaptic gap (between the pre and post-synaptic neuron).
3. At the end of the terminal buttons there are synaptic vesicles that contain and store NTs. These NT are chemical messengers that convert the (electrical) impulse to a chemical message that’s transferred to the next neuron.
4. As the impulse (action potential) travelling to the end of the neuron reaches the synaptic vesicle, they release the NT that then crosses the synaptic gap.
5. As the NT diffuses across the synaptic gap it binds to specialised receptors on the surface of the next cell (on its dendrites) that recognise it and match that particular cell - i.e., dopamine receptors recognise dopamine.
6. Once the next cell is activated the receptor molecules produce either an excitatory effect (that strengthens further impulses) or inhibitory effect (that weakens further impulses) at a post synaptic level.
7. Synaptic transmission is completed (in a fraction of a second) by a process called re-uptake. This is where the NT is taken back up / recycled by the pre-synaptic neuron.

Question 6

Neurotransmitters are defined as…

Answer 6

Chemicals that are released from the end of brain cells (neurons) that allow them to communicate with each other and relay messages to different areas / structures of the brain.

As one neuron releases a NT, receptors on other neurons pick up this message and ‘relay’ this to the next neuron.

Although each neuron creates a nerve impulse (action) and a chemical reaction at the terminal buttons, they can differ in whether they actually encourage further activation or discourage further activation in neighbouring neurons.

Question 7

Describe excitatory NT action

Answer 7

If neurotransmitters create excitation of the post-synaptic neuron they create a positive charge and make the neuron more likely to fire. This rise in action potential will increase activity.

Question 8

Describe inhibitory NT action

Answer 8

If neurotransmitters create inhibition of the post-synaptic neuron, they create a negative charge make the neuron less likely to fire. This fall in action potential will decrease activity.

Question 9

Describe summation

Answer 9

SUMMATION: The excitatory and inhibitory influences are summed (added together). If the net effect on the post-synaptic neuron is inhibitory, the neuron will be less likely to ‘fire’ and if the net effect is excitatory, the neuron will be more likely.