The structure and function of sensory, relay and motor neurons. The process of synaptic transmission, including reference to neurotransmitters, excitation and inhibition.

Question 1

What are neurons?

Answer 1

Neurons are cells that are specialised to carry neural information throughout the body.

Question 2

Which 3 types of neurons do we look at?

Answer 2

Sensory, relay and motor.

Question 3

What do neurons typically consist of?

Answer 3

• a cell body
• dendrites
• an axon

Question 4

Describe how the cell body, dendrites and axon are connected

Answer 4

• Dendrites at one end of the neuron receive signals from other neurons or from sensory receptors. Dendrites are connected to the cell body, the control centre of the neuron.
• From the cell body, the impulse is carried along the axon where it terminates at the axon terminal.

Question 5

What does the myelin sheath do?

Answer 5

This allows nerve impulses to transmit more rapidly along the axon. If the myelin sheath is damaged, impulses slow down.

Question 6

Describe dendrites

Answer 6

Dendrites protrude from the cell body, these carry nerve impulses from neighbouring neurons towards the cell body

Question 7

Describe the cell body

Answer 7

Cell body includes a nucleus, this contains genetic material of the cell.

Question 8

Describe the axon

Answer 8

Axon is covered in myelin sheath that protects the axon and speeds up electrical transmission of the impulse. The axon carries impulses away from the cell body down the length of the neuron

Question 9

Describe myelin sheath

Answer 9

Myelin sheath is segmented by gaps called nodes of ranvier these speed up transmission by forcing it to ‘jump’ across the gaps along the axon.

Question 10

Define motor neurons

Answer 10

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

Question 11

Define sensory neuron

Answer 11

These carry messages from the Peripheral nervous system to the CNS. They have long dendrites and short axons.

Question 12

Define relay neuron

Answer 12

These connect the sensory neurons to the motor or other relay neurons. They have short dendrites and short axons. They are found only in the brain and spinal cord.

Question 13

What are motor neurons?

Answer 13

A motor neuron is a nerve cell (neuron) whose cell body is located in the spinal cord and whose fiber (axon) projects outside the spinal cord to directly or indirectly control effector organs, mainly muscles and glands. Motor neurons’ axons are nerve fibers that carry signals from the spinal cord

Question 14

What are sensory neurons?

Answer 14

Sensory neurons are nerve cells that transmit sensory information (sight, sound, feeling, etc.). They are activated by sensory input, and send projections to other elements of the nervous system, ultimately conveying sensory information to the brain or spinal cord. Not all of these travel to the brain. Some terminate in the spinal cord to allow reflex actions to occur quickly without the delay of sending impulses to the brain.

Question 15

Describe the function of the motor neuron

Answer 15

Form synapses with muscles and control their contractions. When stimulated, the neuron releases neurotransmitters that bind to receptors on the muscles and triggers a response which leads to muscle movement.

Question 16

Describe the function of a relay neuron

Answer 16

Allow sensory and motor neurons to communicate with each other. Relay neurons lie wholly within the brain and spinal cord.

Question 17

Describe the function of a sensory neuron

Answer 17

Sensory neurons carry nerve impulses from sensory receptors (vision, taste, touch) to the spinal cord and brain.

Question 18

Describe the motor neuron’s length of fibres

Answer 18

Short dendrites and long axons

Question 19

Describe the relay neuron’s length of fibres

Answer 19

Short dendrites and long axons

Question 20

Describe the sensory neuron’s length of fibres

Answer 20

Long dendrites and short axons