Neurons

Question 1

Explain the basic structure of a neuron

Answer 1

Neurons vary in size from less than millimetre to up to a metre long but all share the same basic structure
The cell body (or soma) includes nucleus, which contains the genetic material of the cell. Branch-like structures called dendrites hand out from the cell body. These carry nerve impulses from neighbouring neurons towards the cell body.
The axon carries the impulses away from the cell body down the length of the neuron. The axon is covered in a fatty layer of myelin sheath that protects the axon and speeds up electrical transmission of the impulse.
If the myelin sheath was continuous this would have the reverse effect and slow down the electrical impulse. Thus, the myelin sheath is segmented by gaps called nodes of Ranvier. These speed up the transmission of the impulse by forcing it to ‘jump’ across the gaps along the axon.
Finally, at the end of the axon are terminal buttons (axon terminals) that communicate with the next neuron in the chain across a gap known as the synapse

Question 2

What are the three types of neurons?

Answer 2

There are three types of neurons: sensory, relay and motor.
1.Sensory neurons – these carry messages from the PNS to the CNS. They have long dendrites and short axons.
2.Relay neurons – these connect the sensory neurons to the motor or other relay neurons. They have short dendrites and short axons.
3.Motor neurons – these connect the CNS to effectors such as muscles and glands. They have short dendrites and long axons.

Question 3

Explain functions of the sensory neuron

Answer 3

Sensory neurons are found in receptors such as the eyes, ears, tongue and skin, and carry nerve impulses to the spinal cord and brain. When these nerve impulses reach the brain, they are translated into ‘sensations’, such as vision, hearing, taste and touch. However, not all sensory neurons reach the brain, as some neurons stop at the spinal cord, allowing for quick reflex actions.

Question 4

Explain functions of relay neurons

Answer 4

Relay neurons are found between sensory input and motor output/response. Relay neurons are found in the brain and spinal cord and allow sensory and motor neurons to communicate.

Question 5

Explain functions of motor neurons

Answer 5

Motor neurons are found in the central nervous system (CNS) and control muscle movements. When motor neurons are stimulated they release neurotransmitters that bind to the receptors on muscles to trigger a response, which lead to movement.

Question 6

Similarities and differences between the three neuron structures

Answer 6

As you can see from the diagrams above, all three neurons consist of similar parts. The dendrites receive signals from other neurons or from sensory receptor cells. The dendrites are typically connected to the cell body, which is often referred to as the ‘control centre’ of the neuron, as it’s contains the nucleus. The axon is a long slender fibre that carries nerve impulses, in the form of an electrical signal known as action potential, away from the cell body towards the axon terminals, where the neuron ends. Most axons are surrounded by a myelin sheath (except for relay neurons) which insulates the axon so that the electrical impulses travel faster along the axon. The axonterminal connects the neuron to other neurons (or directly to organs), using a process called synaptic transmission.