neurons

Question 1

How many neurons are in the human nervous system?

Answer 1

100 billion

Question 2

what percentage of 100 billion neurons are located in the brain?

Answer 2

80%

Question 3

how do neurons transmit signals?

Answer 3

electrically and chemically

Question 4

what do neurons provide the nervous system with?

Answer 4

with its primary means of communication.

Question 5

explain the three different types of neurons

Answer 5

• sensory
• relay
• motor

Question 6

explain the structure of a neuron

Answer 6

• they vary in size from less than a mm long to up to a metre long.
• they all share the same basic structure
• cell body (soma) includes a nucleus with the genetic material of the cell. Branchlike structures called dendrites protrude from the cell body which carry the 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. Its 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 which speed up the transmission of the impulse by forcing it to jump across the gaps along the axon.
• At the end of the axon are terminal buttons that communicate with the next neuron in the chain across a gap known as the synapse.

Question 7

explain the location of neurons

Answer 7

• The cell bodies of motor neurons may be in the central nervous system but they have long axons which form part of the peripheral nervous system.
• sensory neurons are located outside the CNS, in the PNS in clusters known as ganglia
• relay neurons make up 97% of all neurons and most are found within the brain and the visual system.

Question 8

explain the electrical transmission and firing of a neuron

Answer 8

• 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 by a stimulus, the inside of the cell becomes positively charged for a split second causing a action potential to occur.
• This creates an electrical impulse that travels down the axon towards the end of the neuron.

Question 9

what is a neuron

Answer 9

the basic building blocks of the nervous system, neurons are nerve cells that process and transmit messages through electrical and chemical signals

Question 10

what are sensory neurons

Answer 10

• these carry messages from the PNS to the CNS
• they have long dendrites and short axons

Question 11

explain what relay neurons are

Answer 11

• these connect the sensory neurons to the motor or other relay neurons
• they have short dendrites and long axons

Question 12

explain what motor neurons are

Answer 12

• these neurons connect the CNS to effectors such as muscles and glands
• they have short dendrites and long axons