U3 Nervous system: Neurons

Question 1

Define neuron

Answer 1

Nerve cells that are the basic structural and functional units of the nervous system

Question 2

What is the cell body of a neuron?

Answer 2

• A mass of cytoplasm which surrounds a nucleus
• The nucleus contains the DNA of the cell and directs the activities of the rest of the cell
• The axon and dendrites extend from the cell body

Question 3

What are the dendrites of a neuron?

Answer 3

• Extensions of the cytoplasm of the cell body
• They carry nerve impulses into the cell body

Question 4

What is the axon of a neuron?

Answer 4

• Also called nerve fibre
• A single, long extension of the cytoplasm
• It carries impulses away from the cell body to the axon terminals

Question 5

What are the nodes of Ranvier of a neuron?

Answer 5

Gaps in the myelin sheath of the axon

Question 6

What are the axon terminals of a neuron?

Answer 6

The ends of the branches of the axon terminal

Question 7

What is the myelin sheath of a neuron?

Answer 7

• A layer of fatty material that covers the axon

Functions
- Speeds up movement of nerve impulses along the along the axon
- Protects the axon from damage
- Acts as an insulator

Question 8

Distinguish between myelinated fibres and unmyelinated fibres

Answer 8

Myelinated fibres
- Axon with myelin sheath

Unmyelinated fibres:
- Axons with no myelin sheath

Question 9

How is myelin sheath formed outside the brain and spinal cord?

Answer 9

• Myelin sheath is formed by Schwann cells which wrap around the axon
• The outermost coil of the Schwann cels forms a structure called the neurilemma around the myelin sheath
• The neuriemma helps repair damaged fibres

Question 10

What forms the myelin sheath in the brain and spinal cord?

Answer 10

Oligodendrocytes

Question 11

What are the three functional classifications of neurons?

Answer 11

Sensory/afferent neurons:
- Carry impulses from receptors towards the central nervous system

Motor/efferent neurons:
- Carry impulses away from the central nervous system towards an effector

Interneurons or connector/relay neurons:
- Create a link between sensory and motor neurons in the central nervous system

Question 12

What are the three structural classifications of neurons?

Answer 12

Multipolar neurons:
- One long axon
- Many short dendrites connecting with cell body
- EG: motor neurons, interneurons

Bipolar neurons:
- One axon
- One dendrite connecting with cell body
- EG: neurons in eyes, eys and nose

Psudounipolar neurons:
- One axon that divides into two
- No dendrites
- EG: all sensory neurons except those in eyes, ears and nose