14.3 Reflex arc

Question 1

What is the central nervous system CNS

Answer 1

It is made up of brain and spinal cord

Question 2

What is peripheral nervous system PNS

What is it made up of

Answer 2

It is made up of pairs of nerves that originate from either brain or spinal cord

Sensory and motor neurones

Motor neurones divide into voluntary and autonomic nervous system

Question 3

What are sensory neurones

What are motor neurones

Answer 3

Carry nerve impulses from receptors towards central nervous system

Carry nerve impulses away from central nervous system to effectors

Question 4

Motor nervous system can be subdivided into voluntary and autonomic nervous systems

What are these

Answer 4

Voluntary nervous system carries nerve impulses to body muscles and is under conscious control

Autonomic nervous system carries nerve impulses to glands, smooth muscle and cardiac muscle. It is involuntary so

Question 5

What is the spinal cord

Answer 5

Column of nervous tissue that runs along the back and lies inside the vertebral column for protection

Pairs of nerves emerge at intervals along the spinal cord

Question 6

What is the reflex arc

Answer 6

It is involuntary response, eg when touching a hot object your hand will move away rapidly

They involve only 3 neurones: Sensory, intermediate and motor.
The intermediate is in spinal cord

Question 7

Describe process of reflex arc when touching a hot object

Answer 7

• Stimulus is hot object
• Receptors in the skin detect temperature, which generate nerve impulses in sensory neurone
• Sensory neurone passes nerve impulse to spinal cord
• Coordinator is intermediate neurone links sensory neurone to motor neurone in spinal cord
• Motor neurone carries nerve impulses from spinal cord to effector which is muscle in upper arm
• So this muscle is stimulated to contract
• Response is pulling hand away from hot object

Question 8

Why is it an advantage that reflex arcs are involuntary

Answer 8

• They don’t require decision making in the brain so leave it free to carry out more complex responses

So brain isn’t overloaded with situations where the response is the same

Question 9

What are two other advantages of reflexes

Answer 9

• They protect the body from harm
• They are fast because neurone pathway is short with very few synapses where neurones communicate with each other.
  They are also fast because no decision making needs to occur