Nervous Communication

Question 1

Define stimulus.

Answer 1

A change in the internal or external environment.

Question 2

Why might an organism need to respond to changes in the external environment.

Answer 2

To avoid harmful environments e.g. too hot or too cold.

To inc. chances of survival.

Question 3

Why might an organism need to regulate their internal environment.

Answer 3

To make sure conditions are always optimal for their metabolism.

Question 4

Role of receptors?

E.g.s of receptors

Answer 4

To detect stimuli

E.g. cells or proteins on the cell surface membranes.

Question 5

Role of effectors?

E.g.s of effectors.

Answer 5

To bring about a response to a stimulus.

E.g. muscle cells, cells found in glands.

Question 6

How are receptors and effectors linked?

Answer 6

Receptors communicate with effectors via

• the nervous system
  OR
• the hormonal system

Or both

Question 7

How does the nervous system transmit (send) information around the body?

Answer 7

As electrical impulses

Question 8

3 main neurones and their roles?

Answer 8

• Sensory neurones - transmit electrical impulses from receptors to the
  central nervous system (CNS)
• the brain and spinal cord.
• Motor neurones - transmit electrical impulses from the CNS to effectors.
• Relay neurones - transmit electrical impulses between sensory neurones and motor neurones.

Question 9

Describe a neural pathway.

Answer 9

1. A stimulus is detected by receptor cells and an electrical impulse is sent along a sensory neurone.
2. When an electrical impulse reaches the end of a neurone, chemicals called neurotransmitters take the information across to the next neurone, which then sends an electrical impulse.
3. The CNS (the coordinator) processes the information and sends impulses along motor neurones to an effector.

Question 10

Describe a nervous response to a visual stimulus.

Answer 10

Stimulus E.g. you see a friend waving

Receptors: Light receptors (photoreceptors) in your eyes detect the wave.

CNS: processes info.

Effectors: Muscle cells are stimulated by the motor neurones.

Response: Muscles contract to make your arm wave.

Question 11

What is the nervous system divided into?

Answer 11

Question 12

What is a nervous response?

Answer 12

The pathway of neurones linking receptors to effectors.

Question 13

What is reflex arc?

Answer 13

The pathway of neurones linking receptors to effectors.

Question 14

Why are reflexes advantageous?

Answer 14

You don’t have to spend time deciding how to respond, information travels really fast from receptors to effectors.

Protect because they’re rapid.

Question 15

Describe the reflex arc involved in hand withdrawal in response to heat.

Answer 15

Question 16

How does a reflex differ from a nervous response.

Answer 16

It doesn’t involve the CNS.

Question 17

What do you need to remember about the relay neurone in a reflex arc.

Answer 17

If there’s a relay neurone involved in the simple reflex arc then it’s possible to override the reflex.

e.g. in the example above your brain could tell your hand to withstand the heat.

Question 18

Name and describe the characteristics of nervous system communication.

Answer 18

1) a nervous response is localised

• when an electrical impulse reaches the end of a neurone, neurotransmitters are secreted directly onto target cells (e.g. muscle cells).

2) short-lived - neurotransmitters are quickly removed once the job is done.

3) Rapid - electrical impulses are really fast.

Question 19

The human blink reflex is an involuntary response, which results in the automatic
closing of the eyelids (a blink) when an object touches the surface of the eye.
A reflex arc for the blink reflex is shown in the diagram above.

a) Using the diagram, describe the reflex are involved in this response.

b) The knee-jerk is another reflex response. You can test for it by tapping someone just below their patella (knee cap).
Suggest why the absence of this response could indicate some damage to a person’s CNS.

Answer 19

2 a) Touch receptors on the surface of the eye (A) are stimulated. An electrical impulse is sent along the sensory neurone (B) to a relay neurone (C). The impulse is then passed to a motor neurone (D) which stimulates effector muscles (E) causing them to contract and the person’s eyelids to close.

b) Damage to the CNS could interrupt the transmission of the reflex, preventing the reflex response from occurring.

Question 20

Polio is a virus that can cause damage to the CNS. In severe cases, the virus can damage motor neurones.
Suggest and explain how this might lead to paralysis.

Answer 20

Motor neurones carry electrical impulses from the CNS to effectors which then respond.
Damage to the motor neurones means the CNS can’t communicate with effectors such as muscles, so muscles don’t respond and move/are paralysed.