5.7 The Nervous System, Synapses & Reflexes

Question 1

What is the nervous system made up of?

Answer 1

Neurones (nerve cells) which go to all parts of the body

Question 2

Describe how a neurone transmits information rapidly (5)

Answer 2

• Electrical impulses are passed along the axon of a neurone.
• Neurones have branched endings (dendrites) so they can connect with lots of other neurones.
• Some axons are also surrounded by a fatty (myelin) sheath. This acts as an electrical insulator, speeding up the impulse.
• Neurones are long, which also speeds up the impulse (connecting with another neurone slows the impulse down, so one long neurone is much quicker than lots of short ones joined together).
• The connection between two neurones is a very tiny gap called a synapse. The electrical impulse triggers the release of transmitter chemicals, which diffuse across the gap. These chemicals bind to receptor molecules in the membrane of the next neurone. This sets off a new electrical impulse.

Question 3

Describe how the central nervous system coordinates a response

Answer 3

1) The body has lots of sensory receptors, which can detect a change in your external or internal environment (a stimulus). Different sensory receptors detect different stimuli. For example, receptors in your eyes detect light, and receptors in your skin detect touch (pressure) and temperature change.
2) When a stimulus is detected by receptors, the information is sent as nervous (electrical) impulses along sensory neurones to the central nervous system (CNS). The CNS consists of the brain and spinal cord.
3) The CNS coordinates the response. The CNS sends information to an effector (muscle or gland) along a motor neurone. The effector then responds accordingly - e.g. a muscle may contract or a gland may secrete a hormone.
4) Nervous communication is very fast, but the responses are short-lived.

Question 4

What is the reflex arc?

Answer 4

A technical term for the nerve pathway that underlies our unconscious reflexes

Question 5

What are the 2 benefits of reflexes?

Answer 5

• They’re rapid
• They’re automatic

Question 6

Describe how a reflex may work if someone got stung by a bee (6)

Answer 6

1) Cheeky bee stings finger.
2) Stimuli will be detected by receptor cells in your skin.
3) Impulse travels along the sensory neurone.
4) Impulse is passed along a relay neurone.
5) Impulse travels along a motor neurone.
6) When impulse reaches muscle, it contracts to move arm away from bee. (effector)

Question 7

What passes along nerve cells?

Answer 7

Electrical impulses

Question 8

What is released across a synapse?

Answer 8

Chemicals

Question 9

What is part of the central nervous system (CNS)?

Answer 9

Spinal cord & Brain

Question 10

What is the role of a receptor?

Answer 10

To detect a stimulus

Question 11

What is the role of a sensory neurone?

Answer 11

To transfer a signal from a receptor to the CNS.

Question 12

What is the role of a motor neurone?

Answer 12

To transfer a signal from the CNS to an effector.

Question 13

What is the role of a relay neurone?

Answer 13

To transfer a signal from a sensory neurone to a motor neurone.

Question 14

What are the two main types of effectors?

Answer 14

Muscles & Glands

Question 15

Pathway of a reflex arc

Answer 15

stimulus -> receptor -> sensory neurone -> relay neurone -> motor neurone -> effector -> response