Chapter 13 - The Nervous System

Question 1

Define stimulus.

Answer 1

A change in the environment that causes a reaction.

Question 2

Define response.

Answer 2

An organism’s reaction to a stimulus.

Question 3

Define sensitivity/irritability.

Answer 3

The ability of an organism to detect and respond to changes in the environment.

Question 4

How does an organism usually respond to a stimulus? Give an example.

Answer 4

They move in a way that benefits themselves. For example, plants grow towards the light since they need light for photosynthesis.

Question 5

What is the role of nervous system in humans? (2)

Answer 5

1) allow organisms to detect changes in surroundings and respond to it
2) enables coordination of different parts of the body

Question 6

Define involuntary actions.

Answer 6

Automatic activities that are not controlled consciously

Question 7

Define voluntary actions.

Answer 7

Activities that are controlled consciously

Question 8

What is the nervous system made up of? (2)

Answer 8

1) central nervous system (brain and spinal cord)

2) peripheral nervous system (spinal nerves and cranial (brain) nerves)

Question 9

Define nervous tissues.

Answer 9

They are tissues consisting of nerve cells known as neurones.

Question 10

What are 3 types of neurones?

Answer 10

1) sensory neurone
2) relay neurone
3) motor neurone

Question 11

What is the function of sensory neurone?

Answer 11

Transmit nerve impulses from the sense organs or receptor to central nervous system

Question 12

What is the function of relay neurone?

Answer 12

Transmit nerve impulses from sensory neurone to motor neurone, found within the central nervous system.

Question 13

What is the function of motor neurone?

Answer 13

Transmit nerve impulses from the central nervous system to effectors.

Question 14

What does a motor neurone consist of? (7)

Answer 14

1) irregular cell body
2) short dendron
3) long axon
4) myelin sheath
5) node of ranvier
6) axon terminals
7) motor end plate

Question 15

state the function of dendrons in motor neurones.

Answer 15

Its end branches, dendrites, receive nerve impulses from other neurones.

Question 16

State the function of axons in motor neurones.

Answer 16

Contains dendrites that transmit nerve impulses to the effector.

Question 17

Define+state the function of myelin sheath.

Answer 17

It is the layer of fatty substance enclosing many nerve fibres. It insulates the axon.

Question 18

Define+state the function of node of ranvier.

Answer 18

Regions where myelin sheath is absent. (In between)
They speed up transmission by allowing impulses to jump from node to node, as nerve impulses cannot transmit through the myelin sheath.

Question 19

What is the function of axon terminals in motor neurones?

Answer 19

Transmit nerve impulses to the effector.

Question 20

Define+state the function of motor end plates.

Answer 20

The junction between the axon terminal and muscle fibre. Nerve impulses are transmitted across the motor end plate by chemicals which stimulate the muscles.

Question 21

What is the structure of a sensory neurone? (5)

Answer 21

1) long dendron
2) node of Ranvier
3) myelin sheath
4) circular cell body
5) short axon

Question 22

What is the difference between dendrons and axons?

Answer 22

Axon transmit nerve impulse away from the cell body while dendron transmit nerve impulses towards cell body.

Question 23

Define synapse.

Answer 23

It is a junction between two neurones or a neurone and an effector.

Question 24

How does a synapse work?

Answer 24

Nerve impulses are transmitted from the axon of one neurone to the dendron of another neurone, across a tiny space. Transmission across a synapse is through a chemical called neurotransmitter.

Question 25

Define nerve.

Answer 25

A bundle of nerve fibres enclosed in a sheath of connective tissue.

Question 26

What does spinal nerves contain?

Answer 26

Mixed fibres: both sensory and motor nerve fibres.

Question 27

What is the difference between grey matter and white matter? (2)

Answer 27

1) composition: GM is made up of cell bodies of motor and relay neurones while WM consist of mainly nerve fibres of neurones.
2) location: GM is located at the outer layer of the brain and the centre of the spinal cord (H), while WM is located at the centre parts of the brain, and the outer layers of spinal cord.

Question 28

Where is the central canal located and what is its function?

Answer 28

In the middle of the “H” in the spinal cord.

It contains cerebrospinal fluid that brings nutrients to the spinal cord.

Question 29

What is the structure of the spinal cord? (3)

Answer 29

1) It is encased in the vertebral column.
2) spinal nerves emerge at intervals along the length of the spinal cord, which progressively sub-divides into branches supplying nerve fibres to various parts of the body.
3) each spinal nerve divides into dorsal and ventral roots.

Question 30

What is the function of the dorsal root?

Answer 30

It contains the nerve fibres of sensory neurones that transmit impulses to the spinal cord.

Question 31

What is the dorsal root ganglion?

Answer 31

It is a small swelling in the dorsal root that contains the cluster of sensory neurone’s cell bodies.

Question 32

What is the function of the ventral root?

Answer 32

It contains the nerve fibres of motor neurones that transmit nerve impulses from the spinal cord to the effector.

Question 33

Define reflex actions.

Answer 33

A reflex action is an immediate response to a specific stimulus without conscious control. These actions are involuntary.

Question 34

What is the reflex arc?

Answer 34

The shortest pathway of nerve impulses from the receptor to the effector.

Question 35

What happens when you touch a hot object? (6)

Answer 35

1) heat stimulates the nerve endings in your skin
2) nerve impulses are generated and transmitted along the sensory neurone to the spinal cord
3) in the spinal cord, nerve impulses are transmitted to the relay neurone via a synapse, and then to the motor neurone via another synapse. At the same time, another set of nerve impulses are transmitted to the brain via the relay neurone that is parallel to the spinal cord (just to inform)
5) upon receiving nerve impulses from relay neurone, motor neurone transmits nerve impulses to the effector
6) the biceps contract, resulting in the withdrawal of hand from the hot object.

Question 36

What is a spinal reflex and what is one example?

Answer 36

Reflexes that are cotrolled by the spinal cord, like the withdrawal reflex.

Question 37

What are cranial reflexes and what is one example?

Answer 37

Reflexes that are controlled by the brain, but occur without a person’s consciousness. One example is pupil reflex.

Question 38

Define reflex arc.

Answer 38

The shortest pathway which nerve impulses transmit from the receptor to the effector in a reflex action.

Question 39

What are 4 differences between voluntary actions and reflex actions?

Answer 39

1) VA involves conscious control while RA does not involve conscious control
2) VA may not have an immediate response, while RA is an immediate response
3) VA does not require stimulus while RA occurs in response to stimulus
4) VA is initiated by the brain while RA is not initiated by the brain.

Question 40

What are 3 similarities between a voluntary action and a reflex action?

Answer 40

1) both involve transmission of nerve impulses
2) both involve motor neurones
3) both involve effectors to carry out desired responses