Nervous System

Question 1

What is the CNS?

Answer 1

Central Nervous System

Question 2

What is the PNS?

Answer 2

Peripheral Nervous System

Question 3

What does the CNS consist of?

Answer 3

The brain and spinal cord

Question 4

What does the PNS consist of?

Answer 4

Nerves leading to and from the CNS

Question 5

What does a typical nerve cell contain?

Answer 5

Sensory and motor neurons and ganglia

Question 6

What is a neuron?

Answer 6

Neurons are nerve cells which are specialised to carry impulses.

Question 7

How are neurons classified?

Answer 7

According to their function.

Question 8

What do sensory neurons do?

Answer 8

Transmit impulses from sense organs towards the central nervous system.

Question 9

What do motor neurons do?

Answer 9

Transmit impulses away from the central nervous system towards effectors.

Question 10

What do interneurons do?

Answer 10

Transmit impulses within the central nervous system.

Question 11

What are receptors?

Answer 11

Sensory cells that detect a stimulus and generate impulses.

Question 12

What are effectors?

Answer 12

Muscles or glands that are capable of producing a response e.g muscles cause movement

Question 13

Write a note on interneurons.

Answer 13

They are all located within the CNS.
They are the most abundant neurons.
They lack a myelin sheath.
They transfer impulses from the sensory neurons to the motor neurons within the CNS.

Question 14

Describe the cell body.

Answer 14

Contains the nucleus surrounded by cytoplasm and organelles such as mitochondria.

Question 15

What is the function of the cell body?

Answer 15

Produces neurotransmitter chemicals such as dopamine.

Question 16

Describe an axon.

Answer 16

Elongated nerve fibre.

Question 17

What is the function of the axon?

Answer 17

Transmits impulses away from the cell body.

Question 18

Describe a dendrite.

Answer 18

Branched nerve fibre, generally.

Question 19

What is the function of the dendrite?

Answer 19

Transmits impulses towards the cell body.

Question 20

Describe the myelin sheath.

Answer 20

A fat-enriched membrane around nerve fibres.

Question 21

What is the function of the myelin sheath?

Answer 21

Insulates and speeds up impulse transmission.

Question 22

Describe the Schwann cell.

Answer 22

Wrapped thinly around the axon or dendrite.

Question 23

What is the function of the Schwann cell?

Answer 23

Produces the myelin sheath.

Question 24

What are axon terminals?

Answer 24

Small branches of the main axon, makes contact with the dendrites of other neurons.
Ends in swelling called neurotransmitter swellings.

Question 25

What are the functions of axon terminals?

Answer 25

Neurotransmitter swellings release neurotransmitter chemicals like dopamine.
Dopamine is stored in vesicles within neurotransmitter swellings.

Question 26

What is an impulse?

Answer 26

An electrical message and a positive flow of ions carried by a neuron.

Question 27

What does the transmission of a nerve impulse require?

Answer 27

The movement of Na and K ions in and out of dendrites and axons.
Energy in the form of ATP

Question 28

Name the type of particle whose movement in and out of neurons is an essential feature of nerve impulse transmission.

Answer 28

Ion

Question 29

Describe the characteristics of nerve impulses.

Answer 29

The Threshold Stimulation:
A threshold is the minimum level of stimulus needed for impulse transmission. Once the threshold is reached an impulse is generated and transmitted. Below the threshold, no impulse is generated.
Example: lukewarm water is below the threshold so no impulse is generated.

The all or nothing effect:
The impulse will travel the entire length of the neuron or not at all.

The refractory period:
The timespan after impulse transmission, when the stimulus fails to cause a response.

Speed of impulse:
Impulses are faster when a myelin sheath is present and when the diameter of the nerve fibre is greater.

Question 30

What is a synapse?

Answer 30

A region where two neurons come in close contact, allowing impulses to pass from one neuron to another.

Question 31

What is the synaptic cleft?

Answer 31

A tiny gap between two neurons, ie. between the presynaptic and postsynaptic neurons at the synapse.

Question 32

Describe the sequence of events that allows an impulse to be transmitted across a synapse from one neuron to the next.

                                        OR

Give an account of how neurotransmitters work.

Answer 32

The impulse arrives at the neurotransmitter swelling.

Ions stimulate the vesicles to fuse with the cell membrane and release neurotransmitters into the synaptic cleft for a very short time.

The neurotransmitter diffuses across the synaptic cleft chemically transmitting the impulse into the next neuron.

Neurotransmitter reacts with receptors in the postsynaptic neuron.

An impulse is therefore transmitted to the postsynaptic neuron

Following impulse transmission, the neurotransmitter is broken down by enzymes and reabsorbed by the presynaptic neuron where it is used to make new neurotransmitters.