Biology 3.8: The nervous system

Question 1

How do organisms process stimuli?

Answer 1

Detect stimuli - process the information received about the stimuli - respond to the stimuli in a suitable way.

Question 2

Where is information received?

Answer 2

Sensory cells and transferred to the nervous system to effector cells that carry out the response.

Question 3

What is a reflex action

Answer 3

An inborn response to a stimulus and is rapid, automatic (doesn’t involve conscious part of the brain) and beneficial.

Question 4

A coordinator is …

Answer 4

Either the brain or the spinal cord.

Question 5

What’s the difference between reflex and voluntary actions?

Answer 5

Reflex is rapid and automatic whereas voluntary is slower and involves the conscious part of the brain.

Question 6

What is the HYDRA?

Answer 6

An organism with simple behavioural patterns and therefore, only respond to a limited number of stimuli. They have few sense receptors and effector cells that communicate through a network of simple nerve cells linked together by short, branched communication pathways.

Question 7

What does the sensory neurone do?

Answer 7

They carry nervous impulses from sensory cells to the CNS.

Question 8

What does the coordinator neurone do?

Answer 8

They receive sensory information and coordinate which effectors are activated and communicate with the brain.

Question 9

What does the motor neurone do?

Answer 9

They carry nervous impulses to effector organs - these are muscles or glands - so that the organism can respond to the stimuli they detect.

Question 10

What is the myelin sheath?

Answer 10

It is a chemical synthesised by the Schwann cells that insulate the axon speeding up the transmission of the nervous impulse.

Question 11

What type of impulse is the nerve impulse?

Answer 11

An electrochemical impulse.

Question 12

Nervous impulses are transmitted by neurones. How does this affect the nervous impulse?

Answer 12

Nervous impulses are both directed and localised.

Question 13

Why is nervous control unlike hormonal control?

Answer 13

It is precise rather than being diffuse.

Question 14

What is a microelectrode?

Answer 14

A very fine, hollow, glass needle, filled with salt solution that conducts electricity.

Question 15

What is the resting potential across the axon membrane?

Answer 15

-70mV, the membrane is said to be polarised.

Question 16

How is the inside of the axon charged?

Answer 16

Negative with respect to the outside.

Question 17

When the axon membrane is stimulated, what occurs to the potential difference across the membrane?

Answer 17

There is a local and temporary reversal of the resting potential difference.

Question 18

Why is the impulse said to be unidirectional?

Answer 18

It always travels in the same direction.

Question 19

How is the resting potential of -70mV maintained?

Answer 19

A combination of active transport and facilitated diffusion.

Question 20

What is the threshold intensity?

Answer 20

The minimum value of a stimulus that will initiate an action potential.

Question 21

What is meant by the propagation of a nerve impulse?

Answer 21

How an action potential is passed along an axon.

Question 22

Myelinated neurones

Answer 22

They speed up the rate of transmission by increasing the distance over which the currents can bring about depolarisation.

Question 23

Non-myelinated neurones

Answer 23

They conduct nerve impulses relatively slowly and do not, in general, transmit information to muscles.

Question 24

How are myelinated neurones specialised?

Answer 24

Local currents can only occur at the nodes of ranvier - so the action potential ‘jumps’ from node to node instead of moving along and depolarising the whole of the axon membrane.
This is saltatory conduction and is much faster than in non-myelinated neurones.