15.4- SPEED OF THE NERVE IMPULSE

Question 1

Is an action potential at the end of an axon the same size as when it starts?

Answer 1

yes

Question 2

What is the transmission of an action potential along the axon of a neurone?

Answer 2

nerve impulse

Question 3

Factors that affect the speed at which action potentials pass along an axon? (3)

Answer 3

myelin sheath
diameter of axon
temperature

Question 4

How does the myelin sheath affect the speed at which action potentials pass along an axon?

Answer 4

it acts as an electrical insulator, preventing an action potential forming in the part of the axon covered in myelin
but jumps from node to node increases speed of conductance

Question 5

How does the diameter of the axon affect the speed at which action potentials pass along an axon??

Answer 5

greater the diameter of the axon, faster the speed of conductance
due to less leakage of ions from large axon

Question 6

How does temperature affect the speed at which action potentials pass along an axon?

Answer 6

affects rate of diffusion of ions and so higher the temp, faster the nerve impulse

Question 7

Where does energy for active transport come form?

Answer 7

respiration

Question 8

What is respiration controlled by?

Answer 8

enzymes

Question 9

At what temperatures do enzymes function more rapidly?

Answer 9

at higher temps up to a certain point

Question 10

What happens to enzymes and plasma membrane proteins above a certain temperature?

Answer 10

enzymes + plasma membrane proteins denatured + impulses fail to be conducted at all

Question 11

How does the body temperature of cold-blooded (ectothermic) vary?

Answer 11

varied in accordance with the environment

Question 12

How does temperature affect muscle contractions?

Answer 12

affects speed + strength of muscle contractions

Question 13

What kind of response are nerve impulses described to be?

Answer 13

all-or-nothing responses

Question 14

What is the certain level of stimulus of a nerve impulse called?

Answer 14

threshold value

Question 15

What does the threshold value trigger?

Answer 15

triggers an action potential

Question 16

What is not generated below the threshold value?

Answer 16

no action potential, and so no impulse generated

Question 17

Are all action potentials more or less the same size?

Answer 17

yes

Question 18

As all action potentials are more or less the same size, what cannot be detected?

Answer 18

the strength of the stimulus cannot be detected by the size of the action potentials

Question 19

How can an organism perceive the size of a stimulus? (2)

Answer 19

by number of impulses passing in given time- larger the stimulus, the more impulses generated in given time

by having different neurones with different threshold values- brain interprets number + type of neurones that pass impulses as a result of given stimulus + thereby determines size

Question 20

Once an action potential has been created in any region of an axon, what is prevented for a period afterwards?

Answer 20

inward movement of sodium ions prevented as sodium voltage-gated channels closed

Question 21

What is the refractory period?

Answer 21

time where it’s impossible for further action potentials to be generated

Question 22

What three purposes does the refractory period serve?

Answer 22

ensures action potentials propagated in one direction only

produces discrete impulses

limits number of action potentials

Question 23

How does the refractory period ensure action potentials are propagated in one direction only?

Answer 23

action potentials cannot be propagated in region that’s refractory, which mean they can only move in forward direction
prevents action potentials from spreading in both directions

Question 24

How does the refractory period produce discrete impulses?

Answer 24

new action potential cannot be formed immediately behind first one
ensures action potentials separated from one another

Question 25

How does the refractory period limit the number of action potentials?

Answer 25

as action potentials separated from one another this limits the number of action potentials that can pass along axon in given time, + so limits strength of stimulus that can be detected