15.4 - Speed Of A Nerve Impulses

Question 1

What happens when an action potential set up?

Answer 1

It moves rapidly to one end of the axon to other without any decrease in size

Question 2

What is a nerve impulse?

Answer 2

Transmission if an action potential along the axon of a neurone

Question 3

What factors affect the speed at which action potential travels

Answer 3

• Myelin sheath
• Diameter of an axon
• Temperature

Question 4

How does myelin sheath influence the speed at which action potential travels?

Answer 4

• Passgae of an action potential, myelin sheath acts as an electrical insulator- preventing action potential forming in part of axon covered in myelin

it does jump from one node of Ranvier to another (saltory conduction)
- increases the speed of conductucane from 30ms-1 in unmyelinated neurons to 90ms-1 in myelinated

Question 5

How does diamter of axon influence the speed at which action potential travels?

Answer 5

• The greater the diameter of axon , the faster speed of conduct and
• This is due to the less leakage of ions from large axon (leakage makes membrane potential harder to maintain).

Question 6

How does temperature affect the speed st which action potential - diffusion

Answer 6

•Affects rate of diffusion of ions (high temp, faster rate of nerve impulse

Question 7

How does temperature affect the speed at which action potential travels ? - respiration, enzymes

Answer 7

• The energy for active transport comes from respiration
• Respiration , like sodium-potassium pump is controlled by enzymes
• Enzymes function more rapidly st higher temp up to a point
• Above a certain temp, enzymes and plasma membrane proteins denatured and fail for impulses to be conducted

Question 8

How does temperature affect the speed at which action potential travels? -cold blooded

Answer 8

Important factor in response times in cold-blooded (ectothermic) animals

Whose body temp varies in accordance with the enivnroment

Question 9

How does temperature affect the speed at which action potential travels? - muscle

Answer 9

Also affects the speed and strength of muscle contractions

Question 10

All or nothing principle

What do nerve impulses do when there is a certain level of stimulus?

Answer 10

Reach certain level of stimulus - threshold value

Triggers an action potential

Question 11

All or nothing principle

What happens if it is below the threshold potential?

Answer 11

No action potential

Therefore no impulse is generated

This means any stimulus with whatever strength is below threshold value failed to generate action potential (nothing part)

Question 12

All or nothing principle

What happens with any stimulus that is above the threshold value?

Answer 12

Succeed in generating action potential and so nerve impulse travel

Question 13

What size are all action potentials?

Answer 13

All the same size

Question 14

What is the problem of action potential being the same size?

Answer 14

The strength of the stimulus cannot be detected by the size of an action potential

Question 15

What is the first way an organism can perceive the size of a stimulus?

Answer 15

• number of impulses passing un a given time. The larger the stimulus the more impulses that re generated in a given time

Question 16

What is this second way an organism can perceive the size of stimulus?

Answer 16

• by having different neurons with different threshold values. The brain interprets the number and type of neurons that pass impulses as a result of given stimulus. Thereby determine its size

Question 17

Why is the all or nothing principle important?

Answer 17

It acts as a filter
Preventing minor stimulus from setting up nerve impulses

Preventing the brain becoming overloaded

Question 18

What does the refractory period limit?

Answer 18

The strength of a stimulus that can be detected

Question 19

What are the three purposes of refractory period?

Answer 19

• ensures that action potentials are propagated into one direction only
• it produces discrete impulses
• it limits he number of action potentials

Question 20

Why is it important that refractory period ensures action potentials are propagated in one direction only?

Answer 20

• Action potentials can only pass from an active to resting region
• Action potentials cannot be propagated In a region that is refractory, means they only move forward direction
• prevents action potential from spreading in both directions

Question 21

Why is it important that refractory period produces discrete impulses?

Answer 21

Due to refractory period , a new action potential cannot be formed immediately behind the first one

Ensures action potentials are separated from kne another

Question 22

Why is it important that refractory period limits the number of action potentials?

Answer 22

As action potentials are separated from one another this limits the number of action potentials that can pass along the axon in a given time

Thus limit strength of stimulus that can be detected