3.6.2 - Nervous Coordination

Question 1

What order is info conducted in, in the nervous system ?

Answer 1

Stimulus
Receptor
Coordinator
Effector - Response

Question 2

What is a stimulus ?

Answer 2

An energy change in the environment

Question 3

What is a receptor ?

Answer 3

A cell that detects change i.e - Pacinian corpuscle

Question 4

What is a coordinator ?

Answer 4

This is something that receives nerve impulses from the receptor and makes a decision.

Question 5

What is an effector ?

Answer 5

Muscle or gland which produces a response : either a chemical release or a muscle contraction.

Question 6

What is more likely to happen to organisms that respond appropriately to stimuli ?

Answer 6

They maintain themselves in a favourable environment and are more likely to survive and pass on their genetics to the next generation.

Question 7

What is an action potential ?

Answer 7

When neutron voltage increases beyond resting potential (-70mv)
This generates a nervous impulse

Question 8

What is depolarisation ?

Answer 8

An increase in voltage above the resting potential, voltage gets more positive due to membrane getting more per able to Na+

Question 9

What is Resting potential , how is it maintained ?

Answer 9

• 70 mv
• maintained by Na/K pump and K+ channels which are leakier

Question 10

What is the movement of the ions at resting potential ?

Answer 10

Na+ /K+ ATPase transport protein channel allows 2k+ and 3Na+ ions out.
Via fac. Diffusion, this makes the inside relatively negatively charged.
Creates a con gradient, Na+ ions flow IN through leak channels, K+ channels also open , allowing +ive charge out - decreasing it again

Question 11

What happens when there is a stimulus ?

Answer 11

This provides enough energy, allows the voltage gated Na+ channels to open

Question 12

What happens during depolarisation ?

Answer 12

Voltage gated Na+ channels to open, allows ions to diffuse into axon same time as k+ diffusing out

Question 13

What is the threshold ?

Answer 13

-55 mv

Question 14

What will voltage always peak at ?
Why ?

Answer 14

+ 40 mv
- voltage gated Na+ channels will close when 40mv is reached in axon
- peak = reached, there will be no further increase.

Question 15

What is repolarisation ?

Answer 15

K+ channels are open, they are diffusing out, causing a decrease in voltage.
Voltage gated Na+ channel closes
Cell becomes relatively negatively charged in comp. to what it was b4

Question 16

What is hyperpolarisation ?

Answer 16

There is an overshoot beyond the resting potential, this is because the k+ leaky channels remain open, allowing positive charge to flow out.

Question 17

What’s the all or nothing principle ?
(Nothing)

Answer 17

-55 mv is the threshold
If stimulus isn’t large enough, it won’t provide enough energy to open enough Na+ channels to go above -55

Question 18

What’s the all or nothing principle ?
(All)

Answer 18

If -55 is reached, there will always be an action potential , all of them will peak at the same level (+40)

Question 19

What does a bigger stimuli cause ?

Answer 19

• Higher frequency of action potentials, they fire more quickly along the axon.

Question 20

Why is the all or nothing principle important ?

Answer 20

It ensures animals respond to large enough stimuli, not sky very slight change as it would be overwhelming.
- hinder survival

Question 21

What is the refractory period ?

Answer 21

• Brief period of time after an AP in which neutron is less responsive e to stimulus
• Voltage gated Na+ channels = closed
• Na+ don’t move , meaning new AP can’t occur

Question 22

What does the refractory period allow for ?

Answer 22

Discrete action potentials

Question 23

Why is the refractory period important ?

Answer 23

1. Ensures discrete impulses - each is separate from another
2. Ensures APs travel in one direction - stops AP spreading which could prevent a response

3.limits number of impulse transmission - prevents overreaction : no overwhelming of senses

Question 24

What is a nerve impulse ?

Answer 24

A wave of depolarisation

Question 25

What 3 factors affect the speed of nervous impulses ?

Answer 25

1) Temperature
2) Axon diameter
3) Myelination and saltatory conduction

Question 26

What is saltatory conduction ?

Answer 26

• How info travels down the axon, it jumps from node to node, triggering an AP in the next node of ranvier
• Faster and more efficient, also uses less ATP as less membrane is used