Nervous Coordination- Neurones

Question 1

What is the neurone like (in terms of charge) in resting state?

Answer 1

The outside of the membrane is positively charged compared to the inside

Question 2

Why is the neurones charge more positive on the outside in resting state?

Answer 2

Because there are more positive ions outside the cell than inside so the membrane is polarised

Question 3

What does the membrane being polarised mean?

Answer 3

There’s a difference in charge (potential difference) across it

Question 4

What is the potential difference across the membrane when at rest?

Answer 4

-70 mV which is resting potential

Question 5

What is the resting potential created and maintained by?

Answer 5

Sodium-potassium pumps and potassium ion channel in a neurone’s membrane

Question 6

What is the role of the sodium-potassium pumps with sodium ions?

Answer 6

Move sodium ions out of the neurone, but the membrane isn’t permeable to sodium ions, so they can’t diffuse back in which creates a sodium ion electrochemical gradient (a concentration gradient of ions) because there are more positive sodium ions outside the cell than inside

Question 7

What is the role of the sodium-potassium pumps with potassium ions?

Answer 7

Move potassium ions in to the neurone, but the membrane is permeable to potassium ions so they diffuse back out through potassium ion channels

Question 8

What is the significance of the sodium-potassium pumps?

Answer 8

Makes the outside of the cell positively charged compared to the inside

Question 9

How do sodium ions move in sodium-potassium pumps?

Answer 9

Use active transport to move three sodium ions out of the neurone for every two potassium ions moved in- ATP is needed

Question 10

How do potassium ions move in sodium-potassium pumps?

Answer 10

Allow facilitated diffusion of potassium ions out of the neurone down their concentration gradient

Question 11

What does a stimulus trigger?

Answer 11

Other ion channels called sodium ion channels to open

Question 12

What is triggered if the stimulus is big enough?

Answer 12

A rapid change in potential difference known as an action potential

Question 13

What is step 1 in changes in potential difference during an action potential?- stimulus

Answer 13

Excites the neurones cell membrane, causing sodium ion channels to open- the membrane become more permeable to sodium so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient- makes the inside of the neurone less negative

Question 14

What is step 2 in changes in potential difference during an action potential?- depolarisation

Answer 14

If the potential difference reaches the threshold (-55 mV) then more sodium ion channels open and sodium ions diffuse rapidly into the neurone

Question 15

What is step 3 in changes in potential difference during an action potential?- repolarisation

Answer 15

At a potential difference of around +30 mV the sodium ion channels close and potassium ion channels open- membrane is more permeable to potassium so potassium ions diffuse out of the neurone down the potassium ion concentration gradient and starts to get the membrane back to its resting potential

Question 16

What is step 4 in changes in potential difference during an action potential?- hyperpolarisation

Answer 16

Potassium ion channels are slow to close so there’s a slight ‘overshoot’ where too many potassium ions diffuse out of the neurone- potential difference becomes more negative than the resting potential

Question 17

What is step 5 in changes in potential difference during an action potential?- resting potential

Answer 17

Ion channels are reset- sodium-potassium pump returns the membrane to its resting potential and maintains it until the membrane’s excited by another stimulus

Question 18

Why can’t the neurone cell membrane be excited again straight away after an action potential?

Answer 18

Because the ion channels are recovering and they can’t be made to open- sodium ion channels are closed during hyperpolarisation (refractory period)

Question 19

When do some of the sodium ions diffuse sideways and what does this cause?

Answer 19

When an action potential happens which causes sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part causing a wave of depolarisation to travel along the neurone

Question 20

Why does the wave of depolarisation move away from the parts of the membrane during the refractory period?

Answer 20

Because these parts can’t fire an action potential

Question 21

What is happening during a refractory period?

Answer 21

Ion channels are recovering and can’t be opened

Question 22

What does the refractory period act as?

Answer 22

A time delay between one action potential and the next

Question 23

What are the three things an refractory period means?

Answer 23

• Action potentials don’t overlap but pass along as discrete (separate) impulses
• There’s a limit to the frequency at which the nerve impulses can be transmitted
• Action potentials are unidirectional

Question 24

What does the all-or-nothing principle mean?

Answer 24

Once the threshold is reached, an action potential will always fire with the same change in voltage, no matter how big the stimulus is

Question 25

What happens if the threshold is not reached?

Answer 25

An action potential won’t fire

Question 26

What effect will a bigger stimulus have?

Answer 26

Cause action potentials to fire more frequently

Question 27

What does it mean that a neurone is myelinated?

Answer 27

They have a myelin sheath

Question 28

What is a myelin sheath?

Answer 28

An electrical insulator

Question 29

What cells is the sheath made up of in the peripheral nervous system?

Answer 29

Schwann cells

Question 30

What are between the Schwann cells?

Answer 30

Nodes of Ranvier

Question 31

What are concentrated at nodes?

Answer 31

Sodium ion channels

Question 32

Where does depolarisation happen in a myelinated neurone?

Answer 32

Only at nodes of Ranvier

Question 33

What is saltatory conduction?

Answer 33

Impulse ‘jumps’ between nodes

Question 34

Why is conduction slower in an unmyelinated neurone?

Answer 34

The impulse has to travel along whole length of axon membrane

Question 35

What are the three factors that affect conduction of action potentials?

Answer 35

Myelination, axon diameters and temperature

Question 36

How does axon diameter affect conduction of action potentials?

Answer 36

A bigger diameter means an action potential is conducted quicker along axons

Question 37

How does temperature affect conduction of action potentials?

Answer 37

Speed of conduction increases as temperature increases