Nervous coordination

Question 1

When a neurone is in its resting state, what is established?

Answer 1

• Outside of membrane is positively charged compared to inside
• Membrane is polarised
• So there is a potential difference across it

Question 2

What is the voltage across the neurone’s membrane when its at rest known as?

Answer 2

Resting potential

Question 3

What is the resting potential of a neurone?

Answer 3

-70 mV (millivolts)

Question 4

What is the resting potential created and maintained by?

Answer 4

Sodium-potassium pumps and potassium ion channels in the neurones membrane

Question 5

How many ions are transported out and in of the neurone when its at rest and how is this done?

Answer 5

Na-K pumps use active transport
- 3 Na+ moved out
- 2 K+ moved in

Question 6

What do the potassium ion channels in a neurones membrane allow when its at rest?

Answer 6

Facilitated diffusion of K+ out of the neurone, down their concentration gradient

Question 7

What is the action of sodium ions when a neurone is at rest?

Answer 7

• Na+ moved out of neurone via pump
• Membrane isn’t permeable to Na+
• They can’t diffuse back in
• Na+ electrochemical gradient created

Question 8

What is the action of potassium ions when a neurone is at rest?

Answer 8

• K+ moved into neurone via pump
• Most K+ channels are open
• Membrane is permeable to K+
• Some diffuse back out through channels

Question 9

When at rest, why is the outside of the neurone’s cell membrane more positive than the inside?

Answer 9

In total, more positive ions out of the cell than in

Question 10

When a neurone is stimulated, what is opened?

Answer 10

Sodium ion channels in the membrane

Question 11

If a stimulus is big enough, what will happen to the neurone?

Answer 11

• It’ll trigger a rapid change in potential difference
• Cell membrane becomes depolarised

Question 12

What is the sequence of events of an action potential?

Answer 12

1. Stimulus
2. Depolarisation
3. Repolarisation
4. Hyperpolarisation
5. Resting potential

Question 13

What is the stimulus event in an action potential?

Answer 13

• Neurone cell membrane is excited
• Na+ channels open
• Membrane more permeable to Na+
• Na+ diffuse into neurone down Na+ electrochemical gradient
• Inside of neurone is less negative

Question 14

What is the depolarisation event in an action potential?

Answer 14

• If potential difference reaches threshold, more Na+ channels open
• More Na+ diffuses into neurone

Question 15

What is the repolarisation event in an action potential?

Answer 15

• At a certain potential difference (30 mV), Na+ channels close and K+ channels open
• Membrane more permeable to K+
• K+ diffuses out of neurone down K+ concentration gradient
• Starts to get membrane back to its resting potential

Question 16

What is the hyperpolarisation event in an action potential?

Answer 16

• K+ channels too slow to close
• Slight ‘overshoot’ where too many K+ diffuses out of neurone
• Potential difference becomes more negative than resting potential

Question 17

What is the resting potential event in an action potential?

Answer 17

• Ion channels are reset
• Na-K pump returns membrane to its resting potential
• Resting potential maintained until membrane is excited by another stimulus

Question 18

After an action potential, can a neurone be excited again?

Answer 18

Not straight away - ion channels are recovering and can’t be made to open

Question 19

What is the period of recovery after an action potential known as?

Answer 19

Refractory period - acts as a time delay between one action potential and the next

Question 20

What does the refractory period ensure?

Answer 20

Action potentials don’t overlap but pass along as discrete (separate) impulses

Question 21

What does the refractory period signify?

Answer 21

• There’s a limit to the frequency at which at which the nerve impulses can be transmitted
• Action potentials are unidirectional

Question 22

What happens to some of the sodium ions when an action potential occurs?

Answer 22

Some of the Na+ that enter diffuse sideways

Question 23

How does a wave of depolarisation travel along a neurone?

Answer 23

Na+ that diffuse sideways after an action potential cause Na+ channels in the next region of the neurone to open and Na+ diffuse into that part - this is continued

Question 24

Where does the wave of depolarisation move away from?

Answer 24

Parts of the membrane in the refractory period - these parts can’t fire an action potential

Question 25

Does a bigger stimulus generate a bigger action potential?

Answer 25

No - once threshold is reached, an action potential will always fire with the same voltage

Question 26

What is the all-or-nothing nature of action potentials?

Answer 26

If threshold not reached, no action potential If threshold reached, no matter how big stimulus is, action potential fired always the same

Question 27

What will a bigger stimulus cause in an action potential?

Answer 27

More frequent action potentials fired

Question 28

What are the 3 factors that affect speed of conduction of action potentials?

Answer 28

Myelination Axon diameter Temperature

Question 29

What do some neurones have to speed up conduction?

Answer 29

Myelin sheath - they are myelinated

Question 30

What is a myelin sheath?

Answer 30

An electrical insulator

Question 31

In the peripheral nervous system, what is the myelin sheath made up of?

Answer 31

A Schwann cell

Question 32

What are between Schwann cells on a neurone?

Answer 32

Tiny patches of bare membrane called the nodes of ranvier

Question 33

What is located at the nodes of ranvier?

Answer 33

Many sodium ion channels

Question 34

In a myelinated neurone, where does depolarisation take place?

Answer 34

At the nodes of ranvier (due to Na+ channels here)

Question 35

Where does saltatory conduction take place and what is its speed?

Answer 35

In a myelinated neurone - very fast

Question 36

What is saltatory conduction?

Answer 36

- Neurone's cytoplasm conducts enough electrical charge to depolarise next node - Impulse jumps from node to node

Question 37

In a non-myelinated neurone, how does the impulse travel along the neurone?

Answer 37

Travels as a wave along the whole length of the axon membrane - depolarisation along the whole length of the membrane (slower than saltatory conduction)

Question 38

How does axon diameter affect speed of conduction of action potentials?

Answer 38

Bigger diameter means quicker action potentials

Question 39

Why does a bigger axon diameter increase speed of conduction?

Answer 39

- Less resistance to flow of ions - Depolarisation reaches other parts of neurone cell membrane quicker

Question 40

How does temperature affect speed of conduction of action potentials?

Answer 40

Speed increases as temperature increases

Question 41

Why does a greater temperature increase speed of conduction?

Answer 41

Ions diffuse faster (only up to around 40 degrees, as after that the proteins begin to denature and speed decreases)