Nerve Impulses

Question 1

What is found between the sensory neuron and relay neuron

Answer 1

Synapse

Question 2

Draw out and annotate a myelinated motor neuron

Answer 2

image

Question 4

What is found between the sensory neuron and relay neuron

Answer 4

Synapse

Question 5

Draw out and annotate a myelinated motor neuron

Answer 5

image

Question 6

What is found on the cell surface membrane of the dendrites?

Answer 6

Receptors

Question 7

Receptors

Answer 7

Receptors

Question 8

Specialised cell that produces the myelin sheath

Answer 8

Schwann cell

Question 9

Biological molecule found in myelin sheath

Answer 9

phospholipids

Myelin also contains cholesterol, so similar to cell surface membrane.

Question 10

Released by axon terminals

Answer 10

neurotransmitters

Question 11

Process at nodes of ranvier

Answer 11

saltatory conduction

Question 12

Stages of an action potential

Answer 12

Resting potential,
(Threshold potential),
Depolarisation,
Repolarisation,
Hyperpolarisation,
Re-establish resting potential.

Question 13

Resting potential in mV

Answer 13

-70mV

Question 14

Channel proteins found in axon cell surface membrane

Answer 14

Voltage-gated sodium ion channels

Voltage-gated potassium ion channels

Question 15

Explain how a resting potential is maintained across the axon membrane in a neurone (3 marks).

Answer 15

1. Sodium ions actively transported OUT and potassium ions IN;
2. LESS permeable to sodium ions as voltage-gated channels closedOR membrane MORE permeable to potassium ions as some voltage-gated channels open;
3. Higher concentration of potassium ions inside AND higher concentration of sodium ions outside the axon

Question 16

The sodium potassium ion pump establishes an ________________ gradient.

Answer 16

electrochemical gradient

i.e., higher sodium ion concentration outside the axon, lower inside.

Question 17

Threshold potential in mV

Answer 17

-55mV

Question 18

Channel open at -55mV

Answer 18

Voltaged-gated sodium ion channels

Question 19

The all-or-nothing principle

Answer 19

An action potential is only generated/produced when threshold stimulus is reached (-55mv)

OR

An action potential is not generated/produced until/unless threshold stimules is reached (-55mv);

If stimulus reached, voltage-gated sodium ion channels open

Question 20

Sodium and potassium ions can only cross the axon membrane through channel proteins. Explain why (2 marks).

Answer 20

1. Cannot pass through phospholipid bilayer
   (via simple diffusion)
2. because they are NOT lipid soluble

OR because they are charged;

Question 21

A scientist investigated the effect of inhibitors on neurones. She added a respiratory inhibitor to a neurone. The resting potential of the neurone changed from –70 mV to 0 mV.

Explain why (3 marks).

Answer 21

1. No/less ATP produced;
2. No/less active transport
   OR fewer sodium ions moved out.
   OR Sodium/potassium pump inhibited;
3. Electrochemical gradient not maintained

OR same concentration of sodium and potassium ions either side of axon membrane

Question 22

Sodium ions diffusing into the axon via open voltage-gated channels leads to___________________.

Answer 22

depolarisation

Question 23

Why does the graph increase from -55mV to +40mV?
image

Answer 23

1. Voltage-gated sodium ion channels are open
2. Sodium ions diffuse into the axon via faciliated diffusion (DOWN an electrochemical gradient)
3. Inside of the axon MORE positive

Question 24

What happens at +40mV?
image

Answer 24

Voltage-gated sodium ion channels CLOSE

AND

Voltage-gated potassium ion channels OPEN

Question 25

Why does the graph decrease after +40mV during repolarisation? [image](https://www.researchgate.net/publication/376513136/figure/fig3/AS:11431281212413843@1702610269248/Action-potential-of-a-neuron-Incoming-currents-progressively-raise-the-membrane_Q640.jpg)

Answer 25

1. Voltage-gated potassium ion channels are open (& voltage-gated sodium ion channels are closed). 2. Potassium ions rapidly diffuse OUT of the axon via faciliated diffusion (DOWN an electrochemical gradient) 3. Inside of the axon LESS positive

Question 26

Hyperpolarisation in mV

Answer 26

-90mV

Question 27

What causes hyperpolarisation?

Answer 27

1. Voltage-gated potassium ion channels stay open; 2. Potassium ions diffuse out of axon; 3. Inside of axon becomes even LESS positive (decreasing from -70mV to -90mV).

Question 28

Channels closed at -90mV

Answer 28

Voltage-gated potassium ion channels (close at -90mV) Voltage-gated sodium ion channels (already closed during repolarisation)

Question 29

Explain how the resting potential is re-established (2 marks).

Answer 29

1. Sodium potassium pump uses energy from ATP hydrolysis; 2. Sodium ions actively transported OUT and potassium ions IN. Both ions move AGAINST their concentraton gradient from low to high.

Question 30

Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon (3 marks).

Answer 30

1. Myelination provides insulation; 2. In myelinated axon saltatory conduction occurs OR In myelinated axon depolarisation only occurs at nodes of Ranvier; 3. In non-myelinated axon, depolarisation occurs along whole length of axon;

Question 31

Refractory period

Answer 31

1. Time during which a new action potential cannot be generated; 2. It lasts from the threshold potential until the resting potential has been re-established;

Question 32

Importance of the refractory period

Answer 32

1. Action potentials occur in one direction 2. Each impulse / action potential is discrete 3. Number of action potential is limited

Question 33

Factors affecting speed of impulse conductance along an axon

Answer 33

Myelination Temperature Axon diameter

Question 34

explain how myelination affects conductance of an impulse

Answer 34

insulates axon; Depolarisation only occurs at nodes of Ranvier; Leads to salatory conduction (action potential ‘jumps’ between nodes of Ranvier); Impulse / action potential moves FASTER along axon;

Question 35

Explain how increasing temperature affects conductance of an impulse

Answer 35

More kinetic energy; Faster rate of diffusion of sodium and potassium ions DOWN electronchemical gradient; Faster rate of diffusion of sodium ions within axon; Impulse / action potential moves FASTER along axon

Question 36

Explain how increasing axon diameter affects conductance of an impulse

Answer 36

1. Larger surface area so more cell-surface membrane for voltage-gated sodium/potassium ion channel proteins; 2. Less resistance to flow ions within the axon;

Question 37

Multiple sclerosis is a disease in which parts of the myelin sheaths surrounding neurones are destroyed. Explain how this results in slower responses to stimuli (2 marks).

Answer 37

1. Less / no saltatory conduction / action potential / impulse unable to ‘jump’ from node to node; 2. More depolarisation over length of membranes;