ORTCITIAEE: Nerve impulses

Question 1

Define neurones:

Answer 1

Specialised animal cells that pass on nerve impulses.

Question 2

Name the basic components (structure) of a myelinated motor neurone:

Answer 2

• Dendrites
• Cell body (containing nucleus)
• Axon
• Axon terminal
• Myelin sheath
• Nodes of Ranvier

Question 3

What cells are is the myelin sheath made from?

Answer 3

Schwann cells

Question 4

To get a response from an effector, the receptor first detects a ______.

Answer 4

Stimulus

Question 5

In an axon a nerve impulse is a moving area of ______.

Answer 5

Charge

Question 6

Nerve impulses always travel away from a receptor and to an ______.

Answer 6

effector

Question 7

What are the two main ions involved in establishing a resting potential?

Answer 7

• Sodium ions
• Potassium ions

Question 8

Sodium and potassium ions can be found inside and outside of an _____- with the majority of them being found on the ____ of it.

Answer 8

Axon
Outside

Question 9

The outside of a neurone’s axon is generally more ______ charged than inside the axon.

Answer 9

positively

Question 10

What causes the difference in charge between the outside and inside of a neurone?

Answer 10

Concentration of sodium and potassium ions

Question 11

There is usually a higher concentration of sodium ions _____ the axon, and potassium ions _____ the axon.

Answer 11

Outside
Inside

Question 12

What is a nerve impulse?

Answer 12

A moving area of charge

Question 13

By what process do sodium and potassium ions move across membranes?

Answer 13

Facilitated diffusion

Question 14

What are ion channels?

Answer 14

Channel proteins that specifically transport ions.

Question 15

Sodium and potassium ions are transported by facilitated diffusion via ____ channels.

Answer 15

Ion

Question 16

An ion channel that transports sodium is called a ______ channel.

Answer 16

Sodium

Question 17

An ion channel that transports potassium is called a ______ channel.

Answer 17

Potassium

Question 18

What is an electrochemical gradient?

Answer 18

The difference in concentration and charge across the membrane.

Question 19

overtime why does the inside of the axon become more positive?

Answer 19

sodium ions move down their electrochemical gradient into the inside of the axon.

Question 20

Overtime, the charge of the outside of the axon changes. It is first positive and then it becomes negative and then positive again- why?

Answer 20

• Positive at first due to higher concentration of sodium ions outside of axon
• Then becomes negative as sodium ions are transported from the outside of the axon to the inside of the axon via sodium channels + facilitated diffusion
• Becomes positive again as potassium ions pre-existing inside the axon repel the sodium ions and are transported outside the axon via potassium channels + facilitated diffusion.

Question 21

A ___-______ protein can transport BOTH sodium and potassium ions.

Answer 21

Co-transporter.

Question 22

A co-transporter protein/sodium-potassium pump binds to 3 sodium ions and one molecule of ____.

Answer 22

ATP

Question 23

Co-transporter proteins/sodium-potassium pump bind to one molecule of ATP. What does this do?

Answer 23

Allows for ATP to be hydrolysed to produce on molecule of ADP and an inorganic phosphate ion.

Question 24

When a phosphate ion and three sodium ions are all bonded to the carrier protein, they trigger a series of reactions that cause the sodium-potassium pump to change ______.

Answer 24

shape

Question 25

The sodium-potassium pump changes shape as it is triggered by the binding of 3 sodium ions and a Pi. Where does the energy come from for it to be able to change shape?

Answer 25

The breaking of the bond between the Pi and ADP Yes- it is ADP not ATP. It is the actual bond separation of the Pi from the ADP that provides the energy.

Question 26

The sodium-potassium pump changes shape as it is triggered by 3 sodium ions and ATP. What does the change in shape do?

Answer 26

Provides 2 binding sites for potassium

Question 27

When the phosphate ion is released from the sodium-potassium pump, the sodium-potassium pump reverts to its ______ shape.

Answer 27

original

Question 28

What happens when the Pi molecule is removed from the sodium-potassium pump?

Answer 28

The sodium-potassium pump reverts back to its original shape- 'dropping' the potassium ions on the other side (inside the axon)

Question 29

What is the co-transporter protein actually called?

Answer 29

Sodium-potassium pump

Question 30

The sodium-potassium pump moves ___ potassium ions into the axon, and ___ sodium ions out of the axon.

Answer 30

2 3

Question 31

The sodium-potassium pump maintains a more positive charge ______ the axon, and a less positive charge ______ the axon

Answer 31

Outside Inside

Question 32

The sodium-potassium pump allows for ions to be transported _____ their concentration gradient.

Answer 32

Against (an example of active transport)

Question 33

What is the overall purpose of the sodium-potassium pump?

Answer 33

Maintain a more positive charge outside of the axon, and a less positive charge inside the axon

Question 34

Inside an axon a nerve impulse appears as a ____ charge.

Answer 34

Positive

Question 35

What is the resting potential?

Answer 35

When a neurone maintains a less positive charge inside of an axon, maintained by the sodium-potassium pump.

Question 36

What does it mean if the neurone is 'at rest'?

Answer 36

It is not exposed to a stimulus.

Question 37

Why is the establishment of a resting potential important for neurones?

Answer 37

It allows for neurones to respond to any nerve impulses arriving at its axon.

Question 38

A nerve impulse causes the inside of the axon to become ____ positively charged than the outside of the axon.

Answer 38

More

Question 39

What is a voltage-gated ion channel?

Answer 39

An ion channel that opens in response to the positive charge of a nerve impulse.

Question 40

When a nerve impulse appears next to a voltage-gated ion channel, it causes the inside of the axon to become _____ positively charged.

Answer 40

more

Question 41

Explain the establishment of an action potential:

Answer 41

- The outside of an axon is more positive than the inside because there are more sodium and potassium ions outside. - A nerve impulse will enter the inside of an axon and make it slightly more positively charged. - This causes some voltage-gated sodium channels to open, allowing for some sodium ions to diffuse into the inside of the axon. - The movement of sodium ions makes the inside even more positive, allowing for even more voltage-gated sodium channels to open, and more sodium ions to diffuse inside the axon. - The inside of the axon will become more positively charged than outside the axon - A high number of sodium ions inside the axon will allow it to reach its action potential.

Question 42

When is an action potential reached?

Answer 42

When the inside of an axon has reached its maximum positive charge.

Question 43

What is hyperpolarisation?

Answer 43

when the inside of an axon reaches its minimum positive charge

Question 44

How is a resting potential REestablished?

Answer 44

- Voltage-gated sodium channels close which reduces the number of sodium ions diffusing into the axon. - Voltage-gated potassium channels open, allowing potassium ions to diffuse out of the axon, causing the overall charge inside the axon to become less positive. - The voltage-gated potassium channels remain open, allowing even more potassium ions to diffuse out of the axon, causing the overall charge inside of the axon to become temporarily even less positive (hyperpolarisation). - Sodium ions diffuse into the axon through sodium ion channels down their electrochemical gradient. - The sodium-potassium pump restores the electrochemical gradients of sodium and potassium ions by actively transporting 3 sodium ions out of the axon, and 2 potassium ions into the axon. - The inside of the axon is less positive than outside of the axon.