6.2 - Nervous Coordination

Question 1

Do unmyelinated nerve fibres contain nodes of Ranvier?

Answer 1

No

Question 2

What is the speed of transmission in myelinated nerve fibers?

Answer 2

High speed of transmission

Question 3

What is the speed of transmission in unmyelinated nerve fibers?

Answer 3

Low speed of transmission

Question 4

Where are myelinated nerve fibers located?

Answer 4

Central and peripheral nervous system

Question 5

Where are unmyelinated nerve fibers located?

Answer 5

In the central and peripheral nervous system in the group C nerve fibers.

Question 6

What is impulse conduction like in myelinated nerve fibers?

Answer 6

Do not lose the impulse during conduction.

Question 7

What is impulse conduction like in myelinated nerve fibers?

Answer 7

Can lose the nerve impulse during conduction.

Question 8

What is the length of myelinated axons?

Answer 8

Long

Question 9

What is the length of unmyelinated axons?

Answer 9

Short

Question 10

What is the myelin?

Answer 10

Lipid substance produced by Schwann cells

Question 11

What are Schwann cells?

Answer 11

Special cells that create myelin in the peripheral nervous system

Question 12

What are the nodes of Ranvier?

Answer 12

Gaps in myelin sheath with sodium channels

Question 13

What is saltatory conduction?

Answer 13

When the impulse ‘jumps’ from one node of Ranvier to the next, resulting in rapid conduction.

Question 14

Do myelinated nerve fibres contain nodes of Ranvier?

Answer 14

Yes

Question 15

What do neurones coordinate?

Answer 15

Neurones coordinate the activities of sensory receptors and effectors

Question 16

What is the sheath in a myelinated motor neurone made from?

Answer 16

The sheath is made up of myelin made by specialised Schwaan cells, sheath is made when Schwaan cells wrap themselves around the axon along its length.

Question 17

What are Schwann cells?

Answer 17

Special cells that create myelin in the peripheral nervous system

Question 18

What are the nodes of ranvier?

Answer 18

Gaps in myelin sheath with sodium channels

Question 19

What is saltatory conduction?

Answer 19

When the impulse ‘jumps’ from one node of Ranvier to the next, resulting in rapid conduction.

Question 20

What is the axon of a myelinated motor neurone insulated by?

Answer 20

A fatty sheath with small uninsulated sections along its length (nodes of ranvier.)

Question 21

In what 3 ways are motor neurones adapted to their function?

Answer 21

Motor neurones have:
1) A large cell body at one end, that lies within the spinal cord or brain.
2) A nucleus that is always in its cell body.
3) Many highly branched dendrites extending from the cell body, providing a large surface area for the axon terminals of other neurones.

Question 22

What is the resting potential?

Answer 22

Resting potential is the potential difference across the axon membrane and this keeps the neurone in a state of readiness. The value is -70mV

Question 23

What is the potential difference caused by?

Answer 23

Potential difference is due to an unequal distribution of charge on either side of a plasma membrane. Fluid on the inside of the axon is negative compared to the outside.

Question 24

How is a resting potential established?

Answer 24

1) Resting potential is maintained by a sodium potassium pump, involving active transport and the use of ATP.

2) The pump moves 2K+ in and 3Na+ ions out.

3) This movement of ions creates an electrochemical gradient and results in K+ diffusing out and Na+ diffusing in, however because the membrane is more permeable to K+, more are moved out resulting in a negative resting potential of -70mV.

Question 25

How is the membrane more permable to K+ than Na+?

Answer 25

1) The membrane contains more K+ ion channels than Na+ ion channels. 2) K+ ion channels are almost always open but Na+ channels are closed and open when a high enough voltage is reached.

Question 26

What is an action potential?

Answer 26

An action potential is when the neurone's voltage increases beyond a set point from the resting potential and generates a nervous impulse.

Question 27

What is depolarisation?

Answer 27

Process of sodium influx causing axon activation

Question 28

What are the 5 stages of the generation of an action potential?

Answer 28

1) Detection of stimulus. 2) Depolarisation. 3) Repolarisation. 4) Hyperpolarisation. 5) Resting State

Question 29

What happens in depolarisation in the stages leading to the generation of an action potential?

Answer 29

1) The excitation of the neurone cell causes the Na+ channels to open, making it more permeable to Na+ ions. 2)Na+ diffuse into the axon down their electrochemical gradient, making inside the axon less negative (-55mV) 3) When the threshold of -55mV is reached, even more Na+ channels open eventually giving a potential difference of +40mV.

Question 30

What happens in repolarisation in the stages leading to the generation of an action potential?

Answer 30

1) Sodium channels close and potassium ions open. 2) The potassium ions diffuse out of the neurone down the concentration gradient and eventually the resting potential is restored.

Question 31

What happens in hyperpolarisation in the stages leading to the generation of an action potential?

Answer 31

The closing of the potassium ion channels is slightly delayed which causes the potential of the neurone to decrease below the resting potential of the neurone to decrease below the resting potential, to around -80mV. This causes the refractory period.

Question 32

How is the resting state established after the generation of an action potential?

Answer 32

The resting potential is achieved with the help of the sodium potassium pump which returns the potential difference to -70mV.

Question 33

What is the refractory period?

Answer 33

When the membrane can't be stimulated because Na+ channels are recovering and can't be opened.

Question 34

Why is the refractory period important?

Answer 34

1) Ensures that no action potentials overlap. 2) Ensures that action potentials travel in one direction. 3) it limits the number of impulse transmission.

Question 35

What is the all-or-nothing principle?

Answer 35

If the depolarisation does not exceed -55mV then an action potential and the impulse are not produced (nothing). Any stimulus that does trigger depolarisation to -55mV will always peak at the same maximum voltage (all).

Question 36

How does myelination and saltatory conduction affect the speed of conductance?

Answer 36

Schwann cells form the myelin sheath which is a lipid and does not allow charged ions or the impulse to pass through it therefore increasing the speed on conductance. Action potential moves in saltatory conduction which means the action potential travels along the axon faster as an action potential doesn't need to be generated along the entire length - only at the nodes of Ranvier

Question 37

How does axon diameter affect the speed of conductance along a motor neurone?

Answer 37

With a wider diameter the speed of conductance increases. A wider diameter means that there is less leakage of ions and therefore action potentials travel faster.

Question 38

How does temperature affect the speed of conductance along a motor neurone?

Answer 38

A higher temperature increases the speed conductance as the ions diffuse faster and the enzymes involved in respiration work faster therefore there is more ATP for active transport in the Na+ and K+ pump.

Question 39

What are three characteristics of a myelinated motor neurone?

Answer 39

1) Neurones coordinate the activities of sensory receptors and effectors. 2) The sheath is made of myelin made by specialised Schwaan cells, made when Schwaan cells wrap themselves around the axon along its length. 3) The axon of a myelinated motor neurone is insulated by a fatty sheath with small uninsulated sections along its length (nodes of Ranvier).