3.5.2 - Coordination

Question 1

Myelin sheath definition

Answer 1

Covers the axon and is made up of membranes of the Schwann cells

Question 2

Do myelinated neurones transmit nerve impulses faster or slower than unmyelinated neurones?

Answer 2

Faster, because myelin sheath acts like an electrical insulator, whereby the action potential is prevented from occurring

Question 3

Nodes of Ranvier definition

Answer 3

The gaps in an axon, where there is no myelin sheath

Question 4

Schwann cells definition

Answer 4

They surround the axon, protecting it and providing electrical insinuation. They wrap round the axon many times, so layers of membrane build up around

Question 5

Sensory neurone function

Answer 5

Transmit nerve impulses from a receptor to a relay neurone. They have a dendron that carries the impulse towards the cell body and an axon that carries it away

Question 6

Motor neurone function

Answer 6

Transmit nerve impulses from a relay neurone to an effector (E.G. Gland or muscle). They have a long axon and many short dentrites

Question 7

Dendron definition

Answer 7

Small extensions of the cell body which subdivide into dentrites, that carry nerve impulses towards the cell body

Question 8

Axon definition

Answer 8

A single long fibre that carries the nerve impulses away from the cell body

Question 9

Differences between sensory/ motor neurones?

Answer 9

Sensory neurones have the cell body in the middle, motor neurones have it at the end
Sensory neurones take the electrical impulse from the receptors to the CNS, motor take it from the CNS to the effector

Question 10

Nerve impulse definition

Answer 10

Self-propagating wave of electrical disturbance that travels along the surface of an axon membrane

Question 11

Resting potential value?

Answer 11

70mV

Question 12

Resting potential basic description?

Answer 12

Na+ ions actively transported out of axon
K+ ions actively transported in
More Na ions leave than K ions enter = concentration gradient
Na wants to diffuse in, and K out
Na gates are closed so can’t, but K gates are open
K ions diffuse out of axon = potential difference
When reaches an equilibrium, the resting potential is constant

Question 13

Polarisation of an axon definition?

Answer 13

When the resting potential is achieved

Question 14

Action potential basic description?

Answer 14

Na gates closed, axon is at resting potential
Energy (from nerve impulse) causes Na gates to open, letting Na diffuse into he axon
When potential = 40mV, Na gates close, K gates open
K ions diffuse out, axon repolarises
Hyper polarisation occurs, K gates close and Na/K pump continues
Reaches resting potential again, the axon repolarises

Question 15

Unidirectional definition? What is unidirectional?

Answer 15

Synapses, can only travel one way (pre synaptic knob - post synaptic knob)

Question 16

Neurotransmitter definition?

Answer 16

Neurotransmitter = acetylcholine, is required for transmission across a synapse. Can only be made in the pre synaptic knob.

Question 17

Acetylcholine definition

Answer 17

One type of neurotransmitter, released by the pre synaptic knob of a neurone. Diffuses across the synapse, to bind with a receptor, passing the nerve impulse to another neurone

Question 18

Action potential definition

Answer 18

The change that occurs in the electrical charge across the membrane of an axon when it is stimulates and a nerve impulse is passing

Question 19

Acetylcholinesterase

Answer 19

The enzyme that hydrolysis acetylcholine (the neurotransmitter), making it inactive in the synapse

Question 20

Dendrite definition

Answer 20

A branched extension of the cell body of a neurone, which conducts electrical impulses towards the cell body

Question 21

Refractory period definition

Answer 21

Once an action potential has been created, there’s a period after when inward movement of Na ions is prevented because the sodium gates are closed. Impossible to generate an action potential

Question 22

Repolarisation definition

Answer 22

Return to the resting potential in the axon of the neurone after an action potential

Question 23

Generator potential definition

Answer 23

Depolarisation of the membrane of a receptor cell as a result of a stimulus

Question 24

Resting potential definition

Answer 24

The difference in electrical charge maintained across the membrane of the axon of a neurone when not stimulated

Question 25

Saltatory conduction definition

Answer 25

Propagation of a nerve impulse along a myelinated axon in which the action potential jumps from one node of Ranvier to another

Question 26

Factors affecting the speed of an action potential?

Answer 26

Myelin sheath
Diameter of the axon
Temperature

Question 27

Why bigger diameter of axon increases the speed of an action potential?

Answer 27

There is less leakage of ions, so membrane potentials are easier to maintain

Question 28

Purpose of the refractory period?

Answer 28

Ensures the actin potential goes 1 way only, can’t start in refractory region
Produces discrete impulses because a new action potential can’t be formed immediately
Limits the number of action potentials

Question 29

All or nothing principle

Answer 29

That any level of stimulus below the threshold value will not produce an action potential. Above the threshold value (no matter by how much) will produce 1 action potential

Question 30

How can an organism perceive the size of a stimulus?

Answer 30

The number of impulses passing in a given time

By having different neurones with different threshold values