Nervous Impulses

Question 1

Describe a sensory neuron and its role

Answer 1

• Carry action potential from the sensory receptor to the CNS
• Long dendron
• Short axon

Question 2

Describe a relay neuron and its role

Answer 2

• Connects sensory and motor neurons
• Many short dendrites
• Short axons

Question 3

Describe a motor neuron and its role

Answer 3

• Carries action potential from the CNS to effectors
• Cell body is within CNS
• Long axon

Question 4

What are two examples of an effector?

Answer 4

• Muscle

- Glands

Question 5

What fraction of neurons are myelinated?

Answer 5

1/3

Question 6

What creates a myelin sheath and describe it?

Answer 6

Schwann cells and the sheath involves several layers of membrane and thin cytoplasm

Question 7

What are gaps in the myelin sheath called?

Answer 7

Nodes of ranvier

Question 8

What are the advantages of myelination?

Answer 8

• They can transmit AP more quickly
• They can carry impulses from sensory receptors, to the CNS and from CNS to effectors
• Carry signals over long distances
• Depolarisation only occurs at Nodes of Ranvier
• Rapid response by Saltatory conduction

Question 9

What is resting potential?

Answer 9

An electrical gradient across cell membrane when there is no action potential passing through

Question 10

How is resting potential established?

Answer 10

• -60mV inside cell compared to outside
• Na+ pumped out
• K+ pumped in
• Creates a potential difference

Question 11

How are nerve impulses generated?

Answer 11

• Na+ can move into the cell via voltage gated channels
• This cases the cell to depolarise
• Gated channels stimulated to open by synapse action
• Membrane becomes more permeable as channels open- Na + moves in
• Membrane depolarises, less negatively charged than outside

Question 12

What is threshold potential?

Answer 12

Enough Na + enter the cell to surpass the threshold. Threshold = -50mV

Question 13

What happens when threshold potential is reached?

Answer 13

Initiates a positive feedback loop. More Na+ channels open and the cells become more depolarised and action potential is established.

Question 14

What is the charge once action potential is established?

Answer 14

+40 mV

Question 15

What is the ‘All or Nothing’ principle?

Answer 15

The idea that action potential will not occur unless the threshold is surpassed

Question 16

What is the membrane potential of a neuron at resting state?

Answer 16

-70mV

Question 17

How are nerve impulses along a neuron?

Answer 17

• Once the impulse is established a current exists in the cytoplasm of the neuron
• The local depolarisation triggers neighbouring voltage-gated channels to open
• Action potential travels along the neuron.

Question 18

What is the refractory period?

Answer 18

• Immediately after the cell depolarises it repolarises
• Acts as a time delay so that action potentials don’t overlap and that they are unidirectional. This is where hyperpolarisation occurs. The original resting potential is restored

Question 19

What is hyperpolarisation?

Answer 19

When the potential difference overshoots because K+ ions are diffusing out of the neuron.

Question 20

What factors affect the speed of conduction?

Answer 20

• Myelination and saltatory conduction increase speed
• Axon diameter increases speed (less resistance)
• Higher temp increases speed of conduction.

Question 21

Why does the lack of a myelin sheath lead to slower responses?

Answer 21

• Depolarisation occurs at the length of the neurone more often
• No saltatory conduction