6.5 Neurons and Synapses

Question 1

What are the sections of a neuron?

Answer 1

Dendrites
Axon
Soma

Question 2

What is a soma?

Answer 2

Neuron cell body containing the nucleus, organelles, where essential metabolic process occur to maintain cell survival

Question 3

What may surround the axon?

Answer 3

Myelin sheath

Question 4

Define resting potential

Answer 4

The difference in charge across the membrane when a neuron is not firing
Usually, the inside of the neuron is more negative than the outside (approximately –70 mV)

Question 5

How is resting potential maintained?

Answer 5

Actively controlled by the sodium potassium pumps
3 Na+ expelled and 2K+ admitted (some of which will leak back out)
Creates an electrochemical gradient where the interior is relatively more negative

Question 6

Define active potential

Answer 6

Rapid changes in charge across the membrane that occur when a neuron is firing

Question 7

What are the three stages of action potential?

Answer 7

Depolarisation
Repolarisation
Refractory period

Question 8

What occurs during depolarisation?

Answer 8

In response to a signal from the dendrite Na+ channels open causing an influx and causing membrane potential to become positive

Question 9

What occurs during repolarisation?

Answer 9

The potassium channels open causing a passive efflux of potassium causing cell potential to become negative again

Question 10

What occurs during the refractory period?

Answer 10

Resting potential is actively restored so the neuron can fire again

Question 11

How does a nerve impulse travel down an axon?

Answer 11

Channels in the axon are voltage gated so depolarisation happens in segments down the axon

Question 12

What is the threshold potential?

Answer 12

The minimum level needed to open voltage gated ion channels (~-55mV_

Question 13

What will a stronger electrical signal cause in nerve impulses?

Answer 13

Assuming the threshold limit was reached on each occasion, a stronger impulse does not change the electrical signal generated

Question 14

What does an oscilloscope measure?

Answer 14

Membrane potential over time

Question 15

What is the advantage of myelination?

Answer 15

Improves the speed of electrical transmission

Question 16

What is the disadvantage of myelination?

Answer 16

Takes up significant space

Question 17

What is the difference between grey and white matter?

Answer 17

Grey matter does not have myelination

Question 18

Describe the chemical transfer across a synaptic gap

Answer 18

AP reaches the axon terminal triggering Ca2+ channels to open
Ca2+ diffuses in and promotes neurotransmitter containing vesicles to bind with the cell membrane (exocytosis)
Neurotransmitters bind to receptors in the post synaptic membrane and open ligand-gated channels
This generates an electrical impulse in the post synaptic neuron

Question 19

What happens to neurotransmitter released in the synapse?

Answer 19

Either recycled or degraded

Question 20

What is a graded potential?

Answer 20

Changes in membrane potential that vary in size

Question 21

What are the two types of neurotransmitter?

Answer 21

Excitatory
Inhibitory

Question 22

What do excitatory neurons cause?

Answer 22

Opening ligand-gated Na+ or Ca2+ channels (depolarisation)

Question 23

What do inhibitory neurons cause?

Answer 23

Opening ligand-gated K+ or Cl- channels (hyperpolarisation)

Question 24

Which cells produce Myelin?

Answer 24

Glial cells
Schwann in the PNS
Oligodendrocytes in the CNS

Question 25

Via which mechanism do myelin sheaths increase speed of electrical transmission?

Answer 25

Saltatory conduction

Question 26

What are the nodes of Ranvier

Answer 26

The gaps between myelin sheaths