6.5 Neurons and Synapsis

Question 1

what are neurons?

Answer 1

specialised cells that transmit electrical impulses

Question 2

what are the most important 4 components of neurons?

Answer 2

• dendrites - short-branched fibres that convert chemical information from other neurons to receptor cells into electrical signals
• axon - elongated fibre that transmits electrical signals to terminal regions for communication w/ neurons or effectors
• soma - cell body containing nucleus and organelle where essential metabolic processes occur to maintain cell survival
• myelin sheath - improves conduction speed electrical impulse along axon (require additional space and energy)

Question 3

how do neurons generate and conduct electrical signal?

Answer 3

• pump charged ions (Na+ and K+) across the membrane
• the unequal distribution of ions on different sides of the membrane creates a charge difference -> membrane potential

Question 4

what is a resting potential?

Answer 4

difference in charge across the membrane when a neuron is not firing
(typically more negative)

Question 5

how is the maintenance of a resting potential occur? (5)

Answer 5

• (active process) controlled by sodium-potassium pumps, transmembrane protein that actively exchanges sodium and potassium ions
• it expels 3Na+ for every 2K+
• created an electrochemical gradient where the cell interior is negative compared to extracellular environment (more +tive ions outside)
• exchange of sodium and potassium ions requires the hydrolysis of ATP

Question 6

what are the 3 stages which action potential occurs?

Answer 6

• depolarisation
• repolarisation
• refractory period

Question 7

what is the process of depolarisation? (4)

Answer 7

• depolarisation = sudden change in membrane potential from negative to positive
• in response to signal initiated at a dendrite, sodium channels open in membrane of axon
• as NA+ ions are more concentrated outside of neuron opening of sodium channels cause passive influx of sodium
• influx of sodium causes membrane potential to become more positive

Question 8

what is the process of repolarisation? (4)

Answer 8

• repolarisation = restoration of a membrane potential after depolarisation
• after an influx of sodium potassium channels open within membrane of axon
• as K+ ions are more concentrated inside the neuron, opening potassium channels cause passive efflux of potassium
• efflux of potassium causes membrane potential to return to more negative internal differential

Question 9

what is the process of the refractory period? (4)

Answer 9

• refractory period = period of time following a nerve impulse before neuron is able to fire again
• in normal resting state sodium ions are predominantly outside neuron and potassium ions mainly inside
• following depolarisation and repolarisaion the ionic distribution is reversed
• before neuron can fire again the resting potential must be restored via antiport action of sodium-potassium pump

Question 10

how does the opening of ions channels occur? (4)

Answer 10

• causes a change in membrane potential
• ion channels are voltage gates
• so, depolaristaion at one point fo axon triggers opening of ion channels in the next segment of axon
• causes depolarisation to spread along len gth of axon and unidirectional wave

Question 11

how are axon potentials generated according to the all-or-none principle? (3)

Answer 11

• an action potential of the same magnitude will always occur provided a minimum electrical stimulus is generated
• the minimum stimulus, threshold potential level is requires to open voltage-gated ion channels
• the threshold potential is not reached the action potential cannot be generated and the neuron will not fire

Question 12

how are threshold potentials triggered?

Answer 12

when the combined stimulation from dendrites exceed a minimum level of depolarisation