Membrane potentials. Threshold for excitation and acute local potentials. Nerve action potential.

Question 1

threshold for excitation - definition

Answer 1

• minimum value of depolarisation for cell to get excited enough to generate AP
• most neurones is around -55mV

Question 2

threshold for excitation - step 1

Answer 2

resting membrane potential

• neurone is at rest
• around -70mV
• unequal distribution of na+/k+ ions
• selective permeability to these ions

Question 3

threshold for excitation - step 2

Answer 3

initiation of action potential

• AP travels down neurone along axon
• binds to pre-synaptic terminal membrane to begin process

Question 4

threshold for excitation - step 3

Answer 4

depolarisation

• voltage gated sodium ion channels open
• influx of na+ causing inside making MP -55mv

Question 5

threshold for excitation - step 4

Answer 5

repolarisation

voltgate gated na+ channels close, reached peak value of +30mv allowing for AP

voltage gated potassium channels open,
efflux of k+ making inside more negative

Question 6

threshold for excitation - step 5

Answer 6

hyperpolarisation

overshooting of k+ ions making inside more negative

Question 7

threshold for excitation - step 6

Answer 7

resting membrane potential

• na+/k+-ATPase pump closes ion channels
• value back to -70mv

Question 8

threshold for excitation - characteristic 1

Answer 8

all or nothing principle

= threshold must be reached for AP to occur

Question 9

threshold for excitation - characteristic 2

Answer 9

responds to external environment stimuli to maintain homeostasis

Question 10

threshold for excitation - characteristic 3

Answer 10

rapid communication between nerve/ muscle cells

Question 11

acute local potential - definition

Answer 11

• local + transient change in membrane potential due to stimulus
• depolarisation - opening na+ channels = making inside more positive
• hyperpolarisation - opening k+ channels = making inside more negative

Question 12

acute local potential - characteristic 1

Answer 12

short term response

Question 13

acute local potential - characteristic 2

Answer 13

does not require threshold to occur

Question 14

acute local potential - characteristic 3

Answer 14

graded = stronger stimulus = stronger change in MP

Question 15

nerve action potential - definition

Answer 15

rapid + temporary changes in membrane potential along axon of neurone

Question 16

nerve action potential - phase 1

Answer 16

resting membrane potential

• the neurone is at rest meaning no ions moving in or out of cell
• resting membrane potential of neurone is -70mV
• due to unequal distribution of ions
• due to selective permeability to these ions

Question 17

nerve action potential - phase 2

Answer 17

initiation of action potential

• neurotransmitter binds to cell membrane receptor
• resting potential -70mV to critical threshold -55mV

Question 18

nerve action potential - phase 3

Answer 18

depolarisation

voltage gated sodium channels open + sodium ions enter due to electrochemical gradient

value inside = +30mV

Question 19

nerve action potential - phase 4

Answer 19

repolarisation

sodium has reached peak value so now voltage sodium channel close

voltage gated potassium channels open + potassium ions exit

Question 20

nerve action potential - phase 5

Answer 20

hyperpolarisation

voltage potassium ions remain inside longe than necessary making MP more negative

Question 21

nerve action potential - phase 6

Answer 21

resting state

sodium-potassium pump closes ion channels

RMP restored to -70mv

Question 22

nerve action potential - characteristic 1

Answer 22

absolute refractory period

Question 23

nerve action potential - characteristic 2

Answer 23

relative refractory period

Question 24

nerve action potential - characteristic 3

Answer 24

propagation

= movement of AP from axon to synapatic terminal

• influx of sodium makes MP more positive
• depolarises adjacent cell membrane
• voltage gated sodium ion channels to open