Flashcards in 5.1 Nervous transmission & potentials Deck (36):
what is potential difference? what is it measured in?
difference in electrical charge across the plasma membrane, measured in millivolts
what is the normal resting state of an axon called? what is the p.d. in this state?
in resting state what is the membrane said to be?
when does an action potential occur?
when the p.d across an axon is temporarily reversed
when the action potential/nerve impulse occurs what is the p.d of the membrane and what is the membrane said to be?
when is the axon in resting potential?
when no impulse is present
when is there an action potential?
when an impulse is being transmitted
1. when a neurone has resting potential what are open and what are closed?
some potassium channels are open but voltage gated sodium ion channels are closed
2.a what does the energy of the stimulus trigger? what does this do to the membrane?
some voltage gated sodium ion channels to open
membrane more permeable to sodium ions
2.b what do sodium ions diffuse down? what does this make the axon?
an electrochemical gradient
make inside axon less negative
3. as some channels open sodium diffuses in causing a change in charge, what does this do?
causes more voltage gated sodium ion channels to open allowing more sodium in (POSITIVE FEEDBACK)
4. When the p.d reached +40mv what happens to the channels?
voltage gated sodium ion channels close
voltage gated potassium ion channels open
axon more permeable to potassium ions
5.a after the potassium channels open, what happens to the potassium ions? what does this result in?
potassium ions diffuse out of axon down electrochemical gradient
inside axon more negative
5.b inside of the axon becomes more negative than resting, what is this called?
6. voltage gated potassium ion channels close, what does the sodium potassium pump cause? what happens to the potential of the axon?
3 sodium ions out
2 potassium in
returns to resting potential
For an action potential to be generates, the stimulus must be greater than what?
the threshold value
what would cause a stimulus to be below the threshold value?
insufficient numbers of sodium channels open
what does insufficient numbers of open sodium channels prevent?
full depolarisation of the axon
once the threshold value is reached what is generated?
the action potential
regardless of the strength of the stimuli what is the action potential always?
the same size
what does the size of the stimuli affect?
the number of action potentials generated in a given time.
Larger stimulus = more frequently action potentials are generated
what is the cause of depolarisation? what does it cause the axon to become?
influx of sodium ions into the axon as energy of stimulus opens voltage gated sodium ion channels
causes the axon to be positively charged
what is repolarisation?
axon membrane p.d going from positive to negative resulting in resting potential
what does hyperpolarisation involve?
axon becoming more negative than its resting state due to potassium ions diffusing out
what is the refractory period?
the period of time when the axon can not be excited again
if we didn't have the refractory period what could happen?
action potential could be initiated backwards
action potentials could overlap
1. what does normal resting state allow for in the axon?
an action potential to be generated
2. when does an absolute refractory period occur? what can not happen?
after an action potential has been generated.
another impulse can not be produced regardless of the strength of the stimuli
3. when can an action potential be generated?
in the relative refractory period, only if the stimulus is stronger than the normal threshold value
4. what is the normal resting state?
after refractory period when the axon returns to resting, its possible for a further action potential to be generated
what does the myelinated sheath do?
insulates the axon making the action potential move faster
what do ion channels at the nodes of ranvier allow for?
the movement of sodium and potassium ions across the membrane at these points an action potential can be generated
when the action potential moves from node to node what is it referred to as?
how does the diameter of the axon affect the speed of the impulse?
the greater the diameter of the axon the faster the impulse
axons with a small diameter have a small sa:v ratio what does this cause?
large amount of ions leaking out of the axon making it harder to initiate an action potential