topic 6 neurons/action potential Flashcards
are nerve cells polarised or depolarised at rest?
polarised
why is the inside of a neuron negative compared to the outside?
imbalance of sodium and potassium ions
what is the resting potential of a neuron?
-70mV
how is the resting potential maintained and generated?
by the sodium potassium pump
how is the inside of a neuron made negative compared to the outside?
sodium potassium pump moves sodium out, creating an electrochemical gradient. higher conc of sodium outside the membrane and the membrane is not permeable to sodium.
moves potassium ions into the axon, these can also move by faciliated diffusion. there are more potassium channels and these are mainly open, whereas sodium channels are mainly shut.
how many sodium ions are pumped out of the axon?
3
how many potassium ions are pumped into the axon?
2
what is needed for active transport to occur?
ATP
what does Na+ stand for?
sodium ion
what does K+ stand for?
potassium ion
what is an action potential?
when the neuron’s voltage increases beyond a set point, resulting in a nervous impulse
why does a neuron’s voltage increase/depolarisation occur?
membrane becomes more permeable to sodium
what happens in an action potential when a stimulus is detected?
excites the cell membrane of the neuron, which causes sodium ion channels to open
membrane becomes more permeable to sodium, so sodium ions diffuse into the neuron down the electrochemical gradient
inside of the neuron becomes less negative
what happens in an action potential during depolarisation?
potential differences reaches the threshold at around -55mV
more sodium ion channels open
more sodium ions rapidly diffuse into the neuron
what happens in an action potential during repolarisation?
potential difference of around 30mV
sodium channels close and potassium channels open
membrane becomes more permeable to potassium
potassium ions diffuse out of the neuron down the potassium ion concentration gradient
begins to return to resting potential
what happens in an action potential during hyperpolarisation?
potassium channels are slow to close
overshoot happens where too many potassium ions diffuse out of the neuron
potential difference becomes more negative than resting potential
how does an action potential go from hyperpolarisation to resting potential?
ion channels reset
sodium potassium pump returns membrane to resting potential
what is the ‘all or nothing’ principle?
there is a -55mV threshold
if a stimulus does not exceed this threshold then an action potential is not produced
bigger stimulus increases the frequency of action potentials
only respond to large enough stimuli to prevent someone becoming overwhelmed
what is the refractory period?
after the action potential is generated, the membrane enters the refractory period where it cannot be stimulated
sodium channels are recovering and cannot be opened
why is the refractory period important?
results in discrete impulses- no overlap allows separate action potentials to be processed
action potential travels in one direction- if it is spread in different directions a response is prevented
limits the number of impulse transmissions, prevents over reaction to stimuli and overwhelming the sense
what are waves of depolarisation?
action potential occurs
some sodium ions entering the neuron diffuse sideways
sodium ion channels in the next region of the neuron open
sodium ions diffuse into the next part of the neuron
wave of depolarisation travels along the neuron
wave moves away from parts of the neuron in the refractory period
what is the myelin sheath?
electrical insulator, made up of Schwann cells with Nodes of Ranvier
how can the myelin sheath act as an electrical insulator?
made of lipids so no charged ions can pass through
where are sodium ions concentrated?
at the Nodes of Ranvier
is an action potential quicker with myelinated or non-myelinated neurons?
myelinated
how does conduction occur in myelinated neurons?
depolarisation only happens at the Nodes of Ranvier
cytoplasm conducts enough electrical charge to depolarise the next node
impulse jumps, known as saltatory conduction
how does conduction occur in non-myelinated neurons?
slower
impulse is a wave along the axon membrane so there is depolarisation all along
has to generate an action potential along the whole length
what is an axon?
long fibre that conducts/carries nerve impulses
how does axon diameter impact speed of conduction?
bigger diameter means a quicker action potential
less resistance to flow of ions and depolarisation reaches other parts of the cell membrane faster
less leakage of ions
how does temperature impact speed of conduction?
speed of conduction increases as temperature increases
ions diffuse faster
enzymes involved in respiration are faster so more ATP produced for sodium-potassium pump
however if too high denatures
