Nervous Communication Flashcards
Role of sodium-potassium pump
Uses active transport to move 3Na+ out of neurone for every 2K+ moved in requiring ATP
What is a potassium ion channel
Channel proteins that allow facilitated diffusion of K+ out of neurone down their concen gradient
Describe what happens at resting potential
-neurone not being stimulated
-outside of neurones membrane positive charged compared to inside as more positive ions (3Na+) outside cell than inside (2K+)= membrane polarised with a voltage across the membrane of -70mV
-sodium-potassium pumps move Na+ out of neurone but membrane isn’t permeable to Na+ so cannot diffuse back in= creates sodium ion electrochemical gradient as more outside than inside cell
-sodium-potassium pumps move K+ into neurone but membrane is permeable to K+ so they diffuse back out through potassium ion channels so outside of cell positive charged compared to inside
What happens during action potential(when neurone being stimulated)
-stimulus excited neurone cell membrane causing sodium ion channels(voltage-gated) to open so membrane becomes more permeable to Na+ so it diffuses into neurone down Na+ electrochemical gradient making inside of neurone less negative
-if pd reaches threshold of -55mV depolarisation occurs and more sodium ion channels open so more Na+ diffuse into neurone
-at pd of +30mV, sodium ion channels close and potassium ion channels open(voltage gated), membrane more permeable to K+ and it diffuses out of neurone down potassium ion concen gradient which starts to get membrane back to it’s rp as positive leaving causing repolarisation
-hyperpolarisation occurs as slight overshoot where too much K+ diffuse out of neurone and pd becomes more negative than rp (less than -70mV)
-back to rp and ion channels reset, sodium-potassium pump returns membrane to rp and maintains until excited by another stimulus
What is the refractory period
Period of recovery when after an action potential the neurone cell membrane can’t be excited straight away because the ion channels are recovering and they can’t be made to open- sodium ion channels are closed during depolarisation and potassium ion channels are closed during hyperpolarisation, acts as time delay between one action potential and the next. Makes sure action potentials don’t overlap but pass along as discrete impulses and makes sure they are unidirectional
What is a wave of depolarisation
When during action potential some of the Na+ that enter the neurone diffuse sideways, causing sodium ion channels in next region of neurone to open and Na+ diffuse into that part causing wave of depolarisation to travel along the neurone, moves away from parts of membrane in the refractory period as these parts can’t fire an action potential
Why does action potential have higher conduction velocity in myelinated neurones
-Schwann cells insulate the neurone
-sodium ion channels are concentrated at the nodes of ranvier meaning depolarisation(when Na+ can get through the membrane) only happens here
-saltatory conduction—-> way in which action potential appears to jump from one node to the next
How does impulse travel along non-myelinated neurone
Impulse travels as a wave along the whole length of the axon membrane, slower than saltatory conduction
What are local currents
Movement of ions along neuron close to cell surface membrane to propagate nerve impulses along length of axon
