Nerve Impulses Flashcards
What happens when axon is at rest and what is it called
When axon is at rest (not transmitting an impulse) a potential difference of -70mV exists between inside and outside of axon.
-70mllivolts is called resting potential
What does it mean when the membrane is polarised
When membrane is polarised, it means that axon is at rest (at -70mV)
What is potassium channel protein
Potassium channel protein is a protein that can only move potassium.
What is the “cartwheel” structure in phospholipid bilayer
“Cartwheel” structure in phospholipid bilayer is sodium/potassium pump (used for active transport)
What is process of polarisation
Process of polarisation is:
1) Na+ are actively pumped out of axon
K+ are actively pumped into axon by sodium potassium pump
2)K+ diffuses through potassium channels (facilitated diffusion) out of cell. Outside of membrane is more positive (as it has lots of ions outside) so inside of membrane is more negative.
Membrane is impermeable to Na+ so can’t move in
3) outside of axon is positive relative to inside so electrical gradient will pull K+ back into cell
4)at -70mV potential difference the 2 gradients (steps 2 and 3) counteract each other and there is no more net movement of K+.
Membrane is polarised
Why do only potassium ions get pulled back into membrane
Only potassium ions get pulled back into membrane because membrane is highly permeable to potassium but almost impermeable to sodium.
Why do chloride ions leave cell
Chloride ions leave cell because organic anions are large and stay in cell, so chloride ions move out of cell to balance charge across cell membrane.
What is depolarisation and how is it achieved
Depolarisation is when membrane becomes less negative (more positive)
Achieved by influx of sodium ions when voltage gated Na+ channels open
What is repolarisation and how is it achieved
Repolarisation is when membrane becomes negative again.
Achieved by outflow of potassium ions of axon, potassium ion channels open to compensate for influx of sodium ions
What is hyperpolarisation and how is it achieved
Hyperpolarisation is when membrane becomes more negative than resting potential
Achieved by too many K+ions entering
What are voltage gated channels
Voltage gated channels are channels that open at a specific voltage
What is the process of generating action potential
Process of generating action potential is:
1) Resting potential is achieved by Na/K pump
2) initial depolarisation, some of voltage gated Na+ channels open, Na+ ions move into membrane.
3) As sodium ions enter axon, depolarisation increases so more gates open until threshold potential is reached
4) potential difference across membrane reaches 40mV (action potential)
5) after 0.5ms, Na+ voltage gated channels close. K+ ion channels open and K+ leaves axon causing repolarisation.
6) all voltage gated ion channels close, resting potential is restored by K+ moving out and Na/K pump
What is polarisation and how is it achieved
Polarisation is when inside of neurone is negative and outside is positive.
K+ions diffuse back in, Achieved by Na/K pump pumps out Na+ and pumps in K+
