Action Potential Flashcards
explain the structure of the neuronal membrane
what ions are found in extracellular and intracellular
2 layers of lipid molecules
hydrophobic tails, hydrophilic head creating a partially impermeable barrier to ions and water soluble molecules cannot pass through
extracellular= CATIONS (+VE) sodium, ANIONS chloride intercellular= CATIONS potassium, ANIONS organic ions
what is diffusion
movement of ions down a concentration gradient of high to low concentration
what is electrostatic pressure?
force exerted by extraction or repulsion- charges of opposite attract
what does it mean to say neurons are polarised?
At rest they are -ve compared to extracellular fluid
-ve charge occurs if there are less +ve ions or more -ve ions inside the cell
What do ion channels do?
PASSIVE
selected ions rush down gradients of concertation and electrical potential. this is controlled by a gate which could be voltage or mechanical gates
what do ion pumps do?
CONSUME ENERGY- ACTIVE TRANSPORT
active transport is against gradient meaning it is much slower pumping
it is used to maintain or build gradients
Explain the movement of potassium ions
Diffusion= k+ is highly conc. inside the cell so k+ wants to move out of cell down concentration gradient- this occurs at rest as k+ leak channels allow k+ to leave the neuron down the conc. gradient meaning the cell becomes more -ve charged.
Electrostatic pressure= not a lot of k+ moves out
ions stop moving at equilibrium
Explain the movement of Chloride ions
Diffusion= cl- is highly conc. outside cell so cl- wants to move into cell.
Electrostatic pressure= inside cell is -ve charged so cl- wants to move out of cell due to the repel of same charges.
So net movement is for cl- to stay where it is
Explain the movement of Sodium ions
Diffusion= na+ is highly conc. outside cell so wants to move into cell
electrostatic pressure= inside is -ve charged so na+ wants to move into cell
BUT at rest there are few passive sodium leak channels so not much can move in.
Net force is that na+ moves into cell
What is the resting membrane potential?
2 forces act on ion. At rest membrane is permeable to k+ so mainly k+ move in but this stops at equilibrium.
The result is an unequal distribution of negative ions on the inside and outside
this difference of charge is -70mv which is the resting potential
What does the sodium potassium pump do?
Continues to push sodium out of neurone replacing it with potassium ions
pushes 3 sodium out and 2 potassium in- so more posisitve ions are being pumped out than in allowing the membrane potnetial to stay negative
this keeps the intracellular fluid negatively charged - allowing the cell to keep a conc. gradient and generate a resting potential
requires energy so is an active pump
EXPLAIN THE ACTION POTENTIAL-
- depolarisation- inside cell is more +ve charged so small amount of na+ move into cell making neuron less -ve charged (this is slightly depolarised). If the charge increases by +15mv so reaches -55mv it activates voltage gated channels and an action potnetial is made. channels that open include NA+ channels and k+ channels (Order is sodium channels open then close then potassium channels open)
- sodium channels become refractory at peak and close
- REPOLARISATION- voltage gated k+ channels open at around +40mv - these open channels allow outflow meaning inside cell becomes more -ve charged
- HYPERPOLARISATION- k+ channels are slow to close this causes an overshoot of efflux k+
- resetting potassium sodium pump- the pump moves 3 na+ out and 2+ in the cell. The pump keeps na+ conc. low in neuron and k+ also diffuse back in neurone thus re establishing the resting potential
where do action potentials get stimulated?
the axon hillock
