Neurones - action potential and resting potential
- Created by: tumblrgirl96
- Created on: 22-05-15 21:49
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- Neurones
- Resting potential
- -70 mV
- Inside of the axon is more negative than the outside
- Membrane is polarised
- 1
- Na+/K+ pump creates a conc. gradient across the membrane by pumping out Na+ ions and pumping in K+ ions
- Leads to a high conc. of Na+ outside of the axon and a high conc. of K+ inside the axon
- Helps balance charge across the cell surface membrane
- Pump is driven by energy supplied by the hydrolysis of ATP
- Leads to a high conc. of Na+ outside of the axon and a high conc. of K+ inside the axon
- Na+/K+ pump creates a conc. gradient across the membrane by pumping out Na+ ions and pumping in K+ ions
- 2
- K+ diffuses out of the cell (down the K+ conc. gradient through a K+ channel protein) making the outside of the membrane positive and the inside negative
- Membrane is permeable to K+ ions but impermeable to Na+ ions
- K+ diffuses out of the cell (down the K+ conc. gradient through a K+ channel protein) making the outside of the membrane positive and the inside negative
- 3
- Electrical gradient pulls K+ back into the cell (through the K+ protein channel)
- 4
- at -70 mV the two gradients counteract each other and there's no net movement of K+
- There's an electrochemical equilibrium for K+ and the membrane is polarised
- at -70 mV the two gradients counteract each other and there's no net movement of K+
- Inside of the axon is more negative than the outside
- -70 mV
- Action potential
- Caused by changes in the permeability of the cell surface membrane to Na+ and K+ due to the opening and closing of voltage dependent gated channels.
- 3 Stages
- 1
- Depolarisation
- Neurone is stimulated
- Some depolarisation occurs
- Na+ gate opens, some of the voltage dependent Na+ ion channels open
- Sodium flows in
- Depolarisation increases
- More gates open
- Causes further depolarisation
- Example of positive feedback
- change encourages further change
- Can't control the degree of depolarisation
- Action potential is either there or it's not
- All or nothing
- Action potential is either there or it's not
- Higher conc. of Na+ outside of the axon
- Sodium ions flow rapidly into the axon
- Positive charge builds up
- Potential difference = +40 mV
- Positive charge builds up
- Sodium ions flow rapidly into the axon
- Only occurs in the gaps between the myelin sheath (nodes of Ranvier)
- Neurone is stimulated
- Depolarisation
- 2
- Repolarisation
- Voltage-dependent Na+ channels close
- Na+ permeability reverts to low
- Voltage-dependent K+ channels open due to depolarisation
- K+ moves out of axon
- Inside of cell more negative than the outside
- Voltage-dependent Na+ channels close
- Repolarisation
- 3
- Restoring the resting potential
- Membrane highly permeable to K+ ions
- Hyperpolarisation
- potential difference more negative than resting potential
- Hyperpolarisation
- Resting potential re-established by closing the K+ channels
- K+ ions diffuse into the axon
- Refractory period
- 5 miliseconds
- Time taken to restore the resting potential
- Membrane highly permeable to K+ ions
- Restoring the resting potential
- 1
- 3 Stages
- Caused by changes in the permeability of the cell surface membrane to Na+ and K+ due to the opening and closing of voltage dependent gated channels.
- Untitled
- Resting potential
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