The nerve impulse
- Created by: fahmida1998
- Created on: 06-10-16 15:22
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- THE NERVE IMPULSE
- RESTING POTENTIAL
- Movement of ions (Na+ & k+) , across axon membrane - controlled in + ways:
- 1} Phospholipid bilayer of axon plasma membrane prevents Na+ & K+ diffusing across
- = Inside axon -vely charged compared to outside - RESTING POTENTIAL
- RP- 50-90mv
- 65mv- humans
- Axon is POLARIZED
- POTENTIAL DIFF (diff in charges between inside & outside of axon) DUE TO:
- 1] Na+ actively transported OUT axon by SP PUMP
- 2] K+ actively transported INTO axon by SP PUMP
- 6] Most gates in channel that allow K+ OPEN But most for Na+ CLOSED
- 5] Na+ naturally diffuse back in axon & K+ out axon
- 3] Active transport of Na+ greater than K+ (3 Na+ out for ever 2 K+ in)
- 4] = + Na+ in tissue fluid around axon than in cytoplasm & + K+ in cytoplasm than tissue fluid
- = ELECTROCHEMICAL GRADIENT
- RP- 50-90mv
- = Inside axon -vely charged compared to outside - RESTING POTENTIAL
- 3} Channel proteins on bilayer-> have channel ions
- Some have gates -> open & close -> ions can move through facilitated diffusion
- Some always stay open -> ions freely move (facilitated diffusion)
- = Inside axon -vely charged compared to outside - RESTING POTENTIAL
- RP- 50-90mv
- 65mv- humans
- Axon is POLARIZED
- POTENTIAL DIFF (diff in charges between inside & outside of axon) DUE TO:
- 1] Na+ actively transported OUT axon by SP PUMP
- 2] K+ actively transported INTO axon by SP PUMP
- 6] Most gates in channel that allow K+ OPEN But most for Na+ CLOSED
- 5] Na+ naturally diffuse back in axon & K+ out axon
- 3] Active transport of Na+ greater than K+ (3 Na+ out for ever 2 K+ in)
- 4] = + Na+ in tissue fluid around axon than in cytoplasm & + K+ in cytoplasm than tissue fluid
- = ELECTROCHEMICAL GRADIENT
- RP- 50-90mv
- Some have gates -> open & close -> ions can move through facilitated diffusion
- 2} Sodium potassium pump
- A carrier protein -> actively transports K+ in axon & Na+ out
- 1} Phospholipid bilayer of axon plasma membrane prevents Na+ & K+ diffusing across
- Movement of ions (Na+ & k+) , across axon membrane - controlled in + ways:
- ACTION POTENTIAL
- When stimulus of sufficient size detected by receptor, its energy = TEMPORARY REVERSAL of charges either side of axon membrane
- If stimulus great enough, -ve charge inside membrane (-65mv) turns +ve ( ar. +40mv) - ACTION POTENTIAL
- Axon is DEPOLARISED
- Depolaristion -occurs d.t change of channel's shape so open/close, depending on voltage across membrane
- Therefore called voltage-gated channels
- Depolaristion -occurs d.t change of channel's shape so open/close, depending on voltage across membrane
- Axon is DEPOLARISED
- If stimulus great enough, -ve charge inside membrane (-65mv) turns +ve ( ar. +40mv) - ACTION POTENTIAL
- 1. At RP some K v-g channels open but Na v-g channels closed
- 2. Energy of stimulus = Na v-g channels to open -> Na+ diffuse into axon through these channels along ELECTROCHEMICAL GRADIENT.
- 3. As Na+ diffuse into axon + Na channels open = greater influx of Na+ via diffusion
- 4. Once action potential at ar +40mv -> v-g on Na+ channel close & v-g on K+ channel open
- 5. -> electrical gradient which prevented further outward movment of K+ now reversed = opening of + K+ channels
- 6. Outward diffusion of K+ = temporary overshoot of the electrical gradient, with inside A + -ve (relative to outside) than usual (=HYPERPOLARISATION)
- Closable gates on K+ channel now close & Na k pump again pump out Na+ & K+ in
- RP (-65mv) re-established
- Axon -> REPOLARIZED
- RP (-65mv) re-established
- Closable gates on K+ channel now close & Na k pump again pump out Na+ & K+ in
- Means + K+ diffuse out-> REPOLARISATION of axon
- 6. Outward diffusion of K+ = temporary overshoot of the electrical gradient, with inside A + -ve (relative to outside) than usual (=HYPERPOLARISATION)
- 5. -> electrical gradient which prevented further outward movment of K+ now reversed = opening of + K+ channels
- 4. Once action potential at ar +40mv -> v-g on Na+ channel close & v-g on K+ channel open
- Trigger reversal in PD across membrane d.t being +ve
- 3. As Na+ diffuse into axon + Na channels open = greater influx of Na+ via diffusion
- 2. Energy of stimulus = Na v-g channels to open -> Na+ diffuse into axon through these channels along ELECTROCHEMICAL GRADIENT.
- When stimulus of sufficient size detected by receptor, its energy = TEMPORARY REVERSAL of charges either side of axon membrane
- Self-propagating wave of elec activity -> travels along axon membrane
- Temporary reversal of the elec Potential Difference across axon membrane
- Reversal is between 2 states: RP & AP
- RESTING POTENTIAL
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