NEURONES
- Created by: miz99
- Created on: 05-12-17 16:24
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- Neurones
- In a neurone's resting state, there's a difference in PD between the inside and outside of the cell
- There are more positive ions outside the cell than inside. So the membrane is polarised- there's a difference in charge across it
- Voltage across the membrane when it's at rest is called the resting potential. This is around -70mV
- The resting potential is created and maintained by sodium potassium pumps and potassium ion channels in a neurone's membrane
- NaK pumps use active transport to move 3 Na+ ions out of the neurone for every 2 K+ ions moved in
- Potassium ion channels allow facilitated diffusion of potassium ions out of the neurone, down their concentration gradient
- The sodium potassium pumps move sodium ions out of the neurone but the membrane isn't permeable to sodium ions so they can't diffuse back in.
- This creates a sodium ion electrochemical gradient because there are more positive ions outside the cell than inside.
- + ions are moving in and out of the cell, + move out the cell than enter. Outside of the cell more + than inside
- This creates a sodium ion electrochemical gradient because there are more positive ions outside the cell than inside.
- The sodium potassium pump also moves potassium ions into the neurone
- When the cell's at rest, most potassium ion channels are open. This means the membrane is permeable to potassium ions so some diffuse back out through potassium ion channels.
- This creates a sodium ion electrochemical gradient because there are more positive ions outside the cell than inside.
- + ions are moving in and out of the cell, + move out the cell than enter. Outside of the cell more + than inside
- This creates a sodium ion electrochemical gradient because there are more positive ions outside the cell than inside.
- When the cell's at rest, most potassium ion channels are open. This means the membrane is permeable to potassium ions so some diffuse back out through potassium ion channels.
- The sodium potassium pumps move sodium ions out of the neurone but the membrane isn't permeable to sodium ions so they can't diffuse back in.
- Potassium ion channels allow facilitated diffusion of potassium ions out of the neurone, down their concentration gradient
- NaK pumps use active transport to move 3 Na+ ions out of the neurone for every 2 K+ ions moved in
- The resting potential is created and maintained by sodium potassium pumps and potassium ion channels in a neurone's membrane
- Voltage across the membrane when it's at rest is called the resting potential. This is around -70mV
- There are more positive ions outside the cell than inside. So the membrane is polarised- there's a difference in charge across it
- When neurone is stimulated, sodium ion channels open. If stimulus is big enough it'll trigger a rapid change in PD. Causes CM to become depolarised.
- Sodium ion channels are voltage gated- they only open when the PD reaches a certain voltage
- STIMULUS- this excites the neurone cell membrane, causing the sodium ion channels to open. The membrane becomes more permeable to sodium so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient
- This makes the inside of the neurone less negative
- DEPOLARISATION- if the potential difference reaches the threshold (-55) more sodium ion channels open. More sodium ions diffuse into the neurone
- REPOLARISATION- at a potential difference of 30mV the sodium ion channels close and potassium ion channels open. The membrane is more permeable to potassium to potassium ions diffuse out of the neurone down the potassium ion conc grad. This starts to get the membrane back to its resting pot.
- HYPERPOLARISATION- potassium ion channels are slow to close so there's a slight 'overshoot' where too many potassium ions diffuse out of the neurone. PD BECOMES more NEGATIVE than the RP
- RESTING POTENTIAL- the ion channels are reset. The sodium potassium pump returns the membrane back to its resting state by pumping sodium ions out and potassium ions in and maintains the resting potential until the membrane's excited by another stimulus
- REFRACTORY PERIOD- After an action pot, the neurone cell membrane can't be excited again straight away.
- This is because the ion channels are recovering and they can't be made to open. Sodium ion channels are closed during repolarisation and potassium ion channels are closed during hyperpolarisation.
- The ref period acts as a time delay between one action potential and the next. This makes sure that action potentials don't overlap and pass along as discrete impulses.
- The refractory period also means that there's a limit to the frequency at which the nerve impulse can be transmitted and that action potentials are unidirectional
- The ref period acts as a time delay between one action potential and the next. This makes sure that action potentials don't overlap and pass along as discrete impulses.
- This is because the ion channels are recovering and they can't be made to open. Sodium ion channels are closed during repolarisation and potassium ion channels are closed during hyperpolarisation.
- REFRACTORY PERIOD- After an action pot, the neurone cell membrane can't be excited again straight away.
- RESTING POTENTIAL- the ion channels are reset. The sodium potassium pump returns the membrane back to its resting state by pumping sodium ions out and potassium ions in and maintains the resting potential until the membrane's excited by another stimulus
- HYPERPOLARISATION- potassium ion channels are slow to close so there's a slight 'overshoot' where too many potassium ions diffuse out of the neurone. PD BECOMES more NEGATIVE than the RP
- REPOLARISATION- at a potential difference of 30mV the sodium ion channels close and potassium ion channels open. The membrane is more permeable to potassium to potassium ions diffuse out of the neurone down the potassium ion conc grad. This starts to get the membrane back to its resting pot.
- DEPOLARISATION- if the potential difference reaches the threshold (-55) more sodium ion channels open. More sodium ions diffuse into the neurone
- This makes the inside of the neurone less negative
- When an action potential happens, some of the sodium ions that enter the neurone diffuse sideways. This causes sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part. This causes a wave of depolarisation to travel along the neurone
- The wave moves away from the parts of the membrane in the ref period because these parts can't fire an action potential
- Once the threshold is reached, an action potential will always fire with the same change in voltage no matter how big the stimulus is
- A bigger stimulus won't cause a bigger action potential but it will cause them to fire more frequently
- Once the threshold is reached, an action potential will always fire with the same change in voltage no matter how big the stimulus is
- The wave moves away from the parts of the membrane in the ref period because these parts can't fire an action potential
- STIMULUS- this excites the neurone cell membrane, causing the sodium ion channels to open. The membrane becomes more permeable to sodium so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient
- Sodium ion channels are voltage gated- they only open when the PD reaches a certain voltage
- In a neurone's resting state, there's a difference in PD between the inside and outside of the cell
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