Nervous System: The Resting Potential | A-level Biology | OCR, AQA, Edexcel
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Nervous System: The Resting Potential
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The key points covered of this video include:
1. Potential Difference in Neurones
2. The Sodium-Potassium Pump
3. Removal of Potassium Ions
4. Organic Anions
Potential Difference in Neurones
Neurones have a negative resting potential across their cell membrane. This is because the outside of the neurones has more positive charge than inside. This means that if we were to take a negative ion, it would require energy to make it enter the cell. We call the energy change in negative ions as they move from outside to inside the potential difference. The resting potential is the potential difference across the membrane while the neurone is at rest. Similarly, a positive ion would gain energy by passing the membrane and entering the cell. This is because opposite charges attract and similar charges repel each other. A negative resting potential is only possible when the outside of the cell is more positively charged than the inside. In this case, positive ions are repelled from the outside and attracted towards the inside. We measure the resting potential of neurones in millivolts (mV) and it is about -60mV.
The Sodium-Potassium Pump
The resting potential in neurones is maintained through keeping more positive ions outside the cell than inside. This is done through the action of the sodium-potassium pump. The sodium-potassium pump uses ATP to pump three sodium ions out of the cell and two potassium ions into the cell. This results in a net loss of 1 positive charge from the cell each time. This results in a neurone with more positive charge outside the cell than inside creating a negative resting potential.
Removal of Potassium Ions
The sodium-potassium pump creates a negative resting potential, but it also changes the concentration of ions inside and outside the cell. It results in a high potassium ion concentration inside the cell, and a high sodium ion concentration outside the cell. The membrane of neurones is permeable to potassium ions through potassium channels, but not to sodium. There are two types of gradient acting on the potassium ions: an electrical gradient, and a concentration gradient. The electrical gradient pulls potassium ions into the cell and the concentration gradient pulls them out of the cell. The concentration gradient has the stronger effect, and potassium ions leave the cell. Because even more positive charge has left the cell, the resting potential of the neurone decreases further.
Organic Anions
The last component which contributes to the negative resting potential of neurones are organic anions. These are negatively charged molecules that sit inside the neurone. They cannot leave, and so make the neurone more negative inside.
Summary
Neurones have a negative resting potential across their cell membranes
This resting potential is set up by the action of sodium-potassium pumps which pump more sodium ions out than potassium ions in
Potassium ions diffuse out of the cell down its concentration gradient
Organic anions reduce the resting potential further
SnapRevise is the UK’s leading A-level and GCSE revision & exam preparation resource offering comprehensive video courses created by A* Oxbridge tutors. Our courses are designed around the OCR, AQA, SNAB, Edexcel B, WJEC, CIE and IAL exam boards, concisely covering all the important concepts required by each specification. In addition to all the content videos, our courses include hundreds of exam question videos, where we show you how to tackle questions and walk you through step by step how to score full marks.
Sign up today and together, let’s make A-level Biology a walk in the park!
The key points covered of this video include:
1. Potential Difference in Neurones
2. The Sodium-Potassium Pump
3. Removal of Potassium Ions
4. Organic Anions
Potential Difference in Neurones
Neurones have a negative resting potential across their cell membrane. This is because the outside of the neurones has more positive charge than inside. This means that if we were to take a negative ion, it would require energy to make it enter the cell. We call the energy change in negative ions as they move from outside to inside the potential difference. The resting potential is the potential difference across the membrane while the neurone is at rest. Similarly, a positive ion would gain energy by passing the membrane and entering the cell. This is because opposite charges attract and similar charges repel each other. A negative resting potential is only possible when the outside of the cell is more positively charged than the inside. In this case, positive ions are repelled from the outside and attracted towards the inside. We measure the resting potential of neurones in millivolts (mV) and it is about -60mV.
The Sodium-Potassium Pump
The resting potential in neurones is maintained through keeping more positive ions outside the cell than inside. This is done through the action of the sodium-potassium pump. The sodium-potassium pump uses ATP to pump three sodium ions out of the cell and two potassium ions into the cell. This results in a net loss of 1 positive charge from the cell each time. This results in a neurone with more positive charge outside the cell than inside creating a negative resting potential.
Removal of Potassium Ions
The sodium-potassium pump creates a negative resting potential, but it also changes the concentration of ions inside and outside the cell. It results in a high potassium ion concentration inside the cell, and a high sodium ion concentration outside the cell. The membrane of neurones is permeable to potassium ions through potassium channels, but not to sodium. There are two types of gradient acting on the potassium ions: an electrical gradient, and a concentration gradient. The electrical gradient pulls potassium ions into the cell and the concentration gradient pulls them out of the cell. The concentration gradient has the stronger effect, and potassium ions leave the cell. Because even more positive charge has left the cell, the resting potential of the neurone decreases further.
Organic Anions
The last component which contributes to the negative resting potential of neurones are organic anions. These are negatively charged molecules that sit inside the neurone. They cannot leave, and so make the neurone more negative inside.
Summary
Neurones have a negative resting potential across their cell membranes
This resting potential is set up by the action of sodium-potassium pumps which pump more sodium ions out than potassium ions in
Potassium ions diffuse out of the cell down its concentration gradient
Organic anions reduce the resting potential further
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