Neuron: Difference between revisions

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A nerve impulse is a self-propagating wave of electrical disturbance that travels along the surface of the axon membrane. This electrical disturbance is comprised of a temporary reversal of the electrical potential difference (not an electrical current). The axon is usually negatively charged compared to the outside of the axon; this is known as the resting potential and the value of which is usually around -65mV. When a stimulus is received, a reversal in electrical potential difference is caused, and this is known as the action potential (normally around +40mV).

===Mechanism of propagation of action potentials===

~~To begin with, the~~ inside of the axon is negatively charged compared with the outside of the axon. The change in potential difference that is needed to fire off an action potential is controlled by the movement of sodium and potassium ions (an ion is a positively or negatively charged molecule) in and out of the axon. This movement occurs via the action of ion pumps and channels. The ions cannot just diffuse in and out of the axon uncontrollably; this diffusion is prevented by a membrane around the axon. Periodically placed along the membrane are proteins that act as channels for ions to pass through. Sodium gated channels and potassium gated channels open and close to allow the ions to pass through only at specific times. Sodium-potassium pumps transport both Na+ and K+ in and out of the axon.

The inside of the axon is negatively charged compared with the outside of the axon. The change in potential difference that is needed to fire off an action potential is controlled by the movement of sodium and potassium ions (an ion is a positively or negatively charged molecule) in and out of the axon. This movement occurs via the action of ion pumps and channels. The ions cannot just diffuse in and out of the axon uncontrollably; this diffusion is prevented by a membrane around the axon. Periodically placed along the membrane are proteins that act as channels for ions to pass through. Sodium gated channels and potassium gated channels open and close to allow the ions to pass through only at specific times. Sodium-potassium pumps transport both Na+ and K+ in and out of the axon.

The inside of the axon starts at around -65mV less than the outside of the axon. An action potential is reached when the axon is at +40mV more than the outside of the axon. This value of +40mV is reached by the movement of sodium and potassium ions in and out of the axon. Sodium-potassium pumps transport 2K+ into the axon for every 3Na+ transported out of the axon. However, more sodium is removed from the axon compared to the potassium brought. This means the overall electronegativity is decreasing in the axon, and the axon is getting closer to reaching the potential difference of +40mV. Sodium ions then begin to diffuse back into the axon naturally, and potassium ions diffuse back out. At this stage however, potassium gated channels are open, whereas sodium gated channels are closed. This means the K+ can diffuse out faster than the Na+ can diffuse back into the axon. This increases the potential difference further between the inside and the outside of the axon.

The inside of the axon starts at around -65mV less than the outside of the axon. An action potential is reached when the axon is at +40mV more than the outside of the axon. This value of +40mV is reached by the movement of sodium and potassium ions in and out of the axon. Sodium-potassium pumps transport 2K+ into the axon for every 3Na+ transported out of the axon. However, more sodium is removed from the axon compared to the potassium brought. This means the overall electronegativity is decreasing in the axon, and the axon is getting closer to reaching the potential difference of +40mV. Sodium ions then begin to diffuse back into the axon naturally, and potassium ions diffuse back out. At this stage, however, potassium gated channels are open whereas sodium gated channels are closed. This means the K+ can diffuse out faster than the Na+ can diffuse back into the axon. This increases the potential difference further between the inside and the outside of the axon.

Once an action potential has been established, it “moves” along the axon in a neurone. The action potential does not move in a physical sense of the word; the reversal of electrical charge is instead reproduced at different points along the axon, in a “Mexican wave” effect. One point in an axon will become depolarised (depolarisation is a change in a cell’s membrane potential, making it more positive, or less negative), and this depolarisation is a stimulus for the next region of the axon to depolarise. As the next region depolarises, the previous region returns to normal and repolarises.

Once an action potential has been established, it “moves” along the axon in a neurone. The action potential does not move in a physical sense of the word; the reversal of electrical charge is instead reproduced at different points along the axon in a “Mexican wave” effect. One point in an axon will become depolarised (depolarisation is a change in a cell’s membrane potential, making it more positive or less negative), and this depolarisation is a stimulus for the next region of the axon to depolarise. As the next region depolarises, the previous region returns to normal and repolarises.

Eventually, the action potential will reach the end of an axon, known as a synaptic knob.

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 A nerve impulse is a self-propagating wave of electrical disturbance that travels along the surface of the axon membrane. This electrical disturbance is comprised of a temporary reversal of the electrical potential difference (not an electrical current). The axon is usually negatively charged compared to the outside of the axon; this is known as the resting potential and the value of which is usually around -65mV. When a stimulus is received, a reversal in electrical potential difference is caused, and this is known as the action potential (normally around +40mV).
 ===Mechanism of propagation of action potentials===
-To begin with, the inside of the axon is negatively charged compared with the outside of the axon. The change in potential difference that is needed to fire off an action potential is controlled by the movement of sodium and potassium ions (an ion is a positively or negatively charged molecule) in and out of the axon. This movement occurs via the action of ion pumps and channels. The ions cannot just diffuse in and out of the axon uncontrollably; this diffusion is prevented by a membrane around the axon. Periodically placed along the membrane are proteins that act as channels for ions to pass through. Sodium gated channels and potassium gated channels open and close to allow the ions to pass through only at specific times. Sodium-potassium pumps transport both Na+ and K+ in and out of the axon.
+The inside of the axon is negatively charged compared with the outside of the axon. The change in potential difference that is needed to fire off an action potential is controlled by the movement of sodium and potassium ions (an ion is a positively or negatively charged molecule) in and out of the axon. This movement occurs via the action of ion pumps and channels. The ions cannot just diffuse in and out of the axon uncontrollably; this diffusion is prevented by a membrane around the axon. Periodically placed along the membrane are proteins that act as channels for ions to pass through. Sodium gated channels and potassium gated channels open and close to allow the ions to pass through only at specific times. Sodium-potassium pumps transport both Na+ and K+ in and out of the axon.
-The inside of the axon starts at around -65mV less than the outside of the axon. An action potential is reached when the axon is at +40mV more than the outside of the axon. This value of +40mV is reached by the movement of sodium and potassium ions in and out of the axon. Sodium-potassium pumps transport 2K+ into the axon for every 3Na+ transported out of the axon. However, more sodium is removed from the axon compared to the potassium brought. This means the overall electronegativity is decreasing in the axon, and the axon is getting closer to reaching the potential difference of +40mV. Sodium ions then begin to diffuse back into the axon naturally, and potassium ions diffuse back out. At this stage however, potassium gated channels are open, whereas sodium gated channels are closed. This means the K+ can diffuse out faster than the Na+ can diffuse back into the axon. This increases the potential difference further between the inside and the outside of the axon.
+The inside of the axon starts at around -65mV less than the outside of the axon. An action potential is reached when the axon is at +40mV more than the outside of the axon. This value of +40mV is reached by the movement of sodium and potassium ions in and out of the axon. Sodium-potassium pumps transport 2K+ into the axon for every 3Na+ transported out of the axon. However, more sodium is removed from the axon compared to the potassium brought. This means the overall electronegativity is decreasing in the axon, and the axon is getting closer to reaching the potential difference of +40mV. Sodium ions then begin to diffuse back into the axon naturally, and potassium ions diffuse back out. At this stage, however, potassium gated channels are open whereas sodium gated channels are closed. This means the K+ can diffuse out faster than the Na+ can diffuse back into the axon. This increases the potential difference further between the inside and the outside of the axon.
-Once an action potential has been established, it “moves” along the axon in a neurone. The action potential does not move in a physical sense of the word; the reversal of electrical charge is instead reproduced at different points along the axon, in a “Mexican wave” effect. One point in an axon will become depolarised (depolarisation is a change in a cell’s membrane potential, making it more positive, or less negative), and this depolarisation is a stimulus for the next region of the axon to depolarise. As the next region depolarises, the previous region returns to normal and repolarises.
+Once an action potential has been established, it “moves” along the axon in a neurone. The action potential does not move in a physical sense of the word; the reversal of electrical charge is instead reproduced at different points along the axon in a “Mexican wave” effect. One point in an axon will become depolarised (depolarisation is a change in a cell’s membrane potential, making it more positive or less negative), and this depolarisation is a stimulus for the next region of the axon to depolarise. As the next region depolarises, the previous region returns to normal and repolarises.
 Eventually, the action potential will reach the end of an axon, known as a synaptic knob.