Neuron: Difference between revisions

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==Propagation of action potentials==

All neurones are electrically excitable, maintaining voltage gradients across their membranes by means of metabolically driven ion pumps, which combine with ion channels embedded in the membrane to generate intracellular-versus-extracellular concentration differences of ions such as sodium, potassium, chloride, and calcium. Changes in the cross-membrane voltage can alter the function of voltage-dependent ion channels. If the voltage changes by a large enough amount, an "all-or-nothing" electrochemical pulse called an action potential is generated, which travels rapidly along the cell's axon, and activates synaptic connections with other cells when it arrives.

All neurones are electrically excitable, maintaining voltage gradients across their membranes by means of metabolically driven ion pumps which combine with ion channels embedded in the membrane to generate intracellular-versus-extracellular concentration differences of ions such as sodium, potassium, chloride, and calcium. Changes in the cross-membrane voltage can alter the function of voltage-dependent ion channels. If the voltage changes by a large enough amount, an "all-or-nothing" electrochemical pulse called an action potential is generated which travels rapidly along the cell's axon, and activates synaptic connections with other cells when it arrives.

A nerve impulse is a self-propagating wave of electrical disturbance that travels along the surface of the axon membrane. This electrical disturbance ~~comprises~~ 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).

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.

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 ==Propagation of action potentials==
-All neurones are electrically excitable, maintaining voltage gradients across their membranes by means of metabolically driven ion pumps, which combine with ion channels embedded in the membrane to generate intracellular-versus-extracellular concentration differences of ions such as sodium, potassium, chloride, and calcium. Changes in the cross-membrane voltage can alter the function of voltage-dependent ion channels. If the voltage changes by a large enough amount, an "all-or-nothing" electrochemical pulse called an action potential is generated, which travels rapidly along the cell's axon, and activates synaptic connections with other cells when it arrives.
+All neurones are electrically excitable, maintaining voltage gradients across their membranes by means of metabolically driven ion pumps which combine with ion channels embedded in the membrane to generate intracellular-versus-extracellular concentration differences of ions such as sodium, potassium, chloride, and calcium. Changes in the cross-membrane voltage can alter the function of voltage-dependent ion channels. If the voltage changes by a large enough amount, an "all-or-nothing" electrochemical pulse called an action potential is generated which travels rapidly along the cell's axon, and activates synaptic connections with other cells when it arrives.
-A nerve impulse is a self-propagating wave of electrical disturbance that travels along the surface of the axon membrane. This electrical disturbance comprises 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).
+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.