Neural Impulse: Action Potential & Ion Channels

• An impulse can start when sensory nerve endings are simulated or when an impulse comes from another nerve.
• Afferent (sensory) nerve impulses travel to the brain and central nervous system (CNS).
• Efferent (motor) nerve impulses travel from the brain and CNS.
• Ion channels in the axon are voltage-gated.
• Depolarisation at one axon segment causes the ion channels in the next segment to open.
• Action potential travels along the axon as a wave of depolarisation.

Overview of Neural Impulse

• In a resting neuron, Na+ and K+ gates are closed, maintaining a polarized state.
• During action potential, an excitatory stimulus opens sodium channels, allowing Na+ ions to flow into the neuron.
• Subsequently, potassium channels open, allowing K+ ions to flow outward.
• Charge restoration involves the sodium-potassium pump, restoring the original ion distribution by pumping Na+ out and K+ in.
• Nerve impulses travel down the neuron.
• Nerves are not physically joined or connected.
• Synapse defines the point where a nerve impulse jumps from one nerve to another.
• The brain contains approximately 1000 trillion synapses.
• Synaptic knobs contain spherical, membrane-bound synaptic vesicles that store neurotransmitters, released into the synaptic cleft.

The Journey of a Neurotransmitter

• Synthesized by nerve cell bodies
• Actively transported along the axons
• Stored in the synaptic vesicles
• Released by exocytosis in response to the action potential
• Diffuse across the synaptic cleft
• Act on specific receptor sites on the postsynaptic membrane
• Action is short lived
• After action, either inactivated by enzymes or taken back into the synaptic knob

Local Anaesthetics and Neuralgia

• Local anesthetics work by blocking nerve transmission to pain centers in the central nervous system.
• They bind to and inhibit the function of an ion channel in the cell membrane of nerve cells, specifically the sodium channel.
• This action obstructs the movement of nerve impulses near the injection site, without affecting awareness or sense perception in other areas.
• Excessive nerve impulses can result in neuralgia, most commonly trigeminal neuralgia.
• The herpes simplex virus lies dormant in the trigeminal ganglion. When reactivated, it travels down the trigeminal nerve, emerging on the lip and causing a cold sore.

Explore neural impulses: Sensory impulses travel to the brain and motor impulses travel from the brain. Voltage-gated ion channels in the axon facilitate action potential through depolarization. The sodium-potassium pump restores charge by moving Na+ out and K+ in.