Nerve Impulses and Synaptic Transmission

Study Notes

A nerve impulse is initiated by a stimulus or the passage of an impulse from another nerve.
Afferent (sensory) nerves transmit impulses to the brain and Central Nervous System (CNS).
Efferent (motor) nerves transmit impulses from the brain and CNS.
Nerve impulses are also known as action potentials.
Nerve impulses travel down the neuron.

Nerves are not directly connected.
The point where a nerve impulse jumps from one nerve to another is called a synapse.
There are approximately 1000 trillion synapses in the brain.

Synaptic knobs contain synaptic vesicles.
Synaptic vesicles are membrane-bound sacs that store neurotransmitters.
Neurotransmitters are chemical messengers released into the synaptic cleft.
The journey of a neurotransmitter starts with synthesis in the nerve cell body.
Neurotransmitters are actively transported along axons and stored in synaptic vesicles.
They are released by exocytosis in response to action potentials.
They diffuse across the synaptic cleft.
Neurotransmitters act on specific receptor sites on the post-synaptic membrane.
The action of neurotransmitters is short-lived.
After action, neurotransmitters are inactivated by enzymes or taken back into the synaptic knob.

Local anaesthetics block nerve transmission to pain centers in the central nervous system.
Local anaesthetics bind to and inhibit the function of sodium channels in the cell membrane of nerve cells.
This action obstructs the movement of nerve impulses near the site of injection.
Awareness and sense perception in other areas remain unchanged.

Excessive nerve impulses can result in neuralgia.
The most common type of neuralgia is trigeminal neuralgia.
The Herpes Simplex Virus can lie dormant in the trigeminal ganglion.
Reactivation of the herpes simplex virus causes it to travel down the trigeminal nerve, emerging on the lip and causing cold sores.