Connection-Junction: The Synapse. It’s all about networking. Synapses connect nerve cells to each other, or to muscles and glands.
• The word synapse is derived from the Greek syn (together) and haptein (to clasp).
• There are an estimated 100-500 trillion (that’s 10^14) synapses in the human brain.
• The space (synaptic cleft) at the junction is narrow, only 20 nanometers wide.
• Messages travel down the nerve fiber in the form of an electric pulse known as the action potential. When they get to the synaptic terminal, these messages must be converted to a chemical signal that crosses the narrow cleft (within microseconds) to trigger a new electrical signal at the connecting nerve or muscle cell. The chemical signal is the neurotransmitter (glycine, acetylcholine, etc.).
• These chemicals are packaged into small vesicles that lie just under the nerve membrane, docked and ready to fuse. When the action potential arrives, the vesicles execute a quick “kiss and run” to release the neurotransmitter into the cleft.
• Here is a beautiful scanning electron microscope image of a nerve ending in which the membrane has been sheared away, revealing hundreds of spherical vesicles ready to release their neurotransmitter cargo into the synaptic cleft.
• Synapses are targets for hundreds of toxins, psychoactive drugs and poisons including curare, cocaine, LSD and morphine. Botox is a formulation of botulinus toxin, and works by cleaving the proteins that allow the vesicles to fuse. By blocking neurotransmitter release, the nerve cannot signal the muscle to contract. Voila, no wrinkles!
Image from: http://www.cellimagelibrary.org/images/214