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Diagram of a chemical synaptic connection. In the nervous system, a synapse [1] is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending on the mechanism of signal transmission between neurons.
The number of synapses in the human cerebral cortex has separately been estimated at 0.15 quadrillion (150 trillion) [3] The word "synapse" was introduced by Sir Charles Scott Sherrington in 1897. [4] Chemical synapses are not the only type of biological synapse: electrical and immunological synapses also exist. Without a qualifier, however ...
An excitatory synapse is a synapse in which an action potential in a presynaptic neuron increases the probability of an action potential occurring in a postsynaptic cell. Neurons form networks through which nerve impulses travels, each neuron often making numerous connections with other cells of neurons.
Once at the synapse, synaptic vesicles are loaded with a neurotransmitter. Loading of transmitter is an active process requiring a neurotransmitter transporter and a proton pump ATPase that provides an electrochemical gradient. These transporters are selective for different classes of transmitters.
An electrical synapse, or gap junction, is a mechanical and electrically conductive synapse, a functional junction between two neighboring neurons. The synapse is formed at a narrow gap between the pre- and postsynaptic neurons known as a gap junction .
Synaptogenesis is the formation of synapses between neurons in the nervous system.Although it occurs throughout a healthy person's lifespan, an explosion of synapse formation occurs during early brain development, known as exuberant synaptogenesis. [1]
A neuromuscular junction (or myoneural junction) is a chemical synapse between a motor neuron and a muscle fiber. [1] It allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction. [2] Muscles require innervation to function—and even just to maintain muscle tone, avoiding atrophy.
Once released, a neurotransmitter enters the synapse and encounters receptors. Neurotransmitter receptors can either be ionotropic or g protein coupled. Ionotropic receptors allow for ions to pass through when agonized by a ligand. The main model involves a receptor composed of multiple subunits that allow for coordination of ion preference.