Synapse

The microscopic gap/junction between/among the axon of one neuron and the dendrite of another neuron or effectors is called the synapse.

Formation of synapse

Continuous neurons are so arranged that the axon endings of the neuron are connected to dendrites of the next neuron. There is no cytoplasmic connections between the two neurons and microscopic gaps are left between them. Each of these contact points/areas is called the synapse.
A single neuron may form synapses with many incoming fibers of various neurons.

Nerve impulse through synapse

TWO OR THREE SIMULTANEOUS IMPULSES

A nerve impulse is passed one neuron to other through the synapse, but a single impulse does not necessarily get across the synapse. It may take two or three impulses arriving in rapid succession or perhaps simultaneously. From two or more fibers to originate an impulse in the next neuron.

Neurotransmitter

The action potential cannot bounce from one neuron to the next neuron in line; rather the message/signal is conveyed across the synapse in the form of the chemical messenger called neurotransmitter.

Synaptic transmission


  1. When an impulse reaches a synaptic knob, synaptic vesicles within fuse with the presynaptic membrane, causing the release of neurotransmitter molecules into the synaptic cleft.
  2. The neurotransmitter molecules bind to receptors on the post-synaptic membrane, triggering an actional potential in the post-synaptic neuron, by causing changes in its permeability, to certain ions.

Neurotransmitters

Neurotransmitters are chemicals which are discharged at the axon ending of the presynaptic neurons, at the synapse.

Types of neurotransmitter

Many different types of neurotransmitters are known. These are:

  • Acetylcholine C7NH16O2+
  • Adrenaline ‎C9H13NO3
  • Nor-epinephrine C8H11NO3
  • Serotonin C10H12N2O
  • Dopamine ‎C8H11NO2

Acetylcholine C7NH16O2+

(2-Acetoxy-N,N,N-trimethylethanaminium)
Acetylcholine C7NH16O2+ is the main transmitter for synapses that lie outside the Central Nervous System (CNS). Other transmitters are mostly/commonly involved in synaptic transmission within the brain and spinal cord.
Acetylcholine