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Chemical Synapse

Chemical synapses are links between neurons and non-neuronal cells (glandular cells, muscle cells, sensory cells). The synaptic complex of each chemical synapse is a non-reducible primary component that constitutes the basic minimum for chemical synaptic transmission.

It encompasses three components: the presynaptic (an axon terminal), a synaptic cleft, and a postsynaptic component (dendritic spine).

Table of Contents

Synapse and Chemical Synapse

Synapse

  • The points of contact between neurons where information is transmitted from one neuron to the next are referred to as synapses.
  • The majority of synapses use chemical messengers to communicate. Other synapses are electrical, and ions move directly between cells in these synapses.
  • An action potential causes the presynaptic neuron to produce neurotransmitters at a chemical synapse. These chemicals attach to receptors on the postsynaptic cell, causing it to discharge an action potential more or less frequently.

Synapse

Chemical Synapse

  • Chemical synapses are much more prevalent. Neurotransmitters are responsible for the transfer of nerve signals through chemical synapses.
  • The synaptic cleft is a fluid-filled gap between the two neurons. A nerve impulse cannot travel from one neuron to the next.
  • Synaptic vesicles from the terminal of the presynaptic neuron produce neurotransmitters at the synaptic cleft when the action potential reaches the terminals.
  • Neurotransmitters bind to postsynaptic membrane receptors enabling voltage-gated channels to open, allowing ions to flow.
  • The polarity of the postsynaptic membrane changes and the electric signal is transmitted across the synapse.
  • Neurotransmitters could be inhibitory or excitatory. Various cells respond to the same neurotransmitter in different ways.
  • The neurotransmitter is inhibitory if there is a net influx of positively charged ions within the cell, which causes the action potential to be generated. EPSP (excitatory postsynaptic potential) is the name given to this phenomenon.
  • The membrane is hyperpolarized as the membrane potential gets increasingly negative, and neurotransmitter action becomes inhibitory. They produce IPSP or inhibitory postsynaptic potential.
  • Once connected to the receptor, neurotransmitters are either worked on by enzymes or transferred back and recycled to end the signal after it has been transmitted forward.

Structure of Chemical Synapse

  • Chemical synapses have a larger synaptic cleft (region between the pre and postsynaptic neurons) than electrical synapses. The presence of tiny, membrane-bound structures called synaptic vesicles within the presynaptic terminal is a key feature of all chemical synapses.
  • The chemical signals generated by the presynaptic neuron are filled with one or more neurotransmitters, and it is these chemical agents serving as messengers between the connecting neurons that provides this synapse its name.
  • There are many different types of neurotransmitters, with acetylcholine being the most well-studied. It is used in peripheral neuromuscular synapses, autonomic ganglia, and some central synapses.
  • Synapses are asymmetrical in both structure and function. Only the presynaptic neuron produces the neurotransmitter binding to receptors on the postsynaptic cell’s side of the synapse.
  • The presynaptic nerve terminal (also known as the synaptic button, bouton, or knob) develops from the axon’s tip, whereas the postsynaptic target surface develops from a dendrite, cell body, or another component of the cell.

Difference Between Chemical Synapse and Electrical Synapse

Chemical and electrical synapses are specialised biological structures that connect neurons and carry impulses across them in the nervous system.

Chemical and electrical synapses differ in their way of signal transmission: chemical synapses send signals in the form of chemicals called neurotransmitters, whilst electrical synapses send signals in the form of electrical signals without using chemicals. Because of their various modes of action, chemical and electrical synapses have slightly different structures.

Chemical synapse allows unidirectional transmission by using chemicals called neurotransmitters to send signals along the neurons. The electrical synapse transmits signals along the neurons via an ionic current and allows for transmission in both directions.

The synaptic cleft is the greater space connecting two neurons in a chemical synapse. Neurotransmitters diffuse through the synaptic cleft until they reach their target receptors. The electric synapse is made up of two neurons that are physically connected by gap junctions. As a result, the space between them is very narrow.

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Frequently Asked Questions

What are the steps in chemical synaptic transmission?

The following steps are required for chemical synaptic transmission:

  • The neurotransmitter is synthesised in the presynaptic nerve terminal.
  • Secretory vesicles are used to store neurotransmitters.
  • Neurotransmitter release is regulated in the synaptic gap between pre and postsynaptic neurons.
  • The presence of particular neurotransmitter receptors on the postsynaptic membrane, allows the neurotransmitter to imitate the results of nerve stimulation when applied to the synapse.
  • A method of stopping the released neurotransmitter from responding.

Why does the brain have chemical synapses?

Chemical synapses assist neurons in the central nervous system to create circuits. They play a critical role in the biochemical computations that underpin perception and thinking. They allow the nervous system to communicate with and control other body systems.

Define Desensitisation.

A decrease in reaction to a similar neurotransmitter stimulus is known as the desensitisation of the postsynaptic receptors. It means that as a stream of action potentials arrives in quick succession and the efficacy of a synapse might be reduced—a process known as frequency dependency of synapses. The nervous system takes advantage of this characteristic for functional reasons, and it can fine-tune its synapses by phosphorylating the proteins involved.

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