Electrical synapses are gap junctions. When formed between neurons, they vary from chemical synapses where the separation of the cells is not a concern. They allow current to flow directly from one cell to the next without receptors or decoding units. However, the connected cells lose some individuality, reducing their utility in big neural systems with labelled lines, such as that of mammals.
Electrical synapses are abundant in invertebrates and non-mammalian nervous systems, but they are uncommon in mammals, except for neuroglial cells in which they are the primary means of communication. They have, however, been discovered among mammalian neurons and have been shown to transmit in a few instances.
Table of Contents
- Synapse and Electrical Synapse
- Structure of Electrical Synapse
- Electrical Synapses in the Adult Mammalian Nervous System
- Difference Between Electrical Synapse and Chemical Synapse
- Frequently Asked Questions – FAQs
Synapse and Electrical Synapse
Synapse
A synapse connects a neuron or two neurons with a target or effector cell, such as a muscle cell. It enables electrical as well as chemical impulses to be transmitted.
The presynaptic and postsynaptic neurons create the synapse. The neuromuscular junction is the connection between a neuron and a muscle.
A synapse transmits nerve impulses from one neuron’s axon terminal to the next neuron’s dendrites. It could be either chemical or electrical in nature.
Electrical Synapse
- Chemical synapses take longer than electrical synapses.
- An electric signal transmission across the electrical synapse is identical to the conduction of impulse in an axon because these gap junctions enable immediate ion passage.
- Gap junctions are formed when presynaptic and postsynaptic neurons are close together. Protein channels form a physical link between pre and postsynaptic neurons at the gap junction.
- Electrical synapses are less adaptable than chemical synapses since they can’t switch from excitatory to inhibitory signals.
- Some lower invertebrates have it. It is present between glial cells in humans.
Structure of Electrical Synapse
Several gap junction channels cross the plasma membranes of both cells at each gap junction (nexus junction). The pore of a gap junction channel, with a lumen width of around 1.2 to 2.0 nm, is large enough to permit ions and even medium-size molecules like signalling molecules to move from one cell to the next, effectively linking the cytoplasm of the two cells. As a result, ions may pass through when one cell’s membrane potential changes, carrying a positive charge with them and depolarizing the postsynaptic cell.
In vertebrates, gap junction funnels are made up of two hemi-channels termed connexons, one from each cell at the synapse. Connexons are made up of six connexins, which are 7.5 nm long, with four-pass cell membrane protein subunits that may be similar or differ slightly from one another.
When the axon of one neuron synapses with its own dendrites, it forms an autapse, which is an electrical (or chemical) synapse.
Electrical Synapses in the Adult Mammalian Nervous System
Electrical synapses are common during nervous system development, and while they are not as widespread in the adult nervous system, they do exist in specific locations and play an important role in their functioning.
One way to assess the value of electrical synapses in adults is to remove them one by one and see how the nervous system operates without them. Once a particular connexin gene has been located, a mutant mouse that lacks the associated connexin protein can be created.
In the retina, electrical synapses are also required for the transfer and regulation of rod and cone impulses. Rod photoreceptors in the retina, for example, trigger a subtype of amacrine cells known as “AII.” The retina adjusts the electrical connectivity between these “AII” amacrine cells depending on the amount of light to cater to the needs for responsiveness and positional resolution in our vision.
Electrical synapses function by letting ionic current flow passively from one neuron to another through gap junction pores. The potential difference created regionally by the action potential is the most common source of this current. The presynaptic element is the “upstream” neuron that is the source of current, and the postsynaptic element is the “downstream” neuron into which the current flows.
This configuration has a lot of intriguing implications. One is that transmission can be bidirectional; that is, based on which member of the coupled pair is invaded by an action potential, current can flow in either way across the gap junction. Because passive current flow across the gap junction is almost immediate, communication can occur without the delay seen in chemical synapses.
Also Read:
Difference Between Electrical Synapse and Chemical Synapse
The major distinction between a chemical and an electrical synapse is that in a chemical synapse, the nerve impulse is transmitted chemically via neurotransmitters, whereas in an electrical synapse, the nerve impulse is transmitted electrically via channel proteins.
- A chemical synapse is a cell-to-cell connection via which neurotransmitters send nerve impulses in one way. An electrical synapse, on the other hand, is a cell connection between two nerve cells that allows for rapid transmission of nerve impulses via ions.
- Higher vertebrates have chemical synapses, while invertebrates and lower vertebrates have electrical synapses.
- The transmission of signals at a chemical synapse is one-way, whereas the transmission of signals at an electrical synapse is two-way.
- Electrical synaptic knobs have no synaptic vesicles and only a few mitochondria, whereas chemical synaptic knobs have synaptic vesicles and a significant number of mitochondria.
- Electrical synapses are located in the olfactory bulb, retina, lateral vestibular nucleus, cerebral cortex, and hippocampus, while chemical synapses are found in the majority of neuron junctions.
Related Links:
- What Is The Role Of Synapses In Nerve Impulses?
- Is Impulse Transmission At An Electrical Synapse Faster Than A Chemical Synapse?
- What Happens At The Synapse Between Two Neurons?
Frequently Asked Questions
Give some examples of electrical synapses.
Electrical synapses have been found in the hippocampus, thalamic reticular nucleus, neocortex, locus coeruleus, trigeminal nerve mesencephalic nucleus, inferior olivary nucleus, retina, olfactory bulb, and spinal cord of vertebrates.
Why do electrical synapses work in two directions, but chemical synapses transmit information only in one direction?
Ions flow equally well in both directions (bi-directional) in electrical synapses (gap junctions), so either neuron can be presynaptic. At a chemical synapse, one neuron releases the neurotransmitter while the other neuron has receptors that bind this chemical. As a result, information can only travel in one direction (unidirectional).
What area in the brain contains electrical synapses?
Electrical synapses in the Central and Peripheral nervous systems are uncommon in adults. They appear in select brain locations, including the balance-related vestibular nuclei, the eyes, and one or more pairs of PNS ganglia (ciliary ganglia). They’re also found in some embryonic structures.
Comments