In this article, you will learn about the different components of a Synapse, including the Postsynaptic terminal membrane and the Synaptic cleft. You’ll also learn about electrical and chemical synapses. Hopefully, you’ll be able to answer the question “what is a Synapse?” with confidence.
Synaptic cleft
The synaptic cleft is a structure that is found in neuronal cells. This structure contains synaptic vesicles, which contain neurotransmitters. When action potentials reach the neuron, voltage-gated calcium channels, which are concentrated on the outer surface of the cell, open and allow synaptic vesicles to fuse with the membrane of the presynaptic terminal. The fusion of the two membranes releases neurotransmitters into the synaptic cleft.
The synaptic cleft forms between the axon of a presynaptic neuron and the axon of a postsynaptic neuron. It also occurs between a neuron’s axon and its dendrite, or between the axon and its cell body.
The synaptic cleft is important for the proper functioning of the nervous system because it provides an area for neurotransmitters to diffuse. The small size of the synaptic cleft also allows different enzymes to act on the neurotransmitters, regulating the flow of nerve impulses. Drugs that act in the synaptic cleft are called neurotransmitter antagonists.
The synaptic cleft is a microscopic space between the dendrites of two neurons. The cleft is important for the transmission of nerve impulses from the pre-synaptic neuron to the post-synaptic neuron. Normally, this space is about 200 angstroms wide. The cleft is filled with extracellular fluid.
Postsynaptic terminal membrane
The PSD is a dense layer of proteinaceous material that connects the presynaptic active zone with the postsynaptic plasma membrane. It is anchored to the postsynaptic membrane by cytoplasmic actin filaments and typically has a disc-like shape. Its size ranges from 200 to 800 nm in diameter and has a thickness of thirty to sixty nanometers.
The PSD contains several proteins that interact with one another. The GKAP family of scaffolding proteins (GKAPs) is one such protein. These proteins are located near the cytoplasmic side of the PSD and interact with PSD-95 family proteins.
The IPSPs are formed by the activation of one or more release sites. The number of active zones per synapse and the number of presynaptic interneurons determine the type of IPSP. Using electron microscopy, one can determine how many synaptic complexes are present in a single synapse.
In mammalian neurons, the postsynaptic terminal membrane contains specific ACh receptors, or AChRs. They are located opposite the active zone, and are one of the most well-characterized ion channels. AChRs have a transmembrane structure that consists of four different glycoprotein subunits of 55,000 da molecular weight. These protein subunits assemble to form a five-subunit structure. They have negatively charged side chains that point towards the pore. This creates a selectivity filter and blocks the anion from permeating through the membrane.
Once the signal has reached the postsynaptic terminal membrane, the neurons in the vicinity must clear the synaptic cleft of neurotransmitters before the synapse can function. After this, the neurotransmitter is broken down by an enzyme or diffused away by nearby glial cells.
Chemical synapses
Chemical synapses are structures in the nervous system that facilitate the transmission of information. These synapses are formed by a complex process, including a regulated release of neurotransmitters. These transmitters travel through the synaptic cleft in the presynaptic cell and bind to specific receptors on the postsynaptic cell’s membrane. The binding of neurotransmitters to receptors causes channels in the postsynaptic cell to open and close, altering the ion flow of the neuron. This current flow changes the conductance of the synaptic cell, thereby increasing or decreasing the probability that the neuron will fire an action potential.
Chemical synapses are made up of two parts: the presynaptic axon and the postsynaptic dendritic spine. The presynaptic axonal bouton contains synaptic vesicles. These vesicles contain the neurotransmitters that bind to the receptors on the postsynaptic cell’s membrane.
Chemical synapses are highly specialized junctions that connect neurons and other cells within the nervous system. They are essential for biological computations. They connect the nervous system to other systems in the body. For example, chemical synapses exist between a motor neuron and a muscle cell.
In addition to being fast and enabling the synchronization of groups of neurons, electrical synapses can also carry current in both directions. When an electrical signal reaches the postsynaptic neuron, it will also depolarize the presynaptic neuron. But, electrical synapses have a few limitations. Unlike other types of synapses, they do not have the flexibility, versatility and signal modulation capabilities of chemical synapses.
Electrical synapses
Electrical synapses are different from chemical synapses in that they transmit information by slow, subthreshold changes in the voltage at the synapses. For example, in some cell types, action potentials are followed by large after-hyperpolarizations, the result of delayed activation of voltage-dependent K+ currents. This delay in the transmission of information results in coupling potentials.
Electrical synapses are composed of heterogeneous membrane proteins called gap junctions. These proteins form a barrier between two cells, providing a pathway for intracellular solute diffusion and supporting chemical and electrical coupling. This pathway also allows the movement of ions and represents a low-resistance pathway for direct electrical current to flow between cells. In addition, gap junction communication does not rely on intermediate messengers, which makes it an efficient and fast way to transfer information between neurons.
An electrical synapse forms when specific types of gap junctions on one cell are in close proximity to the same type on another. The electrical synapses can be formed in response to a wide range of stimuli, ranging from small electrical signals to powerful electrical signals. In addition, electrical synapses have an important role in synchronizing neuronal oscillations and transient signal processing.
Electrical synapses also vary in strength. The strength of a synaptic coupling depends on dynamic factors, including the resistance of the postsynaptic cell to the gap junction. Moreover, these factors change over different time scales. Therefore, electrical synapses must be considered equally important as chemical synapses.
Gap junctions
The gap junction at the synapse allows group of neurons to coordinate their function. The junction is a conduit for organic molecules of 1 kDa or smaller, including messengers and metabolites. These molecules influence neuronal physiology and behavior. This research provides new insights into the mechanisms of gap junctions and how they regulate synaptic transmission.
Gap junctions at the synapse are found near NMDA and AMPA receptors. They form complexes with other proteins and are anchored to the cytoskeleton. They also contain regulatory and structural proteins that may be involved in the axon’s assembly and function.
Gap junctions at the synapse may be involved in the transmission of neurotransmitters. They also contribute to neuronal death during glutamate-dependent excitotoxicity. The overactivation of NMDARs causes the formation of new neuronal gap junctions, and genetic or pharmacological blocking of these junctions reduces the neuronal death.
In addition to Cx36, there are also other connexins that form gap junctions at the synapse. These other connexins may contribute to the extent of coupling that occurs in the developing CNS. They are also important in the process of synaptogenesis.
The electrical synapses of the adult nervous system are important for many functions. One major role of electrical synapses is to synchronize the neuronal activity. Inhibitory neurons, in particular, are responsible for synchronizing the activity of the neuronal network. Their pattern of activity may also play a role in learning and memory.
Function of synapses
Several hundred proteins make up the synaptic vesicle. These are organized into distinct types depending on their size, shape, and electron density. In the case of the glutamatergic synapse, PSD95 is the main scaffolding protein, which assembles nNOSa, neuroligins, and ionotropic glutamate receptors. Another protein, PSD93, may be important for the stabilization of nicotinic receptors in cholinergic synapses.
The electrical properties of a synapse include the IPSP (inhibitory postsynaptic potential) and EPSP (excitatory postsynaptic potential). The excitatory neurotransmitter, glutamate, associates with receptors on the postsynaptic cell, causing positive ions to flow. On the other hand, inhibitory neurotransmitters, such as acetylcholine, cause ion channels to open. Three types of synapses are recognized: axoaxonic synapses, axodendritic synapses, and axosomatic synapses.
The electrical response of synapses is an important component of the nervous system. Without these structures, nerve impulses could not jump from neuron to neuron. In addition, the axon terminals contain synaptic vesicles that release an action potential, which binds to receptors on the postsynaptic membrane.
As a result, synaptic structures are highly specialized in their function. Moreover, the function of synapses is to transfer signals from one cell to another via chemical intermediates. Hence, the process of synaptic vesicle exocytosis is critical for the delivery of neurotransmitters. Various toxins target this process and block synaptic transmission.
