Synaptic Cleft (Definition + Function)

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The synaptic cleft is the space between two neurons. It is an essential tool that aids in migrating neurotransmitters from one neuron to another. The synaptic cleft forms part of a larger structure known as the synapse. The synapse includes the cleft and the post-synaptic and pre-synaptic membranes.

The synaptic cleft is a gap found within the synapse. It is part of the circuit between neurons. It refers to the area where neurotransmitters travel from one neuron to the next. As part of the neural pathway, the synaptic cleft helps facilitate communication between the brain and nervous system.

In order to carry out basic and nuanced tasks, our body relies on the communication between neurons within the nervous system. However, this communication would be impossible without the synapse and the synaptic cleft. Our guide on the synaptic cleft will illustrate how this structure fits within the body's day-to-day functioning.

What Is The Synaptic Cleft?

The synaptic cleft is the gap or space between adjacent neurons. It exists within the synapse, between the pre-synaptic and post-synaptic membranes. The synaptic cleft – also known as the synaptic gap – aids the communication between neurons through chemical transmission.

This transmission is called chemical neurotransmission and happens throughout the body's nervous system. These gaps are microscopic and vary in size, depending on their location and purpose.

The synaptic clefts that are within the central nervous system measure 20 to 30 nanometers wide. However, at neuromuscular junctions, they can measure roughly 50 nanometers wide. Neuromuscular junctions are the sites at which the ends of motor or efferent neurons and muscles meet. The neuron's action potential is transferred from the nerve to the muscle at this location.

What Is The Synapse?

The synaptic cleft is a small component of the synapse. The synapse comprises the pre-synaptic membrane, synaptic gap, and post-synaptic membrane. Also known as the neuronal junction, the synapse is the structure that allows electrical or chemical impulses to pass between two neurons or nerve cells.

Structure Of The Synapse

The synapse comprises the pre-and post-synaptic membranes and the synaptic cleft. The pre-synaptic membrane refers to the area at the end of the neuron's axons that is stimulated by electrical signals or action potentials. This stimulation causes the pre-synaptic nerves to release a chemical substance known as neurotransmitters.

Once the neurotransmitters are released, they cross the synaptic cleft and attach themselves to the post-synaptic membrane. This membrane is found at the tip of the receiving neuron's dendrites.

Function Of The Synapse

The function of the synapse is to create a pathway that connects neurons and facilitates communication between neurons by way of electrical impulses and chemical reactions. These impulses travel to and from the brain through the body's nervous system.

The electrical signals that travel through the neurons are known as action potentials and stimulate the release of chemical neurotransmitters that allow them to cross the synaptic gap. Synapses can be split into two types: chemical synapses and electrical synapses.

Electrical synapses allow signals to flow directly through neurons. There is no synaptic gap that the nerve impulses have to cross between electrical synapses. However, they are separated by the gap junction.

The gap junction facilitates uninterrupted molecule and ion relay from one cell to another. Within humans, electrical synapses are extremely rare but can be found within the nervous system – particularly in the brain.

Adversely, chemical synapses have to convert action potentials into a chemical reaction so that neurotransmitters are released and able to cross the synaptic gap. Once they have crossed the synaptic cleft, they attach themselves to the adjacent neuron and stimulate the continuation of electric impulses through the nerve.


Neurotransmitters are chemicals released by chemical synapses in response to stimulation by a neuron's action potential. They provide a way for electrical impulses to travel across the synaptic cleft and relay signals to other neurons or nerve cells.

The neuron contains molecules that they use to create neurotransmitters by way of a chemical reaction. They are stored within synaptic vesicles until the action potential is received. The vesicles merge with the pre-synaptic membrane and release neurotransmitters into the synaptic cleft.

Once neurotransmitters have relayed messages to the receiving neuron, they are removed from the synaptic gap. They are removed by way of diffusion, degradation, or reuptake.

When neurotransmitters move out of the synaptic cleft, neurons can no longer use them to relay messages across the neural pathway. This is known as diffusion. Similarly, enzymatic degradation - also known as deactivation - is caused by an alteration of the neurotransmitter by enzymes that make it unrecognizable to the receiving neuron.

Neurotransmitters can be reabsorbed and reused through a process called reuptake. Reuptake happens when the pre-synaptic neuron absorbs a neurotransmitter that it has previously released. The neuron can then reprocess it to transmit other signals.

When the synaptic cleft suffers from inflammation or injury, cell receptors can no longer absorb as many neurotransmitters as they should. This can cause autoimmune diseases such as Myasthenia Gravis, which impact the neuromuscular system. Myasthenia Gravis can also worsen communication at the neuromuscular junction.

Types Of Neurotransmitters

There are two main types of neurotransmitters. They can either be excitatory or inhibitory neurotransmitters. Depending on which neurotransmitters are released, they can facilitate or prevent the transmission of action potentials.

Excitatory neurotransmitters communicate with the receiving neuron and allow electrical impulses to continue their journey along the neural pathway. This allows the body to react to external stimuli.

For example, touching a hot surface will cause a person to pull their hand away. As a reaction to the high temperature, neurons will begin firing to relay messages to the brain. The brain will then process these messages and send out subsequent messages that evoke a physical response within an individual, such as removing their hand.

Inhibitory neurotransmitters prevent impulses or action potentials from passing along the neural circuit. They are typically used to prevent involuntary movements and calm the nervous system. These neurotransmitters are generally responsible for sleep and relaxation. 

For example, when stopping impulsive reactions during emotionally-charged situations. It inhibits immediate reaction to allow an individual's brain time to process information and allow them to practice self-control and behavioral regulation.

In addition to excitatory and inhibitory neurotransmitters, some types of neurotransmitters can influence multiple neurons simultaneously. These are known as modulatory neurotransmitters or neuromodulators. 

Modulatory neurotransmitters act as hormones and move throughout the body's circulatory system. The function of neuromodulators is to increase the effects of the other neurotransmitters. This increase effectively makes them more excitatory or inhibitory.

Exploring The Neuron

The synaptic cleft is the gap between adjacent neurons. It allows signals and impulses to travel between neurons and is a significant component of the neural pathway. These nerve cells rely heavily on the synaptic cleft but also play a significant role in carrying messages to and from the brain. Without a synaptic gap, neurons would be unable to communicate.

What Is A Neuron?

A neuron is a nerve cell that acts as a foundational structure within the body's nervous system and the brain. They act as receivers for impulses and relay information around the body. This information facilitates fundamental functions of the human body.

Neurons exist before the time we are born, and it is widely believed that neurogenesis – or the generation of new neurons – occurs throughout our lives. They are formed in specific brain areas with a high concentration of neural stem cells. Neurons reproduce by splitting themselves into two new cells.

When neurons are formed, they relocate to different parts of the brain. They typically move along cell fibers or through chemical signals until they reach their destination. However, not all neurons are successful and may die before reaching their pre-determined location. Similarly, other neurons may get lost due to genetic mutations. These mutations may cause disorders within the brain.

Neurons that successfully arrive at their destination will either become sensory, motor, or interneurons and carry out their necessary functions. Specific cells within the brain dictate where the neuron fits within the neural pathway and the type of neurotransmitters it will produce.

Structure Of The Neuron

Neurons are nerve cells that comprise three essential sections. The main structure of the neuron is known as the cell body. This body contains the nucleus, which contains its genetic makeup and regulates actions within the cell. The genetic makeup within the nucleus encompasses the nucleolus and chromosomes responsible for protein production.

The neuron's axon branches from the cell body and acts as a messenger for information. The axon is typically referred to as the nerve fiber and bridges the gap between neurons, muscles, and glands. They may also vary in length, depending on their purpose. At the end of an axon are axon terminals that send information across the synaptic cleft via neurotransmitters.

Lastly, dendrites are branches at the start of a neuron that receives information when neurotransmitters attach themselves. They increase the surface area of a neuron's cell body to catch neurotransmitters easily. Dendrites transfer action potentials from the post-synaptic membrane through the cell body to the axons. This helps to prevent losing information as it travels along the neural pathway.

Types Of Neurons

There are three types of neurons: association, motor, and sensory. Sensory neurons receive information from the environment via the sense organs and relay it to the brain. The sense organs are organs that receive input. Input can either be chemical or physical.

An example of physical input is temperature. For example, when holding an ice block. In this example, the skin is the sense organ that relays this input along sensory neurons and back to the brain. Adversely, chemical input refers to smell and taste. For example, when smelling a flower or tasting food.

Motor neurons can either be classified as upper or lower motor neurons. Upper motor neurons are located within the central nervous system, from the brain to the spinal cord. Motor neurons, on the other hand, send information from the spinal cord into the muscles.

Motor neurons are responsible for motor activity. This activity includes voluntary and involuntary movements. Voluntary movements include moving the arms and legs while running or dancing. In contrast, involuntary movements include the expansion and decompression of the lungs while breathing.

Lastly, association neurons – or interneurons – are nerve cells only found in the central nervous system (CNS). They bridge the gap between spinal motor and sensory neurons. Interneurons are multipolar. Multipolar means they have multiple dendrites to receive input from several neurons simultaneously.

Interneurons can be split into two classes, namely local and relay interneurons. Local interneurons connect with neighboring neurons and form pathways to evaluate information from incoming signals. Relay interneurons are much longer than local interneurons. They link clusters of neurons from different parts of the brain together.

Interneurons allow the brain to learn and form memories. For example, when touching a hot surface, it is instinctual for individuals to pull away. This reaction is because some interneurons received the message from the sensory neurons and sent subsequent messages to the motor neurons to pull away.

In the central nervous system, interneurons can use excitatory or inhibitory neurotransmitters. They use excitatory neurotransmitters to start a motion, such as removing or pulling a hand away from the hot surface. Additionally, interneurons use inhibitory neurotransmitters to maintain stability in the brain system. For example, the brain will dull the pain of being burned to avoid sensory overload.


Neurons are structures within the body that receive and relay information to and from the brain. They are responsible for bodily functions and are constantly firing – even during rest. The information that neurons receive is in the form of electrical signals. The signals are converted to chemical responses at the synapse. In order to move along the neural pathway, these chemicals – known as neurotransmitters – must cross the synaptic cleft between neurons.


Reference this article:

Practical Psychology. (2022, August). Synaptic Cleft (Definition + Function). Retrieved from

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