The key difference synapse and neuromuscular junction is that synapse is a junction between two nerve cells or between a neuron and a muscle cell, while neuromuscular junction is a junction between a motor neuron and a muscle fiber.
Sensory transduction is the process that converts one sensory stimulus from one form to another. Transduction in the nervous system is a stimulus alerting event where a physical stimulus is converted into an action potential. Action potential plays a central role in cell to cell communication. This action potential is transmitted along axons towards the central nervous system for integration. This is a step in larger sensory processing. Synapse and neuromuscular junction are two very important junctions for converting signals in the sensory transduction system of the human body.
CONTENTS
1. Overview and Key Difference
2. What is a Synapse
3. What is a Neuromuscular Junction
4. Similarities Between Synapse and Neuromuscular Junction
5. Synapse vs Neuromuscular Junction in Tabular Form
6. Summary – Synapse vs Neuromuscular Junction
What is Synapse Junction?
Synapse is a junction between two nerve cells or between a neuron and a muscle cell. It is also called a neuronal junction. Synapses are essential elements to the transmission of nervous impulses from one neuron cell to another. Neurons are specialized to pass signals to individual target cells with the help of synapses. At a particular synapse, the plasma membrane of the signal-passing presynaptic neuron comes into close apposition with the membrane of the target postsynaptic neuron cell or other.
Figure 01: Synapse
Synaptic Transmission
In synaptic transmission, a presynaptic cell often releases a neurotransmitter into the space between pre and postsynaptic cells. Then the receptors of postsynaptic cells bind with these neurotransmitters. When the messages are passing in this way between two cells, they have the power to change the behavior of both cells. However, in some cases of electrical synapses, voltage changes in the presynaptic cell will induce voltage changes in the postsynaptic cell, and the messages pass as an electric current.
In synapses, the presynaptic part is usually located on an axon, and the postsynaptic part is located on a dendrite, axon, or soma. Based on this, there are three types of synapses: axodendritic, axoaxonic and, axosomatic. Moreover, the change in the strength of synapses is called synaptic plasticity. Therefore, more a synapse is used, the stronger it becomes and the more influence it can wield over its neighboring postsynaptic neuron cell or other cells.
What is Neuromuscular Junction?
Neuromuscular junction is a junction between a motor neuron and a muscle fiber. It helps the motor neuron to transmit a chemical signal to the muscle fiber. This causes muscle contraction. Muscles need innervation to work. In a neuromuscular junction, the nerves from the central nervous system and peripheral nervous system link together with muscles.
Figure 02: Neuromuscular Junction
Neuromuscular Transmission
This process starts once the action potential reaches the presynaptic motor neuron and activates voltage-gated calcium channels. This allows the calcium ions to enter the motor neuron. Calcium ions bind to sensor proteins on synaptic vesicles and stimulate the subsequent neurotransmitter (acetylcholine) release from the motor neuron into the synaptic cleft. Acetylcholine then binds to the nicotinic acetylcholine receptors (nAChRs) on the cell membrane of the muscle fiber. Furthermore, the binding of acetylcholine to receptors depolarizes the muscle fiber, which eventually causes muscle contraction.
There are neuromuscular junction diseases that are of genetic and autoimmune origin, such as Duchene muscular dystrophy and myasthenia gravis.
What are the Similarities Between Synapse and Neuromuscular Junction?
- Both junctions are converting signals in the sensory transduction system of the human body.
- The neurotransmitter acetylcholine acts in both junctions.
- The neurons of the central nervous system and peripheral nervous system are involved in both junctions.
- Both junctions are between presynaptic and postsynaptic cells.
What is the Difference Between Synapse and Neuromuscular Junction?
A synapse is a junction between two nerve cells or between a neuron and a muscle cell. On the other hand, neuromuscular junction is a junction between a motor neuron and a muscle fiber. So, this is the key difference between synapse and neuromuscular junction. Furthermore, in the synapse, a postsynaptic cell can be a neuron or a muscle, while in the neuromuscular junction, a postsynaptic cell is always a muscle fiber. Thus, this is also a significant difference between synapse and neuromuscular junction.
The below infographic lists the differences between synapse and neuromuscular junction in tabular form.
Summary – Synapse vs Neuromuscular Junction
The process by which a cell converts an extracellular signal such as light, taste, sound, touch, or smell into electric signals is known as the sensory transduction system. Synapse and neuromuscular junction are two very important junctions for converting signals in the sensory transduction system of the human body. A synapse is a junction between two nerve cells or between a neuron and a muscle cell. Neuromuscular junction is a junction between a motor neuron and a muscle fiber. Thus, this is the summary of the difference between synapse and neuromuscular junction.
Reference:
1. Penttila, Nicky. “What Happens at The Synapse?” Dana Foundation, Dana Foundation, 26 Aug. 2019.
2. “Neuromuscular Junctions and Muscle Contractions.” Anatomy and Physiology I – Lumen.
Image Courtesy:
1. “SynapseSchematic en” By Thomas Splettstoesser (www.scistyle.com) – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Electron micrograph of neuromuscular junction (cross-section)” By National Institute of Mental Health; originally uploaded by Nrets at en.Wikipedia. – Synapse Web at the National Institute of Mental Health, National Institutes of Health; originally from en.Wikipedia (Public Domain) via Commons Wikimedia