The neuromuscular junction (NMJ) is an innervated synapse in a motor nerve that forms a bipolar axon and non-bipolar arbour in the muscle's vicinity, connecting the nerve with the muscular-skeletal and cardiac structures. It is where the action potential from a nerve to a muscle is transmitted via the myostatin receptor to the specific muscle concerned. It is a common site of action for numerous pharmacological agents, and it is a known site of disease for several disorders. Among them, MS pain is often reported with dysfunction of the neuromuscular junction. The problem is not confined to MS pain. Many other musculoskeletal disorders of muscular function are linked with this anatomical region.
In fact, the Neuromuscular Junction is so much involved in the generation of muscle contraction in muscles that it has become a synonym for endplate potentiality. Endplate potentialities occur when a force acts on an endplate (the plates at the ends of long, straight fibres of cartilage). When the potentiality rises above a threshold value, the conductive properties of the endplate bend, causing the generation of movement. It has been postulated that such bending of the endplates may underlie the pathophysiology of various myopathies of muscular weakness, spasticity, and silliness, and myositis (muscle atrophy), and rheumatoid arthritis.
At first sight, it may seem that the phenomenon at the neuromuscular junction is simply an example of over-stimulation of the inhibitory system. However, if we look more closely, we will see that the inhibition of the inhibitory system occurs not at the synapse but at the cytoskeleton or the skeleton that produces the proteins needed to form synapses. Neuromuscular junctions are formed by projections called synapses, which themselves are composed of projections. Neuromuscular joints can be seen as projections of tubular structures, whose ends are embedded in the cartilages that make up the skeleton.
Neuromuscular joints are particularly important in motor function. Their ability to move requires the firing of neurons along pathways within the motor cortex of the brain. Neuromuscular pathways may be broken by either local or systemic infection, lesions, or disease. Neuromuscular junctions are characterized by a distinct distribution of nerve fibres. The distribution of nerve fibres depends both on the strength of the afferent impulse and on the strength of the inhibitory impulse. For example, a strong electric current weakly impels the nerve into a conductive path, whereas a weak pulse of acetylcholine generates a conductive pathway through the nerve.
Acetylcholine at the neuromuscular junction is released from the nerve synapse when it receives an input of either a negative or a positive charge. Neuromuscular junctions are formed by the accumulation of both positive and negative ions on the cell walls of the developing cells. Neuromuscular junctions can be formed at synapses where axons meet neurons or where they pass through the epidermis. Neuromuscular connections can be seen in the brain, where many types of synapses are located, including the auditory canal, the spinal cord, and the GI tract.
Neuromuscular junctions are complex in some ways. First, the action potential (the electrical impulse that generates a movement) that imparts a sensation to the body is broken down and sent to the appropriate target area by the nerve impulse, which includes the muscles, bones, organs, and tissues. Neuromuscular junctions are also involved in motor function, as described above. Neuromuscular junctions are also involved in the formation of the anatomical structure of the body, especially the spinal cord.
In the case of a neuromuscular junction involving a motor neuron, the nerve endings (nerve cells) insert into the correct muscle fibre. The strength of the nerve is determined by the strength of the muscle fibre attached to the nerve. Neuromuscular junctions can be characterized by abundant myelin, which is a protective sheath around motor neurons; or by thickened or fragile myelin, which can cause the loss or damage of neurons.
Other important considerations in determining the clinical significance of the Neuromuscular Junction include the existence of a hype threshold, which can occur in some patients with ankylosing spondylitis, and abnormal hype threshold, which can be the underlying pathology of many patients with spondylosis. The presence of hype threshold or abnormal hype threshold may be diagnostic for more serious conditions such as lymphedema. Another significant factor is the presence of asymmetry in the reciprocal arrangement between muscle fibres, which can result in dysfunction of the underlying motor system. If one motor fibre extends beyond its normal length compared to the other, this is called a "shortening" or "shortening of a synapse."