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Myasthenia Gravis and the ACh Receptor

The nerve impulses travel across the neuron- the nerve cell through a complicated process of ionic exchanges across the cell membrane known as Depolarization. The motor axon terminates on specific end plate on the muscle surface. Activity in the nerve cell releases a chemical - Acetylcholine at the end plate. This acetylcholine is taken-up by the specific Acetylcholine Receptors resulting in the initiation of the muscular contraction. Thus while the initial movement of the nerve impulse through the neuron is by ionic exchange, it is through chemical transmission at the neuromuscular junction.

The nicotinic acetylcholine receptor found on the skeletal muscle cell is greatly affected by the autoimmune response in myasthenia gravis. 

 

Acetylcholine Receptor

Acetylchoine

Esterase

Choline

 

 

 

1. Model of normal neuromuscular junction. Nerve action potential invades the nerve terminal, resulting in enhanced release of acetylcholine.
These Nicotinic receptors of Acetylcholine which are situated in the post-junctional membrane of Neuromuscular junction are very important for impulse transmission to the muscles. Constituents of our body are constantly in a state of equilibrium. Thus in common with all body tissues these receptors are also constantly being broken down and re-synthesized. Normally cholinoceptors exist for about seven days. 

 

 

 

 

 

 

 

2. In Patients with Myasthenia Gravis,Cholinoceptors exist for only about a day. Thus there is a scarcity of the receptors which are responsible for taking up the acetylcholine released at the neuromuscular junction creating a deficiency of acetylcholine which in turn results in lack of vital force required for repeated muscular activity. Hence the muscle fatigue in Myasthenia Gravis patients, which is observed after vigorous activity, walking, continuously talking for a long time or staring continuously.

 

 

 

3. With the help of Pyridostigmine Bromide ( MYESTIN ) the Acetylcholine survive from termination and gets another chance for remaining receptors to take it resulting the force required for repeated muscular activity.

 

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