4.3.5 Myasthenia Gravis
Myasthenia gravis（MG）is a chronic autoimmune disorder in which antibodies destroy the communication between nerves and muscles，resulting in weakness of the skeletal muscles.MG affects the voluntary muscles of the body，especially those that control the eyes，mouth，throat and limbs.MG is characterized by destruction of the receptors in the synaptic region that respond to acetylcholine，a substance that transmits nerve impulses（neurotransmitter）.The disease can strike anyone at any age，but is more frequently seen in young women aged 20 and 30 and men aged 50 and older.
As the disease progresses，the muscle becomes increasingly weak because the nerve impulse is not transmitted successfully to the muscle cell from the nerve cell，and may eventually cease to function altogether.
Most individuals with MG develop weakness and drooping of the eyelids（ptosis）（Fig.4-6）；weakness of eye muscles，resulting in double vision（diplopia）；and excessive muscle fatigue following activity.Additional features commonly include weakness of facial muscles；impaired speech（dysarthria）；difficulties chewing and swallowing（dysphagia）；and weakness of the upper arms and legs（proximal limb weakness）.
Fig.4-6 Myasthenia Gravis（Drooping of Eyelid）(https://www.daowen.com)
A common way to diagnose MG is to test how the individual responds to certain medicines.Muscle weakness often dramatically improves for a brief time when an anticholinesterase medicine is given.If one responds to the medicine，MG is confirmed.
Medical management is the usual form of treatment.Anticholinesterase medicines，steroids，or medicines that suppress the immune system’s response（immunosuppressive）may be used.In addition to medications，treatment for MG may require restricted activity and a soft or liquid diet.The care provided for the person and family is supportive and symptomatic.
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Task 7 Write a word with each of the following meanings.
