Clinical anatomy of muscles

The following clinical points related to the muscles of body are of interest for medical students.

Paralysis

Loss of motor power (power of movements) in muscles is called paralysis. This causes inability of the muscles to contract. The root cause of paralysis can be of two types;

• Damage to motor neural pathways
• Inherent disease of muscles

In the type of paralysis caused by damage to motor neural pathways, either the upper or lower motor neuron might be the exact point of damage. In the case of upper motor neuron, spastic paralysis is caused which is accompanied by exaggerated tendon jerks. In the case of lower motor neurons, flaccid paralysis is caused in which there are no tendon jerks.

Disuse atrophy and Overuse hypertrophy

The muscles which arc not used for long times become thin and weak. This is called disuse atrophy. Conversely, adequate or excessive use of particular muscles causes their better development, or even hypertrophy (Fig. 1.2). Muscular ‘wasting’ (reduction in size) is a feature of lower motor neuron paralysis and generalized debility.

Muscle atrophy

Muscle hypertrophy 

(John Cena)

Regeneration of skeletal muscle

Skeletal muscle is capable of limited regeneration. If large regions are damaged, regeneration does not occur and the missing muscle is replaced by connective tissue.

Hyperplasia

Hyperplasia means increase in muscle mass. The most common cause is the increase in number of smooth muscle fibers. Usually occurs in uterus during pregnancy.

Myasthenia Gravis

Myasthenia gravis is an autoimmune disease of muscle of unknown origin. Antibodies are produced that bind to acetylcholine receptor and block it. The nerve impulse transmission to muscle fibers is therefore blocked. This leads to extensive and progressive muscle weakness although the muscles arc normal. Extraocular and eyelid muscles are affected first, followed by those of the neck and limbs. It affects more women that men and usually those between age of 20 and 40 years.

Polymyositis

Polymyositis is a disease of muscle characterized by inflammation of the muscle fibers. It starts when white blood cells (immune cells of inflammation) spontaneously invade the muscle. Muscles close to trunk or torso are mostly affected by polymyositis that results in severe weakness. Polymyositis associated with skin rash is referred to as “dermamyositis”.

Fibrillation

Fibrillation is the abnormal contraction of cardiac muscle. The cardiac chambers do not contract as a whole resulting in the disruption of pumping action. In atrial fibrillation, there is rapid and uncoordinated, contraction of atria, ineffective pumping and abnormal contraction of the AV node. Ventricular fibrillation is characterized by very rapid and disorganized contraction of ventricle. This leads to disruption of ventricular function.

Angina Pectoris

Angina pectoris is episode of chest pain due to temporary ischemia of cardiac muscle. It is usually relieved by rest and nitrites.

Myocardial ischemia

Persistent ischemia due to blockage of more than one artery results in necrosis (death) of the cardiac muscle. Pain is not relieved by rest and gets referred to the left arm, chest and neighboring areas.