Muscular System

What is the Muscular System?
It is that system which helps us carry out our day to day activities like walking, standing, working. Some of these activities are not complicated; e.g. walking. But some activities require fine coordinated movements by the body; e.g. typing. The basis of all our movements are the contraction and relaxation of muscle fibers. These fibers make the movements of all joints possible.

What are muscles?
These are structures present in the body that are attached to the bones. They provide support as well as make the bones work in tandem thus making movement possible.

How can we describe muscles?
Muscles are of three types. These are

• Skeletal muscle
• Cardiac muscle
• Smooth muscle

A. Skeletal Muscles

These are the major muscles of the body. They are present attached to the bones. They provide a constant tension that gives the body its support. This tone does not require consciousness, but requires alertness.

Internal structure of a skeletal muscle
The skeletal muscle comprises of muscle fibres arranged in bundles called as fascicles. Each muscle fiber is made up of myofibrils. Myofibrils are made of thick and thin strands called as myofilaments. Myofilaments are elongated muscle cells having a nucleus. When nerve impulses reach the myofilaments, the thick and thin myofilaments slide into and out of each other like interlacing fingers, thus causing contraction and relaxation of the fiber and ultimately the whole muscle moves. The movement of the myofilaments is controlled by calcium and potassium concentration in the body.

The fascicles made by muscle fibers are enclosed in a sheath called as perimysium. These fascicles are again arranged in bundles to make up the whole muscle.

Microscopically the skeletal muscle is formed of long parallel, strong fibers. These are efficient and they are strong but can contract for only short periods of time. Thus they get tired easily.

The typical appearance of a muscle
Skeletal muscles appear tapered in shape and usually they end in tapered ends called as tendons. The mass of muscle is called as the belly. Tendons are structures made of fibrous tissue and are extremely strong. They are thinner than muscles so that they can be easily inserted on bones. They also prevent the muscle from tearing. Examples of tendons are the tendons of the forearm which tighten up and appear as cords on the forearm when the fist is clenched. The belly of the muscle contains the bulk of muscle fibers, which gives the muscle its strength.

B. Cardiac Muscle

This muscle, as its name suggests, is only present in the heart. This muscle has a unique property, that it does not get tired. It has a very fast recovery after it contracts unlike skeletal muscle and is thus able to contract and relax throughout our lifetime.

Microscopically the cardiac muscle is made of short, branching and interconnected fibers forming a network in a wall of the heart.

C. Smooth Muscle

This is the muscle that occurs in hollow organs like the intestines. The smooth muscle fibers are short and spindle shaped. They are also thinner than skeletal muscle fibers. They too have an unique property as they can remain contracted for a long period of time.

Functions of muscles

The muscles are attached to bones at a point called as the insertion. They also originate from the bone at a point called as the origin. Usually the muscle originates on one bone and it inserts onto a separate bone, adjacent to the former. The two bones form a joint. Whenever a voluntary movement is required to be performed the brain sends an impulse to the appropriate muscle, which then contracts. When the muscle contracts, its length becomes shorter. This causes a pull on the bone to which it is attached and thus causes movement. Whenever an involuntary movement such as walking or running occurs, there is coordinated movement of large groups of muscles and the impulses sent to the muscles in this case are generated by the spinal nerves.

The work done by one group of muscles is usually balanced by another group of muscles called the antagonists. These muscles are required for the body to carry out two functions for e.g. pushing and pulling. An example of antagonists muscles is the group of biceps and the triceps muscles in the arms and forearms. The biceps are present in front and when they contract, the arm is flexed (bent). When the triceps contract, the arm is straightened back again. These opposing muscles have a certain tone that keeps them slightly taut at all times. This tone is present in equal balance in both the groups of muscles. This helps us to maintain a certain posture.

Thus the muscles work along with the bones to perform movement and maintain posture.