Types of Muscles and their functions

 Human body has more than 600 muscles. Muscles perform many useful functions and help us in doing everything in day-to-day life. Muscles are classified by three different methods, based on different factors:

I. Depending upon the presence or absence of striations

II. Depending upon the control

III. Depending upon the situation.

DEPENDING UPON STRIATIONS

Depending upon the presence or absence of cross striations, the muscles are divided into two groups:

1. Striated muscle

2. Non-striated muscle.

Types of Muscles and their functions

1. Striated Muscle

Striated muscle is the muscle which has a large number of cross-striations (transverse lines). Skeletal muscle and cardiac muscle belong to this category.

2. Non-striated Muscle

Muscle which does not have cross-striations is called non-striated muscle. It is also called plain muscle or

smooth muscle. It is found in the wall of the visceral organs.

DEPENDING UPON CONTROL

Depending upon control, the muscles are classified into two types:

1. Voluntary muscle

2. Involuntary muscle.

1. Voluntary Muscle

Voluntary muscle is the muscle that is controlled by the will. Skeletal muscles are the voluntary muscles. These muscles are innervated by somatic nerves.

2. Involuntary Muscle

Muscle that cannot be controlled by the will is called involuntary muscle. Cardiac muscle and smooth muscle

are involuntary muscles. These muscles are innervated by autonomic nerves.

DEPENDING UPON SITUATION

Depending upon situation, the muscles are classified into three types:

1. Skeletal muscle

2. Cardiac muscle

3. Smooth muscle.

 

Skeletal Muscle

Skeletal muscle is situated in association with bones forming the skeletal system. The skeletal muscles form 40% to 50% of body mass and are voluntary and striated. These muscles are supplied by somatic nerves.

Fibers of the skeletal muscles are arranged in parallel. In most of the skeletal muscles, muscle fibers are attached to tendons on either end. Skeletal muscles are anchored to the bones by the tendons.

Cardiac Muscle

Cardiac muscle forms the musculature of the heart. These muscles are striated and involuntary. Cardiac

muscles are supplied by autonomic nerve fibers.

Smooth Muscle

Smooth muscle is situated in association with viscera. It is also called visceral muscle. It is different from skeletal

and cardiac muscles because of the absence of crossstriations, hence the name smooth muscle. Smooth muscle is supplied by autonomic nerve fibers. Smooth muscles form the main contractile units of wall of the various visceral organs.

 MUSCLE MASS

Muscle mass or muscle tissue is made up of a large number of individual muscle cells or myocytes. The muscle cells are commonly called muscle fibers because these cells are long and slender in appearance. Skeletal muscle fibers are multinucleated and are arranged parallel to one another with some connective tissue in between .

Muscle mass is separated from the neighboring tissues by a thick fibrous tissue layer known as fascia.

Beneath the fascia, muscle is covered by a connective tissue sheath called epimysium. In the muscle, the muscle fibers are arranged in various groups called bundles or fasciculi. Connective tissue sheath that covers each fasciculus is called perimysium. Each muscle fiber is covered by a connective tissue layer called the endomysium .

Muscle Mass

 

Each muscle cell or muscle fiber is cylindrical in shape. Average length of the fiber is 3 cm. It varies between 1 cm and 4 cm, depending upon the length of the muscle. The diameter of the muscle fiber varies from 10 μ to 100 μ. The diameter varies in a single muscle. Muscle fibers are attached to a tough cord of connective tissue called tendon. Tendon is in turn attached to the bone. Tendon of some muscles is thin, flat and stretched but tough. Such type of tendon is called aponeurosis.

Each muscle fiber is enclosed by a cell membrane called plasma membrane, that lies beneath the endomysium. It is also called sarcolemma. Cytoplasm of the muscle is known as sarcoplasm.

Structures embedded within the sarcoplasm are:

1. Nuclei

2. Myofibril

3. Golgi apparatus

4. Mitochondria

5. Sarcoplasmic reticulum

6. Ribosomes

7. Glycogen droplets

8. Occasional lipid droplets.

Each muscle fiber has got one or more nuclei. In long muscle fibers, many nuclei are seen. Nuclei are oval or elongated and situated just beneath the sarcolemma. Usually in other cells, the nucleus is in the interior of the cell. All the organelles of muscle fiber have the same functions as those of other cells.

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