The muscular system is responsible for the movement of the human body. Muscles are found within the muscular system, which is the body’s own network of tissues and fibres responsible for both outward and inward movements of the body.
Types of muscles:
Muscles are of three types; skeletal, smooth and cardiac.
1. Skeletal Muscles:
• They are also known as striped, striated, somatic and voluntary muscles
• They are the most abundant type and are found attached to the skeleton. For this reason they are called skeletal muscles.
• They are innervated by somatic nervous system and are therefore under voluntary control.
• They respond quickly to stimuli and are capable of rapid contractions. They get fatigued easily because of their rapidity.
• Each muscle fibre is multinucleated cylindrical cell containing groups of myofibrils. The myofibrils are in turn made up of myofilaments of three types namely actin, myosin, and tropomyosin. Thus the skeletal muscles have three structural levels namely muscle fibres, myofibrils and myofilaments.
2. Smooth Muscles:
• They are also known as plain, unstriped, visceral and involuntary muscles.
• Unlike skeletal muscles, they do not exhibit cross striations under the microscope and thus they got the name “smooth”.
• They are supplied by autonomic nervous system and therefore they are involuntary in their action.
• They respond slowly to stimuli but are capable of long time sustained contractions. They do not get fatigued easily because of their slowness of response.
• They provide motor power for regulating internal environment related to digestion, circulation, secretion and excretion.
• Each smooth muscle fibre is an elongated spindle shaped cell with a single nucleus placed at the centre. They also possess actin and myosin filaments but the structural arrangement of these filaments is very different as compared to the skeletal muscles.
3. Cardiac muscles:
• They form the myocardium of human heart.
• Cardiac muscle is intermediate in structure lying between the skeletal and smooth muscles. They are striated like skeletal muscles but at the same time they are involuntary and have uninuclear cells like smooth muscles.
• They are meant for automatic rhythmic contractions for long period of time.