Skeletal Muscle Physiology

There are three types of muscle skeletal which are voluntary, smooth muscle which are involuntary and cardiac muscle. Muscle is made up of protein filaments, myosin and actin. These filaments slide past each other to produce a contraction which changes both the length and shape of the cell. The primary function of the muscle is to produce both movement and force.
Skeletal muscle is composed of bundles of muscle fibres containing myofibrils of thick and thin filaments (myosin and actin). Skeletal muscle have distinct striations due to the overlapping of the myosin and actin held in place by the sarcolemma. Skeletal muscles cover majority of the skeleton, giving shape and the ability of movement. They are attached to the skeleton by strong tendons
which are capable of contracting to facilitate movement. The skeletal muscles are also referred to as ‘voluntary’ muscles, this is because the body has full control over them via the somatic nervous system where impulses from the brain are sent to tell the muscles what to do.
The skeletal muscles main function is to provide the body with support and the ability to carry out movements.
The muscles in the abdominal regions are constantly contracting to hold the head in place and maintain posture. Within the digestive and urinary systems an important skeletal muscle is present. The sphincter muscle are located at the ends of the digestive and urinary systems and function in controlling the opening and closing of these systems (study.com). Skeletal muscle also has homeostasis functions. Homeostasis is the maintenance of internal environment (study.com). Due to the contraction of skeletal muscles energy is given off and heat produced which each contraction. The heat produced helps to maintain the body's internal temperature and therefore is an effective
regulator.
The contraction of the skeletal muscles can produce fast and powerful movements, or small precise actions. Skeletal muscles can contain different muscle fibres which vary in the rate of fatigue. Slow twitch fibres which are resistant to fatigue, type IIa which are a hybrid of slow and fast twitch fibres so fatigue before slow twitch and fast twitch fibres which provide power instantly but fatigue quickly. Contraction in a skeletal muscle can occur from one of the two theories, the sliding filament theory or the cross bridge theory. For a contraction to occur in the skeletal muscle there must be a stimulation of the muscle in the form of an impulse from a motor neuron. Calcium and ATP must also be present in the cells for the sliding filament theory to take place.
When an impulse is received by the muscle fibres, it stimulates a reaction in the sarcomere of the the actin and myosin filaments. From this reaction the myosin heads are stimulated which reach forwards to attach to the actin filament and pull it towards the sacromere. This results in the shortening of the sacromere. Troponin a complex protein is attached to tropomyosin within is found in the actin filaments. When the skeletal muscle is relaxed tropomyosin blocks the attachment sites for the myosin heads which results in the contraction being prevented. However when the muscle is stimulated from the original impulse calcium channels open in the sarcoplasmic reticulum filling the muscle cell with calcium. Calcium has an important role in the contraction of muscles as it can move the tropomyosin away from the attachment sites so cross bridges can form and a contraction of the muscle occurs (ptdirect.com).
Smooth muscle can be described as involuntary as an individual has no control over their movements. Unlike skeletal muscles a smooth muscle is not striated and has no defining stripes. Smooth muscles are found in the walls of hollow organs, stomach, oesophagus, bloods vessels and ciliary muscles of the eye.
Smooth muscle is stimulated by involuntary impulses, which create slow, rhythmical contractions used to control the organs in the body.
Smooth muscles do not fatigue and are constantly working in the digestive system to move food and substances through the body through peristalsis (contraction and relaxing). They also work continuously within the bladder. The relaxing of the smooth muscles allows an individual to hold their urine until they reach a bathroom and the contraction of these muscles allow the urine to be pushed out. Similarly in a women's uterus smooth muscles help push the baby out when in labor.
For a smooth muscle to contract cross bridges firstly must be established. The thin filaments will slide past the thick filaments. This causes shortening of the muscle in all directions. Similarly calcium ions are required in smooth muscles to relax again. They bind to myosin breaking up ATP into ADP and transfer Pi activating the myosin to form cross bridges with actin. When the calcium is removed from the cell the myosin is not stimulated and therefore relaxes
(howstuffwrks.com).