Muscular System:types of Muscles
In mammals (specifically humans) three types of muscles do exist such as skeletal muscle, cardiac (heart) muscles, and smooth muscles.
Skeletal Muscles: These are form of striated tissues, which are under the control of somatic nervous system. It is attached to the bones in the skeleton and is of voluntary in nature. The skeletal muscle contains spindle shaped cells which can fuse together to form a new cell with 2 nuclei. It is known that surprising that if this fusion continues several times it results in formation of long tubular structure called muscle fiber.
Cardiac Muscles: These constitute the involuntary muscles and appear striated which are formed by thick and thin protein filaments which are arranged alternately. It consists of specific muscle proteins called actin and myosin. The cardiac muscle cells are also known as cardiac myocytes. It is found that cardiac muscles have the power of regeneration.
Smooth Muscles: These are also involuntary and are non-striated with minimal alternate arrangement of protein filaments. These are found in arteries, veins, lymphatic vessels, urinary bladder, uterus, gastrointestinal tract, and respiratory tract.
In muscular system the muscles are classified into 3 categories. They are:
Skeletal muscles
Muscles present in heart
Smooth muscles.
The function of muscles are :
Muscles provide strength
They maintain the body balance
They contribute to the body posture
And mainly helps in movement
It also keeps body worm.
Pathology Related to Muscular System
The disorders or diseases related to muscle system can either be infectious, hormonal, genetic, autoimmune, cancerous, and even poisonous. Several disorders are found which are associated with muscular system.
Arthrogryposis
Central Core Disease
Myopathy
Laminopathy
Diastasis Recti
Zenker's Degeneration
Pelvic Floor Muscle Disorder
Orofacial Myology Disorders
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Muscular Contraction
Muscle system:
Muscle system composed of many elongated cells called muscle fibres which are able to contract and relax. Three types of muscles can be identified skeletal muscle, smooth muscle and cardiac muscle.
The sliding filament theory of muscle contraction
This model of muscular contraction was proposed independently by two research teams, that muscle contracts by the actin and myosin filaments sliding past each other. Nothing actually contracts except the length of the sacromeres and hence the whole muscle. The two research teams who proposed the hypothesis in 1954 were H.E. Huxley and J. Hanson, and A.F. Huxley and R. Niedergerke. One piece of supporting evidence regarding muscular contraction was the fact that, as muscle contracts, the dark bands (A bands) remain the same length and the light bands (I bands) and the H zones gets shorter. This is explained by the hypothesis. Evidence has now confirmed this hypothesis of muscular contraction is known as the sliding filament theory.
Muscular Contraction:filament Types
Myosin (thick filament)
A molecule of myosin consists of two distinct regions, a long rod-shaped region called a myosin rod, and a myosin head which consists of two similar globular parts. The globular heads appear at intervals along the myosin filaments, projecting from the sides of the filament. Where the actin and myosin filaments overlap, the myosin heads can attach to neighboring actin filaments. The importance of this will become clear when we deal with the actual contraction mechanism of the sacromeres.
Actin (thin filament)
Each actin filament is made up of two helical strands of globular actin molecules (G-actin) which twist round each other. The whole assembly of actin molecules is called F-actin (fibrous actin). It is thought that an ATP molecule is attached to each molecule of G-actin.
Muscular contraction mechanism
When the actin and myosin filaments overlap the myosin heads can attach like ‘hooks’ to neighboring actin filaments (f-actin), forming cross bridges. The bridges then move to pull the actin filaments past the myosin filaments and leads to muscular contraction. The energy for this movement is ATP released by the hydrolysis of enzyme ATPase to ADP and phosphate. This sequence of events is described as ratchet mechanism. The bridges form and re-form 50-100 times per second, using up ATP rapidly. This explains the need for numerous mitochondria in the muscle fibre, which can supply the ATP as a result of aerobic respiration.
