MUSCULAR SYSTEM EASY COMPACT BIOLOGY NOTES OF HUMAN PHYSIOLOGY (MUSCULAR SYSTEM) FOR NEET AS WELL AS FOR BOARDS
An organ system Consisting of all types of Muscles. All Muscles arise from mesoderm except ciliary and iridial muscles of eye which arise from ectoderm. There are 650 muscles in human being and they constitute 40-50 PERCENT of the total body weight. Muscles have the property of excitability, contractility, extensibility & elasticity.
Muscle fiber’s (muscle cells) shows the property of all or none rule (BOWDITCH’S LAW) I.E, a single muscle fiber contracts completely as it receives its threshold stimulus, thus rise in degree of stimulus does not effect the fiber but influence the muscle contraction as more and more fiber receive threshold stimulus (muscle fiber contracts only at a particular potential called threshold potential.
TYPES OF MUSCLES
On the basis of location ,appearance and nature of regulation of their activities muscles are of three types.
- Skeletal muscles
These muscles are associated with skeletal components .These can be straited or stripped. They are voluntary controlled by SNS(SOMATIC NERVOUS SYSTEM).
STRTUCTURE OF SKELTAL MUSCLES
Skeletal muscle is made up of number of muscle bundles called fasciculi and they are held together by collagenous connective tissue called fascia. Each muscle bundle contains muscle cell or muscle fiber. Muscle fibers are thread like syncytial (MULTI NUCLEATED) its plasma membrane, mitochondria, endoplasmic reticulum ,and cytoplasm called as sarcolemma , sarcosome , sarcoplasmic reticulum , and sarcoplasm reticulum respectively. Sarcoplasmic reticulum stores calcium which is important for contraction of muscles. characteristic feature of the muscle fiber is the presence of parallel arrangement of filaments in the sarcoplasm called myofibrils. Detailed structure of the myofibrils revealed the presence of light and dark bands.
LIGHT BAND also called the I-band (isotropic band) and contains actin or thin filaments
DARK BAND also called A-band (ANISTROPIC BAND) and it contains myosin or thick filaments.
In the middle of I-band there is an elastic fiber called Z-line which gives attachment to the actin or thin filament. It is called as krause membrane.
In the middle of A-BAND there is a light zone called H-zone. In the middle of H-zone there is a thin fibrous membrane called M-line.