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Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Chapter Contents Movement Locomotion Muscles Motor Unit Mechanism of Muscle Contraction Muscle Relaxation Skeletal System Joints Disorder of Muscular and Skeletal System Movement is a change in posture or position. It is an essential and significant feature of living organisms and hence both unicellular and multicellular organisms show movement. The movement which results in change of place or location is called locomotion. MOVEMENT Both the internal and external structures of an organism (constituted by cell and intracellular structures) show movements. Types of Movements On the basis of structures involved, three basic types of movements occur in the cells of human body namely : amoeboid, ciliary and muscular. Movement Ciliary Movement Muscular Movement Amoeboid or Pseudopodial Movement (i) Amoeboid or Pseudopodial Movements: Due to the streaming of protoplasm or cytoplasm, the surface of the cell forms false feet or pseudopodia. The formation and withdrawl of pseudopodia allows the cell to change its shape regularly. As Amoeba, WBCs, and macrophages show pseudopodial movements they do not have a fixed shape. The leucocytes and macrophages reach each and every part of the body and engulf the antigens or pathogens with pseudopodia. (ii) Ciliary Movements: The free surface of the cells have short fine hair-like projections called cilia. The movement of these projections (cilia) is called ciliary movement. The oar-like activity of the cilia creates a water current which helps in movement of various structures. The tubular structures of human body such as Chapter 7 Locomotion and Movement
2 Locomotion and Movement NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 respiratory tract and reproductive tract are lined by ciliated epithelium and help in the movement of various substances. In oviduct, cilia provide the motive force for the passage of ova. Coordinated movement of cilia in trachea helps in the removal of dust particles inhaled along with atmospheric air. Spermatozoa and protozoa have flagella for locomotion and movement. (iii) Muscular Movement: In humans, movement of limbs, jaws, tongue and other body parts occurs due to contraction of muscles. The muscles contract and relax rhythmically to produce movement and are used effectively for locomotion. LOCOMOTION Locomotion occurs in both unicellular and multicellular organisms with help of different structures. There are certain structures which are essential for both movement and locomotion of internal and external body parts. For example, Hydra uses tentacles for capturing its prey as well as for locomotion. Paramoecium uses cilia for movement of food (ingestion) and locomotion and Amoeba uses pseudopodia for the same purpose. Humans use limbs for change in body postures and locomotion. This suggests that movement and locomotion are not different entities. They are said to be interdependent on each other. Hence, it can also be said that all locomotions are movements but all movements are not locomotion. Functions of Locomotion Locomotion is performed for the following processes : (i) Procurement of food. (ii) Searching and building shelters. (iii) Finding a mate. (iv) Protection from predators. (v) Search of suitable breeding grounds. (vi) Migration. MUSCLES Muscle is a specialised tissue originating from the mesoderm germ layer. The muscular tissue is made up of specialised cells called myocytes. These cells are bound together by a connective tissue and form muscular tissue. It brings about different types of movements in internal and external body parts. A human body is made up of 639 muscles which have unique properties like contractility, excitability, elasticity and extensibility. They make about 40-50 percent of body weight in an adult human. Fig. : Diagrammatic cross-sectional view of a muscle showing muscle bundles and muscle fibres The myocytes have the ability to contract. They can shorten by 1/3rd to 1/2nd of their length due to contraction and then return to its original length, so the property of shortening and then returning to relaxed state of the
NEET Locomotion and Movement 3 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 muscle fibre is called elasticity. A stimulus such as nerve impulse, hormone, mechanical, thermal or chemical stimulus is required for excitation of the muscles which then causes muscles to contract. The stimulus received at one end of the muscle spreads almost immediately to other parts as well as to neighbouring myocytes. Structure of Muscle A muscle is covered by a sheath of connective tissue called epimysium. Inside the epimysium, a muscle has many muscle fibres arranged in a bundle called fasciculi (singular-fasciculus or fascicle). Each fasciculus is surrounded by a sheath of connective tissue called perimysium. The muscle fibres are parallel to each other in the fasciculus and each muscle fibre is surrounded by a connective tissue called endomysium. All the muscle bundles are further bound together by a common collagenous sheath of connective tissue called fascia. Epimysium Perimysium Endomysium Muscle Fibres or cells Nerve Fibre Fasciculus or Fascicle Blood Vessel Fig. : T.S. of a Muscle Tendons: The two ends of the muscles are attached to the bone with the help of an inelastic connective tissue called tendon. One end of the muscle is attached to fixed or less movable bone and the other end is attached to the more movable bone. Types of Muscles Muscles can be classified based on various criteria namely location, appearance, nature of regulation of their activities. Based on location, the muscles can be of following types: (i) Skeletal muscle These muscles are attached to the skeletal component of the body and are primarily involved in the locomotory actions and changes of the body posture. When observed under a microscope, alternate light and dark bands are observed on the muscle fibres. Due to the striated appearance of the muscle fibres, these muscles are called striated or striped muscles. These muscles are voluntary as they are under the control of animals will or conscious. For example, muscles of hindlimbs, forelimbs, body wall, tongue, pharynx and beginning of oesophagus etc. Nucleus Striations Fig. : Skeletal (striated) muscle tissue
4 Locomotion and Movement NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 (ii) Visceral or non-striated: The cells of these muscles are elongated, spindle-shaped, broad from the middle and have tapering ends. These muscles do not have alternate light or dark bands on their muscle fibers and hence give a smooth appearance when observed under a microscope. Their fibres are not organised into parallel arrays. These muscles lines the hollow organs and are involuntary. e.g., posterior region of oesophagus, stomach, intestine, lungs, urinary bladder, urinogenital tract. The transportation of food through the digestive tract and gametes through the genital tract occurs due to the contraction of smooth muscles. Sarcolemma Sarcoplasm Myofibrils Nucleus Fig. : Smooth Muscle fibre as observed under light microscope. (iii) Cardiac muscle: Cardiac means heart, hence muscles of the heart are called cardiac muscle. The cells of cardiac muscle assemble in a branching pattern. These are striated in nature i.e., alternate light and dark bands could be observed on the muscle fibre when kept under the microscope. These are involuntary in nature as they generate their own impulse or excitation and hence allow heart to continue its pumping activity of rhythmic contraction and relaxation. Nucleus Striations Junction between adjacent cells Fig. : Cardiac muscle tissue Differences between Skeletal, Visceral and Cardiac muscle S.No. Skeletal Visceral Cardiac 1. These are cylindrical. These are spindle-shaped. Muscle fibres are cylindrical. 2. Their ends are blunt. Their ends are tapering. Their ends are blunt. 3. Fibres are unbranched. Fibres are unbranched. Fibres are branched. 4. Fibres occur in bundles. They occur singly, in sheets and small bundles. They form three-dimensional network.