Title 17. Locomotion and movement notes.pdf ✅

Locomotion and Movement Locomotion: Voluntary movements such as movement of cilia limbs, jaws, eyelids, tongue, etc. are called locomotion. • All locomotions are movements, but all movements are not locomotions. Types of movement: Cells of the human body exhibit three main types of movements- 1) Amoeboid: Macrophages and leucocytes in blood exhibit amoeboid movement, which is effected by pseudopodia formed by the streaming of protoplasm, and microfilaments are also involved in amoeboid movement. 2) Ciliary: Ciliary movement occurs in internal tubular organs which are lined by ciliated epithelium. • The coordinated movements of cilia in the trachea help in removing dust particles. • Passage of ova through the female reproductive tract is also facilitated by the ciliary movement. 3) Muscular: Movement of our limbs, jaws, tongue, etc, requires muscular movement. • Locomotion requires a perfect coordinated activity of muscular, skeletal and neural systems. Muscle: Muscle is a specialised tissue of mesodermal origin. Based on location, three types of muscles are identified- 1. Skeletal: Skeletal muscles are associated with the skeletal components, which have a striped appearance under the microscope and hence are called striated muscles. BoardStudy
• They are voluntary muscles. • Skeletal muscles are primarily involved in locomotory actions • and changes of body postures. 2. Visceral: Visceral muscles are located in the inner walls of hollow visceral organs of the body and do not exhibit any striation and are smooth in appearance, hence are called smooth muscles. • They are involuntary muscles. • Visceral muscles assist transportation of food through the digestive tract. 3. Cardiac: Cardiac muscles are the muscles of heart. • Cardiac muscles are striated, involuntary in nature. Structure of skeletal muscle: Each organised skeletal muscle in our body is made of a number of muscle bundles held together by a common collagenous connective tissue layer called fascia. • Each muscle bundle contains a number of muscle fibres and each muscle fibre is lined by the plasma membrane called sarcolemma enclosing the sarcoplasm. • Muscle fibre is a syncitium as the sarcoplasm contains many nuclei. • The endoplasmic reticulum, i.e., sarcoplasmic reticulum of the muscle fibres is the store house of calcium ions. • A large number of parallelly arranged filaments is present in the sarcoplasm called myofilaments or myofibrils. • Each myofibril has alternate dark and light bands on it and it is due to the distribution pattern of two important proteins- a) Actin b) Myosin BoardStudy
• The light bands contain actin and is called I-band or isotropic band, whereas the dark band called ‘A’ or anisotropic band contains myosin. • Structure of contractile proteins: Each actin (thin) filament is made of two ‘F’ (filamentous) actins helically wound to each other and each ‘F’ actin is a polymer of monomeric ‘G’ (Globular) actins. • Two filaments of another protein, tropomyosin also run close to the ‘F’ actins throughout its length. • A complex protein troponin is distributed at regular intervals on the tropomyosin. • Each myosin (thick) filament is also a polymerised protein and many monomeric proteins called meromyosins constitute one thick filament. • Each head with a short arm and a tail, the former being called the heavy meromyosin (HMM) and the latter, the light meromyosin (LMM). • The HMM component, i.e, the head and short arm projects outwards at regular distance. • Meromyosin has two important parts, a globular and angle from each other from the surface of a polymerised myosin filament and is known as cross arm. • The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin. Mechanism of muscle contraction • Sliding filament theory states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments. • The junction between a motor neuron and the sarcolemma of the muscle fibre is called the neuromuscular junction or motor-end plate. BoardStudy
• A neural signal, released by central nervous system, when reaches the junction releases a neurotransmitter (Acetyl choline) which generates an action potential in the sarcolemma, which spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm. • Increase in Ca++ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby remove the masking of active sites for myosin. • Utilising the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge, which pulls the attached actin filaments towards the centre of ‘A’ band. • The ‘Z’ line attached to these actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction, where the ‘I’ bands get reduced, whereas the ‘A’ bands retain the length. • The myosin, releasing the ADP and P1 goes back to its relaxed state, a new ATP binds and the cross- bridge is broken and breakage is repeated causing further sliding. • The process continues till the Ca++ ions are pumped back to the sarcoplasmic cisternae resulting in the masking of actin filaments, which causes the return of ‘Z’ lines back to their original position, i.e., relaxation. • Muscle contains a red coloured oxygen storing pigment called myoglobin. • Red fibres contain plenty of mitochondria which can utilise the large amount of oxygen stored; such muscles are called the red fibres. • Myoglobin content is high in some of the muscles which gives a reddish appearance in them for ATP productionand can also be called aerobic muscles. BoardStudy