Test: Locomotion and Movement - Assertion and Reasoning - NEET MCQ

Main movement found in unicellular organisms are ciliary, flagellar and amoeboid movements. In multicellular animals also, phagocytes migrate through tissues by amoeboid movements. Ciliary movement of cells lining the upper respiratory tract, fallopian tubes and vasa efferentia of testes transport, respectively dust particles, ova and sperms in specific direction in those organs. Mammalian sperms move into the female reproductive tract by flagellar movements.

Muscle fibre is a syncitium as the sarcoplasm contains many nuclei. A characteristic feature of the muscle fibre is the presence of a large number of parallelly arranged filaments in the sarcoplasm called myofilaments or myofibrils. Each myofibril has alternate dark and light bands on it.

Visceral muscles are located in the inner walls of hollow visceral organs of the body like the alimentary canal, reproductive tract, etc. They do not exhibit any striation and are smooth in appearance. Hence, they are called smooth muscles (nonstriated muscle). Many cardiac muscle cells assemble in a branching pattern to form a cardiac muscle.

As muscle fibres are lacking in Hydra, the animal uses two types of contractile cells for this purpose. Processes of these cells run in the body wall both along the long axis of the body and arround the central body cavity. Contraction and relaxation of these cells respectively, shorten and elongate these processes. They consequently cause all types of movement of Hydra including shortening, elongation and also bending of body and tentacular movement. Locomotion is carried out by somersaults looping.

Each myofibril contains actin and myosin filaments which give it striated appearance due to dark and light bands. The light bands are made of actin and are called Ibands or isotropic band, whereas the dark bands are called 'A' or anisotropic bands and contain myosin. Both the proteins are arranged as rod-like structres, parallel to each other and also to the longitudinal axis of the myofibrils. In the centre of each 'I' band is an elastic fibre called 'Z' line which bisects it. The portion of the myofibril between two successive 'Z' lines is considered as the functional unit of contraction and is called a sarcomere. During contraction, the 'Z' lines attached to the actins are pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction. Hence, during shortening of the muscle, i.e., contraction, the 'I' bands get reduced, whereas the 'A' bands retain the length.

During strenous exercise, the muscle does not get sufficient oxygen to meet its energy needs immediately. So, it contracts anaerobically and accumulates lactic acid. During recovery, the oxygen consumption of the muscle by far exceeds than in the resting state. The extra oxygen consumed during recovery is called oxygen debt of the muscle.

Antagonistic muscles are those muscles which contract to produce opposite movements at the same joint. When a muscle contracts to produce a movement, its antagonist must relax to allow that movement to take place. Biceps and triceps are called antagonistic muscles. Because during flexion at the elbow, biceps contracts and triceps relaxes; during extension at the same joint, triceps contract and biceps relax.

The muscle fibre always contracts with the maximum force and this force doesn't rise on increasing the strength of the stimulus. If the stimulus is of strength below the threshold, then the muscle fibre doesn't contract at all. This is known as all or none law. But the entire muscle doesn't obey this law, it means that force of contraction of muscle increase with rise in strength of the stimulus. This is due to the fact that the strength of the threshold stimulus varies from muscle fibre to muscle fibre in a muscle

Due to the accumulation of lactic acid, muscles do not respond to a stimuli after a prolonged previous activity.

The phase of muscle contraction occurs when myosin binds and releases actin. Muscle contraction is initiated by a signal sent by the central nervous system via a motor neuron. A motor neuron along with the muscle fibres connected to it constitutes a motor unit.

Mechanism of muscle contraction is best explained by the sliding filament theory which states that contraction of a muscle fibre takes place by the sliding of the actin filaments over the thick myosin filaments.

A neural signal on reaching the neuromuscular junction releases a neurotransmitter (acetylcholine) which generates an action potential in the sarcolemma. This spreads through the muscle fibre and causes the release of calcium ions from sarcoplasmic reticulum into the sarcoplasm. Increase in Ca²⁺ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby, removing the mask of active sites for myosin.

During strenuous exercise, the muscle does not get sufficient oxygen to meet its energy requirement immediately. So, muscle contracts in the absence of oxygen. But it gets fatigued sooner in the absence of oxygen as the metabolic products of cellular respiration mainly lactic acid accumulates. This accumulation of lactic acid leads to muscle fatigue. After strenuous exercise, the oxygen consumption of muscle exceeeds. The extra oxygen consumed during recovery is called oxygen debt of the muscle. It is used in oxidizing the accumulated lactic acid aerobically and in restoring the depletedDuring strenuous exercise, the muscle does not get sufficient oxygen to meet its energy requirement immediately. So, muscle contracts in the absence of oxygen. But it gets fatigued sooner in the absence of oxygen as the metabolic products of cellular respiration mainly lactic acid accumulates. This accumulation of lactic acid leads to muscle fatigue. After strenuous exercise, the oxygen consumption of muscle exceeeds. The extra oxygen consumed during recovery is called oxygen debt of the muscle. It is used in oxidizing the accumulated lactic acid aerobically and in restoring the depleted creatine phosphate and ATP in the muscle fibre. A small part of oxygen debt also goes to myoglobin which binds and stores oxygen for future use.

Muscle contains a red coloured oxygen storing pigment called myoglobin. Myoglobin content is high in some of the muscles which gives a reddish appearance to them. Such muscles are called the red fibres. These muscles also contain plenty of mitochondria which can utilise the large amount of oxygen stored in them for ATP production. These muscles, therefore, can also be called aerobic muscles

Tetany is a spasm and twitching of the muscles, particularly of face, hands and feet. Rapid spasms (wild contractions) in muscle is due to low Ca2+ in body fluid which may be due to underactive parathyroid gland.

Skull has two occipital condyles, with the help of these two condyles, skull is connected by first vertebra of vertebral column, i.e., Atlas, this type of skull is called dicondylic skull which is present in humans.

Ulna is longer than radius. Its upper end has a larger olecranon process that forms the eminence of our elbow. The head of the radius articulates with the humerus

Bone is hard as its matrix has an inflexible material, the ossein. Matrix and of the bone also contains calcium and magnesium salts which also adds in building rigidity of the tissue. Cartilage is soft and pliable as its matrix has a flexible material, the chondrin. Matrix of the cartilage chiefly consists of chondroitin sulphate, that is capable of withstanding considerable pressure

First seven pairs of ribs are called true ribs. Dorsally, they are attached to the thoracic vertebrae and ventrally connected to the sternum with the help of hyaline cartilage.

Synovial fluid is a thick sticky fluid of egg white consistency, secreted by synovial membranes into the synovial cavity. Though the presence of synovial fluid is one of the reasons behind the mobility of the joints, but the most accurate reason is the arrangement of the bones at the joint, the spheroidal ball-like end of one bone articulates here with the cup-shaped depression in another. This allows the bone with the ball head to move freely in many planes. Shoulder joints and hip joints are the ball-and-socket joints.