NEET Questions Bank: Biology Solutions on Human Physiology - Locomotion and Movement

Human Physiology - Locomotion and Movement

(NEET Syllabus): Origin Types of movement- ciliary, fiagellar, muscular; Skeletal muscle- contractile proteins and muscle contraction; Skeletal system and its functions (To be dealt with the relevant practical of Practical syllabus); Joints; Disorders of muscular and skeletal system-Myasthenia gravis, Tetany, Muscular dystrophy, Arthritis, Osteoporosis, Gout.

HUMAN PHYSIOLOGY (Locomotion and Movement)

Theoretical Questions - TQ 3 (Q. No.12 - 15)

Very Long Answer Type Questions

Question.12: How does calcium affect the process of muscle contraction?

Question.13: Explain sliding filament theory of muscle contraction.

Question.14: Explain the bones of fore limbs.

Question.15: Describe the various types of joints present in human body with examples.

Answer 12. Mechanism of muscle contraction is best explained by the sliding filament theory which states that contraction of muscle fibres takes place by the sliding of the thin filaments over the thick filaments.

Muscle contraction is initiated by a signal sent by the central nervous system (CNS) via a motor neuron. A motor neuron along with the muscle fibers connected to it constitutes a motor unit. The junction between a motor neuron and the sarcolemma of the muscle fibre is called the neuromuscular junction or motor-end plate.

A neural signal reaching this 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 into the sarcoplasm.

Increase in Ca²⁺ 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.

This 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. It is clear from the above steps, that during shortening of the muscle, i.e., contraction, the I bands get reduced, whereas the "A" bands retain the length.

The myosin, releasing the ADP and P_i  goes back to its relaxed state. A new ATP binds and the cross-bridge is broken. The ATP is again hydrolysed by the myosin head and the cycle of cross-bridge formation and breakage is repeated causing further sliding.

The process continues till the Ca²⁺ ions are pumped back to the sarcoplasmic cisternae resulting in the masking of actin filaments. This causes the return of "Z" lines back to their original position, i.e., relaxation. The reaction time of the fibres can vary in different muscles.

Answer 13. Two groups of workers (A.F.Huxley and Ralph Niedergerke 1954; H.E.Huxley and Jean Hanson 1954) proposed the sliding filament theory. The essential features of this theory are as follows:

1. During muscle contraction, the thin myofilaments slide inward towards the H-zone.

2. The sarcomere shortens, but the lengths of thin and thick myofilaments do not change.

3. The crossbridges of the thick myofilaments connect with portions of actin of the thin myofilaments. The myosin cross bridges move on the surface of thin myofilaments and the thin and thick myofilaments slide past each other.

4. As the thin myofilaments move past the thick myofilaments, the H-zone narrows and even disappears when the thin myofilaments meet at the centre of the sarcomere. Thus, the length of the sarcomere decreases during contraction. Size of I band also decreases.

5. The lengths of the thick and thin myofilaments do not change during muscle contraction.

Answer 14. Each arm consists of the following 30 bones:

1 humerus, 1 radius, 1 ulna, 8 carpal, 5 metacarpal bones, 5 digits (14 phalanges). Phalangeal formula: 2,3,3,3,3.

Upper rounded end of the humerus is called head which articulates into the glenoid cavity of the pectoral girdle. A greater and a lesser tubercles occur near the head.

The shaft of the humerus has a V-shaped deltoid ridge at about its middle. A pully like trochlea is present between two ridges. Its upper end has a larger olecranon process that forms the eminence of our elbow. The head of the radius articulates with the humerus. Each wrist is composed of eight carpals which are arranged in two rows: scaphoid, lunate, triquetrum and pisiform in proximal row and trapezium, trapezoid, capitate and humate in distal row.

Answer 15. The structural arrangements of tissues by which bones are joined together are called joints. According to the mobility they are classified as fibrous or fixed or immovable joints, cartilaginous or slightly movable joints and synovial or freely movable joints.

1. Fibrous or Immovable Joints: In this type of joints there is no movement between the bones concerned. As the name suggests, there is white fibrous tissue between the ends of the bones. Examples of this type include - the joints between the bones of skull called sutures and the joints between the teeth and the maxilla and teeth and mandible.

2. Cartilaginous or Slightly Movable Joints: In this type there is a pad of white fibrocartilage between the ends of the bones taking part in the joints which allows for very slight movement. Movement is only possible because of compression of pad of cartilages. Examples of cartilaginous joints include the pubic symphysis of pubis and the joints between the vertebrae (intervertebral discs).

3. Synovial or Freely Movable Joints: A considerable movement is possible at all synovial joints. Synovial joints are of six types:

(i). A gliding joint- It is the simplest of the synovial joints. The articular surfaces of two bones are usually flat, permitting only back-and-forth and side-to-side movements. Gliding joints are found between the carpal bones and between the tarsal bones.

(ii). A hinge joint - It allows movement primarily in one plane. In a hinge joint spool (reel) surface of one bone fits into the concave surface of another bone. The elbow, the knee, ankle and interphalangeal hints are examples of hinge joints.

(iii). A pivot joint- This joint also allows movement in only one plane. In a pivot joint rounded or pointed bone fits into a shallow depression in another bone. The primary movement at a pivot joint is rotation.

(iv). Condyloid or ellipsoid joint- Allows movement in two planes, back & forth & side-to side. The joints between the metacarpals and phalanges (metacarpo-phalangeal joint) of the fingers are examples of ellipsoid joints.

(v). A saddle joint allows the same movements as an ellipsoid joint, but the movements are free. The joint between the carpal and metacarpal of thumb of the hand is an example of saddle joint.

(vi). A ball-and-socket joint- One bone of this joint forms a rounded head while the other bone forms a cup shaped structure into which the head fits. It allows free movement in all directions. It is most movable joint. Examples: hip joint and shoulder joint.

 Human Physiology: Locomotion and Movement - Biology Objective Questions 

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