Solution-Class-11-Science-Biology-Chapter-16-Skeleton and Movement-Maharashtra Board

(c) sarcomere

(b) Tarsal

(b) lactic acid

(d) Sphinetro-suprinater

(a) due to osmosis

(b) to bind with troponin, changing its shape so that the actin filament is exposed

(c) Osteoporosis

Fig. (c)

• While reading a class assignment, the neck muscles contract isometrically.
• These contractions are crucial for holding objects in place while supporting them.

Importance :

• A-Vertebral foramen : It houses spinal cord and its meninges
• B- Odontoid process : This process fits into the anterior portion of vertebral foramen of Atlas vertebra forming pivot joint.
• C- Inferior articular facet : It articulates with superior articular facet of axis and permits rotatory movement of head.

While performing exercise of biceps using dumbbells, the joint which should remain stationary are wrist joint or radiocarpal joint, ball and socket joint of shoulder. The only joint which should move is hinge joint of elbow.

• A fracture is a serious and traumatic injury that necessitates medical attention; however, prompt first aid is critical.
• If a bone is fractured, the fractured part must be immobilised to prevent further injury. It can be done with any available wooden plank, batons, or rulers. As a first aid measure, a wooden plank was tied to Moses' fractured leg.
• The sharp edges of a fractured bone are immobilised to prevent them from moving and cutting tissue, muscle, blood vessels, and nerves. Immobilization can also help with pain management and shock control.

• Sprains are injuries to the ligaments (tissues that connect bones at joints), whereas fractures are injuries to the bones.
• Sprains are classified into three severity levels: The first degree is mild with micro-tears, the second degree is partial with a visible tear in the ligament, and the third degree is completely tom ligament.
• A third-degree sprain is more painful than a fracture. This injury usually necessitates surgery, whereas breaking a bone usually does not necessitate surgery.
• Breaks and fractures vary greatly as well. Minor fractures (such as stress/hairline fractures) are far less painful than compound/complex fractures, which may result in the bone being cracked in half.
• Blood flow is required for growth and regeneration. Ligaments are not as well vascularized as bones. This causes the bones to heal more quickly than severe sprains. As a result, the duration of enduring pain until the injury heals varies.
• Furthermore, ligaments have an abundant supply of sensory nerves, which may be responsible for an increased sense of pain during severe sprains.

• Red muscle fibres have a high concentration of myoglobin and mitochondria (the site of aerobic respiration), whereas white muscle fibres have a lower concentration of myoglobin and mitochondria.
• Myoglobin is an iron pigment that transports oxygen molecules to muscle tissues. The presence of these pigments in red muscle fibres promotes faster aerobic respiration, whereas white muscle fibres may respire anaerobically.
• Anaerobic respiration in muscle cells produces lactic acid, and an increase in lactic acid accumulation can cause fatigue in white muscle fibres.
• Thus, red muscle fibres can work for longer periods of time with less fatigue due to lactic acid accumulation, whereas white muscle fibres fatigue after a shorter period of time.

Sarcomere : Sarcomere is the functional unit of myofibril. It has specific arrangement of actin and myosin filaments. The components of sarcomere are organized into variety of bands and zones.

The structure of sarcomere:

• ‘A’ band — dark bands present at the centre of sarcomere and contain myosin as well as actin.
• ‘H’ zone or Hensen s zone — light area present at the centre of ‘A’ band
• ‘M’ line — present at the centre of ‘H’ zone -
• ‘I’ band — light bands present on the either side of ‘A’ band containing only actin
• Z line — adjacent ‘I’ bands are separated by ‘Z’ line.

Sliding filament theory: It was put forth by H.E Huxley and A.F Huxley. It is also known as ‘Walk along theory’ or Ratchet theory.

• The sliding filament theory proposes that the interaction of actin and myosin filaments is the fundamental cause of muscle contraction. Myosin filaments are interdigitated with actin filaments.
• A cross bridge connects the head of myosin to the actin backbone, forming a hinge joint. Myosin head cannot tilt forward or backward from this joint. This movement is an active process because it makes use of ATP.
• ATPase activity is present in the myosin head. It can obtain energy from the breakdown of an ATP molecule. This energy can be used to move the myosin head.
• During contraction, the myosin head binds to the active site of actin filaments and pulls them inward, allowing the actin filaments to slide over the myosinfilaments. This causes muscle fibres to contract.

(i) Osteoporosis is the cause of her problem.

(ii) In this disorder, bones become porous and hence brittle. It is primarily age related disease and is more common in women than men.

Osteoporosis may be caused due to decreasing estrogen secretion after menopause, deficiency of vitamin D, low calcium diet, decreased secretion of sex hormones and thyrocalcitonin.

(iii) As age advances, bone resorption outpaces bone formation. Hence, the bones lose mass and become brittle. More calcium is lost in urine, sweat, etc., than it is gained through diet. Thus, prevention of disease is better than treatment by consuming adequate amount of calcium and exercise at young age.

(iv) A person who has had previous hairline fractures is more likely to have them again. As a result, Ragini must take her medications and supplements correctly, avoid Jerky movements, and maintain her body weight.

Myosin filament:

• Each myosin filament is a polymerized protein, and one thick filament is made up of many meromyosins (monomeric proteins).
• A myosin molecule is made up of two heavy chains (heavy meromyosin/HMM) that coil around each other to form a double helix.
• A cross bridge is one end of each of these chains that is projected outwardly. This end folds to form the myosin head, a globular protein mass.
• Each head has two light chains, resulting in four light chains/light meromyosin/LMM.
• Myosin heads have ATPase activity. It can split ATP to generate energy.
• Myosin accounts for 55% of muscle proteins.

Actin filament: It is a complex type of contractile protein. It is made up of three components.

• F actin: This protein serves as the backbone of actin filaments. F actin consists of two helical strands. Each strand is made up of G actin molecules that have been polymerized. One ADP molecule is bound to one G actin molecule.
• Tropomyosin: The actin filament contains two additional protein strands that are tropomyosin polymers. Each strand is only loosely connected to a F actin. Tropomyosin physically covers the actin strand's active myosin-binding site when it is at rest.
• Troponin: It is a complex of three globular proteins, is attached approx. 2/3^rd distance along each tropomyosin molecule. It has affinity for actin, tropomyosin and calcium ions. The troponin complex is believed to attach the tropomyosin to the actin. The strong affinity of troponin for calcium ions is believed to initiate the contraction process.

Atlas vertebrae:

• Atlas is the ring-like, 1^st cervical vertebrae. It has anterior, posterior arches and large lateral massesa
• It lacks centrum and spinous process. The superior surfaces of the lateral masses are concave and are known as superior articular facets.
• These facets articulate with the occipital condyles of the occipital bone thereby forming atlanto-occipital joints.
• This articulation permits ‘YES movement’ or nodding movement.
• The inferior surfaces of the lateral masses known as inferior articular facets articulate with axis vertebrae.

Axis vertebra :

• It is the 2nd cervical vertebrae.
• Centrum of this vertebra gives out tooth-like ‘Odontoid Process. Odontoid Process projects superiorly through the anterior portion of the vertebral foramen of the atlas.
• The odontoid process forms a pivot on which the atlas and head rotate. This arrangement allows No movement’ or side to side movement of the head.
• The articulation formed between the anterior arch of atlas, the odontoid process of the axis and between their articular facets is called as atlanto-axial joint.

• The level of uric acid is more than normal, thus the patient must be suffering from gouty arthritis.
• The elevated blood urea nitrogen indicates dysfunctional liver and/ or kidneys. It generally occurs due to decrease in GFR, caused by renal disease or obstruction of urinary tract.

Actin filament: It is a complex type of contractile protein. It is made up of three components.

• F actin: This protein serves as the backbone of actin filaments. F actin consists of two helical strands. Each strand is made up of G actin molecules that have been polymerized. One ADP molecule is bound to one G actin molecule.
• Tropomyosin: The actin filament contains two additional protein strands that are tropomyosin polymers. Each strand is only loosely connected to a F actin. Tropomyosin physically covers the actin strand's active myosin-binding site when it is at rest.
• Troponin: It is a complex of three globular proteins, is attached approx. 2/3^rd distance along each tropomyosin molecule. It has affinity for actin, tropomyosin and calcium ions. The troponin complex is believed to attach the tropomyosin to the actin. The strong affinity of troponin for calcium ions is believed to initiate the contraction process.

Myosin filament:

• Each myosin filament is a polymerized protein, and one thick filament is made up of many meromyosins (monomeric proteins).
• A myosin molecule is made up of two heavy chains (heavy meromyosin/HMM) that coil around each other to form a double helix.
• A cross bridge is one end of each of these chains that is projected outwardly. This end folds to form the myosin head, a globular protein mass.
• Each head has two light chains, resulting in four light chains/light meromyosin/LMM.
• Myosin heads have ATPase activity. It can split ATP to generate energy.
• Myosin accounts for 55% of muscle proteins.

• The contraction and relaxation of muscles is significantly influenced by calcium ions.
• When muscles contract, calcium ions are released from the sarcoplasm and are then stored there when muscles relax.
• Release of calcium ions from the sarcoplasm causes muscle contraction. The concentration of calcium ions rises when skeletal muscle is stimulated and an action potential moves along the T tubule.
• These calcium ions bind to troponin, and as a result, tropomyosin moves away from the myosin-binding sites on actin due to a conformational change in troponin. The muscle fibre contracts when these binding sites become free because myosin heads then bind to them to form cross-bridges.
• The decrease in calcium ion concentration in the sarcoplasm causes tropomyosin to slide back and block the myosin binding sites on actin. This causes the muscle to relax.

(i) Synchondroses :

(ii) Symphysis :