Locomotion And Movement

The sternum (also known as the breastbone) is connected to the ribs by hyaline cartilage.

Hyaline cartilage is a type of flexible connective tissue that provides support and allows for slight movement between bones. In the case of the sternum and ribs, the hyaline cartilage forms the costal cartilages, which connect the ribs to the sternum. These costal cartilages allow for some flexibility and movement during activities such as breathing.

The hyaline cartilage is responsible for connecting the sternum and ribs, providing structural integrity, and allowing for some degree of movement in the ribcage.

Elbow joint is an example of the hinge joint.

The arm of the human body is composed of three bones that join together to form a hinge joint called the elbow. The upper arm bone (humerus) connects from the shoulder to the elbow which forms the top of the hinge joint. A hinge joint, a type of synovial joint, is a form of the freely movable joint allowing angular movement in one plane only, increasing and decreasing the angle between the bones. For e.g., the knee joint and the elbow joint. It provides uniaxial movement. 

So, the correct answer is option A 'Hinge joint'.

The glenoid cavity is a shallow cavity found on the scapula bone. Scapula, also known as shoulder blade, is a triangular bone which along with clavicle constitute the pectoral girdle. 

The upper bone of the arm is called as humerus. Its upper end is rounded which is called the head of the humerus. This rounded head articulates into the glenoid cavity forming a glenohumeral joint or shoulder joint. This joint is a type of ball and socket joint that allows free movement of our hands. Biceps brachii, a tendon, keeps humerus within the glenoid cavity. 

The joint formed between the clavicle and acromion of the scapula is called acromioclavicular joint. It forms the roof of the shoulder. 

Answer:

Explanation:

• Tetanus refers to a sustained muscular contraction resulting from a rapid series of nerve impulses.
• In this condition, there is no relaxation between successive stimuli, and the muscle remains in a continuous state of contraction.
• This is different from:
  • Fatigue: Muscle becomes unable to contract after prolonged activity.
  • Tonus: Slight, continuous tension in resting muscles.
  • Spasm: Sudden involuntary muscle contraction.

• Arthritis - Inflamed joints: Arthritis is a condition characterized by inflammation of the joints, causing pain and stiffness. This is a correct match.
• Tetany - high Ca²⁺ level causing rapid spasms: Tetany is actually caused by low levels of calcium (Ca²⁺), not high levels. Thus, this match is incorrect.
• Myasthenia gravis - Genetic disorder resulting in weakening and paralysis of skeletal muscle: Myasthenia gravis is an autoimmune disorder, not a genetic disorder, where the immune system attacks components of nerve-muscle communication, leading to muscle weakening. Thus, this match is incorrect.
• Muscular dystrophy - An autoimmune disorder causing progressive degeneration of skeletal muscle: Muscular dystrophy is a genetic disorder, not an autoimmune one, causing muscle weakening and degeneration. Thus, this match is incorrect.

The question asks us to identify the structure that is present between the adjacent bones of the vertebral column. To solve this, we need to understand the anatomy of the vertebral column.

The vertebral column is made up of individual vertebrae, and between each pair of adjacent vertebrae is an intervertebral disc. These discs are crucial as they allow for movement between the vertebrae and act as shock absorbers.

The intervertebral discs are composed of cartilage, specifically fibrocartilage, which provides strength and flexibility. Thus, the correct answer to the question is Cartilage.

In contrast, let's briefly examine why the other options are incorrect:

• Intercalated discs are specialized structures found in cardiac muscle cells and not related to the vertebral column.
• Areolar tissue is a connective tissue that primarily holds organs in place and is not specifically found between bones of the vertebral column.
• Smooth muscle is found in walls of hollow organs and blood vessels but not between vertebrae.

Therefore, the presence of cartilage between the vertebrae is essential for the vertebral column's structure and function.

Muscle contraction is a complex process involving several steps. Let’s analyze the given statements:

A. Initiation by CNS via sensory neuron: Muscle contraction is initiated by signals from the CNS, but these signals are sent via motor neurons, not sensory neurons. Sensory neurons carry signals from the periphery to the CNS. So, statement A is incorrect.
B. Neurotransmitter and action potential: Neurotransmitters (e.g., acetylcholine) released from motor neurons bind to receptors on the muscle cell membrane (sarcolemma), generating an action potential that spreads across the sarcolemma and into the T-tubules. So, statement B is correct.
C. Calcium binding to troponin: The action potential triggers the release of calcium ions (Ca²⁺) from the sarcoplasmic reticulum. The increased Ca²⁺ concentration in the cytoplasm leads to the binding of calcium with troponin, a protein complex on the actin filaments. This binding causes a conformational change in tropomyosin, exposing the myosin-binding sites on actin. So, statement C is correct.
D. Masking of active site for actin: The active sites on actin are initially masked by tropomyosin, not activated. The increased Ca²⁺ level and its binding to troponin causes tropomyosin to move away from the myosin-binding sites on actin, unmasking them. So, statement D is incorrect.
E. ATP hydrolysis and cross-bridge formation: ATP hydrolysis provides the energy for myosin heads to bind to the exposed active sites on actin, forming cross-bridges. The subsequent ”power stroke” of the myosin heads pulls the actin filaments towards the center of the sarcomere, resulting in muscle shortening (contraction). So, statement E is correct.