Anatomy And Physiology Advanced - Qp3

Explanation
Muscles play a crucial role in the movement and stability of the human body. They are responsible for various functions such as locomotion, posture, and organ movement. With muscles comprising approximately 45% of total body weight, it is plausible to have a significant number of muscles in the human body. Out of the given options, 600 muscles seems like a reasonable estimate considering the complexity and diversity of muscle groups throughout the body.

Explanation
Skeletal muscles are not found in the walls of the heart. The walls of the heart are composed of cardiac muscle, which is a specialized type of muscle tissue. Skeletal muscles are found throughout the body and are responsible for voluntary movements.

Explanation
Skeletal muscle is responsible for movement in the body, as it allows us to walk, run, and perform various activities. It also plays a crucial role in maintaining support and posture by providing stability to the skeletal system. Additionally, skeletal muscle generates heat through the process of muscle contraction, which helps regulate body temperature.

Explanation
The statement is true because the muscle belly is indeed the thick portion of muscle tissue that lies between the origin and insertion points. The origin is the point where the muscle attaches to a stationary bone, while the insertion is the point where the muscle attaches to a movable bone. The muscle belly is the fleshy part of the muscle that contracts and relaxes, allowing movement to occur at the joint.

Explanation
Isometric contractions occur when a muscle increases in tension without actively shortening or lengthening. In this type of contraction, the muscle remains at a constant length while generating force against an immovable object or resisting an external force. This can be seen, for example, when holding a weight in a static position without any movement in the joint. Isotonic contractions involve muscle shortening or lengthening, while isokinetic contractions involve the muscle contracting at a constant speed.

Explanation
The statement is true because myosin and actin filaments in muscle cells are arranged in a way that they run parallel to each other, but they are not physically attached when the muscle is at rest. However, during muscle contraction, the myosin heads bind to the actin filaments, causing them to slide past each other and generate force. This interaction between myosin and actin is essential for muscle contraction and movement.

Explanation
Skeletal muscle does not react to a chemical stimulus conducted from the brain to the muscle via nerves. Instead, skeletal muscle reacts to an electrical stimulus called an action potential, which is conducted from the brain to the muscle via nerves. This electrical stimulus triggers muscle contraction. Therefore, the given statement is false.

Explanation
The correct answer is "all or none law". The all or none law states that once a motor unit is sufficiently stimulated, all of the muscle fibers within that motor unit will contract to their fullest extent. This means that either all of the fibers in the motor unit will contract or none of them will contract, there is no partial contraction. This principle helps to ensure that muscle contractions are coordinated and produce a smooth and efficient movement.