Support and Movement MCQs for MDCAT

Correct answer: D. Troponin

Calcium ions released during muscle contraction bind to troponin, triggering the conformational change that exposes myosin-binding sites on actin.

Correct answer: A. Appendicular skeleton

The mammalian skeleton is divided into the axial skeleton (skull, spine, ribs) and the appendicular skeleton (limbs and girdles).

Correct answer: B. Ball and Socket joint

A ball-and-socket joint, such as the hip or shoulder, permits movement in multiple directions, including rotation.

Correct answer: D. Hyaline Cartilage

Hyaline cartilage is the most abundant type of cartilage in the human body, found in joints, the trachea and the nose.

Correct answer: A. I-bands shorten

According to the sliding filament theory, muscle stimulation causes the I-bands to shorten as actin filaments slide over myosin.

Correct answer: C. Cervical

The cervical spine (neck region) consists of seven bones (C1-C7 vertebrae), which are separated from one another by intervertebral discs.

Correct answer: B. 06

There are Six actin filaments surround each myosin filament, and each actin filament is surrounded by three myosin filaments. This arrangement gives the muscles a striated appearance under magnification.

Correct answer: A. Humerus and radio-ulna

A hinge joint is a type of synovial joint that allows movement in only one plane, like the opening and closing of a door. It is characterized by the convex surface of one bone fitting into the concave surface of another bone. In this case, the hinge joint is present between the humerus (upper arm bone) and the radio ulna (forearm bones).

Correct answer: C. Uninucleate

Muscles that are uni-nucleate, meaning they contain a single nucleus per cell, primarily include cardiac muscle and smooth muscle. Cardiac muscle cells, or cardiomyocytes, are typically uninucleate, although some may have two nuclei. These involuntary muscles are found in the heart and are responsible for pumping blood, with their uni-nucleate structure aiding in the coordinated contraction through intercalated discs. Similarly, smooth muscle fibers are also uninucleate and are located in the walls of hollow organs, such as the intestines and blood vessels. Smooth muscles are involuntary as well, regulating essential functions like peristalsis in the digestive tract and controlling blood flow. Together, cardiac and smooth muscles play crucial roles in various physiological processes due to their uninucleate characteristics.

Correct answer: C. Femur

The femur extends from the hip joint to the knee joint, forming the upper leg. It connects the pelvis to the tibia (shinbone).

Correct answer: B. Calcium

Option B is correct. According to the sliding filament hypothesis, the release of calcium ions from the sarcoplasmic reticulum causes the reorientation of certain components in the thin filament, permitting them to bind with extension from the thick myosin filaments. Calcium ions play a crucial role in muscle contraction by binding to the protein troponin on the thin filament. This binding causes tropomyosin to move out of the way, exposing myosin binding sites on the actin filament. Myosin heads can then bind to these sites, and cross-bridges can be formed. The cross-bridges then power the sliding of the thin filaments past the thick filaments, which results in muscle contraction. The other options are not involved in muscle contraction: Sodium ions are involved in nerve conduction and muscle action potentials. Magnesium ions are cofactors for many enzymes, including those involved in muscle metabolism. Potassium ions are involved in maintaining the resting membrane potential of muscle cells.

Correct answer: C. 6

In a muscle sarcomere, each myosin filament (thick filament) is surrounded by 6 actin filaments (thin filaments) at each end. This arrangement allows for the sliding filament theory of muscle contraction, where the myosin heads bind to the actin filaments and pull them towards the center of the sarcomere, resulting in muscle contraction.