Muscular System Questions and Answers

Answer: A

Skeletal muscles are also known as striated muscles.

Skeletal muscle fibres show alternating light and dark bands (striations) under the microscope, because their actin and myosin filaments are arranged in regular sarcomeres. They are attached to bones and are voluntary.

Smooth muscle, found in the walls of the gut and blood vessels, is non-striated and involuntary. So 'non-striated', 'smooth' and 'involuntary' all describe a different type of muscle.

Answer: B

The study of muscle action through its electrical signals is electromyography.

Electromyography (EMG) records the electrical activity produced by skeletal muscles when they contract, using surface or needle electrodes, and is used to diagnose muscle and nerve disorders (myo-, muscle).

Electrocardiography records the electrical activity of the heart, an X-ray is an imaging technique that shows bones and dense tissue, and a physical check-up is a general clinical examination. None of them measures muscle signals specifically.

Answer: A

Tendons connect muscles to bones.

A tendon is a tough cord of dense connective tissue that attaches a muscle to a bone, so that the pull of a contracting muscle moves the bone. The Achilles tendon, joining the calf muscles to the heel bone, is the best-known example.

Ligaments connect bone to bone at a joint. Cartilage is the smooth tissue covering joint surfaces and forming structures such as the ear and nose. The epidermis is the outer layer of the skin.

Answer: B

The voluntary muscles are skeletal muscles.

Skeletal (striated) muscles are attached to bones and are under conscious control through the somatic nervous system, so they move the body when we decide to.

Smooth muscle in the walls of the gut, blood vessels and bladder is involuntary, controlled by the autonomic nervous system. Cardiac muscle is striated but also involuntary, contracting rhythmically on its own. 'Otic muscles' is not a type of muscle tissue; the small muscles of the middle ear act by reflex.

Answer: A

The diaphragm is a muscle.

The diaphragm is a dome-shaped sheet of skeletal muscle with a central tendon, separating the chest cavity from the abdominal cavity. It is the main muscle of breathing: when it contracts it flattens, enlarging the chest so that air is drawn into the lungs.

It is not cartilage or bone, both of which are rigid supporting tissues. 'Tissue' is too general: muscle is itself a tissue, so the precise category is muscle.

Answer: A

Both are true, and the Reason is the correct explanation of the Assertion.

In old age, especially after menopause in women, bones lose mineral and become thin and brittle (osteoporosis), so they fracture easily.

The Reason explains why. The body keeps the blood calcium level within a narrow range because nerves and muscles depend on it. When intake and absorption of calcium fall, as they often do in the elderly, parathyroid hormone draws calcium out of the bones to maintain the blood level. Over years this withdrawal weakens the bones, which is exactly the Assertion.

Answer: D

The muscle not part of the quadriceps femoris is the sartorius.

The quadriceps femoris has four heads that join in the quadriceps tendon over the patella and extend the knee: rectus femoris, vastus lateralis, vastus medialis and vastus intermedius.

The sartorius is a separate long, strap-like muscle that crosses the front of the thigh from the anterior superior iliac spine to the inner side of the tibia. It is the longest muscle in the body, and it flexes the hip and knee rather than forming part of the quadriceps.

Answer: A

Myosin forms the thick filaments made up of protein.

In a sarcomere, the thick filaments are made of myosin molecules whose heads project outward and bind actin. Pulling on the actin during contraction makes the filaments slide past one another.

The thin filaments are made of actin, with tropomyosin and troponin. The Z-lines (Z-discs) are dense protein bands that mark the boundaries of each sarcomere and anchor the thin filaments; they are not hollow, and they are not myosin. So only the first option describes myosin.

Answer: C

The main fibre in tendons is collagen type I.

Tendons are dense regular connective tissue. Parallel bundles of type I collagen fibrils give them very high tensile strength with little stretch, which is what is needed to pass muscle force to bone. Type I collagen also dominates bone, skin and ligaments.

Elastic fibres are found mainly in arteries, lungs and the ligamenta flava. Reticular fibres (type III collagen) form the supporting mesh of lymphoid organs, liver and bone marrow. Type IV collagen forms the network of basement membranes.

Answer: B

The protein that binds calcium is troponin C.

When Ca2+ is released from the sarcoplasmic reticulum, it binds troponin C. This changes the shape of the troponin complex, which pulls tropomyosin away from the myosin-binding sites on actin. Cross-bridges can then form and the muscle contracts.

Tropomyosin is the regulatory strand that covers the binding sites and does not bind calcium itself. Myosin is the motor protein, and actin is the thin filament it pulls on. In smooth muscle calcium binds calmodulin instead, but the question is about skeletal muscle.