Most Repeated MDCAT Biology: Support and Movement MCQs

Explanation

Voluntary muscles are under conscious control, allowing us to move our bodies intentionally. Striated muscles have a striped appearance under a microscope due to the organization of their contractile proteins, giving them the name "striated." These muscles are also known as skeletal muscles and are responsible for body movements.

Explanation

The correct answer is Sarcolemma. The sarcolemma is the specialized cell membrane that surrounds a muscle fiber. It is crucial for communication between the nervous system and the muscle fiber, allowing the initiation of muscle contraction through electrical signal transmission. The term 'sarco-' denotes its association with muscle cells, differentiating it from the general plasma membrane found in all cell types. Option B, the 'Plasma membrane', refers to the cell membrane in general terms and does not specify its role in muscle cells. Option C, 'Sarcoplasm', is the cytoplasmic content of the muscle cell, not the membrane.

Explanation

Microcephaly is a birth defect where a baby's head is smaller than expected when compared to babies of the same sex and age. Babies with microcephaly often have smaller brains that might not have developed properly.

Explanation

Osteocytes are mature bone cells that are embedded within the bone matrix. They are derived from osteoblasts and are the most abundant cells in mature bone tissue. Osteocytes maintain the bone tissue by regulating mineral content and responding to mechanical stress.

Explanation

During muscle contraction, Ca++ ions are released from the sarcoplasmic reticulum and bind specifically to troponin, a regulatory protein attached to the actin filaments. This binding causes a conformational change in troponin that moves tropomyosin, another protein, away from the myosin-binding sites on actin. This exposure allows the myosin heads to attach to actin, initiating muscle contraction. Myosin and actin are crucial for the contraction process, but they do not directly bind with calcium ions. Tropomyosin is involved in the regulation process, but does not interact directly with calcium ions either.

Explanation

Skeletal muscle fibers in humans do not contain a large amount of hemoglobin. Haemoglobin is a protein found in red blood cells that is responsible for transporting oxygen throughout the body. While skeletal muscle fibers have a rich blood supply to support their metabolic needs, they do not typically contain a significant amount of hemoglobin within the fibers themselves.

Explanation

The human forelimbs each consist of 30 bones: The humerus, which forms a ball and socket joint with the scapula, and two long parallel bones, the radius and ulna, at its distal end. The radius and ulna join the wrist with eight small carpal bones, which articulate with five metacarpals of the palm. From the palm extend the fingers containing 14 small bones called phalanges, arranged in 5 rows, one row in each finger. The relevant detail for this question is that the bones of the palm are called metacarpals, hence option B is correct.

Explanation

D) 6 actin filaments: Each myosin filament is surrounded by 6 actin filaments, which are arranged in a hexagonal pattern. This is the correct answer, as the hexagonal arrangement of actin filaments around each myosin filament is a key feature of muscle cell structure.

Explanation

This is the correct answer. Cardiac muscle is a specialized type of muscle tissue found only in the heart. It is myogenic, meaning it can contract on its own without external stimulation from the nervous system. This property is essential for the heart to beat rhythmically and pump blood continuously.

Explanation

Fibrous joints are also called fixed or immovable joints because they do not allow any movement. These joints are immovable as they have no joint cavity or space present between the bones. They are connected via fibrous connective tissue. There are three types of fibrous joints: sutures, syndesmoses, and gomphoses. Sutures are found only in the skull, An example of a syndesmosis is the joint of the tibia and fibula in the ankle, Gomphoses occur between teeth and their sockets.So, the correct answer is 'Fibrous joint'A. Synovial joints are freely moveable joints.B. Ball and socket joint are example of freely moveable joints.D.

Explanation

During muscle contraction, the laterally projecting heads (cross-bridges) of the thick myosin myofilaments come in contact with the thin actin myofilaments and rotate on them. This pulls the thin myofilaments toward the middle of the sarcomere, past the thick myofilaments. The Z lines come closer together, and the sarcomere becomes shorter. Length of the A band remains constant. Myofilaments (both actin and myosin) stay the same length. Free ends of actin myofilaments move closer to the centre of the sarcomere, bringing Z lines closer together. I bands shorten, and the H zone narrows.

Explanation

A neuron that transmits a stimulus to muscle tissue is called motor neuron. A motor unit consists of a single motor neuron (nerve cell) and the muscle fibres it innervates. The portion of the muscle plasma membrane (sarcolemma) that lies beneath the nerve endings (axon terminals) is called the motor end plate. The axon terminals and the motor end plate together constitute the neuromuscular junction or neuromotor junction. B. Sarcolemma of muscle fibre penetrates deep into the cell to form a hollow elongated tube called transverse tubule.C. Muscle fibres of skeletal muscles are composed of myofibrils which are further of two types thick and thin myofibrils.D.

Explanation

Muscles in the body are categorized into three main types: Smooth, Cardiac, and Skeletal. Skeletal muscles are classified as voluntary muscles because they are consciously controlled, allowing us to perform actions such as walking, lifting, and speaking. This contrasts with Smooth and Cardiac muscles, which are involuntary. Smooth muscles operate automatically within organs, and Cardiac muscles function independently in the heart's rhythmic contractions. Therefore, the correct answer is Option C: Skeletal muscles.

Explanation

The correct answer is periosteum. The periosteum is a dense fibrous membrane covering the surface of bones. It plays a vital role in bone growth and repair and contains blood vessels and nerves that supply nutrients and sensation to the bone.The perichondrium surrounds cartilage, not bone. The prostomium is unrelated to bone, being a part of certain invertebrates. Perimycium pertains to muscle tissue, not bone.

Explanation

Tetanus is an infection of the nervous system caused by Clostridium tetani bacteria. The correct answer is the nervous system because the bacteria affect nerve cells and can lead to muscle stiffness and spasms. The other options (respiratory system, circulatory system, bones, and muscles) are incorrect because they are not the primary systems affected by tetanus infection.

Explanation

An osteocyte, a cell that lies within the substance of fully formed bone. It occupies a small chamber called a lacuna, which is contained in the calcified matrix of bone. Osteocytes derive from osteoblasts, or bone-forming cells, and are essentially osteoblasts surrounded by the products they have secreted.

Explanation

Calcium ions (Ca²⁺) are essential for muscle contraction. When a muscle is stimulated to contract, calcium ions are released from the sarcoplasmic reticulum. These ions bind to troponin, a regulatory protein on the actin filaments. This binding causes a change in the shape of the troponin-tropomyosin complex, exposing binding sites on the actin for myosin heads. This exposure allows myosin to form cross bridges with actin, initiating the contractile process.Option A is incorrect because the actin filaments do not independently move to shorten the muscle; they are pulled by myosin heads.

Explanation

Arthropods are a group of invertebrate animals that have jointed legs and a chitinous exoskeleton. This group includes insects, spiders, crustaceans, and others. Therefore, option B is accurate.

Explanation

Troponin does not directly bind to myosin. Instead, troponin regulates the interaction between actin and myosin by modulating the position of tropomyosin. So, option C is the most appropriate answer.