T-tubules are invaginations of the sarcolemma that allow action potentials to penetrate deep into the muscle fiber.
Correct Answer
True
T-tubules (transverse tubules) are indeed extensions of the sarcolemma, the muscle cell membrane, that dive into the cell interior. This arrangement ensures that the action potential rapidly reaches all parts of the muscle fiber, including the myofibrils deep within, to trigger calcium release.
Category: Muscle Fiber Structure
Question 2
The H zone is the central region of the A band where only thin filaments are found.
Correct Answer
False
The H zone is the central region of the A band, but it contains only thick (myosin) filaments, not thin filaments. The thin filaments do not extend into the H zone in a relaxed sarcomere, though the H zone shortens during contraction as thin filaments slide inward.
Category: Sarcomere
Question 3
After acetylcholine binds to its receptors on the motor end plate, an action potential is generated on the motor neuron.
Correct Answer
False
Acetylcholine binding to receptors on the motor end plate generates an end-plate potential, which can then trigger an action potential on the muscle fiber's sarcolemma. The motor neuron releases acetylcholine into the synaptic cleft, but its own action potential is not generated by this binding event.
Category: Neuromuscular Junction
Question 4
The primary role of calcium ions in muscle contraction is to bind to troponin, causing tropomyosin to move away from the myosin-binding sites on actin.
Correct Answer
True
Calcium ions released from the sarcoplasmic reticulum bind to troponin. This binding causes a conformational change in troponin, which in turn moves the tropomyosin molecule, thereby exposing the active sites on the actin filaments for myosin head attachment and cross-bridge formation.
Category: Excitation-Contraction Coupling
Question 5
During an isometric contraction, the muscle generates tension but does not change in length.
Correct Answer
True
An isometric contraction occurs when the muscle develops tension but remains at a constant length because the load applied to it exceeds the force generated by the muscle. This contrasts with isotonic contractions, where the muscle length changes while tension remains relatively constant.
Category: Muscle Tension
Question 6
Rigor mortis is a state of muscle flaccidity that occurs after death due to the rapid depletion of ATP.
Correct Answer
False
Rigor mortis is a state of muscle stiffness and rigidity that occurs after death. It is caused by the depletion of ATP, which is necessary for myosin heads to detach from actin filaments, leaving the cross-bridges in a permanently bound state.
Category: Muscle Changes
Question 7
The endomysium is a connective tissue layer that surrounds a single muscle fascicle.
Correct Answer
False
The endomysium is a delicate connective tissue sheath that surrounds each individual muscle fiber. A fascicle, which is a bundle of muscle fibers, is surrounded by the perimysium.
Category: Skeletal Muscle Connective Tissue
Question 8
The creatine phosphate system is the primary ATP source for muscle contraction during endurance activities lasting several minutes.
Correct Answer
False
The creatine phosphate system provides a rapid, but very short-lived, supply of ATP for initial muscle contraction, typically lasting only about 10-15 seconds. For endurance activities, aerobic respiration is the primary ATP source.
Category: Muscle Metabolism
Question 9
Fast glycolytic muscle fibers are characterized by a high myoglobin content and a rich capillary supply, making them resistant to fatigue.
Correct Answer
False
Fast glycolytic fibers primarily rely on anaerobic glycolysis, have low myoglobin content, and fewer capillaries, which makes them prone to rapid fatigue. Slow oxidative fibers, in contrast, have high myoglobin and rich capillary supply, making them fatigue-resistant.
Category: Fiber Types
Question 10
Intercalated discs in cardiac muscle tissue contain gap junctions that allow for rapid electrical coupling and desmosomes that prevent cells from pulling apart during contraction.
Correct Answer
True
Intercalated discs are specialized cell junctions found in cardiac muscle. Gap junctions within these discs allow ions to pass directly between cells, enabling rapid propagation of action potentials, while desmosomes provide strong adhesion to resist forces during contraction.
Category: Cardiac and Smooth Muscle
Question 11
Incomplete tetanus occurs when a muscle fiber is stimulated at a high frequency, resulting in a sustained, smooth contraction with no relaxation period between stimuli.
Correct Answer
False
Incomplete tetanus (or unfused tetanus) involves a high stimulation frequency where contractions summate, but there are still periods of partial relaxation between stimuli, creating a wavering contraction. Complete (fused) tetanus is when stimulation is so frequent that there is no relaxation at all, resulting in a smooth, sustained contraction.
Category: Muscle Tension
Question 12
Motor unit recruitment involves increasing the number of active motor units to increase the overall force of muscle contraction.
Correct Answer
True
Motor unit recruitment is the process by which the nervous system activates increasing numbers of motor units to generate greater contractile force. Smaller, weaker motor units are typically activated first, followed by larger, more powerful ones as more force is required.
Category: Muscle Tension
Question 13
In smooth muscle contraction, calcium ions bind to calmodulin, which then activates myosin light chain kinase to phosphorylate the myosin heads.
Correct Answer
True
Unlike skeletal muscle where calcium binds to troponin, in smooth muscle, calcium binds to the regulatory protein calmodulin. The calcium-calmodulin complex then activates an enzyme called myosin light chain kinase (MLCK), which phosphorylates the myosin heads, enabling them to bind to actin and initiate contraction.
Category: Cardiac and Smooth Muscle
Question 14
Tendons, which connect muscle to bone, are primarily composed of dense regular connective tissue.
Correct Answer
True
Tendons are made of dense regular connective tissue, characterized by parallel bundles of collagen fibers. This structural arrangement provides immense tensile strength, allowing tendons to effectively transmit the force of muscle contraction to bones, facilitating movement.
Category: Skeletal Muscle Connective Tissue
Question 15
Oxygen debt, also known as excess post-exercise oxygen consumption (EPOC), represents the amount of oxygen required to restore ATP, creatine phosphate, and glycogen stores after strenuous exercise.
Correct Answer
True
Oxygen debt (EPOC) is the physiological phenomenon where the body consumes extra oxygen post-exercise. This additional oxygen is vital for replenishing depleted ATP and creatine phosphate reserves, converting lactic acid back to pyruvate or glucose, and restoring oxygen bound to myoglobin.
Category: Muscle Metabolism
Question 16
Muscle atrophy is a condition characterized by an increase in muscle fiber size and strength, typically in response to intense resistance training.
Correct Answer
False
Muscle atrophy is the decrease in muscle mass and strength, usually resulting from disuse, nerve damage, or certain diseases. In contrast, hypertrophy is the increase in muscle size and strength, often stimulated by resistance training.
Category: Muscle Changes
Question 17
Cardiac muscle tissue is unique among muscle types because it is both striated and involuntary.
Correct Answer
True
Skeletal muscle is striated and voluntary, while smooth muscle is non-striated and involuntary. Cardiac muscle tissue uniquely possesses both striations, due to organized sarcomeres, and involuntary control, meaning its contractions are not consciously directed.
Category: Types of Muscle Tissue
Question 18
Smooth muscle tissue lacks sarcomeres, which means it does not contain thick and thin filaments.
Correct Answer
False
Smooth muscle tissue does not have sarcomeres, which accounts for its lack of striations. However, it still contains both thick (myosin) and thin (actin) filaments; these are arranged more loosely and diagonally within the cell, anchored to dense bodies rather than Z-discs.
Category: Cardiac and Smooth Muscle
Question 19
A single motor neuron can innervate multiple muscle fibers within a muscle, but each muscle fiber is typically innervated by only one motor neuron.
Correct Answer
True
A motor unit comprises one motor neuron and all the muscle fibers it stimulates. While a single motor neuron branches to excite several muscle fibers, each individual muscle fiber usually receives synaptic input from only one motor neuron to ensure coordinated control.
Category: Neuromuscular Junction
Question 20
During skeletal muscle contraction, the A band of the sarcomere significantly shortens as the thin filaments slide inward.
Correct Answer
False
The A band, which corresponds to the length of the thick filaments, remains constant in length during muscle contraction. While the thin filaments do slide inward, it is the I band and H zone that shorten, bringing the Z discs closer together.
Category: Sarcomere