Which type of muscle tissue is involuntary, non-striated, and found forming the walls of hollow internal organs?
Skeletal muscle
Tendon tissue
Cardiac muscle
Smooth muscle
✓
Correct Answer
Smooth muscle
Smooth muscle tissue is characterized by its lack of striations, involuntary control, and its presence in the walls of visceral organs such as the intestines, stomach, and blood vessels. Skeletal muscle is striated and voluntary. Cardiac muscle is striated and involuntary. Tendon tissue is a type of connective tissue, not muscle.
Category: Types of Muscle Tissue
Question 2
At the neuromuscular junction, what neurotransmitter is released by the motor neuron to stimulate muscle fiber contraction?
Dopamine
Acetylcholine
✓
Norepinephrine
Gamma-aminobutyric acid (GABA)
Correct Answer
Acetylcholine
Acetylcholine is the specific neurotransmitter released from the axon terminal of a motor neuron into the synaptic cleft at the neuromuscular junction. It binds to receptors on the motor end plate, initiating an action potential in the muscle fiber. Norepinephrine, dopamine, and GABA are neurotransmitters found elsewhere in the nervous system but are not the primary neurotransmitter at the skeletal muscle neuromuscular junction.
Category: Neuromuscular Junction
Question 3
Within a sarcomere, which structure is composed primarily of myosin and forms the central region of the A band?
Z disc
Thin filament
Thick filament
✓
M line
Correct Answer
Thick filament
The thick filaments are primarily composed of the protein myosin and are responsible for forming the A band in the center of a sarcomere. Thin filaments are made of actin, troponin, and tropomyosin. Z discs mark the boundaries of a sarcomere. The M line is a protein line in the center of the H zone, which is within the A band.
Category: Sarcomere
Question 4
During excitation-contraction coupling, what ion is released from the sarcoplasmic reticulum and binds to troponin, initiating the muscle contraction cycle?
Calcium
✓
Sodium
Potassium
Chloride
Correct Answer
Calcium
When an action potential reaches the sarcoplasmic reticulum via the T-tubules, calcium ions are released into the sarcoplasm. These calcium ions bind to troponin, causing it to change shape and move tropomyosin away from the actin binding sites, allowing myosin heads to attach and initiate muscle contraction. Sodium, potassium, and chloride are important for action potentials but do not directly unmask actin binding sites.
Category: Excitation-Contraction Coupling
Question 5
What is the term for the increase in muscle fiber size and strength due to increased workload and synthesis of contractile proteins?
Atrophy
Hypertrophy
✓
Rigor mortis
Spasticity
Correct Answer
Hypertrophy
Hypertrophy refers to the growth and increase in the size of muscle cells, leading to increased muscle mass and strength, typically in response to resistance training. Atrophy is the decrease in muscle size. Rigor mortis is the stiffening of muscles after death. Spasticity is a neurological condition causing muscle stiffness and involuntary muscle spasms.
Category: Muscle Changes
Question 6
Which muscle fiber type primarily relies on anaerobic glycolysis for ATP production and is best suited for short, intense bursts of activity?
Fast oxidative fibers
Slow oxidative fibers
Cardiac muscle fibers
Fast glycolytic fibers
✓
Correct Answer
Fast glycolytic fibers
Fast glycolytic fibers contract quickly and powerfully but fatigue rapidly because they primarily generate ATP through anaerobic glycolysis. This makes them ideal for activities requiring short, intense bursts of energy. Slow oxidative fibers are adapted for endurance, and fast oxidative fibers have intermediate characteristics. Cardiac muscle fibers are a type of muscle tissue, not a skeletal muscle fiber type.
Category: Fiber Types
Question 7
What is the term for the constant, slight contraction that is always present in a healthy muscle, even when it is not actively contracting?
Tetanus
Summation
Muscle tone
✓
Twitch
Correct Answer
Muscle tone
Muscle tone refers to the sustained, partial contraction of a muscle, which keeps muscles firm and ready for action. Tetanus is a sustained, maximal contraction without relaxation. Summation is the increase in muscle tension from successive stimuli. A twitch is a single contraction-relaxation cycle in response to a single stimulus.
Category: Muscle Tension
Question 8
A muscle contraction where the muscle shortens and moves a load is described as which type of contraction?
Isotonic
✓
Isometric
Tetanic
Eccentric
Correct Answer
Isotonic
Isotonic contractions involve a change in muscle length while the tension remains relatively constant, resulting in movement. Isometric contractions generate tension without changing muscle length. Tetanic refers to a sustained contraction. Eccentric is a type of isotonic contraction where the muscle lengthens under tension.
Category: Muscle Tension
Question 9
Which region of the sarcomere contains only thin filaments and shortens during muscle contraction?
H zone
A band
M line
I band
✓
Correct Answer
I band
The I band is the lighter region of the sarcomere that contains only thin filaments (actin) and shortens as the thin filaments slide past the thick filaments during contraction. The A band contains thick filaments and overlapping thin filaments. The H zone is the central part of the A band containing only thick filaments. The M line is the center of the H zone.
Category: Sarcomere
Question 10
What connective tissue layer surrounds a bundle of muscle fibers, known as a fascicle?
Epimysium
Endomysium
Perimysium
✓
Sarcolemma
Correct Answer
Perimysium
The perimysium is a dense irregular connective tissue sheath that surrounds groups of 10-100 muscle fibers, forming a fascicle. These fascicles are visible to the naked eye as "grains" in meat. The epimysium surrounds the entire muscle. The endomysium surrounds individual muscle fibers. The sarcolemma is the plasma membrane of a muscle fiber.
Category: Skeletal Muscle Connective Tissue
Question 11
What term describes a single motor neuron and all the individual muscle fibers it innervates?
Motor unit
✓
Sarcomere
Motor end plate
Myofilament
Correct Answer
Motor unit
A motor unit is the fundamental unit of muscle contraction, consisting of one motor neuron and all the muscle fibers it stimulates. The number of muscle fibers per motor unit varies, influencing the precision and strength of muscle contraction. A myofilament is a protein strand like actin or myosin. A sarcomere is the basic contractile unit of a myofibril. The motor end plate is the specialized region of the sarcolemma at the neuromuscular junction.
Category: Muscle Tension
Question 12
In smooth muscle cells, what structures serve a similar function to Z-discs in skeletal muscle, providing an anchoring point for thin filaments?
Gap junctions
Dense bodies
✓
Sarcomeres
Intercalated discs
Correct Answer
Dense bodies
Smooth muscle lacks sarcomeres and Z-discs, but it contains dense bodies scattered throughout the sarcoplasm and attached to the sarcolemma. Thin filaments attach to these dense bodies, which transmit the contractile force to the cell membrane. Gap junctions allow for electrical coupling between adjacent cells in smooth and cardiac muscle. Sarcomeres are the contractile units found in skeletal and cardiac muscle, but absent in smooth muscle. Intercalated discs are specialized junctions found only in cardiac muscle, connecting adjacent cardiac muscle cells.
Category: Cardiac and Smooth Muscle
Question 13
Which energy system provides ATP for muscle contraction during the initial few seconds of intense activity by directly transferring a phosphate group to ADP?
Creatine phosphate system
✓
Anaerobic glycolysis
Aerobic respiration
Lactic acid fermentation
Correct Answer
Creatine phosphate system
The creatine phosphate system is the fastest way to generate ATP at the onset of muscle activity. Creatine kinase transfers a phosphate from creatine phosphate to ADP, quickly forming ATP to power the first few seconds of muscle contraction. Aerobic respiration is a slower, but highly efficient, method of ATP production that requires oxygen. Anaerobic glycolysis breaks down glucose without oxygen to produce a small amount of ATP and lactic acid. Lactic acid fermentation is another name for anaerobic glycolysis in this context.
Category: Muscle Metabolism
Question 14
The cytoplasm of a muscle fiber, which contains organelles like myofibrils, mitochondria, and glycogen stores, is specifically called the:
Sarcoplasmic reticulum
Sarcoplasm
✓
Sarcolemma
Neuromuscular junction
Correct Answer
Sarcoplasm
The sarcoplasm is the specialized cytoplasm of a muscle fiber. It contains the usual cellular components, along with specialized structures such as myofibrils, numerous mitochondria for ATP production, and glycogen granules for energy storage. The sarcolemma is the plasma membrane of the muscle fiber. The sarcoplasmic reticulum is a network of tubules that stores calcium ions. The neuromuscular junction is the synapse between a motor neuron and a muscle fiber.
Category: Muscle Fiber Structure
Question 15
What is the primary function of intercalated discs in cardiac muscle tissue?
To anchor thick and thin filaments within the sarcomere.
To regulate the amount of blood pumped by the heart.
To provide a strong, flexible connection between individual cardiac muscle cells and allow rapid action potential propagation.
✓
To store calcium ions necessary for muscle contraction.
Correct Answer
To provide a strong, flexible connection between individual cardiac muscle cells and allow rapid action potential propagation.
Intercalated discs are unique to cardiac muscle and contain both desmosomes for strong adhesion and gap junctions for electrical coupling, enabling the heart to contract as a functional syncytium. To anchor thick and thin filaments within the sarcomere describes the function of Z-discs. To store calcium ions necessary for muscle contraction is the role of the sarcoplasmic reticulum. To regulate the amount of blood pumped by the heart is a function of the entire heart, not just intercalated discs.
Category: Cardiac and Smooth Muscle
Question 16
Which regulatory protein in smooth muscle binds calcium ions to initiate the contraction process?
Troponin
Tropomyosin
Myosin
Calmodulin
✓
Correct Answer
Calmodulin
In smooth muscle cells, calcium ions bind to calmodulin, which then activates myosin light chain kinase to phosphorylate myosin, enabling cross-bridge formation. Troponin and Tropomyosin are regulatory proteins found in skeletal and cardiac muscle, not smooth muscle. Myosin is the motor protein that forms thick filaments and directly participates in contraction.
Category: Cardiac and Smooth Muscle
Question 17
What specialized invagination of the sarcolemma extends deep into a muscle fiber, allowing action potentials to rapidly reach all myofibrils?
Mitochondrion
Sarcoplasmic reticulum
Myofibril
T-tubule
✓
Correct Answer
T-tubule
T-tubules (transverse tubules) are extensions of the sarcolemma that penetrate into the cell's interior, ensuring that the electrical signal from the surface quickly propagates to the deepest parts of the muscle fiber, triggering calcium release. The sarcoplasmic reticulum is a network of membranes that stores and releases calcium ions. A myofibril is a contractile organelle composed of sarcomeres. A mitochondrion is an organelle responsible for ATP production.
Category: Muscle Fiber Structure