Muscle Anatomy & Organization
What is the connective tissue covering that surrounds a whole muscle?
Epimysium
What is the neurotransmitter released at the neuromuscular junction to stimulate a muscle fiber?
Acetylcholine (ACh).
Approximately how many seconds of ATP are stored in a muscle at any given time?
5–6 seconds.
What is the response of a single muscle fiber to a single action potential called?
A twitch.
Which muscle type is autorhythmic and found only in the heart?
Cardiac muscle.
What are the bundles of muscle fibers called?
Fascicles.
During depolarization, what happens to the electrical charge inside the muscle fiber?
It becomes less negative (more positive) compared to the outside.
Which metabolic process requires oxygen and produces 36 ATP?
Aerobic respiration.
What is the difference between isometric and isotonic contractions?
Isometric: muscle length does not change; Isotonic: muscle length changes.
What are "intercalated disks" in cardiac muscle?
Specialized gap junctions that join cardiac cells to one another.
What are the two main types of myofilaments found in a sarcomere?
Actin (thin) and Myosin (thick).
What is the primary role of the sarcoplasmic reticulum during muscle contraction?
It stores and releases calcium ions.
What is the "Oxygen Deficit" at the start of exercise?
The lag time between the start of exercise and the increase in respiration rate.
What are the characteristics of Slow-twitch (Type I) muscle fibers?
Fatigue resistant, high myoglobin (dark meat), aerobic, suited for posture/endurance.
What protein replaces troponin in the regulation of smooth muscle contraction?
Calmodulin.
What is the "Triad" in a skeletal muscle fiber composed of?
Two terminal cisternae and one associated T tubule.
What occurs during the "power stroke" in the cross-bridge cycle?
The myosin head bends, causing the actin to slide past the myosin.
What is the function of the enzyme Creatine Kinase?
It transfers a phosphate from creatine phosphate to ADP to create ATP.
What is "Wave Summation"?
Shortening the time between stimuli so the muscle fiber does not fully relax, causing tension to increase.
What is the "Latch State" in smooth muscle?
When phosphate is removed from myosin while cross-bridges are still attached, allowing sustained tension with low energy expenditure.
Which specific protein covers the active sites on actin, and which protein is responsible for moving it to expose those sites?
Tropomyosin covers the active sites; Troponin moves it.
What is the function of acetylcholinesterase, and why is it critical for muscle relaxation?
It breaks down ACh in the synaptic cleft; it prevents constant stimulation of the muscle, allowing it to relax.
What are the three primary mechanisms that contribute to muscle fatigue?
Acidosis (interferes with Ca2+), ATP depletion, and Reactive oxidative species (free radicals).
Explain the "Size Principle" of motor unit recruitment.
Motor units are recruited from smallest to largest.
How does smooth muscle contraction regulation differ from skeletal muscle in terms of enzymes?
It uses myosin kinase (to activate) and myosin phosphatase (to relax) rather than the troponin-tropomyosin complex.