Muscle Types and Anatomy Quiz

Study Notes

Skeletal Muscle: Striated, voluntary, attached to bones; large, multinucleated cells responsible for conscious movement.
Cardiac Muscle: Striated, involuntary, found only in the heart; uninucleate, branching cells connected by intercalated discs; contracts at a steady rate set by a pacemaker.
Smooth Muscle: Non-striated, involuntary, located in walls of hollow organs (e.g., stomach, blood vessels); spindle-shaped, uninucleate cells; contract slowly and steadily.

Sarcolemma: Specialized plasma membrane of muscle cells.
Myofibrils: Long organelles within muscle cells, giving muscles their striated appearance.
Sarcomere: The contractile unit within myofibrils, containing thick (myosin) and thin (actin) filaments.
Sarcoplasmic Reticulum (SR): Specialized endoplasmic reticulum that stores and releases calcium, essential for muscle contraction.

Sliding Filament Process: Calcium binds to regulatory proteins on actin, exposing binding sites for myosin heads; myosin heads attach to actin, pivot, detach, and reattach further along the filament, causing actin filaments to slide toward the center of the sarcomere.
Role of ATP: ATP provides energy for each attachment, pivot, and detachment cycle.
Calcium's Role: Triggers binding of myosin heads to actin filaments, initiating contraction.

Motor Neuron: Releases acetylcholine (ACh) across the synaptic cleft at the neuromuscular junction.
Action Potential: ACh binds to receptors on the sarcolemma, opening Na+ channels; Na+ influx depolarizes the membrane, leading to an action potential that triggers contraction.
Acetylcholinesterase (AChE): Enzyme that breaks down ACh, ending the signal and allowing the muscle to relax.

Isotonic: Muscle shortens and movement occurs (e.g., lifting a weight).
Isometric: Muscle tension increases, but the muscle does not shorten (e.g., pushing against an immovable object).

Direct Phosphorylation: Creatine phosphate transfers a phosphate to ADP to create ATP; quick but short-lasting energy.
Aerobic Respiration: Glucose + Oxygen → ATP; provides sustained energy, occurs in the mitochondria.
Anaerobic Glycolysis: Glucose → Pyruvic Acid → Lactic Acid + ATP; quick energy but produces lactic acid, leading to muscle fatigue.

Causes of Fatigue: ATP depletion, ion imbalances, oxygen deficit, and lactic acid buildup.
Recovery: Oxygen deficit is repaid post-exercise by rapid, deep breathing, allowing ATP and oxygen levels to normalize.

Aerobic (Endurance) Exercise: Increases muscle flexibility, stamina, and overall metabolic efficiency.
Resistance (Strength) Exercise: Enhances muscle size and strength by increasing individual muscle fiber size.