Exam 3 Learning objectives

What are four important functions of muscle tissue?

Produces movement, Maintains posture and body position, Stabilizes joints, Generates heat

What are myofibrils and what is their function?

long, rod-like organelles that contain the contractile proteins (actin and myosin) and are responsible for muscle contraction

What is the sarcoplasmic reticulum (SR) and what does it do?

smooth endoplasmic reticulum that stores and releases calcium ions (Ca2+) needed for muscle contraction.

What are T tubules and what is their function?

sarcolemma that carry electrical impulses into the muscle fiber, triggering calcium release from the SR.

What is the sliding filament model of muscle contraction?

During contraction, myosin heads attach to actin filaments and pull them toward the center of the sarcomere, shortening the muscle without changing filament length.

What happens at the neuromuscular junction (NMJ) to start muscle contraction?

Nerve impulse reaches the axon terminal., Acetylcholine (ACh) is released into the synaptic cleft., ACh binds to receptors on the sarcolemma., This triggers an action potential in the muscle fiber.

What are the steps of excitation-contraction coupling?

Action potential travels along sarcolemma and down T tubules.

SR releases Ca2+., Ca2+ binds to troponin, moving tropomyosin and exposing actin sites., Myosin heads bind to actin, cross bridges form.

What are the steps of the cross bridge cycle?

Cross bridge formation: Myosin binds to actin.

Power stroke: Myosin head pivots, pulling actin.

Cross bridge detachment: ATP binds to myosin → detaches.

Cocking of myosin head: ATP is hydrolyzed → myosin resets for next cycle.

What is a motor unit?

one motor neuron and all the muscle fibers it controls.

What is a muscle twitch?

the response of a muscle fiber to a single action potential.

What are the three phases of a muscle twitch?

Latent period: Time between stimulation and contraction; Ca2+ is released.

Contraction phase: Cross bridges form and muscle tension increases.

Relaxation phase: Ca2+ returns to SR and muscle tension decreases.

How are smooth, graded muscle contractions produced?

by changing the frequency of stimulation (wave summation) and the number of motor units activated (recruitment).

What is an isometric contraction?

Muscle tension increases, but the muscle length does not change (no movement).

What is an isotonic contraction?

Muscle tension overcomes load, and the muscle changes length to cause movement.

What are the three ways ATP is regenerated during muscle contraction?

Direct phosphorylation of ADP by creatine phosphate.

Anaerobic glycolysis (glucose → lactic acid).

Aerobic respiration (uses oxygen in mitochondria).

What factors influence the force of muscle contraction?

Number of muscle fibers recruited, size of fibers, frequency of stimulation, and muscle stretch (optimal length).

What factors influence the velocity and duration of muscle contraction?

Muscle fiber type, Load on the muscle, Number of motor units recruited

What are the three types of skeletal muscle fibers?

Slow oxidative fibers: Endurance, fatigue-resistant, use aerobic respiration.

Fast oxidative fibers: Intermediate speed, moderate resistance to fatigue.

Fast glycolytic fibers: Powerful, quick contractions, fatigue quickly, use anaerobic glycolysis.

What is the relative value of each muscle fiber type?

Slow oxidative: Best for endurance (e.g., marathon running).

Fast oxidative: Good for moderate activity (e.g., walking).

Fast glycolytic: Best for short bursts of power (e.g., sprinting or lifting).

How do smooth and skeletal muscles differ?

Smooth: single nucleus, no striations, involuntary.

Skeletal: multinucleated, striated, voluntary.

How do skeletal and smooth muscles contract differently?

Skeletal: uses sarcomeres and troponin.

Smooth: no sarcomeres, uses calmodulin for calcium binding.

What are prime movers, antagonists, and synergists?

main muscle causing movement, opposes the movement, helps the prime mover.

How does a muscle’s position to a joint affect its action?

Determines the direction of pull and type of movement (flexion, extension, etc.).

What are the main fascicle arrangements?

Parallel, pennate, convergent, and circular.

How does fascicle arrangement affect power?

Shorter, pennate muscles = more power; longer, parallel muscles = more movement.

What are the three lever types in the body?

First-class: Fulcrum between effort and load.

Second-class: Load between fulcrum and effort.

Third-class: Effort between fulcrum and load.

Which lever type gives more power or speed?

Second-class = more power.

Third-class = more speed and range of motion.