A&P exam 2 muscles

What are myofilaments?

Protein filaments within muscle fibers responsible for contraction; include actin and myosin.

What are thick filaments composed of?

Myosin protein.

What are thin filaments composed of?

Actin plus troponin and tropomyosin.

What is a sarcomere?

Functional contractile unit of skeletal muscle between two Z-discs.

What is the A band?

Dark region containing full length of thick filaments; does not change length during contraction.

What is the H zone?

Central region of A band with only thick filaments; shrinks during contraction.

What is the M line?

Center of sarcomere holding thick filaments together.

What is the I band?

Light region with only thin filaments; shortens during contraction.

What is the zone of overlap?

Region where actin and myosin overlap and form cross-bridges.

How does a sarcomere change during contraction?

I band and H zone shorten, Z-discs move closer, A band stays same.

What is the sliding filament theory?

Thin filaments slide past thick filaments to shorten sarcomere without changing filament length.

What initiates muscle contraction?

Acetylcholine released by motor neuron.

What is acetylcholine (ACh)?

Neurotransmitter that triggers muscle fiber action potential.

What is the neuromuscular junction?

Synapse between motor neuron and muscle fiber.

What happens when ACh binds receptors?

Triggers action potential in muscle fiber.

Where is calcium released from?

Sarcoplasmic reticulum.

What does calcium bind to?

Troponin.

What happens when calcium binds troponin?

Tropomyosin moves, exposing actin binding sites.

What is a cross-bridge?

Myosin head binding to actin active site.

What is the power stroke?

Myosin pulls actin toward center of sarcomere.

What happens after power stroke?

ATP binds myosin and detaches it from actin.

Why is ATP important in contraction?

Allows detachment and re-cocking of myosin head.

What is rigor mortis?

Muscle stiffness due to lack of ATP after death.

What is muscle fatigue?

Decline in muscle force due to energy or metabolic limits.

What is a motor unit?

One motor neuron and all muscle fibers it controls.

What are cross-bridge cycle steps?

Ca binds troponin, myosin binds actin, power stroke, ATP detaches, ATP recocks head.

What causes muscle relaxation?

Ca pumped back into SR and stimulation stops.

What happens to tropomyosin during relaxation?

Covers actin binding sites again.

What happens without ATP?

Myosin remains attached to actin.

What is muscle tension?

Force produced by muscle contraction.

What is a twitch?

Single contraction response to a stimulus.

What is latent period?

Time between stimulus and contraction start.

What occurs during contraction period?

Cross-bridges form and muscle shortens.

What occurs during relaxation period?

Ca is removed and tension decreases.

What is treppe?

Gradual increase in tension after repeated stimulation.

What is wave summation?

Contractions build when stimuli occur before relaxation.

What is tetanus?

Sustained contraction with no relaxation.

What is incomplete tetanus?

Partial relaxation between stimuli.

What is complete tetanus?

No relaxation between stimuli.

What is muscle heat production?

Heat released from ATP breakdown and metabolism.

What is shivering?

Involuntary contractions to produce heat.

What is sarcolemma?

Muscle cell membrane.

What is sarcoplasm?

Cytoplasm of muscle fiber.

What is myoglobin?

Oxygen-storing protein in muscle.

What are T-tubules?

Sarcolemma invaginations carrying signals deep into fiber.

What is sarcoplasmic reticulum?

Stores and releases calcium.

What is a triad?

T-tubule plus two terminal cisternae.

What are terminal cisternae?

SR regions that store calcium.

Muscle organization order

Muscle → fascicle → fiber → myofibril → myofilaments.

What is a muscle organ?

Whole muscle with fibers, vessels, nerves, and connective tissue.

What is a fascicle?

Bundle of muscle fibers.

What is a muscle fiber?

A single muscle cell.

What are myofibrils?

Threadlike structures inside fibers made of sarcomeres.

What is fascia?

Connective tissue surrounding muscles.

What is superficial fascia?

Fat-containing layer under skin.

What is deep fascia?

Dense connective tissue surrounding muscles.

What is endomysium?

Covers each muscle fiber.

What is perimysium?

Covers fascicles.

What is epimysium?

Covers whole muscle.

What forms tendons?

Merging of endomysium, perimysium, epimysium.

What is a tendon?

Tissue connecting muscle to bone.

What is a tendon sheath?

Protective tube around tendon.

What is an aponeurosis?

Flat sheet-like tendon.

What is a retinaculum?

Band holding tendons in place.

What are skeletal muscle properties?

Excitability, contractility, extensibility, elasticity.

What is excitability?

Response to stimuli.

What is contractility?

Ability to shorten and generate force.

What is extensibility?

Ability to stretch without damage.

What is elasticity?

Return to original shape.

What are skeletal muscle fibers?

Long multinucleated cells.

How do muscle fibers form?

Fusion of myoblasts.

What are satellite cells?

Stem cells for muscle repair.

What are slow oxidative fibers?

Endurance fibers with high fatigue resistance.

Characteristics of slow fibers

Many mitochondria, high myoglobin, aerobic, red, fatigue resistant.

What are fast oxidative fibers?

Intermediate speed and fatigue resistance.

Characteristics of fast oxidative fibers

Moderate mitochondria, both aerobic and anaerobic.

What are fast glycolytic fibers?

Powerful fast fibers that fatigue quickly.

Characteristics of fast glycolytic fibers

Low mitochondria, low myoglobin, anaerobic, white.

What is hypertrophy?

Muscle size increase.

What is atrophy?

Muscle size decrease.

What is an agonist?

Primary mover muscle.

What is an antagonist?

Opposes agonist movement.

What is a synergist?

Assists agonist.

What is a fixator?

Stabilizes muscle origin.

What is a lever?

Rigid bone moving around a fulcrum.

What is a fulcrum?

Pivot point (joint).

What is effort?

Muscle force applied.

What is resistance?

Load being moved.

What is a first class lever? Fulcrum between effort and resistance.

Example of first class lever

Nodding head.

What is a second class lever? Resistance between fulcrum and effort.

Example of second class lever

Standing on toes.

What is a third class lever? Effort between fulcrum and resistance.

Example of third class lever

Biceps flexion.

What are muscle naming criteria? Location, shape, fiber direction, size, action, attachments, number of origins.

Muscle naming by location

Named by body region or bone.

Muscle naming by shape

Named by shape like deltoid or trapezius.

Muscle naming by fiber direction

Rectus, transverse, oblique.

Muscle naming by number of origins

Biceps, triceps, quadriceps.

Muscle naming by attachments

Named by origin and insertion points.