Muscle Structure and Function & Animal Skeletons

Flashcards for muscle structure, function, and skeletal systems.

Muscle Fibers

Long, cylindrical cells that make up skeletal muscles.

Myofibrils

Bundles of sarcomeres within muscle fibers; the basic contractile units.

Sarcolemma

Cell membrane surrounding muscle fibers.

Sarcoplasm

Cytoplasm within muscle fibers.

Sliding Filament Model

Model describing how muscles contract at the molecular level through actin and myosin sliding past each other.

Actin

Thin filament in muscle cells; site for myosin binding.

Myosin

Thick filament in muscle cells; has heads that attach to actin and perform power strokes.

Sarcomere

Repeating unit in myofibrils, between two Z-lines; shortens during contraction.

Troponin

Binds calcium and shifts tropomyosin away from actin's binding sites.

Tropomyosin

Blocks myosin-binding sites on actin in resting muscle.

Acetylcholine (ACh)

Neurotransmitter released at the neuromuscular junction to initiate muscle contraction.

T-tubule

Extensions of the sarcolemma that carry action potentials deep into the muscle fiber.

Sarcoplasmic Reticulum (SR)

Stores calcium ions and releases them in response to an action potential.

Skeletal muscle

Voluntary, striated muscle attached to bones.

Cardiac muscle

Involuntary, striated muscle in the heart; has intercalated discs.

Smooth muscle

Involuntary, non-striated muscle found in organs like the gut and blood vessels.

Type I (Slow-twitch)

Skeletal muscle fiber type with high endurance, uses aerobic respiration, rich in mitochondria and myoglobin.

Type IIa (Fast-twitch oxidative)

Skeletal muscle fiber type with intermediate endurance and strength, uses both aerobic and anaerobic pathways.

Type IIb/x (Fast-twitch glycolytic)

Skeletal muscle fiber type with high strength, low endurance, uses anaerobic metabolism.

Hydrostatic skeleton

Fluid-filled cavity that provides support (e.g., earthworms, jellyfish).

Exoskeleton

External shell (e.g., insects, crustaceans); made of chitin or calcium carbonate.

Endoskeleton

Internal skeleton (e.g., vertebrates); made of bone and/or cartilage.