Lecture 19: Musculoskeletal System

Comprehensive vocabulary flashcards covering muscle properties, cellular organization, the sliding filament model, muscle tissue types, and skeletal structures from Lecture 19.

Musculoskeletal System

The organ system whose primary function is to provide movement and structure for the body, receiving its ability to move from the nervous system.

5 Properties of muscle

include excitability, contractility, extensibility, elasticity, and adaptability.

SEQ Muscle Structure

muscle tissue → Muscle fiber (cells) →Myofibrill → myofillaments

T (Transverse) Tubules

Infoldings of the plasma membrane that carry electrical signals deep into large-diameter muscle fibers.

Sarcoplasmic Reticulum (SR)

Specialized endoplasmic reticulum of muscle cells whose development varies by muscle type; it stores and releases $Ca^{2+}$ during muscle contraction.

Myofibrils

Longitudinal fibers located inside the muscle cell that are made up of hundreds of sarcomeres arranged end-to-end.

Sarcomere

The basic contractile unit of a muscle consisting of overlapping thin and thick filaments.

Actin

Contractile protein forming thin filaments in myofibrils alongside regulatory proteins tropomyosin and the troponin complex.

Myosin

Contractile protein forming thick filaments consisting of ~$350$ molecules, each with associating tails and outward-projecting heads.

Tropomyosin

A blocker protein that covers myosin-binding sites on actin during the resting phase to keep muscles relaxed.

Troponin Complex

Regulatory protein complex on actin that binds $Ca^{2+}$, causing tropomyosin to move out of the way and expose myosin-binding sites.

Sliding Filament Model

The mechanism of muscle contraction where thin and thick filaments slide past each other, pulling actin toward the center of the sarcomere and shortening it.

Cross-Bridge

The structural connection formed when an energized myosin head binds to an exposed binding site on actin.

Power Stroke

The phase of the cross-bridge cycle where ADP is released, causing the myosin head to pivot and pull actin toward the center of the sarcomere.

Skeletal Muscle

Voluntary, striated, multinucleate muscle tissue attached to bones via tendons, coordinated in motor units, and possessing T tubules and a well-developed SR.

Tendons

Cords of connective tissue that attach skeletal muscles to bones.

Cardiac Muscle

Involuntary, striated muscle found in heart walls consisting of branched fibers with $1$ nucleus each, connected by intercalated discs to pump blood simultaneously and independently.

Smooth Muscle

Involuntary, non-striated muscle composed of spindle-shaped fibers with $1$ nucleus each; lacks T tubules, has a poorly developed SR, and produces slow contractions and slow relaxation.

The three general skeletal function

supporting the body, protecting internal organs, and facilitating movement.

Endoskeleton

An internal, hard framework composed of cartilage and bone that is living (able to grow) and moved by muscles pulling on the outside of bones.

Exoskeleton

An external, hard covering composed of chitin (in arthropods) or $CaCO_3$ (in mollusks) that is non-living (does not grow) and moved by muscles pulling on the inside of the shell.

Hydrostatic Skeleton

An internal closed, fluid-filled cavity with fluid held under pressure, used by cnidarians, nematodes, and annelids to produce movement.