Skeletal System, Movement, and Muscular System

Vocabulary practice flashcards covering the anatomy and physiology of the skeletal system, joints, and muscular contraction mechanisms from Concepts 1, 2, and 3 notes.

Insertion

The point where a skeletal muscle attaches to a movable bone.

Origin

The point where a skeletal muscle attaches to an immovable bone (or the bone that moves less).

Prime Mover (Agonist)

A muscle that is most responsible for producing a specific movement, such as the biceps brachii during forearm flexion in a bicep curl.

Antagonist

A muscle that opposes or does the reverse of a certain movement, typically located on the opposite side of a joint from the prime mover and stretched or relaxed when the prime mover is active.

Synergist

A muscle that helps the prime mover by adding extra force or stabilizing across a joint.

Fixator

A specific type of synergist muscle that immobilizes the muscle's origin bone to increase the prime mover's effectiveness and help maintain an upright posture.

Cardiac Muscle Tissue

Striated muscle tissue found in the heart that contracts involuntarily to pump blood throughout the body.

Smooth Muscle Tissue

Nonstriated muscle tissue found in the walls of visceral organs that contracts involuntarily to propel substances down internal passageways.

Skeletal Muscle Tissue

Striated muscle tissue generally attached to bones that contracts voluntarily to produce body movement.

Myofibril

An organelle that makes up most of a muscle cell, composed of myofilaments (actin and myosin) and subdivided lengthwise into sarcomeres.

Sarcomere

The contractile unit of a muscle, separated by Z disc (or Z line) borders on each end along a myofibril.

Muscle Fiber

A single muscle cell, containing multiple nuclei, mitochondria, a specialized sarcoplasmic reticulum, sarcoplasm, a sarcolemma, and packed myofibrils.

Fascicle

A bundle of muscle fibers (cells) wrapped together inside a muscle organ.

Epimysium

The connective tissue layer that wraps around the entire outside of a muscle organ.

Perimysium

The connective tissue layer that surrounds each muscle fascicle.

Endomysium

The connective tissue layer that surrounds each individual muscle fiber.

Sliding Filament Model

The mechanism of muscle contraction where thick myosin filament heads grab onto thin actin filaments and pull them toward the center, increasing filament overlap and shortening the sarcomere.

Tropomyosin

A regulatory protein that blocks myosin from binding to the active sites on actin filaments when a muscle is relaxed.

Troponin

A regulatory protein that binds to calcium ions ($Ca^{2+}$), pulling tropomyosin away from actin to expose binding sites for myosin cross-bridge attachment.

Action Potential (AP)

A large change in membrane potential that spreads rapidly over long distances within an excitable cell, driven by the movement of ions through ion channels.

Resting Membrane Potential

The voltage across a cell membrane when at rest, typically ranging from $-50\text{ mV}$ to $-90\text{ mV}$.

Neuromuscular Junction

The synapse or motor end plate where axon terminals of a somatic motor neuron meet a muscle fiber, including the intervening synaptic cleft.

Acetylcholine (ACh)

The specific neurotransmitter released by motor neurons that diffuses across the synaptic cleft to transmit the contraction signal to a muscle fiber.

First-Class Lever

A lever system where the effort is applied at one end and the load is at the other, with the fulcrum located between them (e.g., the system that raises your head from your chest).

Second-Class Lever

A lever system where the effort is applied at one end and the fulcrum is at the other, with the load positioned in between (e.g., the system that allows you to stand on your toes).

Third-Class Lever

A lever system where the effort is applied between the load and the fulcrum (e.g., the lever system active during a bicep curl).

Ligament

A dense connective tissue band that attaches bone to bone at a joint.

Tendon

A strong band of connective tissue that attaches muscle to bone.

Synarthroses

A functional category of joints that are non-moving (immovable), such as the cranial sutures protecting the brain.

Amphiarthroses

A functional category of slightly movable joints, such as the pubic symphysis in the pelvis.

Diarthroses

A functional category of freely movable joints, found predominantly in limbs (e.g., knee and elbow joints).

Fibrous Joints

A structural classification of mostly immovable joints where bones are joined by dense collagen fibers without a joint cavity (e.g., sutures, syndesmoses, and gomphoses).

Cartilaginous Joints

A structural classification of joints where bones are united by cartilage, either rigid or slightly movable (e.g., synchondroses and symphyses).

Synovial Joints

A structural classification of freely movable joints characterized by articular cartilage, a joint cavity enclosed by an articular capsule, synovial fluid, and reinforcing ligaments.

Flexion

An angular movement that decreases the angle of a joint, bringing articulating bones closer together.

Extension

An angular movement that increases the angle between articulating bones, reversing flexion.

Abduction

A movement that moves a limb away from the median plane along the frontal plane.

Adduction

A movement that moves a limb toward the median plane along the frontal plane, opposite to abduction.

Supination

A twisting or rotational movement that turns a limb or the forearm forward.

Pronation

A twisting or rotational movement that turns a limb or the forearm backward.

Isotonic Contraction

A muscle contraction that produces tension and results in a change in muscle length (e.g., lifting a box or performing push-ups).

Isometric Contraction

A muscle contraction where tension is generated without producing a change in muscle length (e.g., maintaining posture or holding a plank).

Hematopoiesis

The formation of blood cells (red blood cells, white blood cells, and platelets) from hematopoietic stem cells within the red bone marrow.

Osteocalcin

A hormone produced by bone tissue that helps regulate insulin secretion, glucose regulation, and energy usage to maintain homeostasis.

Long Bones

Bones that are longer than they are wide, featuring a central shaft with wider ends, primarily located in limbs to act as levers for movement.

Short Bones

Cube-shaped bones that are approximately as wide as they are long, providing support and stability with minimal movement (e.g., carpals and tarsals).

Sesamoid Bones

A special class of short bones shaped like sesame seeds that are embedded within tendons, such as the patella.

Flat Bones

Thin, flattened, and slightly curved bones with large surface areas for muscle attachment (e.g., sternum, scapulae, ribs, and most cranial bones).

Irregular Bones

Bones with highly specialized, complex shapes that do not fit into the long, short, or flat categories (e.g., vertebrae and hip bones).

Compact Bone

A dense, smooth outer layer of bone tissue composed of repeating cylindrical structural units called osteons.

Spongy Bone

A porous internal layer of bone tissue composed of a network of trabeculae that resist multidirectional stress and contain bone marrow.

Osteon

The basic structural unit of compact bone, consisting of concentric tubes of matrix called lamellae that act as tiny weight-bearing pillars.

Haversian Canal

A central canal that runs through the core of each osteon, carrying blood vessels for nourishment and nerve fibers for signaling.

Trabeculae

Tiny structural bone struts found in spongy bone that help resist mechanical stress and house red or yellow bone marrow.

Osteocyte

A mature bone cell housed inside a lacuna that monitors stress and directs bone remodeling by commanding osteoblasts and osteoclasts.

Osteoblast

A bone cell responsible for building and calcifying bone matrix (osteoid) during bone formation and remodeling.

Osteoclast

A specialized bone cell that breaks down degenerating or unneeded bone tissue by secreting enzymes that dissolve calcium phosphate.

Ossification (Osteogenesis)

The process of bone tissue formation, initiating in embryos at week 8, directing growth through early adulthood, and remodeling bone throughout life.

Intramembranous Ossification

The type of bone development where bone forms directly from a fibrous membrane, giving rise to membranous bones such as the clavicle and cranial bones.

Endochondral Ossification

The process of bone development where bone forms by replacing a precursor hyaline cartilage template.

Bone Remodeling

The continuous cyclical process of bone renewal involving osteoclast resorption, macrophage action, and osteoblast bone formation and mineralization.

Resorption

The bone remodeling stage where osteoclasts digest calcium phosphate with enzymes, releasing calcium and phosphate minerals back into the bloodstream.