Joints, Muscle Tissue, and Bone Physiology Vocabulary

A comprehensive set of vocabulary terms covering joint classifications, muscle tissue structure and contraction, and bone physiology and repair based on the lecture transcript.

Synarthrosis

A functional classification of a joint that is immovable, such as a suture or a gomphosis.

Amphiarthrosis

A functional classification of a joint that permits slight movement, such as a syndesmosis or a symphysis.

Diarthrosis

A functional classification of a joint that is freely movable, which applies to all synovial joints.

Suture

A fibrous joint composed of a thin layer of dense fibrous connective tissue found only in the skull.

Synostosis

A bony joint formed when a fibrous or cartilaginous joint is replaced by osseous tissue during adulthood.

Syndesmosis

A fibrous joint with a greater distance between articulating bones and denser connective tissue than a suture, often forming a ligament or interosseous membrane.

Gomphosis

A fibrous joint where a cone-shaped peg fits into a socket, specifically the articulation between the roots of teeth and their sockets.

Synchondrosis

A cartilaginous joint where the connecting material is hyaline cartilage, such as the epiphyseal plate.

Symphysis

A cartilaginous joint held together by fibrocartilage where all examples occur in the midline of the body.

Synovial Membrane

The inner layer of the articular capsule composed of areolar connective tissue with elastic fibers that secretes synovial fluid.

Synovial Fluid

A viscous, clear fluid containing hyaluronic acid and interstitial fluid that reduces friction, absorbs shock, and supplies nutrients to chondrocytes.

Flexion

An angular movement at a synovial joint that decreases the angle between articulating bones.

Abduction

The movement of a bone away from the midline of the body.

Contractility

A functional characteristic of muscle tissue defined as the ability to shorten forcefully.

Excitability

The ability of muscle tissue to respond to stimulation by nerves and hormones.

Endomysium

A delicate network of loose connective tissue that surrounds each individual muscle fiber.

Perimysium

Heavier connective tissue that surrounds bundles of muscle fibers called fascicles.

Epimysium

Dense collagenous connective tissue that surrounds an entire muscle consisting of many grouped fascicles.

Satellite Cells

Stem cells that allow for partial repair of muscle fibers after an injury.

Sarcomere

The highly ordered unit of actin and myosin filaments that extends from one $Z$ disk to the next.

I Band

The light band of a sarcomere that consists only of actin filaments and includes the $Z$ disk.

A Band

The dark band of a sarcomere that extends the length of myosin filaments and includes areas of overlap with actin.

H Zone

The center of the $A$ band where only myosin is present with no actin overlap.

Tropomyosin

A double-stranded protein in thin filaments that covers the active sites on $G$ actin in a resting muscle.

Troponin

A protein with three globular subunits that binds to tropomyosin, $G$ actin, and calcium ions.

Myosin

The protein that makes up thick filaments, characterized by heads with $ATPase$ activity that form cross-bridges with actin.

Transverse (T) Tubules

Invaginations of the sarcolemma filled with extracellular fluid that conduct action potentials into the muscle fiber interior.

Sarcoplasmic Reticulum (SR)

A specialized smooth endoplasmic reticulum that stores calcium ions and releases them during muscle contraction.

Motor Unit

A functional unit consisting of a single motor neuron and all the muscle fibers it innervates.

Neuromuscular Junction

The functional junction between a nerve ending and a muscle fiber where the neurotransmitter acetylcholine is released.

Acetylcholinesterase

An enzyme located in the synaptic cleft that breaks down acetylcholine to prevent continuous depolarization of the sarcolemma.

Power Stroke

The step in the contraction cycle where stored energy is released and the myosin head pivots toward the $M$ line, pulling the actin filament.

Rigor Mortis

A state of muscle locking several hours after death caused by the depletion of $ATP$ and the leakage of calcium into the sarcoplasm.

Latent Period

The first phase of a muscle twitch where the action potential sweeps across the sarcolemma and calcium is released, but no tension is produced.

All-or-None Law

The principle that an isolated skeletal muscle fiber produces a contraction of equal force in response to any threshold or stronger stimulus.

Wave Summation

A phenomenon where a second muscle twitch is stronger than the first because it is delivered before the muscle has fully relaxed.

Complete Tetanus

A sustained contraction caused by a high frequency of stimulation that eliminates any relaxation phase.

Treppe

A staircase-like increase in maximum tension that occurs when a muscle is stimulated again immediately after each relaxation phase.

Recruitment

The steady increase in tension produced by activating additional motor units within a muscle.

Isometric Contraction

A type of contraction where muscle tension increases but the overall length of the muscle remains constant.

Creatine Phosphate

A high-energy molecule that can quickly generate $ATP$ for about $10-15$ seconds of vigorous muscle contraction.

Oxygen Debt

The amount of oxygen required after exercise to restore $ATP$ and creatine phosphate levels and to convert accumulated lactic acid.

Slow-Twitch Fibers

Muscle fibers that contain high levels of myoglobin and many capillaries, making them well-suited for prolonged, steady contractions.

Agonist

A muscle whose contraction is chiefly responsible for producing a specific movement; also known as a prime mover.

Synergist

A muscle that helps a larger agonist work efficiently by providing additional pull or stabilizing the origin.

Red Bone Marrow

A site within bones responsible for the production of red blood cells, white blood cells, and other blood elements.

Sesamoid Bones

Small, flat bones shaped like a sesame seed that develop inside tendons, such as the patella.

Epiphysis

The enlarged ends of a long bone, consisting mostly of spongy bone and containing red bone marrow.

Medullary Cavity

The central space within the diaphysis of a bone which contains fatty yellow marrow in adults.

Osteoblast

A bone cell responsible for producing new bone matrix through the process of osteogenesis.

Osteoclast

A giant multinucleated cell that removes and recycles bone matrix through osteolysis or resorption.

Osteon

The basic functional unit of mature compact bone, consisting of concentric lamellae around a central canal.

Canaliculi

Small channels that connect lacunae to each other and to the central canal, allowing for the transport of nutrients to osteocytes.

Endochondral Ossification

The process of bone formation in which most bones originate as hyaline cartilage models which are then converted to bone.

Intramembranous Ossification

The process of bone development directly within mesenchymal or fibrous connective tissue, occurring in the flat bones of the skull.

Calcitriol

The active form of Vitamin $D$ that increases the absorption of calcium and phosphate in the digestive tract.

Parathyroid Hormone (PTH)

A hormone released when blood calcium is low that increases levels by stimulating osteoclast activity and decreasing calcium excretion by the kidneys.

Calcitonin

A hormone secreted by the thyroid gland when blood calcium is high that inhibits osteoclast activity and increases calcium excretion.

Osteomalacia

A disorder where bones are weak and flexible due to poor mineralization, appearing normal in shape but structurally soft.

Fracture Hematoma

A large blood clot that forms at the site of a bone break, providing a fibrous meshwork for initial repair.

Greenstick Fracture

A type of fracture common in children where one side of the bone is broken while the other side is bent.