Anatomy and Physiology: Bone Tissue, Skeletal System, Joints, and Muscular Tissue

Comprehensive vocabulary flashcards covering osseous tissue histology, the axial and appendicular skeletal divisions, joint articulations, kinesiology, and skeletal muscle cell physiology.

Osteology

The scientific study of bone tissue and bones.

Compact bone

Dense outer shell of osseous tissue that constitutes three-fourths of the skeleton by weight.

Spongy bone

Loosely organized bone tissue composed of trabeculae found in the center of bones, covered by compact bone, and accounting for one-fourth of the skeleton by weight.

Diaphysis

The tubular shaft of a long bone that provides leverage.

Epiphyses

The enlarged proximal and distal ends of a long bone that strengthen joints and anchor ligaments and tendons.

Periosteum

The external sheath covering most of a bone, containing an outer fibrous layer of collagen and an inner osteogenic layer of bone-forming cells.

Endosteum

A thin layer of reticular connective tissue lining the marrow cavity and internal spaces, containing cells that dissolve osseous tissue and others that deposit it.

Diploe

The spongy middle layer of flat bones that absorbs shock and is sandwiched between inner and outer tables of compact bone.

Osteogenic cells

Stem cells that arise from embryonic mesenchyme, reside in the endosteum and inner periosteum, and multiply continuously to give rise to most other bone cell types.

Osteoblasts

Bone-forming cells arranged in a single layer under the endosteum and periosteum that synthesize the soft organic matrix which subsequently hardens by osteogenesis.

Osteocytes

Former osteoblasts trapped in matrix cavities called lacunae that act as strain sensors to produce biochemical signals regulating adaptive bone remodeling.

Osteoclasts

Large, multinucleated bone-dissolving cells developed from blood stem cells that feature a ruffled border facing the bone surface and reside in resorption bays.

Hydroxyapatite

Crystallized calcium phosphate salt forming $85\%$ of the inorganic matrix of bone, functioning as the ceramic material that supports body weight without sagging.

Osteon

The basic structural unit of compact bone, composed of concentric lamellae arranged around a central (haversian) canal containing blood vessels and nerves.

Endochondral ossification

The embryonic process of bone development in which bone replaces a preexisting model of hyaline cartilage.

Intramembranous ossification

The embryonic process that produces flat bones of the skull, clavicle, and part of the mandible directly from mesenchymal tissue without a prior cartilage model.

Metaphysis

The transition zone on each side of the hyaline cartilage of the epiphysial plate where cartilage transitions into bone through five distinct histological zones.

Appositional growth

The continual widening and thickening of bone occurring at the bone surface through periosteal osteoblast matrix deposition and endosteal osteoclast resorption.

Calcitriol

A hormone that raises blood calcium levels and promotes phosphate absorption by the small intestine.

Calcitonin

A hormone that functions to lower blood calcium levels.

Parathyroid hormone (PTH)

A hormone that raises blood calcium levels and lowers blood phosphate levels by promoting its urinary excretion.

Axial skeleton

The central supporting axis of the human skeleton, comprising the skull, auditory ossicles, hyoid bone, vertebral column, sternum, and ribs.

Appendicular skeleton

The division of the skeletal system comprising the pectoral girdle, upper extremities, pelvic girdle, and lower extremities.

Paranasal sinuses

Air-filled, mucous membrane-lined cavities located within the frontal, sphenoid, ethmoid, and maxillary bones that lighten the skull and add resonance to the voice.

Sella turcica

A saddle-like prominence on the superior surface of the sphenoid bone that houses the pituitary gland.

Ethmoid bone

A delicate, porous cranial bone located between the eyes that contributes to the medial orbit wall, roof and walls of the nasal cavity, and superior nasal septum.

Fontanelles

Fibrous membrane-covered spaces between unfused cranial bones in an infant that allow shifting of bones during birth and rapid brain growth.

Scoliosis

An abnormal lateral curvature of the vertebral column, most commonly occurring in the thoracic region of adolescent girls.

Abnormal spinal curvatures

Pathological deviations of the vertebral column including scoliosis (lateral curve), hyperkyphosis (exaggerated thoracic hunchback), and hyperlordosis (exaggerated lumbar swayback).

Intervertebral discs

Twenty-three fibrocartilaginous pads between vertebrae composed of an inner gelatinous nucleus pulposus and an outer fibrous ring called the anulus fibrosus.

Atlas (C1)

The first cervical vertebra that supports the head, lacks a vertebral body, and articulates via superior articular facets with occipital condyles to enable nodding "yes".

Axis (C2)

The second cervical vertebra characterized by a prominent vertical projection called the dens (odontoid process) that allows rotation of the head gesturing "no".

Transverse foramen

A distinctive opening in each transverse process of cervical vertebrae (C1–C7) that provides passage for the vertebral artery and vertebral vein.

Acromion

A flattened, plate-like extension of the scapular spine that forms the apex of the shoulder and articulates with the clavicle.

Glenoid cavity

A shallow socket on the lateral angle of the scapula that articulates with the head of the humerus to form the glenohumeral joint.

Olecranon

The prominent bony point on the proximal posterior ulna that forms the point of the elbow.

Pelvic girdle

A skeletal ring that supports the trunk and lower limbs, composed of two hip (coxal) bones and the sacrum.

Acetabulum

The deep cup-shaped hip socket formed by the fusion of the ilium, ischium, and pubis that articulates with the head of the femur.

Calcaneus

The largest tarsal bone that forms the heel and serves as the attachment point for the calcaneal (Achilles) tendon.

Talus

The most superior tarsal bone that articulates with the tibia and fibula to form the talocrural joint.

Synostosis

An immobile bony joint formed when the intervening gap between two bones ossifies and merges them into a single bone.

Gomphosis

A specialized fibrous joint attaching the root of a tooth to its bony socket (alveolus) via the collagenous periodontal ligament.

Syndesmosis

A fibrous joint in which two parallel bones are bound together by relatively long collagenous fibers, such as the interosseous membrane between the radius and ulna.

Synovial joint

A freely mobile diarthrosis characterized by facing articular cartilages separated by a fluid-filled joint cavity enclosed within a fibrous and synovial joint capsule.

Meniscus

A C-shaped pad of fibrocartilage extending into the joint cavity of the knee that absorbs compressive shock, prevents side-to-side rocking, and enhances articular fit.

Bursa

A fibrous sac filled with synovial fluid located between muscles, tendons, or bones to cushion tissues and reduce friction during joint movement.

Anterior cruciate ligament (ACL)

An intracapsular ligament of the knee that crosses within the joint capsule to form an "X" and prevents hyperextension of the knee when pulled tight.

Rheumatoid arthritis (RA)

An autoimmune joint disease in which autoantibodies attack the synovial membrane, causing enzymatic degradation of articular cartilage and potential ossification.

Endomysium

A thin sleeve of loose connective tissue surrounding each individual muscle fiber (muscle cell).

Perimysium

A thicker connective tissue sheath that wraps together bundles of muscle fibers known as fascicles.

Epimysium

A fibrous connective tissue sheath that surrounds the entire skeletal muscle and is continuous with the tendon.

Sarcoplasmic reticulum (SR)

The specialized smooth endoplasmic reticulum of a muscle fiber forming a network around each myofibril and acting as an intracellular calcium reservoir.

Triad

A three-unit intracellular complex in skeletal muscle consisting of one transverse (T) tubule flanked by two dilated terminal cisterns of the sarcoplasmic reticulum.

Sarcomere

The functional contractile unit of a muscle fiber, extending from one Z disc to the adjacent Z disc along the length of a myofibril.

Dystrophin

A critical structural protein that links actin in the outermost myofilaments to membrane proteins connecting to the endomysium; defective in muscular dystrophy.

Motor unit

One somatic motor neuron and all of the skeletal muscle fibers innervated by its axon branches.

Acetylcholinesterase (AChE)

An enzyme located in the basal lamina of the neuromuscular junction that breaks down acetylcholine to terminate stimulation and allow muscle relaxation.

Resting membrane potential (RMP)

The electrical charge difference across the sarcolemma in a waiting, unstimulated muscle cell, typically measured at approximately $-90\,\text{mV}$.

Rigor mortis

The postmortem stiffening of skeletal muscles that begins $3\text{ to }4\,\text{hours}$ after death, peaks at approximately $12\,\text{hours}$, and resolves over $48\text{ to }60\,\text{hours}$ due to calcium leakage and absence of ATP.