Musculoskeletal System: Bones, Joints, and Muscles

Comprehensive vocabulary flashcards covering the structure, types, histology, and disorders of bones; joint classifications and kinematics; muscle contraction mechanics; and human musculoskeletal anatomy.

Femur

The longest and strongest bone in the human body.

Stapes

The smallest and lightest bone in the human body, located in the middle ear.

Hematopoiesis

The production of blood cells, which takes place within the bones.

Long Bones

Bones that are longer than they are wide, support body weight, and facilitate movement; found mostly in the appendicular skeleton (e.g., femur, humerus, tibia, ulna, phalanges).

Short Bones

Cube-shaped bones that are approximately equal in length and width, providing stability and assisting in movement (e.g., carpals and tarsals).

Flat Bones

Somewhat flattened bones that act like a shield to protect internal organs (e.g., skull, sternum, ribs, and pelvis).

Irregular Bones

Bones with complex shapes that do not fit into other morphological categories, functioning to protect internal organs (e.g., vertebrae and sacrum).

Sesamoid Bones

Small, round bones embedded within tendons that protect them from stress and wear (e.g., patella).

Compact Bone

The hardest and heaviest bone tissue, comprising about $80\%$ of bone mass, which provides brute force support and protects fragile internal structures.

Osteons

Cylindrical structural units inside compact bone containing osteocytes that form tubes to transmit blood vessels and nerves.

Spongy Bone

Porous bone tissue comprising about $20\%$ of bone mass, located primarily at bone ends and joints, containing pores filled with marrow, nerves, and blood vessels.

Red Bone Marrow

Vascular bone marrow tissue responsible for producing all red blood cells, white blood cells, and platelets.

Yellow Bone Marrow

Fatty bone marrow found in the center of long bones (such as the thigh bone) that replaces red marrow with age.

Joint

The junction where two or more bones meet, linked together by ligaments and protected by cartilage.

Fixed Joints (Fibrous Joints)

Immovable joints with no mobility between connecting bones, such as the sutures uniting the cranium.

Cartilaginous Joints

Slightly movable joints joined by cartilage, exemplified by the joints between vertebrae in the vertebral column.

Synovial Joints

Freely moving joints characterized by a fluid-filled joint capsule containing synovial fluid lined by a synovial membrane; the most common joint type in the human body.

Types of Synovial Joints

The six structural classes of freely moving joints: hinge, saddle, ball and socket, gliding, pivot, and condyloid.

Abduction and Adduction

Abduction is movement away from the midline of the body, whereas adduction is movement toward the midline.

Circumduction

A circular movement pattern executed by the distal end of a bone around an axis.

Osteogenesis Imperfecta (OI)

A genetic disorder that impairs the body's ability to produce type 1 collagen, resulting in extremely brittle bones.

Blue Sclera

A distinct clinical presentation of osteogenesis imperfecta in which the whites of the eyes appear blue.

Ewing’s Sarcoma

A form of bone cancer found primarily in individuals under $30$ years of age, situated in or surrounding bone, associated with a $50\%$ survival rate and requiring aggressive treatment.

Smooth Muscle

Involuntary, non-striated muscle tissue located in the walls of internal organs.

Cardiac Muscle

Involuntary, specialized striated muscle tissue found exclusively in the heart.

Skeletal Muscle

Voluntary muscle tissue attached to bones that generates pulling forces to produce movement and range of motion.

Sliding Filament Theory

The mechanism of muscle contraction where myosin heads bind to actin, perform a working stroke to pull actin toward the M line and shorten the sarcomere, detach upon ATP binding, and recock following ATP hydrolysis.

Actin

The thin protein myofilament that serves as the attachment point for myosin heads during muscle contraction.

Myosin

The thick protein myofilament whose heads bind and pull actin filaments along to shorten the sarcomere.

Anaerobic Respiration (Muscle Physiology)

An emergency metabolic pathway utilized when oxygen levels are insufficient, breaking down sugars into ATP and producing lactic acid.

Hydrogen Ions ($H^+$) in Muscle Fatigue

Substances released by the continuous breakdown of ATP during strenuous exercise that create an acidic environment in muscle cells, directly causing muscle fatigue.

Lactate Threshold

The point during exercise when blood lactate accumulation exceeds the body's rate of removal, triggering muscle fatigue as an early warning system against injury.

Delayed Onset Muscle Soreness (DOMS)

Muscle soreness caused by inflammation at microscopic tears in muscle fibers following exertion; healing these microtears increases muscle size and strength.

Mandible

The lower jawbone, forming the lower portion of the facial skeleton.

Sternum

The central anterior breastbone that articulates with the clavicles and true ribs.

Clavicle

The collarbone connecting the sternum to the scapula on the anterior shoulder girdle.

Calcaneus

The heel bone of the foot situated inferior to the talus.

Deltoideus

The triangular muscle covering the shoulder complex responsible for arm abduction.

Latissimus Dorsi

The broad, superficial muscle of the lower and middle back.

Gastrocnemius

The major superficial muscle forming the calf of the posterior lower leg.

Pectoralis Major

The large fan-shaped muscle covering the upper anterior chest.

Rectus Abdominis

The paired anterior abdominal muscles that flex the vertebral column.

Sternocleidomastoid

A two-headed anterior neck muscle responsible for flexing and rotating the cervical spine.

Sartorius

A long, ribbon-like muscle crossing diagonally over the anterior thigh from the hip to the medial knee.