Musculoskeletal System

Contract

Reduces the distance between parts they are connected to.

Extensibility

The ability of a muscle to be stretched.

Elasticity

The ability of a muscle to return to its original length.

Excitability

The ability of a muscle to be stimulated by a nerve impulse.

Tendon

Fibrous, inelastic connective tissue that attaches muscles to bones.

Bundle

Muscle cells held together in groups by connective tissue.

Sarcolemma

The plasma (cell) membrane of a muscle fibre.

Sarcoplasm

The cytoplasm of a muscle fibre.

Transverse Tubules (T-Tubules)

Narrow tubes continuous with the sarcolemma extending into the sarcoplasm.

Sarcoplasmic Reticulum

Tubular network around each myofibril that stores and releases calcium ions.

Myofibrils

Thread-like structures running parallel along the length of a muscle fibre.

Sarcomeres

The functional, contractile units of skeletal muscle in myofibrils.

Z Lines

Structural lines that mark the boundary between adjacent sarcomeres.

H Zone

The area in a sarcomere between the ends of actin filaments.

A Band

The region of a sarcomere spanning the entire length of myosin.

I Band

The region between the ends of myosin filaments of adjacent sarcomeres.

Myofilaments

Smaller protein units involved in muscle contraction (actin and myosin).

Thick myofilaments

Myofilaments composed mostly of the protein myosin.

Thin myofilaments

Myofilaments composed mostly of the protein actin.

Cross-bridges

Connections formed when myosin heads attach to thin filaments during contraction.

Tropomyosin

Double-stranded proteins that cover active binding sites on actin.

Troponin

Protein that binds to tropomyosin, holding it in place, and binds calcium.

Sliding filament theory

Theory stating thin actin filaments slide over thick myosin filaments during contraction.

Antagonists

Muscles grouped in pairs that produce opposite movements.

Origin

The end of a muscle attached to the stationary bone.

Insertion

The end of a muscle attached to the moveable bone.

Agonist

The muscle that directly causes the desired movement.

Synergists

Muscles that help indirectly by steadying a joint during movement.

Fixator

A synergist muscle that immobilises a joint.

Muscle Tone

The state of partial contraction maintained by skeletal muscles.

Axial Skeleton

Provides support for erect posture and protects the CNS and thoracic organs.

Appendicular Skeleton

Allows for articulation of the limbs with the axial skeleton.

Epiphysis

The end portion of a long bone.

Diaphysis

The shaft making up the main portion of a long bone.

Periosteum

Dense, fibrous outer covering of bone containing blood vessels and nerves.

Medullary cavity

The central cavity of bone filled with yellow bone marrow.

Articular cartilage

Covers each epiphysis to provide protection and cushioning at joints.

Epiphyseal lines

Areas of bone growth found in children.

Compact bone

Dense, rigid outer bone layer protecting spongy bone and marrow.

Spongy (cancellous) bone

Porous bone containing large spaces filled with marrow.

Bone (connective tissue)

Connective tissue consisting of cells separated by a non-cellular matrix.

Matrix

Non-cellular material containing inorganic salts that provide bone strength.

Osteon

The basic structural unit of compact bone; Haversian system.

Central Canal

The channel running through the centre of each osteon.

Lamellae

Concentric layers of bony matrix in compact bone.

Lacunae

Small spaces in the matrix between lamellae containing bone cells.

Canaliculi

Tiny canals connecting lacunae within the bone matrix.

Osteocyte

A mature bone cell found residing in a lacuna.

Trabeculae

Irregular, thin bony plates that make up spongy bone.

Cartilage

Connective tissue made of collagen fibres embedded in a chondrin matrix.

Chondrin

The protein-carbohydrate matrix characteristic of cartilage.

Perichondrium

The fibrous membrane covering the external surface of cartilage.

Chondroblasts

Cells that actively produce the cartilage matrix.

Chondrocytes

Mature cartilage cells.

Joint

The site where two or more bones come together.

Fibrous joint

An immovable joint held together by fibrous connective tissue.

Cartilaginous joint

A slightly moveable joint held together by cartilage.

Synovial joint

A freely moveable joint.

Synovial Cavity

The space between articulating bones in a synovial joint.

Articular capsule

The structure that surrounds and encloses a synovial joint.

Fibrous capsule

Dense connective tissue outer layer that holds articulating bones together.

Synovial membrane

The inner layer of the articular capsule that secretes synovial fluid.

Synovial fluid

Fluid that lubricates the joint and nourishes the articular cartilage.

Articular cartilage (joint)

Provides a smooth, low-friction surface for bone movement.

Bursae

Sacs of synovial fluid that reduce friction in joints.

Accessory ligaments

Ligaments that hold bones together and stabilise the joint.

Flexion

Bending movement that decreases the angle between bones.

Extension

Straightening movement that increases the angle between bones.

Abduction

Movement of a body part away from the midline.

Adduction

Movement of a body part towards the midline.

Rotation

Movement of a bone around its long axis.

Circumduction

Circular movement of a limb describing a cone.

Osteoporosis

Loss of bone mass sufficient to impair normal skeletal function.

Osteoarthritis

Gradual joint deterioration where articular cartilage wears away.

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