Skeletal Muscular System Key Terms

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Support

Gives the body its shape and holds it upright

Protection

Shields organs like the brain, heart & lungs

Movement

Provides attachment points and levers for muscles

Skeletal System

The framework of bones & joints that supports and protects the body

Axial Skeleton

The skull, spine & rib cage — the body's central axis

Appendicular Skeleton

The bones of the arms, legs & girdles

Joint (Articulation)

The point where two or more bones meet

Ligament

Connective tissue that connects bone to bone L=LINK

Tendon

Connective tissue that connects muscle to bone T=TUG

Origin

A muscle's fixed attachment point; doesn't move during contraction

Insertion

A muscle's attachment point that moves during contraction

Agonist

The muscle primarily responsible for a movement (prime mover)

Antagonist

The muscle that opposes and relaxes during a movement

Synergist

A muscle that assists the agonist in a movement

Actin

The thin protein filament involved in muscle contraction

Myosin

The think protein filament that pulls on acting during contraction

Osteoporosis

A condition in which bones become weak & brittle

Atrophy

The wasting or shrinking of muscle tissue from disuse

Hypertrophy

The growth or enlargement of muscle tissue from use

Sarcomere

The basic contractile unit of a muscle fiber

Ball-and-Socket Joint

Hip & shoulder — movement in nearly all directions

Hinge Joint

Elbow & knee — bending & straightening in one plane

Pivot Joint

Neck (C1–C2) — allows rotation

Gliding Joint

Wrist & ankle bones — allows sliding movements

Thumb

Movement in two planes

Wrist (radiocarpal)

Movement in two planes, no rotation

Front of thigh

Straightens the knee

Back of thigh

Bends the knee

Skull

Protects the brain

Vertebral Column

Protects the spinal cord (mostly hidden behind ribs)

Clavicle

The collarbone

Sternum

The breastbone

Ribs

Protect the heart & lungs

Humerus

Upper arm bone

Radius & Ulna

Forearm bones

Pelvis

Protects lower organs, anchors the legs

Patella

The kneecap

Tibia & Fibula

Lower leg bones

Axial Skeleton

The body’s central axis - Skull, Vertebral Column (spine), Rib Cage & Sternum

Appendicular Skeleton

The moving limbs - Shoulder Girdle & Arms (reaching, throwing, lifting), Pelvic Girdle & Legs (standing, walking, running) Allows locomotion and manipulation of objects

Ball-and-Socket

Hip & shoulder — movement in nearly all directions

Hinge

Elbow & knee — bending & straightening

in one plane

Pivot

Neck (C1–C2) — allows rotation

Gliding

Wrist & ankle bones — allows sliding

movements

Saddle

Thumb (carpometacarpal) — movement in

two planes

Condyloid

Wrist (radiocarpal) — movement in two

planes, no rotation

Hinge Joint — ELBOW

Moves in ONE plane — like a door hinge (flexion & extension only)

Ball-and-Socket — HIP

Moves in nearly ALL directions — flexion, extension, abduction, adduction & rotation

Clavicle

The collarbone — runs across the top of the chest

Sternum

The breastbone — center of the chest

Scapula

The shoulder blade — on the upper back

Olecranon

The bony tip of the elbow

iliac Crest

The top ridge of the hip bone

Patella

The kneecap

Pectorals

Chest — pushes the arm forward and across the body

Latissimus Dorsi

Back — pulls the arm down and back

Deltoids

Shoulders — lifts and rotates the arm

Biceps Brachii

Front of upper arm — bends the elbow

Triceps Brachii

Back of upper arm — straightens the elbow

Quadriceps

Front of thigh — straightens the knee

Hamsprings

Back of thigh - bends the knee

Gastrocnemius

Calf — points the foot, pushes off the ground

Pectoralis Major

chest muscle; pushes the arm forward

Rectus Abdominis

abdominal muscle; flexes the trunk

External Obliques

side abdominals; rotate the trunk

Trapezius

upper back & neck; stabilizes the shoulder blade

Gluteus Maximus

buttocks; extends the hip

Origin

The fixed attachment point — doesn’t move during contraction

Insertion

The attachment point that moves during contraction

Agonist (Prime mover)

The main muscle producing the movement

Antagonist

The opposing muscle that relaxes & lengthens

Synergist

A helper muscle that assists and stabilizes

Muscle → Fascicle → Muscle Fiber → Myofibril → Sarcomere

Muscle → Fascicle → Muscle Fiber → Myofibril → Sarcomere

Z-line

Marks each end/boundary of a single sarcomere

A-band

Dark zone where thick (myosin) filaments are found — length stays constant

I-band

Light zone containing only thin (actin) filaments — shrinks during contraction

H-zone

Center zone that narrows as the sarcomere shortens