The musculoskeletal system

The Musculoskeletal System

The Muscular System

The muscular system is responsible for the movement of the human body. Attached to the bones of the skeletal system are about 700 named muscles that make up roughly half of a person’s body weight. Each of these muscles is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendons, and nerves. Muscle tissue is also found inside of the heart, digestive organs, and blood vessels. In these organs, muscles serve to move substances throughout the body.

  • Includes muscle, bone, tendons (connecting muscle to bone) and ligaments (connecting bone to bone).
  • Functions include structural, protection, motion, mineral storage and blood cell production. Bone injuries can result in substantial blood loss (1-2 L from a fractured femur and up to 2 L from a fractured pelvis).
  • Skeletal Muscle: Striated, voluntary, can be consciously controlled. Also called skeletal muscles.
  • Smooth Muscle: Smooth, involuntary, cannot be consciously controlled.
  • Cardiac Muscle: Striated, branched, involuntary.


The Skeletal System

  • Consists of six basic components: The skull, spinal column, thorax, pelvis, upper extremities (arms), and lower extremities (legs).

The Skull

  • Cranium: brain case. Encloses the cranial cavity. Contains flat bones.
    • Occipital: back of the head.
    • Parietal: the upper sides.
    • Temporal: the temples.
    • Frontal: forehead.
  • Face: irregular bones
    • Orbits: eye sockets.
    • Nasal Bones: nose bed.
    • Maxillae: upper jaw.
    • Zygomatic: cheek bones.
    • Mandible: lower jaw.


The Spinal Column

  • Verbebrae: irregular bones that make up the spinal column. 33 vertebrae intercalated with intervertebral discs make up the spinal column, which is divided into 5 parts.
    • Cervical: the neck consists of 7 verbebrae C1-C7.
    • Thoracic: upper back consists of 12 verbebrae T1-T12. The 12 thoracic ribs are attached here.
    • Lumbar: lower back consists of 5 vertebrae L1-L5. These are the least mobile.
    • Sacral: back wall of pelvis consists of 5 fused vertebrae S1-S5.
    • Coccyx: tailbone consists of 4 fused vertebrae.


The Thorax

  • The ribs: there are 24 ribs arranged into 12 pairs, which are attached at the back to the 12 thoracic vertebrae.
    • True ribs: the first 7 pairs attached at the front to the sternum.
    • The next 3 pairs attach at the front to the true ribs.
    • False ribs: last 2 pairs are not attached at the front. Also called floating ribs.
  • Sternum: breastbone.
    • Manubrium: the superior portion of the sternum that attaches the clavicle.
    • Body: the middle portion of the sternum that attaches the ribs.
    • Xiphoid process: the inferior portion of the sternum.

The Pelvis

  • Sacrum and coccyx: the back of the pelvis.
  • Ilium: from the Iliac crest (the “wings” on the sides of the pelvis) to the formation of the acetabulum.
  • Acetabulum: socket for hip-joint.
  • Ischium: the lower back portion. Supports weight while sitting.
  • Pubis: the lower front portion. Area of the genitals. The left and right sides are joined at the pubic symphysis.


The Upper Extremities

  • Consists of the upper limbs from the shoulder to the fingers.
  • The Clavicle, Scapula, and the Acromion: the collar bone (clavicle) and the shoulder-blade (scapula) forms the pectoral (shoulder) girdle, which connects the upper limb. The acromion, or acromial process is the tip on top of the shoulder.
  • The Humerus: the head of the humerus fits in the ball and socket joint of the shoulder. The distal end of the humerus ends at the hinge joint of the elbow.
  • Olecranon: the elbow, formed by the proximal end of the ulna.
  • The Radius and Ulna: from the elbow, two bones form the forearm. The radius is on the thumb side (lateral with palm facing the front) and the ulna is on the pinky side (medial). Both bones end at the wrist joint.
  • Carpals, Metacarpals and Phalanges: makes up the hand from the wrist (carpals) to the hands (metacarpals) to the fingers (phalanges).

The Lower Extremities

  • Consists of the legs from the hip to the toes.
  • Femur: the head of the femur fits into the acetabulum socket in the hip. The femur ends at the patella (the knee).
  • Patella: kneecap.
  • Tibia and Fibula: The bones of the lower leg. The tibia is larger of the two and forms the shin, the distal end of which forms the medial ankle. The fibula is parallel and lateral to the tibia, the distal end of which forms the lateral ankle.
  • Malleolus: the ankle knob. Can be medial or lateral.
  • Calcaneus: heel bone
  • Tarsals, Metatarsals and Phalanges: makes up the foot from the ankles (tarsals) to the foot (metatarsals) to the toes (phalanges).



  • Motion
    • Flexion and Extension: bending (flexing) and straightening (extending).
    • Adduction and Abduction: movement toward (adduct) and away from (abduct) the midline.
    • Circumduction: circular movement. Includes all the above motion.
    • Supination and Pronation: turning the forearm to make the palm face the front (supination) or the back (pronation).
  • Structure
    • Ball-and-Socket: circular in shape, allows for circumduction, the widest range of motion. Examples include the shoulder and hip.
    • Hinged Joint: shaped like a door hinge, allows for flexion and extension. Examples include the elbow, knee and finger.
    • Pivot Joint: semi-circular ring shape, allows for turning motion. Examples include the C1-C2 vertebrae and the wrist.
    • Gliding Joint: planar in shape, allows for sliding motion. Examples include the small bones in the hands and feet.
    • Saddle Joint: saddle (reciprocal concave-convex) in shape, allows for limited circumduction without axial rotation. An example include the carpal-metacarpal joint of the thumb.
    • Condyloid Joint: ovular in shape, allows for limited circumduction without axial rotation. An example include the wrist.





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