The Musculoskeletal System

• The musculoskeletal system enables support and movement of body parts and organs.
• It is comprised of muscles, bones, joints, and related structures, like tendons and connective tissues.

Muscles

• Muscle tissue produces organ/body part movement with contractile cells or fibers.
• Muscles contribute to posture, produce body heat, act as protective coverings for internal organs, and make up most of the body's bulk
• Muscles can be excited by stimuli, contact, relax, and return to regular size/shape.
• Whether attached to bones, internal organs, or blood vessels, muscles' primary function is movement.
• Apparent muscle motion involves walking and talking; less apparent motions include food passage/elimination through the digestive system, blood propulsion through arteries, and bladder contraction to eliminate urine.
• There are three types of muscle tissue: skeletal, cardiac, and smooth.
  • Skeletal muscles, also called voluntary or striated muscles, are under voluntary control and move eyeballs, tongue, and bones.
  • Cardiac muscle is only in the heart, is recognized for its branched interconnections, makes up most of the heart wall, and shares similarities with skeletal and smooth muscles.
    • Like skeletal muscle, it is striated; like smooth muscle, it produces rhythmic involuntary contractions.
  • Smooth muscles, also called involuntary or visceral muscles, are involuntary, found mainly in visceral organs, artery and respiratory passage walls, and urinary and reproductive ducts.
    • Smooth muscles contract using the autonomic (involuntary) nervous system.

Body Movements Produced by Muscle Action

• Adduction: moves closer to the midline
• Abduction: moves away from the midline
• Flexion: decreases the angle of a joint
• Extension: increases the angle of a joint
• Rotation: moves a bone around its own axis
• Pronation: turns the palm down
• Supination: turns the palm up
• Inversion: moves the sole of the foot inward
• Eversion: moves the sole of the foot outward
• Dorsiflexion: elevates the foot
• Plantar flexion: lowers the foot (points the toes)

Attachments

• Muscles attach to bones using fleshy or fibrous attachments.
  • Fleshy attachments occur when muscle fibers arise directly from the bone.
    • Distributing force across wide areas, they are weaker than fibrous attachments.
  • Fibrous attachments occur when connective tissue converges at the muscle's end to become continuous and indistinguishable from the periosteum.
    • Aponeurosis fibrous attachments span a large bone area.
    • Tendons are connective tissue fibers that form a cord or strap.
      • Tendons localize a great deal of force in a bone's small area.
    • Ligaments use flexible bands of fibrous tissue that resist strains; they hold bones close together in a synovial joint.
      • Cruciate ligaments in the knee help prevent anterior-posterior displacement of articular surfaces and secure articulating bones when standing.

Bones

• Bones provide the body's framework, protect internal organs, store calcium and other minerals, and produce blood cells within bone marrow (hematopoiesis).
• Along with soft tissue, bones enclose and protect most vital organs; the skull's bones protect the brain, and the rib cage protects the heart and lungs.
• The skeletal system facilitates movement, providing attachment points for muscles, tendons, and ligaments.
• Bone marrow is responsible for hematopoiesis, producing millions of blood cells to replace those that are destroyed continuously.
• Bones behave as a mineral storehouse, mostly for phosphorus and calcium.
• For a mineral deficiency, like calcium during pregnancy, bodies withdraw it from bones where dietary supply is insufficient.

Bone Types

• There are four principal types of bone: short, irregular, flat, and long.
  • Short bones are somewhat cube-shaped, consisting of a spongy bone core (cancellous bone) and a thin surface layer of compact bone.
    • Short bones include the bones of the ankles, wrists, and toes.
  • Irregular bones cannot be classified as short or long due to their complex shapes.
    • These include vertebrae and the middle ear bones.
  • Flat bones offer broad surfaces for muscular attachment or protection for internal organs like the skull's bones, shoulder blades, and sternum.
  • Long bones are in the appendages/extremities of the body, such as the legs, arms, and fingers.
    • Parts of a long bone include the diaphysis, compact bone, medullary cavity, distal epiphysis, proximal epiphysis, articular cartilage, spongy bone, and periosteum.
      • The diaphysis is the bone's shaft or long, main portion and consists of compact bone.
      • Compact bone forms a cylinder and surrounds a central canal called the medullary cavity (marrow cavity), which contains fatty yellow marrow comprised mostly of fat cells and a few scattered blood cells.
      • Distal and proximal epiphyses are bulbous-shaped ends that provide space for muscle and ligament attachments near joints.
      • Epiphyses have bulbous shapes that give space for muscular and ligament attachments near the joints and consist largely of
      • Porous spongy bone surrounded by a compact bone layer.
      • Within spongy bone is red bone marrow, which is richly supplied with blood and consists of immature and mature blood cells in varying development stages.
      • In adults, red bone marrow is responsible for production of red blood cells (erythropoiesis), formation of white blood cells (leukopoiesis), and platelets.
      • The periosteum uses a dense, white, fibrous membrane that covers bones remaining surface and contains numerous blood and lymph vessels and nerves.
      • Bones that lose periosteal covering due to injury can scale or die, but it otherwise aids repairs and nutrition
      • In growing bones, the inner layer contains bone-forming cells called osteoblasts.
      • The periosteum provides a means for bone repair and general bone nutrition because blood vessels and osteoblasts are there and acts as an attachment point for muscles, ligaments, and tendons.

Surface Features of Bones

• Bones consist of projections, depressions, and openings that are rarely smooth.
  • These provide sites for muscle and ligament attachments, as well as pathways and openings for blood vessels, nerves, and ducts.
  • Projections are evident in bones, where some serve as articulation points, and can be rounded, sharp, or narrow and have a large edge.

Bone Surface Types

• Nonarticulating surfaces are attached to a trochanter, very large irregularly shaped process, found only on the femur.
• Sites of muscle and ligament attachments present tubercles, with small, rounded processes present on the femur.
• There are tuberosities in large, rounded processes, like the humerus' tuberosity.
• Articulating surfaces contain condyles (rounded, articulating knobs) and heads (prominent, rounded, articulating ends of bone).
• These are located examples are located on the humerus' condyle and femur's head.
• Depressions and openings include Foramen ( the skull nerve opening), Fissure (The sphenoid bone slit), Meatus (The temporal bone passage), and Sinus (frontal duct cavity).

Divisions of the Skeletal System

• The skeletal system in a human adult is made of 206 individual bones, separated into axial and appendicular skeletons.

Axial Skeleton

• The axial skeleton has skull, rib cage, vertebral column, contributing to body cavity formation and protecting the brain, spinal cord, and organs.

Skull

• The skull's bony makeup consists of cranial and facial bones, which join by sutures.
• Sutures are the junction lines between 2 skull connecting bones and are usually immovable.
  • Eight bones, known as the cranium/skull, enclose/protect the brain and hearing/equilibrium organs.
  • Cranial bones connected to muscles provide head movements, chewing, and facial expressions.
  • An infant's skull contains an unossified membrane (soft spot, incomplete bone formation) between the cranial bones is called the fontanel.
  • Pulses of blood vessels felt under skin.
  • Fontanels allow fetal bone movement through the birth canal to fuse and become immobile in early childhood.
  • Frontal Bone: Forms the skull's anterior portion (forehead) and bony cavity roofs for eyeballs.
  • Parietal Bone: Located at each skull side just behind the frontal bone and forms the upper sides and cranium’s roof.
  • Coronal Suture: Where Parietal bone meets the frontal bone.
  • Occipital Bone: Forms the back and base of the skull with a spinal cord opening in its base.
  • Temporal Bones: Located on each skull side; forms part of lower cranium.
    • Has a complex shape with cavities/recesses associated with hearing organs.
    • Projects down to form the mastoid process, which allows attachments for neck muscles.
  • Sphenoid Bone: Located at the skull base's middle part to have a central wedge to join other cranial bones.
  • Ethmoid Bone: Forms most of bony area between the nasal cavity and eye orbits, and it is light and spongy.
  • All facial bones besides the mandible (lower jaw) are joined by sutures and are immovable.
• Movement needed for chewing (mastication): The (9) maxillae, paired-upper jaw bones, are fused in the midline by a suture, and make up the upper jaw and hard palate (mouth roof).
• Cleft palate results during improper maxillary fusion before birth.
• Sockets in The maxillae (singular, maxilla) and mandible are for tooth roots.
• Nasal Bones: Lie side-by-side, fused medially for nose shape and bridge.
• Lacrimal Bones: Located at each eye corner.
• These thin, small bones unite to form the groove for lacrimal sac and canals through which tear ducts pass in nasal cavity.
• Zygomatic Bones: Located on face side below the eyes; cheekbones.
• Vomer: a thin, single bone forms the lower section of the nasal septum.
• Paranasal sinuses, such as that of the frontal, ethmoidal, sphenoidal, and maxillary sinuses, function as cavities within the cranial and facial bones, opening into the nasal cavities and lined with ciliary epithelium.
• Difficulty draining sinuses causes a feeling of congestion during upper respiratory infections (URI) or allergies.
• The internal organs of the chest (thorax), are enclosed and protected by a bony rib cage with 12 pairs of ribs attached to the spine.
  • First seven form True Ribs attach directly to the sternum with a costal cartilage strip.
  • The costal cartilage doesn't directly fasten to the sternum in the next five, they are known as false ribs.
  • The last two, a type of false rib, are not connected to the sternum and attach to thoracic vertebrae (floating ribs).
• The vertebral column has 26 bones called vertebrae (singular, vertebra).
  • It provides support, a bony canal for the spinal cord supports, resilient and balanced thanks to spinal curves.
  • The cervical and lumbar regions curve forward and the thoracic and sacral regions curve backward.
• Abnormal curves are due to congenital defect, poor posture, or bone disease.
  • The column has five regions, named from location within the spine column.
    • The seven cervical vertebrae form the neck framework with the first cervical vertebra, the atlas, supports the skull.
    • the second cervical vertebra, the axis, rotates the skull.
    • 12 Thoracic, support the chest and articulate for ribs.
    • The next five, Lumbar, are placed in the lower back, hold the most weight.
    • Sacral has five fused bones in sacrum portion of vertebral column.
    • Coccyx has tail of vertebral for three to five fragmented bones.
• The vertebrae separates round structures found between structure called (intevertebral discs), fibrous substance and the fluid mass on inside.
  • If it has pressure on the nerve root where nerves exit from the back it cause it commonly called hernia nucleus polyposus.