Skeletal System & Human Microbiome Notes

Bones Associated with the Skull

  • Bones associated with the skull but not part of it include:
    • Auditory ossicles: Three bones in the middle ear.
      • Malleus (hammer).
      • Incus (anvil).
      • Stapes (stirrup).
  • Hyoid Bone:
    • U-shaped bone between the chin and larynx.
    • Does not articulate with any other bone.
    • Attachment point for tongue, mandible, and larynx muscles.
    • Fractured hyoid bone can be a sign of strangulation during autopsy.
  • Sinuses:
    • Cavities within the skull.
    • Four pairs of paranasal sinuses named for the bones they reside in.
    • Open into the internal nose.
    • Air-filled to lighten the skull and act as resonators for sound production.
    • Frontal, maxillary, and sphenoid sinuses have well-defined shapes.
    • Ethmoid sinuses are honeycombed.

Pectoral Girdle

  • Pectoral Girdle (Shoulder Girdle):
    • Consists of a clavicle (collarbone) and a scapula (shoulder blade) on each side of the body.
    • Supports the arm.
  • Clavicle:
    • Slightly S-shaped bone.
    • Articulates with the sternum and scapula.
    • Supports the shoulder.
  • Scapula:
    • Located on the posterior portion of the thorax, lying over ribs 2-7.
    • Lateral portion has three main features:
      • Acromion process: Articulates with the clavicle; the only point where the arm and scapula attach to the rest of the skeleton.
      • Coracoid process: Provides a point of attachment for muscles of the arm.
      • Glenoid cavity: Shallow socket that articulates with the head of the humerus (upper arm bone).

Upper Limb

  • Upper Limb (Arm):
    • Consists of the humerus (upper arm bone), radius and ulna (lower arm bones), and carpals (hand bones).
  • Humerus:
    • Long bone of the upper arm.
      • Head: Enlarged end covered with articular cartilage; articulates with the glenoid cavity of the scapula.
      • Olecranon fossa: Depression on the posterior side of the humerus.
      • Olecranon process: Bony point of the elbow; slides in the olecranon fossa when the arm is extended.
  • Radius:
    • One of the two bones of the lower arm; located on the same side as the thumb.
    • Proximal head is a distinctive disc shape that rotates on the humerus when the palm is turned forward and backward.
    • Radial tuberosity is where the biceps muscle attaches to the bone.
  • Ulna:
    • The other bone of the lower arm; it is longer than the radius.
    • Styloid processes of the radius and ulna are bony bumps felt at the wrist.
  • Supination vs. Pronation:
    • Supination: Palm up; radius and ulna lie parallel to each other.
    • Pronation: Palm down; radius and ulna cross.

Types of Bone Tissue

  • Osseous tissue has different characteristics:

    • Spongy (cancellous) bone: Light and porous. Found in the ends of long bones and the middle of most other bones. Always surrounded by compact bone.
    • Compact bone: Dense and solid. Provides strength, forming the shafts of long bones and outer surfaces of other bones.

  • Spongy Bone:

    • Consists of a latticework of bone called trabeculae. Adds strength without adding weight.
    • Cavities between trabeculae are filled with red bone marrow, which supplies blood and produces blood cells.
    • Trabeculae are arranged along lines of greatest stress, realigning to compensate for changes in stress.

  • Compact Bone:

    • Consists of an elaborate network of canals and passageways containing nerves and blood vessels.

    • Well-supplied with oxygen and nutrients, allowing bone injuries to heal quickly.

    • Osteon: Basic structural unit with layers of matrix arranged in concentric, onion-like rings (lamellae) around a central canal (Haversian or osteonic canal).

    • Lacunae: Tiny gaps between rings of the lamellae containing osteocytes.

    • Canaliculi: Microscopic passageways connecting the lamellae to each other.

    • Volkmann's canals: Transverse passageways connecting the Haversian canals, transporting blood and nutrients from the bone's exterior to the osteocytes inside.

Human Microbiome

  • Microorganisms and Humans:

    • Trillions of microorganisms live on and in the human body, regulating metabolism, immune function, and behavior.
    • The human body houses more than 100 trillion microorganisms, potentially outnumbering human cells.
    • This microbial community, known as the human microbiome, is essential for human life and is considered a newly recognized organ.

  • Functions of the Microbiome:

    • Microorganisms constantly work to digest food, synthesize vitamins, and protect against disease-causing bacteria.
    • Research suggests that bacteria can alter brain chemistry, affecting mood and behavior.

  • Dysbiosis and Disease:

    • Imbalances in the microbiome (dysbiosis) are linked to numerous disorders, including diabetes, heart disease, asthma, multiple sclerosis, obesity, inflammatory bowel disease, autism, and cancer.
    • Practitioners recognize the need to cultivate and nurture bacterial communities within our bodies.

  • Future of Microbiome Research:

    • Experts envision mapping individuals' signature microbiomes to monitor microbial balance and make necessary adjustments.