Bones Part 1 (General & Axial)

Introduction

  • This lecture will cover the skeletal system, focusing on bones and their landmarks.
  • The lecture is divided into two parts to allow for memorization of bone structures.

Objectives

  • Refer to the module for specific objectives.

Skeletal System Overview

  • Bones are living tissues that constantly regenerate, unlike dry bone models.
  • Functions of bones:
    • Blood cell production.
    • Mineral storage.
    • Support for delicate structures.
    • Aid in movement via muscle attachment.
  • The skeleton consists of axial and appendicular portions.
  • Bone shape and size determine their function.

Types of Bones

  • Long bones: e.g., femur.
  • Short bones: e.g., carpals.
  • Flat bones: e.g., scapula.
  • Irregular bones: e.g., vertebrae.
  • Sesamoid bones: e.g., patella.

Major Parts of Long Bones

  • Epiphysis: expanded ends of the bone.
  • Diaphysis: bone shaft.
  • Metaphysis: widening part between diaphysis and epiphysis.
  • Articular cartilage: covers the epiphysis.
  • Periosteum: encloses the bone with dense connective tissue.
  • Compact (cortical) bone: forms the wall of the diaphysis.
  • Spongy (cancellous) bone: makes up the epiphyses.
  • Medullary cavity: hollow chamber in the diaphysis containing marrow.
  • Endosteum: lines spaces of the medullary cavity.
  • Bone marrow: red or yellow marrow lining the medullary cavity and spongy bone spaces.

Bone Structure

  • Compact bone is dense.
  • Spongy bone has spaces surrounded by trabeculae.
  • Bone marrow is housed within the spaces of spongy bone.

Bone Cells

  • Bones are living tissues with cells called osteocytes.
  • Osteoblasts: build bone (B in osteoblasts corresponds to B in build).
  • Osteoclasts: break down bone.
  • These cells maintain and remodel the bone matrix continuously.

Bone Composition and Function

  • Bones store calcium and phosphorus.
  • Calcitonin (from the thyroid gland) builds bone.
  • Parathyroid hormone (from the parathyroid gland) breaks down bone.
  • Calcitonin is used in hypercalcemia (high calcium levels).
  • Parathyroid hormone is used in hypocalcemia (low calcium levels).
  • This creates a homeostatic negative feedback mechanism to regulate serum calcium.

Functions of the Skeletal System

  • Provides shape for the head, face, thorax, and limbs.
  • Supports weight through the vertebrae, lower limbs, and pelvis.
  • The skull protects the brain.
  • The rib cage and sternum protect the heart and lungs.
  • Pelvic bones protect reproductive organs.
  • Bones and muscles facilitate movement.
  • Blood cell production occurs in the red marrow of spongy bone.
  • Red marrow transforms into yellow marrow (fat storage) over time.
  • Red marrow is initially in long bones but becomes centralized in the skull, ribs, sternum, clavicles, vertebrae, and hips with age.

Bone Matrix

  • 70% of the bone matrix consists of inorganic mineral salts.
  • Hydroxyapatite (calcium phosphate) is the most abundant.
  • Loss of mineralization can lead to osteoporosis.
  • Calcium regulation involves interactions between calcitonin and parathyroid hormone.

Regulation of Serum Calcium

  • Calcitonin (thyroid) decreases serum calcium when levels are too high.
    • It inhibits osteoclasts.
  • Parathyroid hormone (parathyroid gland) increases serum calcium when levels are too low.
    • It stimulates osteoclast activity.
  • This is a negative feedback mechanism to maintain homeostasis.

Divisions of the Human Skeleton

  • Axial skeleton: 80 bones (skull, middle ear bones, hyoid bone, vertebral column, thoracic cage).
  • Appendicular skeleton: 126 bones (extremities, pectoral girdle, pelvic girdle).

Key Anatomical Terms

  • Articulations: where two bones meet (e.g., knee joint).
  • Head: prominent round surface (e.g., head of the femur).
  • Facet: flat surface (e.g., vertebra).
  • Condyle: rounded surface (e.g., occipital condyles).
  • Projections: raised markings.
    • Spinous process: projection from a vertebra.
    • Protuberance: protruding (e.g., chin).
    • Process: prominent feature (e.g., transverse process of vertebra).
    • Spine: sharp process (e.g., ischial spine).
    • Tubercle: small, rounded process (e.g., tubercle of humerus).
    • Tuberosity: rough surface (e.g., deltoid tuberosity).
    • Line: slight elongated ridge (e.g., temporal lines of parietal bone).
    • Crest: ridge (e.g., iliac crest).
  • Holes and Depressions:
    • Foramen: hole for blood vessels (e.g., foramen magnum).
    • Fossa: elongated basin (e.g., mandibular fossa).
    • Fovea: small pit (e.g., fovea capitis).
    • Sulcus: groove (e.g., sigmoid sulcus of temporal bones).
    • Canal: passage in bone (e.g., auditory canal).
    • Fissure: slit through bone (e.g., orbital fissure).
    • Meatus: opening into a canal (e.g., external auditory meatus).
    • Sinus: air-filled space (e.g., nasal sinus).

The Skull

  • Composed of 22 bones: 8 cranial bones and 14 facial bones.
  • The cranium protects the brain.
  • The orbit of the eye is made up of both cranial and facial bones.
  • Sinuses within cranial and facial bones:
    • Filter air.
    • Reduce skull weight.
    • Intensify the voice.

Anterior Skull

  • Key bones and features include: parietal bone, frontal bone, coronal suture, squamous suture, temporal bone, sphenoid bone, zygomatic bone, maxilla, vomer, mandible, supraorbital foramen, nasal bone, orbital fissure, ethmoid bone, lacrimal bone, infraorbital foramen, middle nasal concha (part of ethmoid bone), inferior nasal concha, mental foramen.

Frontal Section of the Skull

  • Key bones include: frontal bone, zygomatic bone, maxilla, ethmoid bone, vomer, inferior nasal concha, maxillary sinus.

Cranial Bones

  • Frontal bone: forms the forehead, roof of the nasal cavity, and roofs of the orbits; contains frontal sinuses and the supraorbital foramen or notch.
  • Parietal bones (two): form the sides and roof of the cranium.
    • Sagittal suture: joins the two parietal bones.
    • Coronal suture: joins the parietal bones to the frontal bone.
  • Occipital bone: forms the back of the skull.
    • Foramen magnum: opening for the spinal cord to meet the brain.
    • Lambdoid suture: connects the occipital bone to the parietal bones.

Facial Skeleton

  • Made up of 13 bones (only the mandible is movable).
  • Maxillae (two): form the hard palate, floors of the eye orbit, and sides and floors of the nasal cavity.
    • Maxillary sinuses are the largest sinuses.
    • The palatine process fuses along the midline to form most of the hard palate.
    • Failure to merge properly can lead to cleft palate during fetal development.
    • The palatine bones (two, posteriorly) make up the rest of the hard palate.
  • Zygomatic bones: join the temporal processes to form the zygomatic arches, giving prominence to the cheeks.
  • Lacrimal bones: form the medial walls of the orbits.

Bones of the Eye Orbit

  • Bones included: Frontal bone, Ethmoid bone, Lacrimal bone, Palatine bone, Sphenoid bone, Maxilla, and Zygomatic bone.
  • Spatial orientation:
    • Roof: Frontal bone
    • Lateral Wall: Zygomatic bone
    • Medial Wall: Sphenoid bone, Lacrimal bone, Maxilla
    • Floor: Maxilla, Zygomatic bone
    • Far Wall: Sphenoid bone, Palatine bone, Lacrimal bone

Lateral View of the Skull

  • Parietal bone, frontal bone, coronal suture, squamous suture, lambdoid suture, occipital bone, temporal bone, external acoustic meatus, mastoid process, styloid process, nasal bone, sphenoid bone, maxilla, zygomatic bone, ethmoid bone, lacrimal bone, mandible, mental foramen.
  • Temporal bones: located laterally, contain the external acoustic meatus.
  • Mastoid and styloid processes: muscle attachment sites.
  • Zygomatic arch: made by the zygomatic process of the temporal bone.
  • Squamous suture: connects temporal bones to parietal bones.

Inferior Portion of the Skull

  • Occipital bone, temporal bone, sphenoid bone, maxilla, zygomatic bone, frontal bone, vomer, occipital condyle, foramen magnum, external acoustic meatus, mastoid process, styloid process, foramen lacerum, foramen ovale, foramen spinosum, carotid canal, jugular foramen, incisive foramen

Sphenoid Bone

  • Contains the sella turcica, which houses the pituitary gland.
  • Contains the sphenoid sinuses.
  • Pituitary tumors can be removed via the sphenoid sinuses.

Ethmoid Bone

  • Contains the cribriform plates (openings for olfactory nerve axons for sense of smell).
  • The crista galli holds membranes that enclose the brain.
  • The perpendicular plate forms the main portion of the nasal septum.

Floor of the Cranial Cavity

  • Temporal bone, cribriform plate of the ethmoid bone, frontal bone, occipital bone, parietal bone, sella turcica, optic canal, foramen rotundum, foramen ovale, foramen spinosum, foramen lacerum, internal acoustic meatus, jugular foramen, sphenoid bone, foramen magnum, crista galli.

Sagittal Section of the Skull

  • Occipital bone, temporal bone, parietal bone, frontal bone, frontal sinus, sphenoid bone, mandible, nasal bone, ethmoid bone, sphenoidal sinus, sella turcica, palatine bone, maxilla, vomer, jugular foramen, internal acoustic meatus, hypoglossal canal.

Lateral Nasal Cavity

  • Frontal sinus, nasal bone, maxilla, superior nasal concha, middle nasal concha, inferior nasal concha, palatine bone, sphenoidal sinus, sella turcica, cribriform plate of ethmoid bone.

Nasal Bones

  • Nasal bones (two): form the bridge of the nose.
  • Vomer: forms the inferior portion of the nasal septum.
  • Inferior nasal concha: scroll-shaped bones supporting the mucous membranes of the nasal cavity.

Mandible

  • Mandible is the lower jawbone, shaped like a horseshoe.
  • Ramus projects upward on each side.
  • Alveolar process holds the lower teeth.
  • Mandibular and mental foramen: passageway for nerves and blood vessels to enter the lower teeth and chin area, respectively.

Vertebral Column

  • The vertebral column has curvatures.
    • Cervical and lumbar curvatures (secondary).
    • Thoracic and sacral curvatures (primary).
  • Curvatures help distribute weight and absorb shock.
  • Consists of 24 vertebrae, plus the sacrum and coccyx.
  • Scoliosis: abnormal lateral curvature of the vertebral column.
    • Can cause back pain and compress visceral organs.

Vertebrae

  • Vertebrae vary in shape and size based on location.
  • Common traits: body, pedicles, laminae, spinous processes, transverse processes, vertebral foramen, superior and inferior articular processes and facets.

Types of Vertebrae

  • Cervical vertebrae (7): smallest of the three main types, found in the neck region.
    • C1 (atlas) and C2 (axis) are the most unique.
      • C1 (atlas) is named after the Greek Titan who holds up the world.
      • C2 (axis) contains the odontoid process (dens), which enters the atlas and allows for lateral rotation of the neck.
  • Thoracic vertebrae: larger than cervical vertebrae, found in the chest region and articulate with the ribs.
    • Together with the ribs and sternum, they form the thoracic cage.
    • Have long, pointed spinous processes that slope downward.
  • Lumbar vertebrae: largest of the vertebrae, found in the lower back.
    • Weight-bearing with large, prominent bodies and thick, short spinous processes.
  • Sacrum: triangular-shaped and made up of five fused vertebrae.
  • Coccyx: tailbone, made up of about four fused vertebrae, usually fuses between ages 25 and 30.

Thoracic Cage

  • Made up of thoracic vertebrae, ribs, and sternum.
  • Protects vital organs of the thoracic cavity.
  • Plays a role in breathing.
  • 12 pairs of ribs:
    • 7 pairs of true ribs: directly attach to the sternum via cartilage.
    • 5 pairs of false ribs: attach to the sternum indirectly via cartilage.
      • 2 pairs of floating ribs: do not attach to the sternum at all.
  • The head and tubercle of a rib articulate with the vertebra.
  • The shaft is a long and slender portion.
  • Ribs connect to the sternum using hyaline cartilage.

Ribs

  • True ribs (1-7): attach directly to the sternum.
  • False ribs (8-12): do not directly attach to the sternum.
  • Floating ribs (11-12): do not attach to the sternum at all.

Sternum

  • Parts: manubrium, body, xiphoid process.