Bones and Skeleton Functions

Skeleton

• "Skeleton" is derived from the Greek word for "dried-up body."
• The skeleton is well-formed and proportional
• It protects the body and facilitates motion

Functions of Bones

• Support: internal framework supporting soft organs.
• Protection: bones shield soft organs.
• Movement: skeletal muscles attached to bones as levers.
• Storage: bones store minerals and fats.
• Blood cell formation (hematopoiesis): occurs in bone marrow.

Skeleton Divisions

• Axial skeleton: forms the body's longitudinal axis.
• Appendicular skeleton: includes limb and girdle bones.

Microscopic Anatomy of Bone

• Trabeculae: small, needle-like bone pieces with "open" spaces that contain marrow, blood vessels, and nerves.
• Osteocytes: bone cells
• Lacunae: contain osteocytes within the matrix.
• Lamellae: concentric rings of lacunae arrangement.
• Central canal (Haversian canal): central canal with a concentric lamellae arrangement.
• Osteon (Haversian System): central canal and matrix rings complex and functional unit of compact bone.
• Canaliculi: small canals radiating from central canals to lacunae.
• Perforating canal (Volkmann's canal): canals at right angles to the shaft and central canal.

Bone Classification

• Compact bone: dense, smooth, and homogenous.
• Spongy bone: consists of small, porous, needle-like pieces of bone.

Bone Classification by Shape

• Long bones
• Short bones
• Flat bones
• Irregular bones

Long Bones

• Longer than they are wide
• Mostly compact bone
• Includes limb bones (except ankle and wrist)
• Have a shaft with heads at the ends

Short Bones

• Length, width, and height are nearly equal
• Associated with complex movements
• Cube-shaped or "cuboid"

Flat Bones

• Resemble sandwiches
• Consist of two layers of compact bone with marrow in between

Irregular Bones

• Thin layer of compact bone surrounds spongy bone

Bone Formation, Growth, and Remodelling

• Bone cells are involved

Bone Cells

• Osteoblasts: bone-generating cells ("B" means building).
• Osteocytes: mature bone cells maintaining bone tissue.
• Osteoclasts: bone-destroying cells ("C" means chewing).

Bone Formation and Ossification

• Bone formation happens through ossification

Intramembranous Ossification

• Direct bone tissue layering into primitive connective tissue

Endochondral Ossification

• Cartilage transforms into bone

Vertebral Column (Spine)

• The vertebral column consists of 26 irregular bones connected and reinforced by ligaments and is flexible and curved
• The spine consists of 33 separate vertebrae before birth but nine fuse to form the sacrum and coccyx.
• Cervical: 7 vertebrae
• Thoracic: 12 vertebrae (primary curvature)
• Lumbar: 5 vertebrae
• Sacrum and coccyx: primary curvature

Skull

Vertebral Column

• Composed of 26 irregular bones connected by ligaments; results in a flexible, curved structure
• Before birth, a 33 vertebrae structure eventually fuses to form the composite Sacrum and Coccyx bone
• Cervical: 7
• Thoracic: 12, primary curvature
• Lumbar: 5
• Sacrum and Coccyx: primary curvature

Parts of Vertebral Body

• Body or Centrum: weight-bearing part.
• Vertebral Arch: formed by joining the posterior extensions, the laminae, and pedicles.
• Vertebral Foramen: spinal cord passes through it.
• Transverse Processes: two lateral projections from the vertebral arch.
• Spinous Process: projection arising from the vertebral arch.
• Articular Processes: enable joints' formation between vertebrae.

Single Vertebrae

• Cushioned by flexible fibrocartilage intervertebral discs
• The discs cushion and absorb shock for flexibility

Cervical Vertebrae

• C1 allows nodding
• C2 allows pivoting
• C3-C7 are typical vertebrae.
• Transverse processes have foramina for vertebral arteries.

Thoracic Vertebrae

• T1-T12 are typical
• Larger than cervical vertebrae
• Heart-shaped
• Have 2 costal facets where ribs attach

Lumbar Vertebrae

• L1-L5
• Massive block-like bodies
• Short, hatchet-shaped spinous processes
• Sturdy vertebrae

Sacrum

• Formed by 5 fused vertebrae
• Articulates with L5 superiorly and coccyx inferiorly
• Alae: winglike configurations articulating with the sacroiliac joints
• Forms posterior wall of the pelvis
• The vertebral canal continues inside the sacrum as the sacral canal giving a sacral hiatus opening

Coccyx

• Formed by 3-5 fused, irregularly shaped vertebrae
• Human tailbone

Body Thorax

• Includes the sternum

Sternum

• Results from the fusion of the manubrium, body, and xiphoid process
• The sternum is where the first seven ribs attach
• Jugular notch: concave upper border of the manubrium (level T3)
• Sternal angle: where the manubrium and body meet and create a transverse ridge level with the 2nd ribs
• Used to locate the 2nd ICS
• Xiphisternal joint: sternal body and xiphoid process fusion point at the 9th thoracic vertebra

Ribs

• Rib pairs form the walls of the thorax
• All ribs articulate with vertebral column in the posterior body
• True ribs: the first 7 pairs of ribs, attached directly to the sternum
• False ribs: the next 5 pairs of ribs, indirectly attached to the sternum
• Floating ribs: the last 2 pairs of ribs are not attached to the sternum

Appendicular Skeleton

• Comprises of the clavicle and shoulder girdle

Clavicle

• Collar bone
• Doubly curved
• Attaches medially to the manubrium and laterally to the scapula
• Braces the arm away from the top of the thorax

Scapula

• Shoulder blades (wings)
• Acromion processes can be seen
• ACROMIOCLAVICULAR JOINT Acromion: attaches to the clavicle
• Suprascapular notch: nerve passageway
• Glenoid cavity: attaches the head of the humerus
• Has 3 borders: Superior, Medial and Lateral

Shoulder Girdle

• Factors of movement: attachment to axial skeleton at one point (SCJ), a loose attachment allows sliding against the thorax as muscles act and the glenoid cavity is shallow

Upper limb

Pelvis

• True Pelvis: bony pelvis inferior to its brim with inlet, outlet and cavity
• Pelvic Axis: baby path during birth
• False Pelvis: above pelvic brim containing urinary bladder and uterus during pregnancy
• Gynecoid: wide baby delivery channel
• Android: a narrower delivery canal

Lower Limbs

Joints

• Articulations
• Sites where bones meet
• Functions: hold bones together, give mobility

Functional Joint Classification

• Synarthroses: immovable joints
• Amphiarthroses: slightly movable (axial skeleton)
• Diarthroses: freely movable

Structural Joint Classification

• Fibrous joints: bones connected by fibrous tissues, such as sutures of the skull, syndesmoses connecting fibers than sutures.
• Between radius and ulna
• Between tibia and fibula
• Cartilaginous joints: bones connect by cartilage, are slightly movable, and are defined by pubic symphysis and intervertebral joints
• Synovial Joints: use joints for all limbs, have four: articular cartilage, articular capsule joint cavity and reinforcing ligaments

Synovial Joints

• Ball and Socket: hip and shoulder
• Hinge: knee, elbow, and ankle
• Pivot: radio-ulna, atlas/axis
• Saddle: thumb
• Condyloid: wrist
• Gliding: between vertebrae and spine