Functions and Divisions of the Skeleton

Study Notes

Functions of Bones

Provides support as a framework for the body.
Offers protection for vital organs and structures.
Enables movement through attachment of skeletal muscles via tendons.
Acts as a reservoir for mineral storage, primarily calcium and phosphorus.
Facilitates blood cell formation through a process known as hematopoiesis.
Stores triglycerides in yellow marrow, which contains adipose tissue for energy.

Principal Divisions of the Skeleton

Axial Skeleton: Comprises bones around the body's longitudinal axis, such as the sacrum.
Appendicular Skeleton: Includes bones of the upper and lower limbs and the girdles connecting limbs to the axial skeleton, exemplified by the hip bone.

Number of Bones

Total count includes 206 named bones, but additional unnamed bones may exist in various individuals.

Axial Skeleton Details

Skull: 8 cranial bones and 14 facial bones.
Hyoid Bone: 1 singular bone.
Auditory Ossicles: 6 small bones within the ear.
Vertebral Column: Contains 26 vertebrae.
Thorax: Comprises 1 sternum and 24 ribs.
Subtotal: The axial skeleton totals 80 bones.

Appendicular Skeleton Details

Pectoral Girdles: Includes 2 clavicles and 2 scapulae.
Upper Limbs: Total of 28 bones including 2 humeri, 2 ulnas, 2 radii, 16 carpals, 10 metacarpals, and 28 phalanges.
Pelvic Girdle: Composed of 2 hip bones.
Lower Limbs: Contains 28 bones including 2 femurs, 2 patellae, 2 fibulas, 2 tibias, 14 tarsals, 10 metatarsals, and 28 phalanges.
Subtotal: The appendicular skeleton totals 126 bones.

Types of Bones

Long Bones: Characterized by being longer than wide, with a shaft and two ends; examples include all limb bones except carpals, tarsals, and patella.
Short Bones: Cube-shaped bones found in the wrist and ankle regions.
Flat Bones: Thin, flattened bones such as the sternum, ribs, skull, and scapulae.
Irregular Bones: Bones with complex shapes, including vertebrae and hip bones.
Sesamoid Bones: Specialized short bones formed within tendons, with the patella being the largest; these vary in number among individuals.

Bone Types and Structures

Compact Bone: Dense outer layer found in most bones, appearing solid but containing small cavities for nerves and blood vessels.
Spongy Bone: Inner bone structure featuring trabeculae, organized along stress lines, and housing red or yellow marrow.

Long Bone Structure

Diaphysis: Central shaft composed of compact bone surrounding the medullary cavity, which contains yellow/red bone marrow.
Epiphyses: Bone ends made of compact bone outside and spongy bone inside; can contain red or yellow marrow.
Epiphyseal Plate/Line: Growth area in children (plate) that becomes a line in adults as growth ceases.
Membranes:
- Periosteum: Connective tissue covering bone; assists in muscle attachment.
- Endosteum: Delicate inner membrane involved in bone remodeling throughout life.
Articular Cartilage: Covers joint surfaces, cushioning bone ends and absorbing stress.

Short, Flat, Irregular, and Sesamoid Bone Structure

Simplified structure compared to long bones.
Features two layers of compact bone with a spongy bone layer in between, resembling an Oreo cookie.
External layer covered by periosteum, followed by compact bone, spongy bone, and lined with endosteum; marrow spaces contain red or yellow marrow.

Description

Explore the key functions of bones and the principal divisions of the skeleton in this quiz. Learn about the axial and appendicular skeletons, their structures, and the total number of bones in the human body. Test your knowledge of how bones support movement, protection, and mineral storage.