Study Guide: The Skeletal System in Human Anatomy and Physiology

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The Skeletal System

Structural Divisions of the Skeleton

The human skeleton is divided into two main structural divisions: the axial skeleton and the appendicular skeleton. Each division contains specific groups of bones that serve distinct functions in support, movement, and protection.

Axial Skeleton: Forms the longitudinal axis of the body and includes the skull, vertebral column, and thoracic cage.
Appendicular Skeleton: Comprises the bones of the girdles (pectoral and pelvic) and the upper and lower limbs.

Divisions of the skeletal system: axial and appendicular skeleton

Classification of Bones by Shape

Bones are classified based on their shapes, which relate to their functions and locations in the body.

Long Bones: Longer than they are wide; found in limbs (arms, legs, hands, feet, fingers, toes).
Short Bones: Cube-shaped, small and thick; found in wrists and ankles.
Flat Bones: Thin and broad with parallel surfaces; found in skull, pelvis, sternum, and ribs.
Irregular Bones: Complex shapes; found in vertebrae and pelvic bones.
Sesamoid Bones: Small, flat, oval-shaped; located within tendons (e.g., kneecap).

Classification of bones by shape

Bone Markings

Bone markings are anatomical features on bones that serve as sites for muscle attachment, passage of nerves and blood vessels, and articulation with other bones. They are categorized as depressions, openings, and projections.

Depressions

Facet: Shallow convex or concave surface where two bones articulate.
Fossa: Indentation in a bone into which another structure fits.
Groove: Long indentation along which a narrow structure travels.

Table of bone depressions: facet, fossa, groove

Openings

Canal: Tunnel through a bone.
Foramen: Hole in a bone.

Table of bone openings: canal, foramen

Projections

Condyle: Rounded end of a bone that articulates with another bone.
Epicondyle: Small projection usually proximal to a condyle.
Process: Prominent bony projection.
Line: Narrow ridge.

Table of bone projections: condyle, epicondyle, process, line

Skull Structure

The skull is composed of cranial and facial bones, united by immovable joints called sutures. These bones protect the brain and support facial structures.

Cranial Bones: Include the frontal, parietal, temporal, occipital, sphenoid, and ethmoid bones.
Facial Bones: Include the nasal, maxillae, zygomatic, mandible, lacrimal, palatine, inferior nasal concha, and vomer bones.

Basic structure of the skull: cranial and facial bones

Table: Cranial Bones

Bone	Description
Frontal	Forms the forehead and part of the eye socket.
Parietal	Forms the superior and lateral aspects of the skull.
Occipital	Forms the posterior and base of the skull.
Temporal	Forms the lateral sides and base of the skull.
Sphenoid	Forms part of the base and sides of the skull.
Ethmoid	Forms part of the nasal cavity and eye socket.

Table of cranial bones: frontal, parietal, occipital Table of cranial bones: temporal Table of cranial bones: sphenoid, ethmoid

Table: Facial Bones

Bone	Description
Nasal	Forms the bridge of the nose.
Maxillae	Forms the upper jaw and part of the eye socket.
Zygomatic	Forms the cheekbones.
Mandible	Forms the lower jaw.
Lacrimal	Forms part of the medial wall of the eye socket.
Palatine	Forms part of the hard palate.
Inferior nasal concha	Forms part of the lateral wall of the nasal cavity.
Vomer	Forms part of the nasal septum.

Table of facial bones: nasal, mandible Table of facial bones: maxillae, vomer

Vertebral Column

The vertebral column, or spine, is composed of 33 vertebrae grouped into five regions. It provides structural support, protects the spinal cord, and allows flexibility.

Cervical (7): Located in the neck.
Thoracic (12): Articulate with the ribs.
Lumbar (5): Located in the lower back.
Sacral (5 fused): Articulate with the pelvic bones.
Coccygeal (3–5 fused): Located at the most inferior end.

Structure of Vertebrae

Body: Weight-bearing portion.
Vertebral Foramen: Space for the spinal cord.
Pedicles and Laminae: Form the vertebral arch.
Articular Facets: Form joints between vertebrae.
Transverse Processes: Lateral projections for muscle attachment.
Spinous Process: Posterior projection for muscle attachment.

Basic structure of vertebrae

Cervical Vertebrae

Smallest vertebrae with transverse foramina.
Atlas (C1): No vertebral body or spinous process.
Axis (C2): Contains the dens (odontoid process).

Atlas vertebra (C1) Axis vertebra (C2)

Thoracic Vertebrae

Articulate with ribs and have long spinous processes.

Thoracic vertebrae

Lumbar Vertebrae

Largest vertebrae with thick bodies and short spinous processes.

Lumbar vertebrae

Comparison Table: Cervical, Thoracic, and Lumbar Vertebrae

Characteristic	Cervical	Thoracic	Lumbar
Body shape	Small, oval	Larger, heart-shaped	Largest, kidney-shaped
Transverse foramen	Present	Absent	Absent
Spinous process	Forked	Long, point inferiorly	Thick, point posteriorly

Comparison of cervical, thoracic, and lumbar vertebrae

Thoracic Cage

The thoracic cage protects vital organs and supports the upper body. It consists of the sternum and 12 pairs of ribs.

Sternum: Manubrium, body, xiphoid process.
Ribs:
- True ribs (1–7): Attach directly to the sternum.
- False ribs (8–12): Do not attach directly.
- Floating ribs (11–12): Do not attach to the sternum.

The thoracic cage, anterior view

Pectoral Girdle and Upper Limb

The pectoral girdle consists of the clavicle and scapula, which anchor the upper limb to the trunk. The upper limb includes the humerus, radius, ulna, carpals, metacarpals, and phalanges.

Clavicle: S-shaped bone connecting the sternum and scapula.
Scapula: Flat bone with several important features (glenoid cavity, acromion, coracoid process).
Humerus: Upper arm bone; articulates with scapula and forearm bones.
Radius and Ulna: Forearm bones; radius is lateral, ulna is medial.

Overview of the bones of the pectoral girdle and upper limb Structure of the scapula The humerus The bones of the forearm: radius and ulna

Pelvic Girdle and Lower Limb

The pelvic girdle consists of the sacrum and pelvic bones (ilium, ischium, pubis). The lower limb includes the femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges.

Pelvic Bone: Three fused bones (ilium, ischium, pubis) form the acetabulum and obturator foramen.
Femur: Thigh bone; articulates with the pelvis and tibia.
Patella: Sesamoid bone in the quadriceps tendon.
Tibia: Medial leg bone; forms the medial malleolus.
Fibula: Lateral leg bone; forms the lateral malleolus.
Tarsals: Ankle bones; include talus and calcaneus.
Metatarsals and Phalanges: Bones of the foot and toes.

The pelvis and pelvic bones, anterior view The pelvic bone The tibia and fibula Bones of the ankle and foot

Summary Table: Major Bones and Their Functions

Bone	Function
Skull	Protects brain, supports facial structures
Vertebral column	Supports body, protects spinal cord
Thoracic cage	Protects heart and lungs
Pectoral girdle	Anchors upper limb
Pelvic girdle	Anchors lower limb, supports body weight
Upper limb bones	Movement and manipulation
Lower limb bones	Support and locomotion

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