Skeletal System Overview

The skeletal system provides the structural framework for the human body, protects vital organs, enables movement, and serves as a reservoir for minerals. It is divided into two main parts: the axial skeleton and the appendicular skeleton.

General Terms

• Axial Skeleton: The central part of the skeleton, including the skull, vertebral column, and thoracic cage. It supports and protects the brain, spinal cord, and thoracic organs.

• Appendicular Skeleton: The bones of the limbs and girdles (shoulder and pelvic), responsible for movement and manipulation of objects.

Bone Markings

Bone markings are specific features on bones that serve as attachment sites for muscles, passageways for nerves and blood vessels, or articulation points with other bones.

Depressions

• Facet: A smooth, flat surface that forms a joint with another flat bone or bone part.

• Fossa: A shallow depression in a bone, often serving as an articular surface.

• Fovea: A small pit or depression, often the site of attachment for a ligament.

• Groove (Sulcus): A long, narrow depression that accommodates a nerve, blood vessel, or tendon.

Openings

• Canal (Meatus): A tunnel-like passage through a bone.

• Fissure: A narrow slit between adjacent parts of bones through which blood vessels or nerves pass.

• Foramen: A round or oval opening through a bone for the passage of nerves and blood vessels.

Projections

• Condyle: A rounded articular projection, often part of a joint.

• Crest: A prominent ridge or elongated projection.

• Head: A rounded, expanded articular end of a bone, often set on a neck.

• Tubercle: A small, rounded projection.

• Tuberosity: A large, roughened projection.

• Epicondyle: A projection above a condyle, often serving as a muscle attachment site.

• Process: Any bony prominence.

• Spine: A sharp, slender projection.

• Protuberance: A bulging or protruding part of a bone.

• Trochanter: A large, blunt projection found only on the femur.

• Line: A low ridge, less prominent than a crest.

Bones of the Skull

The skull is composed of cranial and facial bones, protecting the brain and forming the structure of the face.

Cranial Bones (Cranium)

• Frontal Bone: Forms the forehead and the superior part of the eye sockets.

• Parietal Bone: Paired bones forming the sides and roof of the cranium.

• Occipital Bone: Forms the posterior and base of the skull.

• Temporal Bone: Paired bones on the sides of the skull, housing the structures of the ears.

• Sphenoid Bone: A butterfly-shaped bone at the base of the skull, contributing to the floor of the cranium.

• Ethmoid Bone: A light, spongy bone between the eye sockets, forming part of the nasal cavity.

Facial Bones

• Nasal Bone: Forms the bridge of the nose.

• Lacrimal Bone: Small bones forming part of the medial wall of each orbit.

• Palatine Bone: Forms part of the hard palate of the mouth and the floor of the nose.

• Zygomatic Bone: Cheekbones; form part of the orbit.

• Vomer Bone: Forms the inferior part of the nasal septum.

• Maxilla (Maxillary Bone): Upper jawbone, forms part of the orbits, nasal cavity, and hard palate.

• Mandible: Lower jawbone; the only movable bone of the skull.

Key Features of Skull Bones

• Occipital Condyle: Articulates with the first cervical vertebra (atlas).

• Foramen Magnum: Large opening in the occipital bone for the spinal cord.

• External Occipital Protuberance: Midline bony prominence on the occipital bone.

• Sella Turcica (Sphenoid): Saddle-shaped depression housing the pituitary gland.

• Crista Galli (Ethmoid): Vertical projection for attachment of brain membranes.

• Cribriform Plate (Ethmoid): Contains olfactory foramina for smell nerves.

• Mandibular Condyle: Articulates with the temporal bone to form the temporomandibular joint (TMJ).

• Mandibular Notch: Curved depression between the condyle and coronoid process.

• Mandibular Angle: The angle formed where the lower jaw turns upward.

• Mental Foramen: Openings in the mandible for nerves and blood vessels.

• Temporomandibular Joint (TMJ): The joint connecting the mandible to the skull.

Fetal Skull

• Fontanel: Soft spots on a baby's skull where bones have not yet fused, allowing for growth and flexibility during birth.

• Suture: Immovable joints between skull bones.

Vertebral Column

The vertebral column, or spine, supports the body, protects the spinal cord, and provides attachment points for ribs and muscles.

• Hyoid Bone: Located in the neck, supports the tongue; not part of the vertebral column.

• Vertebral Column: Composed of 33 vertebrae in five regions.

• Cervical Vertebra: Seven vertebrae (C1–C7) in the neck.

• Thoracic Vertebra: Twelve vertebrae (T1–T12) in the upper back, each articulating with a pair of ribs.

• Lumbar Vertebra: Five vertebrae (L1–L5) in the lower back.

• Sacral Vertebra: Five fused vertebrae forming the sacrum.

• Coccygeal Vertebra: Four fused vertebrae forming the coccyx (tailbone).

• Sacrum: Triangular bone at the base of the spine.

• Coccyx: Small, triangular bone at the end of the vertebral column.

Anatomy of a Vertebra

• Vertebral Body: The thick, disc-shaped anterior portion that bears weight.

• Vertebral Foramen: The opening for the spinal cord.

• Transverse Process: Lateral projections for muscle and ligament attachment.

• Spinous Process: Posterior projection for muscle and ligament attachment.

• Intervertebral Disc: Fibrocartilaginous pad between vertebrae, providing cushioning and flexibility.

Cervical Vertebrae Specializations

• Atlas (C1): Supports the skull; allows nodding motion.

• Atlanto-Occipital Joint: Joint between atlas and occipital bone; enables nodding.

• Axis (C2): Has the dens (odontoid process) for rotation of the head.

• Atlantoaxial Joint: Joint between atlas and axis; allows head rotation.

• Dens (Odontoid Process): Upward projection from axis, acts as a pivot for rotation.

Thoracic Cage

The thoracic cage protects the heart and lungs and supports the shoulder girdles and upper limbs.

• Sternum: Flat bone at the center of the chest.

• Manubrium: Superior part of the sternum.

• Sternal Angle: Junction between manubrium and body of sternum.

• Body (of Sternum): Main, elongated part of the sternum.

• Xiphoid Process: Small, cartilaginous process at the lower end of the sternum.

• Costal Cartilage: Bars of hyaline cartilage connecting ribs to sternum.

• Clavicle: Collarbone; connects sternum to scapula.

Scapula (Shoulder Blade)

• Acromion: Lateral extension of the scapular spine; forms the highest point of the shoulder.

• Coracoid Process: Hook-like projection for muscle attachment.

• Spine (of Scapula): Prominent ridge running across the posterior surface.

• Supraspinous Fossa: Depression above the spine.

• Infraspinous Fossa: Depression below the spine.

• Subscapular Fossa: Broad depression on the anterior surface.

• Glenoid Cavity (Fossa): Shallow socket for articulation with the head of the humerus.

Upper Limb

• Humerus: Upper arm bone.

• Radius: Lateral bone of the forearm (thumb side).

• Ulna: Medial bone of the forearm (pinky side).

• Head (of Humerus): Rounded proximal end that fits into the glenoid cavity.

• Deltoid Tuberosity: Roughened area on the humerus for deltoid muscle attachment.

• Capitulum: Rounded lateral condyle of the humerus, articulates with the radius.

• Trochlea: Spool-shaped medial condyle of the humerus, articulates with the ulna.

• Olecranon: Prominent projection of the ulna forming the elbow.

Wrist and Hand

• Carpals: Eight small bones forming the wrist.

• Metacarpals: Five bones forming the palm.

• Proximal Phalanges: Closest finger bones to the palm.

• Middle Phalanges: Middle finger bones (not present in the thumb).

• Distal Phalanges: Farthest finger bones.

• Pollex: The thumb.

Pelvic Bone

• Ilium: Largest, uppermost part of the hip bone.

• Ischium: Lower, posterior part of the hip bone.

• Pubis: Anterior part of the hip bone.

• Sacroiliac Joint: Joint between sacrum and ilium.

• Acetabulum: Deep socket for the head of the femur.

• Obturator Foramen: Large opening created by the ischium and pubis.

• Pubic Symphysis: Cartilaginous joint uniting the left and right pubic bones.

Lower Limb

• Femur: Thigh bone; the longest and strongest bone in the body.

• Tibia: Medial, weight-bearing bone of the lower leg.

• Fibula: Lateral, slender bone of the lower leg.

• Head (of Femur): Rounded proximal end that fits into the acetabulum.

• Fovea Capitis: Small pit on the head of the femur for ligament attachment.

• Greater Trochanter: Large projection for muscle attachment.

• Patella: Kneecap; a sesamoid bone within the quadriceps tendon.

Ankle and Foot

• Tarsals: Seven bones forming the ankle and proximal foot.

• Talus: Ankle bone that articulates with the tibia and fibula.

• Calcaneus: Heel bone; largest tarsal bone.

• Metatarsals: Five bones forming the midfoot.

• Proximal Phalanges: Closest toe bones to the foot.

• Middle Phalanges: Middle toe bones (not present in the big toe).

• Distal Phalanges: Farthest toe bones.

• Hallux: The big toe.

Summary Table: Major Bone Markings and Their Functions

Additional info:

• Bone markings are essential for understanding muscle attachments, joint movements, and the passage of neurovascular structures.

• Fontanels in the fetal skull allow for brain growth and facilitate childbirth.

• The vertebral column's regional differences reflect their functions: cervical (mobility), thoracic (rib attachment), lumbar (weight-bearing).