Human Anatomy: Axial Skeleton and Vertebral Column

Axial Skeleton

• The skeleton is divided into two parts: appendicular and axial
• Appendicular skeleton includes bones of the upper and lower limbs, and pectoral and pelvic girdles
• Axial skeleton includes cranium, vertebral column, ribs, and sternum

Vertebral Column

• Physically supports the skull and trunk
• Allows for movement
• Protects the spinal cord
• Absorbs stresses from activities like walking, running, and lifting
• Provides attachment for limbs, thoracic cage, and postural muscles
• Consists of 33 vertebrae, not a single bone
• Has intervertebral discs

Vertebral Column Subdivisions

• Cervical vertebrae (7): located in the neck
• Thoracic vertebrae (12): located in the chest
• Lumbar vertebrae (5): located in the lower back
• Sacral vertebrae (5): fused in a single plate, the sacrum
• Coccygeal vertebrae (4): tiny vertebrae, fused to form coccyx

Curvatures of the Vertebral Column

• Beyond age 3, vertebral column slightly S-shaped with four bends
• Cervical, thoracic, lumbar, and pelvic curvatures
• Thoracic and pelvic are primary curvatures (C-shaped)
• Cervical and lumbar are secondary curvatures

Abnormal Spinal Curvatures

• Scoliosis: abnormal lateral deviation
• Kyphosis: exaggerated thoracic curvature (common in old age)
• Lordosis: exaggerated lumbar curvature (common in pregnancy and obesity)

General Structure of a Vertebra

• Vertebral body: weight-bearing spongy bone
• Vertebral foramen: forms the vertebral canal
• Vertebral arch: pedicle + lamina
• Spinous process: prominent, palpable projection
• Transverse process: protrusion between lamina and pedicle

Intervertebral Discs

• Cartilaginous pads between vertebral bodies
• 23 discs in total
• Absorb shock, bind adjacent vertebrae, enhance spinal flexibility, and support body weight
• Excessive stress can cause herniated discs

Regional Characteristics of Vertebrae (C1 and C2)

• Cervical vertebrae (C1-C7) are relatively small
• Function to support the head and allow for movement
• C1 (atlas) and C2 (axis) have unique structures for this purpose
• Transverse foramina present only in C1-C7

Thoracic Vertebrae

• There are 12 thoracic vertebrae (T1-T12)
• Each corresponds to a pair of ribs
• Support the thoracic cage, which encloses the heart and lungs

Sternum

• Bony plate anterior to the heart
• Subdivided into manubrium, body, and xiphoid process

Ribs

• 12 pairs of ribs
• First 7 ribs are true ribs (connect directly to the sternum)
• Ribs 8-10 are false ribs (connect indirectly to the sternum)
• Ribs 11-12 are floating ribs (don't connect to the sternum)

Skull and Cranial Cavity

• Skull is the most complex part of the skeleton
• Made up of 22 bones, sometimes more
• Bones are joined by sutures

Skull Cavities

• Cranial cavity: largest cavity, houses the brain (approximately 1300 mL in adults)
• Orbits (eye sockets)
• Nasal cavity
• Paranasal sinuses
• Oral cavity
• Middle and inner ear cavities

Paranasal Sinuses

• Air-filled cavities in the skull bones (frontal, ethmoid, sphenoid, and maxillary)
• Lighten skull, act as chambers for resonance in the voice.

Cranial Bones

• Neurocranium (cranial): encloses the cranial cavity (8 bones)
• Splanchnocranium (facial bones): makes up the face (14 bones)

Suture, Landmarks, and Foramina

• The skull is composed of multiple bones, most joined by sutures (immovable joints)
• Sutures are identifiable seams on the cranium's surface. Key sutures (coronal, sagittal, lambdoid, squamosal) connecting bones are important for identification
• Foramina ("holes") in the skull are essential for nerves and blood vessels. (e.g., foramen magnum, optic canal, jugular foramen, etc.)

Cranial Fossae

• The cranial base has three depressions (anterior, middle, and posterior fossae) that shape the brain's inferior surface.
• Cranial fossa accommodate the brain's lobes (e.g., the anterior cranial fossa houses the frontal lobes, while the middle cranial fossa protects the temporal lobes).

Pelvic Girdle or Pelvis

• Composed of the sacrum, coccyx, and two hip bones (coxal bones)
• Ligaments and muscles form pelvic cavity floor and walls.
• Supports the trunk, encloses viscera (mainly lower colon, urinary bladder, reproductive organs)
• Pelvic inlet and outlet, important for childbirth

Pelvis Differences (Male vs. Female)

• Males: heavier and thicker pelvis, due to stronger muscles
• Females: pelvis adapted for pregnancy and childbirth, features like a wider pelvic outlet.

Thoracic Cage

• Thoracic cage consists of thoracic vertebrae, sternum, and ribs.
• Conical enclosure for lungs and heart
• Provides attachment for pectoral girdle and upper limb

This quiz covers the axial skeleton, including the cranium and vertebral column. It explores the structure, function, and subdivisions of the vertebral column, along with its curvatures and support system. Test your knowledge on human skeletal anatomy in this informative quiz.