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 the pectoral and pelvic girdles.
• Axial skeleton includes the cranium, vertebral column, ribs, and sternum.

Vertebral Column

• Physically supports the skull and trunk.
• Allows for movement.
• Protects the spinal cord.
• Absorbs stresses from walking, running, and lifting.
• Provides attachment points for limbs, thoracic cage, and postural muscles.
• Consists of 33 vertebrae.
• Vertebral column consists of Cervical, Thoracic, Lumbar, Sacral, and Coccygeal vertebrae.

Vertebral Canal and Cranial Cavity

• The vertebral canal is formed by the vertebral foramen.
• Intervertebral discs are cartilaginous pads that cushion the vertebral column.
• The vertebral canal (and cranial cavity) contains the spinal cord.

Cervical Vertebrae (Neck)

• Seven cervical vertebrae (C1-C7).
• Relatively small, compared to the other vertebrae types in the spine.
• Their function is primarily to support the head and permit movement.
• The first two (C1 and C2) have unique structures for this purpose- transverse foramina.

Thoracic Vertebrae (Chest)

• Twelve thoracic vertebrae (T1-T12).
• Each thoracic vertebrae has ribs attached to them.
• Their function is supporting the thoracic cage, enclosing the heart and lungs.

Lumbar Vertebrae (Lower Back)

• Five lumbar vertebrae (L1-L5).
• Their most distinctive feature is a thick, stout body, adapted to bear the weight of the upper body.

Sacrum and Coccyx

• Five sacral vertebrae (S1-S5) fuse together into a single structure, the sacrum.
• The sacrum is located on the posterior wall of pelvic cavity, and protects the organs within.
• Four (sometimes five) coccygeal vertebrae (Co1-Co5) fuse into the coccyx.

Pelvic Girdle or Pelvis

• The pelvis is a bowl-shaped structure made of sacrum, coccyx, and two hip bones (coxal bones).
• The pelvic girdle supports the trunk and lower limbs.
• It encloses and protects the viscera, including the lower colon, bladder, and reproductive organs.
• The pelvis is composed of the greater (false) pelvis above the pelvic brim and the lesser (true) pelvis below.
• The pelvic inlet and outlet define the boundary between the false pelvis and the true pelvis.

Pelvic Structure

• The pelvis has a bowl-like shape.
• The greater (false) and lesser (true) pelvis are separated by a somewhat round margin called the pelvic brim.
• The greater pelvis forms the walls of the lower abdominal cavity, whereas the lesser pelvis encloses the pelvic cavity.

Pelvic Inlet and Outlet

• The opening of the lesser pelvis, through which the infant's head passes during birth, is called the pelvic inlet.
• The lower margin of the lesser pelvis is called the pelvic outlet.

Sex Differences in the Pelvis

• The male pelvis is more robust (heavier and thicker) than the female pelvis.
• The female pelvis is adapted for childbirth.

Thoracic Cage

• Consists of thoracic vertebrae, sternum, and ribs.
• Its roughly conical shape provides enclosure for lungs and heart.
• Provides attachment for pectoral girdle and upper limb.

Sternum

• A bony plate anterior to the heart.
• Divided into three sections: manubrium, body, and xiphoid process.
• Connects to the ribs via costal cartilages.

Ribs

• Twelve pairs of ribs.
• First seven ribs are true ribs, directly attached to the sternum.
• Ribs 8-10 are false ribs, attached to the sternum indirectly through costal cartilage.
• Ribs 11-12 are floating ribs, lacking anterior connection to the sternum.

Skull and Cranial Cavity

• The skull is the most complex part of the skeleton; consisting of 22 bones (and sometimes a little more).
• The skull is composed of 2 main divisions: neurocranium (cranial bones) and splanchnocranium (face bones).
• The neurocranium encloses the brain and comprises 8 bones.
• The splanchnocranium forms the face and consists of 14 bones.
• The cranial cavity contains the largest cavity, encasing the brain, along with other cavities.

Cranial Fossae

• The cranial base, or floor, has 3 depressions called cranial fossae.
• The anterior cranial fossa is shaped to accommodate the frontal lobes.
• The middle cranial fossa is shaped like outstretching bird wings, accommodating the temporal lobes.
• The posterior cranial fossa encases the cerebellum.

Paranasal Sinuses

• Several cavities within the skull called paranasal sinuses, are named after the bones they are located in.
• These sinuses are connected to the nasal cavity, lined with mucous membranes, and filled with air.
• They lighten the skull, enhance voice resonance, and aid in humidifying and warming inhaled air.

This quiz covers the key components and functions of the axial skeleton, including the vertebral column. It explores the cervical, thoracic, lumbar, sacral, and coccygeal vertebrae, along with the roles of the vertebral canal and cranial cavity. Test your knowledge on the structure and purpose of these essential parts of the human skeleton.