Axial Skeleton
Vertical Column and Thoracic Cage
The axial skeleton's function is to:
Determine the axis of the body (the central axis is highlighted in green).
Protect vital internal organs, including:
The skull encasing the brain.
The vertebral column protecting the spinal cord.
The thoracic cage protecting the heart and lungs.
Number of Bones in the Human Body
The human skeleton has:
A total of 206 bones.
This count can go up to 210 bones in certain classifications.
Groups of Bones
The skull is composed of:
Cranial bones (8 total):
Form a protective casing for the brain.
Facial bones:
Support the structure of the face.
Cranial Bones
Cranial Bones Breakdown:
There are 8 cranial bones encompassing 6 types:
Frontal bone: Position at the front.
Parietal bones (2): Positioned on the sides.
Additional bones include the sphenoid and ethmoid, but they may be optional to remember unless severe trauma occurs.
Sutures
Cranial bones are interconnected by sutures, which are defined as:
A type of joint made of fibrous tissue.
Typically classified as immovable joints.
Major sutures to remember:
Coronal Suture: Between the frontal and parietal bones.
Sagittal Suture: Between the two parietal bones.
Lambdoid Suture: Between the parietal and occipital bones.
Fontanelles in Newborns
Newborns display fontanelles (soft spots on the skull), which are intersections of sutures:
Anterior fontanelle: Between the frontal and two parietal bones.
Posterior fontanelle: Between the two parietal and occipital bones.
Importance of fontanelles:
Important for infant brain growth; they are not sealed and allow flexibility during birth.
Key Skull Anatomical Terms
Emphasize knowing the following bones for Anatomy & Physiology II:
Frontal,
Parietal,
Temporal,
Occipital.
Middle Ear and Hearing Vibration
Function of the three small bones in the middle ear (ossicles):
Transfer vibrations from the eardrum to the inner ear.
Comparison of Vibration Transfer:
Three bones better than one bone, but lesser quality than in other animals.
This is to protect the nerve and enable prolonged functionality of the auditory system.
Vertebrae in the Spine
Standard numbers of vertebrae:
Cervical vertebrae: 7
Thoracic vertebrae: 12
Lumbar vertebrae: 5
Memory aid:
"One week - 7 days, one year - 12 months, and 5 are the remainder."
Structure of Vertebrae
Vertebral body: Anterior solid part that supports body weight.
Vertebral foramen: Space for the spinal cord located behind the vertebral body.
Processes:
Spinous process: Projects posteriorly.
Differences between cervical, thoracic, and lumbar:
Cervical vertebrae have smaller bodies; thoracic vertebrae are intermediate, and lumbar vertebrae have the largest bodies.
Transverse Process in Vertebrae
Cervical vertebrae have small transverse processes with transverse foramina, indicating they hold the vertebral arteries.
Thoracic vertebrae have transverse processes arranged at approximately 90 degrees, while lumbar aligns at about 45 degrees.
Curvature of the Vertebral Column
The spinal column is not straight; it has:
A natural S-shaped curve that acts as a shock absorber, allowing for flexibility and impact resistance during jumps or physical activity.
Thoracic Cage and Ribs
The thoracic cage consists of:
Ribs (12 pairs):
Sternum: The breastbone.
Ribs are categorized as follows:
True ribs (1-7): Directly attached to the sternum.
False ribs (8-10): Attach indirectly to the sternum via the cartilage of rib 7.
Floating ribs (11-12): Do not connect to the sternum.
Functions of the thoracic cage:
Protects internal organs and supports the structure for upper body movement.
Conclusion
Importance of understanding the axial skeleton in a medical context:
Essential for future medical studies, and relevant to anatomical connections using the 50% scale method for more complex medical discussions.