Anatomy & Physiology Study Notes: The Skeletal System and Skull

Skeletal System Overview

Definition and Components

The skeletal system consists of the bones, cartilages, joints, and ligaments of the body. It provides structural support, protection for internal organs, and enables movement.

• Total Number of Bones: There are approximately 206 named bones in the adult human body. The exact number may vary by age and individual due to developmental changes and anatomical variation.

Classification of the Skeleton

• Axial Skeleton: Composed of the skull, spinal column, and thoracic cage (80 bones). It forms the central axis of the body and is responsible for protecting vital organs such as the brain, heart, and lungs.

• Appendicular Skeleton: Includes the limbs (arms and legs), pectoral (shoulder) girdles, and pelvic girdle (126 bones). It is involved in movement and manipulation of the environment.

Table: Comparison of Axial and Appendicular Skeleton

Axial Skeleton	Appendicular Skeleton
Skull, vertebral column, ribs, sternum	Shoulder blades, arms, hands, pelvic bones, legs, feet
Protection of organs	Movement and manipulation

Introduction to the Skull

Structure and Function

The skull is a complex bony structure that protects the brain and forms the framework of the face. It consists of several types of bones:

• Cranial bones: Form the bony house for the brain.

• Facial bones: Provide the structure of the face.

• Associated bones: Involved in hearing and swallowing.

• Cavities & Sinuses: Air-filled spaces that lighten the skull and enhance voice resonance.

Functions of Skull Bones

• Protection: Safeguards the brain and sensory organs.

• Creation: Forms structures for the senses (sight, smell, taste, hearing).

• Openings: Provides passageways for air and food.

• Anchoring: Serves as attachment sites for teeth and muscles.

• Housing: Contains organs such as the eyes and inner ear.

Overview of Cranial Bones

Major Cranial Bones and Their Features

The cranium is made up of eight bones, connected by immovable joints called sutures:

• Frontal (1): Forehead bone.

• Parietal (2): Sides and roof of the cranium.

• Occipital (1): Back and base of the skull; contains the foramen magnum for spinal cord passage.

• Temporal (2): Sides of the skull; houses the auditory meatus (ear canal) and processes such as styloid, mastoid, and zygomatic.

• Sphenoid (1): Butterfly-shaped bone at the base of the skull; contains the sella turcica for the pituitary gland.

• Ethmoid (1): Located between the orbits and nasal cavity; contains the cribriform plate for olfactory nerves.

Clinical Application Example

• During an autopsy, removal of the brain requires cutting through the frontal, parietal, and occipital bones along the cranial vault.

Facial Bones

Major Facial Bones and Their Functions

The face is composed of 14 bones, many of which are paired:

• Maxilla (2): Main facial bone; forms the upper jaw and supports the teeth.

• Mandible (1): Lower jaw; only freely moving bone in the skull.

• Zygomatic (2): Cheekbones; articulate with the temporal bone.

• Nasal (2): Bridge of the nose.

• Lacrimal (2): Inner wall of the orbit; contains the lacrimal fossa for tear drainage.

• Inferior Nasal Conchae (2): Walls of the nasal cavity.

• Vomer (1): Forms part of the nasal septum.

• Palatine (2): Forms the posterior part of the hard palate (roof of the mouth).

Clinical Application Example: Cleft Palate

• A cleft palate results from improper fusion of the palatine bones, leading to complications in feeding, speech, and increased risk of ear infections.

Practice Questions and Applications

• Distinguishing axial vs. appendicular skeleton: Axial includes skull, ribs, spine; appendicular includes limbs, shoulder blades, pelvic bones.

• Associated bones do not house the brain but are involved in hearing and swallowing.

• To access the pituitary gland surgically, the sphenoid bone is approached through the nasal cavity.

• Damage to the temporal bone is most likely to affect hearing due to the location of the auditory canal.

• The mandible is the only freely moving bone in the skull, involved in chewing.

Summary Table: Major Skull Bones and Functions

Bone	Location	Main Function
Frontal	Forehead	Protection, structure
Parietal	Top/sides of skull	Protection
Occipital	Back/base of skull	Protection, spinal cord passage
Temporal	Sides of skull	Hearing, muscle attachment
Sphenoid	Base of skull	Supports brain, pituitary gland
Ethmoid	Between orbits	Olfaction, nasal cavity structure
Mandible	Lower jaw	Chewing, speech
Maxilla	Upper jaw	Supports teeth, forms palate

Additional info: The study notes above expand on the brief points and fill in missing context to provide a comprehensive overview suitable for college-level Anatomy & Physiology students.