Anatomy & Physiology Study Notes: The Skeletal System and Skull

Skeletal System Overview

Introduction to the Skeletal System

The skeletal system consists of bones, cartilages, joints, and ligaments that provide structure, protection, and movement for the human body. It is divided into two main parts: the axial skeleton and the appendicular skeleton.

• Skeletal system: The framework of bones, cartilages, joints, and ligaments.

• Total number of bones: There are approximately 206 named bones in the adult human body. Additional info: The exact number may vary due to anatomical variation.

Axial Skeleton

The axial skeleton forms the central axis of the body and is responsible for supporting and protecting vital organs.

• Components: Skull, spinal column (vertebrae), and thoracic cage (ribs and sternum).

• Number of bones: 80 bones.

• Functions:

  • Provides structure and support for the body.

  • Protects internal organs such as the brain, heart, and lungs.

Appendicular Skeleton

The appendicular skeleton consists of the limbs and the girdles that attach them to the axial skeleton.

• Components: Limbs (arms and legs), pectoral girdle (shoulder), and pelvic girdle (hip).

• Number of bones: 126 bones.

• Functions:

  • Facilitates movement and interaction with the environment.

  • Supports locomotion and manipulation of objects.

Comparison Table: Axial vs. Appendicular Skeleton

Axial Skeleton	Appendicular Skeleton
Skull, vertebral column, ribs, sternum	Shoulder blades, arms, hands, pelvic bones, legs, feet
80 bones	126 bones
Protection of organs	Movement and manipulation

Introduction to the Skull

Skull Structure and Functions

The skull is a complex bony structure that protects the brain and forms the framework of the face. It is composed of cranial bones, facial bones, and associated bones, and contains cavities and sinuses.

• 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 ears.

Overview of Cranial Bones

Cranial Bones and Their Features

The cranium is made up of eight bones connected by immovable joints called sutures. Each bone has distinct anatomical features and functions.

• Frontal (1): Forehead bone; forms the anterior part of the cranium.

• Parietal (2): Paired bones forming the sides and roof of the cranium.

• Occipital (1): Posterior bone; contains the foramen magnum for spinal cord passage.

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

• Temporal (2): Paired bones at the sides of the skull; house the auditory meatus (ear canal) and mastoid processes.

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

Example Application

To remove the brain during an autopsy, the top of the skull is cut along the parietal and frontal bones.

Facial Bones

Major Facial Bones and Their Functions

The face is composed of several bones, many of which are paired. These bones provide structure, attachment sites, and protection for facial organs.

• Maxilla (1): 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 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).

Example Application

A cleft palate involves the palatine bones and can affect speech, hearing, and swallowing.

Practice Questions and Applications

Sample Questions

• Axial vs. Appendicular Skeleton: Identify which bones belong to each division.

• Skull Functions: True/False questions about the roles of associated bones.

• Cranial Bones: Identify bones involved in surgical procedures or affected by trauma.

• Facial Bones: Application questions about bone movement and injury scenarios.

Example Table: Cranial Bones and Functions

Bone	Location	Main Function
Frontal	Forehead	Protection, structure
Parietal	Sides and roof	Protection
Occipital	Back of head	Protection, spinal cord passage
Sphenoid	Base of skull	Supports pituitary gland
Temporal	Sides of skull	Hearing, muscle attachment
Ethmoid	Between orbits	Olfaction, nasal cavity structure

Key Terms and Definitions

• Suture: Immovable joint between skull bones.

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

• Sella Turcica: Depression in the sphenoid bone housing the pituitary gland.

• Auditory Meatus: Canal in the temporal bone for hearing.

• Cribriform Plate: Part of the ethmoid bone with foramina for olfactory nerves.

Summary

The skeletal system is essential for protection, movement, and support. The axial skeleton forms the body's core, while the appendicular skeleton enables movement. The skull is a complex structure with specialized bones for protection, sensory functions, and facial structure. Understanding the anatomy and functions of these bones is fundamental for students of anatomy and physiology.