Lab 5: Joints and the Axial Skeleton – Skull Anatomy

Basic Types of Joints

Classification of Joints (Articulations)

Joints, or articulations, are connections between bones that allow for varying degrees of movement. They are classified based on their structure and function.

• Fibrous Joints: These joints are generally immobile and are connected by strong fibrous connective tissue. Examples: Skull sutures, alveolar tooth sockets.

• Cartilaginous Joints: These joints allow limited mobility and are united by a pad of cartilage. Examples: Intervertebral discs (fibrocartilage), pubic symphysis (fibrocartilage), costal cartilages (hyaline cartilage).

• Synovial Joints: These are freely movable joints characterized by a joint capsule, articular cartilage, and synovial fluid. Examples: Temporomandibular joint, acromioclavicular joint, most limb joints.

Key Terms:

• Articulation: The site where two or more bones meet.

• Synovial Fluid: A lubricating fluid found within synovial joints.

Table: Comparison of Joint Types

Joint Type	Mobility	Main Tissue	Examples
Fibrous	Immovable	Dense connective tissue	Skull sutures, tooth sockets
Cartilaginous	Slightly movable	Cartilage (hyaline or fibrocartilage)	Intervertebral discs, pubic symphysis
Synovial	Freely movable	Joint capsule, synovial fluid	Shoulder, knee, temporomandibular joint

The Axial Skeleton: Skull

Bones of the Skull

The skull is a complex structure composed of two main groups of bones: the cranium and the facial bones. The cranium protects the brain, while the facial bones form the structure of the face.

• Cranium: Consists of 8 bones (frontal, parietal (2), temporal (2), occipital, sphenoid, ethmoid).

• Facial Bones: Consists of 14 bones (including mandible, maxillae (2), zygomatic (2), nasal (2), lacrimal (2), palatine (2), inferior nasal conchae (2), vomer).

Functions of the Skull:

• Protects and supports the brain and sensory organs (eyes, nose, tongue, inner ears).

• Provides attachment points for muscles of the face, neck, and head.

Major Skull Features

• Calvaria: The dome-like upper portion of the cranium.

• Cranial Base: The floor of the cranial cavity, supporting the brain.

• Sutures: Immovable, interlocking joints between skull bones (e.g., coronal, sagittal, lambdoid, squamous sutures).

Example: The sagittal suture runs along the midline between the two parietal bones.

Temporomandibular Joint (TMJ)

The temporomandibular joint is a synovial joint that connects the mandible (lower jaw) to the temporal bone of the skull. It allows for movements necessary for chewing and speaking.

• Movements: Depression (opening mouth), elevation (closing mouth), protraction (forward movement), retraction (backward movement), and side-to-side grinding.

• Articular Surfaces: Mandibular condyle and mandibular fossa of the temporal bone.

Clinical Note: TMJ disorders can cause pain and dysfunction in jaw movement.

Hyoid Bone

The hyoid bone is a unique, U-shaped bone located in the anterior neck. It does not articulate directly with any other bone.

• Serves as an attachment site for muscles of the tongue, larynx, and pharynx.

• Moves during swallowing and speech.

Parts of the Hyoid: Body, greater horns, lesser horns.

Fetal Skull

The fetal skull differs from the adult skull in several ways to facilitate childbirth and brain growth.

• Fontanelles: Soft, membranous gaps between cranial bones that allow for deformation during birth and rapid brain growth.

• Proportion: The cranium is much larger relative to the face compared to adults.

• Ossification: Many bones are not fully ossified at birth.

Example: The anterior fontanelle is the largest and most clinically significant, closing by 18-24 months of age.

Additional info:

• The skull also contains numerous foramina (openings) for the passage of nerves and blood vessels, such as the foramen magnum (for the spinal cord) and optic canal (for the optic nerve).

• The orbits are formed by seven bones and house the eyes and associated structures.