Anatomy & Physiology Study Guide: The Skull and Cranial Nerves

Overview of the Skull

Axial vs. Appendicular Skeleton

• Axial Skeleton: Composed of the skull, vertebral column, and rib cage. Provides support and protection for vital organs (brain, spinal cord, heart, lungs) and serves as attachment sites for muscles, including those involved in respiration.

• Appendicular Skeleton: Includes the limbs (arms and legs) and the girdles (pectoral and pelvic) that attach them to the axial skeleton.

Skull Overview

• Cranium vs. Facial Bones: The cranium protects the brain, while facial bones form the face.

• Function: The skull protects the brain, shapes the face, and provides pathways for cranial nerves, which control senses and muscles in the head and neck.

Major Bones of the Skull

Associated Bones

• Frontal Bone: Forehead and upper part of the eye sockets.

• Parietal Bones (2): Sides and roof of the skull; joined at the sagittal suture.

• Occipital Bone: Back and base of the skull; contains the foramen magnum (large opening for the spinal cord).

• Temporal Bones (2): Sides of the skull, near the ears; house the ear canal and structures for hearing and balance.

• Sphenoid Bone: Butterfly-shaped bone at the base of the skull. It is the "keystone" bone because it articulates with almost every other cranial bone. The sella turcica is a saddle-shaped depression in the sphenoid that houses the pituitary gland.

• Ethmoid Bone: Located inside the skull, between the nasal cavity and the orbits. Contains the cribriform plate (for olfactory nerves) and the perpendicular plate (part of the nasal septum).

• Hyoid Bone: Unique bone in the neck that does not articulate with any other bone. Important for speech and swallowing. Forensic significance: fracture may indicate strangulation.

• Auditory Ossicles: Three small bones in each middle ear (malleus, incus, stapes) that transmit sound vibrations.

Paired vs. Unpaired Bones

• Paired Bones: Parietal, temporal, maxilla, nasal, zygomatic, lacrimal, palatine, inferior nasal conchae.

• Unpaired Bones: Frontal (in adults, fused), occipital, sphenoid, ethmoid, mandible, vomer.

Sutures of the Skull

Definition

Sutures are immovable joints where two or more skull bones meet. They are important for the stability and protection of the brain.

• Sagittal Suture: Between the two parietal bones, runs along the midline.

• Coronal Suture: Between the frontal and parietal bones, runs in the coronal (frontal) plane.

• Lambdoid Suture: Between the occipital and parietal bones, shaped like the Greek letter lambda (λ).

• Squamous Suture: Between the temporal and parietal bones; weakest part of the temporal bone.

Key Bone Features & Structures

• Processes: Bony projections that serve as attachment sites for muscles or ligaments.

• Mastoid Process (Temporal Bone): Large projection behind the ear; attachment for neck muscles (sternocleidomastoid).

• Zygomatic Process (Temporal Bone): Projects anteriorly to form part of the zygomatic arch (cheekbone).

• Styloid Process (Temporal Bone): Slender, pointed projection for muscle and ligament attachment (tongue, larynx, hyoid bone).

• External Occipital Protuberance (EOP): Bump on the back of the occipital bone for muscle attachment.

• Petrous Part (Temporal Bone): Thick, dense portion housing the inner ear structures (hearing and balance).

Ethmoid Bone Features

• Cribriform Plate: Horizontal plate with olfactory foramina for passage of olfactory nerves (smell).

• Perpendicular Plate: Forms the superior part of the nasal septum.

• Crista Galli: Vertical projection for attachment of the dura mater (membrane surrounding the brain).

Other Notable Features

• Vomer Bone: Forms the inferior part of the nasal septum.

• Inferior Nasal Conchae: Located inside the nasal cavity; increase surface area to warm, humidify, and filter air.

Foramina (Holes) and Cranial Nerves

Definition

Foramina are openings in the skull that allow passage of nerves, blood vessels, and other structures.

Key Foramina and Associated Cranial Nerves

Foramen	Associated Nerve(s)	Function
Cribriform Plate	Olfactory nerves (CN I)	Smell
Optic Canal	Optic nerve (CN II)	Vision
Superior Orbital Fissure	Oculomotor (CN III), Trochlear (CN IV), Abducens (CN VI), Ophthalmic branch of Trigeminal (CN V1)	Eye movement, sensation
Foramen Rotundum	Maxillary branch of Trigeminal (CN V2)	Facial sensation
Foramen Ovale	Mandibular branch of Trigeminal (CN V3)	Mastication, facial sensation
Foramen Magnum	Spinal cord, accessory nerve (CN XI)	Brainstem/spinal cord passage
Hypoglossal Canal	Hypoglossal nerve (CN XII)	Tongue movement
Stylomastoid Foramen	Facial nerve (CN VII)	Facial expression
Jugular Foramen	Glossopharyngeal (CN IX), Vagus (CN X), Accessory (CN XI)	Swallowing, taste, head/shoulder movement

Skull Base & Internal Features

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

• Occipital Condyles: Rounded projections on the occipital bone that articulate with the atlas (C1 vertebra).

• Hypophyseal Fossa (Sella Turcica): Depression in the sphenoid bone for the pituitary gland.

Functions of the Skull

1. Protection: Forms a rigid barrier to protect the brain.

2. Sensory Input: Provides passageways for cranial nerves that carry sensory information (e.g., smell, vision, hearing, taste, touch, pain).

3. Motor Control: Provides passageways for cranial nerves that carry motor commands to muscles of the face, head, and neck.

4. Structural Support: Provides attachment points for muscles controlling head movement, facial expressions, and chewing.

Facial Bones (Brief Overview)

• Maxilla: Upper jaw

• Mandible: Lower jaw

• Nasal Bones: Bridge of the nose

Cranial Nerves

There are twelve pairs of cranial nerves that emerge directly from the brain. They control various sensory and motor functions:

• Sensory: Smell, vision, taste, hearing, touch, pain

• Motor: Eye movement, facial expression, swallowing, tongue movement, head/shoulder movement

Additional Information

• Pneumatic Bones: Bones containing air spaces lined by mucosa (frontal, ethmoid, maxillary, sphenoid).

• Structures Not on the Test: Palatine process of the maxilla, pteromoid brand, convoy fragment.

Note: The sphenoid bone is a central bone that articulates with almost every other skull bone and is crucial for the passage of several cranial nerves.