Overview of Head and Neck Anatomy

Head and Neck Anatomy Overview

Introduction

  • This lecture series, led by Mark A. Johnson, DDS from LMU-CDM, introduces the basics of head and neck anatomy.

  • A more detailed course (DMD-705) will follow in the Spring Semester, expanding on specific structures of head and neck anatomy.

  • Understanding anatomy, particularly of the head and neck, is crucial for dental practice and treatment of patients.

Bones of the Head and Neck

Cranium

  • Cranium vs. Skull

    • The cranium is distinct from the skull; it forms the brain case.

    • The skull encompasses the entire bony structure of the head.

    • Composed of 22 bones:

    • Cranial bones: 8

    • Facial bones: 14

Cranial Bones

  • Mnemonic: Old People From Texas Eat Steak

    • Occipital: 1

    • Parietal: 2

    • Frontal: 1

    • Temporal: 2

    • Ethmoid: 1

    • Sphenoid: 1

    • Total: 8 Cranial Bones

    • Note: 6 bones with 2 pairs (parietal, temporal)

Cranial Sutures

  • Cranial sutures are fibrous joints connecting skull bones; they allow for size and shape changes during growth, being flexible in infancy and childhood.

  • Structure: Classification as syndesmoses (a type of fibrous joint).

  • Function: Allows skull expansion with brain growth

Fontanelles

  • Definition: Soft spots in an infant's skull where sutures meet.

  • An infant has SIX (6) Fontanelles:

    • Most notable: Posterior and Anterior Fontanelle

    • Additional four: Two mastoid and two sphenoid that close rapidly post-birth (2-3 months for the posterior; 12-18 months for the anterior).

Cranial Sutures in Adults

  • Sutures:

    • Coronal Suture: Separates frontal from parietal bones

    • Sagittal Suture: Separates the two parietals

    • Lambdoidal Suture: Separates occipital from parietals

    • Squamosal Suture: Separates parietal from temporal bones

Facial Bones

  • Mnemonic: Virginia Can Not Make My Pet Zebra Laugh

  • 14 Facial Bones:

    1. Mandible: 1

    2. Maxilla: 2

    3. Nasal Bones: 2

    4. Zygomatic Bones: 2

    5. Lacrimal Bones: 2

    6. Palatine Bones: 2

    7. Vomer: 1

    8. Inferior Nasal Concha: 2

The Mandible

  • Overview: The only movable bone of the skull.

  • Parts:

    1. Horizontal BODY (includes alveolar process and mental protuberance)

    2. Two vertical RAMI

    • Coronoid Process: Anterior, muscle attachment

    • Condylar Process: Articulates with the skull at TMJ.

Mandibular Anatomy

  • Body:

    • U-shaped portion forming the chin.

    • Alveolar Process: Holds lower teeth.

    • Mental Protuberance: The chin.

  • Ramus Projections:

    • Coronoid Process: Anterior, attachment for the masseter muscle.

    • Condylar Process: Articulates at the TMJ.

Coronoid Notch

  • Significance in Dentistry:

    • Landmark for inferior alveolar injection (IA).

    • Landmarks:

    1. Coronoid Notch: palpated

    2. Mandibular Occlusal Plane: Visualized

    3. Pterygomandibular Raphe: Visualized

Mandibular Foramina

  • Foramina:

    1. Mandibular Foramen: Inner surface entry for inferior alveolar nerve and artery.

    2. Mental Foramen: Outer surface exit for mental nerve (chin sensation).

The Hyoid Bone

  • Description: U-shaped bone in the neck beneath the mandible; does not connect to other bones.

  • Function: Anchors muscles responsible for speech, swallowing, and breathing.

  • Unique because it is the only bone not directly connected to others; held by muscles and ligaments.

Atlas and Axis

  • Cervical Vertebrae:

    • Atlas (C1): Topmost vertebra; supports the skull.

    • Axis (C2): Second vertebra; has the dens projection enabling rotation of the head.

Head Movements

  • Nodding “YES”: Movement between occipital bone and Atlas (atlanto-occipital joint).

    • Facilitates flexion and extension.

  • Turning “NO”: Pivoting movement between Atlas and Axis at the atlanto-axial joint; responsible for 50% of head's rotation.

Bones of the Ear

  • Ossicles: Three tiny bones (6 total) in each ear located in the middle ear, transmitting sound vibrations to the inner ear:

    1. Malleus (Hammer)

    2. Incus (Anvil)

    3. Stapes (Stirrup, the smallest bone in the human body)

Tissues and Muscles of the Head and Neck

The Scalp

  • Description: Soft tissue covering the head (excluding face and neck).

  • Layers:

    1. Skin (S)

    2. Connective Tissue (C)

    3. Galea Aponeurotica (A)

    4. Loose Alveolar Connective Tissue (L)

    5. Pericranium (P)

Scalp Functions

  • Protection against trauma and infection; support for hair growth; rich in blood vessels and nerves.

Scalp Layer Functions

  1. Skin: Thick, hair follicles, sebaceous glands.

  2. Connective Tissue: Dense subcutaneous tissues with blood vessels.

  3. Galea Aponeurotica: Connects occipitofrontalis muscles.

  4. Loose Alveolar Connective Tissue: Allows movement of upper layers.

  5. Pericranium: Membrane adheres to skull bones (periosteum).

Scalp Blood Supply and Innervation

  • Blood Supply:

    • External carotid artery (superficial temporal, posterior auricular, occipital)

    • Internal carotid artery (ophthalmic arteries: supratrochlear, supraorbital).

  • Innervation:

    • Sensory branches of Trigeminal nerve (V) for anterior scalp

    • Cervical spinal nerves (occipital nerves) for posterior scalp

    • Facial nerve for scalp muscles

Muscles of Mastication

  • Responsible for chewing and jaw movements:

    • Four Muscles:

    1. Masseter Muscle: Elevates mandible (closes jaw).

    2. Temporalis: Elevates and retracts mandible (closes and pulls back).

    3. Medial Pterygoid: Elevates and protracts mandible.

    4. Lateral Pterygoid: Depresses and protracts mandible (opens).

    • Innervation: Mandibular division of Trigeminal nerve (V3).

    • Blood Supply: Maxillary artery branches.

Muscles of Facial Expression

  • Approximately 20 muscles control nonverbal communication (smiling, frowning).

  • Categories:

    1. Orbital group: Muscles around the eyes

    2. Nasal group: Movements of the nose

    3. Oral group: Affects the lips and mouth

    4. Epicranial group: Muscles found on the scalp

    5. Auricular group: Muscles around the ear

Muscles of Facial Expression: Blood Supply and Innervation

  • Innervation: All by the Facial nerve (VII).

  • Blood Supply: Divided between lower and upper face; facial artery for lower face, maxillary and superficial temporal for upper face.

Facial Nerve Trauma

  • Traumatic facial paralysis results from injury, leading to weakness/loss in movement of facial muscles.

  • Symptoms:

    • Inability to wrinkle brow, drooping eyelid, inability to close eye, and asymmetrical smile.

Bell’s Palsy

  • Temporary facial nerve paralysis, usually affecting one side; often related to viral infections.

  • Dental Implications: May occur from inferior alveolar nerve block damaging the facial nerve.

Neck Muscles

  • Overview: ~30 muscles support, stabilize the head, neck and assist in movements and functions such as chewing, swallowing, and breathing.

Neck Triangles

  • Divided into Anterior and Posterior Triangles by the sternocleidomastoid muscle.

    • Anterior Triangle: Contains submandibular, submental, carotid, muscular triangles; major blood vessels and nerves present.

    • Posterior Triangle: Contains the brachial plexus, lymph nodes.

Neck Muscle Function

  • Functions include elevating upper ribs for inhalation, aiding in chewing and swallowing, stabilizing and supporting the head and neck, and various facial expressions.

Types of Neck Muscles

  • Categories:

    1. Anterior Neck Muscles (e.g., Sternocleidomastoid, Platysma)

    2. Lateral Neck Muscles (e.g., Anterior/Middle/Posterior Scalene, Levator Scapula)

    3. Posterior Neck Muscles (e.g., Rectus Capitis Posterior Major and Minor)

    4. Deep Neck Muscles (e.g., Longus Capitis, Coli)

    5. Suboccipital Muscles (e.g., Obliquus Capitis Superior and Inferior)

Innervation of Neck Muscles

  • Mainly via cervical plexus (C1-C4) and spinal accessory nerve (CN XI).

Blood Supply of Neck Muscles

  • Supplied by branches from common carotid and vertebral arteries; external carotid artery supplies anterior and lateral muscles (e.g., superior thyroid, occipital arteries).

Venous Return of the Neck

  • Jugular Veins: Primarily convey blood back to the heart.

    • Internal Jugular Vein: Drains blood from brain, face, neck.

    • External Jugular Vein: Drains outer cranium and deep tissues.

    • Anterior Jugular Vein: Drains anterior neck; typically empties into external jugular vein.

Meninges of the Brain and Spinal Cord

  • Definition: Three membrane layers (Dura mater, Arachnoid mater, Pia mater) that protect brain and spinal cord.

    1. Dura Mater: Outer layer closest to the skull

    2. Arachnoid Mater: Middle layer

    3. Pia Mater: Inner layer closest to brain tissue.

Meningeal Spaces

  • Epidural Space: Between skull and dura mater; site for analgesics and anesthetics.

    • Site for lumbar punctures.

  • Subdural Space: Between dura mater and arachnoid; normally nonexistent but can be opened with trauma.

  • Subarachnoid Space: Between arachnoid and pia mater; filled with cerebrospinal fluid, acting as a cushion.

Conclusion

  • Summary of topics covered in Part I, including the bones of the head and neck, scalp anatomy, muscles of mastication and facial expression, and the meninges of the brain and spinal cord. Part II will cover additional structures like the brain and glands related to the head and neck.