Head and Neck Anatomy: Cranial Bones

• Head and neck anatomy encompasses a complex arrangement of bones, muscles, vessels, nerves, and organs within a compact region.

Cranial Bones

• The skull is formed by cranial and facial bones.
• Cranial bones protect the brain and include the frontal, parietal, temporal, occipital, sphenoid, and ethmoid bones.
• The frontal bone forms the forehead and superior part of the orbits.
• The parietal bones form the sides and roof of the cranium.
• The temporal bones contribute to the lateral walls of the cranium and house the middle and inner ear structures.
• The occipital bone forms the posterior part of the skull and the base of the cranium.
• The sphenoid bone is a complex, bat-shaped bone that articulates with all other cranial bones.
• The ethmoid bone contributes to the anterior cranial fossa, the nasal cavity, and the orbits.

Muscles of Mastication

• The muscles of mastication are responsible for movements of the mandible during chewing, speaking, and other oral activities.
• The main muscles of mastication include the masseter, temporalis, medial pterygoid, and lateral pterygoid.
• The masseter muscle is a powerful muscle that elevates the mandible, closing the jaw.
• The temporalis muscle elevates and retracts the mandible.
• The medial pterygoid muscle elevates and protrudes the mandible, and assists in grinding movements.
• The lateral pterygoid muscle depresses and protrudes the mandible, and also assists in side-to-side movements.
• All muscles of mastication are innervated by the mandibular branch of the trigeminal nerve (CN V3).

Vascular Supply

• The head and neck region receives a rich blood supply from branches of the common carotid and subclavian arteries.
• The common carotid artery bifurcates into the internal and external carotid arteries.
• The internal carotid artery supplies blood to the brain, eye, and forehead.
• The external carotid artery supplies blood to the neck, face, and scalp.
• Branches of the external carotid artery include the superior thyroid, ascending pharyngeal, lingual, facial, occipital, posterior auricular, and superficial temporal arteries.
• Venous drainage of the head and neck occurs primarily through the internal jugular vein, external jugular vein, and vertebral vein.
• The internal jugular vein drains blood from the brain, face, and neck.
• The external jugular vein drains blood from the scalp and superficial face.

Nervous System Landmarks

• The cranial nerves provide sensory and motor innervation to structures in the head and neck.
• There are twelve pairs of cranial nerves, each with specific functions and distributions.
• Olfactory nerve (CN I) is responsible for the sense of smell.
• Optic nerve (CN II) is responsible for vision.
• Oculomotor nerve (CN III) controls most of the eye's movements, constricts the pupil, and elevates the upper eyelid.
• Trochlear nerve (CN IV) controls the superior oblique muscle of the eye.
• Trigeminal nerve (CN V) has three branches: ophthalmic (V1), maxillary (V2), and mandibular (V3). It is responsible for facial sensation, and muscles of mastication.
• Abducens nerve (CN VI) controls the lateral rectus muscle of the eye.
• Facial nerve (CN VII) controls facial expression, taste from the anterior two-thirds of the tongue, and lacrimal and salivary glands.
• Vestibulocochlear nerve (CN VIII) is responsible for hearing and balance.
• Glossopharyngeal nerve (CN IX) controls swallowing, taste from the posterior one-third of the tongue, and parotid gland secretion.
• Vagus nerve (CN X) controls the muscles of the pharynx and larynx, and provides parasympathetic innervation to the thoracic and abdominal organs.
• Accessory nerve (CN XI) controls the sternocleidomastoid and trapezius muscles.
• Hypoglossal nerve (CN XII) controls the muscles of the tongue.

Organs of the Neck

• The neck contains several important organs, including the larynx, trachea, esophagus, thyroid gland, and parathyroid glands.
• The larynx, or voice box, is responsible for phonation and protects the airway during swallowing.
• The trachea, or windpipe, carries air to and from the lungs.
• The esophagus transports food and liquids from the pharynx to the stomach.
• The thyroid gland produces hormones that regulate metabolism, growth, and development.
• The parathyroid glands regulate calcium levels in the blood.

Infratemporal Fossa

• The infratemporal fossa is an irregularly shaped space located inferior to the temporal fossa and deep to the mandible.
• Structures within the infratemporal fossa include the lateral pterygoid and medial pterygoid muscles, the mandibular nerve (CN V3) and its branches, the maxillary artery and its branches, and the pterygoid venous plexus.
• The mandibular nerve (CN V3) enters the infratemporal fossa through the foramen ovale and gives off branches to the muscles of mastication and sensory branches to the lower face, teeth, and tongue.
• The chorda tympani nerve, a branch of the facial nerve (CN VII), also passes through the infratemporal fossa to join the lingual nerve.
• The maxillary artery, a branch of the external carotid artery, enters the infratemporal fossa and supplies blood to the muscles of mastication, teeth, and nasal cavity.
• The pterygoid venous plexus is a network of veins that surrounds the pterygoid muscles and communicates with the cavernous sinus.