Anatomy of the Head and Neck
Rahul's Noteblog
Notes on Anatomy
Notes on Anatomy of the Head and Neck
Posterior triangle:
•CN XI (accessory nerve): innervates sternocleidomastoid muscle.
•Lesions cause trapezius wasting and weakened shoulder elevation.
•CN XI and phrenic nerves pass in posterior triangle: supply posterior scalp and skin of neck.
•Brachial plexus compression (by cervical rib or apical lung (Pancoast) tumor) causes weakened shoulder and arm muscles.
Anterior triangle:
•Contains cervical plexus (C1-C4) and carotid triangle.
Middle meningeal a. laceration causes epidural hematoma.
First arch syndrome: facial anomalies.
DiGeorge: pharyngeal pouches 3, 4 failed to develop.
Cleft lip: failed maxillary prominence and medial nasal prominence fusion.
Cleft palate: failed fusion of palatine shelves to fuse with each other, or with primary palate.
Jugular foramen syndrome:
•CN IX, X, XI pressed; hoarseness, dysphagia, loss of sensation over posterior 1/3rd of tongue; weak trapezius and sternocleidomastoid.
Accessory nerve: innervates trapezius; weakness in elevating shoulder.
Lacerations of middle meningeal artery cause epidural hematoma.
Cranial nerves:
• CN 1 (olfactory): smells.
• CN 2 (optic): sees.
• CN 3, 4 and 6 (oculomotor, trochlear, and abducens): moves eyes, CN3 constricts pupils, accommodates.
• CN 5 (trigeminal = ophthalmic (V1) + maxillary (V2) + mandibular (V3)): chews and feels front of head.
• CN 7 (facial): moves the face, tastes, salivates, and cries.
• CN 8 (vestibulocochlear): hears, regulates balance.
• CN 9 (glossopharyngeal): tastes, salivates, swallows, monitors carotid body and sinus.
• CN 10 (vagus): tastes, swallows, lifts palate, talks, communication to and from thoraco-abdominal viscera.
• CN 11 (accessory): turns head, lifts shoulders.
• CN 12 (hypoglossal): moves tongue.
Brain:
• Arterial: internal/external carotid arteries; subclavian artery.
• Venous: cerebral veins drain into dural venous sinuses, which in turn drain into the internal jugular vein; superior sagittal sinus drains into confluens of sinuses.
Cavernous sinus thrombosis: infection spreads from veins of face (mainly the superior ophthalmic vein, which enters the cranium through the superior orbital fissure) into cavernous sinus.
Subarachnoid hemorrhage: rupture of a berry (saccular) aneurysm in circle of Willis; severe headache.
• Common site: branch-point of anterior cerebral and anterior communicating arteries.
Subdural hematoma: torn superficial "bridging" cerebral veins at the point where they enter sagittal sinus.
• Venous hemorrhage between dura and arachnoid.
Epidural hematoma: trauma to lateral aspect of skull.
• Middle meningeal artery lacerated.
• Hemorrhage between dura and skull.
• Loss of consciousness followed by asymptomatic period of up to 48 hours.
CN II: innervates retina.
CN III, IV, V: innervate muscles that move eyeball.
CN III: innervates muscles of accommodation and eyelid elevation.
Left Ocular Muscles and Innervation
Right Ocular Muscles and Innervation
Orbital muscles and their innervations:
• Six muscles that move the eyeball.
• CN III: innervates superior, inferior, and medial rectus, and inferior oblique, and levator palpebrae superioris.
• CN IV: innervates superior oblique.
• CN VI: innervates lateral rectus.
Levator palpebrae superioris moves upper eyelid; also innervated by sympathetic fibers.
• Muscles within the eye: dilator and constrictor pupillae, and ciliary muscle.
Blink reflex: CN VII.
Pupillary light reflex: CN III.
Lesion of CN III: cannot adduct eyeball; ptosis; mydriasis; loss of accommodation, loss of pupillary reflex; caused by berry aneurysms, Subdural/ Epidural hematoma.
Lesion of CN IV: diplopia, difficulty reading/going down stairs; patient tilts head away from lesioned nerve to compensate.
Lesion of CN VI: can't abduct the eye.
Pupillary light and accommodation reflexes:
• Direct and consensual light reflex uses sensory fibers of CN II and parasympathetic fibers of CN III.
• When light is shone into one eye, light travels through the CN II, pretectal nucleus of midbrain, Edinger-Westphal nucleus, CN III, and back to the same eye constricting the pupil (direct light reflex). Furthermore, the Edinger-Westphal nucleus also sends impulses to the other eye through its CN III, then, pupil of other eye also constricts (consensual light reflex).
• When light is shone into one eye, reflexes travel from that eye to the other eye through the optic chiasm.
• Edinger Westphal nuclei (which lie in brain stem) stimulate the eyes to contract.
• Shine light into both eyes separately to localize lesion on either optic or oculomotor nerve.
• Accommodation reflexes used skeletal motor and parasympathetic fibers in CN III.
• Afferent pupillary defect: CN II lesion; swinging flashlight test; affected pupil dilates upon exposure to light.
• Efferent pupillary defect: CN III lesion; light exposure to either eye causes normal pupil to constrict but cause affected pupil to remain unaffected.
Oral cavity:
• CN 12 lesion: tongue deviates toward injured side (licking of wounds); fasciculations and atrophy.
Innervation of tongue:
• Anterior 2/3rd: CN V3 and CN VII.
• Posterior 1/3: CN IX.
• Mucosa at base of tongue: CN X.
Lesion of CN V: pain in mandible, deep to ear, nostril, orbit.
Palate:
• Innervated by CN X.
Pharynx:
• Innervated by CN IX and X.
Gag reflex:
• Sensory: CN IX.
• Motor: CN X.
Cough reflex:
• Sensory: CN X (internal branch of superior laryngeal nerve).
• Motor: CN X (recurrent laryngeal nerve).
Larynx:
• Innervated by CN X (motor and sensory by recurrent laryngeal nerve and superior laryngeal nerve).
Additional Notes:
• Superior oblique muscle: abduction and depression of eyeball.
• Superior rectus muscle: adduction and elevation of eyeball.
• Wernicke’s encephalopathy: hemorrhage and necrosis of mamillary bodies.
• Breathing tube inserted through cricothyroid membrane to avoid damaging the larynx.
• Posterior cricoarytenoid muscle involved in opening vocal cords.
• Cortical area linked to hearing: Heschl’s gyrus.
Additional Reading:
Histology and Cytology
1. Cell Components
2. Nervous Tissue
3. Muscle Tissue
4. Lymphoid Tissue
5. Integument
6. Respiratory System
7. Gastrointestinal System
8. Renal/Urinary System
9. Male Reproductive System
10. Female Reproductive System
Gross Anatomy
1. Back and Nervous System
2. Thorax
3. Abdomen, Pelvis, and Perineum
4. Upper Limb
5. Lower Limb
6. Head and Neck
7. Chest Wall
8. Shoulder
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Page accessed on: September 2, 2010, 5:50 pm.