Anatomy of the Head and Neck

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Posterior triangle:

• Cranial Nerve XI (accessory nerve): innervates sternocleidomastoid muscle.

• Lesions cause trapezius wasting and weakened shoulder elevation.

• Cranial Nerve 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.

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:

• Cranial Nerve 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.

Cranial nerves:

Cranial Nerve 1 (olfactory): smells.

Cranial Nerve 2 (optic): sees.

• Cranial Nerves 3, 4 and 6 (oculomotor, trochlear, and abducens): moves eyes, Cranial Nerve 3 constricts pupils, accommodates.

Cranial Nerve 5 (trigeminal = ophthalmic (V1) + maxillary (V2) + mandibular (V3)): chews and feels front of head.

Cranial Nerve 7 (facial): moves the face, tastes, salivates, and cries.

Cranial Nerve 8 (vestibulocochlear): hears, regulates balance.

Cranial Nerve 9 (glossopharyngeal): tastes, salivates, swallows, monitors carotid body and sinus.

Cranial Nerve 10 (vagus): tastes, swallows, lifts palate, talks, communication to and from thoraco-abdominal viscera.

Cranial Nerve 11 (accessory): turns head, lifts shoulders.

Cranial Nerve 12 (hypoglossal): moves tongue.

Circulations in the 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.

Cranial Nerve II:

• Innervates retina.

Cranial Nerve III, IV, V:

• Innervate muscles that move eyeball.

Cranial Nerve III:

• Innervates muscles of accommodation and eyelid elevation.

Left Ocular Muscles and Innervation

left ocular muscles and innervation

Right Ocular Muscles and Innervation

right ocular muscles and innervation

Orbital muscles and their innervations:

• Six muscles that move the eyeball.

Cranial Nerve III:

• Innervates superior, inferior, and medial rectus, and inferior oblique, and levator palpebrae superioris.

Cranial Nerve IV:

• Innervates superior oblique.

Cranial Nerve VI:

• Innervates lateral rectus.

Function of levator palpebrae superioris:

• Moves upper eyelid; also innervated by sympathetic fibers.

Muscles within the eye:

• Dilator and constrictor pupillae, and ciliary muscle.

Blink reflex:

• Cranial Nerve VII.

Pupillary light reflex:

• Cranial Nerve III.

Lesion of Cranial Nerve III:

• Cannot adduct eyeball; ptosis; mydriasis; loss of accommodation, loss of pupillary reflex; caused by berry aneurysms, Subdural/ Epidural hematoma.

Lesion of Cranial Nerve IV:

• Diplopia, difficulty reading/going down stairs; patient tilts head away from lesioned nerve to compensate.

Lesion of Cranial Nerve VI:

• Can't abduct the eye.

Edinger-Westphal nucleus

Pupillary light and accommodation reflexes:

• Direct and consensual light reflex uses sensory fibers of Cranial Nerve II and parasympathetic fibers of Cranial Nerve III.

• When light is shone into one eye, light travels through the Cranial Nerve II, pretectal nucleus of midbrain, Edinger-Westphal nucleus, Cranial Nerve 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 Cranial Nerve 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 Cranial Nerve III.

• Afferent pupillary defect: Cranial Nerve II lesion; swinging flashlight test; affected pupil dilates upon exposure to light.

• Efferent pupillary defect: Cranial Nerve III lesion; light exposure to either eye causes normal pupil to constrict but cause affected pupil to remain unaffected.

Oral cavity:

• Cranial Nerve 12 lesion: tongue deviates toward injured side (licking of wounds); fasciculations and atrophy.

Innervation of tongue:

• Anterior 2/3rd: Cranial Nerve V3 and Cranial Nerve VII.

• Posterior 1/3: Cranial Nerve IX.

• Mucosa at base of tongue: Cranial Nerve X.

Lesion of Cranial Nerve V:

• Pain in mandible, deep to ear, nostril, orbit.

Palate:

• Innervated by Cranial Nerve X.

Pharynx:

• Innervated by Cranial Nerves IX and X.

Gag reflex:

• Sensory: Cranial Nerve IX.

• Motor: Cranial Nerve X.

gag reflex sensory and motor conduction

Cough reflex:

• Sensory: Cranial Nerve X (internal branch of superior laryngeal nerve).

• Motor: Cranial Nerve X (recurrent laryngeal nerve).

Larynx:

• Innervated by Cranial Nerve 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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1. Video of HEENT Examination in a Clinical Setting

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