Head and Neck Anatomy — Skull, Cranial Nerves, Triangles and Brain
Quick Review
Head and neck anatomy is essential for INI CET — questions frequently involve cranial nerves, spaces in the neck, and the pharynx/larynx. Focus on the cranial nerve foramina, cervical triangles, carotid sheath contents, and the course of the facial nerve.
High-Yield Facts for INI CET:
- 12 cranial nerves: Olfactory (I), Optic (II), Oculomotor (III), Trochlear (IV), Trigeminal (V), Abducens (VI), Facial (VII), Vestibulocochlear (VIII), Glossopharyngeal (IX), Vagus (X), Accessory (XI), Hypoglossal (XII)
- Cavernous sinus: Contains CN III, IV, V1, V2, VI; important in spread of facial infection
- Facial nerve (VII): Motor to muscles of facial expression; lesion causes facial droop, inability to close eye, hyperacusis, loss of taste to anterior 2/3 of tongue, decreased lacrimation
- Mandibular nerve (V3): Has motor (muscles of mastication) and sensory functions; exits through foramen ovale
Exam tip: Cranial nerve lesions: CN VII upper face sparing (peripheral) vs no sparing (central — stroke); CN V sensory loss in dermatomal pattern (V1/V2/V3); CN IX+X dysphagia, dysphonia, loss of gag reflex.
Skull and Scalp
Bones of the Skull
- Neurocranium (8 bones): Frontal (2), parietal (2), temporal (2), occipital (1), sphenoid (1), ethmoid (1)
- Viscerocranium (facial skeleton): Mandible (1), maxilla (2), zygomatic (2), nasal (2), lacrimal (2), palatine (2), inferior nasal concha (2), vomer (1)
- Calvaria (skull cap): Outer table, diploe (trabecular bone with red marrow), inner table; sutures: coronal (frontal-parietal), sagittal (parietal-parietal), lambdoid (parietal-occipital), squamous (temporal-parietal)
Key Foramina and Their Contents
| Foramen | Contents |
|---|---|
| Foramen magnum | Medulla + vertebral arteries + spinal accessory nerve |
| Jugular foramen | CN IX, X, XI + sigmoid sinus (becomes internal jugular vein) |
| Foramen ovale | CN V3 + lesser petrosal nerve |
| Foramen spinosum | Middle meningeal artery (fracture → epidural haematoma) |
| Optic canal | CN II + ophthalmic artery |
| Superior orbital fissure | CN III, IV, VI, V1 |
Scalp — Five Layers (“SCALP”
- Skin
- Connective tissue (dense)
- Aponeurosis (epicranial aponeurosis — Galea aponeurotica)
- Loose areolar tissue (danger zone — infections spread easily)
- Pericranium (periosteum of skull)
The “danger area” is the loose areolar tissue that connects with emissary veins → intracranial venous sinuses; infections can spread to meninges and brain.
Cervical Triangles
Anterior Triangle of Neck
Bounded by: anterior border of SCM (posterior), midline of neck (anterior), superior border of mandible (superior).
Subdivisions:
- Submandibular triangle: Between mandible and anterior + posterior bellies of digastric; contains submandibular gland, submandibular nodes, Wharton duct
- Submental triangle: Between anterior bellies of digastric; contains submental nodes (drain chin and lower lip)
- Carotid triangle: Between SCM, posterior digastric, superior digastric; contains carotid sheath (common/internal carotid, internal jugular, vagus nerve), cervical sympathetic chain, hypoglossal nerve (XII), superior laryngeal nerve, lingual artery
- Muscular triangle: Sternohyoid, sternothyroid, thyrohyoid muscles; contains thyroid gland, parathyroid glands, larynx, trachea, oesophagus
Posterior Triangle of Neck
Bounded by: posterior border of SCM (anterior), anterior border of trapezius (posterior), middle third of clavicle (inferior). Roof is the investing layer of deep cervical fascia.
Contents (superficial to deep): Accessory nerve (XI) — crosses posterior triangle to enter trapezius; brachial plexus roots (C5-C8); supraclavicular nodes; transverse cervical artery; subclavian artery; apex of lung (cupola); subclavian vein; scalene muscles (anterior, middle, posterior); phrenic nerve (C3-C5) on anterior scalene.
Carotid Sheath
Contents: common/internal carotid artery (lateral), internal jugular vein (lateral to artery), vagus nerve (posterior between artery and vein), cervical sympathetic chain (medial — embedded in prevertebral fascia).
The common carotid bifurcates at C4 (upper border of thyroid cartilage) into internal and external carotid. The internal carotid has no branches in the neck and enters the skull via the carotid canal → cavernous sinus → supplies brain and eye.
Cranial Nerve Summary
| Nerve | Type | Foramen | Key Function |
|---|---|---|---|
| I Olfactory | Sensory | Cribriform plate | Smell |
| II Optic | Sensory | Optic canal | Vision |
| III Oculomotor | Motor | Superior orbital fissure | Eye movements (except SR, LR), pupil constriction |
| IV Trochlear | Motor | Superior orbital fissure | Superior oblique |
| V Trigeminal | Mixed | V1: SOF; V2: Rotundum; V3: Ovale | Facial sensation, mastication |
| VI Abducens | Motor | Superior orbital fissure | Lateral rectus (abducts eye) |
| VII Facial | Mixed | Internal acoustic meatus → facial canal → stylomastoid | Face expression, taste ant 2/3 tongue |
| VIII Vestibulocochlear | Sensory | Internal acoustic meatus | Hearing + balance |
| IX Glossopharyngeal | Mixed | Jugular foramen | Taste post 1/3 tongue, carotid body/sinus |
| X Vagus | Mixed | Jugular foramen | Pharynx/larynx muscles, parasympathetic to viscera |
| XI Accessory | Motor | Jugular foramen | Trapezius + sternocleidomastoid |
| XII Hypoglossal | Motor | Hypoglossal canal | Tongue muscles |
The Face
Muscles of Facial Expression
All supplied by facial nerve (CN VII) — all derived from 2nd pharyngeal arch:
- Orbicularis oculi: Closes eye; palpebral (involuntary, blinking) and orbital (forced closure) parts
- Orbicularis oris: Closes lips; forms boundary of mouth
- Buccinator: Keeps food between teeth during chewing; attaches to alveolar processes of maxilla and mandible
Muscles of Mastication (Supplied by V3)
Masseter, temporalis, medial pterygoid, lateral pterygoid — all from 1st pharyngeal arch.
Facial Nerve in the Face
Main trunk exits stylomastoid foramen → enters parotid gland → divides into terminal branches (temporal, zygomatic, buccal, marginal mandibular, cervical). Within parotid, it forms parotid plexus (pes anserinus) but does not supply parotid (secretomotor parasympathetic to parotid is CN IX via auriculotemporal nerve).
Clinical:
- Bell’s palsy: CN VII lesion (peripheral — affects all ipsilateral muscles); cannot close eye, forehead furrows,嘴角 droops, hyperacusis, loss of taste anterior 2/3 tongue; most common cause is viral (HSV reactivation)
- Stroke (UMN lesion): Contralateral lower face affected, forehead spared (bilateral UMN to forehead)
Parotid Gland
Largest salivary gland; serous (watery) secretion. Stensen duct exits anterior border → crosses masseter → pierces buccinator → opens into mouth at upper 2nd molar. Surgical danger: CN VII runs through parotid — can be damaged during parotidectomy.
The Pharynx and Larynx
Pharynx
Muscular tube from base of skull to C6 (where it becomes oesophagus); subdivided into:
- Nasopharynx: Posterior to nose; Eustachian tube opening (torus tubarius), pharyngeal tonsil (adenoids — largest in children)
- Oropharynx: Posterior to mouth; palatine tonsils, posterior 1/3 of tongue (circumvallate papillae), soft palate
- Laryngopharynx (hypopharynx): Posterior to larynx; piriform fossa (site of foreign body impaction)
Muscles of Pharynx
- Circular constrictors (superior, middle, inferior): Constrict pharynx during swallowing
- Stylopharyngeus: Elevates pharynx (CN IX); Palatopharyngeus: Elevates larynx (CN X)
Larynx — Skeleton
Thyroid cartilage (Adam’s apple), cricoid cartilage (only complete ring), arytenoid cartilages (paired, sit on cricoid), corniculate and cuneiform cartilages. Vocal folds (vocal cords): Internal angle of thyroid anteriorly → vocal process of arytenoid posteriorly; space between cords is the glottis. Vestibular folds (false cords): Superior to vocal folds; not involved in sound production.
Muscles of Larynx
- Cricothyroid: Tilts thyroid forward → tenses vocal cords → raises pitch
- Posterior cricoarytenoid: Only abductor of vocal cords (opens glottis)
- Lateral cricoarytenoid: Adductor (closes glottis)
- Thyroarytenoid: Relax vocal cords, helps close glottis
All intrinsic laryngeal muscles supplied by recurrent laryngeal nerve (branch of vagus) except cricothyroid (external laryngeal nerve — superior laryngeal nerve branch).
Airway Management
- Cricothyrotomy: Emergency airway through cricothyroid membrane (between thyroid and cricoid cartilage); used when intubation is impossible
- Coniotomy: Same as cricothyrotomy
Brain and Ventricles
Cerebral Hemispheres
- Frontal lobe: Motor cortex (precentral gyrus), premotor cortex, Broca’s area (left — speech production), prefrontal cortex (personality, executive function)
- Parietal lobe: Sensory cortex (postcentral gyrus), somatosensory association
- Temporal lobe: Auditory cortex, Wernicke’s area (left — speech comprehension), hippocampus (memory)
- Occipital lobe: Visual cortex (calcarine sulcus)
- Insula: Hidden by frontal, parietal, temporal opercula; involved in taste, visceral sensation
Basal Ganglia
Caudate nucleus, putamen (together = striatum), globus pallidus, substantia nigra, subthalamic nucleus; involved in movement control. Parkinson’s disease: degeneration of substantia nigra → loss of dopamine → less inhibition of striatum → less movement → akinesia, rigidity, tremor.
Ventricular System
Lateral ventricles (two — C-shaped, body + frontal, temporal, occipital horns) → interventricular foramen (Monro) → third ventricle → cerebral aqueduct (of Sylvius) → fourth ventricle → central canal of spinal cord + subarachnoid space (via foramina of Magendie and Luschka).
CSF: Produced by choroid plexus of lateral ventricles; flows through all ventricles; exits through foramina in 4th ventricle → subarachnoid space; absorbed by arachnoid granulations → dural venous sinuses (primarily superior sagittal sinus); normal pressure: 70-180mm H₂O.
Meninges and Spaces
- Dura mater: Tough outer layer; forms dural folds (falx cerebri, tentorium cerebelli, falx cerebelli); contains venous sinuses
- Arachnoid: Web-like middle layer; subarachnoid space (contains CSF and vessels)
- Pia mater: Delicate inner layer; adheres to brain surface
- Extradural space: Contains middle meningeal artery (damage → extradural haematoma — lens-shaped on CT)
- Subdural space: Contains bridging veins (damage → subdural haematoma — crescent-shaped)
- Subarachnoid space: Between arachnoid and pia; contains CSF and cerebral vessels