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Anatomy of the Nose - Complete Revision Summary (1st Year BDS)

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1. OVERVIEW & PARTS

• External nose - pyramidal structure projecting from the face
• Nasal cavity - extends from nares (nostrils) anteriorly to choanae posteriorly (where it becomes the nasopharynx)
• Divided into right and left cavities by the nasal septum

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2. EXTERNAL NOSE

Shape & Surface Landmarks

• Pyramidal shape; apex points anteriorly
• Root (upper end, between orbits), Dorsum (bridge), Tip (apex), Alae (wings), Columella (between nostrils), Nares (external openings)
• Skin is thin and loosely adherent over dorsum; becomes thicker with many sebaceous glands at the tip and alae

Skeleton of External Nose

• Nasal bones (paired)
• Parts of frontal bones
• Frontal processes of maxilla

Key: ULC and septal cartilage together form the internal nasal valve (narrowest part of the nasal airway, ~10-15 degrees in Caucasians).

Muscles of External Nose

Subcutaneous Layers (from superficial to deep)

1. Superficial fatty layer
2. Fibromuscular layer (SMAS)
3. Deep fatty layer (contains neurovascular structures)
4. Periosteum/perichondrium

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3. NASAL VESTIBULE

• Anteriormost part of nasal cavity
• Lined by keratinizing stratified squamous epithelium
• Contains vibrissae (coarse hairs), sebaceous glands, sweat glands
• Demarcated by the limen nasi (at caudal border of lower lateral cartilage)

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4. NASAL CAVITY

Boundaries

Epithelium

• Nasal vestibule → Stratified squamous (keratinized)
• Superior part (superior septum, superior turbinate, upper middle turbinate) → Olfactory epithelium
• Remainder → Pseudostratified ciliated columnar (respiratory epithelium)

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5. NASAL SEPTUM

Bony Part

Cartilaginous Part

• Quadrilateral (septal) cartilage - forms anterior septum; firmly attached to nasal bones, perpendicular plate of ethmoid, and vomer by collagenous fibers
• Its sphenoidal process (septal tail) extends posteriorly between vomer and perpendicular plate

Membranous Part

• Segment of connective tissue between caudal septal cartilage and columella

Exam point: Nasal septal deviation is the most common cause of nasal obstruction; the commonest site of septal perforation/epistaxis is Kiesselbach's plexus (Little's area)

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6. LATERAL NASAL WALL & TURBINATES (Conchae)

Turbinates

• 3 main turbinates: Superior, Middle, Inferior
• Middle and superior turbinates arise from ethmoid bone
• Inferior turbinate is an independent osseous structure (separate bone)
• Function: warm, humidify, and filter inspired air; modify nasal airflow resistance

Meatuses (spaces under each turbinate)

Memory tip: "FBI drains Middle" - Frontal, (anterior ethmoid,) maxillary drains into Middle meatus. Posterior ethmoid → Superior meatus. Sphenoid → Sphenoethmoidal recess.

Nasal Cycle

• Turbinates cyclically alternate congestion/decongestion every 0.5-3 hours under sympathetic control - this is normal physiology.

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7. BLOOD SUPPLY

Two major sources: External + Internal carotid

External Carotid Artery (via Maxillary artery → Sphenopalatine artery)

• Sphenopalatine artery - main supply to turbinates and lateral nasal wall; enters via sphenopalatine foramen
  • Posterior septal artery (branch) → posteroinferior septum
• Greater palatine artery → enters via incisive canal → anteroinferior septum
• Superior labial artery (branch of facial artery) → columella and caudal septum
• Angular/lateral nasal arteries (branch of facial artery) → ala and sidewall

Internal Carotid Artery (via Ophthalmic artery → Ethmoidal arteries)

• Anterior ethmoidal artery → anterosuperior septum + dorsum of external nose
• Posterior ethmoidal artery → posterosuperior septum

Kiesselbach's Plexus (Little's Area) ⭐ HIGH YIELD

• Located on the anterior nasal septum
• Anastomosis of: anterior ethmoidal artery + posterior septal artery + septal branch of superior labial artery
• Most common site of epistaxis (nosebleed) due to rich vascularity and susceptibility to trauma/turbulent airflow

Venous Drainage

• Posteriorly via sphenopalatine vessels → pterygoid plexus
• Anteriorly via facial vein
• Superiorly: ethmoidal veins → superior ophthalmic vein → cavernous sinus

⚠️ Danger area: Upper lip and nose infections can spread retrograde through the valveless facial vein to the cavernous sinus via the ophthalmic vein - potentially life-threatening!

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8. NERVE SUPPLY

External Nose

Nasal Cavity (Mucosa)

• Sensory: Ophthalmic (V1) and maxillary (V2) divisions of trigeminal nerve
  • Lateral wall and turbinates: posterolateral nasal nerves from V2 (via sphenopalatine ganglion) + ethmoidal nerves from V1
  • Anterior septum: nasopalatine nerve
• Parasympathetic: Via vidian nerve (greater superficial petrosal nerve) → synapse in sphenopalatine ganglion → regulates nasal secretions
• Sympathetic: Via vidian nerve (deep petrosal nerve) → passes through sphenopalatine ganglion (no synapse) → regulates vascular tone and turbinate congestion

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9. LYMPHATIC DRAINAGE

• External nose: Submandibular, submental, and facial nodes; drainage may also reach parotid nodes
• Nasal cavity (anterior): Submandibular nodes
• Nasal cavity (posterior): Upper deep cervical and retropharyngeal nodes

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10. PARANASAL SINUSES (Quick Summary)

• All sinuses lined by respiratory (ciliated) mucosa and innervated by trigeminal nerve (CN V)
• The maxillary sinus ostium opens high on the medial wall - poor gravity drainage (clinically important!)

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11. QUICK CLINICAL CORRELATIONS (BDS Favorites)

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12. EMBRYOLOGY (Key Points)

• Nose develops in the 4th week of gestation from neural crest cell proliferation forming nasal placodes
• Medial nasal processes → philtrum, columella, premaxilla
• Lateral nasal processes → nasal bones and alar cartilages
• Nasal septum: downgrowth of frontonasal process; fuses with palate from 9th-12th week
• Vomeronasal (Jacobson's) organs: regress before birth; only vomeronasal cartilages remain in adults

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Triangles of the Neck - Complete Revision Summary (1st Year BDS)

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OVERVIEW

• Anterior triangle - medial to SCM
• Posterior triangle - lateral to SCM

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THE STERNOCLEIDOMASTOID (SCM) MUSCLE - KEY LANDMARK

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PART A: ANTERIOR TRIANGLE

Boundaries

Subdivisions

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1. SUBMENTAL TRIANGLE (unpaired/single)

BDS point: Only unpaired triangle of the neck. Submental nodes drain tip of tongue, floor of mouth, lower incisors.

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2. SUBMANDIBULAR (DIGASTRIC) TRIANGLE

⭐ BDS High Yield: The lingual nerve spirals around Wharton's duct going lateral → inferior → medial - a classic exam question! The submandibular ganglion hangs from the lingual nerve like a "bag hanging from a nerve."

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3. CAROTID TRIANGLE ⭐ MOST IMPORTANT

Arteries

Carotid sinus = dilation at origin of ICA → baroreceptor (monitors BP), innervated by CN IX (glossopharyngeal) Carotid body = ovoid body at bifurcation → chemoreceptor (monitors O2/CO2), innervated by CN IX + X

Veins

Carotid Sheath Contents (medial to lateral)

• Medial: Common/internal carotid artery
• Lateral: Internal jugular vein
• Posterior (between): Vagus nerve (CN X)
• Deep (on prevertebral fascia): Cervical sympathetic trunk (outside sheath)

Nerves in Carotid Triangle

Ansa Cervicalis ⭐

• Superior root (descendens hypoglossi): C1 fibers carried by CN XII → innervates superior belly of omohyoid, upper sternohyoid, upper sternothyroid
• Inferior root (descendens cervicalis): C2 + C3 → innervates inferior belly of omohyoid, lower sternohyoid, lower sternothyroid
• Thyrohyoid is innervated by C1 fibers from hypoglossal nerve (not ansa itself)

Memory trick: Ansa cervicalis = "handle/loop" in Latin. It supplies all infrahyoid muscles EXCEPT thyrohyoid (which gets C1 via CN XII directly).

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4. MUSCULAR (STRAP) TRIANGLE

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MUSCLES OF ANTERIOR TRIANGLE

Suprahyoid Muscles (above hyoid - raise hyoid during swallowing)

⭐ Exam point: Digastric has dual innervation - posterior belly (CN VII), anterior belly (V3). This is because they have different embryological origins!

Infrahyoid Muscles (below hyoid - depress hyoid during swallowing)

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PART B: POSTERIOR TRIANGLE (Lateral Cervical Triangle)

Boundaries

Subdivisions

Floor Muscles (superficial to deep, anterior to posterior)

1. Splenius capitis (at apex)
2. Levator scapulae
3. Posterior scalene
4. Middle scalene
5. Anterior scalene

⭐ Brachial plexus roots emerge between anterior and middle scalene muscles

Contents of Posterior Triangle

Nerves

• Exits jugular foramen → passes through/deep to SCM (innervates it) → crosses posterior triangle within investing fascia → reaches trapezius (innervates it)
• Lies superficial to prevertebral fascia (unlike most other motor nerves here)
• Most superior nerve in the posterior triangle
• Vulnerable to injury during lymph node biopsy → causes drooping shoulder (trapezius paralysis)

Mnemonic for cutaneous branches: "My Great Aunt Talks Softly" → Medial/Lesser occipital, Great auricular, Anterior (transverse cervical), Two (C3,C4) Supraclavicular

• Formed on surface of anterior scalene muscle
• "C3,4,5 keeps the diaphragm alive"
• Descends across anterior scalene within prevertebral fascia

• Roots emerge between anterior and middle scalene muscles
• C5 + C6 → Superior trunk; C7 → Middle trunk; C8 + T1 → Inferior trunk

Vessels

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DEEP CERVICAL FASCIA - QUICK SUMMARY (BDS Favorite!)

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QUICK CLINICAL CORRELATIONS (⭐ BDS Exam Favorites)

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MEMORY AIDS

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Fascia of the Neck - Complete Revision Summary (1st Year BDS)

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OVERVIEW

1. Superficial cervical fascia
2. Deep cervical fascia (most important for exams - has 3 main layers + carotid sheath)

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PART 1: SUPERFICIAL CERVICAL FASCIA

• A layer of loose areolar connective tissue lying directly beneath the skin
• Contains:
  • Platysma muscle (most important content)
  • Superficial veins (external jugular, anterior jugular veins)
  • Cutaneous nerves (branches of cervical plexus)
  • Superficial lymph nodes
  • Fat

Platysma ⭐

⭐ BDS Exam point: Platysma is the only muscle in the superficial cervical fascia. It is supplied by the cervical branch of CN VII (not a muscle of mastication nerve). Damage during surgery → loss of lower facial/lip tone.

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PART 2: DEEP CERVICAL FASCIA

1. Investing layer (superficial)
2. Pretracheal layer / middle layer (visceral)
3. Prevertebral layer (deep)
4. Carotid sheath (a separate condensation formed from all 3 layers)

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LAYER 1: INVESTING (SUPERFICIAL) LAYER OF DEEP CERVICAL FASCIA ⭐

Attachments

What it encloses/does

• Envelops the entire neck like a cylinder
• Splits to enclose: SCM, trapezius, omohyoid (with a fascial sling to clavicle), infrahyoid muscles
• Splits to enclose glands:
  • Parotid gland → forms parotid capsule/fascia (deep layer fuses with ICA fascia)
  • Submandibular gland → splits to form a tough supporting membrane
• Forms roof of both the anterior and posterior triangles of neck
• Contains all cervical lymph nodes within its boundary
• Forms the stylomandibular ligament posteriorly (separates parapharyngeal and submandibular spaces)
• Splits inferiorly at manubrium to form the suprasternal space of Burns

Suprasternal Space of Burns ⭐

• A potential space between the two leaves of the investing fascia above the manubrium
• Contains: anterior jugular veins + jugular venous arch, lymph nodes, fat
• Can collect blood/pus after thyroid surgery or neck infections

⭐ Clinical: Because the investing layer forms a tough cylinder, deep abscesses build up under it and cause airway compression before they point superficially. This is why deep neck infections are dangerous.

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LAYER 2: PRETRACHEAL (MIDDLE/VISCERAL) LAYER

Attachments

• Superior: Hyoid bone + oblique line of thyroid cartilage
• Inferior: Descends into superior mediastinum → fuses with fibrous pericardium
• Lateral: Blends/connects to carotid sheath

Buccopharyngeal Fascia ⭐

• Part of the visceral division that overlies the posterior surface of the pharynx and buccinator
• Forms the anterior wall of the retropharyngeal space
• Forms the midline pharyngeal raphe (posterior midline attachment of constrictors)
• Forms the pterygomandibular raphe laterally

⭐ Clinical: Because the pretracheal layer descends into the mediastinum, thyroid infections and pretracheal abscesses can spread directly down into the anterior mediastinum - a life-threatening complication.

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LAYER 3: PREVERTEBRAL (DEEP) LAYER

What it covers

• Cervical vertebrae and their bodies
• Prevertebral muscles (longus colli, longus capitis, scalene muscles)
• Posterior neck muscles (paraspinous)

Attachments

• Superior: Base of skull
• Inferior: Fuses with anterior longitudinal ligament at T3 in the posterior mediastinum
• Lateral: Extends as the axillary sheath (encloses brachial plexus + axillary vessels)

Significance

• Forms the floor of the posterior triangle of neck
• The phrenic nerve (C3,4,5) and brachial plexus run deep to this fascia - protected during neck dissection
• Deep limit/margin of surgical neck dissection - should not be breached unless tumour invades it
• Allows the pharynx to glide freely over vertebral column during swallowing

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ALAR FASCIA ⭐ (often asked separately)

• A supplementary sheet anterior to the prevertebral fascia
• Lies between the prevertebral layer (behind) and the middle/visceral layer (in front)
• Extends from skull base to T2 vertebra (where it fuses with prevertebral fascia)
• Creates the critical "Danger Space" posterior to it

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LAYER 4: CAROTID SHEATH ⭐⭐

Formation

• Formed from contributions of all three layers of the deep cervical fascia
• A tubular condensation running from skull base to thorax

Contents (medial to lateral)

Note: The sheath is thicker around the arteries but loose around the IJV to allow expansion during increased venous flow.

⭐ Classic exam fact: The carotid sheath is called the "Lincoln Highway of the Neck" because it provides a fast route for infection to spread from the skull base to the thorax.

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PART 3: FASCIAL SPACES OF THE NECK ⭐⭐ (Very High Yield for BDS)

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1. Submental Space

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2. Submandibular Space ⭐

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3. Parapharyngeal Space (Lateral Pharyngeal Space) ⭐⭐

⭐ BDS point: Tonsil abscess/peritonsillar abscess can spread to the parapharyngeal space. Parotid tumours can bulge medially into this space (causing medial pharyngeal wall displacement). Parapharyngeal space infections can spread to all adjacent spaces.

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4. Retropharyngeal Space ⭐⭐

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5. "Danger Space" (Space 4) ⭐⭐ MOST CLINICALLY DANGEROUS

⭐ The MOST DANGEROUS space - because it has no natural barriers, infection can spread from the neck all the way to the diaphragm, causing descending necrotizing mediastinitis - a potentially fatal complication with mortality up to 40%.

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6. Prevertebral Space

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7. Masticator Space

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SUMMARY TABLE: LAYERS OF DEEP CERVICAL FASCIA

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SUMMARY TABLE: FASCIAL SPACES

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TOP EXAM POINTS - QUICK RECALL ⭐

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CLINICAL MNEMONICS

• Internal carotid Artery - Medially
• Vagus Nerve - between the two

• Investing → Pretracheal → Prevertebral

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Fascia of the Neck - BDS 1st Year Revision Sheet

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BASIC CONCEPT

1. Superficial cervical fascia - under the skin
2. Deep cervical fascia - deeper, most important for exams (3 layers + carotid sheath)

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PART 1: SUPERFICIAL CERVICAL FASCIA

• Lies directly beneath the skin, above the deep fascia
• Contains loose areolar tissue + fat

Contents:

• Platysma muscle ⭐ (most important content)
• External jugular vein + anterior jugular vein
• Cutaneous branches of cervical plexus
• Superficial lymph nodes

PLATYSMA ⭐⭐

⭐ Exam point: Platysma is the only muscle in the superficial fascia of the neck. It is a muscle of facial expression, NOT mastication, so it is supplied by CN VII (not V3). Injury during surgery causes loss of lower lip tone.

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PART 2: DEEP CERVICAL FASCIA

THE 3 MAIN LAYERS + CAROTID SHEATH:

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LAYER 1: INVESTING (SUPERFICIAL) LAYER ⭐⭐

Attachments:

What it does:

• Wraps the neck like a tight stocking/cylinder
• Splits to enclose muscles: SCM, trapezius, omohyoid (sling to clavicle), infrahyoid strap muscles
• Splits to enclose glands:
  • Parotid gland → forms parotid capsule
  • Submandibular gland → forms tough supporting membrane
• Forms roof of both anterior and posterior triangles
• Contains ALL cervical lymph nodes within it
• Forms the stylomandibular ligament (separates parapharyngeal and submandibular spaces)
• Splits above manubrium → forms Suprasternal Space of Burns

Suprasternal Space of Burns ⭐

• Space between 2 leaves of investing fascia, just above manubrium
• Contains: anterior jugular veins + jugular venous arch, fat, lymph nodes
• Can collect pus/blood after thyroid surgery

⭐ Clinical: Investing layer forms a rigid cylinder around the neck. Deep abscesses are trapped inside it and can compress the airway before pointing superficially - reason deep neck infections are life-threatening.

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LAYER 2: PRETRACHEAL (MIDDLE/VISCERAL) LAYER ⭐⭐

Two divisions:

Attachments:

• Superior: Hyoid bone + thyroid cartilage (oblique line)
• Inferior: Descends into superior mediastinum → fuses with fibrous pericardium
• Lateral: Connects to carotid sheath

Buccopharyngeal Fascia ⭐

• Part of the visceral division
• Covers the posterior surface of pharynx + buccinator
• Forms anterior wall of retropharyngeal space
• Forms pharyngeal raphe (posterior midline)
• Forms pterygomandibular raphe (lateral - between buccinator and superior constrictor)

⭐ Clinical: Pretracheal layer tracks directly into the anterior mediastinum - thyroid infections and pretracheal abscesses can spread to cause anterior mediastinitis (life-threatening).

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LAYER 3: PREVERTEBRAL (DEEP) LAYER ⭐

What it covers:

• Cervical vertebrae + vertebral bodies
• Prevertebral muscles (longus colli, longus capitis)
• Scalene muscles
• Posterior neck (paraspinous) muscles

Attachments:

• Superior: Base of skull
• Inferior: Fuses with anterior longitudinal ligament at T3 (posterior mediastinum)
• Lateral: Extends as axillary sheath (covering brachial plexus + axillary vessels)

Significance:

• Forms the floor of the posterior triangle of the neck
• Phrenic nerve + brachial plexus run DEEP to this fascia - protected during neck surgery
• Deep limit/surgical margin of neck dissection - not breached unless tumour invades it
• Allows pharynx to glide freely over vertebrae during swallowing

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ALAR FASCIA ⭐ (a sub-layer of deep layer)

• An extra fascial sheet that lies anterior to the prevertebral fascia
• Between: prevertebral layer (behind) and buccopharyngeal fascia/middle layer (in front)
• Extends from skull base to T2 (fuses with prevertebral fascia at T2)
• Creates the critical "Danger Space" between itself and the prevertebral fascia

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LAYER 4: CAROTID SHEATH ⭐⭐

Formation:

• Formed from contributions of ALL THREE layers of deep cervical fascia
• A tough tube running from skull base to thorax

Contents (know in order!):

Note: Sheath is thick around arteries, loose around IJV (allows expansion with increased venous flow). Cervical sympathetic trunk lies outside/posterior to the carotid sheath on the prevertebral fascia.

⭐ Classic exam: Carotid sheath = "Lincoln Highway of the Neck" - rapid spread of infection from skull base to thorax along this structure.

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MASTER SUMMARY TABLE

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PART 3: FASCIAL SPACES OF THE NECK ⭐⭐⭐ (Highest Yield!)

1. Submental Space

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2. Submandibular Space ⭐⭐ (Ludwig's Angina)

• Divided by mylohyoid into:
  • Sublingual compartment (superior) - contains sublingual gland
  • Submandibular compartment (inferior) - contains submandibular gland + nodes
• Both communicate around free posterior edge of mylohyoid

⭐ Ludwig's Angina = rapidly spreading bilateral cellulitis of submandibular space, usually from 2nd/3rd molar infection. Starts inferiorly, spreads to sublingual space → parapharyngeal → retropharyngeal space → airway compromise. Life-threatening. No pus/abscess formation - it is a brawny, woody induration.

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3. Parapharyngeal Space ⭐⭐ (Lateral Pharyngeal Space)

⭐ BDS exam: Peritonsillar abscess spreads to parapharyngeal space. Parotid tumours bulge medially into this space → medial pharyngeal wall displaced. Parapharyngeal space is a communicating hub - connects with almost every other space.

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4. Retropharyngeal Space ⭐⭐

⭐ Retropharyngeal abscess is common in children under 5 (nodes still present). Presents with neck stiffness, dysphagia, muffled voice, drooling. X-ray lateral neck shows widening of retropharyngeal space.

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5. DANGER SPACE ⭐⭐⭐ (THE MOST IMPORTANT SPACE)

⭐ THE MOST DANGEROUS SPACE in the neck - infection spreads from neck to diaphragm causing Descending Necrotizing Mediastinitis (DNM) - mortality can reach 40%. That's why it's called the "danger space."

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6. Prevertebral Space

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7. Masticator Space

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FASCIAL SPACES SUMMARY TABLE ⭐⭐

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QUICK-FIRE EXAM FACTS TABLE

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MNEMONICS

"I Prefer Pizza" → Investing → Pretracheal → Prevertebral

"I AM Very Nervous" → Internal carotid Artery Medially, Vagus Nerve posterior

"FAT" → Fat + Arterial (maxillary) + Trigeminal branches (lingual, inf. alveolar, auriculotemporal)

"CASH" → Carotid sheath + Accessory lymphatics + Sympathetic chain + Hypoglossal (CN XII) + CN IX

Submandibular → Sublingual → Parapharyngeal → Retropharyngeal → Mediastinum

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