2 Anatomy Challenge 2026 Review

Anatomy Challenge 2026

Session 2: Taste and Smell

Content Overview

• Themes:
    - Anatomy
    - Olfactory pathways
    - Gustatory pathways
    - Histology

1. Anatomy

1.1 Nasal Cavity

• Separated by nasal septum
• Hard palate separates nasal cavity from oral cavity
• Superior to nasal cavity: Cranial cavity
• Posterior to nasal cavities: Nasopharynx

1.2 Bones of the Nasal Cavity

• Mainly made up of cartilage
• Ethmoid Bone:
    - Constitutes part of medial wall, superior surface, lateral wall, and ethmoidal air cells
    - Cribriform Plate:
      - Where olfactory nerves pass through small perforations
• Relations of ethmoid bone:
    1. Anterior inferior: cartilage
    2. Posterior inferior: vomer
    3. Anterior: Nasal bone, frontal bone
    4. Posterior: sphenoid bone
    5. Posterolateral: maxillary bone
    - Cartilage components:
      1. Septal cartilage
      2. Major alar cartilage
      3. Minor alar cartilage
• Floor of the Nasal Cavity:
    - Palatine bone
    - Maxillary bone

1.3 Blood Supply of Nasal Cavities

• Blood supply:
    - From external carotid artery (ECA): branches of facial (lateral nasal, superior labial artery) and maxillary artery (sphenopalatine, GP artery)
    - From internal carotid artery (ICA): branches of ophthalmic artery -> anterior ethmoidal artery

• Venous Drainage:
    - Follows path of maxillary and facial arteries
      - Pterygoid venous plexus
      - Facial Vein
      - Emissary vein anterior to crista galli via foramen cecum → drains to superior sagittal sinus (SSS)

• Clinical Correlation:
    - Infections that spread to PVP can affect the cavernous sinus in the cranial cavity, leading to cerebral venous sinus thrombosis (CVST).

1.4 Innervation of Nasal Cavity

• Smell: Olfactory Nerve (CN I)
• General Sensation: Trigeminal Nerve (CN V)
    - Anterior: V1 (anterior/posterior ethmoidal -> nasociliary -> V1)
    - Posterior: V2 (nasopalatine)
• Glands: Parasympathetic Fibres in Facial Nerve (CN VII) via the greater petrosal nerve - particularly to the lacrimal gland
• Sympathetic: Sympathetic chain -> Superior cervical ganglion

1.5 Spaces Within the Nasal Cavity

• Concha/Turbinates: extend from lateral walls
    - Recesses: beneath these concha = meatus

1.6 Paranasal Sinuses

• Named according to the bone in which they are found:
    - Frontal sinus (drains via frontonasal duct)
    - Ethmoidal cells
    - Sphenoidal sinus
    - Maxillary sinuses

1.7 Clinical Significance of Sinuses

• Innervation:
    - Frontal: V1
    - Ethmoidal:
      - V1 → nasociliary -> anterior/posterior ethmoidal
      - V2 -> orbital branches from pterygopalatine ganglion
    - Maxillary: V2 (infraorbital and alveolar branches)
    - Sphenoidal:
      - V1 (P ethmoidal branch)
      - V2 (orbital branch)
• Important to know where they empty into:
    1. Frontal -> anterior ethmoidal cells -> semilunar hiatus in the middle meatus
    2. Maxillary: different from frontal and anterior ethmoidal
    3. Sphenoidal: drains into sphenoethmoidal recess above the superior concha

1.8 Holes of the Nasal Cavity

• Choanae
• Cribriform plate
• Sphenopalatine foramen (contains sphenopalatine artery, nasopalatine nerve)
• Incisive canal (contains nasopalatine nerve and greater palatine artery)

2. Olfactory Pathway

2.1 General Overview

• Stages: Nasal Epithelium, Olfactory bulb, Olfactory tract, Primary olfactory cortex (Medial Olfactory area)

2.2 Olfactory Nerves

• Composed of bipolar cells and supporting cells
• Innervate nasal epithelium, trapping odor particles
• Travel through holes in the cribriform plate to the olfactory bulb
• Binding of odor particles activates GPCR leading to:
    - $ext{Na}^{+}, ext{Ca}^{2+}$ influx and Cl efflux → depolarisation

2.3 Within the Olfactory Bulb

• Olfactory nerve fibers synapse with mitral cells
• Second order neurons pass posteriorly into olfactory tract
• Regulated by granule cells secreting GABA, ensuring only excitatory impulses reach cerebral cortex

2.4 Olfactory Tract

• Lies on the inferior surface of the frontal lobe
• Upon reaching the anterior piriform area, it splits into 2 striae:
    - Lateral olfactory stria → Uncus (deep medial part of temporal lobe)
    - Medial olfactory stria → subcallosal gyrus and orbitofrontal cortex (associated with emotion)
• Most fibers are ipsilateral, with some contralateral projections

2.5 Within Uncus, Branches to:

1. Piriform cortex of temporal lobe (primary olfactory cortex)
2. Hippocampal gyrus
3. Amygdaloid complex
4. Entorhinal complex

2.6 Causes of Anosmia (Loss of Smell)

1. Infections (e.g. upper respiratory tract infections)
2. Sinus infections (leading to mucous thickening)
3. Olfactory groove meningioma (just superior to the cribriform plate in the anterior cranial fossa)
4. Trauma (e.g. cribriform plate fracture leading to CSF rhinorrhoea)
5. Neurodegenerative diseases

3. Oral Cavity

3.1 Orientation

• Lateral Wall: Cheek
• Roof: Hard palate
• Floor: Tongue and other soft tissues
• Communicates posteriorly with oropharynx, separated by oropharyngeal isthmus

3.2 Oral Cavity Subdivisions

• Oral vestibule (between the cheeks and gums, and between the lips and gums)
• Oral cavity proper (space in mouth behind rows of teeth)

3.3 Relevant Anatomy

• Key Bones Involved:
    - Maxilla, Palatine, Temporal, Mandible, Sphenoid, Hyoid
• Key Structures:
    - Frenulum of upper lip, Hard palate, Soft palate, Uvula, Palatine tonsil, Dorsum of tongue

3.4 Oral Cavity (Histological Features)

• Contains non-keratinized stratified squamous epithelium (NKSSE) to withstand wear and tear from food grinding.

3.5 Bones & Muscles Involved in Mastication

• Mandible structure includes:
    - Ramus (condylar and coronoid processes, mandibular notch)
    - Body (mental foramen)
• Movements include:
    - Protrusion, Retraction, Depression, and Elevation

4. Muscles of Mastication

4.1 Key Muscles

• Masseter
• Temporalis
• Medial pterygoid
• Lateral pterygoid
• Innervation: predominantly by Mandibular Nerve (CN V3)

4.2 Functions of Muscles

• Masseter: Elevation of mandible
• Temporalis: Elevation and retraction
• Medial Pterygoid: Elevation and side-to-side movement
• Lateral Pterygoid: Main muscle in depression and protraction

4.3 Clinical Relevance of Pterygoids

• In case of CN V3 palsy, jaw swings to the affected side due to unilateral contraction of the contralateral pterygoids.

4.4 Temporomandibular Joint (TMJ)

• Formation:
    - Condylar process of mandible
    - Mandibular fossa of temporal bone

• Features:
    - Synovial joint
    - Articular disc divides TMJ into upper (gliding) and lower (rotation) compartments

• Innervation: Auriculotemporal nerve (branch of CN V3)

4.5 Alterations at TMJ

• Commonly experience anterior dislocations of the condylar process.
• Resolving Technique: Pressing down on the molars to guide back the mandibular condyle into fossa.

5. Pharynx

5.1 Overview

• Extends from cranial base to inferior border of C6 vertebra, communicating with nasal and oral cavities.
• Divided into three parts:
    1. Nasopharynx
    2. Oropharynx
    3. Laryngopharynx

5.2 Muscles of the Pharynx

• Superior constrictor
• Middle constrictor
• Inferior constrictor (subdivided into thyropharyngeus and cricopharyngeus)

5.3 Nerve Innervation

• Primarily by CN IX and CN X forming the pharyngeal plexus providing both motor and sensory innervation.

6. Histology of Glands

6.1 Gland Types

• Parotid Gland: Entirely serous, rich in enzymes.
• Submandibular Gland: Mix of serous and mucous.
• Sublingual Gland: Primarily mucous.

6.2 Innervation and Blood Supply of Salivary Glands

• Parasympathetic Origin:
    - Parotid: glossopharyngeal nerve (CN IX)
    - Submandibular & Sublingual: facial nerve (CN VII)

6.3 Clinical Conditions Related to Glands

• Frey’s Syndrome: Damage to auriculotemporal nerve causes gustatory sweating.

6.4 Teeth and Gingivae

• Comprised of incisors, canines, premolars, and molars.
• Innervated by branches of V2 for upper teeth and V3 for lower teeth.

References

• Student's Gray's
• NinjaNerd
• Teach Me Anatomy