histology of the olfactory and auditory senses

olfactory sense: nasal cavity

Three main parts

• Cutaneous region

• Respiratory region - Vomeronasal Organ

• Olfactory region

Cutaneous region (nasal vestibule)

Cutaneous region (nasal vestibule)

• Rostral region – keratinised stratified squamous epithelium

• Mid vestibule – thinner, non-keratinsed stratified squamous epithelium

• Caudal region – transitional zone (approaching respiratory epithelium) – varies from stratified cuboidal to non-ciliated pseudostratified columnar

respiratory region

• Caudal 2/3 of the nasal cavity

• Respiratory epithelium = ciliated pseudostratified columnar epithelium

• Contains several cell types (e.g. ciliated cells, secretory cells, brush cells, basal cells etc.)

vomeronasal organ

• Vomeronasal organ (VNO) – located in ventral portion of nasal septum

Bilateral blind-ended tubular organ

• Internal epithelial duct (vomeronasal duct)

• Middle propria submucosa

• External cartilaginous support

• Rostrally – incisive duct – connects the nasal cavity with the oral cavity (except horses – blind ended ventrally)

Lateral region of VNO

• Stratified cuboidal – rostral –incisive duct

• Ciliated pseudostratified columnar – caudal

Medial region of VNO - more important in detection of pheromones

• Pseudostratified columnar epithelium has neurosensory, sustentacular, and basal cells

olfactory epithelium

Olfactory region of nasal cavity

• Dorsocaudal portion of the nasal cavity

• Thicker epithelium, more tubular glands and many nerve fibres compared to respiratory region

Olfactory epithelium = ciliated pseudostratified columnar cells with:

• Neurosensory olfactory cells (bipolar neurons) – connect to olfactory bulb via olfactory nerve (CN I) passing through cribiform plate of ethmoid bone

• Support cells / sustentacular cells (columnar cells with narrow base and wide apical portion)

Olfactory glands

• Located in the lamina propria / submucosa, contain pigmented cells (see image)

• Squamous cells line the ducts to the epithelial surface

• Watery secretion to aid olfaction (snot)

Olfactory mucosa has very high levels of cytochrome P450 mono-oxygenase

• Primary site for chemically induced nasal tumours

gustatory sense - tongue

Oral mucosa

• Stratified squamous epithelium

Dorsal surface of tongue has papillae

• Filiform

• Circumvallate

• Fungiform

• Foliate

Taste buds located in circumvallate, fungiform and foliate papillae

• Contain specialised taste cells

Filiform papillae responsible for touch