Secondary Sentient Sense Organs

Organ of Hearing

Organ of Equilibrium

Organ of Taste

Lecturer – professor Boronikhina Tatiana Vladimirovna

Secondary sentient sense organs contain neuroepithelial receptor cells

Neuroepithelial cells form synapses with sensory neuron dendrites

Neuroepithelial cells interact with stimuli

generate nerve impulses

transmit impulses to sensory neurons

dendrite°°°°

Hearing Equilibrium Taste

Organ of hearing

receptor field is the spiral organ or organ of Corti is housed in the cochlea of the inner ear

Cochlea

Inner ear is the bony labyrinth in the temporal bone

Cochlea Vestibule

saccule utricle

Semicircular canals (3)

the temporal bone petrous portion

Bony labyrinth houses the membranous labyrinth

bony labyrinth is filled with perilymph membranous labyrinth is filled with endolymph

perilymph and endolymph communicate with CSF in the meningeal spaces

Inner ear receptor fields

hearing and equilibrium receptor fields

reside in the membranous labyrinth are bathed by endolymph

Cochlea

has a broad base and apex is a bony tube that spirals 2.5 times around

the modiolus

Modiolus

is osseous cochlea axis contains nerve fibers projects laterally into the spiral lamina

n. vestibulocochlearis (VIII)

Spiral lamina

consists of two lips upper lip periosteum thickens to form

the spiral limbus contains the spiral ganglion

limbus

spiral ganglion

upper lip

lower lip

Cochlea passages

Scala vestibuli Scala tympani

contain perilymph

Scala media (cochlear duct) contains endolymphSG

Sv

St

Sm

Cochlear perilymphatic passages

Scala vestibuli and scala tympani

communicate with each other

at the helicotrema

Scala vestibuli and scala tympani associate with the middle ear

Scala vestibuli ends at the oval window

is closed by the stapes stapes transmits vibrations to perilymph

Scala tympani

ends at the round window

is closed by connective tissue membrane

auditory ossicles

Scala media is the cochlear membranous labyrinth

Scala media walls vestibular membrane stria vascularis basilar membrane

Vestibular membrane

extends between the spiral limbus and the cochlear wall separates the scala media from the scala vestibuli consists of two layers of endothelial cells

vestibular membrane

Stria vascularis consists of a pseudostratified epithelium

is vascularized by capillaries secretes endolymph and creates its high positive potential rests on the spiral ligament – thickened periosteum of the cochlear bone

stria vascularis

spiral ligament

Basilar membrane

separates the cochlear duct from the scala tympani includes keratin-like fibrils – hearing cords

basilar membrane

upper surface contains the spiral organ

low surface is lined with endothelium

Basilar membrane fibrils vibrate with perilymph

are slender and long near the cochlea apex vibrate in resonance with low-frequency sounds

are thick and short near the cochlea base vibrate in resonance with high-frequency sounds

Spiral organ lies upon the basilar membrane

Phalangeal cells (supporting)

Hair cells (neuroepithelial) stereocilia (hair) are on the apical surface stereocilia are embeded in the tectorial membrane

Pillar cells (supporting) enclose the tunnel filled with endolymph

Tunnel divides the spiral organ in the two cell groups

Outer group is organized in three or more rows

outer phalangeal cells

outer hair cells

Inner group is organized in a single row

inner phalangeal cells

inner hair cells

inner hair cell

Spiral organ inner group cells

Inner phalangeal cells completely surround the hair cells

Inner hair cells are bulbous in shape have stereocilia arranged in a straight line

Spiral organ outer phalangeal cells

surround only the basal portion of hair cells

phalangeal processes form the cuticular plate

Spiral organ outer hair cells

are columnar in shape

have stereocilia arranged in a V-formation

Scanning electron micrograph of the hair cell stereocilia

inner hair cells

outer hair cells

Spiral organ histology

Spiral organ innervation

Sensory bipolar neurons are

in the spiral ganglion

Afferent fibers are sensory neuron dendrites pass in the tunnel form light synapses on the hair cells

Efferent fibers are the brain neuron axons pass in the tunnel form dark synapses on the hair cells

Spiral ganglion sensory neuron axons

form the cochlear division ofn. vestibulocochlearis (VIII)

pass in the modiolus

Hearing

sound waves transmit vibrations on timpanic membrane auditory

ossicles oval window perilymph basilar membrane fibrils

spiral organ

Hair cells are mechanoreceptors

nerve impulse generation results from stereocilia inclination

microenvironment - endolymph tectorial membrane

dendrite

°°°°°°°°dendrite

Hair cell differentiation

Hair cells perceive in the cochlea base – high-frequency sounds in the cochlea apex – low-frequency sounds

outer hair cells – high intensity sounds inner hair cells – low intensity sounds

Organ of equilibrium or vestibular apparatus

receptor fields are the maculae and the cristae are housed in the vestibule and canals of the inner ear

vestibule and semicircular canals

Equilibrium receptor field localization

maculae (2) are in the saccule and utricle cristae (3) are in the ampullae of the semicircular canals

Vestibular macula and crista ampullaris

crista in the semicircular

canal ampulla

macula in the saccule

Macula structure

supporting cells neuroepithelial hair cells otolithic membrane with otoliths

Crista structure

supporting cells neuroepithelial hair cells cupula

Equilibrium neuroepithelial hair cells

are innervated by afferent

and efferent fibers

apical surface contains

50-100 stereocilia and

a single kinocilium

Equilibrium hair cell types

Type I cells are bulbar in shape basal portion surrounded by

a cap-shaped nerve ending

Type II cells are columnar in shape basal portion has bouton nerve ending

Vestibular apparatus innervation

sensory neuron bodies are housed

in the vestibular ganglion

their dendrites innervate hair cells of

maculae and cristae

their axons form vestibular division of

n. vestibulocochlearis (VIII)

Equilibrium hair cells are mechanoreceptors

nerve impulse generation results from stereocilia inclination

dendrites

microenvironment – endolymph cupula otolithic membrane with otoliths

dendrites

dendrite°°°°

Equilibrium hair cell stereocilium inclination

towards the kinocilium away from the kinocilium

cells become excited cells become inhibited

Equilibrium hair cell differentiation

Maculae are sensors of linear accelerations gravity vibrations

Cristae are sensors of angular accelerations

Organ of taste

receptor field consists of the taste bauds taste buds are located on the lateral surface

of lingual papilae

tongue dorsal surface

Lingual papillae are projections of the mucosaon the tongue dorsal surface

Papilla structure: stratified squamous partially keratinized epithelium a central core (primary papilla) – LCT

taste buds occupy the epithelium of the lateral papilla surface

taste bud is an ovoid

intraepithelial structure

Lingual papilla types

filiform papillae are covered by keratinized epithelium

and lack the taste buds

Taste buds are epithelial structures

epithelial cells are arranged around the taste pit taste pore leads to the taste pit

taste pore

Taste bud morphology

taste pore

photomicrograph

electron micrograph

Taste bud cells

supporting cells neuroepithelial cells basal cells (stem cells)

Taste bud neuroepithelial cells are chemoreceptors

Apical cell surface possesses microvilli pass through the taste pore are bathed by saliva contain membrane chemoreceptors for taste molecules

microenvironment - saliva

Taste bud innervation

Neuroepithelial cell basal portion synapses with

afferent and efferent nerve fibres

• chorda tympani of n. facialis (VII)

• n. glossopharyngeus (IX)

• from taste buds of the epiglotis n. loryngeus superior of n. vagus (X)

Sensory neurons of the taste analyzer

are in sensory ganglia associated

with the cranial nerves:

• n. facialis

• n. glossopharyngeus

• n. vagus

Taste bud neuroepithelial cell differentiation

Perception of the taste sensations

bitter

sour (acid)

salt

sweet

Thank you for attention!