SENSORY SYSTEM

Organs of Hearing, Equilibrium

and

Taste

Part 2Lecture for medical students

Department of histology,cytology and embryology KhNMU

Organ of Hearing and Equilibriumis located in the ear.

• Ear consists of:

• External ear – receives the sound waves • Middle ear – transmits vibrations of

tympanic membrane • Inner ear = labyrinth – contains receptors

for hearing and equlibrium

External, Middle, Inner Ear

External EarAuricle, external auditory meatus, tympanic membrane(individual) (ceruminous glands, earwax) ( fibrous membr. mucous inner)

Middle Earis the tympanic cavity in the temporal bone,

malleus, incus, stapes• contains ossicles:

Middle Ear

• is the air space • bony ossicles are connected with joints • malleus is connected with ear drum• stapes closes the oval window,

leading to the inner ear

Middle Ear is connected with nasopharynx by eustachian tube

Middle Ear. Auditory (Eustachian) tube

auditorytube

Inner ear = labyrinth is located in the temporal bone,

contains cochlea (organ of hearing),

vestibule and semicircular canals (organ of equilibrium)

Inner Ear Vestibule, semicircular canals, cochlea

Inner ear = Bony labyrinth

• is fillled with perilymph• (similar in ionic content to extracellular fluid)

• in it is located:

• Membranous labyrinth is filled with endolymph

• (similar to intracellular fluid)

Section of the inner

ear

Cochlea (C), vestibule (V), semicircular canal (SC).

C

V

SC

Cochlea

G

M

SM Sl

SV

ST

G

The bony cochlea has at its center the bony pillar - modiolus (M) containing spiral nerve ganglion (G).

Bony canal does 2-3 spiral turns around modiolus.

One section of the coclea

spiral canal

Vestibular membrane (VM) and basilar membrane (BM) divide canal into scala vestibuli (SV), cochlear duct (CD) and scala tympani (ST).

SVVM

CD

ST

BM

OC

S lig

Limbus

Sl n

m

SV

CD

ST

VM

BM

Coclear duct

is three angular

The lateral wall of the cochlear duct is formed by the stria vasculrias (vas), which produces endolymph.

OC Limbus S lig BM SL

VAS VM

Stria vascularis

Within the stria vascularis you can see capillaries (c), an unusual feature of this epithelium.

vas

c

One section of the spiral canal

Organ of Corti (OC) is on the basilar membrane.

It is peripheral part of organ of hearing

SVVM

CD

ST

BM

OC

S lig

Limbus

Sl n

m

Organ of Corti OC

On the osseous spiral lamina locates limbus from which extends the tectorial membrane (TM)

TM

OHC

Limbus

IHC

Organ of Corti OC

Under the tectorial membrane locate the three rows of outer hair cells (OHC) – columnar shaped. The single inner hair cell (IHC) is seen medial - pear shaped.

TM

OHC

Limbus

IHC

Organ of Corti OC

tmIHC

OHC

High mag.

At the centre of OC the pillar cells (pc) form tunnel (t).

Hair cells are supported by phalangeal cells (phc).

sl

pc t bsl

bm

phc

tectorial membrane

outer hair cells inner h.c.

outer phalanger cells inner ph.c.

pillar cells

Organ of Corti

G

M

CD

SV

ST

H

G

At the top of the cochlear canal thescala vestibuli connects with the scala tympani -

Helicotrema

HelicotremaSV

ST

CD

Scala vestibuli ends with the oval window, scala tympani with the round window,

located in between middle and inner ear

cochlear duct

oval window

round window

Spiral ganglion

G

The basal parts of hair cells synapse with dendrites of afferent n. cells of the spiralganglion, locating in the osseous spiral lamina, extending from the modiolus.

Mechanism of hearing: under sound tympanic membrane vibrates, ossicles push oval window.

Mechanism of hearing:

cochlear duct

perilymph moves through helicotrema to round window, calls movement of endolymph of cochlear duct and tectorial membrane which irritates hair cells. Dendrites of spiral ganglion cells take impulse.

G

M

SV

CD

SV

ST

H

G

The fibers of the basilar membrane are the shortest at the basal turns – percept high-frequency sounds.

- are the longest at the apical turns –percept low-frequency sounds.

Inner hair cells percept weak sounds, outer - intense sounds.

Pathology• Hearing loss: conductive

sensorineural

• Otosclerosis

Ogran of equilibrium

ACSemicircular canal

M

Utricle

Semicircular canals and vestibule. Perilymph, endolymph.

Within the ampullated end of the bony semicircular canal (bsc) is the ampullary crest (AC).

The flat macula (M) is in the utricle and saccule of the vestibule.

bsc

Vestibule

endolymph

Perilymph

Inner Ear Vestibule, semicircular canals, ampulla

Ampullary crest in the semicircular canals

C

E

N

The sensory epithelium (E) of the crest has kinocilia and stereocilia and sits on a mound of CT (ct) with nerves (N) leading from it.

The crest has a gelatinous cupula (C) resting on top of its receptor(E). Function:

sc AC

ct

Ampullary crest in the semicircular canals

• Movements of endolymph causes the deflection of the cupula and arisement of nerve impulse

• Cells are stimulated by movements of a head and angular accelerations

Macula of the utricle and

succule

Utricle with macula The macula (M) is a flattened collection of sensory hair cells sitting upon their supportive cells.

The kinocilium and stereocilia of each sensory cell are embedded in a gelatinous layer with calcified otoliths (arrow) – otolith membrane.

M

Macula of the utricle and succule

O

R

S

A higher magnification of the edge of the macula showing the otolithic layer (O) resting on a gelatinous layer (light arrow) atop the sensory receptor (R) and supporting cells (S).

Macula of the utricle and succule gives information about the force of gravity, linear acceleration and static position of a head – turning, inclination, or in the dark,

under the water(Pathology -Vertigo – the sence of rotation without equilibrium)

Otolith membrane

Hair cells

Supp.cells

Nerve endings

The membranous labyrinth develops from ectodermal first branchial grooves with contact of neural tube.

The vesicles are lined by pseudostraqtified epithelium

Differentiation of inner ear from otic vesicle

Bony labyrinth and connective tissue develop from mesenchyme. Nerve supply develops from neural

tube

Organ of Taste

• There are taste buds in the epithelium of the tonque papillae.

• There are 4 taste sensations: sweet, biter, acid and salty

Papillae of the tongue

• Tongue. Dorsal surface• Each papilla contains many oval taste buds (tb) on the lateral

surfaces.

• Each taste bud is opened with taste pore

cv

tbve

low

Taste bud

• Tongue, papilla with taste buds

There are 3 types of cells in taste bud: 1. basal are stem cells,

2. elongated supporting cells

3. actual taste cells.

Taste cells are also elongated cells whose microvilli extend into the taste pore which opens to the surface; these cells are contacted by sensory nerves from below.

high

med

fp

tb

Taste sensations

• Tip of the tongue - sensitive to sweet and salt

• Lateral edges - sensitive to sour

• Posterior portion - sensitive to bitter