Sense Organs -

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Sense Organs
1. Sense organs – classification
2. Sensory receptors
3. Gustatory apparatus
4. Olfactory apparatus
5. Visual apparatus – the eye. Visual pathway
6. Vestibulocochlear apparatus – the ear.
Auditory and vestibular pathways
Sense organs
Human sense organs
five senses:
specialized cells – receptors for specific stimuli:
confined to the head region
receptors are not free endings of sensory neurons
Five Senses Icons
Prof. Dr. Nikolai Lazarov
Sense organs
Sense of touch
four kinds of touch sensations:
light touch (contact)
Prof. Dr. Nikolai Lazarov
Sense organs
Sensory receptors – classification
3 main groups – Sherrington, 1906:
by sensory modality:
baroreceptors – respond to pressure
chemoreceptors – chemical stimuli
C.S. Sherrington
mechanoreceptors – mechanical stress
nociceptors – pain perception
thermoreceptors – temperature (heat, cold or both)
by location:
cutaneous receptors
muscle spindles
by morphology:
free nerve endings
encapsulated receptors
Prof. Dr. Nikolai Lazarov
Sense organs
Gustatory apparatus
peripheral gustatory organs:
taste buds
(gustatory caliculi) – 2000-9000:
vallate papillae – most numerous
plentiful in the posterior ⅓ of the tongue
fungiform papillae
soft palate, epiglottis and pharynx
no structural difference among taste buds:
gustatory (taste) pore – 2-3 µm
collection of 50-100 epithelial cells
contain long microvilli
extend through a taste pore
contain two types of
gustatory receptor cells
• with and without dense-cored granules
supporting (non-sensory) cells
basal cells – undifferentiated,
form new receptor cells every 10-14 days
Prof. Dr. Nikolai Lazarov
NB: about 50 fibers innervate a single taste bud!
Sense organs
Gustatory apparatus
traditionally four basic qualities
of taste:
fifth basic taste
umami (“deliciousness”)
deliciousness –
non-salty sensations evoked by some
amino acids – glutamate
Prof. Dr. Nikolai Lazarov
NB: about 50 fibers innervate a single taste bud!
Sense organs
Olfactory apparatus
the sense of smell (olfaction):
receptors are part of the olfactory epithelium
olfactory mucosa – 3 cell types:
cell bodies of olfactory receptor cells
(40 million in human olfactory epithelium)
supporting cells – columnar cells
basal cells – form new receptor neurons (4-8 weeks)
olfactory (Bowman’s) glands – in lamina propria
NB: The smell receptors are sensitive to seven types of sensation:
Prof. Dr. Nikolai Lazarov camphor, musk, flower, mint, ether, acrid, or putrid! 7
Sense organs
Olfactory neuroepithelium
non-myelinated axons of the
olfactory epithelium:
gather into 18-20 bundles –
filaments of the olfactory nerve (CNI)
pass through the cribriform plate of the
ethmoid bone
attach to the olfactory bulbs
Prof. Dr. Nikolai Lazarov
Sense organs
Olfactory bulb
transmits smell information
from the nose to the brain:
supported and protected by the cribriform plate
multi-layered cellular architecture:
glomerular layer
external plexiform layer
mitral cell layer
internal plexiform layer
granule cell layer
olfactory bulb – synaptic glomeruli:
nucleus of termination of cranial nerve I
mitral, granule and periglomerular cells
initial part of rhinencephalon
Prof. Dr. Nikolai Lazarov
Sense organs
Olfactory tract
consists of:
axons of the mitral and tufted cells
centrifugal axons from the opposite bulb
anterior olfactory nucleus:
medium-sized multipolar neurons
their axons continue into the olfactory
striae and trigone
olfactory striae:
lateral olfactory stria limen insulae
medial olfactory stria diagonal band of Broca
anterior perforate substance
olfactory tubercle – reduced in man
Prof. Dr. Nikolai Lazarov
Sense organs
Olfactory cortex (piriform lobe)
primary olfactory cortex:
prepiriform cortex – lateral olfactory gyrus gyrus ambiens
periamygdaloid area – lateral olfactory stria gyrus semilunaris
secondary olfactory cortex:
entorhinal area,
area cranial part of parahippocampal gyrus
Prof. Dr. Nikolai Lazarov
Human eye
Human visual organs
The eye – some amazing facts:
the eyeball of a human weighs approximately 28 g;
although only 1/6th of it is exposed to the outside
world, about half of our brain is involved in the seeing
process – humans are thus very much visual animals!
the only part of our body that can function at 100%
ability at any moment, day or night, without rest;
most complex organs we possess – composed of
more than 2 million working parts;
the external muscles that move the eyes are the
strongest muscles in the human body for the job that
they have to do. They are 100 times more powerful
than they need to be!
the retina contains 120 million rods for "night vision",
and 8 million cones that are colour sensitive and
work best under daylight conditions;
contributes towards 85% of our total knowledge –
can process 36,000 bits of information every hour.
Prof. Dr. Nikolai Lazarov
NB: Human eye: a window to the outside world! 12
Human eye
Anatomy of the eye
The eye – Lat. oculus, Gr. ophthalmos:
eyeball – coats
ocular fibrous tunic
• sclera
• cornea
vascular tunic (uveal tract)
• choroid
• ciliary body
• iris
ocular refractive media
aqueous chamber&humor
vitreous body
accessory structures
extraocular muscles
eyebrows and eyelids
lacrimal apparatus
Prof. Dr. Nikolai Lazarov
Human eye
Eyeball – the peripheral organ of sight:
embedded in the fat of the orbit
enveloped by a fascial sheath (capsule of Tenon)
anterior and posterior poles optic (visual) axis
approximately spherical “ball” – dimensions:
vertical diameter – 23.5 mm
anterioposterior diameter – 24 mm (17.5 mm at birth)
three coats (tunics):
fibrous tunic
vascular, pigmented tunic
nervous layer, retina
content – ocular refractive media
Prof. Dr. Nikolai Lazarov
Human eye
Ocular fibrous tunic
Sclera (tunica sclera) – Gr. skleros, hard:
the outer layer of the eyeball – “the white of the eye”
the posterior five-sixths
of the connective tissue coat of the globe
firm protective membrane maintains the shape of the globe
smooth, provides an attachment
for the extraocular muscle insertions
perforated by many nerves and vessels
lamina cribrosa, sinus venosus sclerae (canal of Schlemm)
opaque with varying thickness:
1 mm at the posterior pole
0.3 mm just behind muscle insertions
fibrous connective tissue – four layers:
lamina fusca
Prof. Dr. Nikolai Lazarov
Human eye
Ocular fibrous tunic
Cornea – “kerat-“, Gr. κέρας, horn
projecting and transparent front part of the eye
refracts (together with the lens) light (~ 43 dioptres)
the anterior one-sixths
of the connective tissue coat of the globe
dense with varying thickness:
~1.2 mm round its periphery
0.5-0.6 mm at its centre
non-vascular structure surface ectodermal origin
richly innervated corneal (blink) reflex
structurally – five layers:
corneal epithelium
anterior limiting membrane (of Bowman)
substantia propria (corneal stroma)
posterior limiting membrane (of Descemet)
endothelium of the anterior chamber
NB: The mnemonic "EBSDEin", read as "Ebstein"
Prof. Dr. Nikolai Lazarov
can be used to remember the layers in sequence!
Human eye
Vascular tunic (uveal tract)
Choroid – ⅔ of the uveal tract surface ~ 0.5 mm in humans:
thin, highly vascular coat,
coat dark brown or chocolate
dense capillary plexus – provides oxygen and
nourishment to the outer layers of the retina
suprachoroid lamina – ~ 30 µm thick
choroid proper:
• vascular lamina
• capillary lamina (choroidocapillaris)
• basal lamina (membrane of Bruch)
NB: uva, Lat. grape
Prof. Dr. Nikolai Lazarov
Human eye
Vascular tunic (uveal tract)
Ciliary body – Lat. cilium, eyelid:
the circumferential tissue inside the eye
triangular in horizontal section
coated by a double layer, the ciliary epithelium
superficial lamina – columnar cells
deep layer – cuboidal cells with pigment granules
ciliary ring, orbiculus ciliaris (pars plana) – 3.5-4 mm
corona ciliaris (pars plicata)
• 70-80 ciliary processes aqueous humor
• ciliary plicae
ciliary muscle zonule of Zinn lens (suspensory ligament)
• meridional (muscle of Brücke)
• radial (oblique) fibers
• circular (muscle of Müller)
aqueous humor production glaucoma
production and maintenance
of the lens zonules
Prof. Dr. Nikolai Lazarov
Human eye
Vascular tunic (uveal tract)
Iris – Greek goddess of the rainbow:
opaque, pigmented diaphragm
two major regions:
pupillary zone pupil
• a sphincter muscle (sphincter pupillae)
• a set of dilator muscles (dilator pupillae)
ciliary zone ciliary body
iridocorneal angle Fontana’s spaces
microscopic structure:
pigmented fibrovascular tissue (stroma)
pigmented epithelial cells
control of the diameter and size of the pupil
the amount of light reaching the retina
responsible for
the “eye color"
Prof. Dr. Nikolai Lazarov
Iris eye recognition
Human eye
Retina – Lat. rete, net:
approx. 72% of the eyeball internal surface
neuronal, light-sensitive layer of the eyeball
two principal parts – ora serrata:
anterior “blind” part
• ciliary part
• iridial part
posterior optic part
• macula lutea fovea centralis
• optic disc – “blind spot”
structure – two major layers:
outer stratum pigmentosum pigment epithelium
inner stratum nervosum
the same function as the film in a camera
• receives the image seen through our eye
• converts a light signal into a neural signal
("signal transduction")
• transmits this image through the optical nerve
to the brain
Prof. Dr. Nikolai Lazarov
Human eye
Structure of the retina
three layers of retinal neurons
two layers of synapses
retinal pigment epithelium
4-6 million hexagonal cells – fuscin
neural part of retina – 5 cell types:
neuroepithelial (photoreceptor) cells
– in stratum neuroepitheliale
bipolar cells
– in stratum ganglionare retinae
ganglion cells
– in stratum ganglionare nervi optici
horizontal cells – GABAergic interneurons
– in stratum plexiforme externum
amacrine cells
– in stratum plexiforme internum
Prof. Dr. Nikolai Lazarov
Human eye
Photoreceptor cells
neurons capable of phototransduction
classic photoreceptors – two main classes:
rods – 75 to 150 million
adapted for low light "night vision“
contain rhodopsin
cones – ~ 7 million
function well in bright light “daylight”
detect colors – three different types
• responding to short (blue)
blue light
• responding to medium (green)
green light
• responding to long (yellow-red)
red light
photosensitive ganglion cells –
1-2% of all (1.3 million) ganglion cells in humans
the same basic structure:
cell body with nucleus in outer nuclear layer
outer segment (discs), stalk (cilium), inner segment
(mitochondria) in photoreceptor layer
Prof. Dr. Nikolai Lazarov
Human eye
Bipolar cells
transmit signals from the photoreceptors to the ganglion cells – interneurons
three types bipolar neurons:
rod bipolar cells
midget (cone) cells
flat bipolar cells
common bipolar cell structure:
a central cell body in inner nuclear layer
outer process
makes synapse with either rods or cones
inner process
accepts synapses from horizontal cells
direct innervation of the photoreceptor above it,
either through a
metabotropic (ON)
or ionotropic (OFF)
Prof. Dr. Nikolai Lazarov
Human eye
Ganglion cells
receive visual information from photoreceptors
via bipolar and amacrine cells
transmit visual information from retina to several regions in brain
~ 1.2 to 1.5 million retinal ganglion cells in the human retina
five main classes of ganglion neurons:
midget ganglion cells – monosynaptic; A cells
parasol (magnocellular; B cells)
polysynaptic (rod and flat) ganglion cells
photosensitive ganglion cells
a central cell body in ganglionic cell layer
inner process
makes synapse with either bipolar or amacrine cells
outer process – long axon extending into the brain
forms the optic nerve
Prof. Dr. Nikolai Lazarov
Human eye
Macular area
macula lutea (Lat.macula, "spot" + lutea, "yellow"):
oval-shaped highly pigmented yellow spot
with diameter of around 5 mm
centre of the macula is the foveal pit, fovea centralis
the fovea contains the largest concentration of
cones in the eye allows for the sharpest vision
optic disk (papilla):
location where ganglion cell axons exit the eye
to form the optic nerve
placed 3 to 4 mm to the nasal side of the fovea
vertical oval with a central depression, optic cup
contains no light sensitive receptor cells –
“the blind spot”
Prof. Dr. Nikolai Lazarov
Human eye
Inverted retina
‘inverted’ arrangement of the vertebrate retina:
the light sensing cells sit at the back side
of the retina
light has to pass through several
inner layers of its neural apparatus
before reaching the photoreceptors
an image of the external environment
is thus focused on the retina which
transduces light into neural signals
neural impulses pass back from
the photoreceptor layer through
the ganlionic cell layer to the optic nerve
opposite directions of light
and nerve impulse!
Prof. Dr. Nikolai Lazarov
Human eye
Ocular refractive media
Ocular refractive media:
aqueous chambers –
anterior and posterior
aqueous humor
vitreous chamber
vitreous body
Prof. Dr. Nikolai Lazarov
Human eye
Aqueous chambers and humor
aqueous chambers:
anterior – between the posterior
surface of the cornea and the iris
posterior – between the iris and
the front face of the vitreous body
aqueous humor:
provides nutrients to the lens
and corneal endothelium
maintains the convex shape of the cornea
carries away waste products from metabolism
water – 99%, glucose, amino acids
ions: HCO3-; Cl-; Na+; K+; Ca2+; PO43 proteins: albumin, β-globulins
production and drainage:
secreted into posterior chamber by the ciliary body
drains into Schlemm’s canal glaucoma
Prof. Dr. Nikolai Lazarov
Human eye
Vitreous chamber and body
vitreous chamber – ~4/5 of the eyeball
the gel in vitreous chamber is stagnant
vitreous body:
transparent, colourless, gelatinous mass
produced by certain retinal cells
vitreous (hyaloid) membrane peripherally
hyaloid canal centrally
very few cells – phagocytes and hyalocytes
contains no blood vessels
water – 99%
some salts
little glycoprotein and hyaluronate
vitrosin (a type of collagen)
refracting media
helps to keep the retina in place
Prof. Dr. Nikolai Lazarov
Human eye
transparent, biconvex body
anterior and posterior poles
equator and capsule
soft cortical substance
firm, central part, nucleus
contains no true elastic tissue
lens fibers (cells) – superficial and deep
helps to refract light to be focused on the retina
contributes about 15-18 dioptres (⅓)
to the total dioptric power
Prof. Dr. Nikolai Lazarov
Human eye
Accessory visual apparatus
Extraocular muscles
Eyebrows and eyelids
Lacrimal apparatus
Prof. Dr. Nikolai Lazarov
Human eye
Extraocular muscles
extraocular muscles:
elevator of the upper eyelid
superior and inferior tarsal muscles
orbital muscle
four recti muscles – annular tendon
superior rectus
inferior rectus
lateral rectus
medial rectus
two obliqui muscles
obliquus superior
obliquus inferior
Prof. Dr. Nikolai Lazarov
Human eye
two arched eminences of skin
numerous short, thick hairs
fibers of orbicularis oculi, corrugator and frontal
belly of occipitofrontalis muscles
protect the eye – prevent moisture, mostly salty
sweat and rain, from flowing into the eye
important to human communication and facial
Prof. Dr. Nikolai Lazarov
Human eye
eyelids, palpebrae:
thin, movable folds
that covers and protects eyes
upper eylid is larger and more movable
palpebral fissure
lateral angle of the eye (lateral canthus)
medial angle (medial canthus)
lacus lacrimalis
lacrimal caruncle – small, reddish, conical body
lacrimal papilla
punctum lacrimale
eyelashes – short, thick curved hairs
ciliary glands (of Moll)
Meibomian (tarsal) glands
Prof. Dr. Nikolai Lazarov
Human eye
transparent mucous membrane
consisting of cells and underlying
basement membrane
over the inner surface of the eyelids
over the front part of the sclera and cornea
palpebral conjunctiva
highly vascular
adherent to the tarsi
conjunctival fornix
ocular conjunctiva
thin, transparent
loosely connected to the eyelid
continues as the corneal epithelium
semilunar fold of conjunctiva
Prof. Dr. Nikolai Lazarov
Human eye
Human lacrimal apparatus
lacrimal gland
lacrimal canaliculi
lacrimal sac
nasolacrimal (tear) duct
Prof. Dr. Nikolai Lazarov
Human eye
Lacrimal gland
almond-like, two parts by the aponeurosis
of the levator palpebrae superioris muscle:
larger upper orbital part – in fossa lacrimalis
smaller lower palpebral part,
part ⅓ of the orbital
small accessory lacrimal glands
more numerous in the upper lid
in and near the conjunctival fornices
~12 ducts
into the superior conjunctival fornix
secretes a complex fluid, the tears
Prof. Dr. Nikolai Lazarov
Human eye
Lacrimal pathways
lacrimal canaliculi – superior and inferior:
~10 mm in length
dilated into ampullae
commence at the puncta lacrimalia
lacrimal sac:
upper blind end of the nasolacrimal duct
connect it with the lacrimal canaliculi
~12 mm in length, lodged in a fossa
nasolacrimal (tear) duct:
membranous canal; ~18 mm long
drains into the inferior nasal meatus
Structure of the tear film
Prof. Dr. Nikolai Lazarov
Obstruction of the lacrimal drainage
Prof. Dr. Nikolai Lazarov
Human ear
Anatomy of the ear
The peripheral auditory apparatus, the ear,
auris, Gr. us, ωτο = genitive for ear:
external (outer) ear,
ear auris externa
auricle (pinna)
external auditory meatus (ear canal)
middle ear,
ear auris media
tympanic membrane (ear drum)
tympanic cavity
auditory (Eustachian) tube
auditory ossicles
internal (inner) ear,
ear auris interna
auditory and vestibular portions:
osseous labyrinth
membranous labyrinth
Prof. Dr. Nikolai Lazarov
NB: Human ear: the organ of hearing and balance 40
Human ear
External ear, auris externa
the first structure of the sound conduction apparatus – serves to
collect and conduct the air vibrations
to the tympanic membrane
auricle (pinna) – auricula
external acoustic meatus
(ear canal)
– meatus acusticus
Prof. Dr. Nikolai Lazarov
Human ear
Auricle, auricula
pinna – Lat. pinna, a feather:
thin skin with fine hairs
elastic fibrocartilage
lobule of auricle
auricular tubercle
(of Darwin)
ligaments of auricle,
collects and funnels the sound waves
into the meatus
extrinsic and intrinsic,
auricular muscles –
extrinsic and intrinsic,
n. facialis
Prof. Dr. Nikolai Lazarov
Human ear
External acoustic meatus,
meatus acusticus externus
external auditory meatus (ear canal),
conducts the sound waves to the ear drum
Lat. meo, a passage
length ~ 2.5 cm; 7 mm in diameter
S-shaped curve (140°)
structure – two parts:
cartilaginous part – outer ⅓ (~8 mm long),
cartilago meatus acustici
osseous part – inner ⅔ (~16 mm long),
meatus acusticus externus
thin skin; the thicker cerumen-producing ear canal
skin has fine hairs, tragi
sebaceous glands in the hair follicles
ceruminous glands ear wax, cerumen
NB: The ear wax assists in cleaning and lubrication, and also
Prof. Dr. Nikolai Lazarov provides some protection from bacteria, fungi, and insects!
Human ear
Middle ear, auris media
a structure of the sound conduction apparatus
primary functions:
transmission of the vibrations of the
tympanic membrane to the internal ear
efficient transfer of acoustic energy
from compression waves in air to fluid –
membrane waves within the cochlea
tympanic membrane –
membrana tympani (tympanica)
tympanic cavity –
cavitas (cavum) tympani
auditory (eustachian) tube –
tuba auditiva
auditory ossicles –
ossicula auditus
Prof. Dr. Nikolai Lazarov
Human ear
Tympanic membrane, membrana tympani
ear drum – thin, semi-transparent,
transparent nearly oval in form:
longest diameter d=10-11 mm
shortest diameter d=8-9 mm
pars flaccida –
Schrapnell’s membrane
pars tensa umbo
cuticular layer
fibrous layer –
absent in pars flaccida:
radiate fibers
circular fibers
mucous layer
Prof. Dr. Nikolai Lazarov
Human ear
Tympanic cavity, cavum tympani
volume – 1.5 cm3, air-filled
vertical – 15 mm
transverse – 6-4-2 mm
antero-posterior – 15 mm
two parts:
tympanic cavity proper
epitympanic recess
three clinically important levels:
Prof. Dr. Nikolai Lazarov
Human ear
Auditory tube, tuba auditiva
Eustachian (pharyngotympanic) tube,
links the pharynx to the middle ear, ~3.5 cm long:
ostium tympanicum tubae
ostium pharyngeum } auditivae
two parts:
cartilaginous part - ⅔ (cartilago tubae auditivae) – 24 mm
bony part - ⅓ (in semicanalis tubae auditivae) – 12 mm
isthmus tubae auditivae
mucous membrane – ciliated columnar epithelium
Prof. Dr. Nikolai Lazarov
Human ear
Auditory ossicles, ossicula auditus
malleus – Lat. = mallet, hammer;
hammer the largest, 8-9 mm long:
head, caput mallei
neck, collum mallei
handle, manubrium mallei
anterior and lateral processes
incus – Lat. = anvil:
body, corpus incudis
long process, crus longum
lenticular process
short process, crus breve
stapes – Lat. = stirrup:
head, caput stapedis
limbs (crura)
base, basis stapedis
m. tensor tympani (Eustachii)
m. stapedius
ligg. et artt. ossiculorum auditus
Prof. Dr. Nikolai Lazarov
Human ear
Internal ear, auris interna
location – in pars petrosa ossis temporalis
main functions:
converts sound waves into nerve impulses
registers changes in equilibrium
osseous labyrinth,
labyrinthus osseus
membranous labyrinth,
labyrinthus membranaceus
Prof. Dr. Nikolai Lazarov
Human ear
Osseous labyrinth, labyrinthus osseus
vestibule vestibulum
three semicircular canals,
canales semicirculares:
canalis semicircularis lateralis
canalis semicircularis anterior
canalis semicircularis posterior
filled with perilymph
Prof. Dr. Nikolai Lazarov
Human ear
Vestibule, vestibulum
lateral wall –
paries labyrinthicus:
fenestra vestibuli closed by basis stapedis,
fixed with lig. annulare stapedis
fenestra cochleae membrana tympani secundaria
medial wall:
elliptical recess utriculus
vestibular crest aqueduct of the vestibule
spheroid recess sacculus
cochlear recess
maculae cribrosae 
pars vestibularis
n. vestibulocochlearis:
macula cribrosa superior
macula cribrosa media
macula cribrosa inferior
Prof. Dr. Nikolai Lazarov
Human ear
Semicircular canals, canales semicirculares
lateral semicircular canal (14 mm) – directed horizontally
anterior (superior) semicircular canal (18 mm) – vertical in direction
posterior semicircular canal (22 mm) – directed sagittally backwards
⅔ of a circle
diameter = all ~ 1 mm
located in three
perpendicular planes
filled with semicircular ducts
initial portion – ampulla ossea
end part – crus osseum:
simplex – for lateral canal
commune – for anterior&posterior canals
Prof. Dr. Nikolai Lazarov
Human ear
Osseous cochlea
spiral canal, canalis spiralis cochleae –
2½-2¾ turns (length ~ 3 cm):
height – 4-5 mm
base – 8-9 mm
basis cochleae
cupula cochleae
Lat. cochlea, snail shell
modiolus – Lat. the hub of a wheel:
basis modioli tractus spiralis foraminosus
lamina modioli
canalis spiralis modioli ganglion cochleare
lamina spiralis ossea hamulus
membrana basilaris
lamina spiralis secundaria Prof. Dr. Nikolai Lazarov
Human ear
Cochlear canal, canalis cochlearis
scala vestibuli
Lat. scala, stairway
scala tympani
scala media (ductus cochlearis)
organum spirale Corti
Prof. Dr. Nikolai Lazarov
Human ear
Membranous labyrinth, labyrinthus membranaceus
a closed system of fluid-filled membranous
channels (sacs) of ectodermal origin
location – within the bony labyrinth
filled with endolymph
surrounded by perilymph –
perilymphatic space
labyrinthus vestibularis –
within the osseous vestibule –
utriculus and sacculus
endolymphatic duct and sac
three semicircular ducts
labyrinthus cochlearis –
membranous cochlea
(cochlear duct)
spiral organ of Corti
Prof. Dr. Nikolai Lazarov
Human ear
Vestibular labyrinth, labyrinthus vestibularis
utriculus – in recessus ellipticus:
ductus utriculosaccularis
macula utriculi – ⅔ mm: pars
utricularis n. vestibulocochlearis
sacculus – in recessus sphericus:
ductus reuniens ductus cochlearis
macula sacculi – pars saccularis
n. vestibulocochlearis
ductus endolymphaticus
saccus endolymphaticus
Prof. Dr. Nikolai Lazarov
Human ear
Vestibular labyrinth, labyrinthus vestibularis
semicircular ducts:
ductus semicircularis lateralis
ductus semicircularis anterior
ductus semicircularis posterior
¼ of the semicircular canals
ampulla membranacea
crus membranaceus:
simplex – for lateral duct
commune – anterior&posterior ducts
wall – thickened, three layers:
inner – simple squamous epithelium
middle – vascular connective tissue
outer – fibrous tissue with blood vessels
clothed by flattened perilymphatic cells
Prof. Dr. Nikolai Lazarov
Human ear
Vestibular system
Statoreceptor spots:
macula utriculi and macula sacculi:
• neuroepithelium:
epitheliocyti sensorii pilosi – 2 types
40-80 stereocilia; 1 kinocilium
epitheliocyti sustentantes
• membrana statoconiorum –
otoliths, statoconia
(Gr. oto-, ear + λιθος, lithos, a stone)
cristae ampullares:
• neuroepithelium:
epitheliocyti sensorii pilosi – type I and II
epitheliocyti sustentantes
• cupula – a glycoprotein substance
Prof. Dr. Nikolai Lazarov
Human ear
Cochlear labyrinth, labyrinthus cochlearis
cochlear duct,
ductus cochlearis:
scala media –
length ~35 mm
cecum vestibulare –
in recessus cochlearis
cecum cupulae –
in cupula cochleae
Prof. Dr. Nikolai Lazarov
Human ear
Cochlear duct, ductus cochlearis
paries vestibularis – vestibular membrane
(of Reissner) – two layers:
basal lamina
simple squamous epithelium
paries externus:
lig. spirale cochleae
stria vascularis: three cell types:
marginal, intermediate and basal – secrete endolymph
paries tympanicus – basilar membrane
(membrana spiralis):
internal zone – sulcus spiralis internus,
limbus spiralis (tympanic and vestibular lips membrana tectoria),
middle zone – spiral organ of Corti
external zone – sulcus spiralis externus
Prof. Dr. Nikolai Lazarov
Human ear
Spiral organ of Corti, organum spirale
Alfonso Corti
located onto basilar membrane: 100 µm basal, 500 µm apical turns
receptor (sensory) and supporting cells:
internal and external rod (pillar) cells of Corti
cuniculus internus (inner tunnel of Corti)
cuniculus medius (space of Nuel)
internal phalangeal cells of Deiters – 1 row and
external phalangeal cells of Deiters – 3 rows
internal (inner) hair cells – 1 row and
external (outer) hair cells – 3 rows
cuniculus externus (outer tunnel)
epitheliocyti limitantes externi
(cells of Hensen) – 3-4 rows
epitheliocyti sustentantes externi
(cells of Claudius)
supporting cells of Boettcher – beneath
Claudius cells in the lower turn of the cochlea
epitheliocyti limitantes interni – 1-2 rows
epitheliocyti sustentantes interni – 2-3 rows
Prof. Dr. Nikolai Lazarov
Tectorial membrane, Human ear
membrana tectoria (Cortii)
overlies the sulcus spiralis internus and the spiral organ of Corti
secreted by the epithelial cells of the
vestibular lip of the limbus laminae spiralis
colorless fibers embedded in a jelly-like matrix:
4 mm filaments of soft keratin
covers the hair cells in organ of Corti,
making contacts with their stereocilia
the vibrating mechanism in the cochlea
Prof. Dr. Nikolai Lazarov
Human ear
Mechanism of the auditory reception
Georg von Békésy
The Nobel Prize
in Physiology or Medicine 1961
"for his discoveries of the physical
mechanism of stimulation within the cochlea"
Helmholtz resonance theory
Rutherford telephone theory
travelling wave theory of Békésy:
basilar-membrane "resonance"
NB: The human ear can nominally hear sounds in the range 12 Hz
Prof. Dr. Nikolai Lazarov
to 20,000 Hz, with intensity levels from 0 to 20 dB!
Human ear
Auditory pathways
Ist neuron –
spiral ganglion:
true bipolar neurons –
30000-33000 cells
cell bodies in the spiral
structure of the cochlea
peripheral processes
spiral organ of Corti
central processes
cochlear part of the
vestibulocochlear nerve
IInd neuron –
cochlear nuclei:
dorsal cochlear nucleus
} lateral lemniscus
ventral cochlear nucleus
Prof. Dr. Nikolai Lazarov
Human ear
Central auditory pathways
IIIrd neuron – nucleus colliculi inferioris
IVth neuron – medial geniculate nucleus
acoustic radiation primary auditory
cortex (A-I) = Brodmann’s area 41
(upper part of gyrus temporalis superior)
Prof. Dr. Nikolai Lazarov
Human ear
Vestibular pathways
Ist neuron –
vestibular ganglion (of Scarpa):
situated in the upper part of the outer
end of the internal auditory meatus
true bipolar neurons –
~20000 cells
peripheral processes statoreceptor spots in:
• maculae utriculi et sacculi –
linear acceleration
• semicircular ducts –
angular acceleration
central processes vestibular part of the
vestibulocochlear nerve
IInd neuron – vestibular nuclei:
superior (Bechterew)
inferior (Roller) } lateral lemniscus
medial (Schwalbe)
lateral (Deiters)  tractus spinocerebellaris posterior
Prof. Dr. Nikolai Lazarov
Human ear
Central vestibular pathways
IIIrd neuron – medial geniculate nucleus
IVth neuron – vestibular cortex
rostral part of
gyrus temporalis superior
tractus vestibulothalamicus –
nucleus ventralis posterolateralis
nucleus ventralis posterior inferior
tractus thalamocorticalis –
internal capsule vestibular area in
gyrus postcentralis (area 3a)
and around sulcus intraparietalis
Prof. Dr. Nikolai Lazarov
Thank you…
Prof. Dr. Nikolai Lazarov

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