Download MBBS 1st Year Physiology Sensory System Physiology Notes

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AUDITORY PATHWAY

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Receptors: Hair cells in organ of corti

Spiral Ganglion

Central peripheral

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processes processes
continuous connected
to hair cells

Receptor Potential / cochlear Microphonic Potential

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Central process Peripheral process
Leave as distributed around hair
cochlear Nerve. cells of organ of corti as
CN VIII afferent N. fibres

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Auditory cortex
Auditory radiation
Inferior colliculus
Lateral Lemniscus
Superior Olivary Nucleus

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Dorsal cochlear Nucleus
Trapezoid body
Central process of
spiral Ganglion/
Auditory Nerve

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Cochlear Nuclei
of auditory pathway
1. Fibres cross the midline
& runs to opp. side
form

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Trapezoid body
fibres goes to
Superior Olivary Nucleus.
2nd group - terminate
at C.O.N. of

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same side via
Trapezoid body of
same side.
3rd grp. From runs in Lateral 4th grp-runs into
lumniscus I terminate reticular form

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in nucleus of Lat Lemniscus cross midbrain as
of same side Intermediate Trapezoid
fibres
3rd Order Neuron:-
are in Superior Olivary Nucleus &

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Nucleus of Lat Lemniscus
Medial Geniculate body
(form subcortical Auditory centres)
Auditory Radiation
(via internal capsule)

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Cortical Auditory area
CONDUCTION Deafness NERVE Deafness
Type of deafness due Deafness caused by
to impairment in damage to any structure
transmission of sound to in cochlea like

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external ear/ middle ear Hair cell,
Organ of corti,
No N. is damaged Basilar membrane
Cochlear duct
Bone conduction > Air conduction Lesion in auditory pathway

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CAUSES: CAUSES:-
1. Obstruction of external Degeneration of hair cell
auditory meatus due to due to antibiotics.
dry wax/ foreign bodies (Ototoxic drugs) like
2. Thickening of tympanic streptomycin.

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membrane due to
repeated middle ear infection. Damage to cochlea
due to prolonged
exposure to loud sound
3. Perforation as tympanic

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membrane due to unequal
P on either side Tumour affecting CN-8
4. Otitis media - inflammation
of middle ear.
5. Otosclerosis- fixation of

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footplate of stapes
against oval window.
RINNE TEST
Base of vibrating tuning fork placed
on mastoid process of arhum until

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subject "feel vibrate"
? I hear sound
Tuning fork held in air in front as
ear of same side.
Normal Person:- hears vibration in air even

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after bone conduction ceases.
A.C. > B.C.
via ossicles
Conduction Deafness: B.C > A.C
vibrations are not heard after

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cessation of bone conduction.
Nerve Deafness:- A.C < B.C
Base of vibrating tuning fork is
placed on vertex of skull / middle of forehead
Normal person- hear the sound equally on both

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sides.
Unilateral Conduction Deafness-
(deafness in 1 ear)
sound is heard louder in
diseased ear.

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Unaffected ear- masking effect of env. noise.
sound through B.C & heard
as clearly as on affected side
Unilateral Nerve Deafness-
sound is heard normal

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louder in normal ear.
TASTE BUDS
sense organs for taste/gustatory sensation are Taste buds
SITUATION OF TASTE buds:-
on papillae of tongue.

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mucosa of palate, epiglottis, pharynx & proximal part
of oesophagus.
Filiform papillae conical shape.
no of taste buds
Fungiform papillae round shape.

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moderate no of taste buds
Circumvallate papillae: large str.
many taste buds (~100).
arranged in shape 'Y'
STRUCTURE OF TASTE BUDS-

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bundle of taste receptor cells with
supporting cells embedded in epithelial covering
of papillae.
Taste buds ~ 40 cells- modified epithelial cells.
Type I / sustentacular cells

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Type II - tuner unknown.
Type III - receptor cells
Type IV / basal cell.
supporting cells-
Type I, II, III cells have microvilli which project

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through an opening on dorsum of tongue called
taste pore.
All cells of taste buds are surrounded by
epithelial cells
tight junctions present b/w epithelial cells &

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thick portion of type I, II, III cells are exposed to fluid
only in oral cavity
receptor organ for hearing
uraepithelial structure
in cochlea

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situated on basilar membrane
extends from apex base of cochlea
spiral shape.
contains highly specialised auditory receptors -
HAIR CELLS.

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processes pierce through membrane like
Reticular lamina-
supported by pillar cells/
Rods of corti
arranged in rows

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Outer hair cells - 3 rows Inner hair cells- 1 row
20,000 3,500
the lateral to the the medial to tunnel
tunnel towards rods
of corti.

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tips are embedded tips not embedded in t.H.
in tectorial membrane
thin, viscous
elastic membrane
5-10% of sensory neurons 90-95 % sensory

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innervate neurons innervate.
most of the efferent
neurons/fibres in
auditory nerve terminate here.
Cell bodies of sensory neurons that arise

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Ground hair cells- located in spiral ganglion
within modiolus
bony core around
which cochlea is wound
that innervate hair cell,

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form auditory (Cochlear
division of CN-8)