Q-1. Stapes foot plate covers
a) Round window
b) Oval window
c) Inferior sinus tympan
d) Pyramid
Answer: Oval window
Explanation:
The oval window, an opening between scala vestibuli and the middle ear, lies at the end of the cochlea nearest the middle ear, the basal end.
The oval window is covered by the footplate at the stapes in the middle ear.
The round window, a membrane-covered opening between the scala tympani and the middle ear also lies at the basal end of the cochlea.
Because fluid of the inner ear in non-compressible, inward movement of the stapes footplate is allowed because of the yielding of the thin membrane which covers the round window.
This is essential to the transmission process, since it provides elastic relief for the fluid of the inner ear, thus permitting movement of the stapes and the structures of the inner ear.
Q-2. Stapedius is supplied by –
a) Maxillary nerve
b) Facial nerve
c) Auditory nerve
d) Mandibular nerve
Answer: Facial nerve
Explanation:
Stapedius:
It attaches to the neck of stapes and helps to dampen very loud sounds thus preventing noise trauma to the inner ear.
Nerve supply- a branch of CN VII
Q-3. Regarding Stapedial reflex, which of the following is true:
a) It helps to enhance the sound conduction in the middle ear
b) It is protective reflex against loud sound
c) It helps in masking the sound waves
d) It is unilateral reflex
Answer: It is protective reflex against loud sound.
Explanation: See above explanation
Q-4. Site where endo-lymph is seen-
a) Scala vestibule
b) Scala media
c) Helicotrema
d) Organ of corti
Answer: Scala media
Explanation:
Membranous labyrinth consists of the cochlear duct or the Scala media or membranous cochlea, the utricle, saccule, the three semi-circular ducts, and the endo-lymphatic duct and sac.
The non-ampullated ends of posterior and superior canals unite to form a common channel called the crus commune.
The membranous labyrinth is filled by endo-lymph while the space between membranous labyrinth and bony labyrinth is filled with peri-lymph.
Q-5. Organ of corti is situated in
a) Scala media
b) S. Tympani
c) S. Vestibuli
d) Saccule
Answer: Scala media
Explanation:
The Scala Media or Cochlear Duct: Organ of Corti
It is a blind sac.
Its three walls are formed by
The basilar membrane, which supports the organ of corti,
The Reissner’s membrane which separates it from the scala vestibule
The stria vascularis, which contains vascular epithelium and is concerned with secretion of endo-lymph
Important Points:
The scala media or cochlear duct is connected to the saccule by ductus reuniens.
Higher frequencies of sound are heard at basal coil while lower ones are heard at the typical coil.
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Q-6. Endolymph in the inner ear-
a) Is filtrate of blood serum
b) Is secreted by Stria vascularis
c) Is secreted by Basilar membrane
d) Is secreted by Hair cells
Answer: Is secreted by Stria vascularis
Explanation: See above explanation
Q-7. Endolymph in inner ear is produced by?
a) Phalangeal cells
b) Stria vascularis
c) Lamina spiralis ossea
d) Cochlear duct
Answer: Stria vascularis
Explanation: See above explanation
Q-8. Endolymph is secreted by
a) Stria vascularis
b) Basilar membrane
c) Cochlear duct
d) Hensen’s cell
Answer: Stria vascularis
Explanation: See above explanation
Q-9. Organ of corti is situated in
a) Scala media
b) Utricle
c) Saccule
d) None of the above
Answer: Scala media
Explanation: See above explanation
Q-10. Organ of corti is arranged along the inner edge of –
a) Reissner’s membrane
b) Basilar membrane
c) Stria Vascular
d) None of the above
Answer: Basilar membrane
Explanation: See above explanation
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Q-11. Peri-lymph contains-
a) Na+
b) K+
c) Mg++
d) Cl –
Answer: Na+
Explanation:
Composition of inner ear fluids
Constituents of endo-lymph:
Na+ (meq/ L) – 5
K+ (meq/ L) – 144
Protein (mg/ dl) -126
Glucose (mg/ dl) -10-40
Constituents of Peri-lymph:
Na+ (meq/ L) – 140
K+ (meq/ L) – 10
Protein (mg/ dl) -200-400
Glucose (mg/ dl) -85
Q-12. The following structure represents all the 3 components of the embryonic disc-
a) Tympanic membrane
b) Retina
c) Meninges
d) None of the above
Answer: Tympanic membrane
Explanation:
Tympanic membrane develops from the all three germinal layers.
Outer germinal epithelial layer is formed by the ectoderm, inner mucosal layer by the endoderm and the middle fibrous layer by the mesoderm.
Q-13. All of the following are concerned with auditory pathways except:
a) Trapezoid body
b) Medial geniculate body
c) Genu of internal capsule
d) Lateral lemniscus
Answer: Genu of internal capsule
Explanation:
Auditory Neural Pathways and their Nuclei:
Hair cells > Dendrites of bipolar cells of spiral ganglion situated in Rosenthal’s canal> Cochlear division of CN-VIII> Cochlear nuclei dorsal and ventral > Superior olivary complex > Lateral lemniscus > Inferior colliculus > Medial geniculate body > Auditory cortex > Superior temporal gyrus (Broadmann’s Area 41)
Important Points:
The auditory fibres travel via the ipsi-lateral and contra-lateral routes and have multiple decussation points.
Thus each ear is represented in both cerebral hemispheres.
Appreciation of sound occurs in Superior temporal gyrus (Broadmann’s Area 41).
Q-14. Appreciation of sound occurs in
a) Organ of corti
b) Basilar membrane
c) Cochlear nuclei
d) Transverse temporal gyrus
Answer: Transverse temporal gyrus
Explanation: See above explanation
Q-15. Surface area of tympanic membrane-
a) 55 mm2
b) 70 mm2
c) 80 mm2
d) 90 mm2
Answer: 90 mm2
Explanation:
Lever action of the ossicles:
Handle of malleus is 1.3 times longer than long process of the incus, providing a mechanical advantage.
Hydraulic action of tympanic membrane ™:
Total surface area of TM = 90 mm2
Effective vibratory area of TM = 45 mm2
Footplate area = 3.2 mm2
Area ratio = 14:1
Lever ratio (ossicles) = 1.3: 1
Total transformer ratio or the product of area ratio and lever action of ossicles = 18.2:1
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Q-16. The effective diameter of the tympanic membrane
a) 25 mm2
b) 30 mm2
c) 40 mm2
d) 45 mm2
Answer: 45 mm2
Explanation: See above explanation
Q-17. Angular movements are sensed by
a) Cochlea
b) Saccule
c) Utricle
d) Semi-circular Canals
Answer: Semi-circular Canals
Explanation:
Cristae:
Located in the ampullated ends of the three semi-circular duct
They respond to angular acceleration.
Maculae:
Located in otolith organs of utricle and saccule
They sense position of head in response to gravity and linear acceleration.
Q-18. Semi-circular canals are stimulated by
a) Gravity
b) Linear acceleration
c) Rotation
d) Sound
Answer: Rotation
Explanation: See above explanation
Q-19. Horizontal semi-circular canal responds to
a) Horizontal acceleration
b) Rotational acceleration
c) Gravity
d) Antero-posterior acceleration
Answer: Rotational acceleration
Explanation: See above explanation
Q-20. All are correctly matched except
a) Otolith – Made up of Uric acid crystals
b) Position of otolith – Changes with head position
c) Otolith – Stretch receptors
d) Otolith organs – Stimulated by gravity and linear acceleration
Answer: Otolith – Made up of Uric acid crystals
Explanation:
Structure of macula:
A macula consists mainly of two parts:
A sensory neuro-epithelium and
An otolithic membrane, which is made up of a gelatinous mass and on the top, the crystals of calcium carbonate called otoliths or otoconia.
The cilia of hair cells project into gelatinous layer.
The linear, gravitational and the head tilt movement causes displacement of otolithic membrane and thus stimulate hair cells which lie in different planes.
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Q-21. Higher auditory centre determines
a) Sound frequency
b) Loudness
c) Speech discrimination
d) Sound localization
Answer: Sound localization
Explanation:
Higher auditory centre determines sound localization and sound localization is markedly disrupted by lesion of auditory cortex.
Q-22. Ear is sensitive to which frequency of sound-
a) 500-3500Hz
b) 1000-3000Hz
c) 3000-5000Hz
d) 5000-8000Hz
Answer: 500-3500Hz
Explanation:
Frequencies of 500, 1000, and 2000 Hz are called speech frequencies as most of human voice falls within this range. PTA (pure tone audiometry) is the average threshold of hearing in these three speech frequencies.
It roughly corresponds to the speech reception threshold.