Physiology of ear , medical topic , for 3 Rd year surgery easy explanation 😊

1. PHYSIOLOGY OF THE
EAR
GUIDED BY DR. HITESH RAO SIR

2. • Ear has 2 main function.
1. Physiology of hearing.
2. Physiology of equilibrium.
• Physiology of hearing.
• For this ear may be divided into 2 parts.
• Conductive apparatus : which conducts the sound and consists of the
external ear, tympanic membrane and ossicular chain.

3. • Perceiving apparatus : where the perception of sound occurs.
• This consists of the cochlea and auditory nerves.
1. Conductive apparatus:
• External ear :
• Pinna : it’s function of collecting the sound waves in the human being.
• The external auditory meatus conduct the sound to the ear drum.

5. • Middle ear :
• Sound conduction middle to inner ear.
• To Amplify sound.
• Attenuation reflex ( to protect from loud sound)
• Damping for efficient transsion.
• Eustachian tube : It remain closed at rest.
• But open during swallowing and yawning and thus equalise the pressure of the air in
the atmosphere. It essential for hearing process.

6. • Bone conduction : bone conduction threshold provides an index of the inner ear
function.
• Perceiving apparatus :
• Inner ear : the sound waves reaching the oval window set into vibration the
perilymph in the cochlea which in turn stimulate the organ of corti.

7. MECHANISM OF HEARING
• Sound waves
• Travel to auditory canal.
• Vibration transmitted to middle ear ossicles malleus, incus, stapes.
• Vibration transmitted to oval window.
• Pressure changes in perilymph in scala vestibule.
• Up and down movement of reissner membrane.
• Pressure changes in Endolymph in scala media.
• Up and down movement of basilar membrane.

8. • Bending of hair cells of organ of corti.
• Development of action potential.
• Excite the cochlear division of 8 cranial nerve.
• Transmitted to medulla(central and dorsal cochlear nuclei)
• Superior olivery nuclei
• Transmitted midbrain.
• Thalamus.
• Auditory cortex ( area no. 41 temporal lobe).
• Identification and recognition of voice.

10. PHYSIOLOGY OF EQUILIBRIUM
• Semicircular canal and vestibule (utricle and saccule) concerned with balance.
• Three semicircular canals are arranged in a way that perceive position of head in
space.
• Change of position of head cause movement of fluid.
• Hair cells ( sensory receptor) present in utricle, saccule and ampulla bend and
stimulates.
• Nerves impulse generates and join the vestibule part of vestibulocochlear nerve.
• Transmitted to cerebellum, then cerebrum.
• Maintain balance and posture.