The document summarizes the anatomy and physiology of the human ear and balance system. It describes the outer, middle, and inner ear structures and their functions in hearing and balance. Specialized sensory receptors in the cochlea and vestibular system detect sound vibrations and head position, transmitting nerve impulses to the brain for hearing and maintaining equilibrium.

1. Prepared by: Mr. Hemant P. Vanjari
(M. Pharm in Pharmacology)

2. Special senses of hearing, sight , smell and taste all have
specialized sensory receptors that collect and transmit information
to specific areas of the brain.
• Ear- Hearing
• Eye- Vision
• Nose- Smell
• Tongue- Taste

3. Ear- Organ of hearing also involved in balance.
Supplied by 8th cranial nerve (vestibulocochlear nerve) which stimulated by
vibration cause by sound.
Structure-
Outer ear-Auricle (,Helix, Lobule) or Pinna , Auditory canal
Middle ear- Auditory ossicles ( Malleus, incus, stapes)
Internal ear-Vestibule, Semicircular canals, cochlea.
Fig. Parts of Ear

4. Outer ear-
Auricle (pinna), external acoustic meatus (Auditory canal)
Auricle (Pinna)- It is visible part of ear.
It is composed of fibroelastic cartilage covered with skin.
Most prominent outer ridge – Helix.
Earlobe is soft pliable part of lower extremity composed of fibrous and adipose
tissue richly supply with blood- Lobule
Auditory canal- Slighly S shaped tube – 2.5cm long , extend from auricle to
tympanic memb. Canal lined with skin having numerous ceruminous gland , hair
follicles associated with sebaceous glands.
Ceruminous glands modified sweat glands secrets cerumen(earwax)
Sticky materials consist bacteriocidal enzyme lysozyme, immunoglobulins
Foreign materials dust, insects, microbes are prevented by this materials.
Movements of temporomandibular joint during cheming and speaking –
Moving of wax towards the exterior.
Tympanic membrane (eardrum) seperates external ear and middle ear
Oval shaped, formed by 3 types tissue.
Outer covering of hairless skin
Middle layer fibrous tissue
Inner lining of mucus membrane.

5. Middle Ear- (Tympanic Cavity)
Irregular shaped air-filled cavity within patrous portion of temporal bone.
Cavity contents air sacs , lined with simple squamous epithelium.
Two openings- Oval window
Round window
Oval window occuled by part of small bone c/s stapes
Air reaches the cavity through pharyngotympanic tube which link to nasolpharynx & middle ear
Presence of Air at atmospheric pressure on both sides of tympanic membrane is maintained by
pharyngotymapanic tube.
Auditory ossicles-
Three very smal bones, few mm in size
• Malleus
• Incus
• Stapes

6. Internal Ear- It is also c/s Labyrinth Contains organs of hearing & balance
Two parts- Bony labyrinth, Membrane labyrinth
Bony Labyrinth- Lined with periosteum
Within bony labyrinth, membrane labyrinth is suspended in watery fluid c/s
perilymph
Membrane labyrinth divided into 3 parts & It is filled with endolymph
• Vestibule ( Utricle & Saccule)
• Three semilunar canals
• Cochlea

7. Vestibule- Expanded part nearest middle ear.
Contains two membrane sacs (Utricle & Saccule) – imp in balance.
Semicircular canal- Three tubes arranged, one of which situated in each of three planes of
space. It is also important in balance.
Cochlea- resembles a snails shell.
C.S. of cochlea contains 3compartments-
Scala vestibuli
Scala media/ Cochlear duct
Scala tympani
Cochlear duct-
On basilar membrane specialised
cochelear hair cells containing
auditory receptors.
Fig. Cross-section of cochlea showing spiral organ

8. Physiology of Hearing-
Sound produces waves/ vibrations in air travel at 332m/ s.
Auricle collects & concentrates the waves.
Directs vibrations to audiotory canals cause tympanic membrane vibrations
Vibrations are transmitted & amplified through movement of ossicles
Force of these waves / vibrations transmitted to scala vestibuli and tympani
But most of pressure is transmitted into cochlear duct.
Vibrations in endolymph resulting in vibration of basilar membrane and
stimulation of auditory receptors in hairs cells of spiral organs.
This nerve impulses generated pass to brain through vestibulocochlear nerve (8th CN)
VC N tranmits impulses to auditory nuclei in medulla and impulses conducted in
to auditory area of temporal lobe of cerebellum.

9. Physiology of Balance -
Semicircular canals and vestibule ( utricle & saccule) concerned with balance/
equilibrium.
Semicircular canals- inner ducts contains endolymph and seperated by bony wall
contains perilymph.
In walls of utricle, sccule fine, specilised epithelial cells with minutes projections
called as hair cells.
In hairs cells, receptors on sensory nerve endings which combine forms
vestibulocochlear nerve.
In arrangement of 3 semicircular canals, not only allows perception of position of
head in space but also direction and rate of any movement.
Any change in position of head causes movement perilymph and endopymph,
which bends haris cell & stimulates sensory receptors in utricel, saccule.
Resultant nerve impulses are transmitted by vestibular nerve which joins cochlear
nerve to form vestibulocochlear nerve.
Vestibular branches passes first to vestibular nucleus then cerebellum.
Cerebellum coordinates incoming impulses fro, vestibular nerve.
Then impulse tranmitted to cerebellum and skeletal muscle enabling perception of
body position and any adjustment needed to maintain posture and balance.