1. Special Sensory Reception
Equilibrium (balance)
and Hearing

2. Middle
ear
Internal ear
(labyrinth)
External
ear
Auricle
(pinna)
Helix
Lobule
External
acoustic
meatus
Tympanic
membrane
Pharyngotympanic
(auditory) tube

3. Anatomy of the Ear Three parts of the ear: External (outer) ear
Includes the auricle (pinna) which surroundes the entrance to the external acoustic meatus (ear canal)
The auricle protects the ear canal and collects and funnels sound into the ear canal
Ceruminous glands are along the external acoustic meatus and secrete a waxy material that helps prevent the entry of foreign objects and insects
The external acoustic meatus ends at the tympanic membrane (eardrum) which separates the inner and middle ear

4. Anatomy of the Ear Middle ear (tympanic cavity) Air-filled chamber
Communicates with the superior portion of the pharynx (nasopharynx). This connection is called the auditory tube (pharyngotympanic tube or Eustachian tube)
Enables equilization of pressure on either side of the eardrum
Contains the auditory ossicles (3 tiny bones together)
Connect the tympamun with the inner ear
The 3 bones are the malleus, incus, stapes
Act as levers that conduct the vibrations to the inner ear

5. Oval window
(deep to stapes)
Semicircular
canals
Entrance to mastoid
antrum in the
epitympanic recess
Malleus
(hammer)
Vestibule
Incus
(anvil)
Auditory
ossicles
Vestibular
nerve
Stapes
(stirrup)
Cochlear
nerve
Tympanic membrane
Cochlea
Round window
Pharyngotympanic
(auditory) tube

6. Anatomy of the Ear Internal (inner) ear
Provides the senses of hearing and equilibrium
Protected by a bony labyrinth
Surrounds and protects the membranous labyrinth
Subdivided into 3 parts:
Vestibule – contains sacs that provide sensations of gravity and linear acceleration
Semicircular canals – receptors here are stimulated by rotation of the head
Cochlea – receptors here provide the sense of hearing
The receptors of the inner ear are the hair cells
Communicate with sensory neurons by continually releasing small quantities of neurotransmitters

7. Superior vestibular ganglion
Inferior vestibular ganglion
Temporal
bone
Semicircular
ducts in
semicircular
canals
Facial nerve
Vestibular
nerve
Anterior
Posterior
Lateral
Cochlear
nerve
Cristae ampullares
in the membranous
ampullae
Maculae
Spiral organ
(of Corti)
Utricle in
vestibule
Cochlear
duct
in cochlea
Saccule in
vestibule
Stapes in
oval window
Round
window

8. Equilibrium 2 aspects of equilibrium:
Dynamic equilibrium
Aids us in maintaining our balance when the head and body are moved suddenly
Static equilibrium
Maintains our posture and stability when the body is motionless
All equilibrium sensations are provided by hair cells

9. Hearing
Receptors of the cochlear duct provide us with the sense of hearing
The receptor responsible are hair cells similar to those in the vestibule and semicircular canals
Sound energy is converted in air to pressure pulses which stimulate hair cells along the cochlear spiral
The frequency (pitch) of the percieved sound is determined by which part of the cochlear duct is stimulated
The intensity (volume) is determined by how many hair cells at that location are stimulated

10. Steps in Hearing Sound waves arrive at the tympanic membrane
Movement of the tympanic membrane causes displacement of the auditory ossicles
The movement of the stapes at the oval window establishes pressure waves in the preilymph of the vestibular duct
The pressure waves distort the basilar membrane on their way to the round window of the tympanic duct
Vibration of the basilar membrane causes vibration of hair cells against the tectorial membrane
Information about the region and intensity of stimulation is relayed to the CNS over the cochlear branch of the cranial nerve VIII