Download Special Sensory Reception

Special Sensory Reception
Equilibrium (balance)
and Hearing
External
ear
Middle Internal ear
ear
(labyrinth)
Auricle
(pinna)
Helix
Lobule
External
acoustic
meatus
Tympanic Pharyngotympanic
membrane (auditory) tube
Anatomy of the Ear
• Three parts of the ear:
1. 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
Anatomy of the Ear
2. 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
Oval window
(deep to stapes)
Entrance to mastoid
antrum in the
epitympanic recess
Auditory
ossicles
Malleus
(hammer)
Incus
(anvil)
Stapes
(stirrup)
Tympanic membrane
Semicircular
canals
Vestibule
Vestibular
nerve
Cochlear
nerve
Cochlea
Round window
Pharyngotympanic
(auditory) tube
Anatomy of the Ear
3. 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
Superior vestibular ganglion
Inferior vestibular ganglion
Temporal
bone
Semicircular
ducts in
semicircular
canals
Facial nerve
Vestibular
nerve
Anterior
Posterior
Lateral
Cochlear
nerve
Maculae
Cristae ampullares
in the membranous
ampullae
Spiral organ
(of Corti)
Cochlear
duct
in cochlea
Utricle in
vestibule
Saccule in
vestibule
Stapes in
oval window
Round
window
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
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
Steps in Hearing
1. Sound waves arrive at the tympanic membrane
2. Movement of the tympanic membrane causes displacement
of the auditory ossicles
3. The movement of the stapes at the oval window establishes
pressure waves in the preilymph of the vestibular duct
4. The pressure waves distort the basilar membrane on their
way to the round window of the tympanic duct
5. Vibration of the basilar membrane causes vibration of hair
cells against the tectorial membrane
6. Information about the region and intensity of stimulation is
relayed to the CNS over the cochlear branch of the cranial
nerve VIII