Download ANPS 019 Beneyto-Santonja 11-30

ANPS 019 Beneyto-Santonja 11/30/12
Special Senses II  Auditory & Vestibular Systems
What is the anatomy of the ear?
 External ear – sound collection
 Middle ear – sound amplification
 Inner ear – sound detection (cochlea) & balance (vestibular apparatus)
External Ear
 Auricle: provides directional sensitivity
 Tympanic Membrane (eardrum): separates external ear from middle ear
Middle Ear aka Tympanic Cavity
 Auditory Ossicles – 3 smallest bones in the body:
o Malleus (hammer), Incus (anvil), Stapes (stirrup)
o Malleus attached to tympanic membrane
o Stapes attached to oval window of cochlea
 Two smallest muscles in body protect ear from prolonged loud sounds:
o Tensor Tympani – stiffens tympanic membrane
o Stapedius – reduces movement of stapes at oval window
 Eustachian tube: equalizes pressure within middle ear
Inner Ear
 Subdivided into:
o Vestibule – balance
o Semicircular canals – balance
o Cochlea – auditory
 Vibration of Tympanic Membrane
o Converts sound waves at tympanic membrane into movement of fluids in
membranous labyrinth of cochlea
 Auditory receptors lie within the Organ of Corti of the cochlea
 Organ of Corti
o Hair cells = mechanoreceptors
o The Organ of Corti rests on the basilar membrane
o The auditory receptors, known as Hair cells, have cilia that are in contact with the
tectorial membrane
o Movement of the basilar membrane causes movement of the cilia and
depolarization of the hair cells
How does the brain perceive sound?
 Sound frequency is mapped on the basilar membrane
 The map is maintained in the cochlear nerve and cochlear nucleus in the brainstem
 The map is maintained all the way to the auditory cortex in the temporal lobe
Auditory Pathway
1. Synapse in Cochlear nuclei in medulla
2. Synapse in inferior colliculus
3. Synapse in medial geniculate nucleus of thalamus
4. Synapse in auditory cortex of temporal lobe
How does the ear help with balance?
 Vestibular System
o The vestibular apparatus in the inner ear consists of two Otolith Organs:
 Utricle: responds to tilting and horizontal movement (moving car)
 Saccule: responds to vertical movement (elevator)

Semicircular Canals detect rotation
o There is one semicircular canal for each plane of space
Gustation and Olfaction (Taste and Smell)
How are smell and taste clinically important?
 Taste intimately linked to sense of smell
 The number of taste buds begins declining rapidly by age 50
 Sense of smell declines with ageing
 Elderly aren’t motivated to eat because food has little taste
 Parkinson’s Anosmia
o In Parkinson’s disease, the incidence of smell loss is greater than the incidence of
tremor.
Taste buds
 Gustatory Receptors = Chemoreceptors
 Clustered in papillae of tongue
 Gustatory receptors are specialized epithelial cells NOT neurons
o Survive only 10 days before replacement
Taste Zones  do not correspond to papillae types
 Primary: sweet, salty, sour, bitter
 Additional
o Umami
 Receptors sensitive primarily to amino acids
 Characteristic of beef/chicken broths and parmesan cheese
o Water
 Detected by receptors in the pharynx (‘dry throat’)
o Fats
Olfactory Receptors = Chemoreceptors
 Olfactory epithelium contains:
o Olfactory receptors = bipolar neurons
o Basal (stem) cells
o One of few examples of neurons replaced throughout life
Olfactory Pathway
 Olfactory tract has 3 primary targets:
o Contralateral olfactory bulb – smell localization
o Thalamus – smell perception
o Limbic system WITHOUT A THALAMIC RELAY – smell emotion
 The Olfactory system project to the Limbic system without a thalamic relay