ANPS 019 BENEYTOSANTONJA 113012 SPECIAL SENSES II  AUDITORY

ANPS 019 Beneyto-Santonja 11/30/12

Special Senses II  Auditory & Vestibular Systems

What is the anatomy of the ear?

External Ear

Middle Ear aka Tympanic Cavity

Auditory Ossicles – 3 smallest bones in the body:
- Malleus (hammer), Incus (anvil), Stapes (stirrup)
- Malleus attached to tympanic membrane
- Stapes attached to oval window of cochlea
Two smallest muscles in body protect ear from prolonged loud sounds:
- Tensor Tympani – stiffens tympanic membrane
- Stapedius – reduces movement of stapes at oval window
Eustachian tube: equalizes pressure within middle ear

Inner Ear

Subdivided into:
- Vestibule – balance
- Semicircular canals – balance
- Cochlea – auditory
Vibration of Tympanic Membrane
- 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
- Hair cells = mechanoreceptors
- The Organ of Corti rests on the basilar membrane
- The auditory receptors, known as Hair cells, have cilia that are in contact with the tectorial membrane
- 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

How does the ear help with balance?

Vestibular System
- 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
- 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
- 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
- Survive only 10 days before replacement

Taste Zones  do not correspond to papillae types

Olfactory Receptors = Chemoreceptors

Olfactory epithelium contains:
- Olfactory receptors = bipolar neurons
- Basal (stem) cells
- One of few examples of neurons replaced throughout life

Olfactory Pathway

Olfactory tract has 3 primary targets:
- Contralateral olfactory bulb – smell localization
- Thalamus – smell perception
- Limbic system WITHOUT A THALAMIC RELAY – smell emotion
The Olfactory system project to the Limbic system without a thalamic relay