Auditory- Olfaction Flashcards
How does hearing work
- Sound waves come into the pinna of the ear, follow the auditory canal, and hit the tympanic membrane
- Sound waves are transduced into vibrational energy, transmitting the signal to the malleus -> incus -> stapes which covers the oval window
- Resulting vibrations from the oval window travel through the perilymph fluid through the scala vestibuli and then through scala tympani. Vibrations leave via the round window
4.Vibrations in the scala vestibuli move the basilar and tectorial membranes within the scala media distorting hair cells leading to transduction at the Organ of Corti
- Fibers travel as CN VIII (cochlear branch) and meet up with the vestibular branch -> vestibulocochlear nerve
Synapse on cochlear nucleus in medulla -> thalamus -> temporal lobe (auditory cortex) where we can perceive it!
Perilymph
Transmits sound waves to endolymph
Found in scala vestibuli and scala tympani
High in sodium and chloride Low in Potassium
(similar to extracellular fluid)
Less positive electric potential
Endolymph
Transmits sound waves to hair cells
Found inside scala media
High in potassium
(similar to intracellular fluid)
More positive electric potential
Created by melanocytes in the stria vascularis
Signal Transduction
- Hair cells reside in endolymph (high potassium) and base of cell in perilymph (low potassium) creating a gradient.
- When stereocilia move toward rigid kinocilium potassium channels open leading to depolarization and nerve stimulation (also how ampulla and macula densa work!)
Two Type of Hair Cells
Inner Hair Cells
Outer Hair Cells
Inner Hair Cells
Receptor for the afferent fibers of the cochlear nerve
Outer Hair Cells
o Protective function to lead to dampening by limiting movement of tectorial membrane
o “Dampening”
Auditory Reflex
- Part of CN VIII synapse on the
caudal colliculus - Makes us turn our head to sound!
- May work with other reflexive systems to “hone in” on disturbances or dangers in our environment
Clinical Notations
- Pigmented associated deafness
o White coat color/ Blue eyes (Merle genes in collie/ Shetlands)
o Melanocytes not present in Stria Vacscularis
§ Leads to degeneration, abnormal endolymph, an death of hair cells - Many Breed Specific Disease
o Dalmatians, Catahoula Leopard dogs - Types of Deafness:
o Conduction
§ Anything blocking the ear canal
v Infection, Foreign body, tympanic membrane rupture
o Sensorineural
§ Nervous system associated
§ Decreases with age
Test Hearing
- Basic/ Early Investigative Testing o Breed/ Genetic Predisposition o Behavior at home o Reflexive responses to sound § Cannot drop heavy things on ground § Animal cannot see you o Otoscopic Exam
- Advanced o CT/ MRI o Brainstem Auditory Evoked Response (BAER)
Where is the olfactory specific mucosa located
on the
ethmoidal labyrinth and
dorsal nasal septum in
the dog
Odoriferous substances
dissolve in the mucus
overlying the mucosa
and vomeronasal organ
Olfactory Epithelium: Cell Types
1.Olfactory Sensory Neurons
* Bipolar neurons
2. Sustentacular Cells
* Provides Structure
* (supporting cell)
3. Basal Cells
* Stem Cells
* Neurogenesis (~2 months)
How do axons reach the olfactory bulb
Axons pass through the cribriform plate to the olfactory bulb
General Olfactory pathway
- Axons from the olfactory mucosa and vomeronasal (Jacobson) organ pass through the cribriform plate and synapse in the olfactory bulb neurons
- From the bulb they travel to the olfactory tract to synapse in
3 potential ways
- Pyriform Cortex
- Limbic Center (behavior/emotion)
- Brainstem (reflexes)
Thalamic relay is not required for cortical perception
- (some axons will go here for secondary cortex perception)
Vomeronasal Organ
Important in detecting pheromones
“Flehmen Response”
Vomeronasal system opens directly into the oral cavity and projects axons to the olfactory bulb with differences seen between species
