2014 Inner Ear Physiology

Lecture Objectives

  1. Describe the structural features of hair cells that are critical to their function.  Identify key similarities and differences between type I and type II hair cells.

  2. Explain the tip link model of transduction.  In particular, be able to describe the generation of a biphasic receptor potential and adaptation.

  3. Contrast the semicircular canals and otolith organs with respect to:  a)  the mechanism of stereocilia displacement, b)  directionality and c)  the type of effective stimulus.  Describe the natural pairing of semicircular canals, and be able to indicate which canals are depolarized/hyperpolarized by specific head movements.

  4. Describe how the mass and stiffness characteristics of the middle ear affect sound transmission.  List the mechanisms used by the middle ear to minimize the impedance mismatch between air and the cochlear fluids.  Graph and be able to interpret the audiograms generated in patients with normal hearing, a conductive hearing loss and sensorineural hearing loss.

  5. Outline how a traveling wave is established on the basilar membrane in response to an acoustic stimulus.  Define the cochlear place code and describe how it is established via the passive properties of the basilar membrane and organ of Corti.

  6. Diagram the active feedback mechanism invoked by contraction of the outer hair cells.  Identify the difference between otoacoustic emissions and tinnitus.  Identify the source of OAE, and describe how they can be used to derive an audiogram (e.g., during newborn hearing screenings).

  7. Describe the generation of the endocochlear potential and its function. Understand the impact on hearing of interfering with the EP (e.g. with loop diuretics).

Auditory and Vestibular Pathways Session

  1. List the components of the primary auditory and vestibular pathways and their major reflexes.  Identify major auditory and vestibular nuclei and pathways in cross-sections of the brainstem and diencephalon.

  2. List the steps in the vestibulo-ocular reflex and describe the changes in firing patterns in each nucleus during head rotation.  Identify the function of the VOR.

  3. Compare and contrast the anatomical and physiological aspects of the medial and lateral vestibulospinal systems with respect to:  overall function, afferent source, vestibular nucleus, efferent projections and effect and control mechanism.

  4. Define nystagmus, and understand its origins (i.e., which part is due to VOR, and which to higher centers).  Describe the differences in caloric nystagmus and doll’s eye movements among a normal individual, a comatose patient and in a person who is brain dead.

  5. Compare the pathways and mechanism for localizing low and high frequency stimuli.  Be able to describe the physiology underlying the Rinne and Weber tests.

Assessing Inner Ear Function

  1. Describe the differences in the caloric test among a normal individual, a comatose patient and a person who is brain dead.

  2. Graph and be able to interpret the audiograms generated in patients with normal hearing, a conductive hearing loss and sensorineural hearing loss.

  3. Be able to describe the physiology underlying the Rinne and Weber tests.

  4. Understand how the information from various types of hearing tests can help localize a lesion in the auditory pathway.

 

Email: Dr. Janet Fitzakerley | ©2014 University of Minnesota Medical School Duluth | Last modified: 15-feb-14 9:04 PM