Special Senses

Describe the mechanism of audition, starting from the introduction of airwaves to the ear through stimulation of the cerebral cortex

  • Airwaves travel through external ear

  • tympanic membrane

  • Ossicle vibration amplify sound

  • Oval window

  • fluid in the cochlea stimulates basilar membrane

  • hairs on the basilar membrane depolarize and activate first order neuron (Cochlear branch of CNVIII)

  • Ascends to Brodmann’s area 41, 42 (both ipsilateral and contralateral)

Hair cell potentials

  • Different heights of hair cells

  • depolarization when bent towards tall cilia

  • voltage gated Ca2+ channels open releasing NT

Contrast the different forms of hearing loss and be able to give examples of each

  1. Conduction

    • can’t convert airwaves into fluid

      • Otitis Media (infection)

      • Cerumen (earwax)

      • Tympanic membrane rupture

  2. Sensorineural

    • Injury to hair cells

      • Presbycusis (age related)

      • Noise induced

      • Genetic (usher’s)

      • Rx (diuretics, Ab, methotrexate)

      • Meniere Disease (increase fluid pressure)

    • Acoustic Neuroma - non cancerous tumor compressing on nerves

      • presents as: unilateral deafness, balance problems, Unilateral Tinnitus.

  3. Central

    • Stroke

    • Tumor

    • Trauma

Describe the systems that are responsible for sensing our equilibrium, and understand that these systems control eye movement

Vestibules responsible for postural reflex and eye movement

Describe the function of the semicircular canals

Senses rotational acceleration

  • Depolarization of nerve on the same side of turn

  • Hyperpolarization of nerve on the opposite side of turn

Vestibulo-ocular reflex:

  • stabilizes image on retina while head is moving

Describe the clinical presentations that can be associated with disease of the vestibular system

  • Diplopia

  • Oscillopsia

  • Horizontal Nystagmus (to the healthy side)

Describe how horizontal vestibular nystagmus is named and given a direction of nystagmus be able to identify in which side of the body the lesion would be located

Name given due to horizontal movement of eyes

direction of nystagmus towards the healthy side

Describe Usher syndrome and contrast the different types of usher syndrome. Given a case be able to provide a differential for the type of Usher syndrome

Dual sensory disorder

  • type 1

    • born with hearing loss

    • progressive vision loss from childhood

    • ongoing balance issues as vision deteriorates

  • type 2

    • Born with mild progressive hearing loss

    • progressive vision loss from adolescence to early adulthood

    • No balance issues

  • type 3

    • Born with normal hearing, later developing progressive hearing loss

    • Progressive vision loss from childhood

    • varying balance

Describe Meniere’s syndrome

  • endolymph hydrops

    • high pressure

  • vertigo

  • Tx: blood pressure meds.