AUDITORY AND VEST VE STIBU IBULA LAR R PATH THW WAYS Alexandria R. Bayaoa, M.D. Department of Anatomy UERMMMC, Inc.
Objectives: Function of the cochlear system Receptors for hearing Tracing the pathway of sound from the environment to the sense organ for hearing
Objectives: Describing the origin, course, and termination of the cochlear nerve Tracing the central auditory pathway from the organ of Corti until the nerve impulse reaches the auditory cortex
Objectives: Role of the olivocochlear bundle of Rasmussen in sound perception Pathways of auditory reflexes Differentiating between conductive and sensory deafness
Objectives: Explaining tinnitus, Rinne’s & Weber’s test Function of the vestibular system Parts of Static labyrinth vs kinetic labyrinth Location of the receptors for vestibular control
Objectives: Origin, course, and termination of the vestibular nerve Describing the role of: MLF, medial vestibulospinal tract, lateral vestibulospinal tract in the maintenance of equilibrium
Objectives: Connections of the vestibular apparatus with the cerebellum Define: vertigo and nystagmus Tests for vestibular function Clinical manifestations of disturbances in vestibular apparatus
EAR
Functions of the Cochlear System
Cochlea:
Auditory Pathway:
COCHLEAR NERVE NUCLEI
Auditory Pathway:
Descending Pathway
Auditory pathway lesion Unilateral lesions of the receptors, cochlear nerve/nuclei result to TOTAL DEAFNESS OF THE AFFECTED EAR Central unilateral lesions (cortex, medial geniculate body, lateral lemniscus) result in IMPAIRED HEARING IN BOTH EARS BUT MORE MARKED ON THE OPPOSITE SIDE
Auditory Reflexes: Audiomotor reflexescontractions of the tensor tympani and stapedius ms. General acoustic muscle reflexgeneralized jerking of the body in response to a loud, sudden sound
Auditory Reflexes: Auditory-palpebral reflex- blink of the eyelids to a loud noise Auditory-oculogyric reflexdeviation of the eyes in the direction of a sound Cochleopupillary reflexdilation of the pupils to loud noise
Doll’s eye/vestibulo-ocular reflex test of brainstem function Head is moved from one side to the other The eyes will normally lag behind then assume a midline position Failure to lag/assume a midline= lesion on the ipsilateral side
CHL vs SNHL
During the Weber test , the stem of a vibrating tuning fork is placed on the head in the midline. If the tone is perceived in the affected ear, this indicates a unilateral conductive hearing loss. In the case of unilateral sensorineural hearing loss, the tone is heard in the unaffected ear instead.
Rinne Test
The stem of the tuning fork is placed on the mastoid
and the subject is asked to indicate when she or he stops hearing the sound.
The fork is then held 2.5 cm from the pinna, and the
patient is asked if she or he still hears the sound.
If the sound is still audible, air conduction is greater than bone conduction (AC > BC in normal ear); if not, BC > AC.
Proper recording of the Rinne test should be
"AC > BC" or "BC > AC" for each ear;
For the Weber test, "Weber → R" or "Weber → L" or "Weber not referred.“
Static vs Kinetic Labyrinth
Dynamic/Kinetic
Dynamic vs Static Semicircular canals: detect motion of the head in space (angular acceleration) Utricle: detect position of the head (and body) in space (linear acceleration)
Vestibular Pathway
Vestibular Pathway
Vestibulospinal tract
Vestibuloocular pathway
Calorics Lying down, head tilted 30 deg Seated, head tilted backward 60 deg Irrigation with cold/warm water Convection current in the endolymph Nystagmus COWS
Vestibular lesions Result in impaired postural adjustments :if unilateral •the eyes, head and body will turn to the affected side •There will be vertigo and a tendency to fall to the side of the lesion •Spontaneous nystagmus is present Nystagmus is characterized by slow movement of the eyes in one direction ff by rapid return to opposite side Vestibular nerve and/or receptors : horizontal and rotatory with fast component opposite the diseased ear Vestibular nuclie and their central connections : usually vertical
References: 1. Snell, R. Clinical Neuroanatomy, 7th ed. 2010 2. Gilman, S. Newman SW. Manter and Gantz’s Essentials of Clinical Neuroanatomy and Neurophysiology, 10th ed. 2003 3. Carague-Lansang,EN, et al. 4th ed. Lansang notes: Modules in Neuroanatomy. 2006
