Lab #8: INNER EAR, AUDITORY PATHWAYS OVERVIEW OF AUDITORY SYSTEM The auditory system allows for conscious perception of sound. Impulses from hair cells of the Organ of Corti traverse the peripheral processes of the cochlear nerve (of VIII). These fibers have cell bodies in the spiral ganglion (modiolus of the cochlea) and central processes that end in the dorsal and ventral cochlear nuclei. From these nuclei, fibers decussate in the auditory stria
and impulses travel up the brain stem bilaterally as the lateral lemniscus, with synapses in the superior olivary nuclei, trapezoid nuclei, and nuclei of the lateral lemniscus. Most ascending fibers terminate in the nucleus of the inferior colliculus, from which fibers traverse the brachium of the inferior colliculus to reach the medial geniculate nucleus of the thalamus. From the thalamus, impulses traverse the auditory radiations (sublenticular fibers) to reach the primary auditory cortex in the transverse temporal (Heschls) gyri. Blackboard 17
Modiolus - bone in core of cochlea Scala Vestibuli Scala Media Part of spiral ganglion Auditory part of CN8 - fibers in central modiolus Scala Tympani
scala vestibuli - upper space (bony labyrinth, perilymph) scala tympani - lower space (bony labyrinth, perilymph) scala media ( cochlear duct ) - middle space (membranous labyrinth, endolymph) - contains receptor cells for hearing vestibular membrane - separates scala media & vestibuli basilar membrane - separates scala media & tympani
Blackboard 18 spiral lamina (on left) - shelf-like projection of modiolus to basilar membrane auditory nerve fibers - dark fibers in spiral lamina vestibular membrane - delicate membrane below scala vestibuli Structures of the cochlear duct: stria vascularis - highly vascularized epithelium that
lines the lateral wall of the scala media from the vestibular membrane to the spiral ligament scala vestibuli Scala media cochlear duct inner hair cell - 1 row outer hair cells - 3 rows
tectorial membrane (TM) - plastic-looking, rigid membrane - receives cilia of hair cells TEMPORAL BONE IMAGE BANK The following images are labeled views of the temporal bone model used in the middle ear lab in Gross Anatomy of the Head and Neck course and the auditory system lab in the Brain and Behavior I course
Malleus: head handle LATERAL WALL OF MIDDLE EAR Mastoid antrum and air cells
LATERAL WALL OF MIDDLE EAR Aditus (hallway) leading from the epitypmanic recess to the mastoid antrum (cave) and air cells LATERAL WALL OF MIDDLE EAR Tympanic
membrane LATERAL WALL OF MIDDLE EAR Stapedius muscle Stapes (on the oval window) MEDIAL WALL OF MIDDLE EAR
Facial canal Facial nerve exiting facial canal through the stylomastoid foramen MEDIAL WALL OF MIDDLE EAR
Promontory (basal turn of cochlea) tympanic plexus containing fibers of CN IX covers the promontory during life Petrotympanic fissure is the space between the petrous part and tympanic part of the temporal bone
Chorda tympani nerve Mastoid process is a branch of facial in the cheek fascia that ascends into the petrous temporal bone
Facial nerve exiting the stylomastoid foramen Styloid process LATERAL ASPECT OF TEMPORAL
BONE MODEL SUPERIOR VIEW OF TEMPORAL BONE MODEL Semicircular canal Cochlea
Genu of the facial nerve Semicircular canals Facial nerve entering the internal acoustic meatus
MEDIAL ASPECT OF THE TEMPORAL BONE MODEL Jugular bulb Blackboard 21 Haines 2-20 2-20
2-34 Blackboard 22 note the relations of cranial nerves 7 and 8 as they pass through the internal auditory canal. Note their relation to the posterior cranial fossa, pons, and cerebellum. Haines 3-1 We rn
icke 's A re a audi to corte ry assoc iatio
x Broc has Are a n Haines 5-12
dorsal and ventral cochlear nuclei - located lateral & dorsal to the inferior cerebellar peduncle (restiform body) - contain cell bodies of second order neurons in auditory path - receive fibers from cochlear nerve - will send axons into the acoustic stria Rostral Medulla Level
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