Download Lab8

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
(Heschl’s) 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
basilar membrane - membranous floor of cochlear duct
Spiral Ligament
scala tympani
Blackboard 19
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
Tensor tympani
muscle
tendon
Auditory tube
LATERAL WALL
OF MIDDLE EAR
Chorda
tympani
nerve
Epitympanic recess
Tegmen
tympani
Aditus
Incus
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
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
Haines 5-18
superior olivary nuclei
trapezoid
Rostral Pons Level
Haines 5-19
Rostral Pons Level
lateral lemniscus -
Haines 5-20
lateral lemniscus and
nuclei of lateral lemniscis
Rostral Pons Level
Haines 5-22
Lateral
Lemniscis
Snake eating egg
Pons/midbrain jctn Level
Inferior
Colliculus
Brachium of
Superior
Colliculus
Medial
Geniculate
Nucleus – receives
fibers from brachium of
inferior colliculus
Rostral Midbrain Level
Haines 5-25
Brachium of
Inferior
Colliculus
Haines 5-26
MGN
Rostral Midbrain Level