Introduction The slides for this lab are located in the “Special Senses: Ear” folder on the Virtual Microscope. This guide provides you with a short description of the slides that you will be examining and a short conceptual framework for studying them.
The ear is composed of outer, middle and inner components. This lab focuses on the structures invisible grossly that lie within the petrous part of the temporal bone – the inner ear. The inner ear has two components:
a. the cochlea which detects sounds and functions in ‘hearing’ b. the vestibular system which detects accelerations experienced by the head and functions in maintaining balance as well as eye position in response to movement.
In this lab you will observe the cells and tissues that comprise both systems
Learning objectives and activities Using the Virtual Slidebox:
A Examine the structures of the external ear (pinna/auricle) and use your knowledge of the basic tissues to identify all components of the tissue.
B Use a histological section of the internal ear to demonstrate how sensory information regarding sounds makes its way to the cochlear nerve.
C Use a histological section of the internal ear to demonstrate how sensory information regarding balance makes its way to the vestibular nerve.
D Complete the self-quiz to test your understanding and master your learning Examine the structures of the external ear (pinna/auricle) and use your knowledge of the basic tissues to identify all components of the tissue.
Examine Slide 1 and identify the following basic structural components
The auricle is the external component of the ear. It is responsible for the collection, localization and local amplification of sound i. General organization
a. Skin Test your The ear is covered in, thin, hairy skin. You should be able to knowledge identify the major features and basic tissues associated with skin about skin using including the epidermis, dermis, hair follicles, sweat and Slide 1 sebaceous glands.
b. Elastic cartilage The major structural feature of the external ear is the elastic Test your cartilage contained within it. This cartilage imparts flexibility to knowledge of the external ear. You should be able to identify the key features of elastic cartilage elastic cartilage in this image. using Slide 1
c. Skeletal muscle Find evidence of You should be able to find evidence of the muscles of facial muscles of facial expression that are associated with movements of the ear. These expression in are the auricular muscles. Slide 1
Use a histological section of the internal ear to demonstrate how sensory information regarding sounds makes its way to the cochlear nerve.
Slide 2 shows only part of the inner ear. Use this slide initially to interpret the general organization of the region shown by locating the structures highlighted in the diagram below
The basic architecture of the inner ear is a bony labyrinth hollowed out within the petrous part of the temporal bone within which sits a membranous labyrinth. Both labyrinths are filled with fluid and both contribute to the cochlea and the vestibular system.
vestibular system: semicircular canal: Find it in Slide 2 oval window stapes ampulla: Find it in Slide 2 incus utricle malleus saccule
vestibular nerve in Slide 2 cochlear nerve in Slide 2
temporal bone
Find it in Slide 2
outer ear (exter nal middle acoustic ear meatus)
tympanic membrane
bony labyrinth
(pink space) cochlea Find it in Slide 2 Find it in Slide 2
membranous
round window labyrinth Eustachian tube (blue space) (contains cartilage) Find it in Slide 2 Find it in Slide 2 i. General organization of the cochlea (Slide 3)
a. Bony labyrinth - is located in the petrous part of the temporal bone Identify the - is formed from compact bone (identify features!) bony labyrinth - forms a spiraling canal that communicates with the in bony labyrinth of the vestibular system via the vestibule Slide 3a - is filled with perilymph (CSF-like in composition) - is divided into the “scala vestibuli” and “scala tympani”
b. Membranous labyrinth Identify the - is completely enclosed within the bony labyrinth membranous labyrinth - is filled with endolymph in - in the cochlea this region is called the ‘scala media’ or ‘cochlear Slide 3b duct’
c. Helicotrema Identify the - the apex of the cochlea (it is broken in this section) helicotrema in - it is at this point that the scala vestibuli becomes Slide 3c the scala tympani
d. Modiolus Identify the - the central, conical shaped, bony core of the cochlea around modiolus in which the bony labyrinth turns 2.75 times in total Slide 3d - it houses the axons that run within the cochlear nerve
cochlea as seen cochlea sectioned in Slide 3
semicircular canals (of vestibular system)
ii. The scala
e. Scala vestibuli of the bony labyrinth - sits ‘above’ the scala media Identify the - is filled with perilymph scala vestibuli - conveys fluid vibrations from the oval window through the in perilymph that fills the region Slide 3e - communicates with the scala tympani at the helicotrema
f. Scala tympani of the bony labyrinth - sits ‘below’ the scala media Identify the scala - is filled with perilymph tympani in - conveys fluid vibrations within the perilymph toward the round Slide 3f window
g. Scala media (cochlear duct/membranous labyrinth) - houses the organ of Corti Identify the scala - is triangular with its acute angle attached to the osseus spiral media in lamina of the modiolus Slide 3g - is filled with endolymph secreted by the stria vascularis
scala vestibuli (perilymph) scala media
(endolymph) osseus spiral lamina of modiolus
organ of Corti
scala tympani (perilymph) iii. The membranes
Identify the h. Vestibular (Reissner’s) membrane vestibular membrane - separates the scala vestibuli and scala media in Slide 3h
i. Basilar membrane - separates the scala tympani and scala media - stretches between the osseus spiral lamina of the modiolus medially and the spiral ligament laterally Identify the basilar - decreases in stiffness and width as it spirals from base to apex membrane in within the cochlea which gives rise to its tonotopic map Slide 3i - vibrates closer to base in response to high frequency sounds - vibrates closer to apex in response to low frequency sounds - the organ of Corti sits on top of this membrane
j. Tectorial membrane - is a gelatinous membrane within the scala media Identify the tectorial - the stereocilia of the hair cells are embedded in it membrane in - when the basilar membrane is displaced by fluid vibrations the Slide 3j stereocilia of the hair cells push against the tectorial membrane triggering the events that result in depolarization the hair cells
vestibular scala
(Reissner’s) vestibuli
membrane stria vascularis scala media tectorial membrane outer hair cells
inner hair cells
scala tympani basilar inner pillar phalangeal membrane tunnel cells cells iii. The Organ of Corti
k. Outer hair cells - a continuous spiraling row of neuroepithelial cells Identify the - sit along the outer aspect of the organ of Corti outer hair cells - form rows three (base) to five (apex) ranks deep in Slide 3k - have stereocilia and a (kino)cilium - are responsible for the tuning function of the ear
l. Inner hair cells Identify the inner hair - a single, continuous row of neuroepithelial cells cells in - sit along the inner aspect of the organ of Corti Slide 3l - have stereocilia and a (kino)cilium - are the primary sensory cells for hearing
m. Tectorial membrane Identify the tectorial - the gelatinous membrane roof of the organ of Corti within which membrane in the stereocilia of the hair cells are embedded Slide 3m
n. Phalangeal cells Identify the phalangeal - surround the base of the outer hair cells cells in - send projections toward the endolymphatic space that flattens Slide 3n and surrounds the apical end of each hair cell. - hold the outer hair cells in place at their base and apex.
o. Pillar cells and inner tunnel Identify the - have broad apical and basal surfaces pillar cells - form a triangular inner tunnel at their central part and inner tunnel - the inner tunnel contains a perilymph like fluid called cortilymph in Slide 3o iv. Other structures
p. Stria vascularis - a pseudostratified columnar epithelium Identify the - differs from all other epithelia in the fact that it is vascularized stria vascularis - is responsible for the secretion of the K+ rich endolymph into the in Slide 3p scala media
q. Spiral ganglion and cochlear nerve Identify the - the sensory ganglion of the cochlea housed in the modiolus spiral ganglion and - contains the cell bodies of bipolar neurons that run within the cochlear nerve cochlear nerve in Slide 3q
Use a histological section of the internal ear to demonstrate how sensory information regarding balance makes its way to the vestibular nerve.
Slide 2 and Slide 4 each show different parts of the inner ear. Use the slides to interpret the general organization of vestibular system by locating the structures highlighted in the diagram below in the appropriate slides.
The vestibular system is composed of the semicircular canals and their ampullae, the utricle and the saccule. vestibular system:
oval window semicircular canals Slide 2 and 4 stapes ampulla Slide 2 and 4 incus utricle Slide 2 and 4 malleus saccule not visible
Find it in Slide 2
temporal bone Find it in Slide 2, and Slide 4 outer ear (exter nal middle acoustic ear meatus)
tympanic membrane
bony labyrinth
(pink space) cochlea
Find it in Slide 2,
and Slide 4 membranous
round window labyrinth Eustachian tube (blue space) (contains cartilage) Find it in Slide 2, and Slide 4 i. General organization of the vestibular system
a. Bony labyrinth - is located in the petrous part of the temporal bone Identify the - is filled with perilymph bony labyrinth - forms a vestibule that contains the utricle and saccule and is in connected to the bony labyrinth of the cochlear Slide 4a - forms the three semicircular canals
b. Membranous labyrinth - is completely enclosed within the bony labyrinth Identify the - is filled with endolymph membranous labyrinth - forms the semicircular ducts within the semicircular canals in Slide 4b - forms sacs in the vestibule called the utricle and saccule
c. Semicircular canals - are three tubes occupying three planes: sagittal, frontal and Identify a section horizontal through a semicircular - all branch from the utricle canal in - have dilated regions closest to the utricle called the ampulla Slide 4c - each ampulla contains a crista ampullaris - are responsible for sensing rotation acceleration
d1. Utricle - is a dilated region of the membranous labyrinth There is a distinctive - contains the macula of the utricle which is oriented in the utricle in horizontal plane Slide 4d - senses horizontal acceleration however, normally it is not possible to d2. Saccule differentiate the two - is a dilated region of the membranous labyrinth histologically - contains the macula of the saccule which is oriented in the (see note below) vertical plane - senses vertical acceleration, changes in gravitational pull
Important note: It is (almost) impossible to differentiate between the utricle and saccule in histological sections. You can identify the utricle distinctly only if you can see its macula in very close proximity to a crista ampullaris (of the ampulla) – without seeing this anatomical relationship it is not possible to differentiate the two.
ii. Utricle (and saccule)
Using the utricle in Slide 4 as the example – locate the following structures and features of both the utricle and saccule. Remember that both utricle and saccule are identical in structure. They only differ in their location within the bony labyrinth and their orientation
d. Utricle Identify the - is a dilated region of the membranous labyrinth utricle - contains the macula of the utricle which is oriented in the in horizontal plane Slide 4d - senses linear, vertical acceleration
e. Macula - is the structure responsible for sensing linear acceleration Identify a macula - is composed of three parts: in i. otolithic membrane Slide 4e ii. otoconia/otoliths iii. sensory epithelium
f. Otolithic membrane Identify the otolithic - a gelatinous membrane that overlies the sensory epithelium membrane in - composed of collagen, ground substance and polysaccharides Slide 4f - contains otoconia/otoliths in its surface
g. Otoliths/otoconia - calcium carbonate crystals in the otolithic membrane - when accelerating the otoliths lag behind in the gelatinous Identify otoliths otolithic membrane in - this bends the stereocilia of the sensory epithelium Slide 4g - once constant speed is achieve, the otoliths ‘catch up’ and acceleration is no longer perceived.
h. Sensory epithelium - a pseudostratified epithelium containing hair cells (with Identify the stereocilia) and supporting cells (no stereocilia) sensory epithelium - the stereocilia are embedded in the otolithic membrane and stereocilia in - movement of the otoliths and otolithic membrane deflects the Slide 4h stereocilia which triggers depolarization of cells
iii. Semicircular canals and ampullae
i. Semicircular canal - one of three tubes, oriented in three planes in the vestibular system Identify a cross-section - is cut in cross-section in this image through a semicircular - is enclosed by a the bony labyrinth (contains perilymph) canal in - contains the membranous labyrinth (contains endolymph) Slide 4i - is responsible for conveying the fluid whose movement is detected by the crista ampullaris and interpreted as rotational movement
j. Ampulla Identify the ampulla - one of three dilated regions of the semicircular canals in - lies immediately adjacent to the utricle Slide 4j - contains the sensory organ – the crista ampullaris
k. Crista ampullaris - are located in the ampullae of the semicircular canal Identify the crista - is the structure responsible for sensing angular movement of the ampullaris head (fluid movement in the semicircular canal) in - is composed of two parts: Slide 4k i. cupola ii. sensory epithelium
l. Cupola - a gelatinous membrane that extends almost the full length of Identify the the ampulla utricle in - composed of collagen, ground substance and polysaccharides Slide 4l - is moved by endolymph within the ampulla during head movements
m. Sensory epithelium - a pseudostratified epithelium containing hair cells (with Identify the stereocilia) and supporting cells (no stereocilia) sensory epithelium in - the stereocilia are embedded in the cupola Slide 4m - movement of the cupola deflects the stereocilia which triggers depolarization of cells
In addition to all the basic tissues in slides and all previously covered items from MOHD1 that are relevant to interpreting tissue structure you must be able to identify the following structures and their features:
Ear (auricle) Vestibular (Reissner’s) membrane Elastic cartilage Tectorial membrane (inc. all cartilage features) Organ of Corti Epidermis Inner hair cells (inc. all epidermis features) Outer hair cells Dermis Stereocilia (inc. all dermis features) Pillar cells Hair Phalangeal cells Sebaceous gland Inner tunnel Sweat gland (eccrine) Spiral ganglion Stria vascularis
Inner ear (common features) Auditory/Eustacian tube Semicircular canal Temporal bone (petrous) Bony labyrinth (inc. all bone features) Membranous labyrinth Bony labyrinth Ampulla Membranous labyrinth Crista ampullaris Cochlear nerve Cupola Vestibular nerve Sensory epithelium Vestibulocochlear nerve Stereocilia Endolymph Perilymph Utricle Cochlea Saccule Cochlear duct (memb. labyrinth) Macula Bony labyrinth Otoliths/Otoconia Helicotrema Sensory epithelium Modiolus Otolithic membrane Scala tympani Scala vestibuli Scala media Cortilymph