BIO210 Weekly Guide #11
GENERAL AND SPECIAL
SENSES
After completing this laboratory you should be able to:
1) Name the cranial nerves servicing the eye, ear, taste buds, and olfactory epithelium
2) Describe the sensory projections into the brain from the special senses of olfaction, vision, audition, taste, and equilibrium
2) Recognize the olfactory mucosa in histological section
3) Identify the chambers and major structures of the eye in models and histological section, providing functions for each
4) Identify the major structures of the inner, middle, and outer ear in models and histological section, describing how each functions in audition and/or vestibular/equilibrial sense
5) Identify taste buds in models and histological section
6) Identify Meissner's and Pacinian corpuscles and describe the sensory function of each.
Guide to Gross Anatomy Guide to Histology Guide to Physiology
Outline
I. Vision
A. Eye {FAP 17-3}
conjunctiva, cornea, sclera, choroid, retina, lens, ciliary body
iris
pupillary sphincter & dilator
anterior, posterior, and vitreal chambers, aqueous and vitreous humors
retinal structure
10 layers
cell types
photoreceptors - rods and cones
bipolar cells
ganglion cells
horizontal, amacrine, and Müller cells
B. Innervation {FAP 17-4; Spotlights 17-13, 17-16}
vision - NII; general sensation - NV ophth.; ciliary body - NIII;
sphincter - parasympathetic (NIII); dilator - sympathetic
extraocular muscles (actions also)
superior rectus, medial rectus, inferior rectus, inferior oblique - NIII
superior oblique - NIV
lateral rectus - NVI
C. Optic nerve, chiasm, projectons {FAP 17-4}
II. Hearing and Vestibular Sense {FAP 17-5}
A. Ear
location - petrous portion of temporal bone
external ear
pinna
external auditory meatus
tympanic membrane
middle ear
ossicles
malleus, incus, stapes
muscles
tensor tympani, stapedius
Eustachian tube
inner ear
bony & membranous labyrinths
perilymph and endolymph
cochlea
vestibular and basilar membranes
scala vestibuli, scala tympani, scala media
oval widow, helicotrema, round window,
organ of Corti
hair cells, tectorial membrane, arch of Corti
spiral ganglion
vestibule, semicircular canals, saccule, utricle
B. Mechanism of hearing
air-->ossicles--> fluid mechanical transduction
basilar membrane tuning
hair cell excitation
C. Mechanisms of vestibular sense
hair cells
semicircular canals
saccule & utricle - otoliths
D. Vestibulocochlear nerve
auditory branch
vestibular branch
E. Auditory and vestibular projections
III. Olfaction {FAP 17-1; Spotlight 17-2}
A. Olfactory epithelium - receptors, sustentacular cells, basal cells
B. Primary olfactory nerve
C. Olfactory bulbs
D. Olfactory projections
IV. Taste {FAP 17-2; Spotlight 17-2}
A. Taste buds
structure
pore
receptors vs. sustentacular cells
location
papillae
distributions of "primary" tastes
innervation
NVII - ant 2/3 of tongue
NIX - post. 1/3 of tongue
NX - epiglottis
B. Gustatory projections
V. Somatosensation {FAP 15-3}
Gross Anatomy List
eye
extrinsic muscles
superior, inferior, lateral medial rectus
superior, lateral oblique
optic nerve (NII)
conjunctiva
sclera
cornea
iris and pupil
crystalline lens
ciliary body
retina
optic disc
fovea
choroid/tapetum
chambers
anterior chamber
posterior chamber
vitreous chamber
nasal cavity
conchae
nasal mucosa
cribriform plate of the ethmoid bone
olfactory nerve rootlets (NI)
oral cavity
tongue
epiglottis
ear
external ear
pinna
acoustic canal
tympanic membrane (eardrum)
middle ear
ossicles
malleus, incus, stapes
muscles
tensor tympani
stapedius
inner ear
bony and membranous labyrinths
utricle
saccule
cochlea
oval window
round window
vestibuilocochlear nerve (NVIII)
spiral ganglion
related structures
internal auditory foramen
petrous portion of temporal bone
Eustacian tube
Key: Know location and function of all structures
Guide to Gross Anatomy
Vision {FAP Fig 17-5, 17-19; APL Ex 15-1}
The visual sensory surface is the retina on the inner posterior surface of the eyeball. The retinal fibers project through the optic nerves, chiasm, and tracts bilaterally to the thalamic lateral geniculate nuclei and the superior colliculi. The lateral geniculate is in the primary visual pathway and projects to the primary visual cortex in the occipital lobe. The superior colliculus is in the eye movement control pathway and projects primarily to the nuclei of the cranial nerves which control eye movement (NIII, NIV, NVI).
a) The eyeball consists of three concentric coats. The outer coat is fibrous and is represented by the sclera and the cornea. The middle coat is vascular and consists of the choroid, ciliary body, and iris. The inner coat is nervous tissue - the retina.
- On the models locate the anterior and posterior chambers of the eye. These are separated by the iris. They contain aqueous humor, a blood plasma filtrate, which is circulated from the posterior to the anterior chamber. Where is the vitreous body? Does the vitreous humor circulate?
- Identify and give the significance for vision of the macula lutea, fovea centralis, and optic disc.
b) Identify and give the innervation and action of the following intrinsic muscles of the eye:
ciliary muscle pupillary sphincter pupillary dilator
c) Identify and give the innervation and action of the following extrinsic muscles of the eye:
superior rectus lateral rectus superior oblique
inferior rectus medial rectus inferior oblique
Hearing and Vestibular Sense {FAP Fig 17-22 to 17-24; APL Ex 15-2}
The auditory sensory surface is four rows of hair cells that run the length of the basilar membrane of the cochlea. This surface projects via the spiral ganglion through the auditory branch of NVIII to the cochlear nucleus of the medulla. From there the pathways ascend bilaterally through a series of brainstem nuclei, through the inferior colliculi to the medial geniculates of thalamus, and then to the primary auditory cortex of the temporal lobes.
The vestibular sensory cells are hair cells of the saccule, utricle, and semicircular canal ampullae of the inner ear. They project via the vestibular ganglion through the vestibular nuclei of the medulla to the cerebellum and spinal cord.
a) The ear has three regions - the external, middle, and inner ears. On the charts and models locate the following structures:
pinna external auditory meatus tympanic membrane
b) On the models locate the following structures of the middle ear:
malleus stapes round window
incus oval window Eustachian tube
- The ossicles (malleus, incus, and stapes) form a bony chain from the tympanic membrane to the oval window. Note that this chain functions as a mechanical amplifier, due to the lever action of the bones and the size difference between the tympanic membrane and the oval window.
- What is the function of the Eustachian tube? With what respiratory passage does it connect?
c) The inner ear consists of an intricately hollowed out space in the petrous portion of the temporal bone - the bony labyrinth. Within this space is suspended a separate membranous sac - the membranous labyrinth. The membranous labyrinth follows all of the convolutions of the bony labyrinth. On the models identify the following structures of the bony labyrinth:
vestibule cochlea semicircular canals
- The cochlea contains the auditory organ, while the vestibule and the semicircular canals contain the vestibular organ. The fine detail of the cochlea will be discussed with microscopic anatomy.
- The motion of the stapes against the oval widow transmits acoustic vibrations to the fluid of the inner ear. What is the function of the other membrane covered aperture between the inner and middle ears, namely the round window?
- What is the functional significance of the fact that the three semicircular canals are oriented orthogonally (at right angles to each other)? What specific sensory information do the semicircular canals provide?
- What specific sensory information is provided by the utricle and saccule chambers of the vestibule?
Olfaction {FAP Fig 17-1; APL Ex 15-3}
The olfactory sensory cells lie in the olfactory mucosa on the roof of the nasal cavity. On each side the olfactory nerve (NI) projects as multiple bundles through the foramina of the cribriform plate of the ethmoid bone to the olfactory bulb.
a) The olfactory bulbs are the primary sensory cortex of the olfactory system. The bulbs project via the lateral olfactory tracts to multiple limbic and cortical sites.
- In the skull locate the cribriform plate of the ethmoid bone with its multiple foramina. Identify the crista galli which separates the two bulbs and the olfactory grooves which support them.
- In the prepared brains and models locate the olfactory bulbs and the lateral olfactory tracts. The olfactory nerves are often sheared off when the brain is removed from the skull.
b) A large part of the aversiveness of noxious odors is due to the stimulation of non-olfactory free nerve endings in the nasal cavity. What branch of what three-part nerve provides these general sensory endings?
Taste {FAP Fig 17-3; APL Ex 15-3}
The sensory cells of taste are located in the taste buds imbedded in the upper surface of the tongue (with a few in the pharyngeal surface of the epiglottis).
a) Taste information is conveyed through the cranial nerve nuclei of the hindbrain, through the thalamus, and on to the gustatory region of the primary somatosensory cortex (postcentral gyrus).
- On the models and charts, identify the region served by each of the cranial nerves which carry taste sensation (NVII, NIX, NX).
b) Identify the regions of the tongue sensitive to each of the four "primary taste qualities".
- What nerves provide general sensation from and motor input to the tongue?
Guide to Histology
Special and General Senses
For each of the special senses we will be concerned mostly with the histological structure of the receptive organ(s).
a) Olfactory Epithelium {APL Fig 17-1b}
The olfactory epithelium is a sheet of chemoreceptors and support cells located in the roof of the nasal cavity.
- Study the olfactory epithelium on demonstration. Try to distinguish between receptor and sustentacular cells. Note that the receptors are actually neurons which send axons directly to the CNS. Olfactory receptor cells are apparently unique among adult neurons in that they are continually dying and being replaced by new neurons.
- Note the cilia of the receptor cells. These are non-motile and contain the actual chemoreceptor molecules.
b) Taste Buds {APL Fig 17-3c}
Taste buds are located principally on the dorsal surface of the tongue, although a few may also be found on the epiglottis.
- Locate the taste buds on the surface of he tongue. They are most numerous in the walls of the circumvallate papillae.
- On each taste bud, note the pore which opens to the surface. Distinguish between the receptor and sustentacular cells. Which cranial nerves carry the taste sense?
c) Retina {APL Fig 17-7}
The retina is located on the inner posterior surface of the eye.
- Study the models and demonstration slide(s) of the eye to identify the labeled structures. Pay particular attention to the diagrams and demonstration slide of the retina.
- Note that the retina has ten distinct layers. Where are the photosensitive segments of the receptors (rods and cones) located? Trace the path of light through the eye to the photoreceptors.
d) Cochlea {APL Fig 17-27, 17-28}
The auditory mechanoreceptors are four rows of hair cells located in the "organ of Corti" of the basilar membrane in the cochlea of the inner ear.
- In the slide of the cochlea, identify the scala tympani, scale vestibuli, scala media, basilar membrane, vestibular membrane, and organ of Corti. Identify the receptor hair cells on either side of the arch of Corti. Trace the transfer of mechanical energy from acoustical vibrations of the air to movement and distortion of the hair cell processes.
e) Somatosensory Organs {APL Fig 15-4}
We will study two specialized sensory endings of the skin. Meissner's corpuscles are small, dense, oval whorls of flattened cells located in the dermal papillae. Pacinian corpuscles are larger and more circular, resemble onions in cross section, and are typically found much deeper in the dermis.
- Identify Pacinian and Meissner's corpuscles in the skin models and microscope slides. What is the function of each? Why is it more important for Meissner's corpuscles to be located just beneath the epidermis?
Guide to Physiology
Simple Vision Tests
Blind Spot
1) Hold the index card with the cross and the circle at arm's length directly in front of you, so that the cross is to your left.
2) Close your left eye.
3) Look directly at the cross.
4) Move the card slowly towards your nose. Again, KEEP LOOKING DIRECTLY AT THE CROSS AT ALL TIMES.
5) At some point (about 12 inches from your nose) the circle will disappear into the blind spot of the retina.
6) Flip the card over, switch eyes, and repeat the above steps.
Q: Is each blind spot in the nasal or temporal visual field? So is it on the nasal or temporal retina?
Q: Why are you not normally aware of your blind spot(s)?
Distribution of Cones/Peripheral Color Vision
1) Find the three index cards with the colored dots.
2) Keeping both eyes open, AND LOOKING STRAIGHT AHEAD, bring each card in slowly from the periphery.
Q: At what point can you really "see" and discriminate color?
Q: What does this tell you about where the color-discriminating cone cells are in your retina?
Spatial Frequency Discrimination
1) Set the 8 1/2 x 11 card with the spatial wave pattern up on the marker tray of the white board.
2) Stand about 3 feet from the card and look directly at it. Now, keeping both eyes open and looking directly at the card, back slowly away.
Q: Where on the horizontal dimension do the vertical lines seem to be the tallest?
Q: Does this location change as your distance from the card gets greater (and its image on your retinas gets smaller)?
Q: What does this tell you about the ability of your visual system to discriminate "spatial frequencies"?
Q: Could measurements tell you something about the spacing of visual receptor cells in the fovea of your retina?
Simple Hearing Tests
Weber Test (APL Unit 15, Exercise2)
1) Hold the tuning fork by its base and strike one of the tines gently on the table.
2) Hold the base of the vibrating tuning fork directly over the center of your partner's head.
Q {partner}): Is the sound louder in one ear (lateralization) or equally loud in both?
Rinne Test (APL Unit 15, Exercise2)
1) Strike the tuning fork and hold the BASE on your partner's mastoid process.
2) Start a stop watch and time how long your partner can hear the sound.
3) When your partner can no longer hear the sound, quickly move the tuning fork to right next to her external auditory canal. Continue timing until she can no longer hear the sound.
Q: Which situation tested bone conduction? Which tested air conduction?
Equilibrium Test
Romberg Test (APL Unit 15, Exercise2)
1) Have your partner stand with her back against the whiteboard and her arms at her side. Draw her outline with a DRY-ERASE marker.
2) Instruct her to close her eyes and stand as still as possible for ONE MINUTE. Record with the marker the limits of how far her body sways.
3) Repeat the experiment with your partner's eyes open.
Q: Under which circumstance did she sway more? Why?
Taste Test
Lingual Distribution of Primary Taste Receptors
1) Use a clean cotton swab and the dilute sugar solution to map out the distribution of "sweet" receptors on your partner's tongue. Have her rinse her mouth with water.
2) Repeat this process for sour (lemon juice), salty (table salt), and bitter (Epson salts).
3) Use the blank template sheets to draw the distribution of each type of receptor.
Q: How does the distribution of each receptor type differ?
Note: The classical distribution of taste receptor types across the tongue has been called into serious questiuon lately. What do your results suggest?
Somatosensation Tests
Two-point Discrimination
Use a pair of sharp probes to CAREFULLY map the "two point discrimination" distance at several locations on your partner's fingers, hands, arms, and back, using the following process:
1) Start with the two tips touching each other, then repeatedly touch them to the area, while slowly separating the tips.
2) Record the "inter-tip" distance at which your partner can discriminate the touch as two separate points.
Q: In what regions of your body do you have the best discrimination? The worst?
Q: What does this tell you about the relative density of light touch receptors in those areas?
Adaptation of Hot and Cold Thermoreceptors
1) Place your left hand in the ice water bowl and your right hand in the warm water bowl. Hold them there for 2 minutes.
2) Quickly transfer both hands to the central room-temperature water bowl.
Q: Do you hands "feel" the same? Which one feels warmer and which cooler?
Q: How can you explain your results?