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Chapter 17: The Special Senses
Muse Bio 2440 w12Lecture #6 5/24/12
Comparison of General and Special Senses
General Senses Include somatic
sensations (tactile, thermal, pain, and proprioceptive) and visceral sensations.
Scattered throughout the body.
Simple structures.
Special Senses Include smell, taste,
vision, hearing and equilibrium.
Concentrated in specific locations in the head.
Anatomically distinct structures.
Complex neural pathway.
Olfaction: Sense of Smell Olfactory epithelium contains 10-100 million
receptors. Olfactory receptor- a bipolar neuron with cilia
called olfactory hairs.
- Respond to chemical stimulation of an odorant molecule.
Supporting cells- provide support and nourishment.
Basal cells- replace olfactory receptors.
Olfactory Epithelium and Olfactory Receptors
Olfactory Epithelium and Olfactory Receptors continued…
Smell (Olfaction)
Olfactory Pathways
Arriving information reaches information centers
without first synapsing in thalamus
Physiology of Olfaction
Can detect about 10,000 different odors. Odorant binds to the receptor of an olfactory
hair→ G-protein activation→ activation of adenylate cyclase→ production of cAMP→ opening of Na+ channels→ inflow of Na+ →generator potential→ nerve impulse through olfactory nerves→ olfactory bulbs→ olfactory tract→ primary olfactory area of the cerebral cortex.
Olfactory transduction
Summary of sense of smellOdorant molecule binds one of 10-100 million receptors.Conformational change in receptor interacts with G proteinG protein activates adenylate cyclase to generate cAMPcAMP opens Na+ channels to initiate depolarization. Information on number of action potentials decoded by olfactorybulbs.
Animals have greater numbers of receptors thus better sense of smellUsually 10,000 times greater.
Gustation: Sense of Taste
Taste bud
Taste
15-11
Taste (Gustation)
Gustatory Discrimination
Primary taste sensations
Sweet (sugars)
Salty
Sour (acids)
Bitter (alkali)
umami - savory (fat)
Taste (Gustation)
Gustatory Discrimination Dissolved chemicals contact taste hairs
Bind to receptor proteins of gustatory cell
Salt and sour receptors
Chemically gated ion channels
Stimulation produces depolarization of cell
Sweet, bitter, and umami stimuli
G proteins: (proteins that bind GTP- secondary messengers)
gustducins
Anatomy of Taste Buds and Papillae Taste bud- made of three types of epithelial
cells: supporting cells, gustatory receptor cells and basal cells.
About 50 gustatory cells per taste bud. Each one has a gustatory hair that projects through the taste pore.
Taste buds are found in the papillae. Three types of papillae: vallate
(circumvallate), fungiform and foliate.
Physiology of Gustation
Five types of taste: sour, sweet, bitter, salty and umami.
Tastant dissolves in saliva → plasma membrane of gustatory hair→ receptor potential→ nerve impulse via cranial nerves VII, IX and X→ medulla→ thalamus→ primary gustatory area of the cerebral cortex.
Gustatory Pathway
Neuronal Pathways for Taste
Chorda tympani (part of VII): carry sensations from anterior one-third of tongue (except from circumvallate papillae
Cranial nerve IX and X carry information from posterior one-third tongue, circumvallate papillae, superior pharynx, epiglottis.
Information goes to medulla oblongata where decussation takes place and information projects from there to the thalamus. Then projects to taste area of cortex (extreme inferior end of the postcentral gyrus)
15-17
Specialist taste buds map to certain regions of tongueMaps differ somewhat , but generally
Actions of the Major Tastants
15-19
Vision or Sight
Visible light: 400-700 nm.
Accessory Structures of the Eye Eyelids or palpebrae-
Eyelashes and eyebrows-
Extrinsic eye muscles-
Accessory Structures of the Eye
The Lacrimal Apparatus
Tears from the lacrimal apparatus- lacrimal glands→ excretory lacrimal ducts→ lacrimal puncta→ lacrimal canals→ nasolacrimal sac→ nasolacrimal duct.
Anatomy of the Eyeball
The Eye
Figure 17–4b The Sectional Anatomy of the Eye.
Wall of the Eyeball Three layers:
Fibrous tunic- outer layer Sclera “white” of the eye Cornea-transparent coat
Vascular tunic or uvea- middle layer Choroid Ciliary body consists of ciliary processes and ciliary muscle Iris lens (alpha crystalin protein)
Retina- inner layer Optic disc Macula lutea- fovea centralis
Responses of the Pupil to Light
Pupil is an opening in the center of the iris.
Contraction of the circular muscles of the iris causes constriction of the pupil.
Contraction of the radial muscles causes dilation of the pupil.
Interior of the Eyeball Lens-
lack blood vessels, consists of a capsule with proteins (crystallins) in layers; transparent.
Lens divides the eyeball into two cavities: anterior and posterior.
Anterior cavity- further divided into anterior and posterior chambers. Both are filled with aqueous humor.
Posterior cavity (vitreous chamber)-filled with vitreous body.
Cavities of the Eyeball
Refraction of Light Rays
Refraction is the bending of light rays.
The cornea and lens refract light rays.
Most refraction done at corneal level - repair with corneal re-mapping (keratotomy)
Accommodation and the Near Point of Vision
Increase in the curvature of the lens for near vision is called accommodation.
Near point of vision is the minimum distance from the eye that an object can be clearly focused.
Refraction Abnormalities and their Correction Nearsightedness (myopia)- close objects
seen clearly. Image is focused in front of the retina. Correction- use of concave lens.
Farsightedness (hyperopia)- distant objects seen clearly. Image is focused behind the retina. Correction- use of convex (magnifyer) lens.
Most scientists
The Eye
Figure 17–6c Photograph of the Retina as Seen through the Pupil.
Most cones in fovea
Retina
15-35
Rods and Cones Named after the shapes of their outer
segments. Rod- (more sensitive to light, but no color ) Cones- three types: red, green and blue. Outer segment- contains photopigments.
Transduction of light energy into receptor potential occurs here.
Inner segment- contains the nucleus, Golgi complex and mitochondria.
Structure of Rod and Cone Photoreceptors Back of eye
Front of eye
Photoreceptors
15-38
Photopigments Two parts: opsin (four types, three in the cones
and one in the rod) and retinal (light absorbing part).
Rhodopsin- photopigment in rods. Cone photopigments- three types. (one for each
color)
Absorption of light by a photopigment → structural changes.
Bleaching and Regeneration of Photopigment
Rod disc in outer segment
Discmembrane
cis-retinal
opsin Isomerizationof retinal
Light
Rhodopsinmolecule
Coloredphotopigment(rhodopsin)
1
Rod disc in outer segment
Discmembrane
cis-retinal
opsin
opsin
Isomerizationof retinal
Light
trans-retinal
Trans-retinalseparatesfrom opsin(bleaching)
Rhodopsinmolecule
Coloredphotopigment(rhodopsin)
1
2
Rod disc in outer segment
Colorless products
Discmembrane
cis-retinal
opsin
opsin
opsin
Isomerizationof retinal
Light
trans-retinal
Retinalisomeraseconverts trans- to cis-retinal
trans-retinal
Trans-retinalseparatesfrom opsin(bleaching)
Rhodopsinmolecule
Coloredphotopigment(rhodopsin)
1
23
Rod disc in outer segment
Colorless products
Discmembrane
cis-retinal
cis-retinal
opsin
opsin
opsin
opsin
Cis-retinalbinds to opsin(regeneration)
Isomerizationof retinal
Light
trans-retinal
Retinalisomeraseconverts trans- to cis-retinal
trans-retinal
Trans-retinalseparatesfrom opsin(bleaching)
Rhodopsinmolecule
Coloredphotopigment(rhodopsin)
1
23
4
15-42
Bleaching and Regeneration of Photopigment1. Isomerization: In darkness, retinal has a
bent shape called cis-retinal. Absorption of photon causes straightening of the retinal (trans-retinal).
2. Bleaching: trans-retinal separates from opsin.
3. Regeneration: trans-retinal→ cis-retinal.
Light and Dark Adaptation
Light adaptation: Dark → light. Faster. Dark adaptation: Light →dark. Slow. Cones regenerate rapidly whereas rhodopsin
regenerates more slowly.
Operation of Rod Photoreceptors
Rods Bipolar photoreceptor cells; black and white vision. Found over most of retina, but not in fovea. More sensitive to
light than cones. Protein rhodopsin changes shape when struck by light; and
eventually separates into its two components: opsin and retinal Retinal can be converted to Vitamin A from which it was originally
derived. In absence of light, opsin and retinal recombine to form rhodopsin.
Rods are unusual sensory cells: when not stimulated they are hyperpolarized. Light causes them to depolarize.
Depolarization of rods causes depolarization of bipolar cells causing depolarization of ganglion cells
Light and dark adaptation: adjustment of eyes to changes in light. Happens because of changes in amount of available rhodopsin.
15-46
Color Blindness and Night Blindness Color blindness- inherited inability to
distinguish between certain colors. Result from the absence of one of the three types
of cones. Most common type: red-green color blindness.
Night blindness or Nyctalopia- vitamin A deficiency.
Cones Bipolar receptor cells. Responsible for color vision and
visual acuity. Numerous in fovea and
macula lutea; fewer over rest of retina.
As light intensity decreases so does our ability to see color.
Visual pigment is iodopsin: three types that respond to blue, red and green light
Overlap in response to light, thus interpretations of gradation of color possible: several millions
15-48
Processing of Visual Input
Receptor potential in rods and cones→ graded potentials in bipolar neurons and horizontal cells→ nerve impulses in ganglion cells→ optic nerve→ optic chiasm→ optic tract→ thalamus→ primary visual area of cerebral cortex in occipital lobe.
Visual Pathway
Visual field ofleft eye
Temporalhalf
Visual field ofright eye
Temporalhalf
Nasalhalf
Midbrain
Left eye
Temporalretina
Opticradiations
Left eye and its pathways
Primary visual area of cerebralcortex (area 17) in occipital lobe
Lateral geniculate nucleusof the thalamus
Opticradiations
Midbrain
Temporalretina
Nasalretina
Right eye
Right eye and its pathways
Nasalhalf
Nasal retina
1 1
Visual field ofleft eye
Temporalhalf
Visual field ofright eye
Temporalhalf
Nasalhalf
Midbrain
Left eye
Temporalretina
Opticradiations
Left eye and its pathways
Primary visual area of cerebralcortex (area 17) in occipital lobe
Lateral geniculate nucleusof the thalamus
Opticradiations
Midbrain
Temporalretina
Nasalretina
Right eye
Right eye and its pathways
Nasalhalf
Nasal retina
1 1
22
Visual field ofleft eye
Temporalhalf
Visual field ofright eye
Temporalhalf
Nasalhalf
Midbrain
Left eye
Temporalretina
Opticradiations
Left eye and its pathways
Primary visual area of cerebralcortex (area 17) in occipital lobe
Lateral geniculate nucleusof the thalamus
Opticradiations
Midbrain
Temporalretina
Nasalretina
Right eye
Right eye and its pathways
Nasalhalf
Nasal retina
1 1
22
33
Visual field ofleft eye
Temporalhalf
Visual field ofright eye
Temporalhalf
Nasalhalf
Midbrain
Left eye
Temporalretina
Opticradiations
Left eye and its pathways
Optictract
Primary visual area of cerebralcortex (area 17) in occipital lobe
Lateral geniculate nucleusof the thalamus
Opticradiations
Midbrain
Temporalretina
Nasalretina
Right eye
Right eye and its pathways
Nasalhalf
Nasal retina
1 1
2244
33
Visual field ofleft eye
Temporalhalf
Visual field ofright eye
Temporalhalf
Nasalhalf
Midbrain
Left eye
Temporalretina
Opticradiations
Left eye and its pathways
Optictract
Primary visual area of cerebralcortex (area 17) in occipital lobe
Lateral geniculate nucleusof the thalamus
Opticradiations
Midbrain
Temporalretina
Nasalretina
Right eye
Right eye and its pathways
Nasalhalf
Nasal retina
1 1
2244
5 5
33
Visual field ofleft eye
Temporalhalf
Visual field ofright eye
Temporalhalf
Nasalhalf
Midbrain
Left eye
Temporalretina
Opticradiations
Left eye and its pathways
Optictract
Primary visual area of cerebralcortex (area 17) in occipital lobe
Lateral geniculate nucleusof the thalamus
Opticradiations
Midbrain
Temporalretina
Nasalretina
Right eye
Right eye and its pathways
Nasalhalf
Nasal retina
1 1
2
3
24
34
5 5
6 6
Neuronal Pathways
15-52
Anatomy of the Ear Three main regions:
External (outer) ear- auricle or pinna, external auditory canal, and tympanic membrane.
Ceruminous glands- Middle ear- auditory ossicles: malleus, incus and
stapes.
Auditory (eustachian) tube. Internal (inner) ear- Labyrinth: bony and
membranous. Bony labyrinth- perilymph and membranous labyrinth- endolymph. Oval window and round window- membranous regions.
Anatomy of the Ear
The Middle Ear and the Auditory Ossicles
The Internal Ear
The Internal Ear Three parts: the semicircular canals, the
vestibule (both contain receptors for equilibrium) and the cochlea (contains receptors for hearing).
Semicircular canals: anterior, posterior and lateral.
Ampulla- Vestibule consists of two sacs: utricle and
saccule.
Semicircular Canals, Vestibule and Cochlea
Semicircular Canals, Vestibule and Cochlea
Tectorial membrane
Basilar membrane
Sprial organ
Inner hair cell
Outer hair cells
Inner phalangeal
cells
Outer phalangeal
cells
Cochlea Snail-shaped. Section through the cochlea shows three
channels: cochlear duct, scala vestibuli and scala tympani.
Helicotrema Vestibular membrane Basilar membrane Spiral organ or Organ of Corti- hair cells.
Physiology of Hearing Audible sound range: 20-20,000 Hz. Sound waves→ auricle→ external auditory
canal→ tympanic membrane→ malleus→ incus→ stapes→ oval window→ perilymph of the scala vestibuli→ vestibular membrane→ endolymph in the cochlear duct→ basilar membrane →hair cells against tectorial membrane → bending of hair cell stereocilia→ receptor potential→ nerve impulse. Sound wave → scala tympani→ round window.
Be able to trace sound thru ear
Events in the Stimulation of Auditory Receptors
Scalavestibuli
Cochlear duct(contains endolymph)
Scalatympani
Perilymph
Basilarmembrane
Cochlea
Sound waves
HelicotremaStapes vibratingin oval window
Malleus Incus
External auditorycanal
Tympanicmembrane
Secondary tympanicmembrane vibratingin round window Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ(organ of Corti)
1
Scalavestibuli
Cochlear duct(contains endolymph)
Scalatympani
Perilymph
Basilarmembrane
Cochlea
Sound waves
HelicotremaStapes vibratingin oval window
Malleus Incus
External auditorycanal
Tympanicmembrane
Secondary tympanicmembrane vibratingin round window Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ(organ of Corti)
1 2
Scalavestibuli
Cochlear duct(contains endolymph)
Scalatympani
Perilymph
Basilarmembrane
Cochlea
Sound waves
HelicotremaStapes vibratingin oval window
Malleus Incus
External auditorycanal
Tympanicmembrane
Secondary tympanicmembrane vibratingin round window Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ(organ of Corti)
1 2
3
Scalavestibuli
Cochlear duct(contains endolymph)
Scalatympani
Perilymph
Basilarmembrane
Cochlea
Sound waves
HelicotremaStapes vibratingin oval window
Malleus Incus
External auditorycanal
Tympanicmembrane
Secondary tympanicmembrane vibratingin round window Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ(organ of Corti)
1 2
34
Scalavestibuli
Cochlear duct(contains endolymph)
Scalatympani
Perilymph
Basilarmembrane
Cochlea
Sound waves
HelicotremaStapes vibratingin oval window
Malleus Incus
External auditorycanal
Tympanicmembrane
Secondary tympanicmembrane vibratingin round window Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ(organ of Corti)
1 2
34
5Scalavestibuli
Cochlear duct(contains endolymph)
Scalatympani
Perilymph
Basilarmembrane
Cochlea
Sound waves
HelicotremaStapes vibratingin oval window
Malleus Incus
External auditorycanal
Tympanicmembrane
Secondary tympanicmembrane vibratingin round window Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ(organ of Corti)
1 2
34
5
6
Scalavestibuli
Cochlear duct(contains endolymph)
Scalatympani
Perilymph
Basilarmembrane
Cochlea
Sound waves
HelicotremaStapes vibratingin oval window
Malleus Incus
External auditorycanal
Tympanicmembrane
Secondary tympanicmembrane vibratingin round window Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ(organ of Corti)
1 2
34
5
6
7
Scalavestibuli
Cochlear duct(contains endolymph)
Scalatympani
Perilymph
Basilarmembrane
Cochlea
Sound waves
HelicotremaStapes vibratingin oval window
Malleus Incus
External auditorycanal
Tympanicmembrane
Secondary tympanicmembrane vibratingin round window Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ(organ of Corti)
1 2
34
5
6
78
8
Scalavestibuli
Cochlear duct(contains endolymph)
Scalatympani
Perilymph
Basilarmembrane
Cochlea
Sound waves
HelicotremaStapes vibratingin oval window
Malleus Incus
External auditorycanal
Tympanicmembrane
Secondary tympanicmembrane vibratingin round window Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ(organ of Corti)
1 2
34
5
6
78
8
9
The Ear
Figure 17–30 Frequency Discrimination.
end
Response map
high low
Effect of Sound Waves on Points Along the Basilar Membrane
15-66
Opening of K+ Channels
15-67
The Auditory Pathway
Physiology of Equilibrium
Two types of equilibrium:
Static- maintenance of the body position relative to the force of gravity.
Dynamic- maintenance of body position (mainly head) in response to rotational acceleration and deceleration.
Receptors for equilibrium are hair cells in the utricle, saccule and semicircular canals and are collectively called vestibular apparatus.
Location and Structure of Receptors in the Maculae
Otolithic Organs: Saccule and Utricle Macula- small thickened regions within the
saccule and utricle. Sensory structures for static equilibrium. Also detect linear acceleration and
deceleration. Contain hair cells and supporting cells. Stereocilia and kinocilium together called hair
bundle. Otolithic membrane rests on the hair cells
and contain otoliths.
Static Labyrinth Utricle has macula oriented parallel to base of skull Saccula has macula oriented perpendicular to base of skull Macula: specialized epithelium of supporting columnar cells
and hair cells with numerous stereocilia (microvilli) and one cilium (kinocilium) embedded in gelatinous mass weighted by otoliths
15-72
–Gelatinous mass moves in response to gravity bendinghair cells and initiating action potentials–Otoliths stimulate hair cells with varying frequencies–Patterns of stimulation translated by brain intospecific information abouthead position or acceleration
Physiology of Equilibrium continued Tilting of the head forward→ sliding of the
otolithic membrane bending the hair bundles→ receptor potential→ vestibular branch of the vestibulocochlear nerve.
Location and Structure of the Semicircular Ducts
Semicircular Ducts Crista, a small elevation in the ampulla
contain hair cells and supporting cells. Cupula, a mass of gelatinous material
covering the crista. Head movement→ semicircular ducts and
hair cells move with it→ hair bundles bend→ receptor potential→ nerve impulses→ vestibular branch of the vestibulocochlear nerve.
Cupula in Still Position versus Rotation
Kinetic Labyrinth Three semicircular canals filled with
endolymph: transverse plane, coronal plane, sagittal plane
Base of each expanded into ampulla with sensory epithelium (crista ampullaris)
Cupula suspended over crista hair cells. Acts as a float displaced by fluid movements within semicircular canals
Displacement of the cupula is most intense when the rate of head movement changes, thus this system detects changes in the rate of movement rather than movement alone.
15-77
Equilibrium Pathway
Hair cells of utricle, saccule and semicircular ducts→
Vestibular branch of the vestibulocochlear nerve →brain stem → cerebellum and thalamus→ cerebral cortex.
End of lesson