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Special Senses
— olfaction, vision, gustation, hearing, equilibrium
— detected by complex receptors in sense organs
Reflex Path for Special Senses
1. Receptor cell receives stimulus
2. changes Receptor Cell potential
3. changes Sensory Neuron potential
4. reach threshold
5. action potential sent
6. much tighter control
-sense oF smell
-receptors react to airborne ordorants
Olfactory Organs (2)
1. Olfactory Epithelium
2. Lamina Propria
Olfactory Epithelium
- has receptors w/ cilia lined knobs
- cilia creates an increased surface area network
Lamina Propria
vessels, nerves, glands and loose connective tissue
Olfactory Pathway
odorants absorbed at cilia and bind receptors then action potential is sent to CNS
Olfactory Discrimination
-chemicals activate receptor combination
-CNS interprets smell due to pattern of receptor activity
Aging and Olfaction
increase age, decrease olfactory sensitivity
-sense of taste
-receptors react to dissolves tastants
Gustatory Organs (2)
1. Tongue
2. Taste Bud
Tongue ( 3 parts)
-contains receptor taste buds
1. Filiform Papillae
2. Fungiform apillae
3. Circumvallate Papillae
Filiform Papillae
(part of the tongue)
-sharp projections grip food, no taste buds
Fungiform papillae
(part of the tongue)
- rounded projections w/ few taste buds
Circumvallate Papillae
(part of tongue)
-rounded projections w/ more taste buds
Taste Bud
(a) formed by gustatory cells + specialized cells
(b) gustatory cell extends taste hairs (microvilli) thru taste pore
(c) basal cells, transition cell, immature forms that develop into mature gustatory cells
(d) opening is taste pore
Gustatory Pathway
tastants absorb at microvilli and bind receptor then Action Potential is sent to CNS
Gustatory Discrimination
-Chemial activate receptor combos
-CNS interprets taste due to pattern
Aging and Gustation
increae age, decrease gustatory sensitivity (neurons begin to break down)
-sense of sight
1. Accessory Structures
2. Eyes
3. Photoreceptors
Accessory Structures (5)
1. Eyelashes - protect eye from debris
2. Eyelids - wipers that clear debris and lubricate the eye
3. Tarsal Glands - secretions lubricate the eyelid
4. Lacrimal Gland - produce tears that lubricate and protect
5. Lacrimal Apparatus - produces, distributes and removes tears
Lacrimal Apparatus
produces, distributes and removes tears
The Eye
(3 layers: FVN)
Visual sensing apparatus

1. Fibrous Tunic (outer layer)
2. Vascular Tunic (middle layer)
3. Neural Tunic (inner layer)
Fibrous Tunic
( 2parts)
-Provides support/protection
1. Sclera
2. Cornea
(fibrous tunic layer)
white of eye w/ high collegen/ elastic, vascularized/ innervated
(fibrous tunic layer)
-Transparent w/ high collegen/ elastic
-not vascularized
Vascular Tunic
( 3 parts)
-controls lens shape, light entery, and aqueous humor production
1. Iris
2. Ciliary body
3. Choroid
(vascular tunic layer)
-contros light entery by changing pupil diameter (aperture)
-Pupillary Constrictor Muscle- decrease pupil size
-Pupillary Dilator Muscles- increase pupil size
Ciliary body
(vascular tunic layer)
— has attachment sites for suspensory ligaments which hold lens
— has Ciliary muscles (constrictor muscle) (changes lens shape)
— when muscle contracts, suspensory ligaments relax and allow lens to round for close vision
— when muscle relaxes, suspensory ligaments are pulled tight and flatten the lens for distant vision
(vascular tunic layer)
Contains capillaries and nerves
Neural Tunic
( 2 parts)
1. Pigmented Region- absorbes stray light, prevents echoes
2. Nerual Region- has photoreceptors that detect light.
Photoreceptors: Rods and Cones
(cells that detect light)
1. Rods
(a) function in low light intensity
(b) no color discrimination
(c) high concentration around retinal periphery
2. Cones
(a) function in high light intensity
(b) color discrimination (RGB)
(c) very high concentration in fovea of macula lutea
(d) you move your eye to focus image on the fovea
Accessory Cells
( 4 )
1. Bipolar Cells (bc)
2. Ganglion Cells (gc)
3. Horizontal Cells
4. Amacrine Cells
Bipolar Cells
Link photoreceptors with ganglion cells
Ganglion Cells
axon bundles and exits eye as the optic disc
Horizontal Cells
facilitate or inhibit communication b/w Photoreceptors and Bipolar Cells
Amacrine Cells
facilitate or inhibit communication b/w Bipolar Cells and Ganglion Cells
Eye Chambers (2)
1. Posterior Cavity
(a) Vitreous Body (maintains shape)
(b) can contain floaters (solidified particles in this area)

2. Anterior Cavity
(a) aqueous humor nourishes lens/cornea
(b) lens is also not vascularized
(c) anterior cavity is broken into anterior chamber and posterior chamber
Aqueous Humor Pathway
➀ Ciliary body produces Aqueous Humor
➁ Humor surrounds and nourishes Lens
➂ Flows forward through Pupil
➃ Flows across and nourishes Cornea
➄ Exits through Canal of Schlemm
Lens Accommodation
— lens changes shape to focus on image regardless of distance object is from the eye
— Ciliary processes are actually what attach to lens
— Ciliary muscle controls suspensory ligament tension, affects lens shape
Ciliary Muscle Contraction
— lens rounds = focus on nearby object
— less tension on suspensory ligaments
Ciliary Muscle Relaxation
— lens flattens = focus on distant objects
Visual Acuity
1. clarity of vision
2. defined as detail seen at 20 feet by person with emmetropic vision (normal vision)
- visual pigment that absorbs light
(a) Opsin - membrane spanning protein
(b) Retinal
— chromosphore that can maintain 11-cis or 11-trans shapes (two configurations)
— configuration is determined by whether light strikes the retinal or not
Membrane spanning protein
-A protein rhodopsin consits of
Light Absorption Process
1. photon strikes 11-cis retinal
2. 11-cis retinal converted to 11-tran retinal
3. opsin activated
4. once 11-cis becomes 11-trans opsin becomes activated
5. once the opsin is activated a cascade of events occue then the info is sent to CNS
(a) breakdown of Retinal and Opsin
(b) enzymatic conversion of 11-trans retinal -> 11-cis retinal requires ATP
Color vision
1. retina contains blue, green and red cones
2. integration of info from these cones results in color vision
Hearing and Equilibrium
Hair cells respond to mechanical movements
External ear (3)
- collects/directs sound
(a) Auricle
— funnel channels sound to tympanic membrane
— half funnel allows for directionality of sound
— encourages some sounds to enter and discourages other sounds
— no difference in sound results in sound confusion
(b) External Acoustic Canal
— passage to tympanic membrane
— converts sound waves into mechanical movements
(c) Tympanic Membrane (tm)
— converts sound waves to mechanical movements
Middle Ear (2)
- conducts sound to inner ear
(a) Auditory (Eustachian) Tube
— permits pressure equalization (between external air and middle ear)
— ear opening is exposed to atmosphere and oral opening is exposed to atmosphere
(b) Auditory Ossicles
— bones (malleus, incus, stapes) transfers tympanic membrane to oval window; acts as a bridge for external ear and internal ear
Auditory Tube
— permits pressure equalization (between external air and middle ear)
— ear opening is exposed to atmosphere and oral opening is exposed to atmosphere
Auditory Ossicles
— bones (malleus, incus, stapes) transfers tympanic membrane to oval window; acts as a bridge for external ear and internal ear
Inner Ear (2)
- contain hair cells (receptors for hearing/equilibrium)

(a) Membranous Labyrinth

(b) Bony Labyrinth

- (1) Vestibule
- (2) Semicircular Canals
- (3) Cochlea
Membranous Labyrinth
— tubes/channels filled with endolymph
Bony Labyrinth
(3 parts)
— dense bone that surrounds the membranous labyrinth
— filled with perilymph
1. Vestibule
2. Semicircular Canals
3. Cochlea
- sense static equilibrium; gravity and linear acceleration
Semicircular Canals
- sense dynamic equilibrium; angular acceleration
(rotation of the head)
Sense sound, snail shaped structure, all fluid filled

- receptors within provide sense of Hearing
Dynamic Equilibrium
ability to control body during motion
Semicircular Ducts
— tubes within ducts
- anterior (yes)
- posterior (side to side)
- lateral (no) semicircular ducts sense rotation
Ampulla (3 parts)
-enlargment at end of each semicircular canal
- filled with ENDOLYMPH
1. Crista
2. Cupula
3. Hair Cells
Crista, Cupula, Hair cells
(parts of the ampulla)

(a) Crista
— balance receptors composed of hair cells and supporting cells
— cilia of hair cells extend upward from crista into cupula

(b) Cupula
— gel structure that floats in endolymph; it is actually submerged

(c) Hair Cells
— contain stereocilia and kinocilium(cilia) in cupula
— kinocilia responsible for stimulating the sensory neuron
Dynamic Balance Sensation
➀ Semicircular Canal moves, Endolymph in Semicircular Ducts moves
➁ Cupula moves
➂ Cilia moves
➃ Signal sent to CNS
Static Equilibrium
ability to control body while body is stationary
Vestibule (3 parts)
- senses Static Equilibrium
— between semicircular canals and cochlea
— has endolymph filled sacs

1. Saccule
2. Utricles
3. Maculae
Smaller of the 2 membranous sacs responds to forward/backward head movements, linear acceleration and gravity
Larger of the 2 membranous sacs responds to forward/backward head movements, linear acceleration and gravity
Maculae ( contains 2)
- are the sensory receptors within the Saccule & Utricle
(a) Otolith - gel matrix structure and carbonate crystals
(b) Hair cells - contain sterocilia/kinocilia embedded in gel matrix
(in maculae part of the vestibule)
gel matrix and carbonate crystals (statoconia)
Hair cells
(in the maculea of vestibule)
-contain numerous stereocilia/ kinocilia embeded in gel matrix
Static Balance Sensation
➀ head movement causes the otolith to slide
➁ cilia move
➂ signal is sent to the CNS
sense of sound
Cochlea (detail)
(3 parts)
- structure in the shape of snail shell
1. Vestibular Duct - perilymph filled tube
2. Tympanic duct - perilymph filled tube
3. Cochlear duct - endolymph filled tube between tympanic and vestibular ducts
(a) Organ of Corti
Organ of Corti (2 parts)
- houses hair cells that stimulate the sensory neurons that convert sound vibrations into nerve impulses
— Basilar Membrane - base of the Organ of Corti below the Hair Cells
— Tectorial Membrane - gel like roof that overlies the Hair cells
Hearing Sensation ( pattern for heairng)
- pattern for hearing
1. Sound Waves
— Sound Waves arrive @ Tympanic Membrane
2. Mechanical Movement of Tympanic Membrane/ Auditory Ossicles
— Vibration of Tympanic Membrane, causes vibration of Auditory Ossicles
3. Oval Window moves
— Stapes pushes against Oval Window creating pressure waves in Perilymph of Vestibular Duct
4. Fluid Vibration
— Pressure waves travel up thru Vestibular Duct, then back thru the Tympanic Duct, to reach Round Window
5. Basilar Membrane moves
— Basilar Membrane is moved by Pressure Waves of Tympanic Duct Perilymph below
6. Hair cells strike Tectorial Membrane
— Basilar Membrane movement presses Hair Cells against the overlying Tectoral Membrane distorting the Stereocilia of the Hair Cells triggering their release of neurotransmitters that stimulate the bipolar sensory neurons that monitor the Cochlear Hair Cells
7. Signal sent to CNS
— Information sent to CNS over Cochlear Branch of Vestibulocochlear Nerve VIII
Image Reversal
1. light from each portion of object is focused on different part of the retina
2. brain is capable of compensating for image reversal
3. as you get closer to a tree, you cannot focus all of the tree on the fovea