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I. Receptors
A. All sensory receptors are transducers of some sort, that is, they change an incoming stimulus of pressure, vibration, light,
etc., into electro-chemical neuron impulses. Each is specific in that it can transduce only certain types of stimuli into
neuron action potentials.
B. Perception - conscious awareness of a sensation
C. Interpretation of Sensory Information
• 1. _receptive field________ - that region monitored by a receptor cell
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D. Central Processing and Adaptation
• 1. _adaptation__ - loss of sensitivity after exposure to a stimulus. • 2. _sensory adaptation_ - result of sensor fatigue , receptor becomes less sensitive to stimulus - smell
has great adaptation
E. Sensory Limitations
• 1. there are many stimuli for which we do not have receptors • 2. stimuli may be out of range for the appropriate receptors - uv light for example - KESTREL,
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Dog whistle
• 3. our awareness depends on interpretation which may be inexact.
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II. General Senses
A._ Exteroceptors _- detect the external environment (temperature, pressure, light, etc.)
B. _Interoceptors - provide information about internal conditions, most often tension or stretch in smooth muscle or
• tendons.
– 1. nociceptor stimulation results in pain. heat, mechanical stress and chemicals can allc ause pain by stimulating
different classes of receptors.
• a. _fast pain - deep cuts, etc. - referred immediately to primary sensory cortex, usually trigger reflexes
• b. __slow pain _ - later, persistent, indistinct source, thalamic
• c. _referred pain - visceral, "incorrect" source perceived
– 2. _thermoreceptors _ - detect heat or absence thereof, phasic, same pathways as pain
– 3. _mechanoreceptors - stimulated by anything moving or physical perturbation.
a. __tactile receptors _ - touch, pressure, vibration
b. _baroreceptorsare sensitive to internal pressures blood pressure, lung stretch, digestive tract tension
c. __proprioceptors_ are kinesthetic monitors of tendon muscle stretch.
– 4. _chemoreceptors- respond to specific chemicals either in solution (taste) or volatilized (smell) or internally in
monitoring blood composition. Internal chemoreceptors monitor blood composition - Na+, pH, osmolarity, etc.
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III. Special senses
A. _Olfactory (Smell)
distant chemical sense, many chemicals can be detected at a distance as long as they are gaseous.
1. receptors -sensory epithelium, olfactory receptors and glands, supporting cells and basal cells - covers
superior nasal conchae and septum.
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B. _Gustation_ (Taste) - taste is chemical also but requires that the dissolved chemicals make contact with the tongue
or mouth.
– 1. gustatory receptors - gustatory __chemoreceptors_____on the sides of taste buds. Taste buds are
incorporated in the papillae which are described by their shapes,
• a. foliate - thin, thread like projections
• b. _fungiform - shaped like mushrooms.
• c. _circumvallate - large target-shaped bumps near the back of the tongue.
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2. gustatory pathways - cranial nerves VII, IX and X to the nucleus solitarius in medulla
oblongata to gustatory cortex
3. gustatory discrimination - six tastes
– a. sour - (H+)
– b. sweet - (organic)
– c. salt - (metallic)
– d. bitter - (alkaloids)
– e. water
– f. umami - (savory)
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C. Equilibrium and Hearing – ears - MECHANORECEPTORS
1. external ear
a. pinna – (auricle) funnels sound waves down the external auditory canal (where ceremen “ear
wax” is found – helps lubricate and protect opening from bacteria, fungi etc..)
b. tympanic membrane – vibrates and transmits sound to malleus (bone) of middle ear
Attached vs Unattached
Problem in children.
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2. middle ear - three bones and space that amplify and transmit sound to the oval window of inner ear.
a. auditory (Eustachian) tube - connects throat and middle ear – (ear/throat infections)
b. auditory ossicles - amplify force of vibration
i. malleus (hammer) – 1st bone
ii. incus (anvil) – 2nd bone
iii. stapes (stirrup) – 3rd bone
c. tensor tympani muscle - stiffens tympanic membrane
d. stapedius muscle - dampens movement of stapes
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3. inner ear
a. labyrinth - membranous and bony - is a series of bones and membranes (line bones) which consists of the
cochlea (hearing) and vestibule (balence(
• i. endolymph & perilymph - fluid that is found inside the triggers hair cells to move, and therefore send
nerve impulse
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b. cochlea
– i. cochlear duct long tube that is rolled like snail shell containing the
– ii. Organ of Corti – group of cells devoted to respond to vibration
– iii. tympanic & vestibular ducts, fluid filled ducts on either side of organ of corti that carries
sound
– iv. tectorial membrane, - membrane that receives vibration and stimulates the hair cells
– v. hair cells with stereocilia - cells that trigger impulse when touched
vi. round window - allows vibrations to leave and occur
vii. oval window - begins vibrations from stapes
c. semicircular canals
– i. three mutually perpendicular- posterior, lateral and anterior
– ii. ampulla - where ends of canals meet vestibule
– iii. maculae - hair cells with otoliths – cupula is gel –like fluid on hair cells. As head moves if
moves the cupula, which bends the hair a certain direction – triggering movement sensation
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IV.. Vision – eye - photoreceptors
A. Accessory Structures
• 1. eyelids – palpebrae, some of the thinist skin in human body
a. medial ( with lacrimal caruncle) and lateral canthus - corners of eyes
b. eyelashes - with sebaceous glands (of Zeis)
c. conjunctiva - mucous membrane lining eyelids
2. lacrimal apparatus
a. _ lacrimal gland _ - superior and lateral to eye
a = lacrimal gland
b. lacrimal puncta - holes near nose to drain tears
b = superior lacrimal punctum
c = superior lacrimal canal
c. _lacrimal canaliculi- drain tears to
d = lacrimal sac
d. nasolacrimal ducts _ - empties to nasal cavity
e = inferior lacrimal punctum
f = inferior lacrimal canal
g = nasolacrimal canal
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B. Eye
1. superficial structures 3 sets of antagonistic muscles that move eye
• a. cushioned by fat pads
2. fibrous tunic - tough outer layer Outer Layer
a. sclera - white part of fibrous tunic
b. cornea - transparent avascular anterior part - window of the eye, protection and adds curvature to focus
light 3 vascular tunic -(uvea)
a. choroid - heavily vascular
b. iris with pupil hole, circular sphincter muscles and radial dilator muscles
c. _ciliary body - muscles attached to suspensory ligament, regulates focus of lens
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4. nervous tunic
a. retina - innermost layer of eye, has photoreceptors
1. outer pigmented layer - cyanolabe, erythrolabe, chloroplabe, rhodopsin
2. inner layer -photoreceptors
» a) _rods - black/white vision, motion detection
b) _cones_ – color vision, intense light
b. ora serrata - anterior edge of retina
c. __macula lutea _ – fovea centralis - all cones, best vision
d. _optic disc _ – blind spot, where optic nerve exits eye
e. optic nerve - Cranial Nerve II – takes impulse to occipital cerebral cortex
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5. lens
a. ciliary body - composed of ciliary muscle and ciliary ligament, when it relaxes the lens flattens and you see
distance better
b. suspensory ligament - hold lens in place
c. anterior chamber with _ aqueous humor - watery substance that baths the cornea
d. posterior chamber with _vitreous body (humor) - “snot like material” that helps give the eye its shape
e. cataract -
Glaucoma – increased intra ocular
pressure
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V. Visual Pathways
___Optic Chiasma _ - optic nerves partially cross in sphenoid
(right side of the field of each eye combining and going to the
lateral geniculate (knee) on the right, those from the left to
the left, of the thalamus which then relays the data to the
visual centers. )
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VI. Cortical Integration
The visual cortex must combine and integrate the incoming
information into a composite which is perceived as depth.
(This is a remarkable feat when one considers that the image
is tiny, curved, inverted, the two images slightly out of
frame, and each missing a large portion at opposite edges
of the field and having a hole in the image.)