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What are the modalities of sense? How are they sensed?
- light, taste, touch, pressure, etc
- sensory receptors
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What do sensory receptors do?
transduce sensation into impulses to be transmitted to sensory nerves
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what do sensory nerves do?
transmit impulses to the CNS for processing and appropriate response
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How are sensory receptors classified?
according to the type of sensation they transduce & according to the type of sensory info delivered to the brain
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List the 5 types of sensory receptors based on type of sensation
- chemoreceptors
- photoreceptors
- thermoreceptors
- mechanoreceptors
- nocireceptors
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what do chemoreceptors do?
sense chemical stimuli in the environment of the blood
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what do photoreceptors do?
sense light sensation for vision
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what do thermoreceptors do?
sense heat and cold
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what do mechanoreceptors do?
sense mechanical deformation due to pressure or touch
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what do nocireceptors do?
sense pain
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List the 2 types of sensory receptors based on the type of sensory info sent to the CNS
- proprioreceptors
- cutaneous receptors
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what do proprioreceptors do?
sense body position and allow for fine motor activity
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what do cutaneous receptors do?
include sensation for touch, pressure, heat, cold and pain
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what do special senses mediate?
sight, hearing and equilibrium
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How do phasic receptors work?
respond to stimuli with a burst of of activity then quickly adapt by decreasing their firing rate
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what is sensory adaptation
ability of phasic receptors to adapt to stimuli
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what are tonic receptors?
receptors that maintain their firing rate in response to stimuli (ex: pain)
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what are some physical examples of sensory receptors?
free nerve endings, pacinian corpuscle, and Meissner's corpuscle
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what happens when sensory receptors are stimulated?
they are depolarized generating a change in the membrane potential called receptor potential or generator potential thus stimulating an action potential in the receptor
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how are cutaneous receptors mediated?
by dendritic nerve endings of different nerves
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how is info transmitted from proprioreceptors and pressure receptors?
proprioreceptors--> spinal cord--> medulla oblongata--> (via lateral leminiscus) thalamus--> postcentral gyrus
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what do the eyes do?
transduce light energy into nerve impulses for vision
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what is the sclera?
outermost layer of the eye, connective tissue seen externally as the white of the eye
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what is the cornea?
continuation of the sclera
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how does light pass through the eye?
through the cornea into the anterior chamber of the eye then through the pupil
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what is the iris?
the smooth muscle that surrounds the pupil
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where does light go after passing through the pupil?
to the lens
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what does the iris do?
increase or decrease diameter of the pupil by constricting (miosis)
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how does miosis take place?
parasympathetic nerve stimulates circular muscle of the iris
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what is mydriasis?
how does it take place?
- dilation of the pupil
- sympathetic nerve stimulates radial muscle of the iris
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How is the lens of the eye suspended?
from a muscular process (ciliary body) by the suspensory ligament
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what is the space between the iris and the ciliary body?
posterior chamber
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what is the space between the cornea and the iris?
anterior chamber
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what fills the anterior and posterior chambers?
aqueous humor secreted by ciliary body
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what is the purpose for aqueous humor in the anterior chamber?
provides nutrition for avascular lens and cornea
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what is the canal of schlemm?
where aqueous humor drains to from the anterior chamber
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what does the canal of schlemm do with aqueous humor?
returns it to veinous blood
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What happens when aqueous humor is drained inadequately?
What is this condition called?
- accessive accumulation of the fluid leading to increase in intraocular pressure
- glaucoma
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what is the danger of glaucoma?
damage retina and cause loss of vision
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what is vitreous humor?
thick viscous fluid located in the part of the eye behind the lens
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where does the light go from the lens?
to the retina
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what is the retina?
neutral part of the eye
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what absorbs light in the retina?
choroid layer
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what happens when light reaches the retina?
stimulates photoreceptors which activate retinal neurons
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what are the photoreceptors in the retina?
cones and rods
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what do the neurons in the retina do?
contribute fibers that are gathered together exiting the eye at the optic disc as the optic nerve
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what happens when normal eyes view an object?
parallel light rays are refracted by the lens to the focus which is located on the retina
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what is accomidation?
ability of the eyes to keep the retina focused on an object as it moves closer to the eye
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how does accomidation occur?
contraction of ciliary muscle causes the lens to be more rounded and convex resulting in near vision
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how does far vision occur?
ciliary muscle relaxes causing the lens to b flatter and less convex so the eye can focus on objects further away
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define visual activity
sharpness of the eyes (ability to distinguish closely placed dots)
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how is 20/20 vision confirmed?
if the person can stand 20 feet from a Snellen eye chart and read the line marked "20/20"
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in nearsightedness (myopia) what is the problem with the eye?
the eye ball is too long and the image is focused in front of the retina
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what is the problem with the eye in farsightedness (hyeropia)?
the eyeball is too short and the image is focused behind the retina
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what causes astigmatism?
the curvature of the lens and the cornea are not perfectly symmetrical
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which type of lense corrects myopia?
concave lense
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what type of lesne corrects hyeropia?
convex lens
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what type of lenses corrects astigmatism?
a cylindrical lens
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what is emmetropia
normal vision
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what activates the photoreceptors (cones and rods) of the retina?
light reaching the retina. this causes a chemical change in the pigmented molecules of the photoreceptors
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What is rhodopsin?
purple pigment in rods
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What does rhodopsin do?
transmits light in the red and blue regions of the visible spectrum and absorbs light in the green region
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what are the 2 components of rhodopsin?
- retinaldehyde- derived from vitamin A
- opsin- a protein
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what is the bleaching reaction?
rhodopsin's reaction to light
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what are rods primarily responsible for?
"night vision"
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How do eyes adjust in dark rooms?
pupils dialate to absorb more light and photoreceptors, especially rods, increase their sensitivity to light
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what is dark adaptation?
the eyes ability to adjust to when entering a dark room
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What are cones responsible for?
color vision and greater acuity
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explain the trichromatic theory of color vision?
color vision is the result of the 3 types of cones designated as blue, green or red according to which each type absorbs to allow for color vision
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according to the trichromatic theory of color vision what protein is associated with the retinine of the cones?
photopsins
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what happens when viewing an object in daylight?
the image falls on the fovea centralis of the retina which contains only rods
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how do the fibers of the optic nerve decussate?
- 1/2 to the contralateral side
- 1/2 to the ipsilateral side
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where do optice nerve fibers travel after the optic chiasma?
up the optic tract to the superior colliculus
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what happens in the superior colliculous?
visual reflexes are processed?
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where do the optic nerve fibers in the optic tract synapse?
at the lateral geniculate nucleus with neurons that end in the occipital lobe
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what are interoceptors?
chemoreceptors that respond to chemical changes in the internal environment
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what are externoceptors?
chemoreceptors that respond to chemical changes in the extrernal environment
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what mediates the sense of taste?
taste buds on the tongue
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list the 4 modalities of taste
sweet sour bitter salty
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which region of the tongue tastes sweet things?
tip of the tongue
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what region of the tongue tastes sour things?
sides of the tongue
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what region of the tongue tastes bitter things?
back of the tongue
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what region of the tongue tastes salty things?
most of the tongue
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what is the suggested 5th modality of taste?
taste for water found only in humans
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what causes salty tastes?
presence of Na+ or other cations
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what causes the taste of sour things?
presence of H+
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How are sweet and bitter tastes produced?
interaction of taste molecules with specific membrane receptor proteins
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what receptors are responsible for the sense of smell?
dendritic endings of sensory neurons located in the nasal cavity
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whats different about olfactory neurons?
they replace themselves every 1-2 months
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whats different about sensory receptors for smell?
they go directly to the cerebral cortex
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