Lec 10 - Sensory Receptors and Vision Flashcards by Alethea Brown

what two types of info does the afferent branch of the PNS receive

-external (sensory receptors)
-visceral (visceral afferents)

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what two sensory systems allow us to sense the external enviro

-somatosensory system
-special senses

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what are the two components of the somatosensory system

-somatic for sensations in skin
-proprioreception for perception of limbs and body position

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what are the special senses

-vision, hearing, balance and eq, taste, smell

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what are sensory receptors

specialized nerve endings (or cells) that detect a sensory stimulus or specific form of energy

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what kinds of receptors does smell vs what the other special senses use

-smell uses neurons as receptors
-other special senses use non neural receptor cells that synapse onto sensory neurons

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how do the nerve endings differ for pain, touch, and ear hair receptors

-pain has free nerve endings
-touch has enclosed nerve ending
-ear has hair receptors

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what is a Pacinian corpuscle

mechanoreceptor sensitive to vibration

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what are the 4 types of sensory receptors

-chemo, mechano, photo, thermo

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what is transduction

-process of converting stimulus energy into electrical energy or a graded potential

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what is modality

-the energy form of a stimulus
-ex light waves, pressure, sound waves, temp, pressure, chemicals

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is transduction the fxn of sensory receptors

yes

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do receptors show specificity to one modality

yes

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what is an adequate stimulus

-modality that a receptor responds best and is most sensitive to

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what is a receptor potential, what kind of potential is it, how does it generate an AP

-change in membrane potential in response to stimulus acting on a sensory receptor
-graded potential caused by opening and closing of ion channels
-can generate an AP if greater than the threshold

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what is adaptation, how does it affect the frequency of APs

-decrease in amplitude of receptor potential over time in the presence of a constant stimulus
-decreases frequency of APs
-decrease in perception of stimulus

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what is the diff of slow adapting and fast adapting receptors

-slow show little adaptation and thus can constantly send the signal for how intense a prolonged stimulus is (ie muscle and touch)
-rapid adapt quickly to detect changes in stimulus intensity, they respond at a stimulus then adapt (ie olfactory)

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what are first, second, and third order neurons

-first: afferent neuron that transmits info from periphery to CNS
-second: interneurons that transmit info to thalamus
-third: synapse w second order in thalamus to transmit info to cerebral cortex

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what two things code stimulus intensity

-frequency of AP (frequency coding)
-number of receptors activated (population coding)

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what is frequency and population coding, and coding for stimulus type

-frequency: stronger stimulus = larger receptor potential
-pop: stronger stimulus activates more receptors
-type: stimulus type is coded by receptor and pathway activated when stimulus is applied

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what is vision, what are the three steps of vision

-process how light reflected from objects is translated into a mental image
1. light enters eye, lens focuses light on retina
2. photoreceptors on retina use transduction to turn light energy into an electrical signal
3. neural pathways from retina to brain process electrical signals into visual images

is the eye fluid filled, what are the three concentric layers of the eye

-yes
-outer (sclera and cornea)
-middle (choroid, ciliary body, iris)
-inner (retina)

what are these structures of the eye for: canal of schlemm, aqueous humor, cornea, pupil, iris, ciliary muscle

-canal of schlemm: drains fluid of anterior chamber
-aqueous humor: fluid around cornea
-cornea: transparent front part of eye
-pupil: changes amt of light entering eye
-iris: two layers of pigmented smooth muscles, gives eye colour
-ciliary muscle: contraction alters curvature of lens

what are these structures of the eye for: zonules, lens, optic disk, retinal artery and vein, optic nerve, fovea, vitreous humor, retina, sclera

-zonules: attach lens to ciliary muscle
-lens: bends light to focus it on retina
-optic disk: blind spot, region where optic nerve and blood vessels leave eye
-retinal artery and vein: emerge from optic disk
-optic nerve: nerves going to brain
-fovea: sharpest vision
-vitreous humor: maintains eye shape
-retina: contains photoreceptors
-sclera: connective tissue

how does ciliary muscle affect the lens

-relaxed muscle causes ligaments to pull on lens and flatten it -contracted muscle releases tension on ligaments and lens becomes round

what type of waves are light, what wavelengths incl visible light, what do diff wavelengths correspond to

-electromagnetic waves (ie light, radio, televison, x rays, gamma rays) on the electromagnetic spectrum -380 nm to 750nm -diff colours

what is the diff b/w reflection and refraction, do animals view mostly reflected or emitted light

-reflection is light waves bouncing off objects -refraction is bending of light -reflected

what affects how we perceive colours

-light absorbed is not seen, light reflected is the colour we perceive

what does the pupil do, what are the two smooth muscle layers of the iris

-pupil is the opening in the centre of iris, its size regulates amt of light entering eye -inner circular muscle (constrictor), outer radial muscle (dilator)

what is a tapetum lucidum, what is its fxn in animals

-layer of tissue behind the retina that is a retroreflector -reflects visible light back through retina to increase the light avail to photoreceptors -increases sensitivity to low light lvls

what kind of tissue makes up the retina, what kinds of photoreceptors does it contain, what do the three layers contain

-neural tissue -rods and cones -outer contains photoreceptors, middle contains bipolar cells, amacrine cells, horizontal cells, inner contains ganglion cells

what is the order of communication of the photoreceptors, bipolar cells, and ganglion cells in the retina

-rods and cones are receptor cells -they communicate w bipolar cells -bipolar cells communicate w ganglion cells rods/cones -> bipolar -> ganglion

what forms the optic nerve, what do horizontal and amacrine cells do

-axons of ganglion cells -provide lateral modulation

what are rods and cones specialized for

-rods are for night vision, black and white (flat shaped) -cones are for colour and high actuity vision, daytime, high light lvls (cone shaped)

where are rods and cones distributed in retina

-cones highest in fovea and decrease moving away -no rods in fovea but high beside it and decrease moving away

compare rods and cones: types of vision, sensitivity to light, abundance, visual acuity, site of greatest conc, degree of convergence w bipolar cells

-rods are for b&w, cones are for colour -rods have high sensitivity, cones are low sensitivity -more rods than cones -cones have higher visual acuity, rods have low -rods are concentrated most in periphery of retina, cones in fovea -rods have high convergence w bipolar cells, and cones have low

how many photopigments are there, what is retinal and opsin

-four -found in photopigments, retinal is the light absorbing portion and opsin is protein

what are the four opsins for, what is rhodopsin and photopsin

-one opsin for rods, three for cones -photopsins for cones - long, medium, and short wavelengths -rhodopsin is for rods

what colour wavelength does L, M, S opsin absorb

L = red M = green S = blue

the retinal portion is the same/diff in all photopigments, but the kind of ____ present determines which light wavelengths are absorbed by a given photopigment

-same -opsin

how does phototransduction happen in the dark

1. cGMP lvls in cytosol are high 2. Na channels open 3. Na enters cell which causes a depolarization spreading to terminal 4. Ca channels open in response to depol 5. Ca enters cell which triggers exocytosis of transmitter (glutamate) 6. transmitter causes graded potential of bipolar cell

how does phototransduction happen in the light

1. light absorbed by photopigment 2. retinal and opsin dissociate 3. transducin is activated 4. phosphodiesterase activated which degrades cGMP 5. cGMP lvls in cytosol decrease 6. Na channels close 7. cell hyperpolarizes due to K leaking out and Na not coming in 8. Ca channels close 9. transmitter (glutamate) release is decreased 10. graded potential in bipolar cells gets smaller

what is the trichromatic colour theory

-there are three cones (blue, green, and red) that respond best to its colour -blue at 420nm -green at 530nm -red at 560nm

what is convergence

-more than one photoreceptor per bipolar neuron and more than one bipolar cell per ganglion cell

do rods or cones converge more, why

-rods -for lower visual acuity, and greater sensitivity

why does one cone communicate w one bipolar cell in the fovea

-for greater visual acuity and lower sensitivity

what transmitter is released from rods and cones, how does it communicate w bipolar neurons

-glutamate -more NT in dark, some inhibitory some excitatory, they are only graded potentials

what cells do bipolar cells synapse w, do they have excitatory or inhibitory effects

-ganglion -both

which cells of the visual pathway generate APs, what forms the cranial nerve II (optic nerve), what is melanopsin

-ganglion -axons of ganglion -melanopsin is a pigment activated by light that sends signals to CNS for circadian rhythm

what is the order of the neural pathway for vision

-ganglion cells (optic nerve, optic chiasm, optic tract) -LGB synapses -optic radiations -visual cortex synapses -right visual field to left cortex and vice versa