CHAPTER 47 ~ Sensory Systems Flashcards
sensory receptor cells
“sensors” or “receptors” transduce physical or chemical stimuli into signals that are transmittable and interpretable (most are modified neurons)
receptor protein
on surface of sensory sensory cells; when they detect a stimuli, either directly or indirectly open or close ion channels in their sensory cell, causing either action potential or release of neurotransmitter
3 types of sensory receptors:
mechanoreceptor, chemoreceptor, light or photo receptor
intensity of stimulus is based on _____ of the action potential generated
intensity of stimulus is based on the FREQUENCY of the action potential generated
In ionotropic sensory detection:
receptor protein itself is part of the ion channel –> opens or closes channel by changing its conformation
In metabotropic sensory detection:
the receptor protein is linked to a G-protein that activates a cascade of intracellular events that eventually open or close ion channels
mechanoreceptor =
ionotropic receptor
chemoreceptor & light receptor =
metabotropic receptor
receptor potential
change in resting membrane potential of a sensory cell in response to a stimulus ( basically an action potential, just in a sensory cell)
primary sensory cell
generate action potentials directly (i.e. crayfish stretch receptor)
secondary sensory cell
generate action potentials indirectly by inducing release of neurotransmitter
adaptation
gradually diminishing response to stimuli while remaining sensitive to new stimuli
Chemoreceptors
receptors that bind to various molecules; are responsible for smell and taste and for monitoring aspects of internal environment (i.e. CO2 in blood)
Olfaction
sense of smell (chemoreceptors). olfactory sensors are neurons embedded in layer of epithelial cells at top of nasal cavity. their dendrites end in olfactory hairs at the surface of nasal epithelium.
Odorant
molecule that activates an olfactory protein receptor on the olfactory cilia. (must diffuse through nasal mucus)
action potentials generated by odorant binding are transmitted to
glomeruli in the olfactory bulb. Neurons in glomerulus receive input only from receptor cells expressing the same receptor gene
Mechanism of Olfaction:
- olfactory receptor protein binds particular odorant molecule –>activates G-protein
- G-protein activates enzyme that increases level of second messenger cAMP.
- cAMP opens cation channel
- leads to depolarization of membrane = action potential
higher concentration of odorant molecules =
higher frequency of action potential, which means stronger smell
Gustation
sense of taste; depends on clusters of sensory cells called taste buds (chemoreceptors)
papillae
bumps on tongue that we see–> most taste buds on there
taste bud
cluster of chemoreceptors; surface of each bud has a pore that exposes the tips of sensory cells. microvilli increase the surface area of the cells. release neurotransmitter to sensory neuron who then conveys signal to CNS.
taste buds can distinguish 5 basic tastes:
sweet, bitter & umami => metabotropic, detected by G-protein coupled receptors
- salty & sour => ionotropic, work through ion channels
Mechanoreceptors
cells that are sensitive to mechanical forces; involved in skin sensations, sensing blood pressure, etc.
- physical distortion of mechanoreceptor membrane causes ion channels to open = graded potential
Merkel’s Discs
found in both hair and non-hairy skin; adapt slowly & provide continuous info about things touching the skin
Meissner’s Corpuscles
very sensitive mechanoreceptors found mostly in non-hairy skin. Adapt rapidly = produce info about CHANGES in things touching skin
Ruffini Endings
adapt slowly and good at providing info about vibrating stimuli of low frequencies
Pacinian Corpuscles
provide info about vibrating stimuli of higher frequencies
two-point spatial discrimination
how far apart two stimuli must be in order to be felt as two separate stimuli. on back, must be fairly far apart, on fingertips or lips spatial discrimination possible because mechanoreceptors much more dense
photosensitivity
sensitivity to light. ranges from ability to orient sun to ability to see.
rhodopsin
family of pigments; can absorb photons of light and undergo conformational changes. Made up of protein opsin and light-absorbing group 11-cis-retinal. 11-cis-retinal is covalently bound in the center of opsin molecule.
when 11-cis-retinal absorbs photon of light:
it changes to all-trans-retinal = changes conformation of opsin = signals detection of light.
Vitamin A deficiency (VAD)
common among developing countries; 200,000-500,000 malnourished children in world go blind every year due to VAD. (lack of adequate amounts of retinal = incomplete regeneration of rhodopsin)
rod cell
photoreceptor; is a modified neuron that releases neurotransmitters that influence other neurons. has an outer segment, an inner segment, and a synaptic terminal
inner segment of rod cell
has nucleus and mitochondria
outer segment of rod cell
stack of discs of plasma membrane densely packed with rhodopsin. function of discs = to capture photons
synaptic terminal of rod cell
where rod cell communicates with other neurons
in the dark, a rod cell…
has a DEPOLARIZED restin potential, because Na+ channels are continually open. light exposure = the outer segment becomes more negative, hyperpolarized
when light absorbed by rhodopsin:
- conformational change due to retinal isomerization leads to activation of G-protein transducin
- activated transducin activates phosphodiesterase, which converts cGMP to GMP.
- Less cGMP = Na+ channels close
- HYPERPOLARIZATION
- system allows for amplification
sclera
tough connective tissue layer that binds the spherical fluid filled structure that is our eye
cornea
at front of eye, formed by sclera; place through which light passes to enter eye
iris
inside cornea; pigmented part of eye that controls the amount of light that reaches photoreceptors at back of eye (constricts in bright, relaxes in dark)
pupil
region where light enters
lens
makes fine adjustments in the focus of images on the photosensitive retina at the back of the eye (attached and controlled by suspensory ligaments and ciliary muscles
suspensory ligaments
pull lens flatter (for far vision)
ciliary muscles
permit lens to round up (for near vision)
most sensitive part of the retina
is the fovea
reception of light to retina:
- light travels through layers of transparent neurons (ganglion, amacrine, etc) and is absorbed by rods and cones in photoreceptive layer at back of retina
- visual info procesed through several layers of neurons and finally converges on ganglion cells, which send their axons to the brain.
retina has 5 layers of cells
ganglion, amacrine, bipolar, horizontal and photoreceptor cells
ganglion cells
fire action potentials; their axons form the optic nerves
amacrine cells
connect neighboring pairs of bipolar cells and ganglion cells –> help make eyes more sensitive to small but rapid changes
bipolar cells
connect ganglion cells to photoreceptor cells
- neurotransmitter release from photoreceptor cells = change in rate of release from bipolar cells = stimulates ganglion cells to fire action potentials
horizontal cells
connect neighboring pairs of photoreceptors and bipolar cells; provide means for lateral flow of information
photoreceptor cells
rods and cones at back of retina
Rod Cells
are more sensitive to light; provide “black and white” vision at low light levels
- human retina has ~125 million rods
Cone Cells
less light sensitive, respond to different wavelengths of light for color vision; provide sharpest vision
- human retina has ~ 6 million cones
- three types of cone cells = L, S, and M types
L-type cone
absorb long wavelength light = yellow/green
M-type cone
absorb medium wavelength light = blue/green
S-type cone
absorb short wavelength light = blue/violet
macula
an oval yellow spot near the center of the retina of the human eye –> for high acuity vision
fovea
at center of macula; responsible for sharp central vision, necessary for reading, watching TV, etc.
Age-Related macular degeneration (AMD)
photoreceptors in macula malfunction and degenerate; leading cause of blindness in US citizens over 50; cause is unknown
