CHAPTER 47 ~ Sensory Systems

Question 1

sensory receptor cells

Answer 1

“sensors” or “receptors” transduce physical or chemical stimuli into signals that are transmittable and interpretable (most are modified neurons)

Question 2

receptor protein

Answer 2

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

Question 3

3 types of sensory receptors:

Answer 3

mechanoreceptor, chemoreceptor, light or photo receptor

Question 4

intensity of stimulus is based on _____ of the action potential generated

Answer 4

intensity of stimulus is based on the FREQUENCY of the action potential generated

Question 5

In ionotropic sensory detection:

Answer 5

receptor protein itself is part of the ion channel –> opens or closes channel by changing its conformation

Question 6

In metabotropic sensory detection:

Answer 6

the receptor protein is linked to a G-protein that activates a cascade of intracellular events that eventually open or close ion channels

Question 7

mechanoreceptor =

Answer 7

ionotropic receptor

Question 8

chemoreceptor & light receptor =

Answer 8

metabotropic receptor

Question 9

receptor potential

Answer 9

change in resting membrane potential of a sensory cell in response to a stimulus ( basically an action potential, just in a sensory cell)

Question 10

primary sensory cell

Answer 10

generate action potentials directly (i.e. crayfish stretch receptor)

Question 11

secondary sensory cell

Answer 11

generate action potentials indirectly by inducing release of neurotransmitter

Question 12

adaptation

Answer 12

gradually diminishing response to stimuli while remaining sensitive to new stimuli

Question 13

Chemoreceptors

Answer 13

receptors that bind to various molecules; are responsible for smell and taste and for monitoring aspects of internal environment (i.e. CO2 in blood)

Question 14

Olfaction

Answer 14

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.

Question 15

Odorant

Answer 15

molecule that activates an olfactory protein receptor on the olfactory cilia. (must diffuse through nasal mucus)

Question 16

action potentials generated by odorant binding are transmitted to

Answer 16

glomeruli in the olfactory bulb. Neurons in glomerulus receive input only from receptor cells expressing the same receptor gene

Question 17

Mechanism of Olfaction:

Answer 17

1. olfactory receptor protein binds particular odorant molecule –>activates G-protein
2. G-protein activates enzyme that increases level of second messenger cAMP.
3. cAMP opens cation channel
4. leads to depolarization of membrane = action potential

Question 18

higher concentration of odorant molecules =

Answer 18

higher frequency of action potential, which means stronger smell

Question 19

Gustation

Answer 19

sense of taste; depends on clusters of sensory cells called taste buds (chemoreceptors)

Question 20

papillae

Answer 20

bumps on tongue that we see–> most taste buds on there

Question 21

taste bud

Answer 21

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.

Question 22

taste buds can distinguish 5 basic tastes:

Answer 22

sweet, bitter & umami => metabotropic, detected by G-protein coupled receptors
- salty & sour => ionotropic, work through ion channels

Question 23

Mechanoreceptors

Answer 23

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

Question 24

Merkel’s Discs

Answer 24

found in both hair and non-hairy skin; adapt slowly & provide continuous info about things touching the skin

Question 25

Meissner's Corpuscles

Answer 25

very sensitive mechanoreceptors found mostly in non-hairy skin. Adapt rapidly = produce info about CHANGES in things touching skin

Question 26

Ruffini Endings

Answer 26

adapt slowly and good at providing info about vibrating stimuli of low frequencies

Question 27

Pacinian Corpuscles

Answer 27

provide info about vibrating stimuli of higher frequencies

Question 28

two-point spatial discrimination

Answer 28

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

Question 29

photosensitivity

Answer 29

sensitivity to light. ranges from ability to orient sun to ability to see.

Question 30

rhodopsin

Answer 30

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.

Question 31

when 11-cis-retinal absorbs photon of light:

Answer 31

it changes to all-trans-retinal = changes conformation of opsin = signals detection of light.

Question 32

Vitamin A deficiency (VAD)

Answer 32

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)

Question 33

rod cell

Answer 33

photoreceptor; is a modified neuron that releases neurotransmitters that influence other neurons. has an outer segment, an inner segment, and a synaptic terminal

Question 34

inner segment of rod cell

Answer 34

has nucleus and mitochondria

Question 35

outer segment of rod cell

Answer 35

stack of discs of plasma membrane densely packed with rhodopsin. function of discs = to capture photons

Question 36

synaptic terminal of rod cell

Answer 36

where rod cell communicates with other neurons

Question 37

in the dark, a rod cell...

Answer 37

has a DEPOLARIZED restin potential, because Na+ channels are continually open. light exposure = the outer segment becomes more negative, hyperpolarized

Question 38

when light absorbed by rhodopsin:

Answer 38

1. conformational change due to retinal isomerization leads to activation of G-protein transducin 2. activated transducin activates phosphodiesterase, which converts cGMP to GMP. 3. Less cGMP = Na+ channels close 4. HYPERPOLARIZATION - system allows for amplification

Question 39

sclera

Answer 39

tough connective tissue layer that binds the spherical fluid filled structure that is our eye

Question 40

cornea

Answer 40

at front of eye, formed by sclera; place through which light passes to enter eye

Question 41

iris

Answer 41

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)

Question 42

pupil

Answer 42

region where light enters

Question 43

lens

Answer 43

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

Question 44

suspensory ligaments

Answer 44

pull lens flatter (for far vision)

Question 45

ciliary muscles

Answer 45

permit lens to round up (for near vision)

Question 46

most sensitive part of the retina

Answer 46

is the fovea

Question 47

reception of light to retina:

Answer 47

1. light travels through layers of transparent neurons (ganglion, amacrine, etc) and is absorbed by rods and cones in photoreceptive layer at back of retina 2. visual info procesed through several layers of neurons and finally converges on ganglion cells, which send their axons to the brain.

Question 48

retina has 5 layers of cells

Answer 48

ganglion, amacrine, bipolar, horizontal and photoreceptor cells

Question 49

ganglion cells

Answer 49

fire action potentials; their axons form the optic nerves

Question 50

amacrine cells

Answer 50

connect neighboring pairs of bipolar cells and ganglion cells --> help make eyes more sensitive to small but rapid changes

Question 51

bipolar cells

Answer 51

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

Question 52

horizontal cells

Answer 52

connect neighboring pairs of photoreceptors and bipolar cells; provide means for lateral flow of information

Question 53

photoreceptor cells

Answer 53

rods and cones at back of retina

Question 54

Rod Cells

Answer 54

are more sensitive to light; provide "black and white" vision at low light levels - human retina has ~125 million rods

Question 55

Cone Cells

Answer 55

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

Question 56

L-type cone

Answer 56

absorb long wavelength light = yellow/green

Question 57

M-type cone

Answer 57

absorb medium wavelength light = blue/green

Question 58

S-type cone

Answer 58

absorb short wavelength light = blue/violet

Question 59

macula

Answer 59

an oval yellow spot near the center of the retina of the human eye --> for high acuity vision

Question 60

fovea

Answer 60

at center of macula; responsible for sharp central vision, necessary for reading, watching TV, etc.

Question 61

Age-Related macular degeneration (AMD)

Answer 61

photoreceptors in macula malfunction and degenerate; leading cause of blindness in US citizens over 50; cause is unknown