Sensory Receptors Flashcards
(100 cards)
1
Q
What do different modalities (forms) of sensation (sound, light, pressure, etc.) result from?
A
Differences in neural pathways and synaptic connections
2
Q
How can sensory receptors be categorized structurally?
A
Dendritic endings of sensory neurons
3
Q
How can dendritic endings be categorized?
A
- Free: those that respond to pain, temperature
- Encapsulated within nonneural structures: those that respond to pressure, touch
- Rods and cones: highly specialized neurons involved in sight
- Modified epithelial cells: taste
4
Q
What determines the functional categories of sensory receptors?
A
Type of stimulus energy they transduce
5
Q
What do chemoreceptors respond to?
A
Chemical stimuli in environment or blood (pH, CO2)
6
Q
What are photoreceptors?
A
Rods and cones
7
Q
What do thermoreceptors respond to?
A
Temperature
8
Q
What do mechanoreceptors respond to?
A
Touch and pressure
9
Q
What do nociceptors respond to?
A
Pain
10
Q
What do proprioceptors respond to?
A
Body position
11
Q
What do cutaneous (skin) receptors include?
A
Touch, pressure, temperature, and pain
12
Q
What are the special senses?
A
Sight, hearing, equilibrium, taste, and smell
13
Q
What are tonic receptors?
A
Produce constant rate of firing as long as stimulus is applied (slow-adapting)
-ex: pain
14
Q
What are phasic receptors?
A
Produce burst of activity when a stimulus is first applied but quickly reduce firing rate (adapt) if stimulus maintained (fast-adapting)
15
Q
What is sensory adaptation?
A
Phasic receptors are responsible for this ability (cease to pay attention to constant stimuli)
16
Q
What is the law of specific nerve energies?
A
The sensation characteristic of each sensory neuron is that produced by its normal adequate stimulus
17
Q
What is meant by “adequate stimulus”?
A
Although a variety of different stimuli may activate a receptor, the adequate stimulus requires the least amount of energy to activate a receptor
18
Q
T or F: Based on how a sensory neuron is stimulated, many different sensory modalities will be perceived.
A
False; Regardless of how a sensory neuron is stimulated, only one sensory modality will be perceived
-Allows brain to perceive the stimulus accurately under normal conditions
19
Q
What are generator potentials?
A
In response to stimulus, sensory nerve endings produce a local graded change in membrane potential
- Potential changes are called receptor, or generator, potential
- Analogous to EPSPs
20
Q
What is phasic response?
A
Generator potential increases with increased stimulus, then as stimulus continues, generator potential size diminishes
21
Q
What is tonic response?
A
Generator potential proportional to intensity of stimulus
22
Q
What are cutaneous sensations mediated by?
A
Dendritic nerve endings of different sensory neurons
23
Q
What are the free nerve endings receptors for?
A
Temperature (heat and cold)
24
Q
Where are the receptors for cold and warm located in the dermis?
A
Cold -> upper region of dermis
Warm -> deeper in dermis
25
Do more receptors respond to cold or warm?
Far more respond to cold
26
How do hot temperatures produce a sensation of pain?
Through a capsaicin receptor
| -Ion channels for Ca2+and Na+ to diffuse into the neuron
27
What are nociceptors?
Free sensory nerve endings that respond to pain
- Use substance P or glutamate as NT
- Ca2+ and Na+ enter through channel, depolarizing the cell
28
What do the encapsulated nerve endings mediate?
Touch and pressure
| -Receptors adapt quickly
29
What do Ruffini endings and Merkel's discs mediate?
Touch
| -Receptors adapt slowly
30
What do somasthetic sensations include?
Proprioceptors and cutaneous receptors
31
What are receptive fields?
Area of skin whose stimulation results in changes in the firing rate of the neuron
32
What is the relationship between receptive fields and the density of receptors in the region?
Inverse relationship
- Back and legs have few sensory endings (receptive field is large)
- Fingertips have large # of cutaneous receptors (receptive field is small)
33
What does the two-point touch threshold measure?
Minimum distance at which 2 points of touch can be perceived as separate
-Measures of distance between receptive fields
34
What is the two-point touch threshold indicative of?
Tactile acuity
| -If distance between 2 points is less than minimum distance, only 1 point will be felt
35
What does lateral inhibition result in?
Sharpening of sensation
36
What is lateral inhibition?
When a blunt object touches the skin, sensory neurons in the center areas are stimulated more than neighboring fields
- Lateral inhibition within the CNS reduces the input from these neighboring sensory neurons
- Stimulation will gradually diminish from the point of greatest contact, without a clear, sharp boundary
- Perceived as a single touch with well defined borders (within area of skin that was stimulated most)
37
What is gustation?
The sensation of taste
38
Are taste cells neurons?
No, but depolarize upon stimulation and if reach threshold, release NT that stimulate sensory neurons
-known as "neuroepithelial cells"
39
T or F: All areas of the tongue are able to respond to all 5 categories of taste.
True; each taste bud contains taste cells responsive to each other the different taste categories
40
What does each taste cell in the taste bud activate?
A sensory neuron that conveys information specific to only one taste modality
41
How does our brain interpret the complex tastes?
Depend on the relative activities of the sensory neurons from each of the five categories of taste, together with the sense of smell
42
What is the salty taste of food due to?
Presence of Na+
- Na+ passes through channels, activates specific receptor cells, depolarizing the cells, and releasing NT
- Anions associated with Na+ modify perceived saltiness (we perceive NaCl as the saltiest)
43
How is sour taste produced?
H+ movement through membrane channels
| -Degree of sourness corresponds to fall in pH within taste cells
44
In contrast to salty and sour taste, how are sweet, bitter and umami tastes produced?
By interaction of taste molecules with membrane receptors coupled to G-proteins (gustducin)
45
What is equilibrium (orientation with respect to gravity) due to?
Vestibular apparatus
46
Where are the sensory structures of the vestibular apparatus located within?
The membranous labyrinth
| -Filled with endolymph
47
What does the vestibular apparatus consist of?
1) Otolith organs (utricle and saccule)
| 2) Semicircular canals
48
What information do the utricle and saccule provide?
Info about linear acceleration
49
What do the hair cells contain?
Hairlike extensions (stereocilia and kinocilium)
50
When stereocilia bend toward kinocilium the membrane _________.
Depolarizes
- Plasma membrane is depressed and K+ channels open
- Releases NT that stimulates dendrites of VIII (vestibulocochlear nerve)
51
When stereocilia bend away from kinocilium, the membrane _________.
Hyperpolarizes
- Releases less NT (inhibitied)
- Frequency of APs carries information about movement
52
What do the utricle and saccule both have?
Macula (patch of specialized epithelium) with hair cells and supporting cells
53
Where do the hair cells of the macula project into?
Endolymph, where hair cells are embedded in a gelatinous otolithic membrane (contains crystals of Ca2+ carbonate that resist change in movement)
54
What kind of acceleration is the utricle more sensitive to?
Horizontal acceleration
| -During forward acceleration, otolithic membrane lags behind hair cells, so hairs pushed backward
55
What kind of acceleration is the saccule more sensitive to?
Vertical acceleration
| -Hairs pushed upwards when person descends
56
When the head is upright how is the otolith organ affected?
The weight of the otoliths applies direct pressure to the sensitive cytoplasmic extensions of the hair cells
57
When the head is bent forward how is the otolith organ affected?
The extensions of the hair cells bend in response to gravitational force and cause the sensory nerve fibers to be stimulated
58
What information do the semicircular canals provide?
Info about rotational acceleration
59
Sound waves travel in all directions from their source and are characterized by?
Frequency (pitch) and intensity (loudness)
60
How is frequency measured?
```
In hertz (cycles per second)
-Pitch is directly related to frequency (greater frequency, higher pitch)
```
61
How is intensity measured?
In decibels
| -Directly related to amplitude of sound waves
62
How do we see light?
Our eyes transduce energy in the electromagnetic spectrum into APS
-Visible light: only wavelengths of 400-700 nm
63
What is the fibrous tunic?
Outer layer of eyeball (made up of sclera and cornea)
- Avascular CT
- Gives shape to eyeball
64
What is the anterior surface of the eyeball?
Cornea
- Tightly packed dense CT
- Transparent and convex
- Transmits and refracts light
65
Which part of the eye is not part of any tunic and refracts light and focuses onto fovea centralis?
Lens
- Between posterior and vitreous chambers; supported by suspensory ligaments of ciliary body
- Tightly arranged protein fibers; transparent
66
Light that passes from a medium of one density into a medium of another density is _________.
Refracted (bent)
67
How does the ciliary muscle accommodate to distances > 20 feet?
It relaxes which places tension on the suspensory ligament -> pulls lens taut
-Lens is least convex and focused for distant vision
68
How does the ciliary muscle accommodate as distance decreases?
It contracts which reduces tension on the suspensory ligament -> lens becomes more rounded and convex
-Lens thick and focused for close vision
69
What does visual acuity depend upon?
Resolving power of the visual system (the ability of the visual system to resolve/distinguish 2 closely spaced dots)
-Better resolving power -> closer together these dots can be and still be seen as separate
70
What is myopia?
Nearsightedness
- Image brought to focus in front of retina
- Corrected by concave lens
71
What is hyperopia?
Farsightedness
- Image brought to focus behind the retina
- Corrected by convex lens
72
What is astigmatism?
Asymmetry of the cornea and/or lens
- Images of lines of circle appear blurred
- Corrected by uneven lens
73
What is emmetropia?
Normal vision
| -Rays focus on the retina
74
What do each rod and cone consist of?
Inner and outer segments
75
Which segment contain the photopigment molecules required for color vision? What function does it have that is important for vision?
Outer segment contains hundreds of flattened discs with these molecules
-Photopigment molecules continously adds new discs at the base of the outer segment as the retinal pigment epithelium removes old tip regions by phagocytosis
76
What is the flow of information in the retina? What is the direction of AP conduction?
Photoreceptors (rods and cones) -> Bipolar cells -> Ganglion cells
- APs conducted outward
- Horizontal cells synapse with photoreceptors and bipolar cells
- Amacrine cells synapse with several ganglion cells
77
When are rods and cones activated?
When light produces chemical change in rhodopsin
78
What is the bleaching reaction?
In response to absorbed light, rhodopsin dissociates into retinene (rentinaldehyde) and opsin
- When light is absorbed, 11-cis retinene is converted to all-trans form and dissociates from opsin
- Dissociation reaction initiates changes in ionic permeability of rod plasma membrane -> AP in ganglionic cells
79
Because of the bleaching reaction what kind of light is provided?
Rods provide black-and-white vision under conditions of low light intensity
-Results in a lower amount of rhodopsin in rods and lowered amount of visual pigments in cones
80
What happens when a light-adapted person first enters a darkened room?
```
Dark adaptation (a gradual increase in photoreceptor sensitivity when entering a dark room)
-Maximal sensitivity reached in 20 mins
```
81
What is the increased sensitivity to low light due to in dark adaptation?
Increased amounts of visual pigments produced in the dark
- Increased pigment in cones produces slight dark adaptation in 1st 5 mins
- Increased rhodopsin in rods produces greater increase in sensitivity (100,000-fold increase in light sensitivity in rods, adaptation after 1st 5 mins)
82
What are the only neurons that produce APs?
Ganglion cells and amacrine cells
83
What cells produce EPSPs and IPSPs?
Rods and cones, bipolar cells, and horizontal cells
84
T or F: The transduction of light energy into nerve impulses follows a cause-and-effect sequence that is the inverse of the usual way in which sensory stimuli are detected.
True; In dark, photoreceptors release inhibitory NT that hyperpolarizes bipolar neurons (bipolar cells do not release excitatory NT to ganglion cells). Light inhibits photoreceptors from releasing inhibitory NT and by this means STIMULATES the bipolar cells, and thus the ganglion cells that transmit APs to the brain
85
What is the dark current?
Rods and cones contain many Na+ channels that are open in the dark -> small inflow of Na+ causes slight membrane depolarization in the dark
86
What happens to the Na+ channels in response to light?
They rapidly close
87
Light causes this conversion and consequently closing of the Na+ channels.
cGMP -> GMP
| -cGMP required to keep the Na+ channels open
88
What is responsible for the conversion of cGMP to GMP?
```
Opsin dissociation (when 11-cis -> all-trans) causes the alpha subunits of G-proteins to dissociate
-G-protein subunits bind to and activate phosphodiesterase, converting cGMP -> GMP
```
89
What does Viagra inhibit?
A phosphodiesterase inhibitor and can affect vision (cones -> psychedelic vision)
90
What does GMP result in?
Hyperpolarizes and release less inhibiting NT -> light can be perceived
-Absorption of single photon of light can block Na+ entry
91
Do rods or cones provide color vision?
Cones provide color vision and greater visual acuity
| -Cones less sensitive than rods to light
92
During the day, high light intensity bleaches out the ___, and color vision with high acuity is provided by ____.
rods; cones
93
What is trichromatic color vision?
The type of vision we have
- 3 types of cones: blue, green, and red
- According to the region of visual spectrum absorbed
94
Rods have opsin; cones have _____.
Photopsins
- Photopsin protein is unique for each of the 3 cone pigments
- Each cone absorbs different wavelengths of light (blue cone is the shortest, red is the longest)
95
What is the most common blindness?
Color red blindness (common in males);
| -Many genes are involved, so there is a lot of variation in disease/blindness
96
Where is visual acuity greatest and sensitivity lowest?
When light falls on fovea
| -Degree of convergence of cones is 1:1
97
What is the degree of convergence of rods?
Much lower (bipolar cells receive input from convergence of many rods)
- Maximize sensitivity to light,
- Low visual acuity
98
The part of visual field that affects activity of particular ganglion cell, can be considered its __________.
Receptive field
99
What are on-center fields?
Ganglion cells that are stimulated by light in the center of visual fields
100
What are off-center fields?
Ganglion cells that are inhibited by light in the center, and stimulated by light in the surround
