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Zoology 523 > Unit 2 Week 2 > Flashcards

Unit 2 Week 2 Flashcards

1
Q

How is the somatic sensory system unique from other sensory systems?

A

Receptors: broadly distributed
-responds to many kinds of stimuli, rather than one (mechanical, thermal, and chemical)
-different types of sensory neurons encode diverse somatosensory stimuli

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2
Q

What does the somatic sensory system provide?

A

-enables the body to feel pressure and sense pain and temperature
-touch, pain, itch, and thermosenstation
-proprioception (sense position/movement of body parts)
-interoception (sense of internal organ function)

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3
Q

Describe the touch sensation

A

-starts at the skin (largest sensory organ)
-touch stimuli: pressure on the skin
-use mechanoreceptors to detect touch (convert mechanical force to neural signals)

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4
Q

What somatic sensory receptor is found within the epidermis?

A

Merkel’s disks

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5
Q

What somatic sensory receptors are found within the dermis?

A

Pacinian corpuscles, Ruffini’s endings, Meissner’s corpuscles

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6
Q

What is a receptive field?

A

the region of a sensory surface (retinal, skin), when stimulated changes the membrane potential of a neuron

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7
Q

How do the receptive fields of different mechanoreceptors compare?

A

they are different sizes

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8
Q

Discuss each mechanoreceptor type including their receptive field size and adaptation

A

Meissner’s: small, rapid
Pacinian: large, rapid
Merkel’s: small, slow
Ruffini’s: large, slow

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9
Q

What does it mean if a mechanoreceptor has a rapid adaptation to a stimulus?

A

transient response mostly at the beginning and the end of the stimulus

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10
Q

What does it mean if a mechanoreceptor has a slow adaptation to a stimulus?

A

more sustained response during the stimulus

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11
Q

What is responsible for the response profile of Pacinian corpuscle?

A

special ending, respond differently when the corpuscle is removed

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12
Q

Describe Mechanosenssitive ion channels

A

-mechanoreceptors express different mechanosensitive channels to detect touch
-mechanosensitive ion channels convert mechanical force into receptor potential of mechanorceptors
-specific types of channels in most somatic sensory receptors are still unidentified

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13
Q

What are the different ways that mechanosensitive ion channels can be opened?

A

-stretching of lipid membrane
-force on extracellular structures
-force on cell’s cytoskeleton

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14
Q

What are Piezo1 and Piezo 2?

A

Mechanosensitive ion channels
-non-selective cation channels
-important for touch sensation

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15
Q

What is Cre/LoxP?

A

Cre: a site-specific recombinase
LoxP: a short sequence from bacteriophage P1, which is recognized by Cre

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16
Q

How does the Cre/LoxP system work for gene knockout?

A

Cre will cut the DNA section between two LoxP sites in the same orientation

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17
Q

What is gene knockout?

A

a powerful genetic technique to understand gene function

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18
Q

What channel do Merkel cells require to transduce mechanical stimuli into electrical signals?

A

Piezo2

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19
Q

Describe primary afferent axons for somatic sensory system.

A

axons bringing information from the somatic sensory receptors to the spinal cord or brain stem

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20
Q

How many types of primary afferent axons for the somatic sensory system are there?

A

4, varying in properties like axons from skin, axons from muscle, diameter, speed, and sensory receptors

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21
Q

What is the trajectory of touch-sensitive AB axons in the spinal cord?

A

divisions of spinal gray matter: dorsal horn, intermediate zone, ventral horn

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22
Q

Describe the segmental organization of the spinal cord

A

spinal segments (30) - spinal nerves within four divisions of the spinal cord

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23
Q

Define dermatomes

A

the area of the skin innervated by the right and left dorsal roots of a single spinal segment

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24
Q

What is a sensory map?

A

one-to-on correspondence between spinal segments and dermatomes

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25
Q

What are the two different central touch pathways?

A

the dorsal column-medial lemniscal pathway and the trigeminal touch pathway (face and the top of the head)

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26
Q

Define somatotopy

A

the topographic organization of somatic sensory pathway in which neighboring receptors in the skin feed information to neighboring cells in a target brain structure
-a sensory map for the somatic sensory system, which helps determines the location of touch sensation

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27
Q

What is somatotopy- Homunculus?

A

a sensory map for touch sensation: the mapping of the body surface onto the primary somatosensory cortex
-more sensitive regions receive more CNS processing

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28
Q

What is Two-Point Discrimination used for? What is considered?

A

to measure spatial resolution of touch sensation
-receptive field density
-receptive field size
-computing power of the brain
-other spacial neural mechanisms

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29
Q

Describe what each of the primary afferent axons is used for.

A

A-alpha fibers: proprioceptors of skeletal muscle
A-beta fibers: mechanoreceptors of skin
A-delta fibers: pain and temperature
C: temperature, pain, itch

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30
Q

What is pain?

A

feeling of sore, aching, throbbing sensations

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31
Q

What triggers pain?

A

stimuli that signal body tissue being damaged or have the potential of causing tissue damage

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32
Q

What are nociceptors?

A

pain receptor neurons

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33
Q

What are the types of nocicptors?

A

most are polymodal
-mechanical
-thermal
-chemical

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34
Q

How are nociceptors activated?

A

ion channels in nociceptors can be opened by
-strong mechanical stimulation, temperature extremes, oxygen deprivation, and chemicals
-substances released by damaged cells
proteases (bradykinin), ATP, K+ ion channels
histamine

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35
Q

What substance promotes swelling?

A

histamine

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36
Q

What are the primary afferent axons for pain?

A

First pain (fast) : A-delta fiber
Second pain (slow) - C fiber

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37
Q

What molecule is responsible for temperature sensation (peppers)?

A

capsaicin

38
Q

What does Capsaicin activate?

A

TRPV1, responds to both hot peppers and hot temps

39
Q

What are transient receptor potentials (TRP)?

A

-cation channels
-can be activated by various external stimuli e.g. temperature, chemicals, and light
-group 1 subfamily: TRPC, TRPV, TRPM, TRPN, and TRPA
-group 2 subfamily: TRPP and TRPML

40
Q

What does TRPV1 detect?

A

hot and capsaicin sensory

41
Q

What does TRPM8 detect?

A

cold and methanol sensor

42
Q

What many distinct TRP channels are there in thermoreceptors?

A

6

43
Q

What is the dorsal-column medial lemniscal pathway responsible for?

A

touch, vibration, two-point discrimination, proprioception

44
Q

What is the spionthalmic pathway responsible for?

A

pain, temperature, some touch

45
Q

Describe the major properties if light

A

-light is electromagnetic radiation
-gamma radiation and cool colors are high energy
-radio waves and hot colors are low energy

46
Q

Describe the structure of the eye, specifically the retina.

A

-eye collects light, focuses on retina , and forms image
-fovea is the thinnest area in the retina
-retina is where we perceive light

47
Q

Describe the laminar organization of the retina

A

-seemingly inside-out layers
-light passes through ganglion cells and bipolar cells before reaching photorecepters

48
Q

What are the two types of photoreceptors in the retina?

A

-rods and cones
-converts light to neural signals
-different in morphology and function

49
Q

Describe the morphology and function of rods

A

one types, more sensitive to light (for nighttime vision), NA

50
Q

Describe the morphology and function of cones

A

three types, less sensitive to light (for daytime vision), color vision

51
Q

There are regional differences in retinal structure and function. Describe the differences between the central retina and the peripheral retina

A

Central Retina (focea) :
-almost all cones
-an area of highest visual acuity
Peripheral Retina
-higher ration of rods to cones
-more sensitive to low light

52
Q

What is the light sensor in rods?

A

Rhodopsin (GPCR)

53
Q

What is retinal?

A

a vitamin A derivative that is light sensitive and serve as a co-factor for rhodopsin

54
Q

How is GPCR activated?

A

light causes change in shape of retinal and this activates the rhodopsin (GPCR)

55
Q

How does cGMP become hydrolyzed?

A

light activates phosphodiesterase, which hydrolyzes cGMP

56
Q

Describe phototransduction in rods in the light vs the dark

A

Dark current: Na+ ions move into cells due to open cGMP-gated sodium channels. Cells are depolarized, and glutamate is released.
Light: depletes cGMP, closing sodium channels. Cells are hyperpolarized (turned OFF) and the glutamate release decreases

57
Q

Describe the mechanism of visual transduction in rods

A

-light activates the rhodopsin (GPCR)
-transducin, the G-protein, is stimulated
-phosphodiesterase (PDE) is activated
-PDE reduces the cGMP level
-Na2+ channels close, and cells become hyperpolarized (turned OFF)
-the release of glutamate is decreased

58
Q

Describe phototransduction in cones

A

-similar process to phototransduction in rods
-three different cones
blue (short wavelength)
green (medium wavelength)
red (long wavelength)

59
Q

Describe how color vision works in cones (Young-Helmholtz trichromacy theory of color vision)

A

cones are sensitive to three different colors : green, blue, and red. When these colors are combined, eyes can tell a difference between millions of colors

60
Q

Why can’t rods see color?

A

rods only have a single opsin- rhodopsin

61
Q

What is scotopic condition?

A

e.g. nighttime lighting
rods contribute to vision ( no color information)

62
Q

What is photopic condition?

A

e.g. daytime lighting
cones contribute to vision

63
Q

What is mesopic conditon?

A

e.g. indoor lighting
both rods and cones contribute to visions

64
Q

What is meant by duplex retinal?

A

two complementary systems in the eye (rods + cones)

65
Q

What is the advantage of duplex retinal?

A

our vision can operate in a wide range of light intensities

66
Q

Describe the central visual pathway

A
  1. photoreceptors in eye
  2. other retinal neurons
  3. LGN
  4. visual cortex
67
Q

Which axons project into the forebrain?

A

ganglion cell axons

68
Q

What are the five types of cells within the retina?

A

vertical pathway
-ganglion cells
-bipolar cells
-photoreceptor cells
indirect pathway
-amacrine cells
-horizontal cells

69
Q

Which retinal cells fire action potentials?

A

ganglion cells

70
Q

What generates AP of ganglion?

A

neural computation with the retinal generate AP of ganglion cells to relay visual information to the brain

71
Q

What is the direct pathway of information flow in the retina?

A

vertical pathway
1. photoreceptors
(excitatory or inhibitory)
2. bipolar cells
(excitatory)
3. retinal ganglion cells

72
Q

What is the indirect pathway of the flow of information in the retina?

A

modulate retinal processing in the direct pathway by lateral connections
amacrine cells and horizontal cells

73
Q

What are Amacrine cells responsible for?

A

receive input from bipolar cells and project to ganglion cells, bipolar cells, and other amacrine cells

74
Q

What are horizontal cells responsible for?

A

receive input from photoreceptors and provide inhibitory feedback signals to other photoreceptors and bipolar cells

75
Q

What is the receptive field?

A

an area of the retina where light changes neurons firing rate
both direct and indirect pathways count

76
Q

Describe the two types of center/surround receptive fields

A

ON-Center/ OFF-Surround = A neuron’s activity is highest when light is on in the center and off in the surround
OFF-Center/ON-Surround = A neuron’s activity is lowest when light is on in the center and off in the surround

77
Q

What does it mean to be “ON”?

A

Depolarized - turned on

78
Q

What does it mean to be “OFF”?

A

Hyperpolarized - turned off

79
Q

Where are Center-Surround receptive fields found?

A

observed in both bipolar cells and ganglion cells

80
Q

Explain the different center-surround receptive fields for bipolar cells and RGCs

A

For ON-center or OFF-center: the nature of the synapse between photoreceptor and bipolar cell
For antagonistic center-sound receptive fieldsL: lateral inhibition via horizontal cells

81
Q

What determines whether a receptor field of a bipolar call is ON-center or OFF-center?

A

the synapse between photoreceptors and bipolar cells

82
Q

How do photoreceptors respond to light?

A

always off (-)

83
Q

What is the cone circuit?

A

surround photoreceptors (PRs) are not directly connected to bipolar cells

84
Q

What types of synapse do Surround PRs have on horizontal cells?

A

excitatory (+)

85
Q

What types of synapse do Horizontal cells have on central PRs?

A

inhibitory (-)

86
Q

What is lateral inhibition?

A

a general mechanism to sharpen the differences between neighboring neurons
lateral inhibition via horizontal cells enhances the differences between light-stimulated photoreceptors and the surrounding unstimulated photoreceptors

87
Q

Describe the circuit mechanism for center-surround receptive fields

A

The synapse type between center photoreceptors and bipolar cells determines Center ON vs Center OFF
-excitatory synapse: Center OFF
-inhibitory synapse: Center ON
Lateral inhibition via horizontal cell yields opposite response at receptive field Center vs. Surround
Bipolar cells and RGCs has the same type of center-surround receptive fields

88
Q

Describe ganglion receptive fields

A

-responses to light-dark edge crossing an OFF-center ganglion cell receptive field

89
Q

Why have center surrounded fields?

A

such receptive fields leads to a neural response that emphasizes the contrast at the light-dark edges
getting most information from edges where intensities change and mat serve the following purposes:
-contrast enhancement
-edge detection
-motion detection

90
Q

Describe parallel processing in the visual system

A

simultaneous input from two eyes
-input from eyes compared in cortex
-determines depth and distance of object
information about light dark: ON-center and OFF-center ganglion cells
information about color vision

91
Q

Where does the dorsal root axon cross over in the dorsal column-medical lemniscal pathway?

A

medulla

92
Q

Where does the dorsal root axons cross over in the spinothalamic pathway

A

in the spinal cord

Zoology 523 (5 decks)

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