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Neurobiology > Chapter 12: The Somatic Sensory System > Flashcards

Chapter 12: The Somatic Sensory System Flashcards

1
Q

What are the two major types of skin?

A
  1. hairy

2. glabrous

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2
Q

Outer layer of skin = […]

Inner layer of skin = […]

A

epidermis

dermis

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3
Q

Most of the sensory receptors in the somatic sensory system are […].

A

mechanoreceptors

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4
Q

Mechanoreceptors are sensitive to …

A

physical distortion (stretch/bend)

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5
Q

At the heart of each mechanoreceptor are […]. These […] have […] and their gating depends on stretching or changes in tension of the surrounding membrane.

A

unmyelinated axons; axon; mechanosensitive ion channels

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6
Q

What is the purpose of unmyelinated axons within mechanoreceptors?

A

axons have mechanosensitive ion channels; their gating depends of stretch/tension

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7
Q

Pacinian corpuscle:

A

mechanoreceptor of the deep skin, selective for high-frequency vibrations

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8
Q

List the mechanoreceptors of the skin:

A
  1. Pacinian corpuscle
  2. Ruffini’s endings
  3. Meissner’s corpuscles
  4. Merkel’s disks
  5. Krause end bulbs
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9
Q

Which mechanoreceptors have large field receptors? Which have small field receptors?

A

L: Pacinian corpuscles and Ruffini’s endings

S: Meissner’s corpuscles and Merkel’s disks

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10
Q

Which mechanoreceptors are rapidly adapting? Which are slowly adapting?

A

R: Meissner’s and Pacinian corpuscles

S: Merkel’s disks and Ruffini’s endings

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11
Q

Rapid adapting vs slowly adapting:

A

RA: respond quickly but stop firing even though the stimulus continues (P and M)

SA: generate a more sustained response during a long stimulus (M. disks and R)

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12
Q

At what vibrational range do Pacinian and Meissner’s corpuscles respond best at?

A

P: 200-300 Hz

M: 50 Hz

**lower frequencies are the smaller field mechanoreceptors

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13
Q

What body part has the highest resolution of two-point discrimination?

A

fingertips

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14
Q

Two-point discrimination test is…

A

a simple measure of spatial resolution

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15
Q

The primary afferent axons enter the spinal cord through the […]; their cell bodies lie in the […].

A

dorsal roots; dorsal root ganglia

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16
Q

Dermatome:

A

a region of skin innervated by the pair of dorsal roots from one spinal segment

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17
Q

Where do the primary sensory afferent axons travel to? What particular region?

A

enter the spinal cord through the dorsal root ganglion

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18
Q

How is the labeling different for the following–

Skin sensory receptor vs muscle and tendon sensory receptors:

A

S: A(alpha), A(beta), A (gamma), C

M/T: I, II, III, IV

**similar sizes

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19
Q

Skin lack which labeled group of axons? What is unique of Group C/IV?

A

S: the largest axons A(alpha)

C/IV: unmyelinated axons
**the rest are myelinated

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20
Q

What type of proprioceptors are in each category of axons:

A

A(alpha) or I–
no skin; proprioceptors of skeletal muscles

A(beta) or II–
mechanoreceptors of skin

Alpha(delta) or III–
pain, temperature

C or IV–
temperature, pain, itch

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21
Q

How many bones in each category of the vertebra?

A

C: 8
T: 12
L: 5
S: 5

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22
Q

When a dorsal root is cut, what occurs?

A

body does not lose all sensation in that region; residual somatic sensation present due to overlapping adjacent dorsal roots

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23
Q

The spinal gray matter is divided into…

A
  1. dorsal horn
  2. intermediate zone
  3. ventral horn
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24
Q

Second-order sensory neurons:

A

neurons that receive sensory input from primary afferents that lie within the dorsal horns

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25
Q

Dorsal column-medial lemniscal pathway purpose:

A

pathway serving touch

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26
Q

Dorsal columns carry information about…

A

tactile information and limb position to brain

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27
Q

What are dorsal columns composed of?

A
  1. primary sensory axons

2. second-order axons from neurons in the spinal gray matter

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28
Q

Dorsal Column- Medial Lemniscal Pathway:

Where do the axons of the dorsal column terminate?

A

dorsal column nuclei

**spinal cord and medulla junction

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29
Q

When does decussation occur along the dorsal lemniscus pathway?

A

when the axons from cells of the dorsal column nuclei arch toward the ventral and medial medulla

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30
Q

Medial lemniscus:

A

white matter tract

  • axons of the dorsal column nuclei ascend to
  • its axons synapse upon neurons of the ventral posterior (thalamus)
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31
Q

What is the major route by which touch and proprioceptive information ascend to the cerebral cortex?

A

large dorsal root axons — dorsal column [spinal cord] — dorsal column nuclei [medulla: medial lemniscus] — thalamus [VP nucleus] — primary somatosensory cortex (S1)

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32
Q

What is meant by the term relay nuclei?

A

used to describe specific sensory nuclei of the thalamus; relay stimuli from lower receptors to coordinating receptors (ex: VP nucleus)

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33
Q

Is the information altered from the stimuli to the cortex? Or is it simply transferred?

A

information is altered at every synapse; typically by inhibitory reactions to enhance the response of the stimuli

process is not a “synaptic relay”

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34
Q

What CN is the trigeminal nerve? What is its purpose?

A

CN V

supplies somatic sensation of the face

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35
Q

Pathway for the face to the cortex:

***decussation

A

large mechanoreceptors from the face — [cranial nerve V/trigeminal nerve] — principal sensory trigeminal nucleus — *** — thalamus [VP nucleus] — somatosensory cortex (S1)

36
Q

Where is the region of the somatosensory cortex?

A

on the postcentral gyrus of the parietal lobe

**right behind the central sulcus

37
Q

Area 3a vs 3b:

A

3a region concerned with a sense of body position rather than touch

3b is the primary somatic sensory cortex

38
Q

Projections of 3b: What info do they mainly receive?

A

area 1– texture information

area 2– size and shape

39
Q

Thalamic inputs to S1 terminate mainly in which layer? Where do these project in turn?

A

IV

the remainder of cells in the striate cortex layers

40
Q

What is unique about the brain undergoing electrode implantation?

A

brain has no pain somatic receptors

no sense of pain either

41
Q

Somatotopy:

A

mapping of the body’s surface sensations onto a structure in the brain

42
Q

The somatic map is sometimes called the […].

A

homunculus (“little man”)

43
Q

If there is a removal of a body part what occurs to the mapping of the cortex?

A

major rearrangement of the cortical somatotopy

44
Q

What happens when the input activity of a body part is increased?

A

representation of stimulated body parts had expanded in comparison with the adjacent/unstimulated ones

45
Q

T/F: Cortical maps are dynamic and adjust on the amount of sensory experience.

A

true

46
Q

Ruffini’s endings found in […] are slightly smaller than […].

A

both glabrous and hair skin; Pacinian corpuscles

47
Q

Meissner’s corpuscles are about 1/10th the size of […] and are located in the […].

A

Pacinian corpuscles; ridges of glabrous skin

**raised parts of your fingertips

48
Q

What mechanoreceptor is being describe: Contains a cell and axon that are mechanosensitive, the two channels cooperate to activate the receptor.

A

Merkel’s disks

49
Q

Krause end bulbs, which lie in the […] and […], the nerve terminals look like […].

A

regions of dry skin; mucous membrane; knotted balls of string

**ex around the lips and genitals

50
Q

Hair grows from […] embedded in the skin; each […] is richly innervated by […].

A

follicles; follicle; free nerve endings

51
Q

What is in charge of mediating goosebumps?

A

erectile muscles (type of hair follicle)

52
Q

When the capsule (CT layers around the nerve terminal) compressed what occurs?

If the stimulus is maintained, what occurs?

When pressure is released, what occurs?

A
  1. energy transferred to the nerve terminal; deformation of the membrane leads to mechanosensitive channels to open; depolarization (if receptor potential is great enough leads to AP)
  2. layers slips past one another in a way that the axon terminal is no longer deformed; receptor potential dissipates
  3. events revers themselves; terminal depolarizes; may release AP
53
Q

Single corpuscles vs naked nerve terminal:

A

SC– extremely sensitive to vibrating stimuli

NNT– more sensitive to steady pressure

54
Q

Why is the fingertip so much better than the elbow (for example) for Braille reading?

A
  1. higher density of mechanoreceptors
  2. fingertips are enriched in receptor types that have small receptive fields
  3. more brain tissue devoted to the sensory info of each square mm of fingertip
  4. special neural mechanisms devoted to high-resolution discrimination
55
Q

What type of axons are the slowest? What do these detect?

A

Group C

mediate pain and temperature sensation

56
Q

To lose all sensation in one dermatome…

A

three adjacent dorsal roots must be cut

57
Q

Large and myelinated A(beta) axons enter the dorsal horn and branch in one of two ways:

A
  1. deep part of the dorsal horn on second-order sensory neurons
  2. ascends straight to the brain
58
Q

Agnosia:

A

inability to recognize objects even through simple sensory skills seem to be normal

59
Q

Agnosia is due to damage of the…

Deficits are often limited to the side…

A

posterior parietal lobes

contralateral to the damage

60
Q

Astereognosia:

A

cannot recognize common objects by feeling them

61
Q

Neglect syndrome:

A

part of the body or a part of the world (entire visual field left of the center of gaze) is ignored or suppressed, and its very existence is denied

62
Q

Neglect syndrome is due to…

A

parietal cortical lesions; typically on the R side

63
Q

In general, what is the posterior parietal cortex involved in?

A
  1. SPTIAL RELATIONSHIPS: perception and interpretation
  2. BODY IMAGE
  3. COORDINATION: learning tasks of body space
64
Q

Somatic sensation depends strongly on…

A

nociceptors

65
Q

Nociceptors description:

A

free, branching, unmyelinated C fibers

little myelinated A delta fibers

66
Q

Nociceptors function:

A

signal body tissue is being damaged or is at risk of being damaged

67
Q

Pain vs nociception:

A

P– feeling, perception, of irritation/sore/stinging/aching/throbbing/miserable

N: sensory process that provides the signals that trigger pain

68
Q

What are nociceptors activated by?

A

activated by mechanically gated ion channels

69
Q

Damaged cells at the site of injury can release a number of substances that cause ion channels on nociceptor membranes to open:

A
  1. proteases
  2. ATP
  3. K+
70
Q

Proteases can break down…

A

abundant extracellular peptide called kininogen to form another peptide called bradykinin

71
Q

Bradykinin:

A
  1. DEPOLARIZATION: binds to specific receptor molecules that activate ionic conductance in some nociceptors
  2. SENSITIZATION: stimulates long-lasting intracellular changes (heat-activated channels more sensitive)
72
Q

What occurs when your tissue oxygen levels do not meet the oxygen demand?

A
  1. cells use anaerobic metabolism to generate ATP
  2. release of lactic acid
  3. excess of H+ ions in EC
  4. ions activate H+ gated ion channels on nociceptors
  5. dull ache
73
Q

What occurs when a bee stings you?

A
  1. mast cells activated due to foreign substance
  2. release HA
  3. HA binds to specific cell surface receptors; causing depolarization
  4. HA causes blood capillaries to become leaky (swelling/redness)
74
Q

Transduction of painful stimuli occurs…

A

in the free nerve endings of unmyelinated C fibers and lightly myelinated A(delta) fibers

75
Q

Polymodal nociceptors respond to…

A

mechanical, thermal, and chemical stimuli

76
Q

Mechanical nociceptors are different how?

A

show selectivity in their responses to different stimuli

77
Q

Thermal nociceptors respond to…

A

selective; extreme temperature

78
Q

Chemical nociceptors respond to…

A

selective; HA and other chemicals

79
Q

Perception of itch is due to

A

small C fibers

80
Q

Hyperalgesia:

A

a reduced threshold for pain, an increased response to painful stimuli, spontaneous pain that follows a localized injury

81
Q

Primary vs secondary hyperalgesia:

A

P– injury site

S– tissues surrounding are affected

82
Q

What are some sensitizing chemicals?

A
  1. bradykinin
  2. prostaglandins
  3. substance P
83
Q

How do prostaglandins sensitize?

A

increase the sensitivity of nociceptors to other stimuli

**ASA and anti-inflammatory inhibit this

84
Q

Substance P:

A

peptide synthesized by the nociceptors

activation of nociceptor axon can lead to its secretion

85
Q

How does substance P cause sensitization?

A

vasodilation and release of HA (from mast cells)

86
Q

What triggers secondary hyperalgesia?

A
  1. substance P

2. ACTIVATION OF A(beta)– leads to cross-talk; where light touch can evoke pain

Neurobiology (12 decks)

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