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Neuroscience > NEUR 0010 - Chapter 12 > Flashcards

NEUR 0010 - Chapter 12 Flashcards

1
Q

What are the four sub-senses of the somatic sensory system?

A

Touch, pain, temperature, body position

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2
Q

What is the largest sensory organ?

A

Skin

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3
Q

What kind of axon is at the heart of every mechanoreceptor? What kind of channels are here?

A

Unmyelinated; mechanosensitive ion channels

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4
Q

What kinds of skin are Pacinian corpuscles found? Ruffini’s endings? Meissner’s corpuscles? Merkel’s disc? Krause ends bulbs?

A

Pacinian in the dermis, Ruffini’s in hairy and glabrous, Meissner’s in glabrous ridges, Merkel’s in epidermis, Krause end bulbs in border of dry/mucous

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5
Q

What do Merkel’s discs in the epidermis look like?

A

Nerve terminal and flattened, non-neural epithelial cell

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6
Q

What do Krause end bulbs in the dry/mucous look like?

A

Nerve terminals look like knotted ball of string

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7
Q

Describe the receptive field sizes of Meissner’s corpuscles, Ruffini’s endings, Merkel’s discs, and Pacinian corpuscles.

A

Meissner and Merkel are small; Pacinian and Ruffini are larger

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8
Q

Which receptors are slow adapting or fast adapting: Meissner, Merkel, Pacinian, Ruffini.

A

Slow adapting is Merkel and Ruffini; Fast is Meissner and Pacinian

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9
Q

Describe how the structure of the Pacinian corpuscle allows for adaptation and sensation of vibration?

A

Football-shaped onion corpuscle with slippery layers: if you maintain deformation, the layers shift so that no pressure is on the nerve ending; but when you cease deformation, the layers shift again to put pressure back on the nerve ending, until they readapt to normal again

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10
Q

What are primary afferent neurons?

A

Axons bringing info from SS receptors to CNS

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11
Q

Where do the primary afferent neurons of the SSS enter the spinal cord?

A

Through the dorsal roots/dorsal root ganglia

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12
Q

Describe the primary afferent neurons from largest diameter to smallest.

A

(A-alpha from skin, Group I from muscle; sensory receptors are proprioceptors of skeletal muscle); (A-beta from skin, Group 2 from muscle; mechanoreceptors of skim); (A-delta from skin, Group 3 from muscle; sensory receptors are pain/temp); (C from skin, Group 4 from muscles; temp/itch/pain)

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13
Q

What axon-from-muscle Group of primary afferent neurons is not present in the skin? Describe the characteristics.

A

Proprioception sensory receptor afferent neurons: A-alpha, Group 1, large diameter, fast conduction

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14
Q

What is the relationship between axon diameter and conduction speed?

A

Larger diameter, faster conduciton

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15
Q

Out of the four groups of primary afferent neurons, which group is unmyelinated?

A

Group C: itch/temp/pain

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16
Q

How many spinal segments are there? What’s a spinal segment?

A

Spinal segment is the area named after the vertebrae where the nerves originate; 30 of them

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17
Q

Describe the breakdown of the 30 spinal segments.

A

8 cervical, 12 thoracic, 5 lumbar, 5 sacral

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18
Q

What is a dermatome?

A

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

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19
Q

Why does a dermatome retain residual sensation even when the dorsal root is cut?

A

Adjacent dorsal roots innervate overlapping areas

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20
Q

What are second-order sensory neurons?

A

Neurons that receive sensory input from primary afferents; mostly lie within dorsal horns

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21
Q

What are the two main branches from when the large, myelinated A-beta (Group 2) neurons enter the dorsal horn of the spinal cord?

A

One branch: synapses with second-order sensory neurons for reflexes; Other branch: goes straight up to the brain for perception and judgment about stimuli touching the skin

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22
Q

What is the dorsal column-medial lemniscal pathway?

A

Pathway serving touch: instead of pain/temperature

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23
Q

What is the ascending part of the DC-ML pathway?

A

Large sensory axons (A-beta) enter ipsilateral dorsal column, which carry tactile sensation info to the brain

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24
Q

What kinds of axons make up the ascending DC-ML pathway?

A

Primary sensory and second-order from neurons in the spinal gray matter

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25
Q

Where do the DC-ML pathway ascending axons end?

A

In the dorsal column nuclei: junction of the spinal cord and the medulla

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26
Q

When does the DC-ML path become contralateral?

A

After the dorsal column nuclei: axons in the DCN branch toward ventral/medial medulla and decussate

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27
Q

What happens to axons in the DC-ML pathway after leaving the dorsal column nuclei?

A

Leave the DCN for the medulla: white matter tract called the medial lemniscus

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28
Q

Where do medial lemniscus axons terminate?

A

In the ventral posterior nucleus of the thalamus, then to the SS cortex (S1)

29
Q

What are the trigeminal nerves?

A

Cranial nerve V: somatic sensation of the face

30
Q

What is the trigeminal touch pathway?

A

Large sensory axons of trigeminal nerves carry info to second-order neurons in the ipsilateral trigeminal nucleus; the decussate and project into medial part of VP nucleus of thalamus, then on to S1 in the cortex

31
Q

Where is most of the SS cortex?

A

Parietal lobe

32
Q

What is the primary SS cortex?

A

Area 3b: on the postcentral gyrus behind the central sulcus

33
Q

Why is area 3b the primary SS cortex?

A

Receives dense input from VP of thalamus; neurons very responsive to SS stimuli but not other senses; lesions impair somatic sensation; electrical stimulation evokes SS experiences

34
Q

How do the projections to Areas 1 and 2 from Area 3b differ?

A

Area 1 is texture, area 2 is size/shape

35
Q

In what layer does thalamic input terminate in S1?

A

Layer IV

36
Q

What is somatotopy?

A

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

37
Q

Does agnosia occur on ipsi/contralateral side of damage?

A

Contralateral

38
Q

How does mechanical damage trigger nociceptors?

A

Stretched mechanically gated ion channels depolarize the cell and generate action potentials; damaged cells can release proteases/ATP/K+; proteases break down kininogen to for bradykinin, which binds to receptors in nociceptors; ATP binds to nociceptors and depolarizes them

39
Q

What types of SS neurons transduce pain?

A

Unmyelinated C fibers, lightly myelinated A-delta fibers

40
Q

What are the four types of nociceptors?

A

Thermal, chemical, mechanical, polymodal

41
Q

What is primary vs secondary hyperalgesia?

A

Primary occurs within damaged area tissue; secondary occurs in surrounding tissue

42
Q

What are three sensitizing chemicals that modulate nociceptors?

A

Bradykinin, prostaglandin, substance P

43
Q

Where is substance P made?

A

In the nociceptors

44
Q

What is bradykinin?

A

Depolarizes nociceptors; stimulates long-lasting intracellular changes, make heat-activated ion channels more sensitive

45
Q

What are prostaglandins?

A

Generated by lipid membrane breakdown; increase sensitivity of nociceptors to other stimuli (NSAIDs inhibit prostaglandins)

46
Q

What is substance P?

A

Made by nociceptors, causes release of histamine and vasodilation, sensitizes nearby nociceptors for secondary hyperalgesia

47
Q

What causes sharp first pain and dull second pain?

A

Activation of A-delta fibers, then activation of C fibers

48
Q

What is the zone of Lissauer?

A

The region of the spinal cord that carries the small-diameter SS fibers (dorsal)

49
Q

What is the substantia gelatinosa?

A

The outer part of the dorsal horn, where the fibers from the zone of Lissauer synapse

50
Q

Where is substance P contained?

A

The storage grandules in the axon terminals of pain fibers

51
Q

What causes referred pain?

A

The fact that nociceptor axons from the viscera and cutaneous enter the spinal cord by the same route: cross-talk that causes visceral pain to seem cutaneous

52
Q

How do nerve endings differ between touch/pain?

A

Touch has specialized receptors, pain has free nerve endings

53
Q

How does diameter differ between touch/pain?

A

Thick and fast conduction, small and slow conduction

54
Q

How do the connections to spinal cord differ between touch/pain?

A

For touch, axons terminate in dorsal horn; for pain, axons terminate in substantia gelatinosa after zone of Lissauer

55
Q

What is the spinothalamic pathway for pain?

A

Second-order neurons decussate IMMEDIATELY and ascending through ventral spinal cord; project up through spinal cord and through medulla/pons/midbrain to the thalamus

56
Q

How does decussation differ in touch/pain’s DC-ML vs spinothalamic pathway?

A

For touch (DC-ML), decussate at dorsal column nuclei (junction of cord and medulla); for pain (spinothalamic), decussate immediately

57
Q

What is Brown-Sequard syndrome?

A

The weird contra/ipsi pain/touch loss due to damage to one side of the spinal cord

58
Q

What is the trigeminal pain pathway?

A

Info from face/head small-diameter fibers synapse on second-order sensory neurons in spinal/trigeminal nucleus of the brainstem; cross and ascend to thalamus in trigeminal lemniscus

59
Q

Where can spinothalamic axons project after reaching the thalamus?

A

In thalamic VP nucleus, in intralaminar nuclei of thalamic, then on to other cortical areas

60
Q

How can mechanoreceptors reduce pain?

A

Simultaneous activation of mechanoreceptors (A-beta fibers) can reduce nociceptor activity

61
Q

What is the gate theory of pain?

A

Certain neurons of the dorsal horns (project axons up spinothalamic tract), excited by large-diameter sensory neurons AND unmyelinated pain axons; inhibited by interneuron, which is excited by large sensory and inhibited by pain

62
Q

How does the periaqueductal gray matter affect pain?

A

Suppression: analgesia

63
Q

How does the PAG’s descending pathway suppress pain?

A

Sends descending axons to medulla (esp. raphe nuclei for serotonin), which project to the dorsal horn and depress nociceptive activity

64
Q

What are the receptors for “hot” and “cold?”

A

TRPV1 and TRPM8

65
Q

How selective are thermoreceptors?

A

Depends on the receptor: some are sensitive only to certain ranges of temperature, others can tell hot or cold

66
Q

What pathway is most similar to the thermoreceptor pathway?

A

Pain pathway

67
Q

What kinds of thermoreceptors are coupled to what kinds of SS fibers?

A

Cold is A-delta and C, warm is C only

68
Q

Where does the thermoreceptor pathway decussate?

A

Same as pain: immediately

69
Q

How does the thermoreceptor pathway ascend?

A

Same as pain: through spinothalamic tract

Neuroscience (19 decks)

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