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Neurophysiology > Sensory System: Receptors and Pain > Flashcards

Sensory System: Receptors and Pain Flashcards

1
Q

sensation

A

the conscious or unconscious awareness of external or internal stimuli

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2
Q

perception

A

the conscious awareness and interpretation of information (allows for the creation of a perceptual representation of our environment)

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3
Q

modality

A

the type of sensation

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4
Q

transduction

A

the conversion of one type of energy to another

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5
Q

conduction

A

the propagation of a signal to a distant site in the nervous system (receptor potential reaches the threshold at the trigger zone)

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6
Q

three types of subsystems in the sensory system

A
  1. a subsystem for the detection of mechanical stimuli (touch, vibration, pressure) 2. a subsystem for the sensation of position 3. a subsystem for the detection of painful stimuli and temperature
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7
Q

fiber type Ia

A

large myelinated, proprioception (muscle spindle), fast (90 m/sec)

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8
Q

fiber A beta

A

large myelinated, vibration pressure touch and stretch, fast (50 m/sec)

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9
Q

fiber A delta

A

small myelinated, touch cold and pain, moderate (20 m/sec)

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10
Q

fiber c

A

small unmyelinated, temperature pain itch, slow (1 m/sec)

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11
Q

large myelinated fibers are associated

A

with the deep tendon reflexes

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12
Q

Fact

A

since the larger the fiber, the lower the threshold for activation, it is theoretically possible to stimulate large fibers with low, non-painful electrical currents.

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13
Q

spinothalamic tract

A

small fiber pain and temperature

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14
Q

hair receptors

A

innervation: alpha beta and alpha delta fibers, fast-adapting, arranged parallel to the hair shaft and are composed of neurites between two schwann cell’s cytoplasm

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15
Q

pacinian corpuscles

A

fast adapting, A beta, central naked axon, some may have more than one axon, resemble a sliced onion, highly sensitive to minimal skin depression and can follow oscillation up to 500 hz (tested by vibration - tuning fork)

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16
Q

meissner’s corpuscles

A

a beta, fast adapting receptors, follow low frequency oscilations (40 Hz) - ‘flutter’, located superficially in the dermal papillae, most common mechanoreceptor of hairless skin important in two point discrimination.

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17
Q

Merkel cells

A

a beta, slow adapting, steady state response, detection of a constant skin indentation without movement

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18
Q

proprioceptors

A

position receptors located in muscles, tendons, joint capsules, and ligaments, provide afferent information to the central nervous system, large diameter type I a sensory fibers coil around and innervate muscle spindles, type Ib fibers innervate golgi tendon organ receptors

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19
Q

golgi tendon organs

A

synapse on interneurons in the spinal cord that inhibit motor neurons innervating the muscle of origin and make excitatory connections with antagonistic muscles

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20
Q

thermoreceptors

A

different sensory receptors that respond to changes in skin temperature. slowly adapting

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21
Q

nociceptors

A

pain receptors, free nerve endings (mechanical nociceptors, polymodal nociceptors - supplied by c fibers respond to chemicals on the skin)

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22
Q

fast pain

A

immediate, short latency, short duration, well-localized pain through A Delta fibers

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23
Q

slow pain

A

diffuse, longer duration, burning sensation, conducted by c fibers

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24
Q

visceral pain

A

particularly sensitive to stretch or distension of visceral organs

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25
Q

sensitization

A

polymodal nociceptors - repeated stimulations are increasingly effective in generating a response

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26
Q

chemoreceptors

A

detect a chemical stimulus such as odor, activates a g protein, which activates adenylate cyclase to synthesize cAMP, increases channel conductance, depolzarizes the receptor membrane and gives rise to receptor potential. (cAMP GATES ION CHANNEL ACTIVITY) i.e. carotid and aortic bodies that respond to the oxygen content of blood

27
Q

mechanoreceptors

A

stimulus is stretch or tension, applied stimulus pulls on carbohydrate chains anchored in the extracellular space and/or membrane cytoskeleton, stretch on the molecular conformation of channel proteins changes their conductance –> this produces receptor potential. (pancinain, meissner, free nerve endings, proprioceptors)

28
Q

intensity of stimulus

A

the greater the stimulus, the great the NUMBER and FREQUENCY of action potentials (in general)

29
Q

duration of stimulus

A

the longer the stimulus duration, the longer the train of generated action potentials (in general)

30
Q

maintaining a stimulus for a longer duration

A

results in a TRAIN of action potentials

31
Q

increasing the stimulus INTENSITY

A

increases the frequency of action potentials

32
Q

sensory adaptation

A

decline in the generator potential with time (can be slow or fast)

33
Q

examples of receptors with slow adaptation

A

merkel cells, thermal receptors

34
Q

examples of receptors with fast adaptations

A

hair receptors, pancinian, messiner’s corpuscles

35
Q

two important factors in the acuity of sensory detection

A

number of receptors and receptive field size of somatic sensory neurons

36
Q

C6, C7, C8, L5, S1

A

you know these

37
Q

Four principle steps in the transfer of information from the level of sensory stimulus to the level of an afferent impulse traveling towards central pathways

A

detection by the sensory end organ –> transduction –> impulse generation through action potential formation –> conduction along the sensory axon

38
Q

specificity of the sensory response

A

resides in the molecular mechanism of the sensory receptor’s membrane

39
Q

Intensity

A

mapped from graded receptor potentials and measured by frequency of action potentials

40
Q

Localization is determined by

A

receptive fields of sensory nerves and the central pathways that carry sensation to the brain

41
Q

nociceptive pain

A

due to the activation of peripheral nociceptors (sharp/stabbing)

42
Q

neuropathic pain

A

perception of pain WITHOUT a noxious stimulus, usually involves the injury to pain transmission pathways (itching/stinging/burning/freezing/shocky pain)

43
Q

paresthesia

A

spontaneous sensation without a stimulus. called DYSESTHESIA (clinically interchangable with neuropathic pain) when it is unpleasant

44
Q

hyperalgesia

A

mild stimuli that are perceived as very painful (can be seen in patients with a pathway injury coupled with a external stimulus) not to be confused with hypesthesia (which is the opposite)

45
Q

allodynia

A

when a non-noxious stimulus produces a perception of pain

46
Q

causalgia

A

persistent neuropathic pain after specific injury to a peripheral nerve

47
Q

sensitization

A

greater intensity of pain per given amount of nociceptive input (shift to the left when pain intensity is on the y-axis, and stimulus intensity is on the x-axis)

48
Q

anesthesia/analgesia

A

absence of sensation/pain perception (hypesthesia/hypoalgesia is abnormally DIMINISHED pain perception)

49
Q

overstimulation of sensory receptors other than a-delta & c-fiber

A

does NOT cause pain

50
Q

3 major classes of nociceptors in the skin

A
  1. a-delta mechano-sensitive nociceptors, 2. a-delta mechno-thermal nociceptors 3. c-fiber polymodal nociceptors
51
Q

first pain, second pain

A

A-delta, C fiber

52
Q

TRP

A

Transient Receptor Potential –> membrane depolarization in response to mechanical, chemical, or thermal stimuli; not all are pain receptors; each TRP channel has high specificity

53
Q

Vanilloid receptors (VR-1, VR-2)

A

part of the TRP family. VR-1 found in A-delta and C fibers, respond to moderate heat and to capsaicin. VR-2 found in A-delta fibers and respond to high heat. Both can be sensitized by chemical signals from damaged tissues

54
Q

free nerve endings in damaged tissue

A

release substances that enhance the inflammatory response via vasodilation and histamine release

55
Q

second/third order nociceptive neurons

A

cross the midline and the level of the spinal cord and then ascend as the anterolateral pathway.= (nociceptive specific neurons and wide dynamic range neurons)

56
Q

WDR

A

wide dynamic range neurons that integrate pain/not painful inputs. excited by c fibers and inhibited by a-beta afferents (GATING!).

57
Q

gating theory

A

when a non-nociceptive input at the same area of a nociceptive input can diminish the nociceptive (or painful) response via inhibition (excitation of inhibitory interneurons, to be exact) of wide dynamic range neurons.

58
Q

Anterolateral System

A

Three tracts (*TMR): spinoreticular tract (through reticular formation of the medulla, dorsal thalamus, and to the association and somatosensory cortex), spinomesencephalic tract (to the PAG and then the hypothalamus, amygdala limbic system), spinothalamic tract (through brainstem reticular formation, PAG, ventral thalamus VPM/VPL, dorsal thalamus, association & somatosensory cortex)

59
Q

visceral pain pathway

A

from dorsal columns, through nucleus gracilis, to ventral thalamus, to the insular cortex (why it is often referred)

60
Q

Pain: Arousal

A

through the reticular formation

61
Q

Pain: “Where”

A

Somatosensory Cortex

62
Q

Pain: “What”

A

supplementary motor area, prefrontal cortex, association cortex, limbic system

63
Q

PAG

A

periaquaductal grey in the midbrain, descending pain control, input from the somatic sensory cortex, amygdala, and the hypothalamus, communicates via brainstem nuclei such as the parabrachial nucleus, medullary reticular formation, locus coeruleus, and the raphe nucleus

64
Q

endogenous opioids

A

used by interneurons of the dorsal horn to relay descending pain modulation via presynaptic inhibition of C fiber terminals onto dorsal horn projection neurons of the anterolateral system

Neurophysiology (6 decks)

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