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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
sensitization
polymodal nociceptors - repeated stimulations are increasingly effective in generating a response
26
chemoreceptors
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
mechanoreceptors
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
intensity of stimulus
the greater the stimulus, the great the NUMBER and FREQUENCY of action potentials (in general)
29
duration of stimulus
the longer the stimulus duration, the longer the train of generated action potentials (in general)
30
maintaining a stimulus for a longer duration
results in a TRAIN of action potentials
31
increasing the stimulus INTENSITY
increases the frequency of action potentials
32
sensory adaptation
decline in the generator potential with time (can be slow or fast)
33
examples of receptors with slow adaptation
merkel cells, thermal receptors
34
examples of receptors with fast adaptations
hair receptors, pancinian, messiner's corpuscles
35
two important factors in the acuity of sensory detection
number of receptors and receptive field size of somatic sensory neurons
36
C6, C7, C8, L5, S1
you know these
37
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
detection by the sensory end organ --> transduction --> impulse generation through action potential formation --> conduction along the sensory axon
38
specificity of the sensory response
resides in the molecular mechanism of the sensory receptor's membrane
39
Intensity
mapped from graded receptor potentials and measured by frequency of action potentials
40
Localization is determined by
receptive fields of sensory nerves and the central pathways that carry sensation to the brain
41
nociceptive pain
due to the activation of peripheral nociceptors (sharp/stabbing)
42
neuropathic pain
perception of pain WITHOUT a noxious stimulus, usually involves the injury to pain transmission pathways (itching/stinging/burning/freezing/shocky pain)
43
paresthesia
spontaneous sensation without a stimulus. called DYSESTHESIA (clinically interchangable with neuropathic pain) when it is unpleasant
44
hyperalgesia
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
allodynia
when a non-noxious stimulus produces a perception of pain
46
causalgia
persistent neuropathic pain after specific injury to a peripheral nerve
47
sensitization
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
anesthesia/analgesia
absence of sensation/pain perception (hypesthesia/hypoalgesia is abnormally DIMINISHED pain perception)
49
overstimulation of sensory receptors other than a-delta & c-fiber
does NOT cause pain
50
3 major classes of nociceptors in the skin
1. a-delta mechano-sensitive nociceptors, 2. a-delta mechno-thermal nociceptors 3. c-fiber polymodal nociceptors
51
first pain, second pain
A-delta, C fiber
52
TRP
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
Vanilloid receptors (VR-1, VR-2)
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
free nerve endings in damaged tissue
release substances that enhance the inflammatory response via vasodilation and histamine release
55
second/third order nociceptive neurons
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
WDR
wide dynamic range neurons that integrate pain/not painful inputs. excited by c fibers and inhibited by a-beta afferents (GATING!).
57
gating theory
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
Anterolateral System
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
visceral pain pathway
from dorsal columns, through nucleus gracilis, to ventral thalamus, to the insular cortex (why it is often referred)
60
Pain: Arousal
through the reticular formation
61
Pain: "Where"
Somatosensory Cortex
62
Pain: "What"
supplementary motor area, prefrontal cortex, association cortex, limbic system
63
PAG
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
endogenous opioids
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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