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Neurophysiology II > Exam I (Somatic sensation) > Flashcards

Exam I (Somatic sensation) Flashcards

1
Q

What is transduction?

A

Where a stimulus is changed into an electrical signal

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2
Q

What are the different types of stimuli?

A

Mechanical, chemical, change of temperature and electromagnetic

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3
Q

What are the four attributes of a stimulus?

A

Modality, location, intensity and Duration (timing)

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4
Q

What are the two systems used for nerve fiber classification?

A

Erlanger’s and Lloyd’s

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5
Q

What is the speed of conduction dependent on for a nerve fiber?

A

Diameter and myelination

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6
Q

How does myelination increase conduction velocity?

A

six fold

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7
Q

What are the diameters of the different nerve classifications in Erlanger’s system?

A 
A(alpha) - 8-20 microns
A(beta) - 5-12 microns
A(gama) - 2-8 microns
A(sigma) - 1-5 microns
B - 1-3 microns
C - < 1 micron
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8
Q

Erlanger’s system is used in what?

A

Motor nerves and skin afferents

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9
Q

What types of nerve fibers represent motor fibers under the Erlanger classification system?

A

A(alpha) and A(gamma)

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10
Q

What types of nerve fibers represent skin afferent fibers under the Erlanger classification system?

A

A(beta) , A(sigma) and C

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11
Q

What are the diameters of the different nerve classifications in Lloyd’s system?

A

I - 12-20 microns
II - 4-12 microns
III - 1-4 microns
IV - < 1 micron

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12
Q

What is Lloyd’s system used for?

A

Afferents from receptors in muscle and spinal joints

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13
Q

Opening of Na+ ion channels is indicative of what?

A

A change in receptor potential

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14
Q

What is the relationship between the frequency of an AP and the negativity of a receptor potential?

A

The less negative the receptor potential the faster the frequency of AP into the CNS.

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15
Q

What is the labeled line principle?

A

the specificity of nerve fibers transmitting only one modality of sensation

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16
Q

The type of sensation felt is dependent on what?

A

The termination point in the CNS

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17
Q

What is adaptation?

A

When the firing rate of a neuron decreases over time due to a sustained stimulus

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18
Q

What are examples of slow-adaptive receptors?

A

Merkel’s discs and Ruffini end organs (corpuscles)

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19
Q

What are merkel’s discs?

A

Punctate receptive fields

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20
Q

How are Ruffini end organs stimulated?

A

by stretching the skin

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21
Q

What are the types of rapid or phasic-adaptive receptors?

A

Pacinian corpuscles and Meissner’s corpuscles

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22
Q

Both types of rapid-adaptive receptors respond to what type of stimulation?

A

Vibration

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23
Q

What is the optimum stimulus rate of Pacinian corpuscles?

A

250 Hz

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24
Q

What is the optimum stimulus rate of Meissner’s corpuscles?

A

30-40 Hz

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25
Q

What is the mechanism of adaptation?

A

Membrane adaptation is thought to be due to the entry of Ca++ ions during APs
- Ca++ opens a K+ channel increasing permeability of the membrane for K+..taking membrane away from threshold

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26
Q

What are the most heavily innervated spinal joints?

A

Cervical joints

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27
Q

Describe type I mechanoreceptors

A
  • Outer layers of joint capsule
  • Fire at a degree proportional to joint movement or traction
  • low threshold
  • dynamic-fire with movement
  • slow adapting
  • tonic effects on lower motor neuron pools
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28
Q

Describe type II mechanoreceptors

A
  • Deeper layers of joint capsule
  • low threshold
  • rapidly adapting
  • completely inactive in immobilized joints
  • functions in joint movement monitoring
  • phasic effects on lower motor neuron pools
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29
Q

Describe type III mechanoreceptors

A
  • recently found in spinal joints
  • very high threshold
  • slow adapting
  • joint version of GTO
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30
Q

Describe type IV receptors

A
  • Nociceptors
  • very high threshold
  • completely inactive in physiologic normal joint
  • activation with joint narrowing, increased capsular pressure and chemical irritation
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31
Q

Information transmitted to the brain from mechanoreceptors in fingers allows us to:

A
  • feel the shape and texture of objects
  • play musical instruments
  • type on computer keyboards
  • palpate and perform adjustments
  • perform a multitude of tasks using our hands
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32
Q

What happens after tactile information is fragmented by receptors?

A

It must be integrated (interpreted) by the brain

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33
Q

Why is tactile information important?

A

It gives us the ability to recognize objects placed in the hand on the basis of touch alone.

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34
Q

How is tactile information obtained?

A

Through palpation

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35
Q

What is Stereognosis?

A

The ability to perceive form through touch

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36
Q

What does stereognosis test?

A

The ability of the dorsal column-medial lemniscal system to transmit sensations from the hand

Also the ability of cognitive processes in the brain where integration occurs

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37
Q

How does the brain interpret an object if most objects are larger than the receptive field of any receptor in the hand?

A

The objects stimulate a large population of sensory nerve fibers. Each of which scans a small portion of the object. The brain reconstructs the pattern.

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38
Q

Does a single sensory axon or class of sensory axons signal all relevant information?

A

No. The CNS constructs a coherent image of an object from fragmented information conveyed in multiple pathways

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39
Q

What are the categories of sensory modalities?

A

Pressure receptors, cold receptors, warmth receptors and nociceptors

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40
Q

Getting wet stimulates what receptors?

A

pressure and temperature receptors

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41
Q

Being tickled stimulates what receptors?

A

Gentle stimulation of pressure receptors

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42
Q

What receptors are stimulated by an itch?

A

Gently stimulation of nociceptors

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43
Q

How do humans detect extremely fine textures?

A

When fine textures are stroked on the fingerpad skin, the fingerprint ridges vibrate and cause Pacinian corpuscles to respond enabling the dection of the microtexture.

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44
Q

Depth of indentation and the change in curvature of the skin surface are encoded by discharge rates of what?

A

Slow adapting afferent fibers

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45
Q

Velocity and the rate of change in skin surface curvature are encoded by discharge rates of what?

A

Both slow adapting and rapidly adapting afferent fibers

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46
Q

Meissner’s corpuscles are found in what type of skin?

A

Glabrous (non hairy)

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47
Q

What are the characteristics of Meissner’s corpuscles?

A

Concentrated in the fingertips
Signals edges, register sideways shearing of the skin
Density declines with age

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48
Q

Where are pacinian corpuscles found?

A

Subcutaneous tissue

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49
Q

What are the characteristics of Merkel’s discs?

A

Slow adapting
Punctate receptive fields
senses curvature of an object’s surface

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50
Q

What are the characteristics of Ruffini end organs?

A

Slow adapting

Activated by stretching of the skin (even at some distance away from receptor)

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51
Q

Which receptors are deep in the skin (large receptive field)?

A

Pacinian Corpuscles and Ruffini Endings

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52
Q

Which receptors are superficial (small receptive field)?

A

Meissner’s corpuscles and Merkel’s discs

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53
Q

What is the somatotopic homunculus based on?

A

the density of receptors

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54
Q

What is lateral inhibition?

A

Where a first order neuron synapses it excites a second order neuron as well as local interneurons (surround inhibition)

55
Q

Describe the dorsal column-medial lemniscal system

A
  • Most aspects of touch, proprioception
  • First order neurons synapse in the brain stem
  • 2nd order neurons of both pathways cross to other side and ascend, synapsing in the thalamus
56
Q

Describe the Anterolateral system

A
  • Sensations of crude touch, nociception, temperature, tickle, itch and sexual sensations
  • First order neurons synapse in the dorsal horn of the spinal cord
  • 2nd order neurons of both pathways cross to other side and ascend, synapsing in the thalamus
57
Q

What is protopathic and what are its characteristics?

A

Primitive feeling

  • Old (phylogenetically)
  • synapse in the cord
  • Contralateral in the cord
  • INITIATE ACTIONS
  • small fibers
  • Pain, temperature, tickle, itch, sexual sensations
58
Q

What is epicritic and what are its characteristics?

A

Precise objective information

  • New (phylogenetically)
  • Synapse in brain stem
  • Ipsilateral in cord
  • MODIFY ACTIONS
  • Large fibers
  • Encapsulated mechanoreceptors
  • Provide feedback used by the brain
59
Q

What is the clinical significance of spinal cord lesions?

A

Hemisection of the cord

  • Loss of vibration/proprioception – ipsilateral
  • Analgesia - contralateral
60
Q

Describe the early stages of cortical processing

A

Dynamic properties of central neurons and receptors are similar (eg rapidly adapting cutaneous receptors connected to rapidly adapting 2nd and 3rd order neurons)

61
Q

Describe the later stages of cortical processing

A

The central nerve cells have complex feature detecting properties and integrate various sensory inputs

62
Q

What are the three different types of neurons in BM area 1 and 2?

A

Motion sensitive neurons, Direction-sensitive neurons and Orientation-sensitive neurons

63
Q

Describe motion sensitive neurons

A

Respond well to movement in all directions but not selectively to movement in any one direction

64
Q

Describe direction-sensitive neurons

A

Respond much better to movement in one direction than in another direction

65
Q

Describe orientation-sensitive neurons

A

Respond best to movement along a specific axis

66
Q

Describe BM 5

A

Integrates tactile information from mechanoreceptors in skin with proprioceptive inputs from underlying muscle and joints

67
Q

Describe BM 7

A

receives visual, tactile and proprioceptive inputs

-integrates stereognostic and visual information

68
Q

What is the posterior parietal cortex?

A

BM 5 and 7

69
Q

Describe the secondary somatic sensory cortex

A
  • located in the superior bank of the lateral fissure
  • projections from S-1 are required for function of S-II
  • projects to the insular cortex, which innervates regions of temporal lobe believed to be important in tactile memory
70
Q

What are the characteristics of thermoreceptors?

A
  • Slow adapting
  • Discharge spontaneously under normal conditions
    • Active over a wide range of temperatures
  • Discharge phasically when skin temperature changes rapidly
71
Q

What are the two types of thermoreceptors?

A

Cold and Warmth

72
Q

When are the two types of thermoreceptors inactivated?

A
  • Cold- when the skin is warmed

- Warmth- when the skin is cooled

73
Q

What are nociceptors activated by?

A

Mechanical, thermal and chemical stimuli

74
Q

What are the sensations of pain?

A

Pricking, burning, aching, stinging and soreness

75
Q

What is the difference between pain and nociception?

A

Pain is the perception of an unpleasant sensation. Nociception provides information about tissue damage that is often extremely painful.

76
Q

Why is pain hard to define and treat clinically?

A

It is highly subjective

77
Q

What is pain?

A

Conspicuous sensory experience that warns of danger

78
Q

What is the least differentiated sensory receptor?

A

Nociceptors

79
Q

What is hyperalgesia?

A

Increased sensitivity to pain

  • repeated heating
  • axon reflex may cause spread of hyperalgesia in periphery
  • sensitization of central nociceptor neurons as a result of sustained activation
80
Q

what does potassium from damaged cells do to nociceptors?

A

activates

81
Q

Characteristics of Fast nociceptive pathways?

A
  • A delta fibers
  • glutamate
  • neospinothalamic
  • mechanical, thermal
  • good localization
  • sharp, pricking
  • Most terminate in VB complex of thalamus
82
Q

Characteristics of Slow nociceptive pathways?

A
  • C fibers *
  • substance P/ glutamate
  • Primary paleospinothalamic
  • polymodal/chemical
  • poor localization
  • dull, burning, aching
  • Diffuse termination;
  • Reticular formation
    • tectal area of mesen.
    • Periaqueductal gray
83
Q

Describe C-fiber nociceptors (first order)

A

Secrete both substance P and glutamate

Synapse primarily in substantia gelatinosa (lamina II & III)

84
Q

Describe Glutamate

A

Effects are transient and short acting

-Fast component of C-fiber

85
Q

Descrive Substance P

A

Released more slowly and concentration builds over seconds-minutes responsible for longer lagging predominant effect (slow pain)

86
Q

What are the different nociceptive pathways?

A 
Spinothalamic-major 
-neo- fast (A delta)
-paleo- slow (C fibers)
Spinoreticular
Spinomesencephalic
Spinocervical (mostly tactile)
Dorsal columns- (mostly tactile)
87
Q

What are the cardinal signs of inflammation?

A

Redness
Heat
Swelling
Pain

88
Q

What is rubor?

A

redness

89
Q

What is Calor?

A

Heat

90
Q

What is tumor?

A

swelling

91
Q

What is dolar?

A

Pain

92
Q

What is the peripheral pain control mechanism?

A

Gating theory

93
Q

What is the gating theory

A

Involves inhibitory interneuron in cord impacting nociceptive projection neurons

  • inhibited by C-fibers
  • Stimulated by A alpha and beta fibers
  • TENS
94
Q

Describe the Central pain control mechanism

A

Direct electrical stimulation to the brain
->Analgesia
Nociceptive control pathways descend to cord
Endogenous opiods
Endogenous cannabinoids

95
Q

Enkephalin projections to Raphe

Endogenous opioids

A

Periaqueductal gray

96
Q

Serotonin projections to the cord

Endogenous opioids

A

Raphe N.

97
Q

Inhibitory interneurons in the cord

Endogenous opioids

A

Release encephalin which can cause pre-synaptic inhibition of incoming C & A delta fibers

Inhibit second order projection neurons

98
Q

BM area that forms muscle stretch receptors

A

3a

99
Q

BM area that forms cutaneous receptors

A

3b

100
Q

BM area that forms deep pressure receptors

A

2

101
Q

BM area that forms rapidly adapting cutaneous receptors

A

1

102
Q

what does serotonin from platelets do to nociceptors?

A

activates

103
Q

What does bradykinin from plasma kininogen do to nociceptors?

A

activates

104
Q

What does histamine from mast cells do to nociceptors?

A

activates

105
Q

What do prostaglandins and leukotriends from ARA damaged cells do to nociceptors?

A

Sensitize

106
Q

What does substance P from the primary afferent do to nociceptors?

A

Sensitize

107
Q

Sensory innervation of most of the head and face

A

Trigeminal N. (V)

108
Q

muscle receptor that responds to stretch

A

Muscle spindle

109
Q

Muscle receptor that responds to tension

A

GTO

110
Q

Where are muscle spindles located?

A

within the belly of the muscle parallel with extrafusal fibers

111
Q

Where are GTOs located?

A

at the junction of the muscle and tendon

112
Q

Innervated by two types of myelinated afferent fibers

A

Muscle spindles

113
Q

What are the two types of myelinated afferent fibers that innervate muscle spindles?

A

group Ia (large diameter) and group II (small diameter)

114
Q

innervated by group Ib afferent fibers

A

GTOs

115
Q

what happens when a spindle is activated by stretch of a muscle?

A

muscle contraction

116
Q

What happens when a GTO is stimulated by either a stretch or a contraction of a muscle

A

inhibition of muscle contraction

117
Q

muscle spindle that is most responsive to muscle shortening?

A

group II

118
Q

muscle spindle that is most responsive to muscle lengthening?

A

group Ia

119
Q

afferent innervation of GTO?

A

group Ib

120
Q

afferent innervation of muscle spindle?

A

Group Ia and II

121
Q

efferent innervation of GTO?

A

none

122
Q

Efferent innervation of muscle spindle

A

y fibers

123
Q

Relationship to extrafusal fiber of GTO

A

series

124
Q

relationship to extrafusal fiber of spindle

A

parallel

125
Q

primary GTO stimulus

A

contraction (tension)

126
Q

reflex response of GTO

A

inhibition of extrafusal fibers

127
Q

reflex response of spindle

A

contraction of extrafusal fibers

128
Q

innervates intrafusal fibers

A

gamma (y) motor system

129
Q

mesencephalic area appears to regulate rhythmic gate in what structure?

A

reticular formation

130
Q

What system fascilitates gamma motor neuron antigravity control?

A

vestibular system

131
Q

Over skeletal muscle, sensory afferent activating gamma motor neurons

A

cutaneous sensory receptors

132
Q

increased signal strength transmitted by progressively greater number of fibers

A

spatial summation

133
Q

increased signal strength by increased frequency of firing with the same number of fibers

A

temporal summation

Neurophysiology II (2 decks)

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