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Neuroscience Exam 2 > Lecture 2. Cutaneous Sensation: Touch and Pain > Flashcards

Lecture 2. Cutaneous Sensation: Touch and Pain Flashcards

1
Q

Define the Somatosensory System

A

A network of neurons that help humans recognize objects, discriminate textures, generate sensory-motor feedback, and exchange social cues

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2
Q

How are cutaneous sensory fibers similar to other sensory fibers?

A
  • Some are encapsulated with specialized endings
  • Some are free nerve ending
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3
Q

List the (3) types of receptors of the Somatosensory System

A
  • Mechanoreceptors
  • Chemoreceptors
  • Nociceptors
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4
Q

Most receptors of the somatosensory system are what kind of receptors?

A

mechanoreceptors

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5
Q

Chemoreceptors respond to what?

A

acidic substances

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6
Q

Nociceptors respond to what?

A

potential damaging stimuli

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7
Q

List the different mechanoreceptors (5) in the skin

A
  • Merkel cell (disks)
  • Meissner corpuscle
  • Ruffini corpuscle
  • Pacinian corpuscle
  • Free nerve ending
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8
Q

Mechanoreceptor

Meissner corpuscle

  • Skin Layer
  • Fiber Type
  • Role in Perception
  • Submodality
  • Conduction Velocity
A
  • Skin Layer: Superficial layer
  • Fiber Type: Aβ
  • Role in Perception: Flutter, motion, more general touch
  • Submodality: SA1
  • Conduction Velocity: 42-72 ms-1
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9
Q

Mechanoreceptor

Merkels Disks (Cell)

  • Skin Layer
  • Fiber Type
  • Role in Perception
  • Submodality
  • Conduction Velocity
A
  • Skin Layer: Superficial
  • Fiber Type: Aβ
  • Role in Perception: Pressure, form, texture, identification of “edges and stripes”
  • Submodality: SA1
  • Conduction Velocity: 42-72 ms-1
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10
Q

Mechanoreceptor

Ruffini Corpuscle

  • Skin Layer
  • Fiber Type
  • Role in Perception
  • Submodality
  • Conduction Velocity
A
  • Skin Layer: Deeper Layer
  • Fiber Type: Aβ
  • Role in Perception: Stretch
  • Submodality: SAII
  • Conduction Velocity: 42-72 ms-1
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11
Q

Mechanoreceptor

Pacinian Corpuscle

  • Skin Layer
  • Fiber Type
  • Role in Perception
  • Submodality
  • Conduction Velocity
A
  • Skin Layer: Deeper Layer
  • Fiber Type: Aβ
  • Role in Perception: Vibration and deep pressure
  • Submodality: PC
  • Conduction Velocity: 42-72 ms-1
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12
Q

Mechanoreceptor

Free nerve ending

  • Skin Layer
  • Fiber Type
  • Role in Perception
  • Submodality
  • Conduction Velocity
A
  • Skin Layer: Superficial Layer
  • Fiber Type: C
  • Role in Perception: Pressure
  • Submodality: RA
  • Conduction Velocity: 0.5-1.2 ms-1
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13
Q

Mechanoreceptors are mostly what type of fiber?

A

Aβ

RA (nerve ending) is the only one that is not β

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14
Q

Thermoreceptors (Warm)

Free nerve ending

  • Fiber Type
  • Role in Perception
  • Submodality
  • Conduction Velocity
A
  • Fiber Type: C
  • Role in Perception: Warmth
  • Submodality: Warm
  • Conduction Velocity: 0.5-1.2 ms-1
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15
Q

Thermorecptors (Cold)

Free nerve ending

  • Fiber Type
  • Role in Perception
  • Submodality
  • Conduction Velocity
A
  • Fiber Type: A𝜎
  • Role in Perception: Cold
  • Submodality: Cold
  • Conduction Velocity: 12-36 ms-1
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16
Q

Nociceptors (Acute pain)

Free nerve ending

  • Fiber Type
  • Role in Perception
  • Submodality
  • Conduction Velocity
A
  • Fiber Type: A𝜎 (acute pain)
  • Role in Perception: sharp,localized pain
  • Submodality: Small, myelinated
  • Conduction Velocity: 12-36 ms-1
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17
Q

Nociceptors (Dull pain)

Free nerve ending

  • Fiber Type
  • Role in Perception
  • Submodality
  • Conduction Velocity
A
  • Fiber Type: C (dull pain)
  • Role in Perception: Burning
  • Submodality: unmyelinated
  • Conduction Velocity: 0.5-1.2 ms-1
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18
Q

What mechanoreceptors do burn patients often have issues with and why?

A

Meissner corpuscles and Merkel’s disk b/c the receptor’s proximity to the surface of the skin, burn pts are more likely to lose light touch and identification of objects by touch

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19
Q

What are Receptive Fields?

A

An area of skin that when stimulated with an adequate stimulus, will cause a specific neuron to alter its activity

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20
Q

Explain important characteristics (3) of receptive fields

A
  • May differ in size
  • Response characteristics differ with the type of receptor
  • Change with location on the skin and the site in the neuro-axis of the neuron being examined
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21
Q

Define an Adequate Stimulus

A

A stimulus to which a receptor is most sensitive

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22
Q

Define Two-Point Discrimination

A
  • The ability to discern that two nearby objects touching the skin are truly two distinct points, not one
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23
Q

Explain the relationship between the size of the receptive field and two-point discrimination

A

The smaller the receptive field the more we are able to distinguish between sensations

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24
Q

Greater two-point discrimination means what type of index?

A

smaller discrimination index

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25
Q

Lesser two-point discrimination means what type of index?

A

higher discrimination index

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26
Q

Where on the body would have a higher discrimination index/lesser two-point discrimination?

A

arms, legs, torso, back

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27
Q

Where on the body would have a smaller discrimination index/greater two-point discrimination?

A

face, lips, nose, fingers

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28
Q

How do mechanoreceptors produce a generator (action) potential?

A

Through voltage-or ligand ion channels

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29
Q

What is the mechanism that causes voltage-or ligand-gated ion channels to open in mechanoreceptors?

A

Physical stimuli/skin deformation (stretch) open the receptors in order to transduce signals

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30
Q

List the (4) features receptors code for

A
  1. Spatial location
  2. Modality
  3. Stimulus duration
  4. Intensity
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31
Q

Explain Rapid adapting receptors

A

Respond to changes in stimuli on the skin

Example: picking something up and putting something down

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32
Q

Explain slow-adapting receptors

A

Respond over the course of the stimulus

Example: Getting dressed in the morning and slowly losing sensation of each item as the day progresses

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33
Q

Which adapting receptor keeps firing as long as you’re holding something?

A

slowly adapting

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34
Q

Which adapting receptor only responds to a change in the stimulus?

A

rapidly adapting

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35
Q

Which mechanoreceptors are rapidly adapting? And what are their receptor fields?

A
  • Pacinian corpuscles (receptive field: large, vague borders)
  • Meissner’s corpuscle (receptive field: small, sharp borders)
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36
Q

Which mechanoreceptors are slowly adapting? And what are their receptive fields?

A
  • Merkel’s discs (receptive field: small, sharp borders)
  • Ruffini’s corpuscle (receptive field: large, vague borders)
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37
Q

What is the function of both rapidly and slowly adapting receptors?

A

Perception of texture and pattern

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38
Q

What perception of texture and pattern is signaled by:

  • Slowly adapting receptors
  • Rapidly adapting receptors
A
  • Slowly Adapting: Place and Duration
  • Rapidly Adapting: Changes in form
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39
Q

What does the inactivation of any of the four mechanoreceptors cause?

A

Inability to interpret shape

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40
Q

What type of fibers are contained in the dorsal root?

A

afferent fibers

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41
Q

Where does somatosensory information enter the CNS?

A

The dorsal root ganglia into the dorsal root

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42
Q

Which type of fibers bifurcate (divide) at the dorsal root entry zone?

A

Large myelinated fibers

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43
Q

After sensory information enters the spinal cord where do the branches separate too?

A
  • One branch ascends in the posterior (dorsal) columns
  • The other branch synapses in deeper laminae of the spinal cord
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44
Q

Which type of sensory information travels up the posterior/dorsal column?

A

Touch, pressure, and vibration (mechanosensory) information

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45
Q

Which type of sensory information travels up the lateral column?

A

Pain and temperature information

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46
Q

What location does lower body sensation enter in the posterior/dorsal column?

A

Most medial portion

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47
Q

What location does upper body sensation enter in the posterior/dorsal column?

A

Most lateral portion

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48
Q

Injury to where can lead to loss of mechanosensation in specific regions of the body?

HIGH yield

A

Either the medial or lateral portion of the posterior/dorsal column

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49
Q

Which type of fibers synapses in the dorsal horn of the spinal cord?

A

Small, unmyelinated fibers

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50
Q

Explain the Medial Lemniscal Sytem. Locations? Beginning destination and final destination?

A
  • Located in the Dorsal/posterior column
  • Begins from mechanosensory receptors from the upper and lower body through the spinal cord
  • End at the medulla specifically the rostral medulla
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51
Q

What is the name of the tract that receives information from the lower body?

A

Gracile tract

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52
Q

What is the name of the tract that receives information from the upper body?

A

Cuneate tract

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53
Q

Explain the mechanosensory pathway from the lower body to the caudal medulla (base of the brainstem)

A

Mechanosensory information from the lower body enters the CNS at the lumbar spinal cord and travels up the gracile tract to the gracile nucleus in the caudal medulla

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54
Q

Explain the mechanosensory pathway from the upper body to the caudal medulla (base of the brainstem)

A

Mechanosensory information from the upper body enters the CNS at the cervical spinal cord and travels up the cuneate tract to the cuneate nucleus in the caudal medulla

55
Q

After entering the caudal medulla (base of the brainstem) what is the next location for the information fibers and what occurs there?

A
  • Location: Internal arcuate fibers
  • Where BOTH will cross and continue traveling on the opposite side
56
Q

What is the term to describe the crossing at the internal arcuate fibers?

Medial Lemniscal System

A

Descussation

57
Q

What occurs when there is a spinal cord injury on the LEFT side and why?

A

Loss of mechanosensation in the LEFT side b/c at the spinal cord level the fibers have not crossed so the effects are on the same side

58
Q

What occurs where there is a brain stem injury on the LEFT side and why?

A

Loss of mechanosensation in the RIGHT side b/c at the brain stem level the fibers have crossed so the effects are on the opposite side

59
Q

Explain Somatotopy

A

Are the different regions of the posterior (dorsal) column of the spinal cord (lateral or medial) that corresponds to different parts of our body (upper and lower)

60
Q

What part of our body corresponds to the lateral region of the posterior column of the spinal cord?

A

Upper body

61
Q

What part of our body corresponds to the medial region of the posterior column of the spinal cord?

A

Lower body

62
Q

After the internal arcuate fibers decussate (cross over), what do they form?

A

Medial lemniscus tract

63
Q

Where do the fibers travel after the medial lemniscus tract?

A

To the Ventral posterior LATERAL nucleus of the thalamus (VPLN)

64
Q

After the VPLN where do the fibers ascend to?

VPLN- Ventral posterior lateral nucleus

A

The primary (SI) and secondary (SII) somatosensory cortex

65
Q

What occurs at the primary and secondary somatosensory cortex?

A

Where integrating somatosensory information begins

66
Q

Where is the somatosensory cortex located?

A

In the Parietal lobe

67
Q

What is the pathway for the trigemino-thalmic-cortical (face recognition)?

A
  1. Cranial nerve carries face info. to trigeminal neuron
  2. trigeminal neuron info. comes through ganglion
  3. info. synapses and crosses immediately
  4. Goes to trigeminal lemniscus and VPMN
  5. Ends in the somatosensory cortex
68
Q

Mechanosensory information from the FACE enters the brainstem via where?

A

Trigeminal ganglion

69
Q

Where do the fibers from the trigeminal ganglion synapse?

A

The principal trigeminal nucleus of the caudal medulla

70
Q

Where do fibers cross and travel in the trigeminal-thalamic-cortical pathway (face sensation)?

A
  • Cross at the Trigeminal leminscus
  • Travel to the Ventral posterior MEDIAL nucleus of the thalamus (VPMN)
71
Q

After the VPMN where do the fibers ascend to?

trigemino-thalamic-cortical pathway

VPMN-Ventral posterior medial nucleus

A

The primary (SI) and secondary (SII) somatosensory cortex

72
Q

For the Body, fill in the blank:
Ventral Posterior _________ Nucleus

A

Lateral

(L)ateral= (L)otion for Body

73
Q

For the Face, fill in the blank:
Ventral Posterior _________ Nucleus

A

Medial

(M)edial= (M)akeup for Face

74
Q

What is a dermatome?

A

slice of skin that one spinal/brainstem cranial nerve root carries info from

75
Q

When do dermatomes develop?

A

At the embryological level

76
Q

What are the characteristics of the somatosensory cortex?

A
  • has plasticity
  • has discrimination (touch, pain, proprioception)
77
Q

What determines how big nuclei are in the ventral posterior complex?

A

Density of information

78
Q

What part of the body uses up the largest area of the ventral posterior complex and the somatosensory cortex? and why?

A
  • Face (VPM; medial)
  • D/t a large density of information coming from a large number of neurons with small receptive fields
79
Q

What is homunculus?

A

representation of how much brain processing area there is for each body part

80
Q

What thermoreceptors are free nerve ending?

A

both warm and cold

81
Q

What are the fiber types of thermoreceptors?

A
  • Warm: C
  • Cold: A𝜎 (acute pain)
82
Q

Which nociceptors are free nerve ending?

A
  • Small, unmyelinated
  • Unmyelinated
83
Q

What are the fiber types for the nociceptors?

A
  • Small, myelinated: A𝜎 (acute pain)
  • unmyleinated: C (warm/dull pain)
84
Q

What are the roles of perception of the nociceptors?

A
  • Small, myelinated: sharp, localized pain
  • Unmyelinated: burning
85
Q

What is an example of acute pain?

A

an initial sting from a bee

86
Q

What is an example of dull/throbbing pain?

A

long-lasting pain after a bee sting

87
Q

Are all A𝜎 and C fibers nociceptors?

A

NO

88
Q

What molecules are associated with A𝜎 fibers?

A𝜎 fibers → Acute pain

Low yield

A

Excitatory amino acids (glutamate, aspartate, ATP)

89
Q

What molecules are associated with C fibers?

C fibers → dull pain

Low yield

A
  • Substance P
  • Neurokinins A&B
  • Cholycstokinin
  • Calcitonin Gene Related Peptide (CGRP)
  • Vasointestinal Peptide (VIP)
90
Q

True or False. We have pain receptors in our body

A

FALSE

Rather nociceptors respond to very intense and possibly harmful stimuli

91
Q

What is an example of how temp and pain can be carried by the same fibers?

A

capsaicin-molecule in chili pepper that gives them their spice

92
Q

What does capsaicin do?

A

binds to VR-1 (vanilloid) receptor to allow Ca2+ and Na to start signaling

VR-1 is synonymous to TRPV1

93
Q

What is the main difference between discriminative touch and pain response?

A

Discriminative touch signaling stays on the same side until it reaches the brain stem, while pain response information crosses right away

94
Q

Explain how nociceptive information enters the CNS

A

Enter the spinal cord via the dorsal horn and cross to the lateral side immediately via the anterior white commissure

95
Q

A patient with a LEFT spinal cord lesion will lose:

  • Discriminative touch on what side?
  • Temperature and pain sensation on what side?
A
  • Loss of discriminative touch on the LEFT side
  • Loss of temperature and pain sensation on the RIGHT side
96
Q

What is the anterior commissure in the spinal cord?

A

a small bundle of fibers connecting 2 hemispheres in the brain

97
Q

What occurs at the anterior white commissure in the spinal cord?

A

where nociceptive information is processed

98
Q

What is Lissauer’s tract?

A

2-3 segments above and below the dorsal root entry zone (DREZ) that add redundancy

Redundancy-allows a set of neurons to perform multiple tasks at once

99
Q

What is the benefit of Lissauer’s tract from an evolution standpoint?

A

Helps us maintain nociceptive perception in case of injury

100
Q

What is the pathway of the pain signal?

Anterolateral ((Neospinothalamic) Tract

A

comes in at dorsal horn -> crosses at the ant. white commissure -> goes to anterolateral tract -> enters brainstem -> ends at primary somatic sensory cortex

101
Q

Where does nociceptive information from BOTH the upper and lower body enter the CNS?

A

Dorsal root ganglion

102
Q

Where does nociceptive information from the body cross and travel to in the spinal cord?

A

IMMEDIATELY crosses at the anterior white commissure to the anterolateral portion of the spinal cord

103
Q

After entering the anterolateral portion of the spinal cord where does nociceptive info. from the body travel to?

A
  • Travels up the spinothalamic/neospinothalamic tract to the ventral posterior LATERAL nucleus (VPLN) of the thalamus
104
Q

After the VPLN, where do the nociceptive fibers from the body ascend to?

A

The primary (SI) and secondary (SII) somatosensory cortex to begin integrating somatosensory information

105
Q

What is the pathway of nociceptive info. from the face?

Trigeminal System

A

comes in from the pons -> drops to the medulla -> crosses at the ant. white commissure-> travels up the spinal thalamic tract -> ends at VPMN and primary somatic sensory cortex

106
Q

Where does nociceptive information from the face enter the CNS?

A

At the PONS

107
Q

Where does nociceptive information of the face travel down and cross into the spinal cord?

A
  • Down the medulla
  • Cross at the anterior white commissure
108
Q

After crossing the ant. white commissure of the spinal cord where does nociceptive info. from the face travel to?

A

Travel up the trigeminal-thalamic tract to the ventral posterior MEDIAL nucleus of the thalamus.

109
Q

After the VPMN, where do the nociceptive fibers from the face ascend to?

A

The primary (SI) and secondary (SII) somatosensory cortex to begin integrating somatosensory information

110
Q

Will an injury to the medulla lose sensation on one or both sides of the face?

A

both

111
Q

The nociceptive pathway goes through what entire system?

A

limbic

112
Q

What are the (6) different targets of the anterolateral system?

A
  • Anterior cingulate/insular cortex
  • Amygdala
  • Hypothalamus
  • Superior colliculus
  • Reticular formation
  • Periaqueductal Gray
113
Q

The periaqueductal grey is responsible for what response?

A

pain modulation (control)

114
Q

The superior colliculus is responsible for what response?

A

Directs our attention to the source of pain

115
Q

The reticular formation is responsible for what response?

A

Arousal (via release of ACh) in order to respond to pain

116
Q

What anterolateral system target is responsible for fight or flight?

A

Hypothalamus

117
Q

What anterolateral system target is responsible for negative emotion?

A

Amygdala

118
Q

What anterolateral system target is responsible for avoidance/emotional component that drives behavioral responses?

A

Anterior cingulate/insular cortex

119
Q

What is allodynia?

A

perception of normally non-nociceptive stimuli being painful

120
Q

Getting a tap on the site of a new shot is an example of what type of sensation a patient can undergo.

A

allodynia

121
Q

What is hyperalgesia?

A

nociceptive stimuli are perceived as being more painful than expected

122
Q

Getting pushed on the arm after getting a shot is an example of what type of sensation a patient can undergo.

A

hyperalgesia

123
Q

What is peripheral sensitization?

A

allodynia and/or hyperalgesia due to peripheral mechanisms

124
Q

What is central sensitization?

A

allodynia and/or hyperalgesia due to central mechanisms

125
Q

What occurs in peripheral sensitization?

A
  • Release of neuropeptides and NTs at the free nerve ending as a result of local damage (e.g. glutamate, substance P, histamine, etc)
  • Sensitization of the area around the site of injury
126
Q

What occurs in central sensitization?

A
  • Neurochemistry (sensitization of NMDA ( N-methyl-D-aspartate) receptors alters synaptic efficacy)
  • Anatomic reorganization in spinal cord (loss of primary afferent results in sprouting of existing afferents in dorsal horn)

NMDA-glutamate receptor

127
Q

Explain descending pain modulation

A
  1. Spinotectal fibers synapse in the periaqueductal grey (PAG) which projects to:
  • Raphe nucleus: serotonergic projections
  • Lateral Tegmental Nucleus: noradrenergic projections
  1. These projections synapse on
    enkephalinergic interneurons in the dorsal horn
128
Q

Explain pain control in the spinal column

A
  1. You have serotonin and norepir (input coming from raphe nuclei) coming down
  2. This activates and releases an enkephalin neuron which inhibits the C fiber (nociceptor) from synapsing onto the dorsal horn projection neuron to the anterolateral system
129
Q

Explain Phantom Limb

A
  • It is when you lose a peripheral body, but you feel like you still have that limb.
  • Trigger points are going to become those areas of skin that were processed proximally at the somatosensory cortex
130
Q
  1. Which of the following correctly identifies the mechanoreceptor responsible for sensing deep pressure/vibration and its respective adaptation type?
    A. Meissner corpuscle; Rapidly adapting
    B. Pacinian corpuscle; Slow adapting
    C. Meissner corpuscle; Slow adapting
    D. Pacinian corpuscle; Rapidly adapting
A

d.Pacinian corpuscle; Rapidly adapting

131
Q
  1. All of the following regarding the dorsal column/medial lemniscal system are true EXCEPT:
    A. Mechanosensory information from the lower body synapses at the gracile nucleus
    B. After entering the cerebrum, fibers synapse at the ventral posterior lateral nucleus
    C. Mechanosensory information decussates at the anterior white commissure
    D. Mechanosensory information from the upper body enters the CNS via a cervical dorsal root ganglia
A

C. Mechanosensory information decussates at the anterior white commissure

132
Q
  1. A 37-year-old man is rushed to the ED following a severe motorcycle accident which has altered somatosensory perception in his lower limbs. MRI indicates the patient has a lesion in the right portion of his spinal cord. What symptoms is the patient likely experiencing?
    A. Loss of both mechanoreceptive and nociceptive sensation in the right leg
    B. Loss of mechanoreceptive sensation on the right leg and nociceptive sensation on the left leg
    C. Loss of both mechanoreceptive and nociceptive sensation in the left leg
    D. Loss of mechanoreceptive sensation on the left leg and nociceptive sensation on the right leg
A

B. Loss of mechanoreceptive sensation on the right leg and nociceptive sensation on the left leg

133
Q
  1. The anterolateral system sends projections to varying portions of the CNS to elicit physiological responses after pain stimulation. Which of the following structures directs our attention to the source of pain?
    A. Superior colliculus
    B. Insular cortex
    C. Periaqueductal Gray
    D. Somatosensory cortex
A

A. Superior colliculus

134
Q
  1. The perception of normally non-nociceptive stimuli as being painful is often caused by a form of sensitization. Which of the following would lead to peripheral/local sensitization?
    A. Loss of primary afferents in the dorsal horn
    B. Sensitization of NMDA receptors on spinal interneurons
    C. Release of neuropeptides from C fibers
    D. Sensitization of NMDA receptors directly on the anterolateral tract
A

C. Release of neuropeptides from C fibers

Neuroscience Exam 2 (9 decks)

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