Lecture 2. Cutaneous Sensation: Touch and Pain Flashcards
(134 cards)
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
2
Q
How are cutaneous sensory fibers similar to other sensory fibers?
A
- Some are encapsulated with specialized endings
- Some are free nerve ending
3
Q
List the (3) types of receptors of the Somatosensory System
A
- Mechanoreceptors
- Chemoreceptors
- Nociceptors
4
Q
Most receptors of the somatosensory system are what kind of receptors?
A
mechanoreceptors
5
Q
Chemoreceptors respond to what?
A
acidic substances
6
Q
Nociceptors respond to what?
A
potential damaging stimuli
7
Q
List the different mechanoreceptors (5) in the skin
A
- Merkel cell (disks)
- Meissner corpuscle
- Ruffini corpuscle
- Pacinian corpuscle
- Free nerve ending
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
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
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
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
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
13
Q
Mechanoreceptors are mostly what type of fiber?
A
Aβ
RA (nerve ending) is the only one that is not β
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
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
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
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
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
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
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
21
Q
Define an Adequate Stimulus
A
A stimulus to which a receptor is most sensitive
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
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
24
Q
Greater two-point discrimination means what type of index?
A
smaller discrimination index
25
Lesser two-point discrimination means what type of index?
higher discrimination index
26
Where on the body would have a higher discrimination index/lesser two-point discrimination?
arms, legs, torso, back
27
Where on the body would have a smaller discrimination index/greater two-point discrimination?
face, lips, nose, fingers
28
How do mechanoreceptors produce a generator (action) potential?
Through voltage-or ligand ion channels
29
What is the mechanism that causes voltage-or ligand-gated ion channels to open in mechanoreceptors?
Physical stimuli/skin deformation (stretch) open the receptors in order to transduce signals
30
List the (4) features receptors code for
1. Spatial location
2. Modality
3. Stimulus duration
4. Intensity
31
Explain Rapid adapting receptors
Respond to changes in stimuli on the skin
## Footnote
Example: picking something up and putting something down
32
Explain slow-adapting receptors
Respond over the course of the stimulus
## Footnote
Example: Getting dressed in the morning and slowly losing sensation of each item as the day progresses
33
Which adapting receptor keeps firing as long as you're holding something?
slowly adapting
34
Which adapting receptor only responds to a change in the stimulus?
rapidly adapting
35
Which mechanoreceptors are rapidly adapting? And what are their receptor fields?
* **Pacinian corpuscles** (receptive field: large, vague borders)
* **Meissner's corpuscle** (receptive field: small, sharp borders)
36
Which mechanoreceptors are slowly adapting? And what are their receptive fields?
* **Merkel's discs** (receptive field: small, sharp borders)
* **Ruffini's corpuscle** (receptive field: large, vague borders)
37
What is the function of both rapidly and slowly adapting receptors?
Perception of texture and pattern
38
What perception of texture and pattern is signaled by:
* Slowly adapting receptors
* Rapidly adapting receptors
* Slowly Adapting: Place and Duration
* Rapidly Adapting: Changes in form
39
What does the inactivation of any of the four mechanoreceptors cause?
Inability to interpret shape
40
What type of fibers are contained in the dorsal root?
afferent fibers
41
Where does somatosensory information enter the CNS?
The dorsal root ganglia into the dorsal root
42
Which type of fibers bifurcate (divide) at the **dorsal root** entry zone?
Large myelinated fibers
43
After sensory information enters the spinal cord where do the branches separate too?
* One branch ascends in the **posterior (dorsal) columns**
* The other branch synapses in deeper laminae of the spinal cord
44
Which type of sensory information travels up the posterior/dorsal column?
Touch, pressure, and vibration (mechanosensory) information
45
Which type of sensory information travels up the lateral column?
Pain and temperature information
46
What location does **lower** body sensation enter in the posterior/dorsal column?
Most **medial** portion
47
What location does **upper** body sensation enter in the posterior/dorsal column?
Most **lateral** portion
48
Injury to where can lead to loss of mechanosensation in specific regions of the body?
## Footnote
HIGH yield
Either the **medial or lateral portion** of the **posterior/dorsal column**
49
Which type of fibers synapses in the **dorsal horn** of the spinal cord?
Small, unmyelinated fibers
50
Explain the Medial Lemniscal Sytem. Locations? Beginning destination and final destination?
* 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
51
What is the name of the tract that receives information from the lower body?
Gracile tract
52
What is the name of the tract that receives information from the upper body?
Cuneate tract
53
Explain the mechanosensory pathway from the lower body to the caudal medulla (base of the brainstem)
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**
54
Explain the mechanosensory pathway from the upper body to the caudal medulla (base of the brainstem)
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
After entering the caudal medulla (base of the brainstem) what is the next location for the information fibers and what occurs there?
* Location: **Internal arcuate fibers**
* Where **BOTH will cross** and continue traveling on the **opposite side**
56
What is the term to describe the crossing at the internal arcuate fibers?
## Footnote
Medial Lemniscal System
Descussation
57
What occurs when there is a **spinal cord** injury on the LEFT side and why?
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
What occurs where there is a **brain stem injury** on the LEFT side and why?
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
Explain Somatotopy
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
What part of our body corresponds to the lateral region of the posterior column of the spinal cord?
Upper body
61
What part of our body corresponds to the medial region of the posterior column of the spinal cord?
Lower body
62
After the internal arcuate fibers decussate (cross over), what do they form?
Medial lemniscus tract
63
Where do the fibers travel after the medial lemniscus tract?
To the Ventral posterior **LATERAL** nucleus of the thalamus (VPLN)
64
After the VPLN where do the fibers ascend to?
## Footnote
VPLN- Ventral posterior lateral nucleus
The primary (SI) and secondary (SII) somatosensory cortex
65
What occurs at the primary and secondary somatosensory cortex?
Where integrating somatosensory information begins
66
Where is the somatosensory cortex located?
In the Parietal lobe
67
What is the pathway for the trigemino-thalmic-cortical (face recognition)?
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
Mechanosensory information from the FACE enters the brainstem via where?
Trigeminal ganglion
69
Where do the fibers from the trigeminal ganglion synapse?
The principal trigeminal nucleus of the caudal medulla
70
Where do fibers cross and travel in the trigeminal-thalamic-cortical pathway (face sensation)?
* Cross at the Trigeminal leminscus
* Travel to the Ventral posterior **MEDIAL** nucleus of the thalamus (VPMN)
71
After the VPMN where do the fibers ascend to?
| trigemino-thalamic-cortical pathway
## Footnote
VPMN-Ventral posterior medial nucleus
The primary (SI) and secondary (SII) somatosensory cortex
72
For the Body, fill in the blank:
Ventral Posterior _________ Nucleus
Lateral
## Footnote
(L)ateral= (L)otion for Body
73
For the Face, fill in the blank:
Ventral Posterior _________ Nucleus
Medial
## Footnote
(M)edial= (M)akeup for Face
74
What is a dermatome?
slice of skin that one spinal/brainstem cranial nerve root carries info from
75
When do dermatomes develop?
At the embryological level
76
What are the characteristics of the somatosensory cortex?
* has plasticity
* has discrimination (touch, pain, proprioception)
77
What determines how big nuclei are in the ventral posterior complex?
Density of information
78
What part of the body uses up the largest area of the ventral posterior complex and the somatosensory cortex? and why?
* Face (VPM; medial)
* D/t a large density of information coming from a large number of neurons with small receptive fields
79
What is homunculus?
representation of how much brain processing area there is for each body part
80
What thermoreceptors are free nerve ending?
both warm and cold
81
What are the fiber types of thermoreceptors?
* Warm: C
* Cold: A𝜎 (acute pain)
82
Which nociceptors are free nerve ending?
* Small, unmyelinated
* Unmyelinated
83
What are the fiber types for the nociceptors?
* Small, myelinated: A𝜎 (acute pain)
* unmyleinated: C (warm/dull pain)
84
What are the roles of perception of the nociceptors?
* Small, myelinated: sharp, localized pain
* Unmyelinated: burning
85
What is an example of acute pain?
an initial sting from a bee
86
What is an example of dull/throbbing pain?
long-lasting pain after a bee sting
87
Are all A𝜎 and C fibers nociceptors?
NO
88
What molecules are associated with A𝜎 fibers?
| A𝜎 fibers → Acute pain
## Footnote
Low yield
Excitatory amino acids (glutamate, aspartate, ATP)
89
What molecules are associated with C fibers?
| C fibers → dull pain
## Footnote
Low yield
* Substance P
* Neurokinins A&B
* Cholycstokinin
* Calcitonin Gene Related Peptide (CGRP)
* Vasointestinal Peptide (VIP)
90
True or False. We have pain receptors in our body
FALSE
| Rather nociceptors respond to very intense and possibly harmful stimuli
91
What is an example of how temp and pain can be carried by the same fibers?
capsaicin-molecule in chili pepper that gives them their spice
92
What does capsaicin do?
binds to VR-1 (vanilloid) receptor to allow Ca2+ and Na to start signaling
## Footnote
VR-1 is synonymous to TRPV1
93
What is the main difference between discriminative touch and pain response?
Discriminative touch signaling stays on the same side until it reaches the brain stem, while pain response information **crosses right away**
94
Explain how nociceptive information enters the CNS
Enter the spinal cord via the dorsal horn and cross to the lateral side immediately via the **anterior white commissure**
95
A patient with a LEFT spinal cord lesion will lose:
* Discriminative touch on what side?
* Temperature and pain sensation on what side?
* Loss of discriminative touch on the LEFT side
* Loss of temperature and pain sensation on the RIGHT side
96
What is the anterior commissure in the spinal cord?
a small bundle of fibers connecting 2 hemispheres in the brain
97
What occurs at the anterior white commissure in the spinal cord?
where nociceptive information is processed
98
What is Lissauer's tract?
2-3 segments above and below the dorsal root entry zone (DREZ) that add redundancy
## Footnote
Redundancy-allows a set of neurons to perform multiple tasks at once
99
What is the benefit of Lissauer's tract from an evolution standpoint?
Helps us maintain nociceptive perception in case of injury
100
What is the pathway of the pain signal?
| Anterolateral ((Neospinothalamic) Tract
comes in at dorsal horn -> crosses at the ant. white commissure -> goes to anterolateral tract -> enters brainstem -> ends at primary somatic sensory cortex
101
Where does nociceptive information from BOTH the upper and lower body enter the CNS?
Dorsal root ganglion
102
Where does nociceptive information from the body cross and travel to in the spinal cord?
IMMEDIATELY crosses at the **anterior white commissure** to the **anterolateral portion of the spinal cord**
103
After entering the anterolateral portion of the spinal cord where does nociceptive info. from the body travel to?
* Travels up the **spinothalamic/neospinothalamic** tract to the **ventral posterior LATERAL nucleus (VPLN)** of the thalamus
104
After the VPLN, where do the nociceptive fibers from the body ascend to?
The primary (SI) and secondary (SII) **somatosensory cortex** to begin integrating somatosensory information
105
What is the pathway of nociceptive info. from the face?
| Trigeminal System
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
Where does nociceptive information from the face enter the CNS?
At the PONS
107
Where does nociceptive information of the face travel down and cross into the spinal cord?
* Down the **medulla**
* Cross at the **anterior white commissure**
108
After crossing the ant. white commissure of the spinal cord where does nociceptive info. from the face travel to?
Travel up the **trigeminal-thalamic tract** to the **ventral posterior MEDIAL nucleus** of the thalamus.
109
After the VPMN, where do the nociceptive fibers from the face ascend to?
The primary (SI) and secondary (SII) **somatosensory cortex** to begin integrating somatosensory information
110
Will an injury to the medulla lose sensation on one or both sides of the face?
both
111
The nociceptive pathway goes through what entire system?
limbic
112
What are the (6) different targets of the anterolateral system?
* Anterior cingulate/insular cortex
* Amygdala
* Hypothalamus
* Superior colliculus
* Reticular formation
* Periaqueductal Gray
113
The periaqueductal grey is responsible for what response?
pain modulation (control)
114
The superior colliculus is responsible for what response?
Directs our attention to the source of pain
115
The reticular formation is responsible for what response?
Arousal (via release of ACh) in order to respond to pain
116
What anterolateral system target is responsible for fight or flight?
Hypothalamus
117
What anterolateral system target is responsible for negative emotion?
Amygdala
118
What anterolateral system target is responsible for avoidance/emotional component that drives behavioral responses?
Anterior cingulate/insular cortex
119
What is allodynia?
perception of normally non-nociceptive stimuli being painful
120
Getting a tap on the site of a new shot is an example of what type of sensation a patient can undergo.
allodynia
121
What is hyperalgesia?
nociceptive stimuli are perceived as being more painful than expected
122
Getting pushed on the arm after getting a shot is an example of what type of sensation a patient can undergo.
hyperalgesia
123
What is peripheral sensitization?
allodynia and/or hyperalgesia due to peripheral mechanisms
124
What is central sensitization?
allodynia and/or hyperalgesia due to central mechanisms
125
What occurs in peripheral sensitization?
* 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
What occurs in central sensitization?
* **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)
## Footnote
NMDA-glutamate receptor
127
Explain descending pain modulation
1. Spinotectal fibers synapse in the **periaqueductal grey (PAG)** which projects to:
* **Raphe nucleus**: serotonergic projections
* **Lateral Tegmental Nucleus**: noradrenergic projections
2. These projections synapse on
**enkephalinergic interneurons** in the dorsal horn
128
Explain pain control in the spinal column
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
Explain Phantom Limb
* 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
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
d.Pacinian corpuscle; Rapidly adapting
131
2. 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
C. Mechanosensory information decussates at the anterior white commissure
132
3. 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
B. Loss of mechanoreceptive sensation on the right leg and nociceptive sensation on the left leg
133
4. 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. Superior colliculus
134
5. 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
C. Release of neuropeptides from C fibers
