11. Sensory Physiology pre-reading and lecture questions Flashcards
1
Q
How are peripheral nerves classified?
A
- How much they contribute to an action potential
- The diameter, thickness of the myelin, and the conduction velocity
These two work together because the velocity helps to contribute to the AP
2
Q
How are the afferent nerves of A(alpha) peripheral nerves classified?
A
Ia and Ib
3
Q
How are the afferent nerves of A(Beta) peripheral nerves classified?
A
II
4
Q
How are the afferent nerves of A(delta) peripheral nerves classified?
A
III
5
Q
How are the afferent nerves of C peripheral nerves classified?
A
IV
6
Q
What is the fiber diameter and conduction velocity of the A(alpha) peripheral nerves? (sensory)
A
Diameter: 13-20
Conduction velocity: 80-20 (m/s)
7
Q
What is the fiber diameter and conduction velocity of the C peripheral nerves? (sensory)
A
Diameter: 0.2-1.5
Conduction velocity: 0.5-2 (m/s)
8
Q
What are the receptors supplied by the A(alpha) peripheral nerves? (sensory)
A
Primary muscle spindles, Golgi tendon organ
9
Q
What are the receptors supplied by the A(beta) peripheral nerves? (sensory)
A
Secondary muscle spindles, skin mechanoreceptors
10
Q
What are the receptors supplied by the A(delta) peripheral nerves? (sensory)
A
Skin mechanoreceptors, thermal receptors, and nociceptors
11
Q
What are the receptors supplied by the C peripheral nerves? (sensory)
A
Skin mechanoreceptors, thermal receptors, and nociceceptors
12
Q
Organize the peripheral nerve afferent fibers from largest to smallest (sensory)
A
A(alpha)
A(Beta)
A(delta)
C
13
Q
Organize the peripheral nerve afferent fibers from fastest to slowest (sensory)
A
A(alpha)
A(Beta)
A(delta)
C
14
Q
These motor (efferent) fibers are extrafusal skeletal muscle fibers
A
A(alpha)
15
Q
These motor (efferent) fibers are intrafusal muscle fibers
A
A(gamma)
16
Q
These motor (efferent) fibers are the preganglionic autonomic fibers
A
Beta (type 2)
17
Q
These motor (efferent) fibers are the postganglionic autonomic fibers
A
C
18
Q
These are low threshold and rapidly adapting receptors
A
Meissners and Pacinian
19
Q
Which receptor is involved with touch and vibration that is less than 100Hz including fluttering and tapping? (on non-hairy skin)
A
Meissner’s
20
Q
What sensation is involved with Pacinian corpuscles?
A
Rapid indentation of the skin such as high frequency vibration
21
Q
Which receptors are low thresholds and slowly adapting?
A
Ruffini corpuscle
Merkel cells
22
Q
Which receptors are both rapid and slowly adapting?
A
hair follicle receptors
23
Q
What are the high threshold slowly adapting receptors?
A
Tactile free nerve endings
24
Q
These receptors are involved with the magnitude and direction of stretch, touch, pressure, and propioception
A
Ruffini corpuscle
25
Which receptors are involved with pressure sensations?
Merkel cells
26
Which receptors are involved with motion across the skin and directionality of that motion?
Hair follicle receptors
27
What receptors are involved with pain and temperature?
Tactile free nerve endings
28
What size of receptor fields are found on the fingertips? Why?
Small receptor fields are found on the fingertips
They allow for a high acuity of sensation, so that you are able to feel a lot with your finger tips
29
Where is tactile acuity the highest? The lowest?
Tactile acuity is the highest in a small receptive field like in the fingers or the lips
Tactile acuity is the lowest in a large receptive field like the back or the back of the calf
30
What does the two point discrimination test?
Spatial resolution of detailed structures
Can test for peripheral sensory deficiencies
31
Describe somatosensory area 1
Involved in the integration of the information for position as a sense as well as size and shape discrimination
Primary sensory cortex in the post-central gyrus
32
What is the first stop for most of the cutaneous senses?
Somatosensory area 1: crude identification of senses
33
Describe somatosensory area 2
Responsible for comparisons between objects; differences in tactile sensations, and determining what becomes a memory
Located in the sylvan fissure and is an association area that receives input from S1
34
What is the PTO? What does she do?
Pariertotemporaloccipital association area
receives input from different areas and helps to identify what they are and how they relate to self and the environment
35
What does the law of projection state?
Regardless of the place in the afferent pathway, when it is stimulated, the sensation is perceived to come from where the innervation arises
Explanation in Tori terms:
If the afferents that are going from the thumb to the brain are hit any way along the path, then the brain will perceive this as coming from the thumb, even if she is not there; because the brain is so conditioned to the stimulus to that pathway being related to the thumb, so when she is activated, she still thinks that it is the thumb
36
Define allodynia (review the terms under LO6- I thought they were fairly intuitive but who knows)
Pain due to a stimulus that usually does not cause pain
37
Describe A(delta fibers)
1. How big are they?
2. What is their conduction velocity?
3. Where do they carry information from?
1. 2-5 mm in diameter, myelinated
2. FAST: 5-40 m/s
3. They carry information from the nociceptive-mechanical or mecahnothermal-specific nociceptors
38
Describe C fibers
1. How big are they?
2. What is their conduction velocity?
3. Where do they carry information from?
1. 0.4-1.2 mm in diameter, unmyelinated
2. SLOW 0.5-2.0 m/s
3. carry information from the polymodal nociceptors
***70% of all fibers carrying nociception
less precise for pain
39
Describe the biphasic response to pain. What are the phases and what fibers contribute to these phases?
1. The first phase is via the A(delta) fibers and this is involved with the initial sharp and localized pain following an injury
2. The second phase is via the C fibers and is a dull and throbbing pain that persists following the injury
40
If I shut my dick in the door, what is going to happen?
The A(delta) fibers are going to kick in for the initial localized response that is sharp (since they are the fast conduction fibers) and then the C fibers kick in slowly and persist as the dull and throbbing pain
41
These receptors are primarily involved in responding to noxious mechanical stimuli and transmit that information to the CNS
A(delta) fibers
42
These receptors are primarily involved in carrying chemical or thermal information
C fibers
C for chemical
43
What are some of the substances that are released by the nociceptive fibers?
```
Substance P
glutamate
aspartate
calcitonin gene related peptide (CGRP)
Vasoactive Intestinal peptide (VIP)
NO
```
44
Describe mechanical nociceptors
Respond to mechanical forces ranging from moderate pressure with a blunt object to overly tissue-damaging stimuli
45
Describe chemical nociceptors
Respond to endogenous or exogenous chemical impounds such as pro-inflammatory mediators, acids, or capsaicin
46
Describe thermal nociceptors
Response to noxious cold and heat will activate the thermal receptors
47
Describe the transient receptor potential family of receptors
major class of the sensory detection and transducers in the nociceptive neurons
48
Describe TRPV1
ligand gated nonselective cation channel; when this is activated, it can cause an action potential to occur
used a lot by C fibers
49
What happens when the TRPV1 is activated?
Action potential firing and neuropeptides are released like CGRP, substance P which leads to vasodilation and activation of immune cells and a pro-inflammatory release that results in a positive signaling feedback loop
50
Which one of the TRP receptors is involved with migraines, dental pain, cancer pain, and neuropathic pain, visceral pain, and osteoarthritis?
TRPV1
51
Which one of the TRP receptors is involved with allergic contact dermatitis, chronic itch, painful bladder syndrome, migraine, IBS, and pancreatitis?
TRPA1
52
What is TRPM8 receptors activated by?
Innocuous cooling and noxious temperatures
53
Describe the Gate control theory of pain
"Rubbing the spot that hurts makes it feel better"
1. Gate is closed when there is no input from the C fibers due to inhibitory interneurons and the gate is closed
2. The gate opens with strong C fiber activation and pain is sensed
3. A(beta) fiber can be activated with a normal stimuli and then is able to synapse with an inhibitory neuron which will reduce the sensation of pain
54
What is the function of the A(Beta) fibers in the theory of pain
They are able to be stimulated and synapse with the interneurons which are inhibitory to pain
So when they are activated, then the perception of pain is lessened due to the activation of the interneurons
55
Why does rubbing the skin reduce the sensation of pain?
Because the A(beta) fiber reduces the sensation of the pain
56
Describe descending inhibition
1. PAG are activated by opiates, EAA, and cannabinoids
2. Descending projections travel to the locus coeruleus and the ralph's nucleus
3. serotonin and NE are released into the dorsal horn and activate the inhibitory interneurons
4. local inhibitory interneurons release opiates
5. These opiates activate the mu receptors on the pre and post synaptic terminals of a C-fiber
6. reduced nociception from the C fiber
57
Descending seroteonergic and noradrenergic neurons activate _____ __________ and supresses ______ _______ neurons
Local interneurons
Spinothalamic
58
Describe central sensitization
Synaptic plasticity in the spinal cord that generates post injury pain hypersensitivity
this is due to a reduced threshold to noxious stimuli in the dorsal horn
59
Why can chronic exposure to peripheral information cause an increased hypersensitivity to pain
The neurons are constantly receiving input, and when this happens they start to get tired
60
What are some of the cellular and molecular mechanisms that are responsible for neuronal plasticity
Alterations in transcription and translation of the ion channels and changes of the synaptic input by the afferent fiber
the receptive field expands
persistent stimulation of EAA receptors, intracellular Ca2+ signaling, and activation of intracellular cascades
61
Describe peripheral centralization
Neuroplastic changes that are related to the function, chemical profile, or structure of the peripheral nervous system that encompasses changes in the receptor, ion channel, and neurotransmitter expression levels
basically the peripheral nervous system is changing
62
What are some of the mechanisms that affect the peripheral sensitization
1. neuroimmune activation can increase intensity and duration of pain
2. Prostaglandin E reduce the firing threshold and increases the responsiveness of the peripheral neuron
63
Why is prostaglandin E so important in the peripheral sensitization?
Sensitizes peripheral nociceptors via activation of the receptors that are present on the terminals of the nociceptors which reduces the firing threshold and increases the responsiveness of the system
64
Describe peptidergic neurons
They express neuropeptides
Respond to NGF (nerve growth factor)
Chronic inflammation up regulates neuropeptides
65
Most of the _____ afferents are peptidergic
and
half of the _______ afferents are peptidergic
Visceral
Cutaneous
66
What are the neuropeptides that are produced by peptidergic nociceptors
Substance P and CGRP
67
Describe non-peptidergic nociceptors
No CGRP or SP neuropeptides
Responsive to GDNF (glacial derived neurotrophic factor)
involved in somatic chronic pain states such as diabetic neuropathy
68
Describe visceral afferents in regards to peptidergic and non-peptidergic nociceptors
Most of the visceral afferents are peptidergic and very few visceral afferents are non-peptidergic
69
True or False
S1 and S2 play a role in the localization of pain because they receive input from the nociceptors
This is true statement
70
The _______ _______ processes information about the internal state of the body, contributes to the autonomic response to pain, and integrates the pain signals
Insular cortex
71
What does damage to the insular cortex cause? Describe this
Asymbolia: loss of the power to understand previously familiar symbols and is a consequence of a brain lesion
72
What does a lesion in the insular cortex cause in regards to pain?
Alters the experience of pain but does not abolish it completely
73
What area of the brain is important in the emotional component of pain?
Amygdala
74
How are physiological changes to pain able to happen?
The visceral input of pain travels through the hypothalamus and the medulla via the autonomic nerves
75
A 45-year-old male with a history of neuropathy presents to the neurology clinic for his regular 3-month evaluation. During the examination, a tuning fork is struck and placed on bony landmarks of the patient's upper limb. The patient describes the sensation as one of vibration. What type of receptor mediates the patient's ability to detect the tuning fork?
a. Meissner corpuscles
b. Ruffini endings
c. Nociceptors
d. Pacinian corpuscles
e. Proprioceptors
D. Pacinian
76
A 80-year-old female presents to the clinic complaining of tingling and numbness in her hands. The physician conducts a sensory exam to test for the integrity of sensory systems. The patient is asked to close her eyes, and the doctor then examines her arms and legs by touching them with the sharp end of a pin, asking the patient if the touch feels sharp or dull. She states that the touch feels sharp and painful. This sensation is carried by which of the following types of fibers?
a. Aα
b. Aβ
c. Aγ
d. Aδ
e. B
d. A(delta)
77
______ fibers carry sensory information from the Golgi tendon organs and Ruffini endings, conveying information about gross touch
A(Beta)
78
A 54-year-old male presents to the clinic with a 1-month history of intermittent numbness in his right hand when he wakes up in the morning. After a few minutes of shaking his right hand, the numbness over the palmar aspect of the right palm, thumb, and index and middle fingers resolves and he is left with intermittent paresthesia in the same region that lasts 2–5 minutes. There is no pain nor sensory symptoms in the arm. He has a 10-year history of type 2 diabetes mellitus and has noticed some intermittent paresthesia in his feet over the past few years that is not bothersome.
The sensorimotor examination of his upper extremity is normal. He has a positive Phalen sign at the right wrist. In the lower extremity, he has a symmetric reduction in light touch, two-point discrimination, pinprick, and temperature sensation from mid-calf to the toes (stocking distribution). He has a slightly reduced vibration threshold at the toes but normal proprioception. His tone and strength are normal. His reflexes are absent at both ankles. The rest of his neurological examination is normal.
Which of the following most likely explains the result of the two-point discrimination test on the foot?
a. Mechanoreceptors in his foot have been degraded.
b. The receptive fields for the foot mechanoreceptors are too small to detect two prongs.
c. Tactile acuity of the foot has been diminished.
d. Allodynia of the foot blunts otherwise normal sensation from mechanoreceptors.
e. Inhibitory interneurons in the spinal cord prevent conscious sensation of the two prongs.
c. tactile acuity of the foot has been diminished
79
The patient likely has carpal tunnel syndrome (CTS) due to compression of the median nerve in the carpal tunnel. Patients with diabetes are at higher risk of developing carpal tunnel syndrome. Shaking of the hand helps to relieve the compression of the median nerve in the carpal tunnel and is a classic feature of CTS.
After several months of conservative treatment, the patient’s pain in his wrist and hands have become constant and intolerable. Which of the following regions is responsible for the interpretation of his pain as uncomfortable?
a. Insular cortex
b. Hypothalamus
c. Somatosensory area II
d. Primary sensory cortex
e. PTO
a. insular cortex
80
In regards to sensory information, what is the primary sensory cortex in charge of?
Crude sense
81
In regards to the sensory information, what is the secondary sensory cortex in charge of?
Cognitive interpretation
82
What is the PTO in charge of in regards to sensory info?
high level of integration of senses
83
What are S1 and S2's role in the interpretation of pain?
crude localization
84
What is the insular cortex in charge of during a reaction to pain?
Interpretation of the pain
85
During the physical examination, the physician taps the skin overlying the area of the median nerve at the wrist. The patient states that the tap produces the sensation of painful tingling in the fingertips. This tap is not normally painful in someone who does not have carpal tunnel syndrome. Which term best describes the response experienced by the patient?
a. Hyperaesthesia
b. Law of Projection
c. Allodynia
d. Hyperalgesia
e. Peripheral sensitization
c. allodynia
86
A 56-year-old female presents to the emergency department after falling down the stairs at home. Examination reveals bruising on her hands, back, and feet, but is otherwise alert and oriented. There are long-term ulcers on the skin of her feet, and states that she has frequently been tripping a lot when she walks around her home. She has a 16-year history of poorly-controlled type 2 diabetes mellitus.
Although she could feel a hand placed on her feet, she was unable to tell which way her toes were moved if her eyes were closed. She was also unable to feel a vibrating tuning fork placed on her ankles but was able to feel the vibrations slightly when the tuning fork was placed on her knees. Her gait was a bit unsteady but improved when she looked down as she walked. While standing with her feet together and her eyes closed, she became very unsteady. Although there was a trace of knee-jerk reflexes bilaterally, the ankle-jerk reflexes were absent.
Which of the following fiber types is most greatly affected by her diabetic neuropathy?
a. Aα (sensory)
b. Aγ
c. Aδ
d. B
e. C
a. A(alpha)
peripheral neuropathy
87
A 73-year-old female noticed that the right side of her face had become extremely painful with a burning sensation that she describes like a bad sunburn. The hypersensitive area then developed a rash with blister-like nodules. She is diagnosed with herpes zoster (shingles). She is treated with antiviral therapy, but returns to the clinic stating that the pain has persisted despite the rash’s disappearance. When pain persists after the shingles outbreak has disappeared, it is called post-herpetic neuralgia for which there is no cure; however, treatments are available. The herpes virus attacks the nerve cell bodies in the ganglia of sensory neurons and is carried to the areas of skin supplied by the peripheral processes of those neurons. Which of the following is the most likely mechanism of ongoing pain in this patient?
a. Down-regulation of peripheral NMDA receptors.
b. Loss of Na+ channels in the postsynaptic membrane of the second-order neuron.
c. Altered synaptic circuitry in the posterior horn of the spinal cord resulting in central sensitization.
d. Up-regulation of opioid receptors on peripheral nerves in the face.
e. A change in the balance of inputs to the face favoring Aβ fibers over Aδ and C fibers.
c. altered synaptic circuitry in the posterior horn of the spinal cord resulting in central sensitization
Explanation:
Postherpetic neuralgia is an example of chronic neuropathic pain. It is most likely due to central sensitization, which includes a lowered pain threshold, disinhibition, and spontaneous activity of nociceptive neurons.
a. NMDA receptor activation plays a role in central sensitization and a down-regulation of NMDA receptor expression would result in less excitability.
b. During sensitization, more Na+ channels are inserted into the membrane of the postsynaptic neuron, which leads to heightened excitability.
c. Correct answer: Altered synaptic circuitry in the posterior horn of the spinal cord resulting in central sensitization.
d. Down-regulation rather than up-regulation of opioid receptors could play a role in increasing pain.
e. Increased pain is likely to involve a shift in the balance of inputs favoring Aδ and C fibers.
88
A 48-year-old male presents to the clinic with abdominal pain that has worsened over the past month such that he has difficulty sleeping and other activities of daily living. He has a history of undergoing laparoscopic abdominal wall surgery to repair an inguinal hernia 8-weeks previously. He states that the pain is localized around the surgical site. It is described as burning, throbbing, and intense, which he rates as a 7/10 at its worst and 3/10 at the best. He has tried over-the-counter pain medications (acetaminophen and ibuprofen) with no relief. Examination reveals a well-healed surgery site and no evidence of ongoing complications from the hernia. Which of the following mechanisms most likely explains his ongoing pain?
a. Synaptic targets of Aδ and C fibers are inhibited at the level of the spinal cord by dorsal horn interneurons.
b. Serotonergic suppression of second-order spinothalamic projection neurons by dorsal horn interneurons
c. Reduced threshold of dorsal horn neurons to noxious stimulation.
d. Persistent activation of TRPM8 receptors by surgical site heat conduction.
e. Prostaglandin E2 (PGE2) sensitization of peripheral nociceptors innervating the abdominal wall at the incision site.
f. Downregulation of neuropeptide signaling due to presence of chronic inflammation at the surgery site.
e. prostaglandin E
