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Sensory Physiology Flashcards

1
Q

What are the two classifications of peripheral nerves?

A
  1. Their contribution to a compound AP (A, B and C waves) recorded from an entire mixed peripheral nerve
  2. Based on fiber diameter, myelin thickness and conduction velocity (classes I, II, III and IV)
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2
Q

How are the two classification systems for peripheral nerves related?

A

Conduction velocity determines a fiber’s contribution to the compound AP
The compound AP and conduction velocity of nerve fibers is often used as a diagnostic test in the evaluation of peripheral nerve disease (e.g. diabetic neuropathy)

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3
Q

What are the different types of sensory (afferent) fiber types?

A

A-alpha, beta and delta

C

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4
Q

What is the classification of sensory A-alpha fibers?

A

Ia and Ib

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5
Q

What is the diameter and conduction velocity of sensory A-alpha fibers?

A 
Large diameter 
Fast velocity (80-120)
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6
Q

What receptors are supplied by sensory A-alpha fibers?

A

Primary muscle spindles and golgi tendon organ

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7
Q

What is the classification of sensory A-beta fibers?

A

II

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8
Q

What receptors are supplied by sensory A-beta fibers?

A

Secondary muscle spindles, skin mechanoreceptors

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9
Q

What is the classification of sensory A-delta fibers?

A

III

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10
Q

What receptors are supplied by sensory A-delta fibers?

A

Skin mechanoreceptors, thermal receptors and nociceptors

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11
Q

What is the classification of sensory C fibers?

A

IV

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12
Q

What is the diameter and velocity of sensory C fibers?

A 
Small diameter 
Slow velocity (0.5-2)
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13
Q

What receptors are supplied by sensory C fibers?

A

Skin mechanoreceptors, thermal receptors and nociceptors

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14
Q

What are the types of motor (efferent) fiber types?

A

A-alpha and A-gamma

B and C

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15
Q

What receptors are supplied by motor A-alpha fibers?

A

Extrafusal skeletal muscle fibers

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16
Q

What receptors are supplied by motor A-gamma fibers?

A

Intrafusal muscle fibers

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17
Q

What receptors are supplied by motor B fibers?

A

Preganglionic autonomic fibers

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18
Q

What receptors do motor C fibers supply?

A

Postganglionic autonomic fibers

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19
Q

What do the cutaneous and deeper subcutaneous mechanoreceptors respond to?

A

External stimuli

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20
Q

What is receptor adaption?

A

When a stimulus persists unchanged for several minutes without a change in position or amplitude, the neural response diminishes and sensation is lost over time

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21
Q

What is a slowly adapting receptor?

A

Receptors that respond to prolonged and constant stimulation

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22
Q

What are rapidly adapting receptors?

A

Receptors that respond only at the beginning or end of a stimulus
Only active when the stimulus intensity increases or decreases

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23
Q

What are the 4 types of mechanoreceptors?

A

Meissner corpuscle, Pacinian corpuscle, merkel disc and ruffini ending

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24
Q

Describe a Meissner corpuscle

A

Low threshold
Rapidly adapting
Found in glaborous skin (hairless)
Within the dermis

25
What type of sensation activates Meissner corpuscles?
Touch and vibration less than 10Hz | Flutter and tapping
26
Describe Pacinian corpuscles
Low threshold Rapidly adapting Found in both hairy and glaborous skin Deepest receptor in the subcutaneous tissue (below dermis)
27
What type of sensation do Pacinian corpuscles respond to?
Rapid indentation of the skin such as that during high frequency vibration (100-400Hz) Vibration
28
Describe Ruffini corpuscles
Low threshold Slowly adapting Found in both hair and glaborous skin Deep in the dermis
29
What type of sensation cause activation of Ruffini corpuscles?
Magnitude and direction of stretch | Touch and pressure and proprioception
30
Describe Merkel cells
Low threshold Slowly adapting Found in glaborous skin Within the dermis
31
What activates a Merkel cell?
Pressure
32
Describe hair follicle receptors
Rapidly and slowly adapting
33
What sensation do hair follicle receptors respond to?
Motion across the skin and directionality of that motion
34
Describe tactile free nerve endings
High threshold | Slowly adapting
35
What sensation do tactile free nerve endings respond to?
Pain and temperature | Located superficially in the epidermis
36
What are receptive fields?
Areas of innervation where individual mechanoreceptor fibers convey information from a limited area of skin Vary in size
37
What is two point discrimination?
A way to test function of receptive fields and innervation fibers Allows for spatial resolution of detailed textures Test is used as a diagnostic tool of peripheral sensory deficiencies
38
Where is tactile acuity the highest?
In fingertips and lips (smallest receptive fields)
39
Where is tactile acuity the lowest?
On the calf, back and thigh (largest receptive field)
40
The sensory cortex includes what?
Primary, secondary and association areas
41
Describe the primary somatosensory cortex (S1)
``` Somatic sensory area I (SI) Located in post central gyrus Brodmann area 3, 1 and 2 First stop for most cutaneous senses Somatotopic representation ```
42
The primary somatosensory cortex (SI) is involved in what?
The integration of the information for position sense as well as size and shape discrimination
43
Describe the secondary somatosensory cortex (S2)
Aka somatic sensory area 2 (S2) Located in the wall of the Sylvian fissure Receives input from S1 Somatotopic representation (but less detailed) Cognitive touch
44
What is the secondary somatosensory cortex involved with?
Comparisons between objects, different tactile sensations and determining whether something becomes a memory
45
Describe the parieto-temporal-occipital association cortex (PTO)
High level interpretation of sensory inputs Receives input from multiple sensory areas Analyzes spatial coordinates of self in environment Names objects Many more function
46
What is phantom limb pain?
Phantom limb describes the pain in a body part that is no longer present which occurs in many amputees Most basic principle that explains this is the Law of Projection
47
What is the law of projection?
No matter where along the afferent pathway a stimulation is applied, the perceived sensation arises from the origin of the sensation
48
What is pain?
An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
49
What is nociception?
The neural process of encoding noxious stimuli (a stimulus that is damaging or threatens damage to normal tissues) Note: consequences of encoding may be autonomic (e.g. elevated BP) or behavior (motor withdrawal reflex or more complex nocifensive behavior) Pain sensation is not necessarily implied
50
What is hypersensitivity?
Increased responsiveness of nociceptive neurons to their normal input and/or recruitment of a response to normally subthreshold inputs
51
What is hyperaesthesia?
Increased sensitivity to stimulation excluding the special senses
52
What is hyperalgesia?
Increased pain from a stimulus that normally provokes pain
53
What is allodynia?
Pain due to a stimulus that does not normally provoke pain | Classical example is laying sheets on skin that has been sunburned
54
What is the biphasic response to pain?
Phase 1: initial response from A-delta fibers (quick sharp pain) Phase 2: a few moments later which is being transmitted by C fibers (sharp pain diminishes and becomes throbbing pain)
55
What sensation modality do A-delta fibers transmit?
Primarily mechanical pain
56
What type of sensation modality do C fibers transmit?
Polymodal: high intensity chemical and thermal pain (can be involved in mechanical pain)
57
What is the receptive field size for A-delta fibers?
Relatively small receptive fields
58
What is the receptive field size for C fibers?
Receptive fields relatively larger than A-delta

NE Exam 2 (19 decks)

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