Sensory Physiology Flashcards
What are the 2 ways peripheral nerves are classified?
1) Their contribution to a compound action potential (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)
What is the classification of A-alpha afferent fibers? What is the fiber diameter? What is the conduction velocity? What is the receptor supplied?
Classification: Ia and Ib
Diameter: 13-20 micro-meters (large)
Velocity: 80-120 m/s (fast)
Receptor: primary muscle spindles, golgi tendon organ
What is the classification of A-beta afferent fibers? What is the fiber diameter? What is the conduction velocity? What is the receptor supplied?
Classification: II
Diameter: 6-12 micro-meters
Velocity: 35-75 m/s
Receptor: secondary muscle spindles, skin mechanoreceptors
What is the classification of A-delta afferent fibers? What is the fiber diameter? What is the conduction velocity? What is the receptor supplied?
Classification: III
Diameter: 1-5 micro-meters
Velocity: 5-30 m/s
Receptor: skin mechanoreceptors, thermal receptors, and nociceptors
What is the classification of C afferent fibers? What is the fiber diameter? What is the conduction velocity? What is the receptor supplied?
Classification: IV
Diameter: .2-1.5 micro-meters (small)
Velocity: .5-2 m/s (slow)
Receptor: skin mechanoreceptors, thermal receptors, and nociceptors
What is the diameter of A-alpha efferent fibers? What is the conduction velocity? What is the receptor supplied?
Diameter: 12-20 micro-meters
Velocity: 72-120 m/s
Receptor: extrafusal skeletal muscle fibers
What is the diameter of A-gamma efferent fibers? What is the conduction velocity? What is the receptor supplied?
Diameter: 2-8 micro-meters
Velocity: 12-48 m/s
Receptor: intrafusal muscle fibers
What is the diameter of B efferent fibers? What is the conduction velocity? What is the receptor supplied?
Diameter: 1-3 micro-meters
Velocity: 6-18 m/s
Receptor: preganglionic autonomic fibers
What is the diameter of C efferent fibers? What is the conduction velocity? What is the receptor supplied?
Diameter: .2-2 micro-meters
Velocity: .5-2 m/s
Receptor: postganglionic autonomic fibers
Describe meissner’s corpuscles, including what sensation they are involved with
Low threshold, rapidly adapting; found in glaborous skin; touch and vibration less than 100 Hz; flutter and tapping
Describe pacinian corpuscles, including what sensation they are involved with
Low threshold, rapidly adapting; found in both hairy/glaborous skin; rapid indentation of the skin such as that during high-frequency vibration (100-400 Hz)
Describe ruffini corpuscles, including what sensation they are involved with
Low threshold, slowly adapting; found in both hairy/glaborous skin; magnitude and direction of stretch; touch and pressure and proprioception
Describe merkel cells, including what sensation they are involved with
Low-threshold, slowly adapting; found in glaborous skin; pressure
Describe hair follicle receptors, including what sensation they are involved with
Rapidly and slowly adapting; motion across the skin and directionality of that motion
Describe tactile free nerve endings, including what sensation they are involved with
High threshold and slowly adapting; pain and temperature
Where is tactile acuity highest?
Fingertips and lips; smallest receptive fields
Where is tactile acuity lowest?
Calf, back, and thigh; largest receptive fields
What is the function of somatosensory area I (S1)?
Involved in the integration of the information for position sense as well as size, shape discrimination; also called primary sensory cortex; somatotopic representation is maintained; crude identification of senses
What is the function of somatosensory area II (S2)?
Responsible for comparisons between objects, different tactile sensations and determining whether something becomes a memory; located in wall of Sylvian Fissure; receives input from S1; somatotopic representation is less maintained; important in cognitive touch
What is the function of the parieto-temporal-occipital association area (PTO)?
Responsible for high-level interpretation of sensory inputs; receives input from multiple sensory areas; analyzes spatial coordinates of self in environment; also functions in identification of objects
What is the Law of Projection?
States that regardless of the place along an afferent pathway that is stimulated, the sensation is perceived to come from the place that the innervation arises
Define pain
Unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
Define nociception
Neural process of encoding noxious stimuli (a stimulus that is damaging or threatens damage to normal tissues)
Define hypersensitivity
Increased responsiveness of nociceptive neurons to their normal input, and/or recruitment of a response to normally subthreshold inputs
Define hyperaesthesia
Increased sensitivity to stimulation, excluding the special senses
Define hyperalgesia
Increased pain from a stimulus that normally provokes pain
Define allodynia
Pain due to a stimulus that does not normally provoke pain; classic example is the lay of sheets on skin that has been sunburned
What is mechanical stimuli?
Response to mechanical forces ranging from a moderate pressure with a blunt object to overtly tissue-damaging stimuli
What is chemical stimuli?
Response to endogenous or exogenous chemical compounds, such as pro-inflammatory mediators, acids, or capsaicin, the pungent ingredient in chili peppers
What is thermal stimuli?
Response to noxious heat and cold will directly activate thermal receptors expressed by nociceptors
What makes up the major class of sensory detection and transducers in nociceptive neurons?
Transient receptor potential (TRP)
What is the TRPV1 receptor?
Ligand-gated nonselective cation channel; sensitive to vanilloid compounds, especially capsaicin
What is the TRPA1 receptor?
Sensitive to allyl isothiocyanate, the active ingredient in mustard oil, wasabi, and horseradish
What is the TRPM8 receptor?
Activated by both innocuous cooling and noxious cold temperatures, as well as a number of cooling agents
What is central sensitization?
Activity-dependent synaptic plasticity in the spinal cord that generates post-injury pain hypersensitivity together with the cellular and molecular mechanisms
What is peripheral sensitization?
Neuroplastic changes relating to the function, chemical profile, or structure of the peripheral nervous system that encompasses changes in receptor, ion-channel, and neurotransmitter expression levels
Describe peptidergic nociceptors
Expresses neuropeptides (substance P and CGRP), responsive to NGF; most visceral afferents are peptidergic; half of cutaneous afferents are peptidergic; chronic inflammation upregulates neuropeptides
Describe non-peptidergic nociceptors
Does not express CGRP or SP neuropeptides; responsive to GDNF; very few visceral afferents are non-peptidergic; half of cutaneous afferents are non-peptidergic; involved in somatic chronic pain states such as that of diabetic neuropathy
