Test 2 - Lecture 2 (Somatosensory System) Flashcards
the capability to localize a stimulus is limited to…
the area of individual receptive fields
the capability to distinguish between two separate stimuli is limited by…
the area of individual receptive fields
_________ is used to preserve identification of the location of peripheral sensory information
somatotopic mapping
peripheral somatosensory neurons are located in the
dorsal root ganglia
pseudo-unipolar
somatosensory system is ______
multimodal, consisting of various receptors and processing centers
A-alpha (peripheral fibers)
large diameter, heavy myelin sheath (fast conducting)
also considered “type 1”
A-beta (peripheral fibers)
medium diameter, myelinated
also considered “type 2”
C (peripheral fibers)
unmyelinated (slowest conducting )
the largest myelinated fibers convey
proprioceptive information
the A(alpha) and A(beta) fibers convey
mechanosensory information from the skin
the smaller A(gamma) and unmyelinated C fibers convey
thermal information and pain
population coding
increasing stimulus energy will activate an increasing number of receptors within a given receptive field
superficial mechanoreceptors
Merkel’s disk (slow adapting) and Meisner’s corpuscle (rapid adapting)
merkel discs
slowly adapting: responsive to continually applied pressure
meissner’s corpuscles
rapidly adapting: responsive to repetitive, low frequency stimuli (light touch)
deep mechanoreceptors
Pacinian (rapid adapting) and Ruffini corpuscles (slow adapting)
Ruffini corpuscles
slowly adapting: signaling sustained pressure
Pacinian corpuscles
rapidly adapting: signaling changes in pressure (vibrations)
slowly adapting mechanoreceptors
stimulus is sustained
maintains signaling throughout the duration that the stimulus is applied
rapidly adapting mechanoreceptors
stimulus “on” and stimulus “off”, generally variations in the stimulus intensity
(maintains signaling while the stimulus intensity is changing)
enable discrimination of the shape and size of objects pressing against the skin
slowly adapting mechanoreceptors
frequency decreases as the skin being pressed in increases
report changing stimulus energy that is caused by vibration or motion or texture
rapidly adapting mechanoreceptors
somatotopic mapping and transmission of sensory information from each receptive field via labeled lines contributes to discernment of
points of contact with the object being grasped, the size and shape of objects that we grasp
mixed population of receptor types allows discernment of
surface texture, movements of the object relative to the surface of the fingers and hand
parallel channels of sensory information provide input to
the sensory cortex, where information is combined to form our perception “of the whole”
each follicle is innervated by
a single nerve ending
deformation of a hair follicle
induces a generator potential
individual cutaneous thermoreceptors respond to either
heat or cold, but not to both (mostly cold)
heat receptors (warm to hot)
non myelinated C fibers
cold receptors (cool to cold)
myelinated A (gamma) fibers
low threshold cold receptors detect
rapid drops in temperature (below 88)
high threshold cold receptors/nociceptors detect
rapid drops in temperature in the lower range (32 and below)
the most sensitive to changes in temperature are
rapidly adapting to sustained temperature
peripheral thermoreceptors
transient receptor potential family of ion channels
pain is the perception of
noxious (tissue damaging) stimuli
polymodal nociceptors
responsive to a combination of mechanical/thermal/chemical modalities
nociceptors have a _________ which prevents their activation by non-noxious stimuli
high stimulus threshold
A(gamma) fibers arise from
mechanical and thermal nociceptors (sharp, short lasting, pain)
C fibers arise from
polymodal receptors (dull or diffuse pain)
first pain
A(gamma) fibers
second pain
C fibers
somatic pain reports
visceral discomfort and injury (referred pain)
relatively few centrally projecting fibers; large receptive field = poor dicrimination
somatic pain (viscera)
visceral afferent fibers synapse on
spinal relay neurons
viscera causing pain referring its pain to a location on surface
somatic site
transient receptor potential (TRP) channels
transduce noxious stimuli can sometimes become sensitized via molecular signaling pathways
(@ given stimulus intensity = result will be greater or lesser action potentials)
molecules released at a site of injury (bradykinin)
induce inflammatory sensitization by lowering the stimulus threshold for the nociceptive receptors
hyperalgesia
sensitization, leading to a perception that the stimulus is MORE painful
analgesia
desensitization, leading to a perception that the stimulus is LESS painful
primary nociceptors
peripheral sensitization or desensitization of the receptors to the noxious stimulus
secondary nociceptors
central sensitization or desensitization of synaptic transmission of peripheral afferent signals arising from nociceptors to the second order relay neurons
released chemicals that sensitize adjacent nociceptors
potassium, bradykinin, histamine, serotonin, leukotrienes, prostaglandins, cytokines, and substance P
released chemicals that directly activate nociceptors
hydrogen, serotonin, bradykinin, histamine
neuropeptides that sensitize or activate surrounding nociceptors
substance P and calcitonin gene-related peptide
neurogenic inflammation is caused by
substance P and calcitonin gene-related peptide (CGRP)
mechanical hyperalgesia
region of tissue outside of the flare (secondary sensitization)
inflammatory flare site
region within the immediate surrounding (primary sensitization)
an increased stimulus threshold of the peripheral nociceptors will produce
primary analgesia
restraints upon synaptic transmission at the second order relay neuron within the dorsal horn will produce
secondary analgesia
analgesia is
reduced sensitivity to a painful stimulus
allondynia
pain due to a stimulus that does not normally provoke pain
central pain
pain initiated or caused by a primary lesion or dysfunction within the CNS
neuralgia
pain in the distribution or a nerve or nerves
neurogenic pain
pain initiated or caused by a primary lesion, dysfunction, or transitory perturbation in the peripheral or CNS
