Sensory Physiology Flashcards
How are peripheral nerves classified
By its contribution to an action potential (A, B, C waves) and by its physical characteristics (diameter, myelin thickness, conduction velocity).
How are conduction velocity and action potential related?
Conduction velocity determines a fibers contribution to the compound action potential
Meissner corpuscle receptor type and sensation
Glaborous skin
Low threshold, rapidly adapts.
Touch/vibration < 100 Hz.
Easily activated because of such a low threhold.
Pacinian corpuscle receptor type and sensation
Hairy and hairless skin
Low threshold, rapidly adapting
Rapid indentation of the skin
100-400 Hz
Ruffini corpuscle receptor type and sensation
Hairy and hairless skin
Low threshold, slowly adapting
Stretch magnitude and direction
Touch, pressure, proprioception
Merkel cell receptor type and sensation
Glaborous
Low threshold, slowly adapting
Pressure
Hair follicle receptor type and sensation
Rapidly and slowly adapting
Motion and directionality across skin
Tactile free-nerve ending type and sensation
High threshold, slowly adapting
Pain and temp
Compare the receptive fields in the fingertips vs. the back
Fingertips have a high density of small receptive fields, whereas the back has large receptive fields. Discriminative touch is easier to do then you have a high density, small receptor field.
How are convergence and receptive fields related?
Convergence can cause you to feel only 1 sensation in 2 receptive neurons. The number of neurons doesn’t necessarily predict the size of the receptive field.
What does the 2 point discrimination test look for?
Test is a diagnostic tool for peripheral sensory deficiencies.
What does the somatosensory area I do? Where is it? What happens to the somatotopic map?
Primary sensory cortex in the post-central gyrus. Cutaneous, crude touch. Integrates position, size, shape. The somatotopic representation is kept.
What does the somatosensory area II do? Where is it? What happens to the somatotopic map?
Compares between objects and different tactile sensations. Has a role in whether something becomes a memory, but does not do the emotional part of pain. Located in the wall of Sylvian fissure. Receives input from S1. Less maintained somatotopic map.
What does the parieto-temporal-occipital association area do?
High-level interpretation of sensory inputs. Analyzes spatial coordinates of self. Identifies objects.
What is the law of projection?
Important to amputees. Stimulation to the point in the cerebral cortex, or anywhere on the pathway, will project the sensation to the location of the receptor.
What is pain?
Sensory and emotional experience assctd. w/ actual or potential tissue damage. It is the FEELING of pain.
What is nociception?
The actual process of neurally encoding noxious stimuli.
Note: encoding consequences may be autonomic (HTN). The pain sensation is not always present.
What is hypersensitivity?
Increase in the responsiveness of neurons more related to pain and/or recruitment of a response to normally subthreshold inputs.
What is hyperaesthesia?
Increased sensitivity to stimulation, EXCEPT special senses. A heightening of any sense makes this different from hypersensitivity, which is more related to pain.
What is hyperalgesia?
abnormally increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves and can cause hypersensitivity to stimulus.
What is allodynia?
Pain due to a stimulus that doesn’t usually cause pain. Ex. laying sheets on sunburnt skin
Describe A delta fibers. Size, speed, what they carry, location of pain, and receptive field?
Size: 2-5 mm, myelinated Speed: 5-40 m/s, faster than C fibers Carry nociceptive mechanical or mechanothermal specific nociceptors Small receptive fields Precise localization of pain
Describe C fibers. Size, speed, what they carry, location of pain, and receptive field?
Size: 0.4-1.2 mm, unmyelinated
Speed: 0.5-2 m/s
Activated by high-intensity mechanical, chemical, and thermal stimulation and carry info from polymodal nociceptors
Larger receptive area, less precise pain localization
What is the biphasic response to pain?
The combination of sensations elicited initially by A delta then by C-fibers. It is why we feel a sharp, localized pain at first, then the pain becomes dull and less localized.
