Sensory Physiology Flashcards
What are the 2 ways you classify a peripheral nerve?
Based on their contribution to an action potential and
Based on their fiber diameter, myelin thickness and conduction velocity
What is the lettering for a peripheral nerves contribution to an action potential?
A, B, C waves
What is the classification for a peripheral nerves fiber diameter, myelin thickness and conduction velocity?
Classes I, II, III, and IV
How are the peripheral classification systems related?
The fiber’s conduction velocity directly determines the fibers contribution to an action potential
What are the afferent peripheral nerve classifications?
A alpha
A beta
A delta
C
What are the respective classes of the afferent peripheral nerves?
A alpha = Class 1A and 1B
A beta = Class II
A delta = Class III
C = Class IV
Describe the fiber diameter and conduction velocity for A alpha - Classes IA and IB fibers
Large fiber diameter and fast conduction velocity (80-120m/s)
Describe the fiber diameter and conduction velocity for C - Class IV fibers
Small fiber diameter and a slow conduction velocity (0.5-2m/s)
What are the motor efferent peripheral nerve classes?
A alpha, A gamma, B and C
What is receptor adaptation?
When a stimulus persists at a constant intensity and the neural response diminishes causing sensation to be lost over time
What is a slowly adapting receptor?
Receptors that respond to constant and prolonged stimulation
What is a rapidly adapting receptor?
Receptors that only respond when a stimulus begins or ends or when the stimulus intensity increases or decreases
What are the mechanoreceptor types that are involved in responding to touch, vibration, pressure and pain?
Meissner corpuscle, Pacinian corpuscle, Merkel Disk, Ruffini ending, hair follicle receptor and tactile free nerve ending
What are the rapidly adapting mechanoreceptors?
Pacinian corpuscle (very)
Meissner corpuscle
Hair follicle receptor
What are the slowly adapting mechanoreceptors?
Merkel disc
Ruffini ending
Tactile free nerve ending
An area of skin innervation supplied by a single mechanoreceptor
Receptive field
What is the 2 point discrimination test?
Applying 2 stimuli to the skin at the same time and testing a person’s ability to differentiate between just one or 2 stimuli as the stimuli are moved closer and closer together
What can the 2 point discrimination diagnose?
Peripheral sensory nerve deficiencies
Where is tactile acuity the highest and what size of a receptive field does it have?
Fingertips and lips - small receptive field
Where is tactile acuity the lowest and what size of a receptive field does it have?
Calf, back, thigh - large receptive field
Hypoaesthesia
Abnormal sensory response - diminished; detected with the 2 point discrimination test
Where is the primary somatosensory cortex?
Post central gyrus
Where is the secondary somatosensory cortex?
In the sylvian fissure
What are the inputs to the secondary somatosensory cortex?
From S1
Which somatosensory cortex has cognitive touch? (Ability to think about what you are touching)
S2
Where is the highest level of sensory interpretation occuring?
Parieto-Temporal-occipital association cortex (PTO)
- Receives sensory inputs from multiple areas
What is phantom limb pain?
Pain in a body part that is no longer there like in amputees
What is the mechanism behind phantom limb pain?
Law of projection
Describe the law of projection
No matter where along an afferent pathway that a stimulation is applied, the perceived sensation is still the origin
ex. Pathway is still somehow stimulated from absent leg to brain, and the brain perceives that the leg hurts though it is not there
What are the 2 components of pain?
Unpleasant sensory AND emotional experience
What is nociception?
The neural process of encoding noxious stimuli
Increased pain from a stimulus that normally DOES produce pain
Hyperalgesia/Hypersensitivity
Increased sensitivity to stimulation
Hyperaesthesia
Pain due to a stimulus that does NOT normally produce pain - i.e. laying sheets on sunburned skin
Allodynia
What are the afferent fibers that respond to pain evolving from sharp to dull/throbbing?
Sharp and quick = A delta
Slow to respond and dull/throbbing = C
Phase 1 of pain involved A delta and Phase 2 involved C fibers, which one is myelinated?
A delta fibers - fast conduction
What are nociceptors?
Receptors with an increased threshold that can transduce noxious stimuli
What are the modalities of nociceptors?
Mechanical, chemical and thermal
Are the modalities of nociceptors the same everywhere?
Nope, only the skin has thermal nociceptors; mechanical and chemical are found everywhere else such as the muscle, viscera and joints
Where is referred pain likely coming from?
Viscera
What are the reasons for referred pain?
The brain requires experience and training to know where the pain is coming from; viscera does not get that early enough
The afferents converge in the dorsal horn and mix
What type of receptors sense noxious stimuli?
TRP
What are the 3 TRP receptors?
TRP V1, TRP A1, TRP M8
This TRP receptor is sensitive to capsaicin, bradykinin and heat greater than 43 degrees celsius
TRP V1
This TRP receptor is sensitive to allyl isothiocyanate found in mustard oil and wasabi
TRP A1
This TRP receptor is sensitive to menthol and noxious cold temps
TRP M8
What TRP receptors does C fibers have?
TRP V1
2 types of free nerve endings on c fibers or A delta fibers?
Peptidergic (C) or non-peptidergic (Adelta)
- peptidergice express neuropeptides such as substance P/CGRP and are found in viscera
- Non-peptidergic do not express them and are mostly cutaneous
What are 2 ways nociceptors are modulated?
Gate Control Theory and Descending inhibition
What is the main components of the gate control theory?
Rubbing the injured area to activate a A beta fiber that will slightly activate the inhibitory neuron to inhibit the C fiber from sending pain
With descending inhibition, what NT’s inhibit C fibers from nociceptors?
NE and Serotonin (5HT)
Reduces threshold of involved neurons to noxious stimuli and involves synaptic plasticity
Central sensitization
This area in the brain interprets nociception and integrates all signals related to pain
Insular cortex
Damage to the insular cortex can result in?
Asymbolia
What is asymbolia?
Pain is experienced withOUT the unpleasantness emotional experience
What area of the brain is an emotional component of the brain?
Amygdala
Do lesions in any area associated with pain in the brain abolish it?
Nope, just alter experience of pain
What do Meissner’s corpuscles sense?
Flutter, tapping, touch
What do merkel’s discs sense?
Pressure
What do pacinian corpuscles sense?
Vibration
What do hair follicle receptors sense?
Direction of motion on skin
What do ruffini corpuscles sense?
Stretch
What do free tactile nerve endings sense?
Pain, temperature
What receptors are only found in glaborous (non-hairy) skin?
M! = Meissner’s corpuscle and Merkel discs
What receptors are found in both glaborous and hairy skin?
Pacinian, ruffini corpuscle
