sensory receptors and pain science Flashcards
first order neuron
brings information from sensory receptors to the spinal cord or brainstem
second order neuron
conveys information between the spinal cord or brainstem to the thalamus
third order neuron
conveys information from the thalamus to the cerebral cortex
cutaneous
sensory information from the skin
pain (nociception)
the perception of tissue damage or potential tissue damage. The brain usually interprets stimuli that activate nocicepetors as painful
what is mechanoreception/tactile?
touch
what is nociception?
pain
what is thermoreception?
temperature
what type of sensory information does the musculoskeletal system include?
nociception
proprioception
what is proprioception?
where your body or body parts are in space, WITHOUT the need for vision
what information is the body’s proprioception based on?
stretch of muscles and skin, tension on tendons, and positions of joints and deep vibration
what sensory information about movement does proprioception include?
static joint position and kinesthetic sense
what are the four components of sensory system?
- stimulus
- receptor
- conduction
- translation
what is a stimulus?
when applied to receptor, it triggers graded membrane potential in receptor
what is a receptor?
converts stimulus energy into action potential
what is a conduction?
conduction of impulse over sensory pathway to CNS
what is translation?
CNS receives impulse, integrates info, and may prepare response
in one take, how would you describe the four steps of a sensory system?
when a stimulus is applied to a receptor, it triggers graded membrane potential in the receptor. The receptor then converts the stimulus energy into an action potential. The impulse is then conducted over the sensory pathway to CNS. The CNS receives the impulse, integrates info, and may prepare a response
what are three types of stimulus?
mechanical, chemical, and thermal
what are sensory receptors?
specialized sensory cells or nerve endings that detect sensory stimuli
mechanoreceptors
respond to mechanical deformation of the receptor by touch, pressure, stretch, or vibration
chemoreceptors
respond to exogenous chemicals or substances released by cells, including damaged cells following injury or infection
thermoreceptors
respond to temperature
proprioceptors
position and kinesthetic sense found in muscles, tendons, and ligaments
photoreceptors
vision
what are the two jobs of nociceptors?
- they are sensitive to stimuli that either damage or have potential to damage tissues
- provides input to the brain to allow rapid automatic movements to minimize injury prior to awareness occurring
what type of receptor are most somatosensory receptors?
mechanoreceptors
what are the four types of cutaneous mechanoreceptors?
Meissner’s corpuscles
Merkel’s disks
Pacinian corpuscles
Ruffini’s Endings
Function, Receptive Field, and Adaptation Speed: Meissner’s corpuscles
function:
light touch
vibration
texture
receptive field: small
adaptation: rapid
Function, Receptive Field, and Adaptation Speed: Merkel’s disks
function:
light touch
texture
pressure
receptive field: small
adaptation speed: slow
Function, Receptive Field, and Adaptation Speed: Pacinian corpuscles
function: deep pressure, touch, and vibration
receptive field: large
adaptation speed: rapid
Function, Receptive Field, and Adaptation Speed: Ruffini’s ending
function: stretch, deformation within joints, heat
receptive field: large
adaptation speed: slow
Function of free nerve endings
course touch (pleasant touch/pressure, tickle, itch)
pain
temperature
Based on morphology, receptors can be divided into three groups…
simple receptors
complex neural receptors
specialized receptors/ens
what are simple receptors?
free nerve endings (unmyelinated terminal branches)
what are complex neural receptors?
encapsulated types (nerve endings enclosed in connective tissue capsules)
what are specialized receptors/end-organs?
release NTs onto sensory neurons, initiating an AP
where are general receptors? and what are they responsible for?
widely distributed throughout the body
responsible for detecting a broad range of stimuli
what is the structure for general receptors?
free nerve endings or simple encapsulated structures
what are the four types of somatic general receptors?
tactile, thermal, pain, proprioceptive
what are visceral general receptors?
conditions within internal organs
where are specialized receptors?
located in specific areas of the body to detect specific types of stimuli
what precise sensory functions do specialized receptors allow us to perform?
smell, taste, vision, hearing
balance and equilibrium
what do exteroreceptors do?
detect/react to external stimuli, or stimuli from the external environment
what do interoreceptors do?
detect/react to internal stimuli from within the body
what are examples of stimuli that interoreceptors detect?
blood pressure, pH, oxygen concentration, internal temperatures
where are exteroreceptors located?
at or near the body surface (superficial, cutaneous)
where are interoreceptors located?
deep (internal organs, blood vessels, muscles, joints)
what are tonic receptors? and what do they detect?
respond continuously as long as a stimulus is present
detect object pressure and form (static)
what are phasic receptors? and what do they detect?
adapt to continuous stimulus and then stop responding, even while stimulus is present
detect motion, vibration, rate of change
are tonic receptors slow or fast adapting?
slow adapting
are phasic receptors slow or fast adapting?
fast/rapid adapting
what are primary afferent axons?
axons that bring info from somatic sensory receptors to spinal cord or brain stem
where do primary afferent axons enter the spiral cord?
the dorsal roots
what is an axon diameter determinant of?
conduction velocity
larger diameter axons transmit information _____ than smaller sensory axons/afferents
faster
what are the four types of sensory axons?
A-alpha, A-beta, A-delta, C fibers
list the sensory axons from largest to smallest
A-beta, A-delta, and C fibers
what type is the fastest sensory axon?
A-beta
what do A-beta axons do?
conduct touch sensations (touch, vibration, pressure) via cutaneous mechanoreceptors
what type are the slowest sensory axons?
C fibers
what makes C fibers the slowest sensory axons?
they are the smallest in diameter and unmyelinated
what are examples of what C fibers do in the body?
mediate temperature, throbbing pain, itch
why is conduction faster in large diameter axons?
resistance to current flow is lower in large diameter axons
large-diameter axons are myelinated, allowing saltatory conduction of the action potential
what body part has the highest 2-point discrimination?
fingertips
why do fingertips have the highest 2 point discrimination?
- much higher density of mechanoreceptors
- fingertips have a lot of Merkel’s disks, which have small receptive fields
- more brain tissue is devoted to each square mm of the fingertip
- special neural mechanisms devoted to high resolution discriminations located in the fingertips
what are four attributes to conduction?
modality
location
intensity
duration
what is modality?
receptors specialized for specific types of stimulation
what is location?
receptor’s receptive field and precise area
tracts/pathways between receptors and CNS
what is intensity?
amplitude, number of sensory receptors activated, and frequency of receptor potentials and activation
what is duration?
time course of receptor potential, number of sensory receptors activated
signal processing for integration occurs at what three levels in the somatosensory system?
receptor level
circuit level
perceptual level
the speed of information processing is determined by what three factors?
axon diameter
amount of axon myelination
number of synapses in pathway (fewer synapses, faster transmission)
at the receptor level, what is a receptor potential?
graded membrane potential in receptors
what is divergence in the circuit level processing?
synapses can spread action potentials to several areas of CNS
what is convergence in the circuit level processing?
synapses can focus action potentials from several sensory neurons onto narrowed area of CNS (precise)
what is the highest level of sensory processing?
perceptual level processing
what happens at the perceptual level of processing?
where the brain processes, integrates and interprets sensory information
what does the somatosensory cortex process in the perceptual level?
intensity, location, duration and modality of stimuli to create a conscious perception
what is the topographical organization the primary somatosensory cortex is organized in is referred to as what?
homunculus
what does the homunculus do?
maps out how sensory information from different body parts is represented in the brain
what does a nerve conduction velocity testing composed of?
electrical stimulation to peripheral nerve, comparing results to normal
what does a somatosensory evoked potentials test do?
test peripheral and central pathways1
what is the order of impact for types of axons with nerve compression?
large myelinated axons first and smaller nociceptive thermal and autonomic axons last
what is the order of sensory loss?
conscious proprioception and light touch
cold
fast sharp, stinging pain
heat
slow aching pain
what is the order of sensation return?
slow aching pain
heat
fast sharp, stinging pain
cold
conscious proprioception and light touch
what is sensory ataxia?
injury to peripheral sensory nerves, dorsal roots, and dorsal columns of the spinal columns, or medial lemnisci
what test would do you perform to differentiate sensory and cerebellar ataxia?
eyes open/closed test
what is the difference between sensory vs cerebellar ataxia in the eyes open/closed testing?
patients with cerebellar ataxia will have similar motor performance eyes open/closed
patients with sensory ataxia show a marked worsening in symptoms with the absence of vision, and be much better when watching their feet
what is herpes zoster (Shingles)?
presents as a painful rash with clusters of fluid-filled vesicles (blisters)
what is varicella zoster caused by?
varicella zoster virus which remains latent in sensory ganglia for many years
the virus breaks out of nerve cells and travels distally to nerve endings causing painful eruptions on skin
what type of nerve endings are nociceptors?
free, branching, unmyelinated nerve endings that respond to noxious stimuli
where are nociceptors located?
within skin, muscle, and joints
a-delta transmit what type of pain to the spinal cord and how fast?
sharp, localized pain quickly to the spinal cord
c fibers transmit what type of pain to the spinal cord and how fast?
transit dull, achy pain slowly to the spinal cord
where do alpha delta and C fibers synapse?
in the dorsal horn
what is nociceptive pain?
acute or chronic tissue injury stimulation activation of nociceptors to cause perception of pain
what is non-nociceptive pain?
malfunction of neural pain regulating processes causing pain without the presence of tissue injury includes neuropathic pain, central sensitivity syndromes, and pain syndromes
what two ways does pain inhibition occur?
descending analgesic pathways
endogenous opioid system
what are endogenous opioids also known as?
endorphins
what are three types of endogenous opioids?
enkephalins
dynorphin
B-endorphins
brainstem areas that provide intrinsic antinociception from a neuronal descending system, arise from the following…
rostral ventromedial medulla (raphespinal tract)
PAG in the midbrain
locus coeruleus in the pons (ceruleospinal tract)
the spinal cord has inhibitory neurons that respond to what two types of endorphins?
enkephalin and dynorphin
which fibers transmit pain informaiton?
A-delta and C fibers
which fibers transmit touch, pressure, and vibration informaiton?
A-Beta fibers
what is gate control theory of pain?
activation of non-nociceptive sensory neurons (A-Beta) closes a gate for central transmission of nociceptive signals (C fibers)
What fiber brings info to the CNS about pain first? and how does it feel?
A-delta activation; fast and sharp
what fiber brings info to the CNS about pain second? and how does it feel?
C activation; duller, longer lasting
where does the A-delta and C-activation synapse within?
substantia gelatinosa of the dorsal horn
what is the main neurotransmitter of pain afferents?
glutamate
what are the five levels of antinociception?
periphery
dorsal horn
brainstem
