Pain Quiz 2 Flashcards
What are the four major somatosensory modalities?
Sensory receptor cells located on which organs?
Stimuli encoded as?
- Discriminative touch
- Proprioceptive - awareness of own body position
- Temperature
- Nociception - pain
Sensory receptor cells located on sense organs
Stimuli encoded as action potentials
Dorsal Root Ganglion (DRG) - primary receptor cell
What type of cells?
Neuron cell body is located in the what and adjacent to the what?
The axon of the DRG neuron has what kind of transmission line? With one polarity between what? Has two branches?
For which organs in the body?
Anatomy of the DRG
Dorsal root vs Ventral root?
Pseudounipolar cells: a type of sensory neuron that appears to have only one process extending from its cell body
Neuron cell body is located in the DRG adjacent to the spinal cord
The axon of the DRG neuron single transmission line
- With one polarity between receptor terminal and CNS
- Has two branches(one branch to spinal cord or to brain and other branch is like a dendrite it receives on the receptor), one projects to the periphery and one to the CNS
For skin, muscle and viscera
Anatomy of the DRG
Dorsal root: sends sensory info revised from periphery to brain
Ventral root: motor info send from brain and spinal cord out to periphery
Which correctly ranks the diameter of afferent sensory axons from smallest to largest?
C, A-delta, A-beta, A-alpha
C smallest
A-alpha largest
How do we sense a number of different sensations in the periphery?
What are Primary Afferents?
Fiber are?
Non-Noxious(painful or damaging)(another word for non-noxious is innocuous), Touch
Primary Afferents = periphery to spinal cord or brain stem
Primary afferents are sensory neurons (axons or nerve fibers) in the peripheral nervous system that transduce information about mechanical, thermal, and chemical states of the body and transmit it to sites in the central nervous system.
Fiber are axons
What are the 3 myelinated afferent sensory axons/fibers and for what body?
What is the 1 unmyelinated afferent sensory axons/fibers and for what body?
Myelinated:
Aα(alpha) - proprioception - fast mainly skeletal muscle
Aβ(beta) - mechanoreception - little smaller for skin
Aδ(delta) – pain and temperature - smaller diameter
Unmyelinated:
C – pain, temperature, itch - more than 90% and slow
Merkel (non painful superficial layer):
what adapting?
receptive field/resolution?
responds to?
slowly adapting(constant rate of firing like holding heavy object - activate for entire length of stimulus,
small receptive field/high spatial resolution (dark and smaller area - the smaller the field the higher resolution so able to pinpoint where stimulated)
responds to edges, corners, and points
Mechanoreceptors so not painful
Meissner (non painful superficial layer):
what adapting?
receptive field/resolution?
responds to?
rapidly adapting
small receptive field/high spatial resolution
responds to stroking, fluttering, and low frequency vibration, example wind or feather or shirt fluttering on skin
Mechanoreceptors so not painful
Pacinian (glabrous, deep layers subcutaneous):
what adapting?
receptive field/resolution?
responds to?
high frequency vibration,
rapidly adapting (abrupt - changing throughout stimulus like wind)
large receptive field/low spatial resolution, example standing near bus and feel vibration or like earthquakes
Mechanoreceptors so not painful
Mechanoreceptors
Glabrous, superficial layers includes which two?
Glabrous, deep layers (subcutaneous) have more receptive fields includes which two?
Hairy skin is which layer?
Hair receptors innervate how many hairs in same what cm and feel?
Fingertips higher density of?
Palm lower amounts of what but more or equal of?
Forearm have them inches apart bc of?
Reading braille is best for which area?
Glabrous, superficial layers:
Meissner’s corpuscles → storking, fluttering - decet initial contact
Merkel disks → edges, corners, points
Glabrous, deep layers (subcutaneous) have more receptive fields:
Pacinian corpuscle → vibration
Ruffini ending → skin stretch and feel large objects
Hairy skin is superficial layer
Hair receptors - innervate 10-30 hairs in same 2-3 cm and feel stroking and fluttering
Fingertips higher density of superficial
Palm lower amounts of superficial but more or equal of subcutaneous
Forearm have them inches apart bc of density of mechanoreceptors and respective fields so density is different
reading braille so superficial will have smaller areas therefore will have accurate signals sent for merkel vs Pacinian/Ruffini will have larger area and can’t sense braille
Which two adaptation types?
Receptive Fields and Adaptation of Mechanoreceptors reflects?
Rapidly adapting (Mesinner RA1 and Pacinian RA2)
Slowly adapting SA1 Merkel and SA2 Ruffini - burst at the start and then constant
Receptive Fields and Adaptation of Mechanoreceptors - reflects location and distribution
Receptive Field Plasticity
Newly discovered mechanoreceptors for innocuous mechanical stimuli? What does it mediate? What happens if knockout?
Piezo-2: mediates mechanosensitive currents in sensory neurons; enhanced activity associated with mechanical hypersensitivity (non-painful stimuli is now painful so knockout Piezo-2 decreases allodynia
Proprioceptive Receptors
Which fibers?
Muscle spindles?
Golgi tendon organs?
Golgi Tendon Reflex?
Mostly Aα- myelinated fast condition, some Aβ
Muscle spindles: Stretch sensitive ion channels in muscle spindle so depo is proportional to velocity and amp - fast or large muscle stretch is proportional
Golgi tendon organs: between muscle and tendons that measures forces generated by muscle contraction
joint capsule receptors
Golgi Tendon Reflex: Curial reflex arc that operates as a feedback mechanism
Temperature (Noxious and NonNoxious) - TRP channels
Thermal Receptors?
Senses temperature changes: 4 classes, have preferred range?
Thermal sensitivity of neuron is determined by?
TRPA1?
TRP4 and TRPV3?
TRPV1?
Thermal Receptors: A-Delta and C fibers
Senses temperature changes: 4 classes, have preferred range - cold, cool, warm, hot
Cold and hot are painful
Cool and warm are innocuous
Thermal sensitivity of neuron is determined by TRP receptors expressed
TRPA1(allium like garlic and radish) and 8(mint) are for cooling and cold stimuli
TRP4 and TRPV3 at skin temp resting are stimulated
TRPV1 spicy
TRP are channels that respond to different channels of temp - pain and no pain - located at A-delta and C fibers which include both noxious and non noxious
Pain - is TRPV1(heat and chemicals like peppers) and TRPV2 damage hat
TRPA1 cold damage - dry ice
TRPM8 cool not damage
TRPV4, TRPV3 not pian temp
Where are TRP receptors expressed?
At peripheral nerve terminals by skin - TRP determines reception
Transduction of noxious heat
What is the most painful temp?
Multiple TRP receptors sensitive to these temperature ranges?
Knockout lines of TRP receptors sensitive to noxious temperatures have deficits in?
> 42 degrees Celsius (108 F)
Multiple TRP receptors sensitive to these temperature ranges TRPV1 and TRPV2
Knockout lines of TRP receptors sensitive to noxious temperatures have deficits in heat sensitivity
TRPV1 - Phenotype of TRPV1 KO mice
Transduction mechanisms for low pH - TRP temp and low PH
Which fibers with TRP express low PH?
pH activated currents in sensory neurons are?
TRPV1 most likely mediates?
heteromeric Acid sensing channels (ASIC) channels may underlie?
~ 30% of C-fibers with TRP receptors expressed on them respond to low pH
pH activated currents in sensory neurons are sustained or transient
TRPV1 most likely mediates sustained pH responses
heteromeric Acid sensing channels (ASIC) channels may underlie transient pH responses
ASIC3: role in cardiac ischemia
Mediators released during tissue damage and inflammation:
ATP, bradykinin
ATP released from damaged cells can signal through P2X and P2Y receptors (P2X3 and P2Y2)
bradykinin-induced thermal hyperalgesia requires both TRPV1 and TRPA1
Merkel cell afferent fibers convey information about which variable(s)?
Shape and texture
The Uniqueness of Itch
Itch is different from pain bc pain causes a withdraw from stimulus while itch?
Pruritic itch inducing agents at which afferents in skin - information sent from periphery travels through which located in to what?
Two agents that cause itch?
Neuron firing rate decreases with scratch?
When tissue damage or inflammation skin cells like keratin ascites and fibroblasts addition to infiltrating resident immune cells can release what? that active which receptors in which fibers like what? so can bind to which protein and recruit in increase intracellular what through what
Itch is different from pain bc pain causes a withdraw from stimulus while itch causes scratch
Pruritic itch inducing agents at primary afferents in skin - information sent from periphery travels through primary afferents C fibers(no myelin) located in DRG to brain
Cause itch:
Histamine
Chloroquine
Neuron firing rate decreases with scratch - so itchy stimuli cause AP — neurons responding to histamine sending const AP saying itchy so when scratch no more AP - dont feel itchy anymore bc inhibiting neurons sending itch
When tissue damage or inflammation skin cells like keratin ascites and fibroblasts addition to infiltrating resident immune cells can release Pruritogens that active pruritic receptors in C fibers like Histamine and other RNAS and can bind to G protein and recruit in increase intracellular Ca through TRPV1
Nociception (nociceptors located in skin muscles joints and viscera)
Primary afferent preferentially sensitive to a?
Mechanical?
Thermal?
Polymodal?
First pain is?
Second pain is?
Primary afferent preferentially sensitive to a noxious stimulus that damage tissue
Mechanical – high threshold, mostly Aδ - (delta as short latency which is sharp and prickly)
Thermal - Aδ and C fibers(dull diffuse)
Directly mechanical and thermal but indirectly chemical
Polymodal – C fibers - medicinal, thermal, chemical
Propagation in nociceptors - cross sectional diameter:
– First pain is sharp and fast mediated by A-delta
– Second pain is throbbing and aching and lingers mediated by C-fibers
Tissue injury damages cells, attracts inflammatory cells - release chemokines that attract immune cells like mast cells, macrophages, and dendritic
Damaged/Inflammatory cells release several substances:?
Stimulated nociceptors release: ?
Substance P VS Glutamate
Damaged/Inflammatory cells release several substances:
Histamine
Arachadonic acid → prostaglandins
Stimulated nociceptors release:
Substance P
Increases vasodilation so more can be recruited by circulation, inflammation makes redness, release of histamine
Excites interneurons(2* afferents) in spinal cord
Glutamate
Excites interneurons(2* afferents) in spinal cord - send pain to brain
Which processes contribute to sensitization (increasing pain) following tissue damage?
How are signals sent from the periphery to the brain?
Which fibers conduct the sensation of first pain?
Which processes contribute to sensitization (increasing pain) following tissue damage? Release of peptides and NT from nociceptors, migration of immune cells to the site of damage, release of proinflammatory substances by the non-neuronal cells, damage skin cells releasing cytokines to recruit immune cells
How are signals sent from the periphery to the brain? Somatosensory Pathways
Which fibers conduct the sensation of first pain? Myelinated A-delta
Projections of Sensory Neurons - pseudounipolar
Neurons carry APs from skin to spinal cord
Spinal nerves: ? Divisions VS “Mixed” nerves
Central Somatosensory Pathways: The 3 neuron rule - For touch, temperature and pain: It takes 3 neurons for a sensory signal to be relayed from the body to the sensory cortex
Pain/Temp VS Touch?
Spinal nerves:
Divisions: 8 Cervical, 12 Thoracic, 5 Lumbar, 5 Sacral, 1 Coccygeal
“Mixed” nerves
Contain both motor and sensory neurons in periphery – contains information sent from mechanoreceptors and nociceptors - for touch, pain, temp, and pain
Pain/Temp: 1 ipsilateral Sensory Neuron, 2(second order neuron) Spinal Neuron (crosses), 3 Thalamic Neuron
Touch: 1 ipsilateral Sensory Neuron, 2 Medulla Neuron Brain Stem (crosses), 3 Thalamic Neuron
Sensation Pathway – Touch Discrimination
Medial Leminiscal Pathway(dorsal column) – BODY
Carries information about discriminative touch
1* afferents terminate in medulla (ipsilateral – same side):
2* afferents from dorsal column nuclei to dorsal thalamic nuclei
Decussate – cross over to contralateral (opposite) side
3* afferents from VPN(dorsal thalamus) to primary somatosensory cortex parietal lobe
Ascending Nociceptive Pathways - don’t split until get to brain - palo neo
Anterolateral Pathway – 2 Parts: pain, itch, temp, visceral
Paleospinothalamic tract – SLOW
To thalamus and parietal cortex: From C fiber nociceptor axons
To the reticular activating system: Affects arousal, mood, attention response
Neospinothalamic tract - FASTER
To the thalamus and parietal cortex:
From Aδdelta fiber nociceptor axons
Both decussate (cross-over) to the contralateral side in the spinal cord!
