Quiz 2-- Lectures 3, 4 Flashcards
Role of pain
functional role for survival– pain stimuli induce escape and withdrawal responses. it can also activate behavior
what is pain?
tissue destruction induced by thermal or chemical stimuli or mechanical force
T or F: Pain reception is highly localized
False
Relationship between pain and emotion
pain involves an emotional component to modify the magnitude of pain perception
who is pain most prevalent for?
adults in poverty, less than high school education, and public health insurance
nociception
the neural encoding and processing of noxious stimuli
what are noxious stimuli?
stimuli that elicit tissue damage and activate nociceptors
nociceptors
sensory receptors that detect signals from damage tissue– free nerve endings found in skin, muscles, joints, bone, viscera
how do peripheral nociceptive axons end?
free nerve endings
axon types for nociceptors
a delta, C– slowerr, C is unmyelinated
A delta fibers
respond to intense mechanical and thermal stimuli
type 1 a delta– mechanical, not thermal
type 2– thermal, not mechanical
what do c fibers respond to
thermal, mechanical, and chemical stimuli
true or false: non-pain somatosensory neurons increase in intensity for painful stimuli
false
t or f: nociceptive afferents always fire at stimuli
false, only when high intensities of stimuli are reached– 43 c is threshold for pain
fast pain
a delta fibers– sharp, first pain
slow pain
unmyelinated c fibers– give a dull, longer lasting burning pain
type 1 a delta fibers
respond to intense mechanical and chemical, have high heat thresholds
type 2 a delta
low heat threshold, but high threshold for mechanical stimulation
type c fibers
respond equally to all types of nociceptive stimuli
what is the pain and temperature pathway?
the anterolateral system
first order neurons in the anterolateral system
the dorsal root ganglia and immediately synapse on second order neurons
second order neurons
located in rexed’s alminae 1,11, and V of spinal cord– 1 anf 5 go to brainstem and thalamus, 2 has interneurons
C fibers go to 1 ans 2, A delta go to 1 and 5
projections immedately cross midline and give rise to the anterolateral tract and brainstem and thalamus vpl
difference between dorsal column medial lemniscus vs the anterolateral system
dorsal crosses near top, anterolateral immediately decussates
anterolateral system 3rd order neurons
go to somatosensory cortex
trigeminothalamic tract
first order neurons in trigemical ganglia descend to medulla and synapse on spinal trigeminal nugleus, second order decussate and ascent to brainstep and VPM thalamus in trigeminothalamic tract, third order to somatosensory
visceral (internal) pain pathway
pain from visceral organs
first order in dorsal root ganglia synapse in dorsal horn or in the intermediate gray region of spinal cord
intermediate second orders ascend through dorsal columns to dorscale column nuclei (gracile nucleus
third orders decussate and ascent to vpl thalamus
midline myelotomy
transection of axons in medial dorsal column brings pain relief from visceral cancers in abdominal area
Referred pain
visceral pain misperceived as cutaneous pain– angina (poor perfusion of heart muscle perceived as pain in shoulder/chest)
lamina 5
receives inputs from nociceptive and non-nociceptive afferents, and multimodal neurons in the area integrate both
threshold for thermal stimulus as pain
43 C
TRP channels
receptors sensitive to ranges of heat and cold
trpv1
sensitivity to heat and caspaicin
capsacin
first pain pathway
anterolateral–vpl—somatosensory cortex
affective-motivational pathway
goes to reticular formation, periaqueductal gray, superior colliculus, hypothalamus, amygdala, anterior cingulate cortex and insula, medial thalamic nuclei, parabrachial nucleus
interpretation of pain
reality of stimulus and how responsive the subject is– this means pain perception is subject to modulation due to context specificity (soldiers in battle w no pain) or placebo (perceived relief)
stimulation of periaqueductal gray
located in midbrain, is an analgesic and stops activity of nociceptive projection neurons in dorsal horn
four nuclei that the periaqueductal gray controls
parabrachial nucleus, medullary reticular formation, locus coeruleus, raphe nuclei (all in brainstem)
how is the flow of nociceptive information reduced
simultaneous activity in touch fibers
what are endogenous opioids
peptides binding to same postsynaptic receptors as opium
morphine, heroin, opiates like methadone and fentanyl are
analgesics
endogenous opioid ligands
endorphins, enkephalins, dynorphins
endorphins, enkephalins, dynorphins
released in periaqueductal gray
the source of pain modulating pathways to the dorsal horn in the spinal cord
opioid sensitive neurons
can be found in dorsal horn
where are enkephalins released
directly into spinal cord to blunt nociceptor activation
phantom limb syndrome
following amputation, nearly all patients have an illusion that missing limb is still present– mismatch between cortical and physical input
prevalence of phantom pain
higher in upper limb than lower limb
3 tissue layers of the eye
- retina– light sensitive receptors, part of cns
- uveal layer
- sclera
parts of uveal layer
choroid (capillaries and melanin for light absorption)
ciliary body to adjust lens
iris for pupil regulation
sclera (fibrous tissue with cornea at front
aqueous humor
nutrients to cornea and lens, replaced 12 times a day
glaucoma
failure of aqueous humor fluid drainage, eventually reducing blood supply
vitreous humor
80% volume of eye, maintains shape and has phagocytic cells– floaters are debris too large for consumption
cornea and lens do what
bend light (refraction) to achieve a focused image on retina
accommodation
dynamic change in shape of lens– lens is flat to view distant objects and round for near objects
zonule fibers
hold lens in place and keep lens flat
ciliary muscle contraction
reduces tension in zonule fibers and allows elasticity of lens to increase curvature
cataracts
opacities in transparent lens
myopia
unable to bring distant objects into focus, cornea too curved or eyeball too long
hyperopia
farsighted– cant focus on near objects, refractory muscles too weak or eye too short so focus behind retina
macula lutea and fovea
region of highest visual activity: 3 mm in diameter
optic disk
no photoreceptors in area of retina where blood vessels enter and axons leave, cortical mechanisms fill in missing info
macular degeneration
progressive loss of vision in center of visual field because of damage to retina– peripherral vision remains, difficult to read or recognize faces
dry form
debris between retina and choroid and thinning of macula- gradual disappearance of retinal pigment epithelium and loss of photoreceptors
wet form macular
more serious, blood vessel growth leaks fluid and blood and can damage retina – laser coagulation
five classes of neuron in eye
photoreceptors, bipolar, ganglion, horizontal, amacrine
3 neuron chain in eye
photoreceptor– biporal– ganglion (ganglion axons form optic nerve, horizontal and amacrine cells help with lateral interactions between bipolar and amacrine cells
rods and cones distinguished by
shape, sensitivity to light, photopigment, distribution across the retina, pattern of connection
retinal pigment epithelium
the reason retina is inverted
lifespan of photoreceptor disks
12 days, disks then pinch off
t or f: receptor potentials are all or nothing
false– graded
when does light receptor become depolarized
in dark (40 mV)– light hyperpolarizes them
receptor in the dark
outer segment– higher cgmp, which binds to na channels and allowing sodium and cations like ca to enter– this inward current causes a dark current
in the inner segment, outward current is mediated by potassium selective channels
light does what
reduces cgmp, so channels close, meaning hyperpolarization (outward low of K+) dominates
rods
sensitive to light but low resolution
cones
insensitive to light but high spatial resolution– help with color
do rods or cones adapt more efficiently
cones adapt more quickly– connected 1-1 to bipolar cells but rods saturate quickly - 15-30 rods per bipolar cell
cones frequency
highest in center– area of most acuity, fewer elsewhere
rods frequency
no rods in fovea but found high ddensity everywhere else
human cones
L (red peak), M (green peak), S (short peak)
protanopia
loss of red wavelength
deuteranopia
loss of medium wavelength
tritanopia
blue colorblinees
on center ganglion cells
increase when luminance increases in center
off center ganglion
increase when luminance decreases in center
on center bipoloar vs off center bipolar
on center– light increase
off center– light decrease
on center bipolar cells have what receptors
mGluR6 receptors that close Na channels, leading to hyperpolarization in response to glutamate release from dark photoreceptors
off center bipolar
ionotropic AMPA and kainate receptors that depolarize bipolar cell w/glutamate release
move spot of light across on center receptive field
response decreases w/distance from center
if in surround inhibition occurs
out of field= resting potential
opposite for off center
horizontal cells
generate surround antagonism because they are depolorized by glutamate from photoreceptors and release gaba to hyperpolarize photoreceptors
other species have
better lenses, msucle control, nictitating membranes (3rd eyelid), photodetectors, blood vessels, neurons, acons, two fovea, better acuity
