Unit 2 - Sensory Systems Flashcards
sensory receptors that generate APs directly
somatic and olfactory receptors
(the receptor cell itself generates AP to communicate w/ sensory neuron)
vs. graded potential (photoRs, hair cells, gustatory Rs):
make graded potential to elicit 1st AP in (post-synaptic) sensory n
Adaptation
decreased response to a sustained stimulus bc temporarily lose sensitivity (R stops working/inactivates);
- NOT the same as habituation (learned)
- amt/speed of adaptation depends on the R type
- quantified w/ Steven’s number*
2 phases to sensory receptor response
w/ stimulus presentation: (generally…)
- Dynamic (phasic): rate of fire == speed of stimulus presentation
- Static (tonic): amplitude/rate of fire == intensity of stimulus
Steven’s Law
way of quantifying the level of adaptation of a R to a stimulus;
I == S^n n = Steven’s number
I = percieved intensity of stimulus; S = actual stimulus intensity
n1 increased sensitivity (for intense stimuli, ie: weight, pain)
information conveyed by sensory systems
- intensity
- timecourse
- location
- modality (type of sense - sound, touch, taste, etc.)
synesthesia
psychological experience where segregation of modalities breaks down
ie: experience colors when hear sound
(matching brain areas DO show increased activity in brain scans)
- genetic basis?
types of sensory transduction (sensory receptor mechs)
- Mechanoreceptors: pressure/stress transferred to cytoskeleton –> opens channel, permeable to Na+ and K+
- Photoreceptors: rhodopsin + light –> activate transducin –> hyperpolarization (closes Na+ channels)
- others
population and frequency codes
2 mech.s of encoding information about stimulus intensity, allow for dynamic range of “sensation” (very low - very high intensity)
- Frequency code: w/ high frequency stimuli –> high firing rate
- Population code: w/ larger area stim. –> more cells activated
Response Region
the field within which the receptor recognizes sensation
- receptor cells: small field, = defined by sense organ.
- higher order neurons: larger, for all convergent inputs to that neuron
Sense most represented by cortical maps
Vision! –> “retinotopic maps”
- mapped onto multiple different parts of cortex (ie: V1, V2, …)
and superior colliculus
Sensory maps in superior colliculus
- Multiple visual maps in several layers
- -> represent diff. visual characteristics
- maps of OTHER sensory modalities as well (to inform vision)
* integrates distinct sensory modalities to direct eyes accordingly*
* * strokes affecting the sup. colliculus will cause poor orientation to visual and auditory stimuli**
stimulus properties
features of sensations such as pitch, shape, etc.
–> inhibitory neurons increase contrast in sensory signal
=> allow feature extraction
somatic sensory system
codes and transmits information about the body.
receptor types include:
- cutaneous (external stimuli)
- proprioreceptive (sense limbs in space - muscle length/position, joint angles)
- visceral (internal: distention/pain)
nocioception
pain sensation
– pain Rs = nocioceptors
hypalgesia
decreased sensation of pain
Analgesia
no/extremely reduced pain sensation
hyperalgesia
increased sensation of pain
allodynia
when innocuous stimuli cause pain
ie: lukewarm water = painful for sunburned skin
Paresthesia
Tingling sensation
considered a pain response
Pruritis
chronic itching,
sensation by pain receptors
Merkel Disc (S.A. I)
cutaneous mechanoreceptor; axons = A-beta;
* high localization in fingers and lips*
Rec. F: very small (~exact); slow adaptation
stim: skin indentation, *thresh: >15microm
dynamic: speed of indent
static: depth of indent
Ruffini ending (S. A. II)
cutaneous mechanoreceptor; axon = A-beta
RF: large
stim: lateral skin stretching
slow adaptation
Hair follicle
cutaneous mechanoreceptor, axon = A-beta/delta, C; RF: 1 hair follicle, *fast adaptation* stim: move hair - stretch channel dynamic: velocity of hair mvmt static: -----
Pacinian Corpuscle
mechanoreceptor, axon = A-beta;
RF: large **in tendons and joints, NOT cutaneous*
stim: indentation and vibration; thresh: <1 microm
dynamic: 1 for presence * fast adaptation
static: —-
Meissner’s Corpuscle
Cutaneous mechanoreceptor, axon = A-beta; * high localization in fingers and lips* RF: tiny * fast adaptation* stim: light touch dynamic: 1 for presence static: ----
TRPM8
thermoreceptor for cooling, A-delta axons - free nerve endings - thresh: 20-40 C Na+ channel * menthol = agonist
TRPV3
thermoreceptor for warmth, axon = C
- releases ATP to activate P2X –> depolarization
thresh: < 45 C
TRPV1
thermoreceptor for noxious heat, axon = A-delta;
- free nerve endings -
thresh: <45 C
agonist: capsaicin (in chili peppers) - firing continues after end of stimulus!*
TRPV2
thermoreceptor for painful heat, axon = C;
- senses changes in pH in tissue (injury –> low pH)
thresh:»_space; 45 (~53) C
- senses changes in pH in tissue (injury –> low pH)
- firing continues after end of stimulus!*
Sensitization of nocioceptors causes…
(increase sensitivity of receptors after injury, ie: sunburn, etc.)
- allodynia (decrease threshold)
- increase response to = stimulus intensity
- increase spontaneous activity (may fire beloe threshold)
1st order neuron in somatic sensation
carries sensory info for ipsilateral side,
from sensory R to spinal cord (dorsal horn).
lose 2 pt discrimination, vibratory and/or propriocep. if damaged
2nd order neuron in somatic sensation
carries contralateral sensory info,
from dorsal column (dorsal horn) to thalamus (esp. VPL).
* maintains spatial segregation from 1st order neuron*
3rd order neuron in somatic sensation
carries contralateral sensory info,
from thalamus to cortex (esp. post-central gyrus).
organization of sensory info in dorsal column
sacral/lumbar nn: most medial, extend whole length from inferior to superior **GF
thoracic nn: in middle of gracile and cunate fasciculi (thinnest set)
cervical nn: most lateral, only appear in cervical segment of spinal cord (~superior), **CF
relative receptive field sizes of 1,2,3 order neurons
3rd order neurons have largest receptive field (bc most # sensory receptors feed into it);
* 2nd order neurons have RF 40-100x larger than 1st order nn.
Shingles
varicella-related virus,
rests dormant in dorsal root ganglion;
when flares up –> affects that single dermatome.
what % of neurons extend from spinal cord into brain?
only 25% 1st order neurons go to the dorsal column nuclei in medulla (GN and CN);
– other 75% stay in spinal cord and make “propriospinal connections” (for reflexes, central pattern generation, etc.)
Spinothalamic tract
Pathway of 1-3rd order neurons, carries pain and temperature info.
Dorsal horn –[cross midline]–> VLF (spinal cord) –>
a) reticular formation, b) central gray, c) thalamus (VPL; Central Lateral Nuc.) –> Cortex (1 somatosensory area; limbic areas)
Path of 1st order neuron in STT
- nocioceptor –> Dorsal root
- Lissauer’s tract –> Substancia Gelatinosa ==> interneuron.
** NTs = glutamate and SP; if enough –> Long Term change:
alter 2nd mess, so modulate synaptic f(x)** - int.n –> marginal zone & lamina V (dorsal horn) ==> 2nd o.n.
Path of 2nd order neuron in STT
- Dorsal horn --> Ventral 1/2 of Lateral Funiculus (“VLF”)
* cross midline via anterior white commissure w/in 2 segments - ascend to… a) Reticular formation
b) Central Gray
c) Thalamus
Path of 3rd order neurons in STT
(3 targets)
- reticular formation (medulla): evoke arousal [cortex]
- central gray (midbrain): modulate STT
- Thalamus
a) Central Lateral nucleus: emotion/suffering [limbic cortex]
b) VPL nucleus: map/localize pain [1 somatosensory cortex]
role of Ventral Posterolateral nucleus (VPL) in pain sensation
sends 3rd order neuron of STT to primary somatosensory cortex,
for localization of pain information.
* ipsilateral from thalamus to cortex (not to body)*
Role of Central Lateral nucleus in pain sensation
sends 3rd order neuron of STT to limbic cortical structures (cingulate gyrus and insula) for “emotional/suffering”responses to pain.
* large receptive fields bc do not localize pain* (not somatotopic)
= fast, general “feeling” response to pain
Cordotomy
surgical procedure for pain management in terminally ill patients,
= unilateral cutting of VLF in spinal cord.
–> unilateral (contralateral) analgesia and athermia AT and below the level of the cut.
BUT: pain returns bc other pathways take up pain info!!
Syringomyelia
a central cord degeneration syndrome where a hole develops in the center of the spinal cord; usually expands up and down spinal column.
–> cuts off only STT axons crossing the midline at the affected point (remember rule of w/in 2 segments for crossing)
Bladder pain referred to
Lower back and supra-public regions
Heart pain referred to
Males: Chest and left arm
Females: back and left shoulder
Kidney pain referred to
Back
Esophagus pain referred to
Chest
Sometimes confused for heart attack
Duodenum pain referred to
Mid epigastric region
Lung pain referred to
Upper back
Migraine pain referred to
Cranium and orbits
