Mkgrady8 Neuro 2 Anterolateral System

Front 1

anterolateral systems: what sensations, what tracts does it include

Back 1

crude touch, pressure, nociception (pain), and thermal sensations for the body; anterolateral system= spinothalamic, spinoreticular, and spinomesencephalic tracts

Front 2

definition of nociception and it is composed of what 4 processes

Back 2

the neural processes of encoding and processing noxious stimuli; physiologically it is composed of 4 processes= detection of noxious stimuli, transduction, transmission, and perception and modulation

Front 3

detection of noxious stimuli: how

Back 3

ACTIVATION OF NOCICEPTORS (also called PAIN RECEPTORS) that can detect MECHANICAL, THERMAL, OR CHEMICAL CHANGES above a SET threshold (or intensity of stimuli)

Front 4

transduction: how

Back 4

the AFFERENT ACTIVITY produced by stimuli that can damage tissue or that have the potential to damage tissue

Front 5

transmission: how

Back 5

once stimulated a nociceptive sensory unit transmits a signal along the spinal cord, to the brain conveying exposure to noxious stimuli (labeled line)

Front 6

perception and modulation: how

Back 6

nociception TRIGGERS A VARITY OF AUTONOMIC RESPONSES and may also result in the experience of PAIN in sentient beings

Front 7

definition of nociceptor

Back 7

a receptor that effectively and reliably distinguishes between noxious and innocuous stimuli from the periphery and transmits the noxious signals via afferent nerve fibers (sensory unit) to the CNS; includes damaging stimuli; intent to damage; slowly adapting, free nerve ending that sense multiple types of stimuli; polymodal receptors that can sense mechanical, thermal, and chemical sensations that are painful; ASSOCIATED ONLY WITH ADELTA (III, LIGHTLY MYELINATED) and C (IV, UNMYELINATED) nerve fibers; but this is only true under normal conditions and not true for pathologic pain

Front 8

specific types of nociceptor: transient receptor potential (TRP) channels

Back 8

cationic channels that lead to depolarization and firing of action potentials; found on C and Adelta fibers endings; polymodal in that are activated by heat, changes in pH, and chemicals

Front 9

specific types of nociceptors: TRPV1 receptors

Back 9

aka Vanilloid receptor, VR-1, or capsaicin receptor; responds to capsaicin (ingredient in hot chilies), heat, and low pH; elicits intense burning pain sensation; results in an additive or synergistic effect (with temp and pH)= capsaicin activates receptor from the inside and heat from the outside

Front 10

method of detection/distinction of potentially noxious stimuli from innocuous

Back 10

receptor and nerve fiber specific; ex a flat warm stone on your back= activate free nerve endings on Adelta specific for temp and pressure but not pain, a flat very HOT stone on your back= activate free nerve endings on C fibers and Adelta (now because have exceeded threshold of activation, have moved from activation of innocuous stimuli to painful stimuli)

Front 11

pain can be divided into 2 parts=

Back 11

a first sharp pain (Adelta fibers) and a prolonged diffuse continued pain (C fibers)

Front 12

components of anterolateral system

Back 12

one of the 3 major long tracts in the CNS; subserving sensations of crude touch, pain, and temp; located in lateral part of the ventral/anterior white matter of the spinal cord; 3 components= spinothalamic tract (STT, direct pathway) (which is the newest component of the system, most direct route to the thalamus and ultimately the post central gyrus), spinoreticular tract (SRT), and spinomesencephalic tract (SMT) (both comprise the indirect pathway to the thalamus as well as other parts of the brain)

Front 13

the INTEGRITY OF THE ANTEROLATERAL SYSTEM is tested clinically by

Back 13

assessing the function of the STT

Front 14

the SRT and SMT lack

Back 14

strong anatomical segregation (terminate on the post central gyrus) and laterality (ipsilateral tracts) to be useful as a test of the system's functional integrity but their physiological activity is very important= SRT is involved with persistent and chronic pain, SMT is involved in endogenous pain suppression mechanisms

Front 15

the 3 similarities of all 3 tracts

Back 15

1. the axons of the pseudounipolar nerons are Adelta or C fibers with free nerve ending dendrites and somas in DRG that enter in the more lateral part of the dorsal horn entry; 2. these axons travel up or down the cord for several (2-3) segments in the dorsolateral fasciculus of Lissauer (Lissauer's tract) and then synapse on second order neurons in the dorsal horn in distinct lamina; 3. the second order neurons give rise to axons that cross the midline in the ventral white commissure and ascend contralaterally in the anterolateral fasciculus

Front 16

the spinothalamic tract (STT) differs from the other 2 how

Back 16

final termination(s) of tracts occur at different brain regions and not the primary SS cortex (aka only the STT terminates at the primary SS cortex and not the others terminate at other brain regions); good versus poor somatotopic organization= in the SST incoming simuli is somatotopically organized at the level of the spinal cord and maintains this somatotopy as ascends to final destination of cerebral cortex (postcentral gyrus); STT also conveys temp, crude touch, and fast component of pain (mainly Adelta fibers, this is the pathway you test clinically)

Front 17

ALS path after spinal cord (SC) entry prior to SC decussation

Back 17

while both Adeta and C fibers (C FIBERS SYNAPSE AT REXED'S II AKA SUBSTANTIA GELATINOSA (NEED TO KNOW)) enter the dorsal horn of the spinal cord, they immediately synapse in different regions prior to crossing via the anterior white commissure to form STT on contralateral side and ascend all the way to VPL nucleus of thalamus; then these Adelta and C fibers travel 2-3 segments up or down the cord in Lissauer's tract, then synapse in the dorsal horn and secondary afferents cross to form STT on contralateral side

Front 18

Lissauer's tract is a component of the

Back 18

spino-spinal or propriospinal tract

Front 19

clinical significance of Lissauer's tract

Back 19

a subdivision of the PROPRIOSPINAL TRACT (aka SPINOSPINAL TRACT) that allows communication among spinal segments; distributes crude touch, pain, and thermal sensations among spinal segments on the ipsilateral side of the spinal cord; interruption of lesion of the STT on one side produces hypoalgesia and therm anesthesia several segments below the level of the lesion on the contralateral side (BECAUSE SENSATIONS ARE DISTRIBUTED OVER SEVERAL SPINAL CORD (2-3 SEGMENTS) IN LISSAUER'S TRACT)

Front 20

Lissauer's tract and spinal cord lesions

Back 20

hemisection of the R spinal cord immediately below L3 then, instead of contralateral loss of pain and thermal modalities from L3 down, you get contralateral loss of these modalities below L5 (due to lissauer's)

Front 21

pathway and termination of SRT

Back 21

spinoreticular tract (SRT); some tracts ascend ipsilaterally (lack of laterality for deficits); many collaterals as pathway ascends (RF); terminate in different brain regions (not somatosensory cortex); project to different brain regions (not postcentral gyrus)= association cortices, amygdala, hypothalamus, limbic regions, LOCATION ON BODY IS DIFFICULT TO ID

Front 22

pathway and termination of SMT

Back 22

crossed and uncrossed secondary or tertiary afferents ascend and terminate in periaqueductal grey (PAG) or superior colliculus; PAG= location of descending pain suppression pathways; THIS PATHWAY ALSO INCLUDED COLLATERALS FROM STT

Front 23

the direct pathway of ALS summary

Back 23

refers to axons in spinothalamic tract (STT) with specific somatotopic relay in thalamus and projection to somatosensory cortex; sensation determined by free nerve endings primarily on Adelta; ALLOWS LOCALIZATION AND QUANTITATION; conveys crude touch, temp, pressure (PAINFUL), and FAST (FIRST) PAIN I.E. NOCICEPTION; THE INTEGRITY AND FUNCTION OF THIS PATHWAY IS ASSESSED CLINICALLY BY APPLYING HOT, COLD, PINPRICK, PINCH, ETC AND SERVES AS A MARKER FOR THE INTEGRITY OF THE ENTIRE ALS

Front 24

the indirect pathway of the ALS (summary)

Back 24

refers to axons in= collaterals (branches) of STT to reticular formation, PAG, intralaminar thalamus that convey input from C FIBERS PRIMARILY, SRT and SMT; subserves slow, persistent, annoying SECOND pain (poor localization and quantitation, nonspecific without somatotopic map); subserves subjective/effective/motivational aspects of pain= nonspecific multiple diffuse projections from RF and intralaminar thalamus to hypothalamus and limbic system (behavioral aspects of pain, amount of pain depends on its context or specific situation or expectation based on experience, pain can cause changes in affect (mood)= irritability, depression, etc); activation of descending pain suppression system (SMT and more later)