Download physio unit 9 [4-20

Physio Unit 9
Items that directly increase chemical pain:
Bradykinin, serotonin, histamine, K+, acid, proteolytic enzymes
Which fibers localize a pain stimulus?
Aδ pain fibers (almost all pain travels via anterolateral system) localizes pain with the help of the
dorsal column-medial lemniscal system’s Aβ tactile receptors
Aδ fibers on the anterolateral system synapse in lamina I
Items that enhance sensitivity only to chemical pain only:
Prostaglandins and substance P
(P2—That’s the Party Posse!)
Aβ tactile receptors (5)
Meissner’s, Iggo dome (Merkel’s), hair receptors, pacinian, Ruffini’s
(PHIRM Aβs)
First synapse of epicritic system
Dorsal/cuneate and gracile nuclei in the lower medulla; followed by decussation
Protopathic / epicritic synonyms
Protopathic = anterolateral system; epicritic = dorsal column-medial lemniscal
Thalamic destinations of somatosensory pathways
Protopathic => ventrobasal and intralaminar nuclei;
epicritic => ventrobasal nucleus ONLY
Additional destinations of anterolateral system
Protopathic => spinoreticular tract & spinomesencephalic tract ( + spinothalamics above)
Anterior/lateral white columns travel by anterior/lateral spinothalamic tracts
Cortical entrance level
Input to cortex: layer IV
Asterogenesis
= inability to judge neither shape nor form (bilateral destruction of somatosensory area 1)
Amorphosynthesis
= inability to recognize complex objects on the opposite side of the lesion
from unilateral destruction of the somatosensory association area
Weber-Fechner principle
Discrimination ability of stimulus strength is proportional to the log of stimulus strength
Purpose of corticofugal signals
MODULATE sensory signals
Decrease signal transmission when input intensity is too great
They travel backwards from cortex to thalamus, medulla, and spinal cord
Amplifying Divergence Example
Characteristic of corticospinal pathway, which controls skeletal muscles
Divergence into multiple tracts
Occurs in information transmitted by dorsal column-medial lemniscal system
Labelled line principle
Only one modality of sensation is transmitted by a nerve fiber
Accommodation of Receptors
Lessening neuronal excitability due to:
Progressive inactivation of sodium channels
Decremental conduction
Decrease in membrane potential as it spreads electrotonically to soma
Strychnine
inhibits action of glycine – therefore strychnine excites neurons
Acidosis / alkalosis effects on CNS
Alkalosis increases excitability => seizures; Acidosis depresses => comas
Neuropeptides versus small-molecule transmiters (ACh, amines, amino acids, NO)
Neuropeptides are produced in the soma and axonally streamed, more potent
Possible Ionophore components (2, exclusive)
Either an ion channel or second messenger activator