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The Sensory Axis

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The Sensory Axis The sensory axis By Gustav Emil Dietrichson Things I’m going to cover and you’re going to understand • The basics • Cutaneous receptors • Dorsal column-medial lemniscus • Spinothalamic tract • The thalamus and the cortex • Pain • Quesons Receptors • Smulus à Conducon change à Generator poten?al • Intereceptors, exteroceptors, proprioceptors, teleceptors Thermoreceptors Chemoreceptors Photoreceptors Mechanoreceptors Nerve fibers • A • B – Preganglionic • C – Pain, temp • Aα – Propriocep?on autonomic ggl • 0,5-2m/s • 70-120m/s • 3-12m/s • Cggl – Postsynap?c • Aβ – Touch sympathe?ch ggl • 5-12m/s • 0,7-2,3m/s • Aγ – Motor • 3-6m/s • Aδ – Pain, temp • 12-30m/s A fibers = Thickest C fibers = Thinnest Cutaneous receptors • Merkel discs • Ruffini endings • Fine touch • Skin stretch • Discriminave touch Apical • Sustained pressure Basal • Meissner corpuscles • Pacinian corpuscles • Texture change • Deep touch • Slow vibraons • Fast vibraons • Both ”Corpuscles” are PHASIC receptors, while the other two are TONIC receptors • *ALL USE Aβ FIBERS Thalamus • What is the Thalamus? • Ventroposterolateral nucleusàBrodmann area 3,1,2 Dorsal column- medial lemniscus • Receives all informaon from • Merkel discs, Meissner corpuscles, Pacinian corpuscles, Ruffini endings • Muscles spindles and Golgi tendon organs • Propriocep?on • Fine touch • Vibraon (Low and high) • Pressure (deep and superficial) • Two touch discriminaon • DRAW! Spinothalamic tract Lateral spinothalamic tract • Anterior spinothalamic • Crude touch • Lateral spinothalamic • Temperature • Pain Everything • Itching annoying • Sexual arousal • DRAW! Fast and slow pain Fast pain Slow pain Aδ fibers C fibers Myelinated Unmyelinated Glutamate Substance P Sharp, specific Not sharp, dull, intense and diffuse Terminates in VPL nucleus of Thalamus 75-90% terminates in the re?cular formaon VR-1/TRPV-1 VRL-1 High temperatures (above 43C) High temperatures (above 43C) H+ change H+ change Capsaicins *Nociceptors called free nerve endings Re?cular formaon • Responsible for alertness in CNS Interpretation of pain • Sorts s?muli and chooses most important one • During sleep it ignores non- crucial smuli Re?cular Brodmann area formaon 3,1,2 Painful smuli VPL nucleus of Cingulate gyrus Thalamus Insular cortex The pain gate Large fibers (+) DCML connues DCML Pain gate Lateral Re?cular Dorsal grey horn Cerebral cortex spinothalamic formaon relieving =Pain Descending analgesic system PVG/PAG Endorphin Nucleus Raphe magnus Enkephalin Limbic system -Serotonin Dynorphin Re?cular formaon Lateral spinothalamic Sensory cortex Interneuron -Serotonin tract in spinal cord Locus coerelus Spinothalamic tract -Norepinephrine PVG = Periventricular gray maer PAG = Periaqueductal gray maer What types of sensation does the pacinian corpuscles convey? • a) Fine touch and discriminave touch • b) Deep touch and fast vibraon • c) Skin stretch and slow vibraon • d) Heat and pain • e) Skin stretch and sustained pressure Where does the DCML decussate? • a) Pons • b) Midbrain • c) Spinal cord above T6 • d) Medulla • e) Spinal cord below T6 Where do most of the fibers from the lateral spinothalamic tract end up? • a) Ventroposterolateral nucleus • b) Postcentral gyrus • c) Re?cular formaon • d) The auau centre of the brain • e) Superior colliculus What types of substances inhibit the lateral spinothalamic tract at the level of spinal cord to numb pain? • a) Opioids • b) Substance P • c) Glutamate • d) Prostaglandins • e) Acetylcholine Thank you for me Gustav.
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