Chapter 19Chapter 19Viscerosensory Viscerosensory

PathwaysPathwaysMP. Thibeault-Eybalin, R4MP. Thibeault-Eybalin, R4

Academic Half-DayAcademic Half-Day

March 25March 25thth, 2009, 2009

OutlineOutline

In parallel to somatosensory system In parallel to somatosensory system conveying info from external conveying info from external environment, viscerosensory system environment, viscerosensory system conveys info about internal conveys info about internal environmentenvironment

Viscerosensory receptors, fibers, Viscerosensory receptors, fibers, ascending sympathetic and ascending sympathetic and parasympathetic pathwaysparasympathetic pathways

Examples of reflexes based on aboveExamples of reflexes based on above

Viscerosensory receptorsViscerosensory receptors

2 types2 types1.1. NociceptorsNociceptors

Free nerve endings of AFree nerve endings of Aδδ and C fibers located in heart, and C fibers located in heart, respiratory, GI and GU tractsrespiratory, GI and GU tracts

Project to Lamina 1 and 5 in dorsal hornProject to Lamina 1 and 5 in dorsal horn Mediate visceral pain, e.g. angina pectorisMediate visceral pain, e.g. angina pectoris

2.2. Physiologic receptorsPhysiologic receptors MechanoreceptorsMechanoreceptors

Rapidly adapting, e.g. coughRapidly adapting, e.g. cough Slowly adapting, e.g. full stomach or urinary bladderSlowly adapting, e.g. full stomach or urinary bladder

Baroreceptors, e.g. baroreflexBaroreceptors, e.g. baroreflex Chemoreceptors, e.g. in carotid and aortic bodiesChemoreceptors, e.g. in carotid and aortic bodies Osmoreceptors, e.g. osmolarity and ADH production Osmoreceptors, e.g. osmolarity and ADH production Internal thermal receptors, e.g. core temperature in Internal thermal receptors, e.g. core temperature in

hypothalamushypothalamus

Classification of viscerosensory Classification of viscerosensory receptors and their respective receptors and their respective

stimulistimuli

A)A) BaroreceptorBaroreceptor

B)B) ChemoreceptorChemoreceptor

Viscerosensory fibersViscerosensory fibers A.K.A. General visceral A.K.A. General visceral afferentsafferents Travel with general visceral efferents in Travel with general visceral efferents in SympatheticSympathetic nerves nerves

e.g. splanchnic and cardiac nervese.g. splanchnic and cardiac nerves EfferentsEfferents>afferents>afferents Mainly info from nociceptorsMainly info from nociceptors

ParasympatheticParasympathetic nerves nerves e.g. vagus and pelvic nervese.g. vagus and pelvic nerves AfferentsAfferents>efferents>efferents Mainly info from physiologic receptorsMainly info from physiologic receptors

Ascending sympathetic Ascending sympathetic pathwayspathways

Mainly nociceptive info from thoracic and Mainly nociceptive info from thoracic and abdominal viscera via splanchnic and cardiac abdominal viscera via splanchnic and cardiac nervesnerves

Cell bodies are in DRG T1 to L2Cell bodies are in DRG T1 to L2 Synapse onto 2Synapse onto 2ndnd order neurons order neurons

AfferentAfferent In lamina 1 and 5, cross through anterior white commissure to In lamina 1 and 5, cross through anterior white commissure to

project to ALS contralaterally, about 2 sensory levels higher project to ALS contralaterally, about 2 sensory levels higher → → VPL of thalamus → inferolateral post-central gyrus (parietal VPL of thalamus → inferolateral post-central gyrus (parietal opeculum) and insular cortexopeculum) and insular cortex

In lamina 7 and 8 to project to spinoreticular tracts bilaterallyIn lamina 7 and 8 to project to spinoreticular tracts bilaterally→ periaqueductal gray → dorsal longitudinal fasciculusperiaqueductal gray → dorsal longitudinal fasciculus→ mesencephalic reticular formation → mammillary peduncle and mesencephalic reticular formation → mammillary peduncle and

medial forebrain bundlemedial forebrain bundle→ ultimately to hypothalamus and intralaminar thalamic nucleiultimately to hypothalamus and intralaminar thalamic nuclei

EfferentEfferent In intermediolateral column at same level In intermediolateral column at same level → anterior horn → → anterior horn →

pre-ganglionic sympathetic efferentpre-ganglionic sympathetic efferent Large receptive fields in brain, poorly localizingLarge receptive fields in brain, poorly localizing

1st order visceral afferent2nd order visceral afferentVisceral efferent

→ dorsal longitudinal fasciculus

→ mammillary peduncleand medial forebrain bundle

Referred painReferred pain Noxious stimuli originating Noxious stimuli originating

from visceral organs are from visceral organs are perceived as arising from perceived as arising from somatic tissues (skin, somatic tissues (skin, bone, muscle, etc.)bone, muscle, etc.) Whose afferents enter the Whose afferents enter the

spinal cord at the same levelspinal cord at the same level Due to collateral synapses Due to collateral synapses

between visceral and somatic between visceral and somatic afferents in dorsal hornafferents in dorsal horn

Example: Angina pectorisExample: Angina pectoris Pain referred to retrosternal Pain referred to retrosternal

area and left area and left ± right arms, ± right arms, neck, jaw, TMJneck, jaw, TMJ

Classic patterns of Classic patterns of referred painreferred pain

Angina pectorisAngina pectoris

Sympathetic trunk

Ascending parasympathetic Ascending parasympathetic pathways (cranial and pathways (cranial and

sacral)sacral) CranialCranial

Only CN 9 and 10 have significant parasympathetic Only CN 9 and 10 have significant parasympathetic afferentsafferents

CN 9CN 9 Chemoreceptors from carotid bodiesChemoreceptors from carotid bodies Baroreceptors from carotid sinus wallBaroreceptors from carotid sinus wall Nociceptors from oropharynx (afferent limb for gag Nociceptors from oropharynx (afferent limb for gag

reflex)reflex) CN 10CN 10

Chemoreceptors and baroreceptors in aortic archChemoreceptors and baroreceptors in aortic arch Physiologic receptors from thoracic and abdominal Physiologic receptors from thoracic and abdominal

viscera above splenic flexure of colonviscera above splenic flexure of colon Both enter skull through jugular foramenBoth enter skull through jugular foramen Cells bodies located in INFERIOR ganglia of CN 9 and 10Cells bodies located in INFERIOR ganglia of CN 9 and 10

Superior ganglia contain cell bodies of somatic afferentsSuperior ganglia contain cell bodies of somatic afferents Synapse onto 2Synapse onto 2ndnd order neuron in solitary nucleus order neuron in solitary nucleus Mediate vasopressor and vasodepressor responsesMediate vasopressor and vasodepressor responses

Dual role of solitary nucleus in Dual role of solitary nucleus in baroreflexbaroreflex

Reticular formationHypothalamus

Ascending parasympathetic Ascending parasympathetic pathwayspathways

SacralSacral Parasympathetic afferents from S2-3-4 Parasympathetic afferents from S2-3-4

travel through pelvic nerves, then spinal travel through pelvic nerves, then spinal nervesnerves

Relay info on bowel and bladder distensionRelay info on bowel and bladder distension Via ALS and spinoreticular fibersVia ALS and spinoreticular fibers To VPL of thalamus, reticular formation, and To VPL of thalamus, reticular formation, and

hypothalamushypothalamus Spinal and supraspinal autonomic Spinal and supraspinal autonomic

reflexesreflexes

Summary pointsSummary points Viscerosensory afferentsViscerosensory afferents1.1. SympatheticSympathetic

Mostly nociceptorsMostly nociceptors Referred pain due to collaterals with somatosensory Referred pain due to collaterals with somatosensory

afferentsafferents

2.2. ParasympatheticParasympathetic Mostly physiologic receptorsMostly physiologic receptors Bowel, bladder, baroreflexBowel, bladder, baroreflex

Information goes to reticular formation, Information goes to reticular formation, periaqueductal gray, VPL and intralaminar periaqueductal gray, VPL and intralaminar nuclei of thalamus, hypothalamus, and cortexnuclei of thalamus, hypothalamus, and cortex

Brief chapter but essential to neurophysiologyBrief chapter but essential to neurophysiology