Chapter 19 Viscerosensory Pathways MP. Thibeault-Eybalin, R4 Academic Half-Day March 25 th, 2009

Outline In parallel to somatosensory system conveying info from external environment, viscerosensory system conveys info about internal environment In parallel to somatosensory system conveying info from external environment, viscerosensory system conveys info about internal environment Viscerosensory receptors, fibers, ascending sympathetic and parasympathetic pathways Viscerosensory receptors, fibers, ascending sympathetic and parasympathetic pathways Examples of reflexes based on above Examples of reflexes based on above

Viscerosensory receptors 2 types 1. Nociceptors Free nerve endings of Aδ and C fibers located in heart, respiratory, GI and GU tracts Free nerve endings of Aδ and C fibers located in heart, respiratory, GI and GU tracts Project to Lamina 1 and 5 in dorsal horn Project to Lamina 1 and 5 in dorsal horn Mediate visceral pain, e.g. angina pectoris Mediate visceral pain, e.g. angina pectoris 2. Physiologic receptors Mechanoreceptors Mechanoreceptors Rapidly adapting, e.g. cough Rapidly adapting, e.g. cough Slowly adapting, e.g. full stomach or urinary bladder Slowly adapting, e.g. full stomach or urinary bladder Baroreceptors, e.g. baroreflex Baroreceptors, e.g. baroreflex Chemoreceptors, e.g. in carotid and aortic bodies Chemoreceptors, 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 hypothalamus Internal thermal receptors, e.g. core temperature in hypothalamus

Classification of viscerosensory receptors and their respective stimuli

A) Baroreceptor B) Chemoreceptor

Viscerosensory fibers A.K.A. General visceral afferents A.K.A. General visceral afferents Travel with general visceral efferents in Travel with general visceral efferents in Sympathetic nerves Sympathetic nerves e.g. splanchnic and cardiac nerves e.g. splanchnic and cardiac nerves Efferents>afferents Efferents>afferents Mainly info from nociceptors Mainly info from nociceptors Parasympathetic nerves Parasympathetic nerves e.g. vagus and pelvic nerves e.g. vagus and pelvic nerves Afferents>efferents Afferents>efferents Mainly info from physiologic receptors Mainly info from physiologic receptors

Ascending sympathetic pathways Mainly nociceptive info from thoracic and abdominal viscera via splanchnic and cardiac nerves Mainly nociceptive info from thoracic and abdominal viscera via splanchnic and cardiac nerves Cell bodies are in DRG T1 to L2 Cell bodies are in DRG T1 to L2 Synapse onto 2 nd order neurons Synapse onto 2 nd order neurons Afferent Afferent In lamina 1 and 5, cross through anterior white commissure to project to ALS contralaterally, about 2 sensory levels higher → VPL of thalamus → inferolateral post-central gyrus (parietal opeculum) and insular cortex In lamina 1 and 5, cross through anterior white commissure to project to ALS contralaterally, about 2 sensory levels higher → VPL of thalamus → inferolateral post-central gyrus (parietal opeculum) and insular cortex In lamina 7 and 8 to project to spinoreticular tracts bilaterally In lamina 7 and 8 to project to spinoreticular tracts bilaterally → periaqueductal gray → dorsal longitudinal fasciculus → mesencephalic reticular formation → mammillary peduncle and medial forebrain bundle → ultimately to hypothalamus and intralaminar thalamic nuclei Efferent Efferent In intermediolateral column at same level → anterior horn → pre-ganglionic sympathetic efferent In intermediolateral column at same level → anterior horn → pre-ganglionic sympathetic efferent Large receptive fields in brain, poorly localizing Large receptive fields in brain, poorly localizing

1 st order visceral afferent 2 nd order visceral afferent Visceral efferent

→ dorsal longitudinal fasciculus → mammillary peduncle and medial forebrain bundle

Referred pain Noxious stimuli originating from visceral organs are perceived as arising from somatic tissues (skin, bone, muscle, etc.) Noxious stimuli originating from visceral organs are perceived as arising from somatic tissues (skin, bone, muscle, etc.) Whose afferents enter the spinal cord at the same level Whose afferents enter the spinal cord at the same level Due to collateral synapses between visceral and somatic afferents in dorsal horn Due to collateral synapses between visceral and somatic afferents in dorsal horn Example: Angina pectoris Example: Angina pectoris Pain referred to retrosternal area and left ± right arms, neck, jaw, TMJ Pain referred to retrosternal area and left ± right arms, neck, jaw, TMJ

Classic patterns of referred pain

Angina pectoris Sympathetic trunk

Ascending parasympathetic pathways (cranial and sacral) Cranial Cranial Only CN 9 and 10 have significant parasympathetic afferents Only CN 9 and 10 have significant parasympathetic afferents CN 9 CN 9 Chemoreceptors from carotid bodies Chemoreceptors from carotid bodies Baroreceptors from carotid sinus wall Baroreceptors from carotid sinus wall Nociceptors from oropharynx (afferent limb for gag reflex) Nociceptors from oropharynx (afferent limb for gag reflex) CN 10 CN 10 Chemoreceptors and baroreceptors in aortic arch Chemoreceptors and baroreceptors in aortic arch Physiologic receptors from thoracic and abdominal viscera above splenic flexure of colon Physiologic receptors from thoracic and abdominal viscera above splenic flexure of colon Both enter skull through jugular foramen Both enter skull through jugular foramen Cells bodies located in INFERIOR ganglia of CN 9 and 10 Cells bodies located in INFERIOR ganglia of CN 9 and 10 Superior ganglia contain cell bodies of somatic afferents Superior ganglia contain cell bodies of somatic afferents Synapse onto 2 nd order neuron in solitary nucleus Synapse onto 2 nd order neuron in solitary nucleus Mediate vasopressor and vasodepressor responses Mediate vasopressor and vasodepressor responses

Dual role of solitary nucleus in baroreflex Reticular formation Hypothalamus

Ascending parasympathetic pathways Sacral Sacral Parasympathetic afferents from S2-3-4 travel through pelvic nerves, then spinal nerves Parasympathetic afferents from S2-3-4 travel through pelvic nerves, then spinal nerves Relay info on bowel and bladder distension Relay info on bowel and bladder distension Via ALS and spinoreticular fibers Via ALS and spinoreticular fibers To VPL of thalamus, reticular formation, and hypothalamus To VPL of thalamus, reticular formation, and hypothalamus Spinal and supraspinal autonomic reflexes Spinal and supraspinal autonomic reflexes

Summary points Viscerosensory afferents Viscerosensory afferents 1. Sympathetic Mostly nociceptors Mostly nociceptors Referred pain due to collaterals with somatosensory afferents Referred pain due to collaterals with somatosensory afferents 2. Parasympathetic Mostly physiologic receptors Mostly physiologic receptors Bowel, bladder, baroreflex Bowel, bladder, baroreflex Information goes to reticular formation, periaqueductal gray, VPL and intralaminar nuclei of thalamus, hypothalamus, and cortex Information goes to reticular formation, periaqueductal gray, VPL and intralaminar nuclei of thalamus, hypothalamus, and cortex Brief chapter but essential to neurophysiology Brief chapter but essential to neurophysiology