Transcript Chapter 19 Viscerosensory Pathways

Chapter 19
Viscerosensory Pathways
MP. Thibeault-Eybalin, R4
Academic Half-Day
March 25th, 2009
Outline



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
Examples of reflexes based on above
Viscerosensory receptors
2 types
1. Nociceptors



2.
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
Mediate visceral pain, e.g. angina pectoris
Physiologic receptors

Mechanoreceptors






Rapidly adapting, e.g. cough
Slowly adapting, e.g. full stomach or urinary bladder
Baroreceptors, e.g. baroreflex
Chemoreceptors, e.g. in carotid and aortic bodies
Osmoreceptors, e.g. osmolarity and ADH production
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
Travel with general visceral efferents in
Sympathetic nerves




e.g. splanchnic and cardiac nerves
Efferents>afferents
Mainly info from nociceptors
Parasympathetic nerves



e.g. vagus and pelvic nerves
Afferents>efferents
Mainly info from physiologic receptors
Ascending sympathetic pathways



Mainly nociceptive info from thoracic and abdominal viscera via
splanchnic and cardiac nerves
Cell bodies are in DRG T1 to L2
Synapse onto 2nd order neurons
 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 7 and 8 to project to spinoreticular tracts bilaterally
→
→
→

Efferent


periaqueductal gray → dorsal longitudinal fasciculus
mesencephalic reticular formation → mammillary peduncle and medial forebrain
bundle
ultimately to hypothalamus and intralaminar thalamic nuclei
In intermediolateral column at same level → anterior horn → pre-ganglionic
sympathetic efferent
Large receptive fields in brain, poorly localizing
1st order visceral afferent
2nd 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.)



Whose afferents enter the spinal cord
at the same level
Due to collateral synapses between
visceral and somatic afferents in
dorsal horn
Example: Angina pectoris

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





Only CN 9 and 10 have significant parasympathetic afferents
CN 9
 Chemoreceptors from carotid bodies
 Baroreceptors from carotid sinus wall
 Nociceptors from oropharynx (afferent limb for gag reflex)
CN 10
 Chemoreceptors and baroreceptors in aortic arch
 Physiologic receptors from thoracic and abdominal viscera above
splenic flexure of colon
Both enter skull through jugular foramen
Cells bodies located in INFERIOR ganglia of CN 9 and 10



Superior ganglia contain cell bodies of somatic afferents
Synapse onto 2nd order neuron in solitary nucleus
Mediate vasopressor and vasodepressor responses
Dual role of solitary nucleus in baroreflex
Reticular formation
Hypothalamus
Ascending parasympathetic
pathways

Sacral
Parasympathetic afferents from S2-3-4 travel
through pelvic nerves, then spinal nerves
 Relay info on bowel and bladder distension
 Via ALS and spinoreticular fibers
 To VPL of thalamus, reticular formation, and
hypothalamus


Spinal and supraspinal autonomic reflexes
Summary points

1.
Viscerosensory afferents
Sympathetic


2.
Parasympathetic




Mostly nociceptors
Referred pain due to collaterals with somatosensory afferents
Mostly physiologic receptors
Bowel, bladder, baroreflex
Information goes to reticular formation, periaqueductal gray,
VPL and intralaminar nuclei of thalamus, hypothalamus, and
cortex
Brief chapter but essential to neurophysiology