Innervation of the GI Tract
GI tract is made of smooth muscle
●innervation is from autonomic system
● parasympathetic (for peristalsis)
● sympathetic (for regulation of blood flow)
88
Posterior vagal
trunk
L. greater
splanchnic nerve
Celiac ganglion
Lesser and least
splanchnic nerves
Superior
mesenteric
ganglion
Left sympathetic
trunk
Inferior mesenteric
ganglion
Superior
hypogastric
plexus
R and L
hypogastric
nerves
Right inferior
hypogastric
plexus
89
Greater, lesser,
least splanchnic
nerves
Vagus n.
Celiac
ganglion
T5 -T9
Superior
mesenteric
ganglion
T10
T11
T12
Aorticorenal
ganglion
L1
L2
S2
S3
Sacral
splanchnic
n.s
Lumbar
splanchnic n.s
Inferior
mesenteric
ganglion
S4
90
Pelvic splanchnic n.s
91
Nerves
(sympathetic,
parasympathetic,
afferent)
Myenteric
(Auerbach’s)
plexus
Mesentery
Submucosal
(Meissner’s)
plexus
Submucosa
Circular muscle
92
Vagus nerve
provides
parasympathetic
innervation up to
proximal 2/3 of
transverse colon
Pelvic Splanchnic Nerves
93
Hirschsprung’s Disease
● Congenital absence of enteric parasympathetic ganglia
in distal colon
→Absence of peristalsis
→ Dilation of proximal colon
→ Constipation, failure to pass
meconium, distension of abdomen
● 1 case / 5000-7000 births
94
Motility of the Large Intestine
• Haustral contractions
– Slow segmenting movements that move the
contents of the colon
– Haustra sequentially contract as they are
stimulated by distension
• Presence of food in the stomach:
– Activates the gastrocolic reflex
– Initiates peristalsis that forces contents toward
the rectum
95
Defecation
• Distension of rectal walls caused by feces:
– Stimulates contraction of the rectal walls
– Relaxes the internal anal sphincter
• Voluntary signals stimulate relaxation of the
external anal sphincter and defecation
occurs
96
Defecation
External anal sphincter is
contracted by voluntary
motor stimulation from
pudendal nerve
97
Parasympathetic stimulation
relaxes internal anal sphincter –
which is normally contracted by
sympathetic stimulation – when
rectum is distended, and
prepares for defecation
Visceral Afferents and Referred Pain
dorsal root ganglion
Visceral sensory nerves [GVA]
• run with sympathetic &
parasympathetic nerves
• cell bodies in dorsal root ganglion
• nerve ending in viscera
Somatic sensation:
• conscious, sharp, well-localized
• touch, pain, temperature, pressure, proprioception
Visceral sensation:
• often unconscious; if conscious: dull, poorly-localized
98
• distension, blood gas, blood
pressure, cramping, irritants
Visceral Afferents and Referred Pain
Referred Pain:
• Pain originating in a visceral structure
perceived as being from an area of skin
innervated by the same segmental
level as the visceral afferent
• Results from convergence of somatic &
visceral afferents on the same
segmental level of the spinal cord
• “Cross-talk” in the dorsal horn
somatic afferent
www.merck.com
99
visceral afferent
convergence &
“cross-talk”
T10 dermatome = umbilicus
100
Point-Specific Referred Pain Travels Along
Sympathetic Fibers
Splanchnic Nerves
Ganglion
Viscera
Region of
referred pain
Greater – T5 – T9
Celiac
- Foregut
Epigastric
Lesser – T10/T11
Sup. Mesenteric – Midgut
Periumbilical
Least – T12
Aortico-renal
Kidneys
Lower Thoracic
Lumbar – L1/L2
Inf. Mesenteric
Hindgut
Hypogastric
101
Visceral Afferents and Referred Pain
Maps of Referred Pain
Grant’s Atlas 11 2005
102
Overview of the Autonomic Nervous System
Differences between Sympathetic & Parasympathetic
Location of Preganglionic Cell Bodies
Sympathetic
Parasympathetic
Thoracolumbar
Craniosacral
T1 – L2/L3 levels
of the spinal cord
Brain: CN III, VII, IX, X
Spinal cord: S2 – S4
103
Structure of spinal nerves: Somatic pathways
dorsal
ramus
dorsal root
ganglion
dorsal root
spinal
nerve
dorsal
horn
CNS
interneuron
somatic
sensory
nerve
(GSA)
ventral somatic
ramus motor
ventral
horn
nerve
ventral root
Mixed Spinal
Nerve
gray ramus
communicans
sympathetic
ganglion
104
(GSE)
white ramus
communicans
Structure of spinal nerves: Sympathetic pathways
dorsal
ramus
intermediolateral
gray column
spinal
nerve
ventral
ramus
gray ramus
communicans
sympathetic
ganglion
105
white ramus
communicans
Sympathetic System: Postganglionic Cell Bodies
1. Paravertebral ganglia
• Located along sides of vertebrae
• United by preganglionics into Sympathetic Trunk
• Preganglionic neurons are thoracolumbar (T1–L2/L3)
but postganglionic neurons are cervical to coccyx
• Some preganglionics ascend or descend in trunk
Paravertebral
ganglia
sympathetic
trunk (chain)
synapse at
same level
Prevertebral
ganglia
• celiac ganglion
• sup. mesent. g.
• inf. mesent. g.
ascend to
synapse at
higher level
descend to
synapse at
lower level106
aorta
Moore’s COA5 2006
Sympathetic System: Postganglionic Cell Bodies
2. Prevertebral (preaortic) ganglia
• Located anterior to abdominal aorta, in plexuses
surrounding its major branches
• Preganglionics reach prevertebral ganglia via
abdominopelvic splanchnic nerves
Paravertebral
ganglia
sympathetic
trunk (chain)
Prevertebral
ganglia
• celiac ganglion
• sup. mesent. g.
• inf. mesent. g.
abdominopelvic
splanchnic
nerve
aorta
107
Moore’s COA5 2006
Sympathetic System: Summary
visceral tissues
(organs)
Cardiopulmonary Splanchnics:
postganglionic fibers to thoracic
viscera
somatic tissues
(body wall, limbs)
T1
postganglionics
via 31 spinal
nerves
to somatic tissues
of neck, body wall,
and limbs
sympathetic
trunk
Moore’s COA5 2006
Abdominopelvic Splanchnics:
preganglionic fibers to
prevertebral ganglia,
postganglionic fibers to
abdominopelvic viscera
L2
prevertebral
108
ganglia
Parasympathetic
Pathways
Cranial outflow
• CN III, VII, IX, X
• Four ganglia in head
• Vagus nerve (CN X) is major
preganglionic parasymp.
supply to thorax & abdomen
• Synapse in ganglia within
wall of the target organs (e.g.,
enteric plexus of GI tract)
Sacral outflow
• S2–S4 via pelvic splanchnics
• Hindgut, pelvic viscera, and
external genitalia
109
Clinical Relevance
» Surgery for colorectal cancer
puts pelvic splanchnics at risk
» Damage causes bladder &
sexual dysfunction
sympathetic motor fibers
Splanchnic Nerves
Greater: T5 – T9
2
Lesser: T10, T11
Least: T12
Lumbar: L1,L2
1
Pelvic: S2-S4
3
110
Greater, lesser,
least splanchnic
nerves
Vagus n.
Celiac
ganglion
T9
Superior
mesenteric
ganglion
T10
T11
T12
Aorticorenal
ganglion
L1
L2
S2
S3
Sacral
splanchnic
n.s
Lumbar
splanchnic n.s
Inferior
mesenteric
ganglion
S4
111
Pelvic splanchnic n.s
Visceral Afferents and Referred Pain
Maps of Referred Pain
Grant’s Atlas 11 2005
112