Visceral pain

Question 1

What is the enteric nervous system

Answer 1

ENS is considered as the “brain of the gut”
ENS consists of more than 100 million (400 – 600 million in humans) intrinsic neurones that extend most of the length of the GI tract

Question 2

What is the enteric nervous system arranged into

Answer 2

ENS is arranged in ganglionated plexuses with interconnecting bundles of unmyelinated nerve fibres
ganglion- cell body of neurones- plexus- unmyelinated nerve fibres that connect ganglia or supply organs

Question 3

What are the functions of the enteric nervous system

Answer 3

ENS enables the GI tract to perform its basic reflex functions of secretion, absorption, mixing and gut movements without the influence of the central nervous system (CNS) or autonomic nervous system (ANS)
However, the CNS via the sympathetic and parasympathetic nerves communicate with the intrinsic neurones of the ENS and bring about modulation GI tract functions
Axons of the intrinsic neurones of ENS also project to sympathetic ganglia, the pancreas, gall bladder, trachea, spinal cord and brain stem.

Question 4

Describe the myenteric plexus

Answer 4

Myenteric plexus (of Auerbach)
Found in the muscularis of the gut wall
Controls longitudinal and circular muscle in peristalsis and contractions

Question 5

Describe the submucosal plexus

Answer 5

Submucosal plexus (of Meissner)
works with secretory glands and smooth muscle wall (muscularis mucosae)- controls contraction and relaxation of the inner lining of the gut wall

Question 6

Describe the distribution of the enteric nervous system

Answer 6

The intrinsic network of neurons of the ENS is situated in the tissues of the gut wall from oesophagus to anus

Question 7

What is meant by the autonomic nervous system

Answer 7

The structure of the ANS is different from that of the somatic NS (e.g. ganglia, myelination, neuro-transmitters)

2 divisions of the ANS, sympathetic and parasympathetic, innervate organs of the abdomen & pelvis

Question 8

Describe the ANS

Answer 8

They arise from different anatomical regions of the CNS
The sympathetic nervous system arises from spinal cord segments T1-L2
The parasympathetic system arises from cranial nerves III, VII, IX, X (oculomotor, facial, glossopharyngeal & vagus) in the brain stem, and spinal cord segments S2-4

Question 9

Summarise the functions of the ANS supply to the abdomen

Answer 9

Efferent nerves:
motor to smooth muscle
secretomotor to glands
Afferent nerves:
Sympathetic: pain
Parasympathetic: specific functional sensation, e.g. stretch

Question 10

Outline the sympathetic innervation of the abdomen and pelvis

Answer 10

Preganglionic sympathetic fibres may pass through the sympathetic trunk and paravertebral ganglia without synapsing, together with similar fibres from other levels form splanchnic nerves (greater, lesser, least, lumbar and sacral), which pass into the abdomen and pelvic regions.
These preganglionic fibres are derived from T5-L2
The splanchnic nerves generally connect with sympathetic ganglia around the roots of major arteries that branch from the abdominal aorta
These ganglia are part of a large prevertebral plexus that also has input from the parasympathetic nervous system
Postganglionic fibres are distributed in extensions from the plexus, predominately along arteries, to viscera in the abdomen and pelvis

Question 11

Describe the greater splanchnic nerves

Answer 11

Arise from t5-T9 paravertebral galglia
Pre-ganglionic
Travel to coeliac ganglion in the abdomen (part of the prevertebral plexus)

Question 12

Describe the lesser splanchnic nerves

Answer 12

Arise from T10-T11 paravertebral ganglia- travel to aorticorenal ganglia

Question 13

Describe the least splanchnic nerve

Answer 13

T12

Travels to renal plexus

Question 14

Describe the lumber splanchnic nerves

Answer 14

2-4 lumbar splanchnic nerves which pass from the lumbar part of the sympathetic trunk and enter the prevertebral plexus.

Question 15

Describe the sacral splanchnic nerves

Answer 15

Pass from sacral part of the sympathetic trunk

Enter inferior hypogastric plexus, which is an extension of the prevertebral plexus into the pelvis

Question 16

What happens in the sacral region

Answer 16

Preganglionic PSNs fibres form special visceral nerves (the pelvic splanchnic nerves)- which originate from the anterior rami of S2-S4 and enter pelvic extensions of the prevertebral plexus formed in the abdominal aorta
In organs of the G.I system, the preganglionic fibres synapse directly on neurons in the ganglia of the enteric nervous system
THERE ARE NO POSTGANGLIONIC PSNS MOTOR NEURON IN THE PATHWAY.

Question 17

Summarise the parasympathetic supply

Answer 17

From vagus and sacral outflow

Question 18

Describe the parasympathetic innervation of the vagus nerve

Answer 18

Provide parasympathetic innervation to the foregut and midgut (everything until distal one third of transverse colon)
These branches contain preganglionic parasympathetic fibres and visceral afferent fibres, which are distributed with the other components of the prevertebral plexus along the branches of the abdominal aorta.

Question 19

Describe the pelvic splanchnic nerves

Answer 19

Carry parasympathetic preganglionic fibres from the S2-S4 anterior rami
Enter inferior hypogastric plexus of the pelvis
Some fibres move upwards into the inferior mesenteric part of the prevertebral plexus
Once there, these fibres are distributed with branches of the inferior mesenteric artery and provide parasympathetic innervation of the hindgut.

Question 20

Summarise the distribution of the autonomic nerves

Answer 20

To peripheral vessels and skin
(sympathetic only):
Sympathetic nerves run with somatic nerves to the same region

To organs (viscera) lacking somatic innervation:
most nerves run with the arteries to the same organs
there are a few cases where autonomic nerves run separately

Question 21

Describe sympathetic innervation of skin and blood vessels

Answer 21

Follow the somatic nerves to the periphery (glands, smooth muscle)

Question 22

Describe sympathetic innervation of the viscera

Answer 22

Sympathetic nerves run with the arteries

Question 23

Summarise autonomic plexuses and ganglia

Answer 23

The autonomic nerves to the abdomen are routed via plexuses* surrounding the aorta and its branches.

Sympathetic nerves synapse at ganglia associated with these plexuses.

Plexuses and ganglia are named according to the associated blood vessels (e.g. coeliac plexus and ganglia, renal plexus and ganglia).

Question 24

What is meant by a plexus

Answer 24

*Plexus = interconnecting network of nerves (or vessels)

Question 25

List the autonomic plexuses and ganglia

Answer 25

Superior mesenteric 
ganglion
Coeliac trunk & ganglion
Inferior mesenteric 
ganglion
Sympathetic trunk 
& ganglion
Superior hypogastric plexus
Inferior hypogastric plexus

Question 26

Describe the organ supply of the plexuses

Answer 26

Coeliac Artery T5-9 / X 
SMA T10-11 / X 
Renal Arteries T10-12 / X 
Gonadal Arteries T10-11 / X 
IMA T12-L2 / S2-4 
Sup/Inferior Hypogastric Plexuses T12-L2 / S2-4

Question 27

Summarise referred pain

Answer 27

The cerebral cortex of the brain has no ‘sensory map’ for visceral organs and the diaphragm. w we Image the Human Body?
Therefore, the brain cannot localise pain sensation from these structures.
In these cases, pain is referred to the regions of skin supplied by nerves with the same segmental supply (dermatomes).
In the abdomen, the nerve supply to the organs is autonomic.

Question 28

Define what is meant by a dermatome

Answer 28

Definition: An area of skin supplied by a single spinal nerve (i.e. single segment of the spinal cord)

Question 29

What is a consequence of adjacent dermatomes overlapping

Answer 29

Adjacent dermatomes overlap so that on the trunk, at least three spinal nerves would have to be blocked to produce a region of complete anaesthesia
damage 2 or 3 dermatomes before loss of sensation

Question 30

What is special about C1

Answer 30

No dermatome

Question 31

Describe pain from foregut structures

Answer 31

Foregut (organs supplied by coeliac trunk)
Afferent pathway- Greater splanchnic nerve T7/T8
Epigastric pain: pain from foregut structures (as far as duodenal papilla) is referred to this region.
Structures involved: Stomach, proximal duodenum, pancreas, liver, gall bladder.

Question 32

Describe referred pain from midgut structures

Answer 32

Midgut (organs supplied by superior mesenteric artery)
Afferent pathway; lesser splanchnic nerve (T10)
Afferent pain fibres from midgut structures enter the spinal cord at T10 segment.
Skin of umbilical region is also supplied by T10 spinal nerve

Question 33

Describe umbilical pain associated with referred pain from midgut structures

Answer 33

Umbilical pain: pain from midgut structures (from duodenal papilla to splenic flexure) including inflamed appendix referred to periumbilical region. It is usually colicky (intermittent with bowel contractions)

Question 34

Describe the progress of pain in appendicitis

Answer 34

When the inflammation of the appendix spreads to the surrounding peritoneum the pain becomes localized and constant at the right inguinal region.
Movement of the hip joint, coughing elicits pain. becomes sharp and constant
T12/L1 – Inguinal region

Question 35

Describe referred pain from hindgut structures

Answer 35

Hindgut (organs supplied by inferior mesenteric artery) and lower ureter
Afferent pathway: lumbar splanchnic nerve and least splanchnic nerve
T12/L1-2-suprapubic (hypogastric) region
Suprapubic (hypogastric) pain: pain from hindgut structures, descending colon to anal canal is referred here

Question 36

Describe referred pain

Answer 36

Sensory information comes to the spinal cord from one location but is interpreted by the CNS as coming from another location innervated by the same spinal cord level
Usually happens with the gut- which has a low amount of sensory input- these afferents converge on neurons at the same spinal cord level that receive information from the skin

Question 37

Describe how pain can be referred from one somatic region to another

Answer 37

Irritation of the peritoneum of the inferior surface of the diaphragm, which is innervated by the phrenic nerve, can be referred to the skin on the top of the shoulder, which is innervated by somatic nerves arising at the same spinal cord level