Abdominal and pelvic autonomic plexuses and ganglias, enteric system

Abdominal plexuses:

celiac plexus:

located along the celiac trunk and its branches.

• Sympathetic Input:
  • Pre-synaptic Fibres: Received from the greater thoracic splanchnic nerves and the first lumbar splanchnic nerve.
• Parasympathetic Input:
  • Pre-synaptic Fibres: Comes from the celiac branches of the vagus nerve. However, these parasympathetic fibres don’t synapse at the plexus. Instead, they pass through it and travel with the post-synaptic sympathetic fibres to reach their targets.
• Target Innervation: The celiac plexus provides autonomic innervation to several key organs:
  • Oesophagus
  • Stomach
  • Proximal duodenum
  • Kidneys
  • Pancreas
  • Liver
  • Gallbladder
• Ganglia: Includes the right and left celiac ganglia.

---

The superior mesenteric plexus:

Vital nerve network that follows the path of the superior mesenteric artery and its branches. It facilitate communication between the sympathetic nervous system and the digestive organs it innervates.

• Sympathetic Input:
  • Pre-synaptic Fibres: These originate from the celiac plexus, sending sympathetic signals downstream to the superior mesenteric plexus.
• Target Innervation:
  • Organs: The superior mesenteric plexus provides autonomic innervation to:
    • Small intestine
    • Large intestine (up to the distal third of the transverse colon)
• Ganglion: It features an unpaired ganglion known as the superior mesenteric ganglion, which serves as a key center for coordinating autonomic signals in this region.

---

The inferior mesenteric plexus:

It specifically focus on innervating hindgut structures.

• Sympathetic Fibres:
  • Source: Originates from the abdominal aortic plexus and the intermesenteric plexus, providing sympathetic innervation to the structures of the hindgut.
• Parasympathetic Supply:
  • Origin: Derived from spinal cord levels S2-S4, these parasympathetic fibres contribute to the autonomic regulation of hindgut functions.
• Target Innervation:
  • Structures: The inferior mesenteric plexus supplies autonomic control to hindgut structures, which include:
    • Distal part of the transverse colon
    • Descending colon
    • Sigmoid colon
    • Rectum
• Ganglion: An unpaired ganglion known as the inferior mesenteric ganglion serves as a central hub for integrating autonomic signals in this region.

---

The abdominal aortic plexus:

It receives contributions from both the celiac and lumbar splanchnic nerves,integrating sympathetic nerve fibers into its network. It is located anteriorly and along the sides of the abdominal aorta, creating a dense nerve network that envelopes the aorta itself.

Branches:

• Inferior Mesenteric Plexus: This branch extends from the abdominal aortic plexus to provide autonomic innervation to the hindgut, including structures like the distal transverse colon, descending colon, sigmoid colon, and rectum.
• Hypogastric Plexus: Also known as the pelvic plexus, this branch continues the autonomic pathway into the pelvic region, influencing the bladder, reproductive organs, and lower gastrointestinal tract.

---

Pelvic autonomic plexuses:

The superior hypogastric plexus:

Critical autonomic nerve plexus located in the lower abdominal and pelvic regions. More specifically, it is positioned inferiorly to the inferior mesenteric plexus along the abdominal aorta, it crosses over the common iliac artery and it enters the pelvis.

It presents a continuation of the intermesenteric plexus, which receives contributions from sympathetic fibers originating from lower lumbar spinal nerves . ( specifically L3 and L4)

Parasympathetic Input:

This plexus does not contain parasympathetic fibers; its function is primarily sympathetic in nature.

Branching:

Upon entering the pelvis, the superior mesenteric plexus gives rise to the right and left hypogastric nerves. These nerves continue inferiorly to form the inferior hypogastric plexus (also known as the pelvic plexus or pelvic autonomic plexus).

---

The inferior hypogastric plexus:

Complex network of autonomic nerves located within the pelvic cavity. Branches:

• Prostatic Plexus: Provides autonomic innervation to the prostate gland in males.
• Rectal Plexus: Supplies autonomic nerves to the rectum, influencing bowel movements and sensation in the lower part of the rectum.
• Ureteric Plexus: Innervates the ureters, assisting in the regulation of urine transport from the kidneys to the bladder.
• Uterovaginal Plexus: Provides autonomic control to the uterus and vagina in females, regulating functions such as uterine contractions and vaginal sensation.

---

Enteric system:

It is found from esophagus to the anus. It is effected by the parasympathetic and sympathetic systems, but it can also work independently.

The system uses neurotransmitters that are also found in the CNS, and it has more neurons than the spinal cord. It is because of this reason that sometimes we refer to it as the "second brain".

Submucosal (Meissner's) Nervous Plexus:

• Location: Runs within the submucosal layer of the gastrointestinal tract.
• Function: Primarily responsible for regulating the function of glands within the mucosa and controlling blood supply to the intestinal wall. It plays a crucial role in coordinating secretion and absorption activities in the gut.

Myenteric (Auerbach's) Nervous Plexus:

• Location: Positioned between the circular and longitudinal layers of smooth muscles in the gastrointestinal tract.
• Function: This plexus is instrumental in controlling the muscles of the gut wall, including the coordination of peristalsis—the wave-like muscular contractions that propel food and digestive materials through the digestive tract. It helps regulate the movement and mixing of contents within the intestines.

Its cells consist of unipolar and bipolar neurons and associated with supporting cells that resemble astrocytes, which originate from the neural crest.

reference:

Salvador final notes