Lumbar and sacral parts of the sympathetic trunk
Autonomic innervation of the pelvic region begins with the lower parts of the sympathetic trunk.
Lumbar part includes three to five lumbar ganglia (ganglia lumbalia). Important connecting branches arise from these structures. First, these are grey rami communicantes (rr. communicantes grisei), which run to the lumbar spinal nerves. Second, these are lumbar splanchnic nerves (nn. splanchnici lumbales), which carry sympathetic fibers directly to the abdominal aortic and hypogastric plexuses.
Sacral part of the sympathetic trunk has a distinct topography: it is located on the pelvic (anterior) surface of the sacrum. The trunks run strictly medially relative to the pelvic sacral foramina. In this section, the trunk typically contains 3–4 sacral ganglia (ganglia sacralia). An important anatomical feature is that at the very bottom, the right and left sympathetic trunks converge to form a single unpaired ganglion — ganglion impar. Sacral splanchnic nerves (nn. splanchnici sacrales) arise from the sacral ganglia and travel to the autonomic plexuses of the lesser pelvis, supplementing them with sympathetic fibers.
Superior hypogastric plexus
Superior hypogastric plexus (plexus hypogastricus superior) is the direct anatomical continuation of the abdominal aortic plexus.
Topographically, this large plexus is located in a strictly defined zone: it lies at the level of the aortic bifurcation and extends inferiorly, situated anterior to the bodies of the fifth lumbar and first sacral vertebrae (L5–S1). Descending into the pelvic cavity, this plexus divides into two symmetrical parts — the right and left inferior hypogastric plexuses (plexus hypogastricus inferior).
Inferior hypogastric (pelvic) plexus
Inferior hypogastric plexus (plexus hypogastricus inferior, or plexus pelvicus) is the largest autonomic plexus of the lesser pelvis.
It has a mixed character, as it is formed by two types of nerve fibers:
- Sympathetic fibers: arrive via the lumbar and sacral splanchnic nerves (nn. splanchnici lumbales et sacrales).
- Parasympathetic fibers: arrive as part of the pelvic splanchnic nerves (nn. splanchnici pelvici).
The main function of the pelvic plexus is the innervation of the pelvic organs. In addition, fibers from this major plexus actively participate in the formation of smaller, secondary (organ) plexuses.
Derived pelvic plexuses
From the inferior hypogastric plexus, nerve branches diverge to specific organs, forming specialized secondary plexuses around them. Depending on the patient's sex, the composition of these plexuses has its own anatomical features.
Main derivatives of the pelvic plexus:
- Vesical plexus (plexus vesicalis) — provides innervation to the urinary bladder.
- Prostatic plexus (plexus prostaticus) — present only in males.
- Ductus deferens plexus (plexus deferentialis) — also characteristic exclusively of the male organism.
- Uterovaginal plexus (plexus uterovaginalis) — forms in females to innervate the corresponding organs of the reproductive system.
- Superior and inferior rectal plexuses (plexus rectalis superior et inferior) — are responsible for the innervation of the rectum.
Briefly: answers to topical questions
Which specific organs are innervated by the uterovaginal plexus?
The uterovaginal plexus (plexus uterovaginalis) innervates the vagina, uterus, internal parts of the uterine tubes, and urinary bladder.
Which sensory (afferent) fibers pass through the inferior hypogastric plexus?
Afferent sensory (viscerosensory) fibers coming from the internal organs pass through the inferior hypogastric plexus (plexus hypogastricus inferior). Sources also indicate that afferent fibers from nociceptors and proprioceptors of the urinary bladder wall respond to its distension.
From which spinal cord segments do the pelvic splanchnic nerves receive preganglionic fibers?
The pelvic splanchnic nerves (nn. splanchnici pelvini) receive parasympathetic preganglionic fibers from the sacral spinal cord. Sources indicate segments S2–S4, as well as S3–S5.
Class and exam questions
What fibers form the inferior hypogastric plexus?
It is formed by sympathetic fibers (nn. splanchnici lumbales et sacrales) and parasympathetic fibers (nn. splanchnici pelvici).
Where is the superior hypogastric plexus located?
The plexus is located at the level of the aortic bifurcation, situated anterior to the vertebral bodies of L5–S1.
Which ganglia form the sacral part of the sympathetic trunk?
The sacral part includes 3–4 sacral ganglia (ganglia sacralia), and inferiorly the right and left trunks join into a single unpaired ganglion (ganglion impar).
What else to study on this topic
- Grey rami communicantes of the lumbar part (rr. communicantes grisei)
- Parasympathetic pelvic splanchnic nerves (nn. splanchnici pelvici)
- Sexual differences of secondary pelvic plexuses
- Connection between the superior hypogastric and abdominal aortic plexuses
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