Innervation of the male pelvis.
Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be talking about the nerves of the male pelvis. Essentially what we’re going to be doing here on this tutorial is covering the innervation of the male pelvis and its viscera, a fancy word for organs. We’re also going to be seeing this image that you now see on the screen which is an image of a cut of the male pelvis where we cut and removed then the right part and are left now with the lateral left part of the male pelvis. You can clearly see here a few main structures. One of then, the bladder. You also see here the rectum, the prostate, a lot more structures that we’re going to be covering. But, essentially, what we’re going to be doing is highlighting these yellow structures which are then the nerves of the male pelvis.
Now, the innervation of the male pelvis involves both somatic nerves for motor and sensory functions. In addition, visceral nerves or autonomic for the innervation of then the organs or the viscera. So, let’s starts with the somatic nervous system which is then responsible for motor and sensory functions. We’re going to have a quick overview on the somatic nervous system and the autonomic nervous system as this will help us in further understanding the role and function of the nerves we will later describe on this tutorial.
Now, the somatic nervous system is a division of the peripheral nervous system which you probably know very well as the PNS that is then associated with voluntary control of body movement carried out by skeletal muscles. It is comprised of efferent and afferent nerves and can be divided into three groups: the spinal nerves, cranial nerves and associated nerves. We’d like to also briefly talk about the autonomic nervous system – quick overview – and this is also part of the peripheral nervous system. This division of the PNS is then regulated by the hypothalamus in the brain and it influences the function of your internal organs, for example. It is responsible for several functions including but not limited to then regulation of your heart rate, respiratory rate, pupillary response, digestion, urination, and even sexual arousal.
The autonomic nervous system is then divided into the sympathetic nervous system and the parasympathetic nervous system. For more detailed information on these two divisions of the autonomic nervous system, please check out our tutorial on the nerves of the heart or the innervation of the heart.
For purpose of this tutorial, we will be then discussing the nerves of the pelvis beginning with the somatic nerves and finally ending with then the autonomic nerves of the pelvis. Starting with then the quick list of the somatic nerves of the male pelvis and they are then the obturator nerve, the pudendal nerve, the inferior rectal nerves, the dorsal nerve of penis, the perineal nerve, and the posterior scrotal nerves.
We’re going to start off then with the very first one here on the list that you can see on this image – notice this green highlight – this is known as the obturator nerve. Now, this one arises from the anterior or also known the ventral division of the lumbar nerves at the level of L2 to L4 lumbar vertebrae – so the second to fourth lumbar vertebrae. This nerve gives off an anterior branch, a posterior branch, and a cutaneous branch. The branches of the obturator nerve will be providing motor innervation to the adductor muscles of the lower limb but not to the obturator internus – just a reminder here.
We’re going to move on to the next slide, still on the obturator nerve, but this time, I would like to show you from a different perspective here now from an anterior view of the pelvis and also a bit of the lumbar vertebrae – as you can see here – and notice the obturator nerve then highlighted in green. This nerve will also be providing sensory innervation to the skin on the medial aspect of the thigh. As you can see here on this image, the obturator nerve passes beneath the psoas major muscle and then eventually through the obturator canal.
The next image that we’re going to be seeing here and that is highlighted – notice this structure here – this nerve that is now highlighted is known as the pudendal nerve. This is the major somatic nerve of the perineum. It is a paired nerve that arises from the level of S2 to S4 vertebrae. It provides sensory innervation to external genitalia including the skin around the anus and the perineum. I can also show you here an image now of the dorsal view of the pudendal nerve highlighted in green. Just for a bit of location, you see here the coccyx, the sacrum, a bit of the hip bone then you see here the pudendal nerve. To also add here that this nerve will be providing motor innervation to muscles of the perineum and the floor of the pelvis. The pudendal nerve leaves the pelvic cavity through the greater sciatic foramen and enters the anal triangle of the perineum. You can also see here on this image how it exits the greater sciatic foramen.
The next nerves that we’re going to be seeing here highlighted on this image – notice these really thin nerves here – that are known as the inferior rectal nerves. The inferior rectal nerves arise from the level of S3 to S4 vertebrae and these nerves usually are branches of the pudendal nerve but have also been known to arise directly from the sacral plexus in some cases. The inferior rectal nerves provide motor innervation to the external anal sphincter and sensory innervation to the skin around the anus.
For the next image that we’re going to be highlighting here, notice these nerves – really thin nerves along this image – these are known as the dorsal nerve of the penis. This is another branch of the pudendal nerve. It is a paired nerve found on the dorsum of the penis. It is the deepest branch of the pudendal nerve and also gives off branches to the lower side of the penis. This nerve is mainly sensory and provides innervation to the skin of the penis.
Next, we’re going to be seeing then these highlighted nerves – notice here – these are known as the posterior scrotal nerves. The posterior scrotal nerves are the largest of the sensory braches of the perineal nerve. These 2 nerves found medially and laterally correspond to the posterior labial nerves found in the female pelvis. They will be innervating the then the scrotum – the skin of the scrotum – and then communicate with the posterior femoral cutaneous nerve via its perineal branch.
Now, that we have covered the somatic nerves of the male pelvis, it’s time to move on to the visceral or autonomic nerves that innervate this particular region of the body. The autonomic nerves of the pelvis – as I mentioned at the beginning of this tutorial – are the nerves to the pelvic viscera and whose function is to regulate unconscious or involuntary functions. The parts of the ANS or autonomic nervous system found in the male pelvis that I will discuss in the coming slides include then the lumbar ganglion on the sympathetic trunk, of the sympathetic trunk; also the lumbar splanchnic ganglion, gray ramus communicans, the superior hypogastric plexus, the hypogastric nerve, the inferior hypogastric plexus, the inferior rectal plexus, also the middle rectal plexus, the prostatic plexus, the cavernous nerves of penis, the deferential plexus, the vesical plexus, the pelvic splanchnic nerves, and, finally, the iliac plexus.
And starting off with the very first one of this long list – this one that you see here highlighted in green – is known as the lumbar ganglion of the sympathetic trunk. First, let’s understand a bit about the lumbar ganglia of the sympathetic trunk. Now, these are four ganglia found on the lumbar portion of the sympathetic trunk. Now, these ganglia are located on either side of the lumbar vertebral column and are also known as paravertebral ganglia. The lumbar splanchnic nerves and the gray rami communicantes arise from the lumbar ganglia.
We’re going to move on to the next highlight which you see here on the superior portion of this image – this highlighted nerve – which is then the lumbar splanchnic nerves. As I just mentioned in the previous slide, the lumbar splanchnic nerves arise from the lumbar ganglia of the sympathetic trunk at the level of L1 and L2 vertebrae. Now, these four nerves are comprised of general visceral fibers as well as preganglionic sympathetic fibers. The postsynaptic fibers provide then innervation to the hindgut and to the lower ureter as well as to the smooth muscle of the pelvic viscera.
Next image that we’re going to be highlighting here – these structures that you now see on this image highlighted – are known as the gray ramus communicans. This is singular because plural will be gray rami communicantes. Now, the gray rami communicantes also arise from the lumbar ganglion on the sympathetic trunk and carry postganglionic sympathetic fibers from the sympathetic ganglia to then the spinal nerves and they provide a branch to each of the spinal nerves. These gray rami communicantes provide innervation via the appropriate spinal nerves to the smooth muscles and glands of the abdominal wall and lower limbs.
The next structure that we’re going to be highlighting here – notice here on the image – we’re now looking at the superior hypogastric plexus. Now, this structure will be receiving branches from the lumbar ganglia of the sympathetic trunk via the lumbar splanchnic nerves at the level of L1 and L2 lumbar vertebrae. This plexus is located anterior to the bifurcation of the abdominal aorta as you can see here – this is the abdominal aorta and here is where the bifurcation is happening – and then continues as the left and right hypogastric nerves which we will also talk about on the next slides. Connects the abdominal and inferior hypogastric plexuses and this plexus gives off branches to the ureter and genital organs, in this case, would be then the epididymis and testes. We can even zoom in here a bit more so you can clearly see here then the superior hypogastric plexus.
But now we’re going to move on to the next slide where we’re highlighting two structures that I already mentioned on the previous slide. On the left image, you see then the left hypogastric nerve and on the right image, you see then the right hypogastric nerve. The left and right hypogastric nerves are the right and left branches of the superior hypogastric plexus that we talked about, which you can also see here on these images. These two nerves together go on to form the inferior hypogastric plexus. The left and right hypogastric nerves contain both pre- and post-ganglionic sympathetic fibers from the level of T10 to L2 vertebrae.
Next image that we’re going to be looking at is now an image where you don’t see any highlight because I just wanted to briefly talk about the inferior hypogastric plexus which is the continuation of the left hypogastric nerve and also the right hypogastric nerve so as you could see here where we would be on the image. Now, these are the terminal branches of the left and right hypogastric nerves as I mentioned in the previous two slides and they form the then inferior hypogastric plexus. Now, since it is a paired structure, the inferior hypogastric plexus is found on either side of the rectum.
Aside from the hypogastric nerve, the inferior hypogastric plexus also receives contributions of sympathetic fibers from the lumbar and sacral splanchnic nerves L1 to L2 as well as pelvic parasympathetic fibers from S2 to S4 and pelvic splanchnic nerves. This plexus gives rise to numerous branches which will innervate the viscera of the pelvis which we will discuss further in the next slides.
Next slide will be then this structure that you see here highlighted in green which is known as the inferior rectal plexus. Now, some of the branches of the inferior hypogastric plexus form the inferior rectal plexus which passes to both sides of the rectum. On this image, you can see here, they are located then on the right side of the rectum. This autonomic nerve plexus which is located around the branches of the internal iliac artery provides innervation to the lower part of the rectum.
On the next image, we’re going to be highlighting these structures which are known as then the middle rectal plexus. The middle rectal plexus which is also a continuation of the inferior hypogastric plexus provides innervation to the middle part of the rectum.
We’re going to be seeing another plexus here now highlighted on this part of the image. This is known as the prostatic plexus. Now, the nerves of the prostatic plexus which also receive fibers from the inferior hypogastric plexus – as the name suggests – are then located around the prostate which you can see here – this structure – specifically on the posterior and inferior surfaces of the prostate. The nerves also extend as far as the membranous part of the urethra as well as to the seminal vesicles, the ejaculatory duct, the bulbourethral bulb, and corpus cavernosum.
The next structures we will be highlighting here on this image – notice these structures highlighted – which are known as the cavernous nerves of the penis. The cavernous nerves of the penis arise from cell bodies in the inferior hypogastric plexus and are comprised of greater cavernous and lesser cavernous nerves. Now, these nerves arising from the prostatic plexus provide then innervation to the cavernous bodies of the penis facilitating then erection.
The next structure we’re going to be talking about that you see here – these really thin nerves highlighted in green which are surrounding this structure – these are known as the deferential plexus. The deferential plexus is another autonomic plexus of nerves that arises from the inferior hypogastric plexus. The nerves from this plexus are found around the ampulla of the ductus deferens as well as the seminal vesicle.
Next on the next slide, we’re going to be seeing these more prominent highlights, these structures which are then the vesical plexus. The vesical plexus is the final plexus that arises from the inferior hypogastric plexus and it is located on either side of this organ here, the urinary bladder, and then regulates the emptying mechanism of this organ. This plexus comprises parasympathetic fibers and its nerve fibers accompany the vesical arteries.
Next slide we’re going to highlighting here these structures – notice here – now these really thin nerves which are known as the pelvic splanchnic nerves. Now, that we have covered the inferior hypogastric nerve and its branches, we are now going to move on and talk about the next autonomic nerves of the pelvis which are the pelvic splanchnic nerves, these that we’re now highlighting. They arise from the anterior rami of spinal nerves at the level of S2 to S4. They are comprised of parasympathetic fibers as well as afferent fibers and provide innervation to the pelvic and genital organs. They also regulate evacuation of the urinary bladder, erection, and opening and closing of the internal urethral sphincter and even play a role in the motility of the rectum.
Last structure we’re going to be highlighting here on this tutorial, notice these structures that are here – these really thin nerves here on this image – these are known as the iliac plexus. So, this is the last autonomic plexus of the male pelvis that we will be looking at. It is an autonomic nerve plexus that is arising from the abdominal aortic plexus and the nerves from the iliac plexus are found on both iliac arteries.
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Now, good luck everyone, and I will see you next time.