Sacral Plexus
By : Omar M. Subhi Altaie● Overview
• Name
The word Sacral means near or related to the sacrum which is the bone that continues the vertebral column at its end, between the pelvis bone framework. And the word Plexus is simply a network of nerves that are collected in this particular area.
• Origin
It originates from the anterior rami of spinal nerves from S1, S2, S3 , and S4, it also takes contributions from the lumbosacral trunk , when it joins the nerves after they get through the foramina of the sacrum.
Those nerves in turn divided into anterior and posterior branches whiches supply different groups of muscles.
Those nerves in turn divided into anterior and posterior branches whiches supply different groups of muscles.
• Sympathetic trunks
Medial and near to nerves' roots and the foramina they get through, there are the sacral sympathetic trunks, which are the continuation of the lumbar sympathetic trunks above. Each of the sacral trunks usually has four sympathetic ganglia. These trunks send communicat-ing branches (gray rami communicantes) to each of the anterior rami of the sacral and coccygeal nerves.
The main function of the sympathetic trunks is to give sympathetic innervation to the areas where these nerves distribute, such as the vasomotor; which is the control of the blood vessels' diameters, and the pilomotor; whiches are fibers that move and erect the hair in the skin. There are also the sudomotor; whiches control and respond to environmental changes, when the temperature raises, these nerves tend to make the sweat glands excrete sweat to regulate body temperature.
The main function of the sympathetic trunks is to give sympathetic innervation to the areas where these nerves distribute, such as the vasomotor; which is the control of the blood vessels' diameters, and the pilomotor; whiches are fibers that move and erect the hair in the skin. There are also the sudomotor; whiches control and respond to environmental changes, when the temperature raises, these nerves tend to make the sweat glands excrete sweat to regulate body temperature.
• Location
Located within the pelvis muscles and structures from its posterior wall, related anteriorly to the piriformis muscle , and there are vessels of the pelvis anterior to the plexus.
• Significance
This plexus gives motor innervation to such important muscles in the pelvis and posterior of the thigh by the largest nerve in the body that formed here that later divided into its terminal branches tibial and common peroneal . The plexus also gives sensory branches that reach large parts of the thigh, leg, and foot.
● Nerves
The anterior rami of the sacral spinal nerves from S1 to S5 and the lumbosacral trunk, divide into several cords that may combine with other divided cords or continue as terminal nerves that innervate particular areas.
Note : we should say that in this article, we are not going to take all details of each branch, if you are interested to explore more information, please click on the underlined title of any of the branches.
• Superior Gluteal Nerve:-
It originates from the dorsal divisions of the fourth, fifth lumbar, and first sacral spinal nerves. leaves the pelvis through the greater sciatic notch meeting some of the vessels there. It is then divides into two smaller branches the superior one ends in the gluteus minimums and the inferior one gives filaments to the gluteus medius , minimums , and ends in the Tensor fasciæ latæ.
• Inferior Gluteal Nerve:-
It originates from posterior divisions of the fifth lumbar and first and second sacral spinal nerves. From below the piriformis muscle, it leaves the pelvis and divides into many smaller branches that end and innervate the gluteus maximus.
• Sciatic Nerve:-
It is the largest nerve in the body (2 cm in width) originating from the fourth and fifth roots of lumbar, and the first three sacral nerves. It passes below the piriformis muscle from the greater sciatic foramen descending inferiorolatly leaving the pelvis.
The motor innervation of this nerve is to the muscles in the back of the thigh ( hamstring muscles ) and part of adductor Magnus
It is then divides in the apex of the popliteal fossa into two terminal branches Tibial and common peroneal (Fibular) nerves. These two nerves continue to innervate the muscles in the leg and foot and also give sensory innervation to large areas of them.
In a small amount of people the sciatic nerves divide into their two terminal branches before it leaves the pelvis, continuing as two separated nerves innervating different groups of muscles.
The motor innervation of this nerve is to the muscles in the back of the thigh ( hamstring muscles ) and part of adductor Magnus
It is then divides in the apex of the popliteal fossa into two terminal branches Tibial and common peroneal (Fibular) nerves. These two nerves continue to innervate the muscles in the leg and foot and also give sensory innervation to large areas of them.
In a small amount of people the sciatic nerves divide into their two terminal branches before it leaves the pelvis, continuing as two separated nerves innervating different groups of muscles.
Gluteal region and posterior region of right thigh)
• The posterior cutaneous nerve of thigh:-
It originates from the anterior and posterior divisions of the first three sacral nerves (S1, S2, S3) , it leaves the pelvis through the greater sciatic foramen inferior to the piriformis muscle, giving sensory innervation to the posterior surface of thigh and leg. It also gives sensation to the skin of the perineum.
• Pudendal nerve:-
It originates from anterior divisions of the second, third, and fourth sacral spinal nerves passing anterior to the piriformis muscle it enters the pudendal canal and gives several other branches:-
• perineal nerve originates from the pudendal nerve before or after it exits its canal it gives sensory innervation to part of the posterior of the scrotum in men and the outer part of the female genitals or the vulva, it also give sensation to the mucus membrane of the urethra and vagina, it has some motor innervation to the muscles of the perineum.
• dorsal nerve to the clitoris/penis that gives sensory innervation to skin that covers them.
• inferior rectal nerve that innervates the anal canal which is the last part of the gastrointestinal tract and the surrounding of its inferior portion which is the external anal sphincter, and the skin on the perianal.
• perineal nerve originates from the pudendal nerve before or after it exits its canal it gives sensory innervation to part of the posterior of the scrotum in men and the outer part of the female genitals or the vulva, it also give sensation to the mucus membrane of the urethra and vagina, it has some motor innervation to the muscles of the perineum.
• dorsal nerve to the clitoris/penis that gives sensory innervation to skin that covers them.
• inferior rectal nerve that innervates the anal canal which is the last part of the gastrointestinal tract and the surrounding of its inferior portion which is the external anal sphincter, and the skin on the perianal.
• Nerve to levator ani and ischiococcygeus muscles:-
These two nerves originate from the last two roots of the sacral spinal nerves and pass downward to provide motor innervation to the two muscles whiches located in the pelvis and they are named after them.
• Nerve to piriformis:-
it originates from the posterior divisions of the first and second sacral spinal nerves and passes to the anterior surface of the muscle and supplies it.
• Nerve to quadratus femoris:-
It originates from the anterior divisions of the anterior rami of the fourth and fifth lumbar and first sacral spinal nerves. it passes to reach the quadratus femoris muscle . Before it ends there, it gives a branch to the inferior gemellus muscle and the other one to the hip joint.
• Nerve to obturator internus:-
it originates from the anterior divisions of the anterior rami of the fifth lumbar and first and second sacral spinal nerves. It leaves the pelvis through the greater sciatic foramen, passing inferior to the piriformis, where it gives off a branch to supply the superior gemellus muscle. It then runs around the ischial spine and enters the pelvis once again through the lesser sciatic foramen and piercing and supplying the obturator internus muscle.
• perforating cutaneous nerve:-
it originates from posterior divisions of the anterior rami of second and third sacral spinal nerves. It gets through the greater sciatic foramen, passing over the Gemelli and obturator internus, piercing the sacrotuberous ligament and gluteus maximus. This nerve gives sensory innervation to a small area of skin on the inferiomedial side of the buttock.
right side view
● Clinical Relevance
• Sacral injury:-
many types of sacral injury may happen to lead to different severe damages depending on the part of the sacrum that is damaged
If the affected part is near to S1 nerves, that affect the groin area and hips. Nerve damage of S2 and S3 may lead to loss of control of muscles and loss of the sensation in the back of the thigh and parts of the buttocks, respectively. Approximately, all organs located in the pelvis are controlled by the sacral spinal nerves including the sex organs and the urinary organs there.
Damage in sacral spinal nerves leads the patient to no control of any of the organs in the pelvis and loss the function in a big part of the lower limbs in both muscles and sensation, But patients might still be able to walk.
Recovery of this injury depends on the patient's body health and other injuries that may have occurred previously.
many types of sacral injury may happen to lead to different severe damages depending on the part of the sacrum that is damaged
If the affected part is near to S1 nerves, that affect the groin area and hips. Nerve damage of S2 and S3 may lead to loss of control of muscles and loss of the sensation in the back of the thigh and parts of the buttocks, respectively. Approximately, all organs located in the pelvis are controlled by the sacral spinal nerves including the sex organs and the urinary organs there.
Damage in sacral spinal nerves leads the patient to no control of any of the organs in the pelvis and loss the function in a big part of the lower limbs in both muscles and sensation, But patients might still be able to walk.
Recovery of this injury depends on the patient's body health and other injuries that may have occurred previously.
• Nerve pressure:-
some pregnant women feel pain or some kind of discomfort at their late stages of pregnancy when the fetal head is moved down to the pelvis region, causing pressure to the plexus and that lead to some sort of pain that can be released by changing sleeping positions.
some pregnant women feel pain or some kind of discomfort at their late stages of pregnancy when the fetal head is moved down to the pelvis region, causing pressure to the plexus and that lead to some sort of pain that can be released by changing sleeping positions.
Nerve Invasion by Malignant Tumors ; these tumers extend from the near structures to invade the plex-us and causes severe pain down in the lower limbs
• lumbosacral plexopathy:-
A damage that might occurs to the nerves bundle in a rare syndrome that called lumbosacral plexo-pathy affecting one or both lumbar and sacral plexuses, patients cannot feel their weak muscles, they also feel burning and numbness, or even be so sensitive to a small touch.
The more obvious cause of the nerve damage that occurs by the high level of blood sugar in what called diabetic amyotrophy causing a severe pain i the hip and buttocks. Idiopathic plexopathy is also a cause of that disorder.
Tumours can cause this plexopathy due to the compression that is disturbing of the plexus and causes that pain, the treatment of this condition in mainly removing of that tumor if possible, high-dose corticosteroids is used as treatment for the Idiopathic plexopathy and diabetic amyotrophy .
A damage that might occurs to the nerves bundle in a rare syndrome that called lumbosacral plexo-pathy affecting one or both lumbar and sacral plexuses, patients cannot feel their weak muscles, they also feel burning and numbness, or even be so sensitive to a small touch.
The more obvious cause of the nerve damage that occurs by the high level of blood sugar in what called diabetic amyotrophy causing a severe pain i the hip and buttocks. Idiopathic plexopathy is also a cause of that disorder.
Tumours can cause this plexopathy due to the compression that is disturbing of the plexus and causes that pain, the treatment of this condition in mainly removing of that tumor if possible, high-dose corticosteroids is used as treatment for the Idiopathic plexopathy and diabetic amyotrophy .
REFERENCES
• Snell's clinical anatomy by Region's (10th edition) page 1046,1048
• Keith L. Moore, Arthur F. Dalley, Anne M. R Clinically Oriented Anatomy (7th Edition) page 358-359
• An Overview of the Sacral Plexus Heidi Moawad, MD Updated on January 06, 2022 Medically reviewed by Chris Vincent, MD very well health https://www.verywellhealth.com/sacralplexusanatomy-4689205
• TeachMeAnatomy The Sacral Plexus Author Kristen Davies Last updated: April 21, 2020 https://teachmeanatomy.info/lower-limb/nerves/sacral-plexus/
• Henry Gray (1821–1865). Anatomy of the Human Body. 1918. 6e. The Sacral and Coccygeal Nerves https://www.bartleby.com/107/213.html
• Sacral plexus Author: Lorenzo Crumbie MBBS, BSc • Reviewer: Dimitrios Mytilinaios MD, PhD Last reviewed: July 19, 2022 kenhub website: https://www.kenhub.com/en/library/anatomy/sacral-plexus
• Sacral Spine Injury shepherd website https://www.shepherd.org/patient-programs/spinal-cord-injury/levels-and-types/sacral-spinal-cord-injury#:~:text=Typically%2C%20with%20a%20sacrum%20injury,their%20own%20with%20special%20equipment.
• Keith L. Moore, Arthur F. Dalley, Anne M. R Clinically Oriented Anatomy (7th Edition) page 358-359
• An Overview of the Sacral Plexus Heidi Moawad, MD Updated on January 06, 2022 Medically reviewed by Chris Vincent, MD very well health https://www.verywellhealth.com/sacralplexusanatomy-4689205
• TeachMeAnatomy The Sacral Plexus Author Kristen Davies Last updated: April 21, 2020 https://teachmeanatomy.info/lower-limb/nerves/sacral-plexus/
• Henry Gray (1821–1865). Anatomy of the Human Body. 1918. 6e. The Sacral and Coccygeal Nerves https://www.bartleby.com/107/213.html
• Sacral plexus Author: Lorenzo Crumbie MBBS, BSc • Reviewer: Dimitrios Mytilinaios MD, PhD Last reviewed: July 19, 2022 kenhub website: https://www.kenhub.com/en/library/anatomy/sacral-plexus
• Sacral Spine Injury shepherd website https://www.shepherd.org/patient-programs/spinal-cord-injury/levels-and-types/sacral-spinal-cord-injury#:~:text=Typically%2C%20with%20a%20sacrum%20injury,their%20own%20with%20special%20equipment.
IMAGES REFERENCES
• Cover image by https://www.alamy.com/lumbosacral-plexus-anatomy-illustration-a-nerve-plexus-is-a-network-or-grouping-of-nerves-the-four-primary-nerve-plexuses-are-the-cervical-brachia-image335305543.html
• Fig1,2&3 Frank H. Netter, Atlas of Human Anatomy (6th edition) plate 484, 486
• Fig4 & fig5 Chihiro Yokochi, E. Lutejen-Drecoll, and Johannes W. Rohen Color Atlas of Human Anatomy 7th Edition page 471
• Fig1,2&3 Frank H. Netter, Atlas of Human Anatomy (6th edition) plate 484, 486
• Fig4 & fig5 Chihiro Yokochi, E. Lutejen-Drecoll, and Johannes W. Rohen Color Atlas of Human Anatomy 7th Edition page 471
