Sacral Plexus Flashcards
What is the sacral plexus?
A network of nerve fibres that supplies the skin and muscles of the pelvis and lower limb
Where is the sacral plexus located?
On the surface of the posterior pelvic wall, anterior to the piriformis muscle
What is the sacral plexus formed by?
The anterior rami (divisons) of the sacral spinal nerves S1, S2, S3, and S4.
It also receives contributions from the lumbar spinal nerves L4 and L5
Where does the sacral plexus begin?
As the anterior fibres of S1, S2, S3, and S4
What forms the lumbosacral trunk?
The 4th and 5th lumbar roots
What happens to the lumbosacral trunk?
It descends into the pelvis, to meet the sacral roots as they emerge from the spinal cord
What happens to the anterior rami of the S1-S4 spinal roots and the lumbosacral trunk?
They divide into several cords, which then combine together to form the five major peripheral nerves of the sacral plexus
Where do the give major peripheral nerves of the sacral plexus travel?
They descent down the posterior pelvic wall, and then either-
Leave the pelvis via the greater sciatic foramen
Remain in the pelvis
What happens to the nerves that leave the pelvis via the greater sciatic foramen?
They enter the gluteal region of the lower limb, innervating the structures there
What happens to the nerves that remain in the pelvis?
They innervate the pelvic muscles, organs and perineum
What are the five major peripheral nerves of the brachial plexus?
Superior gluteal nerve Inferior gluteal nerve Sciatic nerve Posterior femoral cutaneous Pudendal
What course does the superior gluteal nerve take?
It leaves the pelvis via the greater sciatic foramen, entering the gluteal region superiorly to the piriformis muscle
What is the superior gluteal muscle accompanied by for much of its course?
The superior gluteal artery and vein
What are the roots of the superior gluteal nerve?
L4, L5, S1
What muscles does the superior gluteal nerve innervate?
Gluteus minimis
Gluteus medius
Tensor fascia latae
What are the sensory functions of the superior gluteal nerve?
None
What course does the inferior gluteal nerve take?
It leaves the pelvis via the greaer sciatic foramen, entering the gluteal region inferiorly to the piriformis muscle
What is the inferior gluteal nerve accompanied by for much of its course?
The inferior gluteal artery and vein
What are the roots of the inferior gluteal nerve?
L5, S1, S2
What muscle does the inferior gluteal nerve innervate?
Gluteus maximus
What is the sensory function of the inferior gluteal nerve?
None
What are the roots of the sciatic nerve?
L4, L5, S1, S2, S3
What are the parts of the sciatic nerve?
Tibial portion
Common fibular portion
What muscles does the tibial portion of the sciatic nerve innervate?
All muscles of posterior compartment of thigh, including the hamstring portion of the adductor magnus, apart from the short head of the biceps femoris
All muscles in the posterior compartment of the leg
All muscles in sole of foot
What muscles does the common fibular portion of the sciatic nerve innervate?
Short head of biceps femoris
All muscles of anterior and lateral compartments of the leg
Extensor digitorum brevis
What are the sensory functions of the tibial portion of the sciatic nerve?
Innervates the skin on the posterolateral and medial surfaces of the foot, as well as the sole of the foot
What are the sensory functions of the common fibular portion of the sciatic nerve?
Innervates the skin on the anterolateral surface of the leg and the dorsal aspect of the foot
What course does the posterior femoral cutaneous nerve take?
It leaves the pelvis via the greater sciatic foramen, entering the gluteal region inferiorly to the piriformis muscle. It descends deep to the gluteus maximus, and runs down the back of the thigh to the knee
What are the roots of the posterior femoral cutaneous nerve?
S1, S2, S3
What muscles does the posterior femoral cutaneous nerve innervate?
None
What is the sensory function of the posterior femoral cutaneous?
Innervates the skin on the posterior surface of the thigh and leg
Innervates skin of perineum
What course does the pudendal nerve take?
The nerve leaves the pelvis via the greater sciatic foramen, then re-enters via the lesser sciatic foramen. It moves anterosuperiorly along the lateral wall of the ischiorectal fossa
How does the pudendal nerve terminate?
By dividing into several branches
What are the roots of the pudendal nerve?
S2, S3, S4
What are the motor functions of the pudendal nerve?
Innervates skeletal muscles in the perineum, the external urethral sphincter, the external sphincter, levator ani
What is the sensory function of the pudendal nerve?
Innervates the penis and clitoris, and most of the skin of the perineum
What is found in addition to the five major nerves of the sacral plexus?
A number of smaller branches
What do the smaller branches coming from the sacral plexus tend to be?
Nerves that directly supply muscles
What is the exception to the smaller branches of the sacral plexus directly supplying muscles?
The perforating cutaneous nerve, which supplies the skin over the inferior gluteal region
The pelvic splanchnic nerves, which innervate the abdominal viscera
What are the important smaller branches of the sacral plexus?
Nerve to piriform
Nerve to obturator internus
Nerve to quadrator femoris
