Podcast
Questions and Answers
Which nerve is directly responsible for innervating the piriformis muscle?
Which nerve is directly responsible for innervating the piriformis muscle?
What is the primary path of the nerve to Obturator Internus after it exits the pelvis?
What is the primary path of the nerve to Obturator Internus after it exits the pelvis?
From which spinal segments does the Nerve to Quadratus Femoris originate?
From which spinal segments does the Nerve to Quadratus Femoris originate?
What distinguishes the second course of nerves from the sacral plexus?
What distinguishes the second course of nerves from the sacral plexus?
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Which course of nerves involves traveling through the lesser sciatic foramen?
Which course of nerves involves traveling through the lesser sciatic foramen?
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What is the primary function of the sacral plexus?
What is the primary function of the sacral plexus?
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Which spinal nerves contribute to the formation of the sacral plexus?
Which spinal nerves contribute to the formation of the sacral plexus?
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Which nerve is primarily responsible for innervating the gluteus maximus?
Which nerve is primarily responsible for innervating the gluteus maximus?
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What components make up the sciatic nerve?
What components make up the sciatic nerve?
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Which nerve provides sensory innervation to the perineum?
Which nerve provides sensory innervation to the perineum?
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Which of the following muscles is NOT innervated by the tibial component of the sciatic nerve?
Which of the following muscles is NOT innervated by the tibial component of the sciatic nerve?
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Which nerve originates from the S2 and S3 spinal roots and innervates the inferior gluteal region?
Which nerve originates from the S2 and S3 spinal roots and innervates the inferior gluteal region?
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What structure is the sacral plexus located anterior to?
What structure is the sacral plexus located anterior to?
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Which of the following nerves emerges anteriorly from the psoas major muscle?
Which of the following nerves emerges anteriorly from the psoas major muscle?
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From which spinal roots does the ilioinguinal nerve originate?
From which spinal roots does the ilioinguinal nerve originate?
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Which of the following statements regarding the lumbar plexus is incorrect?
Which of the following statements regarding the lumbar plexus is incorrect?
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Which mnemonic helps identify the originating roots for the nerves of the lumbar plexus?
Which mnemonic helps identify the originating roots for the nerves of the lumbar plexus?
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Which of the following nerves primarily innervates the anterior compartment muscles of the thigh?
Which of the following nerves primarily innervates the anterior compartment muscles of the thigh?
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Study Notes
Sacral Plexus Anatomy
- The sacral plexus is a network of nerve fibers supplying the skin and muscles of the pelvis and lower limb.
- Located on the posterior pelvic wall, anterior to the piriformis muscle.
- Formed from the anterior rami of sacral spinal nerves S1, S2, S3, and S4.
- Receives contributions from lumbar spinal nerves L4 and L5, forming the lumbosacral trunk.
- Spinal nerves S1 to S4 form the sacral plexus's foundation.
- Each nerve branches into anterior and posterior rami.
- Anterior fibers of S1, S2, S3, and S4 emerge through anterior sacral foramina.
- Joining the fourth and fifth lumbar roots forms the lumbosacral trunk, descending into the pelvis.
- The sacral plexus is located on the anterior surface of the piriformis muscle.
Major Nerves of the Sacral Plexus
- Superior Gluteal Nerve: originates from L4, L5, and S1; innervates gluteus minimus, gluteus medius, and tensor fasciae latae.
- Inferior Gluteal Nerve: originates from L5, S1, and S2; innervates gluteus maximus.
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Sciatic Nerve: the largest nerve; derived from L4 to S3; composed of common fibular and tibial components.
- Common Fibular Component: formed from dorsal divisions of L4 to S2; innervates the short head of biceps femoris, anterior and lateral leg muscles, and extensor digitorum brevis.
- Tibial Component: formed from ventral divisions of L4 to S3; innervates all posterior thigh muscles except the short head of biceps femoris, hamstring portion of adductor magnus, and posterior leg and foot muscles.
- Posterior Femoral Cutaneous Nerve: originates from S1, S2, and S3; innervates skin of the posterior thigh and leg, and perineum.
- Pudendal Nerve: originates from S2, S3, and S4; innervates perineal skeletal muscles (external urethral sphincter, external anal sphincter, and levator ani), and provides sensory innervation to the penis/clitoris and perineal skin.
Smaller Branches of the Sacral Plexus
- Perforating Cutaneous Nerve: originates from S2 and S3; innervates inferior gluteal skin; pierces the sacro-tuberous ligament.
- Nerve to Piriformis: formed from S2 (sometimes S1); innervates the piriformis muscle directly.
- Nerve to Obturator Internus: originates from L5 to S2; exits the pelvis via greater sciatic foramen, loops around sacrospinous ligament, re-enters via the lesser sciatic foramen to innervate obturator internus and superior gemellus.
- Nerve to Quadratus Femoris: originates from L4 to S1; exits the pelvis via greater sciatic foramen inferior to the piriformis; innervates quadratus femoris and inferior gemellus.
Nerve Courses
- Nerves from the sacral plexus follow three courses:
- First Course: leave the pelvis through the greater sciatic foramen, entering the gluteal region of the lower limb.
- Second Course: remain within the pelvis, innervating pelvic muscles, organs, and perineum.
- Third Course: leave the greater sciatic foramen, loop around the sacrospinous ligament, re-entering via the lesser sciatic foramen to supply lateral pelvic and perineal structures.
Lumbar Plexus
- The lumbar plexus is formed from the anterior rami of L1 to L4 and receives fibers from T12.
- Formed within the psoas major muscle.
- Mnemonic "I twice get laid on Fridays" helps remember six main nerves:
- Iliohypogastric
- Ilioinguinal
- Genitofemoral
- Lateral Femoral Cutaneous
- Obturator
- Femoral
- All nerves except genitofemoral and obturator emerge from the lateral aspect of the psoas major muscle.
- The genitofemoral nerve emerges anteriorly from the psoas major muscle, splitting into genital and femoral branches.
- The obturator nerve emerges medial to the psoas major muscle.
Nerve Roots
- Mnemonic "2 from 1, 2 from 2, 2 from 3" helps determine nerve root origins:
- "2 from 1": Iliohypogastric nerve originates from L1, Ilioinguinal nerve originates from L1.
- "2 from 2": Genitofemoral nerve originates from L1 and L2, Lateral femoral cutaneous nerve originates from L2 and L3.
- "2 from 3": Femoral nerve originates from L2, L3, and L4, Obturator nerve originates from L2, L3, and L4.
Other Points:
- The subcostal nerve (branch of T12) contributes to the lumbar plexus.
- The accessory obturator nerve is not always present, originating from L3 and L4.
- Muscular branches of the femoral nerve innervate the psoas and iliacus muscles.
Innervation
- Obturator nerve: Innervates the medial compartment muscles of the thigh.
- Femoral nerve: Innervates the anterior compartment muscles of the thigh.
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Description
Test your knowledge on the anatomy of the sacral plexus, including its formation, location, and major nerves. This quiz covers details on the nerve fibers that supply the pelvis and lower limb. See how well you understand the intricate network vital for movement and sensation in these areas.