Human Anatomy Week 5b

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Questions and Answers

Which dermatome is primarily responsible for sensory perception on the medial malleolus?

L4 (correct)

What is the key sensory distribution area for the femoral nerve?

Lateral foot

Medial ankle

Anterior thigh (correct)

Posterior thigh

Which nerve contributes to the sensory innervation of the plantar surface of the foot?

Sural nerve

Lateral cutaneous nerve

Medial plantar nerve (correct)

Deep fibular nerve

Where is the primary sensory area for the lateral foot found?

S1 Signup and view all the answers

Which nerve is responsible for the sensory innervation of the medial leg?

Saphenous nerve Signup and view all the answers

What is a dermatome?

A portion of skin innervated by a single spinal nerve level. Signup and view all the answers

Which spinal nerve root corresponds to the anterior portion of the thigh?

L2 Signup and view all the answers

Why are there two different diagrams of dermatomes?

To represent variability in dermatomes among individuals. Signup and view all the answers

In terms of innervation, what is the role of the lumbosacral plexus in the lower extremity?

It supplies sensory innervation to specific areas of the lower extremity. Signup and view all the answers

What does the ASIA map help to remember regarding dermatomes?

The sensory distribution of each nerve root in the body. Signup and view all the answers

Which of the following statements accurately describes the function of the gluteal nerves?

They are responsible only for muscular innervation. Signup and view all the answers

Which nerve roots are associated with the lumbar plexus?

L1-L4 Signup and view all the answers

What is the significance of the lumbosacral trunk?

It functions as a conduit for certain nerve roots to the pelvic region. Signup and view all the answers

Which of the following nerves is NOT part of the lumbar plexus?

Sciatic nerve Signup and view all the answers

What does the term 'common' imply in anatomical terminology?

The structure will split into two branches or more. Signup and view all the answers

What is the primary function of the obturator nerve?

Innervates all adductor muscles in the medial compartment Signup and view all the answers

What happens if the femoral nerve is damaged?

Loss of knee extension and difficulty with hip flexion Signup and view all the answers

Which statement about the femoral nerve is true?

It emerges lateral to the psoas muscle and passes deep to the inguinal ligament. Signup and view all the answers

Which muscles are primarily affected by the femoral nerve?

Quadriceps and iliacus Signup and view all the answers

What is the sensory function of the lateral femoral cutaneous nerve?

Provides sensation to the skin over the lateral thigh Signup and view all the answers

Where do all the nerves from the lumbar plexus typically emerge from?

Anterior of the pelvis Signup and view all the answers

Which nerve runs medial to the psoas muscle?

Obturator nerve Signup and view all the answers

Which of the following nerves provides sensory input to the superolateral portion of the thigh?

Lateral cutaneous nerve to the thigh Signup and view all the answers

Which major nerve of the lumbar plexus passes under the inguinal ligament into the anterior thigh?

Femoral nerve Signup and view all the answers

What spinal nerve root levels contribute to the femoral nerve?

L2 to L4 Signup and view all the answers

Study Notes

Lumbosacral Plexus Overview

The lumbosacral plexus is a network of nerves that innervates the lower extremity.
It is formed by the ventral rami of spinal nerves L1-L4 (lumbar plexus) and L4-S4 (sacral plexus).
Major nerves of the lumbar plexus: Lateral cutaneous nerve of the thigh, femoral nerve, obturator nerve.
Major nerves of the sacral plexus: Nerve to quadratus femoris, nerve to obturator internus, nerve to piriformis, superior gluteal nerve, inferior gluteal nerve, posterior femoral cutaneous nerve, tibial nerve, common fibular nerve.
The sciatic nerve is the largest nerve in the body and is formed by the tibial and common fibular nerves.

Lumbar Plexus in Detail

The lumbar plexus is formed within and around the psoas major muscle.
Lateral cutaneous nerve of the thigh: Emerges from the lumbar plexus lateral to the psoas muscle and runs towards the ASIS, providing sensory innervation to the lateral thigh.
Femoral nerve: Largest nerve of the lumbar plexus, emerges lateral to the psoas muscle, runs under the inguinal ligament, and provides motor and sensory innervation to the anterior thigh, knee, and leg.
Obturator nerve: Emerges medially from the psoas muscle, runs through the obturator foramen, and provides motor and sensory innervation to the medial thigh.
Nerve root contributions to lumbar plexus nerves:
- Lateral cutaneous nerve of the thigh: L2, L3
- Femoral nerve: L2-L4
- Obturator nerve: L2-L4

Clinical Relevance

The proximity of the lumbar plexus to the psoas muscle highlights the importance of considering psoas muscle tension or impingement as a potential source of nerve-related issues.
Learning the nerve root contributions and sensory distributions of the nerves in the lumbar plexus helps to pinpoint the source of pain, numbness, or weakness in the lower extremity.

Femoral Nerve

The femoral nerve innervates the anterior compartment of the thigh
It innervates the quadriceps, which is responsible for knee extension
It also contributes to hip flexion through its innervation of iliacus, rectus femoris, sartorius, and pectineus
Damage to the femoral nerve would result in difficulty with hip flexion and complete inability to extend the knee
The femoral nerve runs deep to the inguinal ligament
It emerges into the thigh in the femoral triangle
The femoral nerve passes anterior to the hip joint, thus hip extension would increase tension on this nerve
The femoral nerve passes slightly anterior to the knee, so knee flexion may also cause tension on the nerve

Obturator Nerve

The obturator nerve shares the same nerve roots as the femoral nerve and overlaps with similar dermatomes
The obturator nerve innervates all of the muscles in the medial compartment of the thigh, which are the adductors
It also provides innervation to the hip joint and the medial thigh
Abduction of the hip or thigh could lead to increased tension on the obturator nerve

Lumbar Plexus

The lateral femoral cutaneous nerve emerges from psoas, heads towards the ASIS, and pierces the fascia lata of the thigh
The lateral femoral cutaneous nerve gives sensory innervation to the lateral thigh
The lumbar plexus gives rise to the femoral, obturator, and lateral femoral cutaneous nerves

Sacral Plexus

The sacral plexus is responsible for innervating the muscles of the gluteal region and the posterior thigh
It also innervates the posterior leg and plantar foot
Almost all nerves of the sacral plexus, most notably the sciatic nerve, emerge from the greater sciatic foramen just inferior to piriformis
The sciatic nerve is susceptible to impingement by piriformis

Sciatic Nerve

The sciatic nerve emerges from the greater sciatic foramen just deep to piriformis
It runs through the gluteal region, and posterior thigh, diving into the popliteal fossa at the back of the knee
The sciatic nerve splits into the tibial and common fibular nerves at the popliteal fossa
The sciatic nerve may be restricted due to excessive tension or scarring around the piriformis muscle
Hip flexion will tension the sciatic nerve

Tibial Nerve

The tibial nerve, one of the main branches of the sciatic nerve, is responsible for innervating the posterior thigh, leg, and plantar foot
It innervates the hamstring muscles
It innervates muscles in the posterior compartment of the leg, including gastrocnemius and soleus
It continues into the plantar foot
The tibial nerve runs inferiorly directly through the midline of the popliteal fossa
It dives between the 2 heads of gastrocnemius and passes deep to soleus
The tibial nerve runs along the medial malleolus and passes into the plantar surface of the foot
The tibial nerve splits into the medial and lateral plantar nerves that innervate the plantar foot
Hip flexion will tension the tibial nerve

Common Fibular Nerve

The common fibular nerve, the second branch of the sciatic nerve, is responsible for innervating the short head of biceps femoris
It splits into the superficial and deep fibular nerves
The deep fibular nerve innervates the anterior compartment of the leg, supplying muscles like dorsiflexors and long toe extensors
The superficial branch of the fibular nerve innervates the lateral compartment of the leg, supplying the fibularis muscles, primarily the evertors
It wraps around the lateral aspect of the knee
The common fibular nerve runs inferiorly to the knee

Other Sacral Plexus Nerves

The superior and inferior gluteal nerves, nerve to quadratus femoris, nerve to obturator internus all innervate the smaller gluteal muscles
The posterior femoral cutaneous nerve supplies cutaneous sensation to the buttock and posterior thigh
The internal pudendal nerve innervates the perineum and provides sensation to that region
The pudendal nerve innervates small muscles in the genital region
The nerve to levator ani comes off the sacral plexus, and as its name says, goes to the pelvic floor

Other Important Information

The lumbar plexus is involved in innervation of the lower limb, while the sacral plexus is responsible for innervation of the pelvic region
The sciatic nerve is the longest nerve in the body
The obturator nerve is responsible for adduction of the thigh
The superior and inferior gluteal nerves innervate the gluteal muscles
The posterior femoral cutaneous nerve innervates the skin over the glutes and posterior thigh
The internal pudendal nerve innervates the perineum and provides sensation to that region ### Lumbosacral Plexus Sensory Distributions
Lateral Cutaneous Nerve of the Thigh: Innervates the proximal lateral thigh, wrapping from anterior to posterior.
Obturator Nerve: Innervates the medial thigh, wrapping from anterior to posterior.
Femoral Nerve: Innervates the anterior thigh.
Saphenous Nerve: Innervates a large portion of the medial leg, extending from the femoral nerve.
Posterior Femoral Cutaneous Nerve: Innervates a large portion of the posterior thigh, as its name suggests.
Sural Nerve: Innervates the lateral and posterior area of the leg, with variation in some individuals.
Fibular Nerve: Covers the top of the foot with its superficial branch.
Tibial Nerve: Innervates the plantar foot with its lateral and medial branches.

Anterior Hip Sensory Innervation

Nerves like the genitofemoral, ilioinguinal, and iliohypogastric provide sensation to the hip crease and genitals.

Clunial Sensory Innervation

The clunial nerves, superior, middle, and inferior, provide sensation to the buttocks or clunial region.
These nerves are branches of the posterior rami of the lumbar and sacral nerve roots.

Dermatome Distribution

The femoral nerve distribution overlaps with L2, L3, and L4 dermatomes.
The L5 dermatome runs down the lateral leg to the dorsum of the foot, corresponding to the sural, superficial, and deep fibular nerves which have L5 contributions.
The plantar foot is innervated by the tibial nerve, which carries S1 and L5 nerve roots.

Clinical Implications

Numbness or tingling in the lower extremity can point to sensory involvement of a peripheral nerve or a nerve root.
Understanding dermatome and sensory distributions is crucial for differential diagnosis, distinguishing between peripheral nerve and nerve root involvement.

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Description

Test your knowledge on dermatomes and sensory innervation in the lower extremities. This quiz covers key concepts such as the roles of various nerves, sensory distribution areas, and the lumbosacral plexus. Perfect for students in anatomy or neurology courses.

Human Anatomy Week 5b - Transcripts