Final = Nervous System of Lower Limb

How is the nervous system structurally divided?

CNS - brain and spinal cord
PNS - cranial nerves, spinal nerves, rami, plexuses, named peripheral nerves, ganglia

Spinal cord

• extends from foramen magnum → L1/L2

• enlarges at the cervical at the cervical and lumbosacral regions

  • This is because there are more motor cell bodies (more grey matter) within the ventral horns at these points as this is where the brachial and lumbosacral plexuses are formed supplying the highly muscular upper and lower limb

How many pairs of spinal nerves?

31 pairs:

8 cervical

12 thoracic

5 lumbar

5 sacral

1 coccygeal

How many pairs of cranial nerves?

12 pairs;

2 arise from the cerebrum

10 arise from brainstem

How is the nervous system functionally divided?

Somatic - voluntary

Autonomic - involuntary (parasympathetic vs sympathetic)

Where are cell bodies to efferent axons?

Somatic: ventral horn

Autonomic:

• presynaptic cell body in grey matter of CNS

  • sympathetic: lateral horn

  • parasympathetic: spinal cord or brain stem

• postsynaptic cell body in PNS autonomic ganglia
  
  both multipolar axons

Where are the cell bodies to afferent axons?

Somatic: dorsal root ganglia

Autonomic: dorsal root ganglia or cranial ganglia

• both pseudounipolar neurons

Describe formation of spinal nerve - somatic

• efferent (motor) - cell body in ventral horn

  • axons carries signal through ventral root, spinal nerve and either ventral or dorsal horn

• afferent (sensory) - cell body in dorsal root ganglia

  • axons carry signal from receptor down axon through either ventral or dorsal horn, spinal nerve, dorsal root ganglion, dorsal root and dorsal horn

What is the difference between ventral and dorsal rami?

• Dorsal ramus → innervates muscle and skin of deep (intrinsic) muscles of back

• Ventral ramus → innervates all muscle and skin of the anterolateral trunk, upper and lower limbs, superficial back (muscles only) and most of the neck

  • also combine to form plexuses which give off named peripheral nerves

Why does the back have decreased sensation?

Back skin has a lower density in of tactile receptors, contributing to a less fine tuned sensory perception. This makes evolutionary sense, as we don’t interact with our environment using our backs.

Intercostal nerves - cutaneous innervation

• in the ribcage, the intercostal nerves are direct continuations of the the ventral rami

• give off lateral and anterior cutaneous branches to innervate skin of the lateral and anterior trunk

Dermatomes

• each spinal nerve with somatic sensory axons (all but C1, typically lacks dorsal root ganglion) provide sensory information for a strip of skin

• face cutaneous innervation is done by cranial nerves

L1 dermatome

anterior thigh/inguinal region

L2 dermatome

anterior lateral thigh (superior to knee)

L3 dermatome

anterior medial thigh and knee

L4 dermatome

medial leg and malleolus

L5 dermatome

anterior lateral leg, medial dorsum of foot, digits 1-3

S1 dermatome

distal posterior lateral leg, ankle and foot, digits 4-5

S2 dermatome

posterior midline of the thigh and posterior knee

S3 dermatome

outermost ring of gluteal region posteriorly and superior genital area anteriorly (toilet lid)

S4 dermatome

intermediate ring of the gluteal region posteriorly and inferior genital area anteriorly (toilet lid hole)

S5 dermatome

innermost ring of gluteal region at anus/coccygeal area posteriorly

Myotome

the motor axons within each spinal nerve are responsible for innervating specific muscle fibers

Herpes Zoster virus

• causes shingles

• viral infection that presents following a reactivation of a previous infection of the virus (chickenpox)

• virus typically remains dormant within the dorsal root ganglion

• the rash is referred to as a “self-limited dermatomal rash” as it spreads long the are of skin associated with the sensory nerve it laid dormant within

How would injury to a spinal nerve compare to injury of a named nerve?

• Ventral rami form plexuses from multiple spinal nerve levels that intertwine to give off named nerves

• This means if a single spinal nerve was injured, there may be multiple structures weakened but function wont be entirely depleted as other spinal nerves also contribute

• Contrarily, if the actual named nerve is injured, this would cut off all spinal nerve contributions, meaning the structures it supplies will lose all signaling.

  • There are some exceptions with dual innervated muscles, such as pectineous

Herniated (slipped) disc: what is it? what can it cause? symptoms?

• between each vertebral body is a disc

• if the disc ruptures, the inside material can leak posteriorly

• common consequence → compression of the nerve roots for a single spinal nerve (radiculopathy)

• if a single spinal nerve is compressed, a patient will present with sensory and motor deficits associated with the same dermatome/myotome

What invervates the hip joint?

• femoral n.

• obturator n.

• superior gluteal n.

• nerve to quadratus femoris n.

what inervates the knee joint?

• femoral

• saphenous

• tibial

• common fibular

what innervates the ankle joint?

• saphenous

• tibial

• sural

• superficial fibular

• deep fibular

Hip joint myotomes

• hip flexion: L1-L2

• hip adduction: L2-L3

• hip extension: L5-S1

What structures travel through the greater sciatic foramen?

• superior and inferior gluteal avn.

• piriformis m.

• pudendal nva.

• sciatic n.

• posterior femoral cutaneous n.

What structures travel through the lesser sciatic notch?

• pudendal nva. (reenters pelvis)

• obturator internus tendon passes through to attach to femur

What is cutaneous innervation? how does it compare to dermatomes?

• Named nerves almost always provide sensory information to an area of skin, called cutaneous innervation

• Named nerves that are formed by a plexus differ from dermatomes because there are typically multiple spinal nerves contributing

• dermatomes are the strips of skin that only a single spinal nerve contributes to

• cutaneous innervation and dermatome maps are visibly different

Lumbar plexus ventral rami? where does it form?

• L1-L4

• within psoas major

subcostal n. (levels, path, innervation)

• T12 (lumbar)

• runs inferior to 12th rib

• lateral cutaneous branch innervates

  • skin of hip region inferior to anterior part of iliac crest and anterior to greater trochanter

iliohypogastric n. (levels, path, innervation)

• L1 (lumbar)

• emerges from upper lateral border of psoas major and crosses over quadratus lumborum

• lateral cutaneous branch innervates

  • superolateral quadrant of buttocks

Ilioinguinal n. (levels, path, innervation)

• L1 (lumbar)

• runs on iliac crest to ASIS where inguinal canal starts

• innervates

  • skin over medial femoral triangle

Genitofemoral n. (levels, path, innervation)

• L1-L2

• runs through center of psoas major, pops out along anterior surface and runs down

  • gives off genital and femoral branch

• innervates

  • femoral branch → skin over lateral part of femoral triangle

Lateral femoral cutaneous n. (levels, path, innervation)

• L2-L3

• runs diagnolly across ilaicus and pops up out just below ASIS

• innervates

  • skin of anterior and lateral margin of the thigh

Anterior femoral cutaneous n. (path, innervation)

• from anterior division of femoral n.

• intermediate anterior thigh, distal medial margin of thigh, proximal lateral knee

Saphenous n. (path, innervation)

• from posterior division of femoral n.

• medial knee, medial margin of leg, ankle and foot

Femoral n. (levels, path, innervation, injury (motor/sensory)?)

• L2-L4

• runs lateral to psoas major and exits pelvis deep to inguinal ligament

  • divides into anterior and posterior divisions

  • lateral circumflex a. runs in between

• innervates

  • iliacus and pectineus

• Injury → motor

  • Femoral n. → flexion, adduction and medial rotation of hip

  • Anterior division of Femoral n. → flexion, abduction, and lateral rotation of hip, knee flexion

  • Posterior division of Femoral n. → flexion of hip, extension of knee

• Injury → sensory

  • Anterior femoral cutaneous n. → anterior and medial thigh

  • Saphenous. n. → medial knee, leg, ankle and margin of foot

Anterior division of femoral n. (levels, path, innervation)

• L2-L4

• splits after femoral n. exits pelvis deep to inguinal ligament

  • mainly sensory, with little motor

• innervates

  • sartorius m.

• Injury → motor

  • flexion, abduction, and lateral rotation of hip, knee flexion

• Injury → sensory

  • Anterior femoral cutaneous n. (medial and intermediate branches) → anterior and medial thigh

Posterior division of femoral n. (levels, path, innervation, injury (motor/sensory)?

• L2-L4

• splits after femoral n. exits pelvis deep to inguinal ligament

  • mainly motor, with little sensory

• Innervates:

  • rectus femoris, vastus lateralis, vastuc medialis, vastus intermedius

• Injury → motor

  • extension of knee, flexion of hip

• Injury → sensory

  • Saphenous. n. → medial knee, leg, ankle and margin of foot

Obturator n. (levels, path, innervation, injury (motor/sensory)?

• L2-L4

• runs medial to psoas major and exist pelvis to medial thigh through obturator canal of obturator membrane

  • divides into anterior and posterior divisions that sandwhich over adductor brevis m.

• Innervate

  • obturator externus m.

• Injury → motor

  • Obturator n. → lateral rotation and stabilization of hip

  • Anterior division of obturator n. → adduction, flexion, and medial rotation of hip, knee flexion and rotation when flexed

  • Posterior divsion of obturator n. → hip adduction and flexion

• Injury → sensory

  • medial thigh

Anterior division of obturator n. (levels, path, innervation, injury (motor/sensory)?

• L2-L4

• sits anterior to adductor brevis m.

• Innervate

  • adductor longus, adductor brevis, gracilis, pectineus

• Injury → motor

  • Anterior division of obturator n. → adduction, flexion, and medial rotation of hip, knee flexion and rotation when flexed

• Injury → sensory

  • medial thigh

Posterior division of obturator n. (levels, path, innervation, injury (motor/sensory)?

• L2-L4

• sits posterior to adductor brevis m.

• Innervates

  • adductor portion of adductor magnus m.

• Injury → motor

  • adduction and flexion of hip

Lumbosacral trunk (levels, path, function

• L4-L5

• medial and deep to psoas major

• nerve bridge fromed by L4-L5 connecting lumbar and sacral plexus

Sacral (lumbosacral) plexus ventral rami

• L4-S3

Superior gluteal nerve (levels, path, innervation, injury (motor/sensory)?)

• L4-S1 (sacral)

• exits the pelvis via the greater sciatic foramen superior to piriformis m

  • travels with the superior gluteal artery and vein

• innervates

  • gluteus medius, gluteus minimus, tensor fascia latae

• injury → motor

  • weakness of medial hip rotation, abduction, stabilization of the hip (pelvic drop), some hip flexion

Inferior gluteal nerve (levels, path, innervation, injury (motor/sensory)?)

• L5-S2 (sacral)

• exists the pelvis via the greater sciatic foramen inferior to the piriformis m

  • travels with the inferior gluteal artery and vein

• Innervates

  • Gluteus maximus

• injury → motor

  • weakness in extension of the hip, particularly with rising from sitting/walking up stairs and lateral rotation of the hip

Nerve to piriformis (levels, innervation, injury (motor/sensory)?)

• S1-S2 (sacral)

• Innervation

  • piriformis m.

• Injury → motor

  • weakness of lateral rotation of extended hip, abduction of flexed hip, hip stability

Nerve to obturator internus (levels, innervation, injury (motor/sensory)?)

• L5-S2 (sacral)

• Innervation

  • obturator internus m

  • gemellus superior m.

• Injury → motor

  • weakness of lateral rotation of extended hip, abduction of flexed hip, hip stability

Nerve to quadratus femoris (levels, innervation, injury (motor/sensory)?)

• L4-S1 (sacral)

• Innervation

  • quadratus femoris m.

  • gemellus inferior m.

• Injury → motor

  • weakness of lateral rotation of extended hip, abduction of flexed hip, and stabilization of hip

Posterior femoral cutaneous n. (levels, path, innervation, injury (motor/sensory)?)

• S1-S3 (sacral)

• Exits pelvis via the greater sciatic foramen, inferior to piriformis m.

  • gives off inferior clunial n.

• Innervation

  • cutaneous innervation to the inferior buttocks (inferior clunial n) and skin along the posterior thigh and popliteal fossa

• Injury → cutaneous

  • above

Pudendal n. (levels, path)

• S2-S4 (sacral plexus)

• Exits pelvis via the greater sciatic foramen

  • enters the perineum via the lesser sciatic foramen

Sciatic nerve (levels, path, innervation, injury (motor/sensory)?)

• L4-S3 (sacral)

• Continuation of sacral plexus, exiting the plevis via the greater sciatic foramen

  • inferior to piriformis m. between the ischial tuberosity and the greater trochanter

• Innervation

  • none, but composed of two nerves (tibial and common fibular)

• Injury → motor

  • Tibial n. (posterior thigh) → extension of hip, flexion of knee, medial/lateral rotation of flexed knee

  • Tibial n. (posterior leg) → plantarflexion, toe flexion, inversion

  • Medial plantar n. (foot) → hallux MTP flexion/abduction, digit 2-5 flexion MTP/PIP, digit 2 (1st lumbrical) MTP flexion and IP extension

  • Lateral plantar n. (foot) → digit 3-5 adduction, digit 2-4 abduction, digit 2-5 toe flexion MTP/IP, hallux adduction, digit 3–5 (2-4 lumbricals) MTP flexion and IP extension

  • Superficial fibular n. (lateral leg) → eversion, weak plantarflexion

  • Deep fibular n. (anterior leg) → dorsiflexion/inversion, hallux extension MTP/IP, digit 2-5 extension MTP/IP.

  Injury → sensory

  • Tibial → inferior heel

  • Medial plantar n. → plantar surface of medial 3.5 digits and nails

  • Lateral plantar n → plantar surface of lateral 1.5 digits and nails

  • Superficial fibular n. → distal anterolateral leg and dorsum of foot excluding medial and lateral margins, 1st interweb space and toe nails

  • Deep fibular n. → 1st web space

  • Sural n. → lateral foot, lateral malleolus and posterior distal leg

  • Lateral sural cutaneous n. → proximal anterior/posterior lateral leg

Tibial n. (levels, path, innervation, injury (motor/sensory)?)

• L4-S3

• starts as part of sciatic n. exiting pelvis through greater sciatic notch, inferior to piriformis

• branches off of sciatic n. near the popliteal region, running medially down posterior leg between two heads of gastrocnemius and through tendinous arch of soleus muscle and then wrapping posteriorly around medial malleolus (tarsal tunnel)

  • gives off medial and lateral plantar n. in plantar foot and medial calcaneal branch either before or within the tunnel

  • runs with popliteal av.

  • also gives off medial sural cutaneous n. which joins with lateral sural cutaneous n. to form sural n.

• Directly innervates

  • posterior thigh → semitendinosus, semimembranosus, and biceps femoris long head

  • posterior leg → gastrocnemius, plantaris, soleus, popliteus, tibialis posterior, flexor digitorum longus, flexor hallucis longus

• Injury → motor

  • Tibial n. (posterior thigh) → extension of hip, flexion of knee, medial/lateral rotation of flexed knee

  • Tibial n. (posterior leg) → plantarflexion, toe flexion, inversion

  • Medial plantar n. (foot) → hallux MTP flexion/abduction, digit 2-5 flexion MTP/PIP, digit 2 (1st lumbrical) MTP flexion and IP extension

  • Lateral plantar n. (foot) → digit 3-5 adduction, digit 2-4 abduction, digit 2-5 toe flexion MTP/IP, hallux adduction, digit 3–5 (2-4 lumbricals) MTP flexion and IP extension

• Injury → sensory

  • Tibial → inferior heel

  • Medial plantar n. → plantar surface of medial 3.5 digits and nails

  • Lateral plantar n → plantar surface of lateral 1.5 digits and nails

  • Sural n. → lateral foot, lateral malleolus and posterior distal leg

  • medial calcaneal branch → posterior heel triangle

Medial sural cutaneous n. (path, injury)

• branches off of tibial n. in popliteal fossa and combines with sural communicating branch (of lateral sural cutaneous n.) to form sural n.

• Injury → sensory

  • sural n. → lateral foot, lateral malleolus and posterior distal leg

Medial calcaneal branches of tibial n. (path, innervation)

• branches off tibial n. either before or within the tunnel

• innervates

  • posterior heel triangle

Medial plantar n. (path, innervation, injury (motor/sensory)?)

• branches from tibial nerve after passing deep to flexor retinaculum from tibial n.

  • enters foot by passing deep to abductor hallucis m.

  • after motor innervation divides into 3 common plantar digital n. which then divide into proper plantar digital n. for cutaneous innervation

• innervates

  • plantar foot → abductor hallucis, flexor digitorum brevis, 1st lumbrical and flexor hallucis brevis

• Injury → motor

  • hallux MTP flexion/abduction, digit 2-5 flexion MTP/PIP, digit 2 (1st lumbrical) MTP flexion and IP extension

• Injury → sensory

  • plantar surface of medial 3.5 digits and nails

Lateral plantar n. (path, innervation, injury (motor/sensory)?)

• branches from tibial nerve after passing deep to flexor retinaculum from tibial n.

  • enters foot by passing laterally between the flexor digitorum brevis and quadratus plantae m.

  • after motor innervation divides into proper plantar and common plantar digital n, which will divide into proper plantar digital n.

• Innervates

  • foot → abductor digiti minimi, quadratus plantae, lumbricals 2-4, adductor hallucis, flexor digitorum brevis and plantar/dorsal interossei

• Injury → motor

  • digit 3-5 adduction, digit 2-4 abduction, digit 2-5 toe flexion MTP/IP, hallux adduction, digit 3–5 (2-4 lumbricals) MTP flexion and IP extension

• Injury → sensory

  • plantar surface of lateral 1.5 digits and nails

Common fibular n. (levels, path, innervation, injury (motor/sensory)?)

• L4-S2

• branches off of sciatic nerve near the popliteal region, running laterally over fibular neck

  • divides into deep (anterior leg) and superficial fibular (lateral leg) n.

  • lateral sural cutaneous n branches in popliteal fossa giving off sural communicating branch that joints medial sural cutaneous n. to form sural n.

• Innervates

  • biceps femoris short head

• Injury → motor

  • common fibular n. → flexion and lateral rotation of the knee

  • deep fibular n. → dorsiflexion/inversion, hallux extension MTP/IP, digit 2-5 extension MTP/IP.

  • superficial fibular → eversion of ankle, weak plantarflexion

• Injury → sensory

  • deep fibular n. → 1st web space

  • superficial fibular n. → distal anterolateral leg and dorsum of foot excluding medial and lateral margins, 1st interweb space and toe nails

  • lateral sural cutaneous n. → proximal anterior/posterior lateral leg

  • sural n. → lateral foot, lateral malleolus and posterior distal leg

Lateral sural cutaneous (path, innervation)

• branches off of common fibular n. and gives off sural communicating branch that joints medial sural cutaneous n. to form sural n.

• innervates

  • lateral sural cutaneous n. → proximal anterior/posterior lateral leg

  • sural n. → lateral foot, lateral malleolus and posterior distal leg

Superficial fibular n. (levels, path, innervation, injury (motor/sensory)?)

• L4-S2

• branches off common fibular nerve at fibular neck and dives into lateral leg compartment b/w fibularis longus and brevis

  • become subcutaneous halfway down the leg

• Innervates

  • fibularis longus and fibularis brevis

• Injury → motor

  • eversion of ankle, weak plantarflexion

• Injury → sensory

  • distal anterolateral leg and dorsum of foot excluding medial and lateral margins, 1st interweb space and toe nails

Deep fibular n. (levels, path, innervation, injury (motor/sensory)?)

• L4-S1

• branches off common fibular nerve at fibular neck and dives into anterior leg

  • runs along anterior surface of interosseous membrane, sitting lateral to tibialis anterior belly/tendon and running with anterior tibial a

  • passes deep to extensor retinacula running between extensor digitorum and hallucis brevis (anterior tibial becomes dorsalis pedis)

  • after motor innervation, it transitions to common dorsal digital n. which will divide into proper dorsal digital n. in the first interdigital space

• Innervation

  • anterior leg → tibialis anterior, extensor hallucis longus, extensor hallucis brevis, fibularis tertius

  • dorsal foot → extensor hallucis brevis, extensor digitorum brevis

• Injury → motor

  • dorsiflexion/inversion, hallux MTP and IP extension, digit MTP and IP 2-5 extension

• Injury → sensory

  • 1st web space

Superior cluneal n. (levels, innervation)

• dorsal rami of L1-L3 (no plexus)

• innervates

  • skin overlying superior and central parts of buttocks

Middle cluneal n. (levels, innervation)

• dorsal rami of S1-3

• innervates

  • skin of medial buttock and intergluteal cleft

Sciatic nerve variations

can travel below, split around or through piriformis