Lower plexuses

Question 1

Where do rr. anteriores of lumbar, sacral and coccygeal region exit the vertebrae?

Answer 1

• L: through foramina intervertebralia
• S1-4: through foramina sacralia anteriora
• S5 + Co1: through hiatus sacralis

Question 2

Which nerves contribute to plexus lumbosacralis?

Location in relation to hip joint?

Answer 2

• plexus lumbalis: rr. anteriores T12 - L4
• truncus lumbosacralis: rr. anteriores L4 - 5, connect both plexuses
• plexus sacralis: rr. anteriores L4 - S5, Co1

→ nn. of plexus lumbalis ventral to hip joint, nn. of plexus sacralis dorsal to hip joint

Question 3

List all 7 branches of plexus lumbalis and their spinal origin.

Answer 3

• rr. musculares (T12 - L4)
• n. iliohypogastricus (L1)
• n. ilioinguinalis (L1)
• n. genitofemoralis (L1 - 2)
• n. cutaneus femoralis lateralis (L2 - 3)
• n. femoralis (L2 - 4)
• n. obturatorius (L2 - 4)

_{rr. musculares not shown, 2 - 7 = cf. above}

Question 4

Which mm. are innervated by rr. musculares of plexus lumbalis?

Where do they originate from?

Answer 4

T12 - L4

• m. iliopsoas
• m. quadratus lumborum
• mm. intertransversarii laterales lumborum (autochthonal back mm.)

Question 5

What are common features of n. iliohypogastricus and n. ilioinguinalis?

Answer 5

• originate from L1
• innervate caudal parts of mm. abdominales + overlying skin

Question 6

Nerve?

Pathway + function.

Answer 6

n. iliohypogastricus (L1)

dorsally to kidney on m. quadratus lumborum, pierces, then runs btw m. transversus abdominis and m. obliquus internus abdominis, 3 branches

• rr. musculares → m. transversus abd. + obliquus internus abd.
• r. cutaneus lat. → lat. hip
• r. cutaneus ant. → mons pubis

₁₃

Question 7

Nerve?

Pathway + function.

Answer 7

n. ilioinguinalis (L1)

dorsally to kidney on m. quadratus lumborum, pierces, then runs btw m. transversus abdominis and m. obliquus internus abdominis, then through canalis inguinalis to labia maj./scrotum

→ caudal parts of mm. abdominales + sensory innervation of uppermost parts of labia maj./scrotum

Question 8

Nerve?

Pathway + function.

Answer 8

n. genitofemoralis (L1 - 2)

below n. ilioinguinalis/hypogastricus, pierces m. psoas, then bifurcates into 2 branches:

• r. genitalis (cf. own card)
• r. femoralis (cf. own card)

Question 9

Nerve?

Pathway + function.

Answer 9

r. genitalis n. genitofemoralis

runs in spermatic cord/lig. teres uteri to scrotum/labia majores

→ m. cremaster, sensory innervation of scrotum/labia majora + upper medial part of thigh

_1a

Question 10

Nerve?

Pathway + function.

Answer 10

n. femoralis n. genitofemoralis

runs below lig. inguinale in lacuna vasorum of hiatus saphenus to surface

→ sensory innervation of upper ventral region of thigh

_1b

Question 11

Pointing at 2 different sections of the same nerve.
Which nerve is it?

Pathway + function.

Answer 11

n. cutaneus femoralis lateralis (L2 - 3)

runs on m. iliopsoas downwards, emerges medially to SIAS through lacuna musculorum, then changes direction in right angle, pierces fascia lata

→ sensory innervation of lat. side of thigh

₁₂

Question 12

Nerve?

Pathway + function.

Answer 12

n. femoralis (L1 - 4)

btw m. psoas and iliacus down to lacuna musculorum lat. to v./a. femoralis, reaches down to thigh, then branches into

• 2 rr. cutanei ant. in fascia lata → ventral thigh
• rr. musculares → m. iliopsoas, pectineus, sartorius, quadriceps fem.
• n. saphenus (cf. own card) → medial side of calf, knee

_{<u>REMEMBER:</u> IVAN - inside, vein, artery, nerve}

_{1 = rr. cutanei ant., 2 = n. saphenus}​

Question 13

5.

Pathway + function.

Answer 13

n. saphenus

branch of n. femoralis, enters canalis adductorius together w/ a./v. femoralis, pierces septum intermusculare vastoadductorium, runs to medial side of calf w/ v. saphena magna, gives off branches

• r. infrapatellaris → knee
• rr. cutanei cruris medialis → medial side of calf

Question 14

Nerve?

Pathway + function.

Answer 14

n. obturatorius (L2 - 4)

runs behind m. psoas along wall of lesser pelvis, leaves it through foramen obturatum, gives off branch to m. obturatorius ext., then bifurcation into

• r. anterior → m. adductor long., brev. gracilis, pectineus, sensory inn. of medial part of thigh
• r. posterior → m. adductor magnus

Question 15

Which spinal nerve segment connects plexus lumbalis and plexus sacralis in order to form together plexus lumbosacralis?

Answer 15

L4

Question 16

Which spinal nerve segments form plexus sacralis?

Through which structure do all the fibers pass?

Answer 16

L4 - S3

→ fibers leave through foramen ischiadicus major

_{NOTE: 5 and 6 are not considered part of plexus sacralis}

Question 17

Which branches (incl. single muscular branches) are given off by plexus sacralis?

What is their spinal origin)

Answer 17

in craniocaudal direction, 4 m. + 4 nerves

• muscular branches to
  
  • m. obturatorius int.
  • mm. gemelli
  • m. piriformis
  • m. quadratus femoris
• n. gluteus sup. (L4 - S1)
• n. gluteus inf. (L5 - S2)
• n. cutaneus femoris post. (S1 - 3)
• n. ischiadicus (L4 - S3)

Question 18

Nerve?

Spinal origin?

Pathway + function.

Answer 18

n. gluteus sup. (L4 - S1)

leaves through foramen suprapiriforme together w/ vasa glutea sup., runs branches to mm.

→ m. gluteus med., min. + m. tensor fasciae latae

Question 19

Nerve?

Spinal origin?

Pathway + function.

Answer 19

n. gluteus inf. (L5 - S2)

leaves through foramen infrapiriforme, runs to m.

→ m. gluteus max.

Question 20

Nerve?

Spinal origin?

Pathway + function.

Answer 20

n. cutaneus femoris post. (S1 - 3)

through foramen infrapiriforme w/ … (cf. own card), then beneath m. gluteus max. to subcutis, there giving off branches (see below), continues to mid of dorsal thigh

• nn. clunium inferiores → caudal gluteal region
• rr. perineales → perineum - scrotum/labia majora

_{nn. clunium inf. on picture just cranial to n. cutaneus fem. post.}

Question 21

Nerve?

Spinal origin?

Pathway + function.

Answer 21

n. ischiadicus (L4 - S3)

through foramen infrapiriforme, first covered by m. gluteus max., then m. biceps femoris, in most cases (88%) bifurcates into n. tibialis and n. peroneus communis after 2/3 of thigh, BUT: can bifurcate earlier, still perceived as one nerve bc covered by same epineurium

→ knee flexors, all mm. of calf, foot + sensory innervation of calf + foot (exc. medially)

₁

Question 22

Nerve?

Spinal origin?

Pathway + function.

Answer 22

n. peroneus communis (L4 - S2)

1. branch of n. ischiadicus, runs lateralyl to n. tibialis on dorsal side of knee flexors
2. gives off cutaneus branches at level of popliteal fossa
3. runs laterally around caput fibula
4. enters compartmentimentum cruris laterale + bifurcates into terminal branches n. peron. prof., superf.

​→ mm. peronei, extensors of foot, digits + sensory innervation of parts of calf, dorsum of foot

NOTE: n. ischiadicus = L4 - S3

Question 23

Which branches are given off by n. peroneus communis?

Where?

Answer 23

in craniocaudal direction, 3 branches

• n. cutaneus surae: in popliteal fossa
• 2 terminal branches: in compartimentum cruris lat.
  
  • n. peroneus superf.
  • n. peroneus prof.

_{​4 = n cut. surae lat., 7 = n. per. prof., 8 = n. per. sup.}

Question 24

Nerve?

Pathway + function.

Answer 24

n. cutaneus surae lat.

branch of n. peroneus comm., originates in popliteal fossa, gives off r. communicans to anastomose w/ n. cutaneus surae med., form n. suralis

→ sensory innervation of lateral calf

_{4 = n. cut. surae lat., 5 = r. comm., 6 = n. suralis}

Question 25

Nerve? Pathway + function.

Answer 25

**_n. peroneus superficialis_** terminal branch of n. peroneus comm., runs btw 2 mm. peronei down to dorsum of foot, bifurcates into **n. cutaneus dorsalis medialis, intermedius** → **mm. peronei** + sensory innervation of **dorsum of foot** 8 = n. per. sup., 2 = sens. inn.

Question 26

Nerve? Pathway + function.

Answer 26

**_n. peroneus prof._** terminal branch of n. peroneus communis, pierces septum intermusculare, enters extensor compartment , runs downwards btw m. tibialis ant., m. extensor hallucis long. together w/ a. tibialis ant. to dorsum of foot, then sensory branch → **all extensors** (m. tibialis ant., extensor hallucis long., brev., extensor digitorum long., brev.) + sensory innervation of **halfs of 1. and 2. toe** 7 = n. per. prof., 3 = sens. innervation

Question 27

Which nerves give off nn. digitales dorsales pedis? Function?

Answer 27

* n. cutaneus dorsalis medialis * n. cutaneus dorsalis intermedius * n. fibularis profundus **​****​**→ sensory innervation of**skin of digits till middle phalanges** (terminal phalanges inn. by plantar nn.) _{2 = n. cutaneus dors. med./intermed., 3 = n. peron. prof.}

Question 28

Nerve? Spinal origin? Pathway + function.

Answer 28

**_n. tibialis_** (L4 - S3) 1. branch of n. ischiadicus, runs medially to n. peroneus comm. on dorsal side of knee flexors 2. continues straight pathway of n. ischiadicus, submerges btw heads of m. gastrocnemius, downwards btw m. soleus and deep flexors together w/ a. tibialis post. 3. runs together w/ tendons of deep flexors below **malleolus medialis** to plantar side of foot 4. terminal branches **n. plantars med., lat.** ​→ **ALL flexors of ancle, digits, plantar foot mm.** + sensory innervation of **lat. side around ancle, plantar side of foot** _{NOTE: n. ischiadicus = L4 - S3, hence all its fibers}

Question 29

Which branches are given off by n. tibialis? Where?

Answer 29

_in craniocaudal direction, "5" branches_ * **rr. musculares** to flexors in calf * **n. interosseus cruris** on membrana interossea * **n. cutaneus surae med.** in fossa poplitea * 2 terminal branches at malleolus med. * **n. plantaris med.** * **n. plantaris lat.** _{​3 = n. cut. sur. med., 4 = n. suralis, 5 = rr. musc., 6 = n. plant. med., 7 = plant. lat., n. int. cruris not shown}

Question 30

Which muscles are innervated by rr. musculares of n. tibialis?

Answer 30

_all flexors of ancle, digits in calf_ * m. triceps surae * m. plantaris * m. popliteus * m. tibialis post. * m. flexor digitorum long. * m. flexor hallucis long.

Question 31

Nerve? Which nerve does it eventually form? Pathway + function.

Answer 31

**_n. cutaneus surae med._** from n. tibialis, together w/ v. saphena parva running down on calf, anastomosis w/ r. communicans of n. cutaneus surae med. to form * **n. suralis →** area around **lat. malleolus** * then gives off **rr. calcanei** → **heel** * eventually becomes **n. cutaneus dorsalis** lat. → **lat. side of foot** _{pathway: 3 = n. cut. surae med., 4 = n. suralis
inn: 1 = n. suralis, 2 = rr. calcanei}

Question 32

Nerve? Pathway + branches.

Answer 32

**_n. plantaris medialis_** terminal branch of n. tibialis, gives off branches * **rr. musculares** * 3 **nn. digitales plantares communes****​** **→ n. medianus**

Question 33

What is the function of plantaris med.?

Answer 33

resembles **n. medianus of foot**, hence: * _motor innervation via **rr. musculares**_ * m. abductor hallucis * med. head of m. flexor hallucis brevis * m. flexor digitorum brevis * m. lumbricalis I * _sensory innervation via **nn. digit plant. comm.**_ * medial 3,5 toes on plantar side * terminal phalanges ₃

Question 34

Nerve? Pathway + function.

Answer 34

**_n. plantaris lat._** terminal branch of n. tibialis, originates at level of malleolus, runs to lat. side of sole, bifurcates into **r. superficialis, profundus** → **n. ulnaris of foot**

Question 35

What is the function of n. plantaris lat.?

Answer 35

resembles **n. ulnaris of foo**t, hence: * _r. superficialis_ → 3 nn. digitales plantares comm. → 6 nn. digitales plantares proprii → **lat. 1,5 toes on plantar side + terminal phalanges (both sides)** * _r. profundus + r. superficialis_ * ​m. flexor hallucis brevis, caput lat. * m. adductor hallucis * m. quadratus plantae * mm. lumbricales II, III, IV * mm. interossei * all mm. of pinky ₄

Question 36

What is special about n. pudendus? Spinal origin? Pathway + function.

Answer 36

forms own **_plexus pudendus_** (S2 - 4) 1. through foramen infrapiriforme 2. together w/ a. pudenda int. around spina ischiadica through foramen ischiadicum minus 3. enters fossa ischioanalis, then on lateral wall in Alcock's canal → there giving off branches → **function of perineum, continence, sexual activity**

Question 37

Which structure forms Alcock's canal?

Answer 37

**fascia of m. obturator int.**

Question 38

Which branches are given off by n. pudendus, resp. which mm. are innervated by its plexus? Function.

Answer 38

* **nn. rectales inf.:** m. sphincter ani ext. + sensory innervation of perineum * **nn. perineales:** * m. transversus perineus sup., prof. * m. sphincter ureathrae ext. * mm. bulbo-, ischiocavernosus * sensory innervation of scrotum, labia majora * **n. dorsalis penis/clitoridis:** sensory innervation of penis/clitoris

Question 39

How is m. levator ani innervated?

Answer 39

by direct branches of **plexus sacralis, S3 - 4** __NOTE:_ _{according to other sources direct branch of n. pudendus?}