Pelvis 2: Neurovasculature/pelvic Plexus

Front 1

Pelvic Inlet

Back 1

Bony pelvis divided into greater (false) and lesser (true) pelves by an oblique plane, the pelvic inlet.

It is somewhat rounded and defined by the sacral promontory, arcuate lines, pectineal lines, and pubic symphysis.

Above this point is the greater pelvis (abdominal organs) below this point is lesser (true) pelvis, which has reproductive organs.

Front 2

Pelvis Outlet

Back 2

Inferior pelvic aperture.
Perimeter defined by pubic arch, ischiopubic rami, ischial tuberosities, tip of the coccyx.
Pelvic outlet is sealed by pelvic diaphragm.

Front 3

Muscles of pelvic cavity

Back 3

Divided into muscles that form lateral wall of pelvis and muscles that form floor of pelvis.

Lateral walls formed by piriformis and obturator internis.

Floor is formed by coccygeus and levator ani muscles. AKA pelvic diaphragm.

Front 4

Pelvic Diaphragm

Back 4

Dynamic floor (thanks to levator ani in particular).

Anus and urethra (and vag in females) pass through the levator ani. By surrounding these orifiices, levator ani assists in voluntary control of urination/defecation.

Also work to resist an increase in intra-abdominal pressure. Otherwise, abdominopelvic contents would be forced through outlet.

Levator ani part of diaphragm consists of:
- iliococcygeus (from obturator fascia to coccyx)
- pubococcygeus (from pubis to coccyx)
- puborectalis (from pubis to pubis, making a loop)

INNERVATED BY VENTRAL RAMI OF S4/S5

Front 5

Injury to the pelvic floor

Back 5

Tears can occur during childbirth in diaphragm.
Pubococcygeus is strongest of the three, and a tear here really weakens floor.
Result: incontinence, defecatory dysfunction

Front 6

Prolapsed Uterus

Back 6

Weakened pelvic diaphragm leads to prolapse of uterus.

Prolapses into vaginal canal, or beyond.

Treatments are varied, depending on severity (from hyesterectomy to pelvic floor reconstruction).

Front 7

Muscles with respect to Pelvis

Back 7

Obturator internis forms part of lateral wall of lower pelvis. Tendon exits through lesser sciatic foramen, attaches to greater trochanter of femur.

Piriformis exits greater sciatic foramen and also attaches to foramen.

Front 8

Four major gateways or passageways

Back 8

1) Greater sciatic foramen
2) Lesser sciatic foramen
3) Obturator canal
4) Beneath inguinal ligament

Front 9

Greater sciatic foramen

Back 9

Transmits:
- piriformis muscle
- Superior and inferior gluteal nerve/vessels
- Pudendal nerve
- Sciatic nerve
- Internal pudendal artery/vein

Front 10

Lesser sciatic foramen

Back 10

Transmits:
- obtrurator internis muscle/tendon
- Pudendal nerve/internal pudendal vessels to perineum

Front 11

Obturator canal

Back 11

Small opening in the obturator membrane that transmits:
- obtrurator nerve/vessels into medial thigh (adductor) compartment

Front 12

Beneath inguinal ligament

Back 12

Crescent shaped passage beneath ligament transmits the following from abdominopelvic to thigh:

1) Iliopsoas muscle
2) Lateral femoral cutaneous nerve
3) Femoral nerve
4) Femoral artery
5) Femoral vein

Muscular lacuna is lateral space beneath inguinal ligament

Vascular lacuna is similar space.

Front 13

Lumbosacral plexus

Back 13

Formed by group of ventral rami of lumbar and sacral spinal nerves.

Innervates pelvic/lower limb muscles, and associated cutaneous regions.

Often separated into:

Lumbar plexus: ventral rami of L1-L4, and associated nerves

Sacral plexus: ventral rami of L4, L5 and S1-S4, and associated nerves.

Coccygeal plexus: ventral rami of S5 and Co1.

Nerves arising form plexuses contain all four types of nerve fibers (both somatic and visceral)

Front 14

Lumbar Plexus

Back 14

L1-L4

1) Iliohypogastric nerve, branch of L1 supplying sensation to hypogastric region

2) Ilioinguinal nerve: branch of L1 ventral ramus that courses through inguinal canal and supplies sensation to scrotum/labia.

3) Lateral femoral cutaneous, formed by ventral rami of L2-L3 supplies sensation to anterolateral thigh. Goes below inguinal ligament.

4) Genitofemoral nerve (L1-L2)
Genital branch traveses inguinal canal and supplies scrotum and cremaster / innervates labia majora
Femoral branch innervates adjacent thigh.

Two major nerves arise from ventral rami of L2, L3, L4:
Femoral nerve (L2-L4) innervates quadriceps
Obturator nerve (L2-L4): innervates adductor muscles

Lumbosacrap trunk is large stout nerve formed by union of L4 and L5. Contributes to sacral plexus.

Front 15

Sacral Plexus

Back 15

1) Lumbosacral trunk (L4-L5) from lumbar plexus
2) Sciatic nerve: formed by union of L4/L5, S1-3. Exits greater sciatic foramen below piriformis.
3) Pudendal nerve: S2-4: exits greater sciatic foramen and enters lesser sciatic foramen, innervates perineum.
4) Superior gluteal nerve (L4-L5, S1): exits greater sciatic foramen above piriformis (innervates hip adductors)
5) Inferior gluteal nerve (L5/S1-2): exits greater sciatic foramen below piriformis, innervates gluteus maximus.

Posterior femoral cutaneous nerve: S1-3, cutaneous innervation to posterior thigh.

Front 16

Lumbosacral plexus

Back 16

Nerves that come from plexus convey somatic motor to skeletal muscle. Also convey general sensory info back to CNS.

Visceral motor also travel in here, as well as visceral sensory.

Front 17

Internal iliac artery

Back 17

Comes after bifurcation of common iliac artery.
Divided into posterior and anterior division.

Front 18

Posterior Divisions of Internal Iliac Artery

Back 18

1) Iliolumbar
2) Lateral sacral artery
3) Superior gluteal artery: runs between lumbosacral trunk and S1. Exits pelvis via greater sciatic foramen above piriformis. Supplies muscles to buttocks.

Front 19

Anterior divisions of internal iliac artery

Back 19

1) Inferior gluteal artery
2) Internal pudendal artery
3) Obturator artery: runs through upper part of obturator foramen, supplies muscles of medial thigh
4) Umbilical artery (distally turns into umbilical ligament)
5) Uterine artery
6) Vaginal artery
7) Middle rectal

Front 20

Differences in Male Vascular Supply

Back 20

1) Artery of ductus deference is branch of umbilical artery (replaces uterine artery) and supplies much of reproductive apparatus.
2) Inferior vesical artery (replaces vaginal artery), supplies reproductive system
3) Middle rectal: supplies rectum AND prostate, seminal vesicles, ureter...