lumbar and sacral Flashcards
is formed by the union of ant. (ventral) rami of spinal nerves T12-L4.
L1, gives rise to two sensory nerves known as iliohypogastric and ilioinguinal. The iliohypogastric supplies the skin of lower ant. abdominal wall while the ilioinguinal passing through the inguinal canal will supply the skin of scrotum/labia majora.
The remaining part of nerve referred to as genitofemoral N.This nerve has some sensory branches for the upper medial aspect of the thigh and also motor fibers for cremasteric muscle.
Some part of L2 and L3 will join to make lat. cutaneous nerve of thigh that supplies the lateral side of the thigh.
The major part of L2, L3, and L4 will combine to form the femoral N. The same spinal nerves will contribute in the formation of another mixed nerve, the obturator N.
There may be another name known as accessory obturator nerve with L3, and L4 segments.
The rest of L4 joins with L5 to make the lumbosacral trunk. This trunk joins with the sacral plexus.
Lumbar Plexus
Later divides to 2 branches genital (motor) and femoral (sensory) branch. Femoral triangle is supplied by the femoral branch. Genital branch goes to cremaster (surrounds the testis, pulls up the testis in the abdominal cavity.
- MP note: Meralgia Paresthetica compression of the lat cutaneous nerve of thigh
- to go to the lateral side of the thigh the nerve passes 1 inch medial to ASIS, and needs to dive under the inguinal lig. Anything that increases tension to the inguinal lig will cause the lat cutaneous nerve to be pinched. Inguinal lig will be in tension during pregnancy, hernia, obesity, jobs that require heavy belts ei police, and wearing tight underwear of pants
branches off into several motor branches (for quadriceps femoris, sartorius, and pectineus) and also some sensory branches (intermediate and medial cutaneous nerves of thigh, and saphenous nerve). These sensory branches will supply the skin of anterior and medial aspects of the thigh and also the skin of the medial side of the leg down to the base of the big toe.
It is important to know that the femoral nerve has a sensory branch of proprioceptive type for the hip joint.
L2 – L4) emerges from the lateral side of the psoas major muscle and enters the thigh region after passing posterior to the midpoint of inguinal ligaments
is the Largest and main branch of LP, it’s a mixed nerve
Femoral nerve
*only branch of the femoral nerve that crosses the knee and goes to the leg. Supplies the medial side of the led and medial border of the foot
When in the thigh region, the nerve divides to anterior and posterior branches which pass ant. and post, to the adductor brevis muscle respectively.
These branches will supply all the adductor muscles and in 50% of cases the pectineus muscle is also supplied by them. There are two major sensory nerves derived from the obturator nerve which supply the hip and knee joints with somatic sensory fibers.
(L2 – L4) emerges from the medial side of the psoas major muscle and after traveling around the pelvic inlet, passes through the obturator foramen to leave the pelvis and enter the thigh region.
obturator nerve
*Ant branch = mixed nerve = motor branches supply add. Muscles EXCEPT add magnus and obturator externus. Sensory branches = reach skin of distal third of the medial side of the thigh
This plexus is formed in front of piriformis muscle, by the ant. (ventral) rami of L4-Co spinal nerves.
It has so many sensory and motor branches for the muscles and the skin of gluteal region, post. Aspect of the thigh and the whole of leg and foot.
The largest branch of the plexus is the sciatic nerve which is formed by L4-S3 spinal nerves.
There are 4 nerves with 3 segments
Sup. Gluteal N. and Quadratus Femoris N. (L4,L5, S1)
Inf. Gluteal N. and Obturator Internus N. (L5,S1,S2)
Post. Cutaneous nerve of thigh (S1,S2,S3)
Pudendal N. (S2, S3, S4)
There are 3 nerves with 2 segments:
Perforating cutaneous (S2, S3)
Nerve to levator ani (S3, S4)
The remaining parts of spinal nerves S4-Co will supply some sensory branches to the perineal and coccygeal regions.
Sacral Plexus
- Pudendal Nerve = Mixed nerve: Sensory = reaches sensory of genitalia post. Half
- Post cutaneous nerve of thigh = Pure sensory that supplies the skin in the back of the thigh
Sciatic nerve passes through the greater sciatic foramen to enter the gluteal region just inferior to piriformis muscle. It is covered by a superficial layer of gluteal muscles and has no branches in this area.
Posterior cutaneous nerve of the thigh has a similar course and lies just medial to the sciatic nerve.
Deep to these two and underneath gemelli muscles, one can find nerves to quadratus femoris.
Superior gluteal nerve is a motor nerve and supplies the gluteus medius and minimus muscles as well as the T.F.L muscle.
Inferior gluteal nerve is also a pure motor nerve which just supplies the gluteus maximus muscle.
Pudendal nerve is a mixed nerve which wraps around the sacro-spinous ligament and gives sensory branches to the skin of the perineal area and external genitalia as well.
Nerve to obturator internus, runs superficial to obturator internus muscle.
Nerves in Gluteal region
*Sciatic nerve: some anatomists believe that there is no sciatic nerve, it’s just a union of the tibial and common fibular nerve wrapped by a connective tissue.
*11 percent of cadavers the tibial and CF are not fused and are separate causing piriformis syndrome = tibial nerve passes through piriformis and gets compressed
Is a mixed nerve, that gives motor fibers to the hamstring muscle group and the posterior portion of adductor magnus.
Sciatic nerve usually divides into two major branches as common peroneal and tibial nerves at the distal third of the thigh.
The only muscle in post. Compartment of the thigh which is supplied by the common peroneal nerve in this area is the short head of the biceps femoris and all other muscles are innervated by the branches from the tibial nerve.
Sciatic Nerve
In the popliteal fossa it is just covered by the skin and fascia.
It has some sensory branches for the knee joint mainly of proprioceptive type. The other sensory branch is called sural nerve which supplies the distal 2/3 of the posterior and lateral aspects of the leg.
The nerve also supplies the superficial layer of muscles in the posterior compartment of the leg (gastrocnemius, soleus, plantaris, and popliteus).
then lies between the superficial and deep layers of the muscles of the posterior compartment of the leg and continues downwards as it supplies (flexor hallucis longus, flexor digitorum longus, and tibialis posterior).
Finally after passing behind the medial malleolus, the tibial nerve enters the sole of the foot. Just before doing that, the nerve has some sensory branches (medial calcaneal N.)for the skin of the heel area.
Tibial nerve
Terminal branches of the tibial nerve are known as medial & lateral plantar nerves.
Medial plantar nerve supplies the skin of the medial 2/3 of the sole of the foot and also the medial 3 ½ toes. This nerve innervates the abductor hallucis, flexor hallucis brevis, flexor digitorum brevis, and the first three lumbrical muscles.
Lateral plantar nerve supplies the lateral 1/3 of the sole of the foot and the lateral 1 ½ toes. This nerve also innervates abductor digiti minimi, flexor digiti minimi, quadratus plantae, adductor hallucis, the fourth lumbrical, and all of the interosseous muscles.
Passes downward and laterally in the popliteal fossa. Here it has some sensory branches to the knee joint and also another sensory nerve for the upper lateral side of the leg ( lateral cutaneous nerve of the leg).
After turning around the neck of the fibula it lies deep to the peroneal muscles and divides into superficial and deep branches.
Upper half of the lateral side of the leg is supplied by sensory branch coming from sensory fibular = lateral sural nerve
Superficial branch descends between peroneus longus and brevis muscles and innervates both of them. Then it lies beneath the skin and as a pure sensory nerve supplies the lower third of the anterior aspect of the leg and dorsum of the foot.
Deep branch lies deep to the muscles of the anterior compartment of the leg (tibialis anterior, extensor digitorum longus, and extensor hallucis longus) and innervates all of them. Then the nerve enters the dorsal surface of the foot to innervate extensor digitorum brevis and extensor hallucis brevis muscles. It also gives off a tiny sensory branch for the web of the big toe.
Steppage gait = foot drop means common peroneal is intoxicated with lead
Common Peroneal/Fibular Nerve
Are 12 pairs in number
Mostly arise from the brainstem (except the first two that are extensions of the brain itself).
Are mixed nerves (sensory, motor and
parasympathetic)
Leave the cranium by passing through foramina at the base of the cranial fossae.
CN are usually numbered in roman numerals (opposite of spinal nerves)
cranial nerves
*CN III and IV arise from the highest part of the brain (mid brain)
- CN V Arises from the second part of the brain stem aka pons
- CN VI, VII, VIII arise from pontomedullary sulcus
- CN IX, X, XI, XII arise from different parts of medulla
- 1) Foramen cecum: small vein passes through. The vein connects veins from the outside of the skull to the veins inside the skull. It also supplies the triangle area around the nose. Infection to this area could affect the meninges = meningitis
- 2) Cribriform plate: provides access to CN I (olfactory)
- 3) Optic Canal: Passage for CN II (optic)
- 4) Sup. Orbital fissure: Passage for CN III, CN IV, one division of CN V known as V1 or ophthalmic N
- 5) Foramen Rotundum: passage for V2 maxillary N of CN V
- 6) Foramen Ovale: passage for V3 mandibular N of CN V
- 7) Foramen spinosum: passage for middle meningeal artery (supplies meninges)
- 8) Carotid Canal: passage for internal carotid artery
- 9) Internal auditory meatus: passage for CN VII and CN VIII
- 10) Jugular Foramen: Internal jugular vein starts here. Passage for CN IX, X, XI
- 11) Hypoglossal canal: passage for CN XII
- 12) Foramen Magnum: passage for medulla of brainstem and vertebral arteries
Pure sensory (smell)
Starts as bipolar neurons at the level of cribriform plate of ethmoid bone.
These neurons end at the olfactory bulb which inturn gives rise to the olfactory tract.
The olfactory tract ends to enthorhinal area (frontal lobe).
Olfactory N. CN I
Is a pure sensory (vision) nerve.
Arises from retina (cone & rods to bipolar cells to ganglion cells to optic nerve)
Left and right optic nerves exchange some (temporal field of view) fibers at optic chiasm and turn into optic tract.
Optic tract ends to the lateral geniculate body (thalamus) and continues as optic radiation.
Optic radiation ends to visual cortex (occipital lobe
Optic N. CN II
Is a mixed (motor & parasympathetic) nerve.
Arises from midbrain and passes through superior orbital fissure.
Motor fibers supply some of the extraocular muscles (sup, inf, med, recti and inf. Oblique plus levator palpebra superioris).
Parasympathetic fibers: reaches iris of the eye (after synaps in ciliary ganglion) supply sphincter muscle of pupil (constricts iris)
Occulomotor N. CN III
Is a pure motor nerve.
The only cranial nerve that shows up posterior to the brainstem.
Is the smallest of all cranial nerves.
Arises from midbrain and passes through superior orbital fissure.
Only supplies one of the extraocular muscles (sup. oblique).
Trochlear N. CN IV
CN V is the only CN that has a dermatome
Arises from pons and enters the semilunar ganglion and then divides into three divisions:
Ophthalmic (V1); pure (general) sensory, enters the orbital cavity through superior orbital fissure, here it divides into the following branches:
Lacrimal; for lacrimal gland
Naso-cilliary; supplies the eyeball, nasal cavity mucous membrane
Supra-orbital for the skin of forehead ( highest point of skull is called vertex)
Nerve exits through supraorbital foramen
Trigeminal N. CN V
