Lumbar plexus
Encyclopedia
The lumbar plexus is a nervous plexus in the lumbar
region of the body which forms part of the lumbosacral plexus
. It is formed by the ventral divisions of the first four lumbar nerves
(L1-L4) and from contributions of the subcostal nerve
(T12), which is the last thoracic nerve
. Additionally, the ventral rami of the fourth lumbar nerve pass communicating branches, the lumbosacral trunk
, to the sacral plexus
. The nerves of the lumbar plexus pass in front of the hip joint and mainly support the anterior part of the thigh.
The plexus is formed lateral to the intervertebral foramina
and pass through psoas major
. Its smaller motor branches are distributed directly to psoas major, while the larger branches leave the muscle at various sites to run obliquely downward through the pelvic area to leave the pelvis under the inguinal ligament
, with the exception of the obturator nerve which exits the pelvis through the obturator foramen
.
runs anterior to the psoas major
on its proximal lateral border to run laterally and obliquely on the anterior side of quadratus lumborum
. Lateral to this muscle, it pierces the transversus abdominis
to run above the iliac crest
between that muscle and abdominal internal oblique
. It gives off several motor branches to these muscles and a sensory branch to the skin of the lateral hip. Its terminal branch then runs parallel to the inguinal ligament
to exit the aponeurosis
of the abdominal external oblique
above the external inguinal ring where it supplies the skin above the inguinal ligament (i.e. the hypogastric region
) with the anterior cutaneous branch
.
The ilioinguinal nerve
closely follows the ilihypogastric nerve on the quadratus lumborum, but then passes below it to run at the level of the iliac crest. It pierces the lateral abdominal wall and runs medially at the level of the inguinal ligament where it supplies motor branches to both transversus abdominis and sensory branches through the external inguinal ring to the skin over the pubic symphysis
and the lateral aspect of the labia majora
or scrotum
.
The genitofemoral nerve
pierces psoas major anteriorly below the former two nerves to immediately split into two branches that run downward on the anterior side of the muscle. The lateral femoral branch
is purely sensory. It pierces the vascular lacuna
near the saphenous hiatus
and supplies the skin below the inguinal ligament (i.e. proximal, lateral aspect of femoral triangle
). The genital branch
differs in males and females. In males it runs in the spermatic cord
and in females in the inguinal canal
together with the teres uteri ligament
. It then sends sensory branches to the scrotal skin in males and the labia majora in females. In males it supplies motor innervation to the cremaster
.
The lateral cutaneous femoral nerve
pierces psoas major on its lateral side and runs obliquely downward below the iliac fascia
. Medial to the anterior superior iliac spine
it leaves the pelvic area through the lateral muscular lacuna
. In the thigh it briefly passes under the fascia lata
before it breaches the fascia and supplies the skin of the anterior thigh.
The obturator nerve
leaves the lumbar plexus and descends behind psoas major on it medial side, then follows the linea terminalis
into the lesser pelvis
, and finally leaves the pelvic area through the obturator canal
. In the thigh, it sends motor branches to obturator externus
before dividing into an anterior and a posterior branch, both of which continues distally. These branches are separated by adductor brevis
and supply all thigh adductors with motor innervation: pectineus
, adductor longus
, adductor brevis, adductor magnus
, adductor minimus
, and gracilis
. The anterior branch contributes a terminal, sensory branch which passes along the anterior border of gracilis and supplies the skin on the medial, distal part of the thigh.
The femoral nerve
is the largest and longest of the plexus' nerves. It gives motor innervation to iliopsoas, pectineus
, sartorius
, and quadriceps femoris; and sensory innervation to the anterior thigh, posterior lower leg, and hindfoot. In the pelvic area, it runs in a groove between psoas major and iliacus giving off branches to both muscles, and exits the pelvis through the medial aspect of muscular lacuna
. In the thigh it divides into numerous sensory and muscular branches and the saphenous nerve
, its long sensory terminal branch which continues down to the foot.
Lumbar
In tetrapod anatomy, lumbar is an adjective that means of or pertaining to the abdominal segment of the torso, between the diaphragm and the sacrum ...
region of the body which forms part of the lumbosacral plexus
Lumbosacral plexus
The anterior divisions of the lumbar nerves, sacral nerves, and coccygeal nerve form the lumbosacral plexus, the first lumbar nerve being frequently joined by a branch from the twelfth thoracic. For descriptive purposes this plexus is usually divided into three parts:* lumbar plexus* sacral plexus*...
. It is formed by the ventral divisions of the first four lumbar nerves
Lumbar nerves
The lumbar nerves are the five spinal nerves emerging from the lumbar vertebrae. They are divided into posterior and anterior divisions.-Posterior divisions:...
(L1-L4) and from contributions of the subcostal nerve
Subcostal nerve
The anterior division of the twelfth thoracic nerve is larger than the others; it runs along the lower border of the twelfth rib, often gives a communicating branch to the first lumbar nerve, and passes under the lateral lumbocostal arch.It then runs in front of the Quadratus lumborum, perforates...
(T12), which is the last thoracic nerve
Thoracic nerves
The thoracic nerves are the spinal nerves emerging from the thoracic vertebrae. Branches also exit the spine and go directly to the Sympathetic Chain Ganglia of the Autonomic Nervous System where they are involved in the functions of organs and glands in the head, neck, thorax and abdomen.-Anterior...
. Additionally, the ventral rami of the fourth lumbar nerve pass communicating branches, the lumbosacral trunk
Lumbosacral trunk
The lumbosacral trunk is nervous tissue that connects the lumbar plexus with the sacral plexus.-Structure:The lumbosacral trunk comprises the whole of the anterior division of the fifth and a part of that of the fourth lumbar nerve; it appears at the medial margin of the psoas major and runs...
, to the sacral plexus
Sacral plexus
-External links:*...
. The nerves of the lumbar plexus pass in front of the hip joint and mainly support the anterior part of the thigh.
The plexus is formed lateral to the intervertebral foramina
Intervertebral foramina
When the spinal vertebrae are articulated with each other the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramina constitute a canal for the protection of the medulla spinalis...
and pass through psoas major
Psoas major muscle
-External links: - "Posterior Abdominal Wall: Muscles of the Posterior Abdominal Wall"* *...
. Its smaller motor branches are distributed directly to psoas major, while the larger branches leave the muscle at various sites to run obliquely downward through the pelvic area to leave the pelvis under the inguinal ligament
Inguinal ligament
The inguinal ligament is a band running from the pubic tubercle to the anterior superior iliac spine. Its anatomy is very important for operating on hernia patients.-Anatomy:...
, with the exception of the obturator nerve which exits the pelvis through the obturator foramen
Obturator foramen
The obturator foramen is the hole created by the ischium and pubis bones of the pelvis through which nerves and muscles pass.- General structure :...
.
Branches
The iliohypogastric nerveIliohypogastric nerve
The iliohypogastric nerve is the superior branch of the anterior ramus of spinal nerve L1 after this nerve receives fibers from T12 . The inferior branch is the ilioinguinal nerve....
runs anterior to the psoas major
Psoas major muscle
-External links: - "Posterior Abdominal Wall: Muscles of the Posterior Abdominal Wall"* *...
on its proximal lateral border to run laterally and obliquely on the anterior side of quadratus lumborum
Quadratus lumborum muscle
The Quadratus lumborum is irregular and quadrilateral in shape, and broader below than above.-Origin and insertion:It arises by aponeurotic fibers from the iliolumbar ligament and the adjacent portion of the iliac crest for about 5 cm., and is inserted into the lower border of the last rib for...
. Lateral to this muscle, it pierces the transversus abdominis
Transversus abdominis muscle
The transversus abdominis muscle, also known as the transverse abdominus, transversalis muscle and transverse abdominal muscle, is a muscle layer of the anterior and lateral abdominal wall which is deep to the internal oblique muscle...
to run above the iliac crest
Iliac crest
-External links: - "Superficial muscles of the gluteal region and posterior thigh." - "Anterior Abdominal Wall: Osteology and Surface Anatomy " - "The Back, Posterior View" * *...
between that muscle and abdominal internal oblique
Abdominal internal oblique muscle
The internal oblique muscle is the intermediate muscle of the abdomen, lying just underneath the external oblique and just above the transverse abdominal muscle.-Structure:...
. It gives off several motor branches to these muscles and a sensory branch to the skin of the lateral hip. Its terminal branch then runs parallel to the inguinal ligament
Inguinal ligament
The inguinal ligament is a band running from the pubic tubercle to the anterior superior iliac spine. Its anatomy is very important for operating on hernia patients.-Anatomy:...
to exit the aponeurosis
Aponeurosis
Aponeuroses are layers of flat broad tendons. They have a shiny, whitish-silvery color, are histologically similar to tendons, and are very sparingly supplied with blood vessels and nerves. When dissected, aponeuroses are papery, and peel off by sections...
of the abdominal external oblique
Abdominal external oblique muscle
The external oblique muscle is the largest and the most superficial of the three flat muscles of the lateral anterior abdomen.-Structure:...
above the external inguinal ring where it supplies the skin above the inguinal ligament (i.e. the hypogastric region
Hypogastrium
The hypogastrium is an area of the human abdomen located below the navel. The pubis bone constitutes its lower limit....
) with the anterior cutaneous branch
Anterior cutaneous branch of iliohypogastric nerve
The anterior cutaneous branch continues onward between the Abdominal internal oblique and transverse muscles....
.
The ilioinguinal nerve
Ilioinguinal nerve
The ilioinguinal nerve is a branch of the first lumbar nerve . It separates from the first lumbar nerve along with the larger iliohypogastric nerve....
closely follows the ilihypogastric nerve on the quadratus lumborum, but then passes below it to run at the level of the iliac crest. It pierces the lateral abdominal wall and runs medially at the level of the inguinal ligament where it supplies motor branches to both transversus abdominis and sensory branches through the external inguinal ring to the skin over the pubic symphysis
Pubic symphysis
The pubic symphysis or symphysis pubis is the midline cartilaginous joint uniting the superior rami of the left and right pubic bones. It is located anterior to the urinary bladder and superior to the external genitalia; for females it is above the vulva and for males it is above the penis...
and the lateral aspect of the labia majora
Labia majora
The labia majora are two prominent longitudinal cutaneous folds that extend downward and backward from the mons pubis to the perineum and form the lateral boundaries of the pudendal cleft, which contains the labia minora, interlabial sulci, clitoral hood, clitoral glans, frenulum clitoridis, the...
or scrotum
Scrotum
In some male mammals the scrotum is a dual-chambered protuberance of skin and muscle containing the testicles and divided by a septum. It is an extension of the perineum, and is located between the penis and anus. In humans and some other mammals, the base of the scrotum becomes covered with curly...
.
The genitofemoral nerve
Genitofemoral nerve
In human anatomy, the genitofemoral nerve originates from the upper part of the lumbar plexus of spinal nerves. Its roots are L1 and L2 .The genitofemoral nerve is responsible for both the efferent and afferent limbs of the cremasteric reflex...
pierces psoas major anteriorly below the former two nerves to immediately split into two branches that run downward on the anterior side of the muscle. The lateral femoral branch
Lumboinguinal nerve
The lumboinguinal nerve descends on the external iliac artery, sending a few filaments around it, and, passing beneath the inguinal ligament, enters the sheath of the femoral vessels, lying superficial and lateral to the femoral artery.It pierces the anterior layer of the sheath of the vessels and...
is purely sensory. It pierces the vascular lacuna
Vascular lacuna
The vascular lacuna is the medial compartment beneath the inguinal ligament, for the passage to the femoral vessels, lymph node, and femoral branch of the genitofemoral nerve. Medial to lateral these are the: Rosenmuller lymph node, femoral vein, femoral artery, and gem oral branch of...
near the saphenous hiatus
Saphenous opening
The saphenous opening is an oval opening in the superomedial part of the fascia lata, lies 3–4 cm inferolateral to the pubic tubercle. It is about 3 cm long and 1.5 cm wide.-Description:...
and supplies the skin below the inguinal ligament (i.e. proximal, lateral aspect of femoral triangle
Femoral triangle
The femoral triangle is an anatomical region of the upper inner human thigh.-Boundaries:It is bounded by:* the inguinal ligament* the medial border of the adductor longus muscle...
). The genital branch
Genital branch of genitofemoral nerve
The genital branch of the genitofemoral nerve arises from the ventral primary divisions of L1 and L2 spinal nerve roots, passes outward on the Psoas major, and pierces the fascia transversalis, or passes through the deep inguinal ring; it then descends behind the spermatic cord to the scrotum,...
differs in males and females. In males it runs in the spermatic cord
Spermatic cord
The spermatic cord is the name given to the cord-like structure in males formed by the ductus deferens and surrounding tissue that run from the abdomen down to each testicle.-Contents of spermatic cord:...
and in females in the inguinal canal
Inguinal canal
The inguinal canal is a passage in the anterior abdominal wall which in men conveys the spermatic cord and in women the round ligament. The inguinal canal is larger and more prominent in men.-Site:...
together with the teres uteri ligament
Round ligament of uterus
The round ligament of the uterus originates at the uterine horns, in the parametrium. The round ligament leaves the pelvis via the deep inguinal ring, passes through the inguinal canal and continues on to the labia majora where its fibers spread and mix with the tissue of the mons...
. It then sends sensory branches to the scrotal skin in males and the labia majora in females. In males it supplies motor innervation to the cremaster
Cremaster muscle
-Contraction:Its function is to raise and lower the testes in order to regulate the temperature of the testes and promote spermatogenesis. Contraction may also occur during arousal which can prevent injury to the testicles during sex....
.
The lateral cutaneous femoral nerve
Lateral cutaneous nerve of thigh
The lateral cutaneous nerve of the thigh is a cutaneous nerve that innervates the skin on the lateral part of the thigh.-Structure:...
pierces psoas major on its lateral side and runs obliquely downward below the iliac fascia
Iliac fascia
The iliac fascia is a fascia in the pelvic area of the human body.It has the following connections:* laterally, to the whole length of the inner lip of the iliac crest....
. Medial to the anterior superior iliac spine
Anterior superior iliac spine
The anterior superior iliac spine is an important landmark of surface anatomy. It refers to the anterior extremity of the iliac crest of the pelvis, which provides attachment for the inguinal ligament, and the sartorius muscle...
it leaves the pelvic area through the lateral muscular lacuna
Muscular lacuna
The Muscular lacuna is the lateral compartment beneath the inguinal ligament, for the passage of the iliopsoas muscle and femoral nerve; it is separated by the iliopectineal arch from the vascular lacuna....
. In the thigh it briefly passes under the fascia lata
Fascia lata
-Thickness:It is an investment for the whole of the thigh, but varies in thickness in different parts.Thus, it is thicker in the upper and lateral part of the thigh, where it receives a fibrous expansion from the Glutæus maximus, and where the Tensor fasciæ latæ is inserted between its layers; it...
before it breaches the fascia and supplies the skin of the anterior thigh.
The obturator nerve
Obturator nerve
The obturator nerve in human anatomy arises from the ventral divisions of the second, third, and fourth lumbar nerves; the branch from the third is the largest, while that from the second is often very small.-Path:...
leaves the lumbar plexus and descends behind psoas major on it medial side, then follows the linea terminalis
Linea terminalis
The linea terminalis or innominate line consists of the pectineal line, the arcuate line, and the sacral promontory.It is part of the pelvic brim, which is the edge of the pelvic inlet. The pelvic inlet is typically used to divide the abdominopelvic cavity into an abdominal and a pelvic cavity...
into the lesser pelvis
Lesser pelvis
The lesser pelvis is that part of the space enclosed by the skeleton of the pelvis which is situated between the pelvic inlet and the pelvic floor. Some authors call this cavity the pelvic cavity...
, and finally leaves the pelvic area through the obturator canal
Obturator canal
The obturator canal is a passageway formed in the obturator foramen by part of the obturator membrane. It connects the pelvis to the thigh.The obturator artery, obturator vein, and obturator nerve all travel through the canal.-Pathology:...
. In the thigh, it sends motor branches to obturator externus
Obturator externus muscle
The obturator externus muscle is a flat, triangular muscle, which covers the outer surface of the anterior wall of the pelvis.It is sometimes considered part of the medial compartment of thigh, and sometimes considered part of the gluteal region....
before dividing into an anterior and a posterior branch, both of which continues distally. These branches are separated by adductor brevis
Adductor brevis muscle
The adductor brevis is a muscle in the thigh situated immediately behind the pectineus and adductor longus.-Origin and insertion:It is somewhat triangular in form, and arises by a narrow origin from the outer surfaces of the superior and inferior rami of the pubis, between the gracilis and...
and supply all thigh adductors with motor innervation: pectineus
Pectineus muscle
The pectineus muscle is a flat, quadrangular muscle, situated at the anterior part of the upper and medial aspect of the thigh....
, adductor longus
Adductor longus muscle
In the human body, the adductor longus is a skeletal muscle located in the thigh. One of the adductor muscles of the hip, its main function is to adduct the thigh and it is innervated by the obturator nerve...
, adductor brevis, adductor magnus
Adductor magnus muscle
The adductor magnus is a large triangular muscle, situated on the medial side of the thigh.It consists of two parts. The portion which arises from the ischiopubic ramus is called the "adductor portion", and the portion arising from the tuberosity of the ischium is called the "hamstring portion"...
, adductor minimus
Adductor minimus muscle
In human anatomy, the adductor minimus is a small and flat skeletal muscle in the thigh which constitutes the upper, lateral part of the adductor magnus muscle....
, and gracilis
Gracilis muscle
The gracilis is the most superficial muscle on the medial side of the thigh. It is thin and flattened, broad above, narrow and tapering below.-Origin and insertion:...
. The anterior branch contributes a terminal, sensory branch which passes along the anterior border of gracilis and supplies the skin on the medial, distal part of the thigh.
The femoral nerve
Femoral nerve
The femoral nerve, the largest branch of the lumbar plexus, arises from the dorsal divisions of the ventral rami of the second, third, and fourth lumbar nerves...
is the largest and longest of the plexus' nerves. It gives motor innervation to iliopsoas, pectineus
Pectineus muscle
The pectineus muscle is a flat, quadrangular muscle, situated at the anterior part of the upper and medial aspect of the thigh....
, sartorius
Sartorius muscle
The Sartorius muscle – the longest muscle in the human body – is a long thin muscle that runs down the length of the thigh. Its upper portion forms the lateral border of the femoral triangle.-Origin and insertion:...
, and quadriceps femoris; and sensory innervation to the anterior thigh, posterior lower leg, and hindfoot. In the pelvic area, it runs in a groove between psoas major and iliacus giving off branches to both muscles, and exits the pelvis through the medial aspect of muscular lacuna
Muscular lacuna
The Muscular lacuna is the lateral compartment beneath the inguinal ligament, for the passage of the iliopsoas muscle and femoral nerve; it is separated by the iliopectineal arch from the vascular lacuna....
. In the thigh it divides into numerous sensory and muscular branches and the saphenous nerve
Saphenous nerve
The saphenous nerve is the largest cutaneous branch of the femoral nerve.-Path:It approaches the femoral artery where this vessel passes beneath the sartorius, and lies in front of the artery, behind the aponeurotic covering of the adductor canal, as far as the opening in the lower part of the...
, its long sensory terminal branch which continues down to the foot.
| Nerve | Segment | Innervated muscles | Cutaneous branches |
|---|---|---|---|