- 14 - Group of students - Rawan almujabili د. محمد المحتسب - 1 P a g e
Nerves of the posterior abdominal wall The spinal cord gives off spinal nerves between the vertebrae. In the abdomen, through the lumbar vertebrae, there are 5 lumbar spinal nerves on each side. Remember: a shows H-shaped grey matter, with anterior, posterior and lateral horns. In the abdomen, there are a sympathetic chain with 4 or 5 ganglia on each side of the vertebral column. The sympathetic fibers originate from the lateral horn of the grey matter, from the thoracolumbar region. Thoraco refers to all thoracic spinal nerves(t1-t12). Lumbar refers to L1 and L2. The sympathetic fibers arise from their lateral horns and a nucleus known as the sympathetic nucleus. The number of the sympathetic fibers then is 14; 12 arising from thoracic spinal origin(t1-t12) and two arising from lumbar origin(l1-l2). Remember: brachial plexus is a plexus that innervates the upper limb, originating from cervical vertebrae C5-C8 in addition to T1 and occasionally T2. It gives branches like radial, ulnar, median and axillary nerves, all supply different structures in the upper limb. Lumbar plexus is found in the abdomen and it supplies the lower limb. It originates from the anterior rami of the upper four lumbar vertebrae. It gives off branches like: iliohypogastric, ilioinguinal, lateral cutaneous nerve of the thigh, femoral and obturator nerves. 2 P a g e
Iliohypogastric: originates from L1, provides sensory and motor innervation; motor for abdominal muscles and sensory for the skin between the umbilicus and symphysis pubis. Ilioinguinal: originates from L1, provides sensory and motor innervation; motor for abdominal muscles and sensory for the skin of scrotum in males and labium majus in females. NOTE: the ilioinguinal penetrates the posterior wall of the inguinal canal and attaches closely to the spermatic cord while remaining not a part of its content. Together they will move in the inguinal canal and exit through the superficial inguinal ring, where the spermatic cord will go to the testis and the ilioinguinal will reach the scrotum to supply its skin. (this was mentioned to clear a question in the exam). NOTE: abdominal muscles receive motor innervation from the lower 6 costal nerves in addition the iliohypogastric and ilioinguinal nerves. Lateral cutaneous nerve of the thigh(l2 and L3): it passes medially to ASIS and deep laterally to the inguinal ligament. It Supplies the skin of the lateral surface of the thigh. Femoral nerve: originates from L2, L3, L4, passes behind the inguinal ligament, present in the femoral triangle outside the femoral sheath. It divides into anterior and posterior branches, each then divides into sensory and motor branches. NOTE: both the femoral and obturator nerves originate from the anterior primary rami of L2, L3 and L4. However, the difference in their origin is that the anterior rami further divide into anterior and posterior branches; the femoral originates from the posterior branch while the obturator originates from the anterior branch. L4 gives 2 branches: upper and lower branches. The last one is called lumbosacral trunk as it participates in the lumbosacral plexus. L5 is a part of lumbosacral plexus. 3 P a g e
The upper branch of L4 contributes in the formation of both: obturator and femoral nerves(as mentioned before). So, the lumbar plexus of nerves is formed from the anterior primary rami of the upper three lumbar nerves and the upper division of the forth one. The Obturator nerve (L2, 3, and 4) leaves the pelvis by passing through the obturator foramen with an artery and vein into the thigh. It innervates the muscles of the medial compartment of the thigh (gracilis, adductor longus, adductor brevi, pubic part of adductor magnus), this was about the motor branch of the obturator. It also gives a sensory branch which innervates the skin of the medial part of the thigh just above the knee joint. The genitofemoral nerve (L1 and L2) emerges from the anterior surface of the psoas muscle.(note that iliohypogastric nerve, ilioinguinal nerve, lateral cutaneous nerve of the thigh, and femoral nerves emerge from the lateral side of the muscle, while the obturator and the lumbosacral trunk emerge from the medial side of the muscle). The GF nerve runs downward in front of the muscle and divides into : 1- A genital branch(motor), which enters the spermatic cord and supplies the Cremasteric muscle. 2- A femoral branch(sensory), which runs deep to the inguinal ligament and supplies a small area of the skin of the anterior surface of the thigh. Cremasteric reflex:. When stimulating the skin of the thigh(which is innervated by the femoral branch of the GF) in the male, reflex contraction of the Cremasteric muscle happens resulting in drawing the testis upward within the scrotum, HOW? When itching the skin, sensory impulses run via the femoral branch toward L1 and L2, as a result, reflux occurs resulting in motor impulses running via the Genital branch toward the Cremasteric muscle. **Cremasteric reflex may be absent with: testicular torsion, upper and lower motor neuron disorders, as well as a spine injury of L1-4 P a g e
L2. It can also occur if the ilioinguinal nerve is accidentally cut during a hernia repair. Sympathetic Trunk It starts from the neck and ends in the coccyx. It runs along the lateral side of the vertebral column. The sympathetic divisions -In the neck there are 3 cervical ganglia: superior, middle and inferior sympathetic ganglia. Mainly they give the sympathetic fibers to the chest and neck. - In the chest there are 12 thoracic ganglia. - In the abdomen: 4-5 lumbar ganglia - 4 sacral ganglia - 1 Coccygeal ganglion which is the end of the chain. Note: They are 2 chains, one at each side of the vertebral column (so divisions are pairs). *to better understand, follow the figure below while reading the following points. The preganglionic fibers originate from the sympathetic nucleus which is present in the lateral Horn of the spinal cord(as mentioned before). 5 P a g e
They are 14 in number; run within the 12 thoracic and the upper 2 lumber spinal nerves. Sympathetic fibers leave the sympathetic nucleus of the spinal cord via the anterior(ventral)roots of the spinal nerves. Then they leave the spinal nerve as white rami to join the sympathetic chain(ganglia) ( 14 white rami; 12 thoracic and 2 lumbar). (It s called like that since it s myelinated). After that, they synapse in paravertebral ganglion and leave it, going back to the spinal nerves as gray rami(to innervate sweat glands, errector papillae muscle & blood vessels). (It s called like that since it s not myelinated). **So, the sympathetic fibers enter the ganglia as white rami (preganglionic) and leave as grey rami (postganglionic). Lumbar sympathetic chain or (abdominal part of sympathetic chain): There are 2 chains, one at each side. the right chain is located on the right margin of I.V.C the left is located on the left edge of abdominal aorta, it descends behind common iliac vessels to continue as pelvic sympathetic chain. NOTE: the thoracic sympathetic chain reaches the abdomen by passing deep to medial arcuate ligament of diaphragm. Grey rami are 31, since they are the postganglionic nerve fibers that emerge from sympathetic ganglia to join the spinal nerves again, each spinal nerve has grey rami to innervate glands, smooth muscles, blood vessels and errector pili muscles of the skin. Aortic plexus: Plexus always contains sympathetic and parasympathetic fibers. Aortic plexus or prevertebral plexus are located anterior to the aorta. 6 P a g e
Aortic plexuses: 1-The celiac plexus Receive preganglionic sympathetic nerves from the thorax, specifically from the greater splanchnic nerves T5-T9 occasionally T10, these are preganglionic sympathetic fibers that run together to form the greater splanchnic nerves. They are called splanchnic since they are preganglionic and are emerged from the vertebral Column without synapsing in the sympathetic chain, they rather synapse in the celiac ganglion. These splanchnic nerves leave the thorax to the abdomen through the diaphragm. Celiac ganglion also contains preganglionic parasympathetic nerves, they leave the celiac ganglion without synapsing since they synapse in the myenteric plexus in the walls of organs. Both sympathetic and parasympathetic fibers accompany the branches of the celiac trunk. 2-Renal plexus: Receives preganglionic sympathetic from the lowest splanchnic nerves T11& T12 which synapses in the renal plexus, receives parasympathetic fibers from the sacral parasympathetic and doesn t synapse in the renal ganglion. Both leave with renal arteries branches. 3-superior mesenteric: Receives preganglionic sympathetic from Lesser splanchnic nerves (T9&T10, fibers join superior mesenteric artery branches. 4-inferior mesenteric: Receives preganglionic sympathetic from the Lumber splanchnic nerves(l1&l2, nerve fibers join inferior mesenteric artery branches. 7 P a g e
1. After the white rami emerge from the lateral horn of T1-T12 and L1-L2 vertebrae to enter the sympathetic chain, they may:. 1-Synapse in a corresponding ganglion(same level) e.g.: white ramus of T2 spinal nerve, synapses in T2 sympathetic ganglion. 2-ascend upward to synapse with higher ganglia e.g.: white ramus of T2 moves upward through the chain then it synapses in T1 sympathetic ganglion or in the cervical ones. 3-Descend downward to synapse in lower ganglia. e.g.: white ramus of L1 moves downward through the chain then synapses in lumbar or sacral sympathetic ganglia. **Another option that they may not synapse in sympathetic chain & continue as preganglionic fibers to form ( splanchnic nerves) which synapsing in pre-vertebral (pre-aortic) ganglia like celiac, superior mesenteric, inferior mesenteric. Parasympathetic nerves,like vagus have long pre-ganglionic fiber, synapse in the wall of GIT (in the myenteric plexus), and have very short post-ganglionic fibers. Sympathetic fibers have short preganglionic fibers and long post ganglionic fibers. Nerves which leave the sympathetic chain: 1-They leave as grey rami ( 31 post ganglionic fibers join spinal nerves to reach sweat glands, errectore papillae & blood vessels): - Superior, middle and inferior sympathetic cervical ganglia are found in the neck region, superior gives lower 4 cranial nerves and upper 4 cervical nerves. Middle gives 5 th and 6 th nerves while the inferior gives 7 th and 8 th. -Thoracic, lumbar and sacral plexuses give nerves that correspond to each segment. 2-sympathetic visceral nerves, go to blood vessels, they are:. 8 P a g e
1- Int, & Ext. carotid nerves from S.C.S.G to corresponding arteries 2- pharyngeal branch : from S.C.S.G to pharyngeal plexus 3- pulmonary nerves : 2nd, 3rd& 4 th thoracic ganglia 4- cardiac nerves : 2nd, 3 rd & 4 th thoracic ganglia + 3 cervical ganglia 5-splanchnic nerves : greater, lesser and lowest splanchnic nerves: arise from the thorax to supply the abdomen. Splanchnic nerves :. Greater splanchnic : arises from T5 to T9(sometimes T10), penetrates the diaphragm, then synapses in the celiac ganglion. Postganglionic fibers follow the branches of celiac artery to reach the smooth muscle and the glands of the stomach. lesser splanchnic : arises from T9 and T10, pierces the crus of the diaphragm, ends in the superior mesenteric ganglia. Post ganglia fibers follow the branches of superior mesenteric artery to reach the smooth muscle and the glands of the small intestines and parts of the descending an transverse colon. lowest splanchnic : May be absent, if present arises from the last one or two thoracic ganglia, Pierces the diaphragm to end in renal plexus(which goes to the suprarenal glands). Lumber splanchnic branch: It Arise from L1& L2 and synapses in inferior mesenteric ganglia (it is mainly traveling to the pelvic viscera). The postganglionic fibers go to sigmoid and pelvic colon. Also, other postganglionic fibers form the descending hypogastric plexus to supply urinary bladder, rectum and genitalia. However, the parasympathetic (S2, S3, & S4) throughout the plexus are preganglionic they travel to viscera in the abdomen and pelvis and to the genitalia. 9 P a g e
Thoracic sympathetic chain: Site: - enters the thorax in front of neck of 1st rib and leaves it by passing behind the medial arcuate ligament. - In the upper part it lies on the necks of the ribs while in the lower part it lies on the side of the bodies of vertebrae. Ganglia: (10-12 ganglia in number), 1st ganglia sometimes fuses with the I.C.S.G stellate ganglia Branches: 1. Gray & white rami communicants. 2. 2 nd, 3 rd & 4 th ganglia ( cardiac & pulmonary ). 3. The upper five ganglia give aortic oesophageal branches. 4. Greater, lesser and lowest splanchnic nerves. Visceral sensory and autonomic neurons participation in visceral reflex arcs: Many of the visceral reflexes are spinal reflexes(generated within the spinal cord), we need these reflexes in defecation and micturition processes. The sensory nerves enter from the dorsal root to the grey matter in the spinal cord. Then they will be processed and leave spinal nerve as a reflexes (through anterior root (motor or autonomic response)), then travel to ganglia underneath the viscera. Some reflexes only involve peripheral neurons; spinal cord is not involved. The end we advise you to refer to the slide as it includes lots of explanatory figures and pictures. BEST OF LUCK 10 P a g e