Lumbar and Sacral Plexuses PDF

0  Lumbar and Sacral Plexuses Lumbar Plexus The lumbar plexus is formed from the anterior rami of the upper four lumbar nerves (L1-L4). o It’s is formed in the psoas major muscle. The branches of the plexus emerge from borders of this muscle: o Most...

0  Lumbar and Sacral Plexuses Lumbar Plexus The lumbar plexus is formed from the anterior rami of the upper four lumbar nerves (L1-L4). o It’s is formed in the psoas major muscle. The branches of the plexus emerge from borders of this muscle: o Most branches emerge from the lateral border of the psoas. ▪ These branches, from above downward: The iliohypogastric nerve, The ilioinguinal nerve, Lateral cutaneous nerve of the thigh, The femoral nerve. o Obturator nerve emerges from the medial border of the psoas. ▪ L4 nerve root also emerges from the medial border. o Genitofemoral nerve emerges on the anterior surface of the psoas. - Branches from lateral border of the psoas: iliohypogastric and ilioinguinal nerves (L1) Both nerves arise from L1. o Some sources say iliohypogastric receive some fibers from the subcostal nerve (T12). They enter the lateral and anterior abdominal walls. o Both supply muscles of anterior abdominal wall. ▪ External oblique, internal oblique, transversus abdominis muscles. The iliohypogastric nerve supplies the skin of the lower part of the anterior abdominal wall. The ilioinguinal nerve passes through the inguinal canal. o To supply the skin of the groin and the scrotum (or labium majus in females). Lateral cutaneous nerve of the thigh (L2-L3) It arises from L2-L3. It crosses the iliac fossa in front of the iliacus muscle. o Then enters the thigh passing behind the lateral end of the inguinal ligament. It supplies the skin over the lateral surface of the thigh. The femoral nerve (L2-L4) It arises from L2, 3, and 4. The largest branch of the lumbar plexus. o Most inferiorly located branch of branches from lateral border of the psoas. It runs downward and laterally between the psoas and the iliacus muscles. o Enters the thigh behind the inguinal ligament ▪ Lateral to the femoral vessels and the femoral sheath. ▪ Femoral nerve doesn’t pass through the femoral sheath. It supplies the iliacus, pectineus, sartorius, quadriceps femoris muscles. It gives many branches in the lower limb: o Cutaneous branches, it supplies the skin of the anterior surface of the thigh. o Saphenous branch, it supplies the skin of the medial side of the leg and foot. o Articular branches to hip and knee joints. 1  - Branches from anterior border of the psoas: Genitofemoral nerve (L1-L2) It arises from L1-L2. It runs downward in front of the psoas muscle, and divides into: o Genital branch, which enters the spermatic cord and supplies the cremaster muscle. o Femoral branch, which supplies a small area of skin on the anterior surface of thigh. This nerve is involved in the cremasteric reflex. - Branches from medial border of the psoas: The obturator nerve (L2-L4) It arises from L2-L4. It enters the pelvic brim (pelvis) in front of the sacroiliac joint and behind the common iliac vessels. It leaves the pelvis by passing through the obturator foramen into the thigh. In the thigh: o It supplies muscles of medial compartment of the thigh (adductor muscles). ▪ Gracilis, adductor brevis, adductor longus, adductor portion of adductor magnus muscles. o It supplies obturator externus, pectineus muscles o It supplies skin on medial surface of thigh. NOTE: There are segmental branches from lumbar plexus to supply quadratus lumborum and psoas major. Sacral Plexus The sacral plexus lies on the posterior pelvic wall in front of the piriformis muscle. o Posterior relation of sacral plexus: piriformis muscle. o Anterior relation of sacral plexus: internal iliace vessels. It is formed from anterior rami of (L4-S3) nerves. o the anterior rami of the L4-L5 nerves. ▪ The L4 nerve arises from medial border of the psaos ▪ Then, part of L4 nerve joins the L5 nerve to form the lumbosacral trunk. ▪ The lumbosacral trunk passes down and joins the sacral nerves o The anterior rami of the S1-S3 nerves. ▪ They emerge from the anterior sacral foramina. Branches to the gluteal region and thigh o Leave the pelvis through the greater sciatic foramen: The sciatic nerve (L4-S3) Arise from L4-S3. The largest branch of the plexus and the largest nerve in the body. It emerges from the lower border of piriformis muscle. The sciatic nerve divides into tibial nerve and common peroneal nerve. o It divides in the lower third of the thigh ▪ It can sometimes divide in the upper part of the thigh or in the gluteal region. 2 Common peroneal (fibular) nerve In thigh, It supplies Biceps femoris muscle (short head). In leg, it divides into deep and superficial peroneal nerves. The Deep peroneal nerve supplies the muscles of anterior compartment of the leg. o Tibialis anterior, extensor hallucis longus, extensor digitorum longus, peroneus tertius, extensor digitorum brevis. o It also supply skin over cleft between first and second toes. The superficial peroneal branch supplies muscles of lateral compartment of the leg o The fibularis (peroneus) longus and fibularis brevis muscles o It also supply skin over lower third of anterior surface of leg and dorsum of foot. Tibial nerve In thigh, It supplies Hamstring muscles. o Semitendinous, biceps femoris [long head], adductor magnus [hamstring part]. In leg, it supplies muscles of posterior compartment of the leg. o Gastrocnemius, soleus, plantaris, popliteus, tibialis posterior, flexor digitorum longus, flexor hallucis longus. It divides into medial and lateral plantar branches to supple muscles of sole of foot; It gives a sural branch to supply skin on lateral side of leg and foot The superior gluteal nerve It emerges from the upper border of piriformis muscle. Supplies the gluteus medius and gluteus minimus and the tensor fasciae latae muscles The inferior gluteal nerve It emerges from the lower border of piriformis muscle. Supplies the gluteus maximus muscle The posterior cutaneous nerve of the thigh, It emerges from the lower border of piriformis muscle. Supplies the skin of the buttock and the back of the thigh The nerve to the quadratus femoris muscle, Supplies quadratus femoris and inferior gemellus muscle. The nerve to the obturator internus muscle Supplies obturator internus and superior gemellus muscle. The nerves to the piriformis muscle Supplies piriformis muscle. Branches to perineum: The pudendal nerve (S2-S4) Leaves the pelvis through the greater sciatic foramen & enters the perineum through the lesser sciatic foramen. Supplies structures in the perinuem. 3 4  Autonomic Nervous System (ANS) The autonomic nervous system has: afferent neurons, connector neurons , and efferent neurons. The afferent impulses originate in visceral receptors and travel via afferent pathways to the CNS. o Then, impulses are integrated through connector neurons at different levels o The CNS send impulse via efferent pathways to visceral effector organs. The efferent pathways made up of preganglionic and postganglionic neurons. 1. Preganglionic neurons: o Cell bodies are situated in: ▪ The lateral gray column of the spinal cord. ▪ The motor nuclei of the 3rd, 7th, 9th, and 10th cranial nerves. o The axons of these cell bodies synapse on the cell bodies of the postganglionic neurons 2. Postganglionic neurons: o Cell bodies of the postganglionic neurons are collected together to form ganglia. The control exerted by the autonomic system is extremely rapid and widespread. o Because one preganglionic axon may synapse with several postganglionic neurons. Autonomic plexuses are large collections of afferent and efferent fibers and their associated ganglia. o Present in the thorax, abdomen, and pelvis. ANS is distributed throughout the central and peripheral nervous systems. ANS is divided into two parts: o Sympathetic o Parasympathetic Both the sympathetic and parasympathetic divisions produce opposite effects in most organs. Sympathetic Part of the Autonomic System The sympathetic system is the larger of the two parts of ANS. o Widely distributed throughout the body ▪ Innervating the heart and lungs, the muscle in the walls of many blood vessels, the hair follicles and the sweat glands, and many abdominopelvic viscera. The function of the sympathetic system is to prepare the body for an emergency: o A redistribution of blood ▪ It leaves the skin and gastrointestinal tract and passes to the brain, heart, and skeletal muscle. ▪ The heart rate is increased ▪ Arterioles of the skin and intestine are constricted ▪ Arterioles of skeletal muscle are dilated o Blood pressure is raised. o Pupils are dilated o Smooth muscles of the bronchi, intestine, and bladder wall are dilated; and the sphincters are closed. o The hair is made to stand on end, and sweating occurs. Efferent Nerve Fibers (Thoracolumbar Sympathetic Outflow) Cell bodies of sympathetic connector neurons are located in the lateral gray columns of T1-L2 segments of the spinal cord. o Sometimes they’re present in L3 segment. The myelinated axons (preganglionic fibers) of these cells leave the spinal cord in the anterior nerve roots. o They pass via the white rami communicantes. o To reach the paravertebral ganglia of the sympathetic trunk. 5  - Preganglionic fibers in paravertebral ganglia in the sympathetic trunk are distributed as follows: 1. Preganglionic fibers synapse with an excitor neuron in the ganglion: o The postganglionic nonmyelinated axons leave the ganglion and pass to the gray rami communicantes. ▪ Postganglionic fibers pass via the gray rami communicantes to join the thoracic spinal nerves. o The postganglionic fibers are distributed in branches of the spinal nerves to: ▪ Smooth muscle in the blood vessel walls. ▪ Sweat glands. ▪ Arrector muscles of the hairs of the skin. 2. Preganglionic fibers travel: a. Up in the sympathetic trunk to synapse in ganglia in the cervical region. i. Then, the postganglionic nerve fibers pass via gray rami communicantes to join the cervical spinal nerves. b. Down in the sympathetic trunk to synapse in ganglia the lower lumbar and sacral regions. i. Then, the postganglionic nerve fibers pass via gray rami communicantes to join the lumbar, sacral, and coccygeal spinal nerves. 3. Preganglionic fibers may pass through the ganglia of the sympathetic trunk without synapsing. o These preganglionic myelinated fibers leave the sympathetic trunk as: ▪ The greater splanchnic, lesser splanchnic, and least (lowest) splanchnic nerves. The splanchnic nerves The splanchnic nerves are preganglionic fibers that didn’t synapse in paravertebral ganglia. o They synapse in prevertebral ganglia The postganglionic fibers arise from the excitor neurons in the peripheral plexuses (prevertebral ganglia). o Then, they’re distributed to the smooth muscle and glands of the viscera. A few preganglionic fibers end directly on the chromaffin cells of the suprarenal medulla. o These fibers are traveling in the greater splanchnic nerve. o Chromaffin cells are modified sympathetic excitor neurons (postganglionic neurons). ▪ Responsible for the secretion of epinephrine and norepinephrine. The greater splanchnic nerve Formed from branches from the 5th-9th thoracic ganglia. It pierces the crus of diaphragm. o To synapse in the ganglia of the celiac plexus, the renal plexus, and the suprarenal medulla. The lesser splanchnic nerve Formed from branches of the 10th-11th thoracic ganglia. It pierces the crus of diaphragm. o To synapse in ganglia in the lower part of the celiac plexus. o Or passes through the celiac plexus to synapse in the aorticorenal ganglion and superior mesenteric ganglion of the superior mesenteric plexus. The lowest splanchnic nerve Formed from the 12th thoracic ganglion (it’s not always present). Pierces the crus of diaphragm, and synapses in the ganglia of the renal plexus. 6 Afferent Nerve Fibers (Sympathetic) Afferent myelinated nerve fibers travel from the viscera through the sympathetic ganglia without synapsing. They pass from white rami communicantes to the spinal nerve. Then, reach their cell bodies in the dorsal (posterior) root ganglion of the corresponding spinal nerve. o Cell bodies in DRG are pseudounipolar neurons. ▪ With central and peripheral processes. The central axons then enter the spinal cord, and here: o It may form the afferent component of a local reflex arc. o It may ascend to higher centers. ▪ such as the hypothalamus. Sympathetic Trunks The sympathetic trunks are two ganglionated nerve trunks extending the vertebral column. o In the neck, each trunk has 3 cervical ganglia. ▪ The trunks lie anterior to transverse processes of cervical vertebrae. o In the thorax, each trunk has 11 or 12 thoracic ganglia. ▪ The trunks lie anterior to the head of the ribs ▪ On the sides of the vertebral bodies. o In the lumbar (abdomen) region, each trunk has 4 or 5 lumbar ganglia. ▪ In the abdomen, the trunks are anterolateral to the sides of the bodies of the lumbar vertebrae. o In the pelvis, each trunk has 4 or 5 sacral ganglia. ▪ The trunks are anterior to the sacrum. o Below, the two trunks end by joining together to form a single (unpaired) ganglion, called the ganglion impar. ▪ Blocking the ganglion impar is used to relieve pain in cancer patients. Parasympathetic Part of the Autonomic System The activities of the parasympathetic part are directed toward conserving and restoring energy: o Heart rate is slowed o Pupils are constricted o Peristalsis and glandular activity is increased o Sphincters are opened o Bladder wall is contracted. Efferent Nerve Fibers (Craniosacral Parasympathetic Outflow) The parasympathetic connector neurons' cell bodies are located in: o The brainstem and the sacral segments of the spinal cord. 1. The cranial connector nerve cells: Located in the brainstem form nuclei in the following cranial nerves: o Oculomotor (III): parasympathetic (Edinger-Westphal) nucleus. o Facial (VII): superior salivatory nucleus and lacrimatory nucleus. o Glossopharyngeal (IX): inferior salivatory nucleus o Vagus (X): dorsal nucleus of the vagus The myelinated axons of these connector nerve cells emerge from the brain within the cranial nerves. 2. The sacral connector nerve cells: Found in the gray matter of the S2-S4 segments of the spinal cord. o Not sufficiently numerous to form a lateral gray horn. The myelinated axons leave the spinal cord in the anterior nerve roots of the corresponding spinal nerves. They then leave the sacral nerves and form the pelvic splanchnic nerves (preganglionic fibers). 7  The myelinated efferent fibers of the craniosacral outflow are preganglionic fibers. o They synapse in peripheral ganglia located close to the viscera they innervate. - Peripheral ganglia: The cranial parasympathetic ganglia: o Ciliary ganglion o Pterygopalatine ganglion o Submandibular ganglion o Otic ganglion In certain locations, the ganglion cells are placed in nerve plexuses, such as: o Cardiac plexus. o Pulmonary plexus. o Myenteric plexus (Auerbach plexus). o Mucosal plexus (Meissner plexus). The pelvic splanchnic nerves synapse in ganglia in the hypogastric plexuses. The postganglionic parasympathetic fibers are nonmyelinated and of relatively short length compared with sympathetic postganglionic fibers. o Because the ganglia is close to the effector organ. Afferent Nerve Fibers (Parasympathetic) Afferent myelinated fibers travel from the viscera to their cell bodies. o Located either in the sensory ganglia of the cranial nerves or in the DRG of the sacral spinal nerves. o The central axons then enter the CNS and take part in: ▪ The formation of local reflex arcs ▪ Pass to higher centers of the ANS, such as the hypothalamus. The nerve endings in the autonomic afferent component are activated by stretch or lack of oxygen. o They may not be activated by heat or touch. Once the afferent fibers enter the CNS, they travel alongside the somatic afferent fibers. The Large Autonomic Plexuses Large collections of sympathetic and parasympathetic afferent and efferent nerve fibers & their associated ganglia. o Found in the thorax, abdomen, and pelvis. o Branches from these plexuses innervate the viscera. In the thorax: o Cardiac, pulmonary, and esophageal plexuses. In the abdomen: o Celiac, superior mesenteric, inferior mesenteric, and aortic plexuses. ▪ The plexuses are associated with the aorta and its main branches. In the pelvis: o superior hypogastric and inferior hypogastric plexuses. 8 Autonomic Ganglia The autonomic ganglion is the site where preganglionic nerve fibers synapse on postganglionic neurons Ganglia are situated along the course of efferent nerve fibers of the autonomic nervous system. Sympathetic ganglia: o Paravertebral in sympathetic trunk. o Prevertebral in position (e.g., celiac and superior mesenteric ganglia). Parasympathetic ganglia: are situated close to or within the walls of the viscera. An autonomic ganglion consists of: o a collection of multipolar neurons together with capsular or satellite cells and a connective tissue capsule. Nerve bundles are attached to each ganglion and consist of: o Preganglionic nerve fibers that enter the ganglion. o Postganglionic nerve fibers that have arisen from neurons within the ganglion and are leaving the ganglion o Afferent and efferent nerve fibers that pass through the ganglion without synapsing. The preganglionic fibers are; o myelinated, small, and relatively slow–conducting B fibers. The postganglionic fibers are: o unmyelinated, smaller, and slower-conducting C fibers. ➔ Small intensely fluorescent (SIF) cells are small interneurons in the autonomic ganglia. Preganglionic Transmitters and Postganglionic Transmitters In both sympathetic and parasympathetic, preganglionic nerve endings release acetylcholine. o That excite the postganglionic neurons ganglia. Parasympathetic postganglionic nerve endings release acetylcholine Most sympathetic postganglionic nerve endings release norepinephrine Some sympathetic postganglionic nerve endings release acetylcholine. o In sweat glands and the blood vessels in skeletal muscle, Many viscera do not possess dual control from the ANS. For example, the smooth muscle of the hair follicles (the arrector pili muscle) is made to contract by sympathetic activity, and there is no parasympathetic control. 9