hey guys it's medicosa's perfect net is where medicine makes perfect sense today we'll talk about the lumbar plexus and the sacral plexus what do they do well it's the nerve supply of your lower extremities pelvis and perineal area where do they come from from the spinal cord the spinal cord itself is part of the central nervous system but any nerve that comes out of the spinal cord is part of the peripheral nervous system this video is part of my anatomy playlist where you'll find more videos including another video on the lower extremity the muscles of the lower extremity and the video on the anatomy of the upper limbs now it's time to talk about the lumbosacral plexus as you know in nervous system is made of CNS and pns the central nervous system is brain and spinal cord the peripheral nervous system is the cranial nerves and the spinal nerves spinal nerves are 8 in the cervical region 12 in the thoracic 5 in the lumbar 5 in the sacral only one in the coccygeal region all spinal nerves are mixed what does that mean they have sensory they have motor together here's the slice of your spinal cord anteriorly you have efferent which is motor posteriorly you have dorsal which is sensory but then when we lump them together in one spinal nerve it is mixed it has sensory and motor and then the spinal nerve will divide into a dorsal ramus and aventor ramus Each of which has sensory and motor which one is more important of course the ventral the dorsal is just almost nothing I want you to touch the skin of your back that's about it that's the function of the dorsal Remus IT Supplies motor and sensory fibers for skin and muscles of the back that's it anything else is vento ramus how about my lumbosacral plexus it comes from the Venter ramus this winter ramus is divided into interior divisions and posterior divisions lumbar plexus sacral plexus coccygeal plexus this is the spinal nerve in the lumbosacrocoxygeal area the spinal nerve is gonna take the number of the vertebral body above it so this is L1 vertebra this is L1 spine nerve lumbosacral plexus is made of Lumbar plexus and sacral plexus lumbar plexus has two main loyal Suns the obturator nerve and the femoral nerve above the sacral plexus two loyal daughters sciatic nerve and pudendal nerve lumbar plexus obturator and femoral sacroplex sciatic and pitender what's the sciatic nerve it's a thick nerve and it's actually like not one nerve but two nerves lump together the tibial nerve medially and the common fibular nerve laterally do you remember the compartments of the thigh here is the beauty the anterior compartment muscles are supplied with the femoral nerve the steel compartment supplied by the sciatic nerve the medial compartment is supplied by the obturator nerve translation the quadriceps muscle and the Sartorius muscles are supplied by femoral nerve gracilis pictines adductor lungs adductor brevis a ductor Magnus are supplied by the obturator nerve moreover biceps femoris semitendinosis semimembranosus are supplied by the sciatic nerve easy peasy lemon squeeze oh Anatomy is just so hard and nothing makes sense oh shut up it makes sense if explained properly now let's leave the thigh and go to the leg the leg also has compartments but different kinds of compartments here you have anterior posterior and lateral compartment which is lateral to the fibula the muscles of the anterior compartment are foot extensors by extension here I mean dorsiflexion however the compartment foot flexors or plantar flexors this way above the lateral compartment will is just next to the fibula so we call them fibular and they cause a virgin what are the muscles of the anterior compartment of the leg tibialis anterior of course because it's anterior to the tibia no kidding extensor Hellas is longus extensor digitorum longus extensor digitorum previous and pernius tertius how about the muscles of the posterior compartment which are the foot flexors or plantar flexors gastrocnemius and Soleus never ever forget these two plantaris papleteus the two P's to the two sisters and the two P's and then two flexors flexor halluces longus flexor digitorum longus and tibialis posterior not anterior posterior this time how about the lateral compartment lateral is the fibula and the fibular is peroneal so we have two muscles here you can call them peroneus longus and pernius previous or fibularis longness and fibularis brevis what is the nerve supply of the leg compartments easy do you remember when we talked about the sciatic nerve yeah and the sciatic nerve is made of two nerves right we have the tibial nerve posteriorly and the common fibular nerve the common fibular nerve will subdivide into musculocutaneous nerve or superficial fibular and anterior tibial or deep fibular the anterior tibial is for the anterior compartment The Superficial fibula is for the lateral compartment and the tibial nerve is for the posterior compartment pause and review so who's going to supply tibialis anterior extensor extensor extensor and pernia Sturgis anterior tibial nerve who's going to supply fibularis longus and fibularis brevis this is The Superficial fibular nerve who's going to supply gastrocodemia Soleus plantaris papletes flexor flexor tibialis posterior this is your posterior tibial nerve or just tibial nerve here is the lumbar plexus here is the same micro plexus how do we bridge the gap between Lumbar and sacral plexus there is a beautiful beautiful nerve that Bridges the Gap and this is called the lumbosacral trunk look at this beauty let's start by talking about the lumbar plexus okay where does it come from remember the posterior ramus is useless except for the skin and muscles of the back everything else is anterior or ventral ramus so the number plaques of course come from anterior primary Rami of L1 through L4 where do I find them embedded within the fibers of the psoas major muscle each lovely lumbar spinal nerve is going to divide into anterior divisions posterior divisions anterior divisions posterior divisions if you collect the interior divisions of L2 3 and 4 you get the obturator nerve if you collect the posterior divisions of the same l234 you get the femoral nerve remember when we said that the lumbar plexus had two lower Sons the obturator and the femoral this is the nerve of the anterior compartment of the thigh and this is the nerve of the medial compartment of the thigh who makes the obturator anterior divisions of L2 L3 and L4 who makes the femoral posterior divisions of L2 L3 and L4 this is so easy medicosis hold your horses it's gonna get nasty let's do it again anterior divisions of L2 3 and 4 upturator nerve posterior divisions of l23 and 4 you get the femoral nerve next let's start by L1 L1 is going to give you ileo hypogastric Elio inguinal genito femoral how about L2 you already know that anterior division of L2 is going to contribute to the obturator nerve posterior division of L2 is going to contribute to the femoral nerve add to this that L2 to your division is going to contribute to lateral femoral cutaneous nerve provides sensory supply to the lateral part of the thigh oh chemicalsis I got this this is easy no you did not unless you bring out a blank piece of paper and draw the lumbar plexus from scratch otherwise I will smack your gluteus maximus no pun intended we're done with the lumbar let's talk about the sacral plexus who are the two loyal Daughters of the sacral plexus oh we have the sciatic nerve and the pudendal nerve since we're not talking about the pelvis and the perineum today forget the pudendal nerve let's focus on the sciatic nerve is this one nerve well yeah it's one nerve made of two separate nerves medially tibial nerve laterally common fibular nerve near the tibia near the fibula the tibial nerve came from anterior divisions of L4 L5 S1 S2 and and S3 how about the common fibular posterior divisions of L4 L5 S1 S2 and stop there is no S3 S3 is only for tibial the mnemonic is tibial is too much then gets ridiculous if you collect some posterior divisions from L4 L5 S1 you get Superior gluteal nerve let's inch a little lower so forget L4 we'll go L5 S1 and S2 and you'll have inferior gluteal nerve let's inch a little lower so forget L5 let's go S1 S2 nerve to the periforms muscle what are the two allele daughters sciatic nerve and the pudendal nerve s234 l45s123 please draw it from scratch dermatomes so umbilicus is next to T10 and then t11 T12 L1 we're getting close to the genitalia from the front but on the back it's here it's below the intergluteal cleft on the medial side only then L2 L3 is getting larger L4 is getting ridiculous L4 supplies the hallux which is the big toe then L5 middle toes and then S1 little toe from the back there is no thoracic here so this is L1 L2 L3 L4 L5 getting ridiculous and then we have two huge stories S1 and S2 have you ever seen a patient with sciatica yeah they always complain of tingling and numbness on the back of the thigh back of the leg it makes perfect sense now let's take it to the next level you remember that the lumbar plexus gave us what it gave us the femoral nerve the obturator and lateral femoral continuous nerve forget the obturator let's focus on the femoral nerve and the lateral femoricutinous nerve the lateral femoral cutaneous nerve is going to supply the Skin So sensory fibers of the lateral part of the thigh lateral part over the femur Apple the medial femoral cutaneous nerve the medial part above the intermediate it is here see lateral femroscience nerve came from L2 and L3 makes perfect sense lateral part of the thigh medial and intermediate came from L2 3 and 4 which makes perfect sense where does the posterior femoral cutiness nerve come from from the sacral plexus not lumbar sacral and the root value is s123 here is S1 and here is S2 let's talk about your foot as you know this is called dorsiflexion This is called plantar flexion who's responsible for dorsiflexion if you're talking about the root it's L4 and L5 if you're talking about the nerve it's the common fibular nerve or the anterior tibial or the Deep fibular if you you're talking about the muscle responsible for this it's mainly the tibialis anterior how about plantar flexion if you're talking about the root value S1 S2 the nerve is the tibial nerve or the posterior tibial nerve the muscles are the sisters gastrocnemius and Soleus if you want to be super sophisticated dorsiflexion usually comes with inversion same nerve and same root plantar flexion usually comes with eversion dorsiflexion with inversion plantar flexion with evergion what happens if I injure my tibial nerve and what happens if I injure my common fever nerve the two components of the sciatic nerve let's go tibial nervous S1 S2 mainly S1 common fibular is L4 and L5 mainly L5 so basically our campaign between S1 injury and L5 injury you might think oh lumbar 5 and sacral number one are very close to each other it doesn't matter shut up it's a huge deal it's a big difference I injured my tibial nerve who's going to suffer gastrocnemius and Soleus muscles therefore who's going to suffer plantar flexion if I can't plant or Flex what's going to happen you will dorsiflex and when you dorsiflex you will never be able to walk on tiptoes and you will not be able to walk downhill because you cannot walk on tippy toes so when I injure my tibial nerve I cannot walk on tippy toes the symptoms caused by tibial nerve injury can be collectively called tulipas calcaneal valgus let's talk about the injury to the common threader nerve root L5 who is going to suffer tibialis anterior muscle who is going to suffer dorsiflexion if I cannot dorsiflex I will plantar Flags this is called foot drop or high stippage gate because when you walk you walk in a weird way it's as if you're stepping on eggshells or something you cannot walk up hell because you cannot dorsiflex these symptoms are known as talipus equinovarus some quick notes about that Trindle and bur gate first let's talk normal and then let's talk about the pathology normally you have Superior gluteal nerve and inferior gluteal nerve both are branches of the sacral plexus L4 L5 S1 L5 S1 and S2 so Superior gluteal and then inferior gluteal here is gluteus maximus here is gluteus medius and gluteus Minimus and then you crisscross normally the superior gluteal nerve supplies the gluteus medius and Minimus but the inferior gluteal nerve supplies the gluteus maximus when you are arrogant you will fall but when you have some humidity it will rise like a superior Phoenix so what the flip is tyrindellenberg gate basically this is a patient with injury to the superior gluteal nerve when I injure enter my Superior gluteal nerve who's gonna suffer gluteus medius and gluteus Minimus what's going to happen pelvis is gonna tilt down towards the opposite side because you cannot stabilize the epsilateral side because you lost your epsilateral Superior gluteal nerve and you have weakness of the epsilateral gluteus medius and Minimus now pay attention to the upcoming sentence because it's freaking gold you ask the patient to stand on the right leg then the left hip dropped what's the problem well this is a positive right to lindenberg sign which means the problem is on the right side the problem is with the right Superior gluteal nerve and right gluteus medius and gluteus Minimus that's why the hip dropped to the left side my YouTube channel has more than 1400 free videos plus some premium courses which you can find on my website meticosisperfectsnetis.com such as the surgery high yields course which will teach you about trauma surgery orthopedic surgery with some fractures acute limb ischemia compartment syndrome with evokeman contracture and my emergency medicine high yields which will teach you about ards many cardiac arrhythmias angina myocardial infarction ischemic stroke hemorrhagic stroke and much more the 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