Wet Lab 8 - Nerve Supply To The Lower Limb Flashcards
What does plexus mean?
An interweaving
What is the lumbosacral plexus ?
It is an interweaving of neurons from different levels (Segments) of the spinal cord, into final destination nerves that are either motor, sensory or mixed (both sensory and motor)
What does motor neurons do?
They fire muscles
What do sensory neurons do?
They provide information to the CNS from the periphery of the body, usually the skin but from many other specialised organs as well
What is Hilton’s law ?
It is that a nerve which supplies a muscle also supplies the joint the muscle acts across
What are the main features of a typical spinal nerve?
- Anterior (ventral) root which is purely motor (which means it has only motor neurons in it). Cell body of these in the front (ventral) part of the grey horn of the spinal cord (the “H” in this diagram).
- Posterior (dorsal) root which is purely sensory (has only sensory neurons in it). Cellsbodies in the dorsal root ganglion.
- Where these two roots join is the beginning of the mixed spinal nerve. Called mixed because it now has both motor and sensory neurons in it.
How does every nerve of the spinal cord start?
Every nerve at every level of the spinal cord starts the same way
What happens as the limbs grow out from the trunk ?
As the limbs grow out from the trunk, with several levels of nerves in them and for an evolutionary/functional reason, the neurons from the neighbouring segments often mix together and then group into proper nerves
Where does the plexus start ?
At the ventral ramus
Is every nerve in the body paired?
Yes, every nerve in the body is paired - there is a left nerve and right nerve
What is the lumbosacral plexus comprised of?
Lumbar plexus and sacral plexus that are joined by the lumbosacral trunk (L4 and L5)
Where does the full plexus interweave from?
From L1 to L5
What does the lumbosacral trunk cross ?
It crosses the sacral Ala to add the L4 and L5 segments to the sacral plexus
What does the tibial nerve start off as?
As part of the sciatic nerve
What is the sciatic nerve?
It is the tibial nerve and the common Fibular (peroneal) nerve, bound together by fascia
Where do the tibial and common fibular nerves seperate?
In or above the popliteal fossa
Where does the sciatic nerve form and exit ?
It forms within the pelvis and then exists the pelvis through the greater sciatic foramen beneath piriformis
Where does the sciatic ten travel between ?
The lateral rotators and the gluteus Maximus about half way between the ischial tuberosity and the greater trochanter
What does the sciatic nerve sen branches to
It continues between the hamstring muscles and adductor Magnus and sends branches to the hamstrings in the posterior thigh and the ex-hamstring part of adductor Magnus
What does the sciatic nerve separated from?
The common fibular nerve
After the sciatic nerve separates, what is it now called?
The tibial nerve in the popliteal fossa
What does the tibial nerve send branches to?
The Plantaris and gastrocnemius, Popliteus and soleus
Where does the tibial nerve run down ?
It runs downward immediately behind the tibia and supplies Tibialis posterior, FDL and FHL
What does the tibial nerve in the popliteal fossa send a branch to?
It sends a branch to what becomes the cutaneous (sensory) sural nerve once another branch off the common fibular nerve joins
Where does the tibial nerve then pass ?
It passes medial to the ankle joint behind the medial malleolus through the tarsal tunnel, where it branches into the calcaneal nerve and then the medial and lateral plantar nerves
What does the calcaneal nerve do?
It provides sensation from the skin of an area over the heel
What are medial and lateral plantar nerves?
They are motor to the plantar intrinsic muscles of the foot as well as sensation from the skin to the sole
What does the common peroneal (fibualar) nerve (L4-S2) seperate from?
It separates from the tibial nerve in or variably proximal to the popliteal fossa
What does the common peroneal nerve send, higher up in the thigh ?
It has sent a motor branch to the short head of biceps Femoris
Where does the common fibular nerve travel around?
Travels around the neck of the fibula (where it is easily palpable, and vulnerable to injury) and passes deep to Fibularis longus muscle
What does the common fibular nerve branch and continue as
As it passes deep the the Fibularis longus muscle, it branches and continues as the deep and superficial fibular nerves
Where does the common fibular nerve send a branch to?
In to the popliteal fossa to join the branch off the tibial nerve. This nerve is called the sural nerve
What does the sural nerve do?
It provides sensation from an area of skin over the posterior and lateral leg
What is a branch of the common fibular nerve called?
Lateral sural nerve
What does the lateral sural nerve do?
It provides sensation from an area of skin over the proximal lateral leg
Where does the deep fibular nerve (L4 and L5) run down?
It runs down the front surface of the interosseous membrane of the leg, deep to the anterior compartment muscles, which it supplies. (This approach from deep - to the muscles is most common throughout the body as it protects the nerve from damage)
What are the muscles in the anterior compartment of the leg?
TA, EHL, EDL and Fibularis tertius
Where does the deep fibular nerve pass ?
It passes anterior to the ankle joint deep to the extensor retinaculum and sends one branch t provide sensation from between the great and second toe, and another branch that supplies the muscles in the dorsum of the foot (namely EDB and EHB)
Where does the superficial fibular nerve (L4 - S1) arise from?
It arises deep near the neck of the fibula
What does the superficial fibular nerve supply?
It supplies the 2 muscles in the lateral compartment of the leg - FL and FB
What does the superficial Fibularis nerve provide ?
It provides sensation from the skin over the lateral leg and most of the dorsum of the foot
Where does the femoral nerve (L2-4) arise from?
It arises from the lumbar plexus
Where does the femoral nerve travel through?
It travels through psoas major, and supples iliacus.
What is the iliacus and psoas major supplied by?
They are also supplied by direct branches off the lumbar plexus
What does the femoral nerve pass beneath ?
The Inguinal ligament into the femoral triangle lateral to the femoral artery
What does the femoral nerve immediately send branches?
To the muscles it supplies - pectineus (whose supply it often shares with the Obturator nerve), sartorius, rectus Femoris and the 3 vasti (including articulates genu)
Where does the femoral nerve continue through ?
Through the adductor canal
What does the femoral nerve become?
The purely sensory saphenous nerve that supplies the skin of the medial-anterior leg
Where does the femoral nerve send branches to ?
The anterior and medial thigh
Where does the Obturator nerve (L2-4) arise from ?
From the lumbar plexus
Where does the Obturator nerve travel to?
It travels down wards through psoas major and then enters the Obturator canal to exit the pelvis with the Obturator vessels
What does the Obturator nerve branch to
It branches to supply the adductor muscles - pectineus (whose supply is often shared with the femoral nerve), gracilis, adductor brevis and the true adductor part of adductor magus and obturator externus
What does the Obturator nerve continue as ?
As a sensory nerve to an oval area of skin on the medial thigh
Where does the superior gluteal nerve (L4-S1) arise from?
The sacral plexus
Where does the superior gluteal nerve exit ?
It exits the pelvis through the greater sciatic foramen, above piriformis with the superior gluteal vessels.
What does the superior gluteal nerve supply ?
It is a purely motor nerve, supplying gluteus med and minimus and tensor fascia Latae
Where does the inferior gluteal nerve (L5-S2) arise from?
The sacral plexus
Where does the inferior gluteal nerve exit?
It exists through the greater sciatic foramen, below piriformis with the inferior gluteal vessels.
What does the inferior gluteal nerve supply
It is a purely motor nerve, supplying gluteus Maximus
What is the pudendal nerve?
It is a mixed (contains both sensory and motor neurons) nerve that provides sensation from and motor supply to muscles in the genital and perineal region
Where does the pudendal nerve exit?
It exits through the pelvis through the lower part of the greater sciatic foramen - between the piriformis and coccygeus
Where does the pudendal nerve run?
It then runs around behind the ischial tuberosity and the sacrospinous ligament, and re-enters the pelvis through the lesser sciatic foramen. It then passes through a sheet of fascia called the pudendal canal (called Alcock’s canal)
What does the pudendal nerve send a branch of
It sends a branch called the inferior rectal (or anal) nerve to the external anal sphincter and the skin around the anus
Where else does the pudendal nerve send branches to?
- it sends a perineal branch to the levator ani muscles and the perinuem
- supplies the coccygeus (ischiococcygeus), the other muscle of the pelvic diaphragm
What are the levator ani muscles
They are pubococcygeus (with its puborectalis) and illiococcygeus
Where does the perineal branch send a deep branch to?
To the muscles of perinuem, the traverse perineal muscles - bulbospongiosus, ischiocavernosus and the urethral sphincter
Where else does the perineal nerve send a branch to ?
It sends a branch called the superficial perineal nerve for sensation from the scrotum/labia
What does the perineal nerve terminate as?
As the dorsal nerve of the penis/clitoris
What are other nerves arising from the lumbosacral plexus - DONT need to find in the wet lab
- iliohypogastric and ilioinguinal nerves (T12 and L1)
- genitofemoral nerve (L1 and L2)
- lateral femoral cutaneous nerve (L2 and L3)
- poster femoral cutaneous nerve (S1-S3) passes through the greater sciatic foramen beneath piriformis medial to the sciatic nerve
- nerve to piriformis (S1 and S2)
- nerve to Obturator internus and Gemellus superior (L5 - S2)
- nerve to Gemellus inferior and quadratus Femoris (L4-S1)
- nerve to Obturator externus is a branch of the Obturator nerve
