Week 2: Nerve Supply Flashcards
What types of nervous tissue contribute to grey and white matter?
Grey matter: Cell bodies of neurons
White matter: Axons
What is the function of white matter columns?
To carry signals from the PNS to CNS or vice versa
What information passes through the dorsal columns?
Sensory
What information passes through the ventral columns?
Motor and sensory
What information passes through the lateral columns?
Motor and sensory
How many points of attachment does each spinal nerve have to the spinal cord?
2
Where do the dorsal rootlets enter the spinal cord and how many are there?
6-8 rootlets from the dorsal root enter dorsally (from the back)
What is the dorsal root ganglion, and what does it contain?
It is a swelling on the dorsal root that contains the cell bodies of afferent (sensory) neurons
How many rootlets form the ventral root of a spinal nerve?
6-8
What forms when the dorsal and ventral roots merge?
They form the spinal nerve proper
Where does the spinal nerve proper enter after merging?
The intervertebral foramen
What happens to the spinal nerves after emerging from the vertebral column?
Each spinal nerve divides into a dorsal ramus and a ventral ramus (ramus=branch)
In general, which structures are innervated by the dorsal rami?
Joints and muscles of the surrounding (dorsal) region and skin of the back
The ventral rami anastomose to form what type of structures?
Nerve plexuses
Note: there is one exception for the thoracic ventral rami, which form the intercostal nerves
What is the likely effect of a lesion to a dorsal root?
Dorsal root - sensory information
* Loss of sensation from areas innervated by the specific spinal nerve
What is the likely effect of a lesion to a ventral root?
Ventral root - motor information
* Loss of voluntary movement to areas innervated by the specific spinal nerve
What is the likely effect of a lesion to a spinal nerve?
Spinal nerve - mixed information
* Loss of both sensation and voluntary movement
Is the spinal cord part of the central nervous system or the peripheral nervous
system?
Central nervous system
What are the 31 segments of the spinal cord?
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal (in most humans)
Why do enlargements develop in the cervical and lumbar regions of the spinal cord?
They contain the cell bodies of the motor neurons that innervate the muscles of the upper (cervical) and lower (lumbar) extremities
What is the conus medularis?
The tapering caudalmost extremity of the spinal cord
What level does the conus medullaris extend to in the adult and infant?
It extends to L1/L2 vertebrae in the adult, and 1 – 2 levels more caudally in the infant
How would you explain the disparity between the respective cord and vertebral levels that one sees in an adult?
- In the early embryo the segments of the spinal cord and the vertebral levels are in register
- However, the spinal cord stops elongating during development, while the vertebral column continues to elongate as the body grows.
Explain the formation of the cauda equina:
- Collection of spinal nerve roots distal to the conus medullaris
- Early in development they pass through the intervertebral foramina to exit the vertebral column
- As the vertebral column grows, the spinal nerve roots elongate along with it
What is the filum terminale?
- A piece of connective tissue that extends from the distal tip of the spinal cord (conus medullaris) to the dorsal surface of the coccyx
- It does not contain nerve fibers
What is the function of the filum terminale?
To anchor the distal tip of the spinal cord to the distal aspect of the vertebral column so the spinal cord does not “swing” around within the vertebral column
Describe the path of afferent signals in the spinal cord:
The afferent signals come in to the dorsal root ganglion, then into the dorsal root on their way to the dorsal horn of the spinal cord grey matter
Describe the path of efferent signals in the spinal cord:
The efferent signals begin in the ventral horn of the spinal cord grey matter and exit out via the ventral root
Describe how the spinal nerves are named and numbered according to their emergence from the vertebral canal:
- C1 emerges between the skull and the C1 vertebra
- C2-C7 spinal nerves emerge through the intervertebral foramina
- The C8 nerve emerges between vertebrae C7 and T1 as there are 7 cervical vertebrae but 8 cervical spinal nerves
- The remaining spinal nerves emerge below the respective vertebrae e.g. T1 spinal nerve emerges between vertebrae T1 and T2
What are the 31 pairs of spinal nerves?
Cervical: C1-C8
Thoracic: T1-T12
Lumbar: L1-L5; intercostal nerves (T1-T11)
Sacral: S1-S5
Coccygeal: Co1
What are the 5 spinal cord plexuses?
Cervical: C1-C5
Brachial: C5-T1
Lumbar: L1-L4
Sacral: L4-S4
Coccygeal: S4, S5 and Co
What regions of the body do the spinal cord plexuses innervate?
- Cervical: Head and neck
- Brachial: Upper limb
- Lumbar: Lower limb
- Sacral (coccygeal): Lower limb
What plexus are the nerves of the lower limb derived from?
Lumbosacral plexus
What forms the lumbosacral plexus?
The lumbar and sacral plexus which arise from the lumbar and sacral ventral rami
What makes up the lumbar plexus?
It arises primarily from the ventral rami of the lumbar nerves (T12) L1-L4
What are the 2 main branches of the lumbar plexus?
Femoral and obturator nerves
What is the root derivation of the femoral nerve?
L2, L3, L4 (posterior/dorsal division of ventral rami)
What is the root derivation of the obturator nerve?
L2, L3, L4 (anterior/ventral division of ventral rami)
What is the root deviation of the superior gluteal nerve?
L4, L5, S1
What is the root deviation of the inferior gluteal nerve?
L5, S1, S2
What is the lumbosacral trunk?
- It is formed by part of L4 ventral ramus and the ventral ramus of the L5 nerve
- Connects lumbar and sacral plexus
What forms the sacral plexus?
The lumbosacral trunk and the ventral rami of S1-S3(4)
What is the sciatic nerve?
- Formed by the anterior and posterior divisions within the sacral plexus
- The anterior divisions form the tibial nerve
- The posterior divisions form the common fibular (peroneal) nerve
- These are bound together to form the sciatic nerve
- L4 - S3
Which compartment of the thigh is innervated by the femoral nerve and what are the functions of the muscles in these compartments?
Anterior compartment; muscles pass anterior to hip and knee joints therefore flex the hip and extend the knee
What are the clinical implications of interruption of the femoral nerve at a site in the proximal thigh?
Greatly diminishes active knee extension
Describe two activities of daily living that would be difficult to accomplish following an interruption of the femoral nerve:
Any activities that require active knee extension particularly those requiring eccentric contraction to control gravity eg: moving from standing to/from sitting, up/down stairs
What muscle test (myotome) could you undertake to evaluate the neurological levels L2, L3, L4?
- Resisted knee extension – femoral nerve L2-L4
- Resisted hip adduction – obturator nerve L2-L4
Which compartment of the thigh is innervated by the obturator nerve, and what is the function of the muscles in this compartment?
Medial compartment; hip adduction (as muscles located medial to hip joint)
Describe the gross morphology of the sciatic nerve:
The sciatic nerve consists of two nerves, the tibial and common fibular nerves contained within a common connective tissue sheath
Where do the two nerves of the sciatic nerve divide?
- At the upper limit of the popliteal fossa
- In 10% of cases the nerves are separated proximally by all or part of the piriformis muscle
What is the tibial nerve derived from?
The anterior division of the ventral roots of L4-S3
Which compartments of the thigh, leg and foot where the muscles are innervated by the tibial nerve, and what are the functions of these muscles?
- Posterior compartment of thigh and leg, plantar aspect of foot
- Muscles posterior to the knee flex the knee
- Muscles posterior to the ankle joint plantarflex the ankle
- Muscles in the posterior leg or plantar aspect of the foot and run on the plantar aspect of the phalanges flex the toes
What are the medial and lateral plantar nerves branches of?
Terminal branches of the tibial nerve in the foot
Which compartments are innervated by the medial and lateral plantar nerves?
- Medial supplies the medial compartment
- Lateral supplies the remainder of the plantar muscles of the foot
What part of the thigh does the common fibular nerve innervate?
(L4-S2) - innervates one muscle in the posterior thigh - short head of biceps femoris
What are the 2 main branches of the common fibular nerve?
The superficial fibular nerve
and the deep fibular nerve
Describe the course of the common fibular nerve through the popliteal fossa and into the leg
Runs along the lateral aspect of the popliteal fossa (follows the margin of the biceps femoris short head muscle), then winds around the neck of the fibula before dividing into its superficial and deep components
Where along its course is the common fibular nerve most vulnerable to injury?
As it passes around the neck of the fibula - vulnerable to compression
Which compartment of the leg is innervated by the superficial fibular nerve and what is the main action of these muscles?
Lateral compartment; eversion of the foot
Which compartment of the leg is innervated by the deep fibular nerve and what is the main action of these muscles?
Anterior compartment; dorsiflexion
What is the cutaneous nerve distribution?
In addition to supplying muscles, joints and other structures, each particular peripheral nerve of the lower limb will also innervate a specific area of skin
What is the medial cutaneous nerve of the thigh derived from?
Femoral nerve
What is the lateral cutaneous nerve of the thigh derived from?
Lumbar plexus
What is the posterior cutaneous nerve of the thigh derived from?
Sacral plexus
What is the saphenous nerve derived from?
Femoral nerve
What is the lateral cutaneous nerve of the calf derived from?
Common fibular nerve
What is the sural nerve derived from?
Tibial nerve
What is a dermatome?
An area of skin supplied by the sensory axons of a single nerve or spinal cord level (e.g.: L2)
What are the dermatomes of the lower limb?
- over the inguinal ligament—L1
- lateral side of the thigh—L2
- lower medial side of the thigh—L3
- medial side of the great toe (digit I)—L4
- medial side of digit II—L5
- little toe (digit V)—S1
- back of the thigh—S2
- skin over the gluteal fold—S3
- S4 and S5 are tested in the perineum
There’s a decreased sensation in the antero-lateral aspect of the leg, extending from the level of the knee joint to half way down the leg. What peripheral cutaneous nerve may be affected? What spinal nerve (dermatome) may be affected?
- Lateral cutaneous nerve of the calf (from the common fibular nerve, L4-S2)
- L5
What is a myotome?
The skeletal muscle(s) supplied by the motor axons of a single nerve or spinal cord level (e.g. L2)
What are the myotomes of the hip?
L2/L3 - Flex
L4/L5 - Extend
What are the myotomes of the knee?
L3/L4 - Extend (spinal reflex)
L5/S1 - Flex
What are the myotomes of the ankle?
L4/L5 - Dorsiflex
S1/S2 - Plantarflex (spinal reflex)
What is the myotome of knee extension and the knee jerk reflex?
L3/L4
What is the myotome of plantarflexion and the Achilles tendon reflex?
S1/S2
