Clinical Anatomy of Spinal Nerves and Testing Flashcards
Describe what dermatomes are?
area of skin supplied with sensory innervation from a single spinal nerve
also supplies sensory innervation to deeper structures
If you damage a spinal nerve why may you not lose complete sensation to the corresponding dermatome?
innervation of skin by adjacent spinal nerves shows overlap (so you would have to damage the nerves above and below too!)
Describe what myotomes are?
the skeletal muscles supplied with motor innervation from a single spinal nerve
may be deep to dermatome of same spinal nerve, but not always
Does C1 have a dermatome?
No
can’t determine as up to 50% of the population don’t have posterior rootlets in the C1 spinal cord segment
What are two landmarks for trunk segmentation of dermatomes?
- Nipple = T4 segment
- Umbilicus = T10 segment
Describe limb, neck and shoulder segmentation for dermatomes?
Posterior scalp, neck and shoulder = C2-C4
Upper limb = C5-T1
Lower limb, gluteal region and perineum = L2-Co1
Describe the places you can test sensation in the C2-C8 dermatomes?
C2 – back of scalp & Adam’s apple C3 – back of neck & jugular notch C4 – clavicle & shoulder tip C5 – “badge patch” C6 – thumb C7 – middle finger C8 – little finger
Describe the places you can test T1 T2 T4 T8 T10 T12
T1 – medial forearm T2 – medial arm & sternal angle T4 – nipple T8 – xiphoid process T10 – umbilicus T12 – pubic symphysis
Describe the places you can test the L1-L5 dermatomes?
L1 – groin L2 – anterior thigh L3 – anterior knee L4 – medial malleolus L5 – dorsum of foot
Describe the places you can test the S1-S5 dermatomes?
S1 - heel S2 – posterior knee S3 - buttock S4 - perineum S5 – perianal skin
Describe how you test true dermatomes vs peripheral cutaneous nerves and how you may determine where the problem is?
If you test a peripheral nerve that has 3 true dermatomes, then when you test the area of that nerve of one dermatome it is only that spinal root being stimulated.
So if you have lost sensation across all the dermatomes in the nerve’s area that suggests there is an issue lower down with the nerve. However if you have lost sensation only in one dermatome area then that suggests a problem at the spinal nerve root.
Because if the roots combine lower down if you knock out the nerve then all areas are knocked out but if you knock out one root of the nerve higher up the other parts of the nerve still work.
Cervical plexus is from roots _______ and supplies _____
cervical plexus (C1-C4):
neck postural & strap muscles
diaphragm
Brachial plexus is from roots ______ and supplies __________
brachial plexus (C5-T1):
muscles of the upper limb
extrinsic back muscles
Intrinsic back muscles, anterolateral abdominal wall and intercostal muscles are supplied by which nerve roots?
T2-L3
The lumbosacral plexus is from roots ________ and supplies ________
lumbosacral plexus (L1-S4):
muscles of the lower limb
perineal skeletal muscles
How do you test the C5 and C7 myotomes with shoulder movements?
At the shoulder
- abduction – C5,
deltoid - adduction - C7,
pec major & lat.
dorsi
How do you test the C7-T1 myotomes with finger movements?
At the finger joints
- flexion – C8, digit flexors - extension – C7, digit extensors - abduction – T1, dorsal interossei - adduction – T1, palmar interossei
How do you test the C5-C8 myotomes with elbow movements?
At the elbow joint
- flexion – C5, C6,
biceps brachii - extension - C7, C8,
triceps brachii
How do you test the C6 and C7 myotomes at the wrist joint?
- flexion – C6, C7,
carpal flexors - extension – C6, C7,
carpal extensors
Abduction at the shoulder is testing what myotome?
C5
Adduction at the shoulder is testing what myotome?
C7
Flexion of the digits is testing what myotome?
C8
Extension of the digits is testing what myotome?
C7
Abduction and adduction of the digits is testing what myotome?
T1
Flexion of the elbow joint is testing what myotomes?
C5 and C6
Extension of the elbow joint is testing what myotomes?
C7 and C8
Flexion and extension of the wrist is testing what myotomes?
C6 and C7
How do you test the L2 and L3 myotomes at the hip joint?
- flexion – L2, L3,
psoas major
How do you test the L5 and S1 myotomes at the hip joint?
- extension - L5, S1
glut. max & hamstrings
How do you test the L5 and S1 myotomes at the knee joint?
- flexion – L5, S1,
hamstrings