Anatomy 3 - Spinal Nerves

Question 1

embryology of dermatomes in upper limbs?

Answer 1

horizontal stripes of dermatomes

arms emerge through this like putting arm through cling film

Question 2

examples of somatic sensory symptoms?

Answer 2

pain (neuralgia
pins and needles (paraesthesia)
numbness (anaesthesia)
sensitivity (hyperaesthesia)
thermal (hot or cold)
loss of co-ordination/balance/clumsiness (ataxia)

Question 3

somatic motor symptoms?

Answer 3

muscle stiffness, tightness or spasm (cramp)
muscle floppiness or looseness (reduced tone or hypotonia)
muscular weakness (reduced power)
loss of coordination/balance/clumsiness (ataxia)

Question 4

each pair of spinal nerves supplies what to a specific segment of body wall?

Answer 4

general somatic sensation (GSA)
general somatic motor (GSE)
sympathetic motor (GVE)(autonomic control - vessels, hair follicles)
spinal reflexes (circuit of sensory - afferent - and motor - efferent - nerve fibres)

Question 5

testing of spinal nerve function?

Answer 5

test each spinal nerve’s dermatome, myotome and spinal reflex (sensation and muscle function)

Question 6

dermatomes of each spinal nerve?

Answer 6

C1 = no significant cutaneous sensory axons
C2 = back of scalp and adams apple
C3 = back of neck and jugular notch
C4 = clavicle
C5 = badge patch
C6 = thumb
C7 = middle finger
C8 = little finger
T1 = medial forearm
T2 = medial arm and sternal angle
T4 = nipple
T10 = umbilicus
T12 = pubic symphysis

Question 7

why are thoracic dermatomes not as simple as they look?

Answer 7

overlap

Question 8

lower limb dermatomes?

Answer 8

L1 = groin (hands in pockets)
L2 = anterior thigh
L3 = anterior knee
L4 = medial malleolus
L5 = dorsum of foot
S1 = heel
S2 = posterior knee
S3 = buttock
S4/S5 = bullseye around anus

Question 9

only sensory deficit indicates lesion where?

Answer 9

dorsal doot

Question 10

only motor indicates lesion where?

Answer 10

ventral root

Question 11

sensory and motor indicates what?

Answer 11

spinal nerve

Question 12

how can you test sensory component of posterior rami?

Answer 12

Posterior rami supply sensation to a strip of skin centrally down the posterior neck and back from T2 - L3

Question 13

all plexuses are formed by what?

Answer 13

anterior rami

Question 14

anterior rami of T2-T12 don’t contribute to any plexus, what do they do instead?

Answer 14

form intercostal nerves (T2-11)

T12 forms subcostal nerve

Question 15

how can you test the sensory component of anterior rami?

Answer 15

anterior rami forms plexuses

- cervical, brachial, lumbar and sacral

Question 16

named nerve comes from known spinal level?

Answer 16

no

most come from several so dysfunction can be due to a lesion in one of many spinal nerves

Question 17

example of femoral nerve as a named nerve?

Answer 17

femoral nerve = L2-L4
contains axons (sensory, motor and sympathetic) that connect via spinal nerve roots L2, L3 and L4 from spinal cord segments L2, L3 and L4
therefore the area of cutaneous innervation of the femoral nerve covers 3 true dermatomes - that of spinal nerves L2, L3 and L4

Question 18

named cutaneous innervation of the neck?

Answer 18

little goats tread softly
lesser occipital (C2) = behind ear
great auricular nerve (C2,3) = over angle of mandible and some of ear
transverse cervical (C2, 3) = anterior neck
suprclavicular nerves (C3,4) = skin over clavicle and tip of shoulder

Question 19

dermatomal vs named nerve pattern?

Answer 19

//
specific area but dermatome is fine could just be compression/damage to named nerve
loss of large area = spinal nerve???

Question 20

named nerve cutaneous innervation of the arm?

Answer 20

anterior surface
- shoulder = supraclavicular
- regimental badge area = axillary
- lateral edge = cutaneous branch of musculocutaneous 
- anatomical snuff box = radial
- thumb and first 2.5 fingers = median
- last 1.5 fingers = ulnar
- medial edge = T1 & T2 anterior rami
posterior
- shoulder = supraclavicular
- badge area = axillary
lateral edge = radial
- later 1/2 of back of hand = radial
- medial 1.5 fingers and hand = ulnar
- medial edge = T1 and T2 anterior rami

Question 21

sensory pathway (e.g femoral nerve)?

Answer 21

stimulation in area innervated by femoral nerve
AP generated by receptors in that area (e.g touched in the L2 dermatome)
AP continues along axons weaving through the lumbar plexus
AP continues to L2 anterior rami
AP continues along axons to L2 spinal nerve
AP continues along axons to L2 posterior root
AP continues along to L2 posterior rootlets
AP continues into the posterior horn of spinal cord

Question 22

where else could the lesion be to cause numbness etc?

Answer 22

CNS ascending tract
internal capsule
primary sensory cortex
- would usually be more widspread

Question 23

cervical plexus C1-C4?

Answer 23

neck postural and strap muscles

diaphragm

Question 24

brachial plexus C5-T1?

Answer 24

muscles of upper limb

extrinsic back muscles

Question 25

T2-L3 motor axons?

Answer 25

postural back muscles (via posterior rami)
intercostal muscles (via anterior rami)
anterolateral abdominal wall muscles

Question 26

lumbosacral plexus L1-S4?

Answer 26

muscles of lower limb

perineal skeletal muscles

Question 27

named motor nerve innervation of the femoral nerve?

Answer 27

femoral nerve = L2, L3, L4

therefore area of motor innervation of the femoral nerve crosses 3 true myotomes

Question 28

how do you examine myotomes C5-T1?

Answer 28

C5 = shoulder abduction (deltoid)
C6 = elbow flexion (biceps brachii)
C7 = elbow flexion (triceps brachii)
C8 = finger flexion (flexor digitorum superficialis)
T1 = finger abduction (dorsal interossei)

Question 29

clinical testing of myotomes L3-S2?

Answer 29

L3 = knee extension (quadriceps femoris)
L4 = ankle dorsiflexion (tibialis anterior)
L5 = great toe extension (extensor hallucis longus)
S1 = ankle plantarflexion (gastrocnaemius)
S2 = knee flexion (biceps femoris)

Question 30

testing of motor function of a peripheral nerve?

Answer 30

APs generated by voluntary insertion in the primary somatomotor cortex
AP conducted via upper motor neuron axons of the corticospinal tract
AP continues along axons to anterior horn of L3 spinal cord
UMN axons synapse with L3 LMNs stimulating another AP
AP continues along axons to L3 spinal nerve
AP continues to either L3 posterior ramus or anterior ramus
APs via L3 anterior rami often weave through the lumbar plexus via a named nerve
APs then reach the NMJ of the supplied muscle

Question 31

give an example of a monosynaptic stretch reflex arc and describe how it occurs?

Answer 31

patellar tendon tapped
stretches quadriceps fibres
muscle spindles initiate APs in the anterior rami axons within the femoral nerve
sensory APs conducted to the dorsal horn of L3
axons pass into the anterior horn to synapse on LMNs that supply quadriceps
APs conducted via the LMN axons in the femoral nerve to reach the quariceps NMJ
muscle contracts to extend knee (brain not involved)

Question 32

monosynaptic reflex arc is controlled by which pathways?

Answer 32

descending pathways

Question 33

which spinal reflexes are routinely tested?

Answer 33

biceps brachii (C5, C6)
brachioradialis (C6)
triceps brachii (C7)
Knee jerk (L3)
ankle jerk (S1)

Question 34

function of brachioradialis?

Answer 34

beer drinking muscle

Question 35

sensory deficit in a dermatomal pattern?

Answer 35

means it could be anywhere from spinal nerve backwards
test myotome as well to check
if myotome is also affected it must be spinal nerve lesion as it is mixed
if it is only dermatome then lesion must be in posterior root

Question 36

how might compression of a named nerve present?

Answer 36

most named nerves encompass several spinal nerves so would have symptoms across several dermatomes