Anatomy 3 - Spinal Nerves Flashcards
embryology of dermatomes in upper limbs?
horizontal stripes of dermatomes
arms emerge through this like putting arm through cling film
examples of somatic sensory symptoms?
pain (neuralgia pins and needles (paraesthesia) numbness (anaesthesia) sensitivity (hyperaesthesia) thermal (hot or cold) loss of co-ordination/balance/clumsiness (ataxia)
somatic motor symptoms?
muscle stiffness, tightness or spasm (cramp)
muscle floppiness or looseness (reduced tone or hypotonia)
muscular weakness (reduced power)
loss of coordination/balance/clumsiness (ataxia)
each pair of spinal nerves supplies what to a specific segment of body wall?
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)
testing of spinal nerve function?
test each spinal nerve’s dermatome, myotome and spinal reflex (sensation and muscle function)
dermatomes of each spinal nerve?
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
why are thoracic dermatomes not as simple as they look?
overlap
lower limb dermatomes?
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
only sensory deficit indicates lesion where?
dorsal doot
only motor indicates lesion where?
ventral root
sensory and motor indicates what?
spinal nerve
how can you test sensory component of posterior rami?
Posterior rami supply sensation to a strip of skin centrally down the posterior neck and back from T2 - L3
all plexuses are formed by what?
anterior rami
anterior rami of T2-T12 don’t contribute to any plexus, what do they do instead?
form intercostal nerves (T2-11)
T12 forms subcostal nerve
how can you test the sensory component of anterior rami?
anterior rami forms plexuses
- cervical, brachial, lumbar and sacral
named nerve comes from known spinal level?
no
most come from several so dysfunction can be due to a lesion in one of many spinal nerves
example of femoral nerve as a named nerve?
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
named cutaneous innervation of the neck?
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
dermatomal vs named nerve pattern?
// specific area but dermatome is fine could just be compression/damage to named nerve loss of large area = spinal nerve???
named nerve cutaneous innervation of the arm?
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
sensory pathway (e.g femoral nerve)?
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
where else could the lesion be to cause numbness etc?
CNS ascending tract
internal capsule
primary sensory cortex
- would usually be more widspread
cervical plexus C1-C4?
neck postural and strap muscles
diaphragm
brachial plexus C5-T1?
muscles of upper limb
extrinsic back muscles
T2-L3 motor axons?
postural back muscles (via posterior rami) intercostal muscles (via anterior rami) anterolateral abdominal wall muscles
lumbosacral plexus L1-S4?
muscles of lower limb
perineal skeletal muscles
named motor nerve innervation of the femoral nerve?
femoral nerve = L2, L3, L4
therefore area of motor innervation of the femoral nerve crosses 3 true myotomes
how do you examine myotomes C5-T1?
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)
clinical testing of myotomes L3-S2?
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)
testing of motor function of a peripheral nerve?
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
give an example of a monosynaptic stretch reflex arc and describe how it occurs?
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)
monosynaptic reflex arc is controlled by which pathways?
descending pathways
which spinal reflexes are routinely tested?
biceps brachii (C5, C6) brachioradialis (C6) triceps brachii (C7) Knee jerk (L3) ankle jerk (S1)
function of brachioradialis?
beer drinking muscle
sensory deficit in a dermatomal pattern?
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
how might compression of a named nerve present?
most named nerves encompass several spinal nerves so would have symptoms across several dermatomes
