Anatomy of Spinal Nerves

Question 1

In embryological terms, the upper and lower limb dermatome formation can be compared to what?

Answer 1

Like pushing your hand through clingfilm

Question 2

The higher up the limb the higher/lower the root level of the plexus

Answer 2

Higher!

Question 3

What do each pair of spinal nerves supply?

Answer 3

Somatic general sensory
Motor functions- somatic motor and sympathetic
Spinal reflexes

Question 4

What are the symptoms of somatic general sensory pathology?

Answer 4

Pain (neuralgia)
Pins and needles (paraesthesia)
Numbness (anaesthesia)
Hot or cold
Loss of co-ordination/balance/clumsiness (e.g. ataxia)

Question 5

What are the symptoms of somatic motor pathology?

Answer 5

Muscle stiffness, tightness or spasm (cramp)
Muscle floppiness or looseness (reduced tone or hypotonia)
Muscular weakness (reduced power)
Loss of co-ordination/balance/clumsiness (e.g. ataxia)

Question 6

How do you test each spinal nerve segment’s sensory function?

Answer 6

Test dermatome

Question 7

How do you test each spinal nerve segment’s motor function?

Answer 7

Test myotome

Question 8

How do you test both sensory and motor function of the spinal nerve simultaneously?

Answer 8

Spinal cord reflexes

Question 9

Describe the route of a somato-sensory action potential from skin to somatosensory cortex

Answer 9

Sensation from body wall in posterior root of spinal nerve–> Axons within spinal cord ascending tract –> Thalamus (Internal capsule) –> Primary somatosensory cortex

Question 10

Where does C1 dermatome supply?

Answer 10

Trick question!

No significant cutaneous sensory axons

Question 11

Which dermatome corresponds with the “badge patch”?

Answer 11

C5

Question 12

Which dermatome is the male nipple at?

Answer 12

T4

Question 13

Which dermatome is the umbilicus at?

Answer 13

T10

Question 14

List dermatomal landmarks of the lower limb

Answer 14

L1- Groin
L2- Anterior thigh
L2- Anterior knee
L4- Medial malleolus
L5- Dorsum of foot
S1- Heel
S2- Posterior knee
S3- Buttock
S4- Perineum
S5- Perianal skin

Question 15

Which posterior rami supply a strip of skin centrally down back and posterior neck?

Answer 15

C2-C8

Question 16

What are the plexuses formed by anterior rami?

Answer 16

Cervical
Brachial
Lumbar
Sacral

Question 17

Which anterior rami do not contribute to a plexus?

Answer 17

T2-T12

Question 18

What’s the difference between a spinal nerve and a named nerve?

Answer 18

Spinal nerve contains axons originating from one spinal cord level
Named nerve contains axons originating from one or more spinal cord levels

Question 19

Name the cutaneous nerve innervation of the neck from superior to inferior

Answer 19

Little Goats Tread Softly

Lesser occipital (C2)
Greater auricular nerve (C2,3)
Transverse Cervical (C2,3)
Supraclavicular nerves (C3,4)

Question 20

What is Erb’s point?

Answer 20

The nerve point of the neck where sensory nerves of cervical plexus converge
Pass from superficial to deep fascia
At midpoint of posterior border of SCM

Question 21

Describe the course of sensory input to L2 dermatome of a peripheral nerve

Answer 21

Stimulation of area innervated by femoral nerve –> AP generated by receptors in L2 dermatome–> AP continues along axons through lumbar plexus –> L2 anterior rami –> spinal nerve –> L2 posterior root –> L2 posterior rootlets –> spinal cord

Question 22

Describe the pathway from primary somatomotor cortex to muscle

Answer 22

Upper motor neurone within primary somatomotor cortex of precentral gyrus–> Axons within spinal cord descending tract, cross at medulla –> 3rd order neutron to muscle

Question 23

Which muscles are supplied by cervical plexus C1-C4 motor axons?

Answer 23

Neck postural & strap muscles

Diaphragm

Question 24

Which muscles are supplied by brachial plexus C5-T1 motor axons?

Answer 24

Muscles of upper limb

Extrinsic back muscles

Question 25

Which muscles are supplied by T2-L3 motor axons?

Answer 25

``` Postural back muscles (via posterior rami Intercostal muscles (via anterior rami) Anterolateral abdominal wall muscles (via thorax-abdominal, subcostal, iliohypogastric & ilioinguinal nerves) ```

Question 26

Which muscles are supplied by lumbosacral plexus L1-S4 motor axons?

Answer 26

Muscles of lower limb | Perineal skeletal muscles

Question 27

How do you clinically test C5 myotome and which muscle is being tested?

Answer 27

Shoulder abduction | Deltoid

Question 28

How do you clinically test C6 myotome and which muscle is being tested?

Answer 28

Elbow flexion | Biceps brachii

Question 29

How do you clinically test C7 myotome and which muscle is being tested?

Answer 29

Elbow extension | Triceps brachii

Question 30

How do you clinically test C8 myotome and which muscle is being tested?

Answer 30

Finger flexion | Flexion digitorum superficialis

Question 31

How do you clinically test T1 myotome and which muscle is being tested?

Answer 31

Finger abduction | Dorsal interossei

Question 32

How do you clinically test L3 myotome and which muscle is being tested?

Answer 32

Knee extension | Quadriceps femoris

Question 33

How do you clinically test L4 myotome and which muscle is being tested?

Answer 33

Ankle dorsiflexion | Tibialis anterior

Question 34

How do you clinically test L5 myotome and which muscle is being tested?

Answer 34

Great toe extension | Extensor hallucis longus

Question 35

How do you clinically test S1 myotome and which muscle is being tested?

Answer 35

Ankle plantarflexion | Gastrocnemius

Question 36

How do you clinically test S2 myotome and which muscle is being tested?

Answer 36

Knee flexion | Biceps femoris

Question 37

What is a spinal cord reflex?

Answer 37

Involuntary response to stimulus

Question 38

How does the patellar reflex work?

Answer 38

Patellar tendon tapped Stretches quadriceps fibres Muscle spindles imitate APs in anterior rami within femoral nerve Sensory APs conducted to dorsal horn of L3 Pass into anterior horn to synapse on lower motor neurons that supply quadriceps APs conducted via LMN axons in femoral nerve to reach quadriceps NMJ Muscle contracts to extend knee

Question 39

What are the clinical signs of an upper motor neurone lesion and lower motor neurone lesion?

Answer 39

UMN lesions= spasticity | LMN lesions= flaccidity

Question 40

List the spinal reflexes that can be clinically tested

Answer 40

``` Biceps brachii= C5, C6 Triceps brachii = C7 Brachioradialis= C6 Knee jerk = L3 Ankle jerk = S1 ```