Anatomy of Spinal Nerves Flashcards
In embryological terms, the upper and lower limb dermatome formation can be compared to what?
Like pushing your hand through clingfilm
The higher up the limb the higher/lower the root level of the plexus
Higher!
What do each pair of spinal nerves supply?
Somatic general sensory
Motor functions- somatic motor and sympathetic
Spinal reflexes
What are the symptoms of somatic general sensory pathology?
Pain (neuralgia) Pins and needles (paraesthesia) Numbness (anaesthesia) Hot or cold Loss of co-ordination/balance/clumsiness (e.g. ataxia)
What are the symptoms of somatic motor pathology?
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)
How do you test each spinal nerve segment’s sensory function?
Test dermatome
How do you test each spinal nerve segment’s motor function?
Test myotome
How do you test both sensory and motor function of the spinal nerve simultaneously?
Spinal cord reflexes
Describe the route of a somato-sensory action potential from skin to somatosensory cortex
Sensation from body wall in posterior root of spinal nerve–> Axons within spinal cord ascending tract –> Thalamus (Internal capsule) –> Primary somatosensory cortex
Where does C1 dermatome supply?
Trick question!
No significant cutaneous sensory axons
Which dermatome corresponds with the “badge patch”?
C5
Which dermatome is the male nipple at?
T4
Which dermatome is the umbilicus at?
T10
List dermatomal landmarks of the lower limb
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
Which posterior rami supply a strip of skin centrally down back and posterior neck?
C2-C8
What are the plexuses formed by anterior rami?
Cervical
Brachial
Lumbar
Sacral
Which anterior rami do not contribute to a plexus?
T2-T12
What’s the difference between a spinal nerve and a named nerve?
Spinal nerve contains axons originating from one spinal cord level
Named nerve contains axons originating from one or more spinal cord levels
Name the cutaneous nerve innervation of the neck from superior to inferior
Little Goats Tread Softly
Lesser occipital (C2) Greater auricular nerve (C2,3) Transverse Cervical (C2,3) Supraclavicular nerves (C3,4)
What is Erb’s point?
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
Describe the course of sensory input to L2 dermatome of a peripheral nerve
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
Describe the pathway from primary somatomotor cortex to muscle
Upper motor neurone within primary somatomotor cortex of precentral gyrus–> Axons within spinal cord descending tract, cross at medulla –> 3rd order neutron to muscle
Which muscles are supplied by cervical plexus C1-C4 motor axons?
Neck postural & strap muscles
Diaphragm
Which muscles are supplied by brachial plexus C5-T1 motor axons?
Muscles of upper limb
Extrinsic back muscles
Which muscles are supplied by T2-L3 motor axons?
Postural back muscles (via posterior rami Intercostal muscles (via anterior rami) Anterolateral abdominal wall muscles (via thorax-abdominal, subcostal, iliohypogastric & ilioinguinal nerves)
Which muscles are supplied by lumbosacral plexus L1-S4 motor axons?
Muscles of lower limb
Perineal skeletal muscles
How do you clinically test C5 myotome and which muscle is being tested?
Shoulder abduction
Deltoid
How do you clinically test C6 myotome and which muscle is being tested?
Elbow flexion
Biceps brachii
How do you clinically test C7 myotome and which muscle is being tested?
Elbow extension
Triceps brachii
How do you clinically test C8 myotome and which muscle is being tested?
Finger flexion
Flexion digitorum superficialis
How do you clinically test T1 myotome and which muscle is being tested?
Finger abduction
Dorsal interossei
How do you clinically test L3 myotome and which muscle is being tested?
Knee extension
Quadriceps femoris
How do you clinically test L4 myotome and which muscle is being tested?
Ankle dorsiflexion
Tibialis anterior
How do you clinically test L5 myotome and which muscle is being tested?
Great toe extension
Extensor hallucis longus
How do you clinically test S1 myotome and which muscle is being tested?
Ankle plantarflexion
Gastrocnemius
How do you clinically test S2 myotome and which muscle is being tested?
Knee flexion
Biceps femoris
What is a spinal cord reflex?
Involuntary response to stimulus
How does the patellar reflex work?
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
What are the clinical signs of an upper motor neurone lesion and lower motor neurone lesion?
UMN lesions= spasticity
LMN lesions= flaccidity
List the spinal reflexes that can be clinically tested
Biceps brachii= C5, C6 Triceps brachii = C7 Brachioradialis= C6 Knee jerk = L3 Ankle jerk = S1
