Exam 3: Spinal Nerves

Question 1

Spinal Nerves

Answer 1

• come directly off spinal cord
• peripheral nervous system
• 31 pairs of spinal nerves
• on each side 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal

Question 2

Spinal Nerves Composition

Answer 2

• anterior (ventral root): axons from motor neurons
• posterior (dorsal) root: axons from sensory neurons
• when they unite make the spinal nerve

Question 3

2 Main Branches of Spinal Nerves

Answer 3

• posterior (dorsal) ramus

- anterior (ventral) ramus

Question 4

Posterior (Dorsal) Ramus

Answer 4

• innervates skin of back, deep back muscles

- motor and sensory

Question 5

Anterior (Ventral) Ramus

Answer 5

• innervates everything else from neck inferiorly
• also forms nerve plexuses
• motor and sensory

Question 6

Nerve Plexus

Answer 6

• network of converging and/or diverging axons
• formed from anterior rami of spinal nerves
• named nerves come off of plexus
• allows for multiple nerves to innervate multiple structures
• most thoracic spinal nerves do not form plexuses (remain as individual spinal nerves)

Question 7

Cervical Plexus

Answer 7

• anterior rami of C1-C4

- innervates sensory-SKIN of neck, ear, and shoulders. motor-anterior neck muscles

Question 8

Phrenic nerve

Answer 8

• receives SOME axons from cervical plexus
• C3-C5
• supplies diaphragm (3, 4, and 5 keep the diaphragm alive)

Question 9

Brachial Plexus

Answer 9

• anterior rami of C5-T1
• primarily innervates upper limb
• each nerve has both motor and sensory components

Question 10

Axillary Nerve

Answer 10

• part of brachial plexus
• innervates deltoid and teres minor
• can be injured with use of a crutch
• test for nerve damage: have patient abduct arm

Question 11

Musculocutaneous Nerve

Answer 11

• part of brachial plexus
• innervates most muscles on anterior surface of ARM (coracobrachialis, biceps brachii, brachialis)
• elbow/forearm flexion is impaired when this nerve is damaged
• test for nerve damage: have patient flex elbow

Question 12

Radial Nerve

Answer 12

• part of brachial plexus
• innervates posterior ARM muscles (triceps brachii-extend elbow/forearm) and posterior FOREARM muscles (extend wrist/fingers)
• nerve may be damaged if humerus is broken or with use of a crutch
• test for nerve damage: extend wrist, elbow, and fingers
• symptom of radial nerve damage is wrist drop

Question 13

Median Nerve

Answer 13

• part of brachial plexus
• innervates almost all anterior FOREARM muscles (flex wrist/fingers) THENAR muscles (move thumb) and lumbricals going to fingers 2 and 3.
• may be damaged if someone tries to slit their wrists or by carpal tunnel syndrome
• test for nerve damage: flex wrist, move thumb

Question 14

Ulnar Nerve

Answer 14

• part of brachial plexus
• innervates 1.5 anterior FOREARM muscles (medial 1/2 of flexor digitorum profundus and flexor carpi ulnaris) and most intrinsic hand muscles (hypothenar, lumbricals to 4 and 5, palmar and dorsal interossei)
• test for nerve damage: abduct and adduct fingers

Question 15

Lumbar Plexus

Answer 15

• anterior rami of L1-L4
• innervates inferior abdominal wall, part of lower limb
• each nerve has motor and sensory components

Question 16

Femoral Nerve

Answer 16

• part of lumbar plexus
• innervates anterior thigh muscle (illiacus, quadriceps, psoas-extend knee, flex hip)
• test for nerve damage: test knee reflex, have patient extend knee

Question 17

Obturator Nerve

Answer 17

• part of lumbar plexus
• innervates medial thigh muscles (adductors, gracilis, pectinius-adduct and flex thigh)
• test for nerve damage: can patient adduct thigh when resistance is present?

Question 18

Sacral Plexus

Answer 18

• anterior rami of L4-S4
• innervats the buttocks, pelvic structures, and majority of lower limb
• each nerve has motor and sensory components

Question 19

Sciatic Nerve

Answer 19

• major nerve of sacral plexus

- splits into tibial nerve and common fibular nerve

Question 20

Tibial nerve

Answer 20

• branch of sicatic nerve
• innervates mos posterior thigh muscles (hamstrings-flex knee, extend thigh) posterior leg muscles (plantar flex, flex toes) and muscles on sole of foot
• -test for nerve damage:difficulty extending hip against resistance? flex knee with resistance? flexing (curling) toes?

Question 21

Common Fibular Nerve

Answer 21

• branch of sciatic nerve
• innervates anterior leg muscles (dorsiflex, extend toes), lateral leg muscles (evert foot), muscles on dorsum of foot (extend toes)
• injury: may fall asleep when you cross your legs, may be injured by leg cast/tight ski boots
• test for nerve damage: dorsiflex, evert foot, extend toes, have foot drop?