Major Plexuses and Peripheral Nervous System

Question 1

Peripheral Nervous System

Answer 1

• consists of cranial nerves and spinal nerves, which link CNS to peripheral tissues
• neurons contributing to peripheral nerves are partly contained in CNS
• 12 cranial
• 31 spinal
• p. 325 table 8.1

Question 2

Spinal Nerves

Answer 2

• spinal nerve is approximately 1 cm long
• shortly after exiting the intervertebral foramen, the spinal nerve divides into anterior and posterior rami
• roots combine to make spinal nerve then make rami

Question 3

Rami

Answer 3

• posterior rami: supplies erector spinae muscle and the overlying skin of trunk
• anterior rami: supplies muscle and skin of side and front of trunk as well as muscles of limbs-cervical, brachia, and lumbosacral plexi are all derived from anterior rami

Question 4

Cervical Plexus C1-C4

Answer 4

• C3, C4, C5 combine to make phrenic nerve
• supplies diaphragm
• lesion above or at C3 unable to breathe on own
• lesion at C4/C5 may be able to breathe on own without ventilators for brief periods of time

Question 5

Scalenes

Answer 5

• CAD=cervical acceleration and deceleration aka whiplash

- thoracic outlet syndrome: compression –> altered signaling up and down pathway impingement of brachial plexus

Question 6

Cervical Parts of Sympathetic Trunk

Answer 6

• superior cervical ganglion
• middle cervical ganglion
• inferior cervical ganglion
• look up function

Question 7

Brachial Plexus

Answer 7

• other impingements of brachial plexus: pec minor or first rib
• 5 roots: anterior rami of C5-T1
• 3 trunks
• 6 divisions
• 3 cords
• 4 terminal nerves: MMRU

Question 8

Brachial Plexus: Nerve Root Branches

Answer 8

• dorsoscapular is branch of C5 nerve root: supplies rhomboids and levator scapulae
• long thoracic is branch of C5, C6, C7 nerve roots: supplies serratus anterior

Question 9

Brachial Plexus: Trunk Branches

Answer 9

-suprascapular is branch of superior trunk: supplies supraspinatus and infraspinatus

Question 10

Brachial Plexus: Branches of Cords

Answer 10

• branches of medial cords…
• median pectoral comes from C8-T1 and supplies pec major and minor
• medial brachial cutaneous nerve comes from T1
• median antebrachial cutaneous nerve comes from C8-T1
• ulnar nerve comes from C7-T1
• lateral cord branches…
• lateral pectoral nerve supplies pec major and comes from C5-C7
• musculocutaneous nerve innervates biceps, coracobrachialis, and brachialis
• branches of posterior cord…
• STAR or ARTS pneumonic
• upper subscapular nerve C7, C8 supplies subscapularis
• lower subscapular nerve supplies teres major C5, C6
• thoracodorsal nerve supplies latissimus dorsi C6-C8
• axillary supplies teres minor and deltoid and does sensation to shoulder C5, C6
• radial nerve supplies triceps, brachioradialis, extensor carpi radialis ms, extensor and abductor muscles of thumb C5, C6

Question 11

Radial Nerve

Answer 11

• C6, C7**, C8
• sensation
• innervates triceps, brachioradialis, extensor carpi radialis, extensor and abductor muscles of thumb
• motor function

Question 12

Median Nerve

Answer 12

• C5-T1
• sensation
• carpal tunnel CTS
• innervates pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis
• motor function

Question 13

Ulnar Nerve

Answer 13

• C7-T1
• sensation
• cubital fossa
• innervates flexor carpi ulnaris, flexor digitorum profundus, interosseus muscle, lumbricals, flexor pollicis brevis
• motor function

Question 14

Axillary Nerve

Answer 14

• C5 and C6
• sensation
• innervates deltoid, teres minor
• motor function

Question 15

Musculocutaneous Nerve

Answer 15

• C5-C7
• sensations
• innervates BBC: biceps, brachialis, coracobrachialis
• motor function

Question 16

Three Nerves Acting on Thumb

Answer 16

• radial nerve: thumb abduction in plane of thumb
• ulnar nerve: adduction
• median nerve: opposition, flexion (FPL and FPB), and thumb abduction perpendicular to palm
• RUM mnemonic

Question 17

Intrinsic Muscles of Hand

Answer 17

• intrinsic: C8-T1, ulnar nerve supplies all except lumbricals I and II, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis superficial head
• thenar eminence: opponens pollicis, abductor pollicis brevis, flexor pollicis brevis, adductor pollicis
• hypothenar eminence: opponens digiti minimi, abductor digiti minimi, flexor digiti minimi, lumbricals, interossei

Question 18

Lumbrosacral Plexus

Answer 18

• lumbar: anterior rami of spinal nerves L1-L3 and part of L4
• sacral plexus: anterior rami of S1-S4 and lumbosacral trunk
• femoral, obturator, sciatic, tibial, peroneal

Question 19

Femoral Nerve

Answer 19

• L2-L4 dorsal deviations
• course: passes beneath inguinal ligament into thigh divides into anterior and posterior divisions
• muscles: sartorius, rectus femoris, vastus lateralis, vastus medialis, articularis genu, pectineus

Question 20

Obturator Nerve

Answer 20

• L2, L3 some L4
• course: leaves pelvis through superior obturator foramen-has anterior and posterior branches
• muscles: gracilis, adductor brevis, adductor longus, adductor magnus with tibial division of sciatic nerve

Question 21

Sciatic Nerve

Answer 21

• L4-S3 some branches from sacral plexus
• course: passes through greater sciatic foramen deep to piriformis in 90% of cases; travels in posterior thigh deep to hamstrings and enters popliteal fossa where it divides into common peroneal nerve and tibial nerve
• injury to this nerve would see weakness of knee flexors, hip extensors, all muscles below knee paralyzed, foot drop, absent achilles DTR
• tibial division of sciatic: adductor magnus, biceps femoris, semitendinosus, semimembranosus

Question 22

Straight Leg Raise

Answer 22

• used to test source of back and leg pain (stretch spinal cord, cauda equina, and/or sciatic nerve
• position: patient supine or seated
• technique: keeping patients lower extremity straight, slowly lift leg until pain or discomfort is felt, decrease angle slightly and dorsiflex ankle
• interpretation: determine if pain is hamstring or sciatic nerve related

Question 23

Tibial Nerve

Answer 23

• L4-S3
• course: travel deep in leg with posterior tibial artery then travels posterior to medial malleolus into foot and divides into medial and lateral plantar nerves
• muscles: gastroc, soleus, plantaris, tibialis posterior, popliteus, FDL, FHL

Question 24

Common Peroneal (Fibular) Nerve

Answer 24

• L5-S2
• course: travels laterally from popliteal fossa towards fibula, courses around fibular neck and then divides into deep and superficial peroneal nerves
• muscle: biceps femoris short head

Question 25

Superficial and Deep Peroneal (Fibular) Nerves

Answer 25

• superficial peroneal L5-S2, muscles: peroneus longus, peroneus brevis
• deep peroneal L4-S1 muscles: tibialis anterior, EHL, EDL, peroneus tertius

Question 26

Lateral and Medial Plantar Nerves

Answer 26

• lateral plantar nerve S2-S3 adductor hallucis, FDM, ADM, quadratus plantae, lumbricals 2-4, dorsal interossei, plantar interossei
• medial plantar S2-S3 abductor hallucis, FHB, FDB, 1st lumbrical

Question 27

Superficial vs. Deep Tendon Reflexes

Answer 27

• superficial: UMN, controlled by CNS, require stimulation of skin, presence of superficial reflex indicates UMN integrity, absences indicates UMN lesion
• deep: LMN, mediated by ventral horn cell of spinal cord, require stimulation of tendon, CNS inhibits DTRs

Question 28

DTRs

Answer 28

• biceps: C5, C6
• brachioradialis: C6
• triceps: C7
• patellar: L4
• achilles: S1
• monosynaptic stretch reflex: provides rapid local feedback for motor control; reflex arc begins with specialized receptors called muscle spindles which detect amount and rate of stretch in muscles, info transmitted to distal processes of sensory neurons then conveyed to dorsal roots; in roots sensory neuron form multiple synapses including some direct onto LMNs in anterior horn; LMNs project via ventral roots out into muscle causing contraction
• afferent sensory neurons also form synapses onto excitatory and inhibitory interneurons which synapse onto LMNs

Question 29

Superficial Abdominal Reflex

Answer 29

• supine
• sharp edge of reflex hammer stroke each quadrant of abdomen looking to see if it moves toward that point
• absent = UMN lesion

Question 30

Superficial Cremasteri Reflex

Answer 30

• supine
• sharp edge of reflex hammer stroke the inner side of upper thigh looking to see if scrotum pulls upward to cremaster muscle
• absent bilaterally = UMN, absent unilaterally = LMN lesion L1-L2

Question 31

Superficial Anal Reflex

Answer 31

• prone
• touch perianal skin looking for anal sphincter to contract
• bilaterally absent = UMN lesion, absent unilaterally = LMN lesion

Question 32

Pathologic Reflexes

Answer 32

• superficial reflexes that are mediated through CNS
• presence means UMN lesion, absent means intact UMN
• babinski: seated or supine; sharp instrument stroke plantar foot negative if toes do not move or bunch together, positive UMN lesion if great toe extends or others flex and splay
• oppenheim test: supine or seated; sharp instrument or fingernail stroke crest of tibia, negative no reaction or pain, positive UMN lesion great toe extends and other toes flex and splay