Spinal Cord and Plexuses (Ch. 16)

Question 1

What is the spinal cord a part of (CNS or PNS)?

Answer 1

CNS

Question 2

What are fxns of the spinal cord?

Answer 2

Sensory and motor innervation of body
Two-way conduction pathway for signals between body and brain
Major center for reflexes

Question 3

Where does the Spinal Cord travel?

Answer 3

Extends from foramen magnum (occipital bone) to level of L1 or L2 (lumbar vertebrae)

Question 4

How many pairs of spinal nerves are there (part of PNS)?

Answer 4

31 pairs of spinal nerves

Question 5

What are the 2 enlargements of the spinal cord? Why do they exist?

Answer 5

Cervical and Lumbar enlargements for nerves supplying upper and lower limbs

Question 6

What is the inferior end of the actual spinal cord?

Answer 6

Conus Medullaris

Question 7

The nerve roots at the inferior end of the vertebral canal is called the ______ _______?

Answer 7

Cauda Equina

Question 8

What is the Filum Terminale?

Answer 8

A long filament the extends past Conus Medullaris and attaches to coccyx

Question 9

What protects the spinal cord?

Answer 9

Bone, meninges, and CSF

Question 10

What is the Epidural Space?

Answer 10

Filled with fat and veins

Question 11

Are the subdural space, arachnoid mater, subarachnoid space, and pia mater the same in the spinal cord as the brain?

Answer 11

Yes

Question 12

What are the Denticulate Ligaments?

Answer 12

Anchor spinal cord to dura mater

Question 13

Where is an Epidural Nerve Block inserted? Why? What is it used for?

Answer 13

Needle between L4 and L5 vertebrae permits injection of anesthesia into epidural space without risk of damage to spinal cord. The Cauda Equina gets “pushed” out of the way if necessary.

Epidural. Commonly used during childbirth

Question 14

Spinal Cord Gray Matter

Answer 14

Gray matter forms an “H,” surrounded by white matter

Gray commissure is composed of unmyelinated axons crossing from one side of the CNS to the other

Central canal is the central cavity (hollow) of the spinal cord

Dorsal (posterior) arms of H are dorsal horns

Ventral (anterior) arms are ventral horns

Question 15

Anterior (Ventral) and Posterior (Dorsal) Roots

Answer 15

Dorsal horns receive info from sensory neurons (cell bodies located in dorsal root ganglia)

Signal from sensory neurons reach spinal cord via dorsal roots.

Ventral horns send out info to skeletal muscle. Signals going out to motor neurons travel via ventral roots

Question 16

Spinal Nerves

Answer 16

Dorsal and Ventral roots merge to form spinal nerve

Spinal nerve has BOTH sensory and motor axons

Exits vertebral column at intervertebral foramina

Immediately splits into dorsal and ventral rami

Question 17

Dorsal (Posterior) and Ventral (Anterior) Rami

Answer 17

Ventral and Dorsal Rami carry both sensory and motor fibers

Ventral rami innervate most of the body, including trunk and limbs. Dorsal rami innervate small portion of the back

Question 18

Reflexes

Answer 18

Very simple neuron chain

Basic structural plan of NS

Reflexes EXCLUDE brain; rapid, automatic, unlearned motor response to stimulus

Can be somatic (hot stove) or visceral (vomiting)

Signal comes in and synapses at interneurons. Interneurons stimulate and inhibit as appropriate

Question 19

What are Dermatomes?

Answer 19

Area of skin supplied by a single spinal nerve. All spinal nerves EXCEPT C1

Numbness can pinpoint spinal cord injuries

Question 20

What is Referred Pain?

Answer 20

(Dermatomes)

When pain from an organ is mistakenly referred to dermatome.
ex: Appendicitis starts as pain in T10 dermatome

Question 21

Nerve Plexuses

Answer 21

A network of nerves…formed by VENTRAL rami only

All spinal nerves except T2-T12 branch and rejoin

Each muscle in a limb receives its nerve supply from more than one spinal nerve…damage to one spinal nerve cannot completely paralyze any limb muscle

Question 22

What are the 4 nerve plexuses?

Answer 22

1. Cervical plexus (C1-C5)
2. Brachial plexus (C5-T1)
3. Lumbar plexus (L1-L4)
4. Sacral plexus (L4-S4)

Question 23

Cervical Plexus

Answer 23

Ventral rami of first 4 cervical nerves

Most branches are cutaneous sensory. Some motor to anterior neck

Phrenic Nerve receives fibers from C3, C4, and C5; innervates diaphragm for respiration

Question 24

Brachial Plexus

Answer 24

Partly in neck, partly in axilla

Gives rise to most nerves of the upper limb.

Mixing of ventral rami of C5-C8 and most of the ventral ramus of T1

Main components:
–ventral rami, trunks, divisions, cords, terminal branches

Question 25

Brachial Plexus: Number of roots, trunks, divisions; Anterior and Posterior Divisions

Answer 25

5 roots give rise to 3 trunks which branch into 2 divisions Anterior Division: nerves that innervate anterior compartment muscles of upper limb and skin Posterior Division: nerves that serve posterior compartment and skin

Question 26

Brachial Plexus: C5-T1

Answer 26

Roots: C5-T1 Trunks: upper, middle, lower Anterior Divisions (cords): lateral and medial --lateral (from upper trunk) --> supplies musculocutaneous nerve --medial (from lower trunk) --> supplies medial and ulnar nerves Posterior Division (from middle trunk): supplies radial nerve and axillary nerve

Question 27

What are the terminal branches of the Brachial Plexus?

Answer 27

``` Axillary Nerve Radial Nerve Musculocutaneous Nerve Median Nerve Ulnar Nerve ```

Question 28

Musculocutaneous Nerve

Answer 28

brachial plexus Sensory innervation: skin sensation for lateral arm Motor innervation: anterior compartment of arm

Question 29

Ulnar Nerve

Answer 29

brachial plexus aka "funny bone" nerve Sensory Innervation: skin of medial hand, medial side of digit 4, all of digit 5 Motor Innervation: flexors and intrinsic hand muscles

Question 30

Median Nerve

Answer 30

brachial plexus Sensory Innervation: skin of lateral palm and digits 1-3 and lateral side of digit 4 Motor innervation: anterior compartment of forearm (w/ ulnar); intrinsic muscle of lateral palm, muscles that oppose the thumb

Question 31

Median Nerve Lesion

Answer 31

aka Carpal Tunnel Syndrome Affects motor nerve to thenar muscles Pain/numbness in lateral palm From compression of nerve near hand

Question 32

Axillary Nerve

Answer 32

brachial plexus Sensory Innervation: shoulder joint and skin on part of deltoid Motor innervation: Teres Minor and Deltoid

Question 33

Radial Nerve

Answer 33

brachial plexus Sensory Innervation: skin over dorso-lateral arm, forearm, and hand Motor Innervation: posterior compartment of arm and forearm (extensors)

Question 34

Lumbar Plexuses

Answer 34

Ventral Rami: branches into Iliohypogastric, Ilioinguinal, Genitofemoral, and Obturator Anterior Division Posterior Divison: branches into Lateral Femoral Cutaneous and Femoral

Question 35

Femoral Nerve

Answer 35

lumbar plexus Sensory Innervation: skin of antero-medial thigh; skin of medial foot Motor Innervation: muscles of anterior thigh (thigh flexors, leg extensors [ex: quadriceps femoris])

Question 36

Phrenic Nerve

Answer 36

cervical plexus Phrenic Nerve receives fibers from C3, C4, and C5; innervates diaphragm for respiration "C3, C4, C5 keep the diaphragm alive"

Question 37

Obturator Nerve

Answer 37

lumbar plexus Sensory Innervation: skin of medial thigh Motor Innervation: muscles of medial thigh *Adductor Magnus innervated by both Obturator and Tibial Nerves

Question 38

Sacral Plexus: Sciatic Nerve

Answer 38

Tibial Nerve and Common Fibular Nerve together in common sheath = "Sciatic Nerve" Longest and thickest nerve of body. Senses all of lower limb except anterior/medial thigh

Question 39

Sacral Plexus: L4-S4; Anterior Division

Answer 39

Ventral Rami: L4-S4 Anterior Division: Tibial and Pudendal Posterior Division

Question 40

Tibial Nerve

Answer 40

Anterior compartment of sacral plexus Sensory Innervation: skin of postero-lateral leg, skin of sole of foot (subdivides into plantar nerves) Motor Innervation: muscles of posterior thigh and muscles of posterior leg --plus Adductor Magnus (w/ Obturator N.) and Biceps Femoris (w/ Common Fibular N.)

Question 41

Sacral Plexus: L4-S4; Posterior Division

Answer 41

Ventral Rami: L4-S4 Posterior Division: Common Fibular, Superior Gluteal, Lumbosacral Trunk, Inferior Gluteal Anterior Compartment

Question 42

Common Fibular Nerve

Answer 42

Posterior compartment of sacral plexus Sensory Innervation: skin of anterolateral leg, skin on dorsum of foot Motor Innervation: muscles of anterior leg (deep fibular), muscles of lateral leg (superficial fibular) --Common Fibular N. also innervates Biceps Femoris (w/ Tibial N.)

Question 43

Fibular Nerve Lesion

Answer 43

Foot-Drop Fibular Nerve = Peroneal Nerve

Question 44

What is the longest and thickest nerve of the body?

Answer 44

Sciatic Nerve

Question 45

The Sciatic Nerve serves all of the lower limb except _____?

Answer 45

Anterior/medial thigh