Dermatomes/Myotomes and spinal nerve plexuses

Question 1

Name the 3 primary germ layers

Answer 1

Endoderm, mesoderm, ectoderm

Question 2

What does the endoderm create?

Answer 2

Internal linings of the body, and some internal organs

Question 3

What does the ectoderm create?

Answer 3

Outer linings of the body; skin and hair

Question 4

What does the mesoderm create?

Answer 4

All other tissues; dermis, heart, muscles, bones, blood, connective tissue, formation of internal body cavity

Question 5

What does the paraxial mesoderm create?

Answer 5

The head and somites

Question 6

What do somites create?

Answer 6

The sclerotome, myotome, dermotome

Question 7

Sclerotome is

Answer 7

Bones and cartilage

Question 8

Mytome is

Answer 8

Skeletal muscles

Question 9

Dermotome is

Answer 9

Dermis layer of skin

Question 10

What happens to somite cells that migrate anteriorly?

Answer 10

They give rise to the muscles/skin of the trunk and upper limbs (hypaxial muscles)

Question 11

What happens to somite cells that migrate posteriorly?

Answer 11

They give rise to intrinsic muscles/skin of the back (epaxial muscles)

Question 12

What is the main job of the posterior horn?

Answer 12

Sensory

Question 13

What is the main job of the anterior horn?

Answer 13

Motor function

Question 14

Posterior ramus innervates?

Answer 14

Epaxial muscles of back/skin

Question 15

Anterior ramus innervates?

Answer 15

Hypaxial muscles of trunk and upper limbs

Question 16

What will an injury to a posterior root cause?

Answer 16

Sensory deficits only

Question 17

What will an injury to an anterior root cause?

Answer 17

Motor deficits only

Question 18

What is a dermatome?

Answer 18

Single area of skin that is supplied with afferent nerve fibers from a SINGLE posterior spinal root

Question 19

What causes the dermatomes of the lower extremities to have a pulled look?

Answer 19

Internal rotation of the leg during development

Question 20

What is a myotome?

Answer 20

All of the muscles innervated by a SINGLE efferent anterior root – most muscles are composed of multiple myotomes

Question 21

What happens if there is an injury to 1 segment of anterior rootlets?

Answer 21

This may lead to weakness of the muscle but NOT complete loss of function due to the muscle being innervated by multiple myotomes

Question 22

What is a plexus?

Answer 22

Multiple spinal nerves combining to form 1 PERIPHERAL nerve

Question 23

Femoral nerve

Answer 23

L2-L4 spinal nerves

Question 24

Obturator nerve

Answer 24

L2-L4 spinal nerves

Question 25

Sciatic nerve

Answer 25

L4-S3 spinal nerves

Question 26

Tibial nerve

Answer 26

Branch of sciatic; L4-S3

Question 27

Common fibular nerve

Answer 27

Branch of sciatic; L4-S2

Question 28

Lateral femoral cutaneous nerve

Answer 28

L2-L3 spinal nerves

Question 29

Posterior femoral cutaneous nerve

Answer 29

S1-S3 spinal nerves