Lecture 10: Dermatomes, Myotomes, Plexi

Question 1

The paraxial mesoderm differentiates into the head and somites

What 3 primary things does the somite differentiate into?

Answer 1

Sclerotome (cartilage)

Myotome (skeletal muscle)

Dermatome (dermis, skeletal muscle)

____________________________
Also differentiates into:
Syndetome (tendons)

Endothelial cells (dorsal aorta)

Question 2

Cells of the myotome will migrate to form the ______ and ________

Answer 2

Epimere

Hypomere

Question 3

Posterior migrators populate the epimere and form _____ muscles

Answer 3

Epaxial

Question 4

Anterior migrators populate the hypomere, forming the _____ muscles

Answer 4

Hypaxial

Question 5

_______ cells condense aound the notochord to form the vertebrae

Answer 5

Sclerotome

Question 6

The notochord contributes to the ________ _______ of the intervertebral disc

Answer 6

Nucleus pulposus

Question 7

Somitic innervation occurs as branches of neural tissue migrate toward their corresponding muscles. Where does this neural tissue branch from?

Answer 7

Neural tube

Question 8

Do epaxial or hypaxial have long processes for their developing innervation?

Answer 8

Hypaxial. Epaxial lie closer to nerve contacts

Question 9

________ is the area of skin supplied with afferent nerve fibers by a single posterior spinal root

Answer 9

Dermatome

Question 10

There are cranionuchal dermatomes, but other than that the face is one of the exceptions to dermatome innervation. Why is this?

Answer 10

The face is primarily controlled by cranial nerves

Question 11

Anterior rootlets of the spinal cord refer to the ventral side, and provide ______ innervation

(Motor vs. sensory)

Answer 11

Motor

Question 12

Posterior rootlets of the spinal cord refer to the dorsal region, and provide ______ innervation

(Motor vs. sensory)

Answer 12

Sensory

Question 13

Afferent spinal nerves conduct what type of info?

Answer 13

Sensory

Question 14

Efferent spinal nerves conduct what type of info?

Answer 14

Motor

Question 15

A _________ is a unilateral area of skin innervated by the sensory fibers of a single spinal nerve

Answer 15

Dermatome

Question 16

A ________ is a unilateral muscle mass receiving innervation from fibers conveyed by a single spinal nerve

Answer 16

Myotome

Question 17

Posterior and anterior roots of the spinal cord unite to form _____ ______, which then split into posterior and anterior _____

Answer 17

Spinal nerves

Rami

Question 18

________ ramus supplies the deep muscles of the skin of the back (epaxial)

Answer 18

Posterior ramus

Question 19

_______ ramus supplies anterior and lateral musculature/dermis of trunk/limbs (hypaxial)

Answer 19

Anterior

Question 20

What rami form the cervical plexus?

Answer 20

Anterior rami of C1-C4

Question 21

What does the cervica plexus innervate?

Answer 21

Anterior neck muscles

Skin of neck, head, and shoulders

Question 22

What are the following branches of the brachial plexus based on this anterior rami distribution:

C5-C7
C6-T1
C8-T1

Answer 22

C5-C7 = Musculocutaneous n.

C6-T1 = Median n.

C8-T1 = Ulnar n.

Question 23

What are the following branches of the brachial plexus based on this anterior rami distribution

C5-T1
C8-T2
CA-T1

Answer 23

C5-T1 = Radial n.

C8-T2 = Medial brachial cutaneous n.

CA-T1 = Medial antebrachial cutaneous n.

Question 24

What are the 5 branches of the lumbosacral plexus to the lower extremity?

Answer 24

Femoral n.
Obturator n.
Sciatic n. (Branches into tibial and common fibular nn.)
Lateral femoral cutaneous n.
Posterior femoral cutaneous n.

Question 25

When looking at anterior-posterior innervation patterns, which ramus will appear larger, the anterior or posterior?

Answer 25

Anterior

Question 26

When looking at anterior-posterior innervation patterns, why does the anterior ramus appear larger?

Answer 26

Because it supplies the lateral and ventral body wall and dermis (recall from hypomere-hypaxial muscles)

The posterior is shorter and smaller because it is specifically innervating dorsal musculature and skin (epimere –> epaxial)

Question 27

Anterior rami of spinal nerves tend to follow what anatomical structures?

Answer 27

Ribs

Question 28

What is the difference between segmental and plexus innervation?

Answer 28

Segmental innervation (such as with skin of the trunk) consists of separate spinal nerves travelling to their destination in a distinct linear pattern. Each individual spinal nerve contacts multiple dermatomes but they each have their own individual primary area of contact.

With plexus innervation (such as with skin of limbs), spinal nerves combine into one peripheral nerve through plexus formation. The nerves then emerge from the plexus as separate nerves again prior to supplying their distribution area.

Question 29

How many nerves must be damaged in order to have an area of the body affected?

Answer 29

At least 2, due to overlapping

Question 30

What embryological process leads to the “twisting” or “barbar-pole” pattern of innervation seen on adult nerve maps?

Answer 30

Limb rotation

Question 31

Nerve plexuses like the brachial plexus and lumbosacral plexus have somatic sensory and somatic motor function.

There are also autonomic nerve plexuses, what type of information is transmitted in these?

Answer 31

Visceral sensory

Visceral motor

Question 32

What are some examples of autonomic nerve plexuses?

Answer 32

Thoracic autonomic plexuses
Abdominal aorta autonomic plexuses
Mesenteric plexus

Question 33

What are the terms for the divisions of the brachial plexus from roots to terminal branches?

Answer 33

Roots (5)
Trunks (3)
Anterior (3) and posterior (3) divisions
Cords (3)
Terminal branches

Question 34

Lesions in the spinal cord result in varying degrees of severity based on the level of damage. What area of the spinal cord could be damaged with the least severe anatomical effects?

Answer 34

Conus medullaris or cauda equina

[the higher the level of damage, the more spinal cord mass you have separated from the brain = more severe damage]