Anatomie Prufung1

Question 1

What are the segments that are formed by paraxial mesoderm called?

Answer 1

somites

Question 2

What does each somite differentiate to form?

Answer 2

sclerotome, dermatome, and myotome

paraxial mesoderm –> somite….–>

a. sclerotome –> vertebrae, ribs, part of intervertebral discs
b. dermatome –> dermis of back
c. myotome –> skeletal muscle of back, body wall, limbs

Question 3

What does a sclerotome differentiate into?

Answer 3

Vertebrae, ribs, parts of intervertebral discs

Question 4

What does a myotome differentiate into?

Answer 4

skeletal muscle of back, body wall, limbs

Question 5

What does a dermatome differentiate into?

Answer 5

dermis of back

Question 6

The myotome further develops into 2 regions, which are: ?

Answer 6

1. Epaxial group (dorsally located)

2. Hypaxial group (ventro-laterally located)

Question 7

Muscles of the limbs are derived from which group and are innervated by which ramus?

Answer 7

Hypaxial muscle group

Innervated by branches of the ventral ramus

Question 8

When do limb buds first become visible, and where?

Answer 8

• Time: End of 4th week

- Where? They become visible on the ventrolateral body wall of the embryo.

Question 9

What does a limb bud consist of?

Answer 9

1. Outer layer of surface ectoderm –> gives rise to epidermis
2. Underlying core of mesenchyme (derived from somatic layer of lateral plate mesoderm) –> gives rise to bones and connective tissue of the limbs

Question 10

At the distal tip of each limb, what is the thickened ridge of ectoderm called and what does it do?

Answer 10

1. AER: apical ectodermal ridge - thickened ridge of ectoderm along the distal edge of the limb bud.
2. What does the AER do? It induces proliferation of the underlying mesenchyme –> causes the limb to grow in LENGTH

Question 11

What direction does the limb grow in and why?

Answer 11

limb grows in a proximal to distal direction.
Why?
- The AER induces growth of what is underneath it. As it grows outward, the AER moves. So what was originally underneath it now differentiates. So that bone (arm bone) forms first compared to what is more distal (the hand bone).

Question 12

What are bones derived from?

Answer 12

Somatic layer of lateral plate mesoderm

The mesenchymal cells differentiate into chondroblasts –> endochondral ossification –> bones.

Question 13

What do the terminal portions of the limb buds form?

Answer 13

Hand and foot plates, which are separated from the rest of the developing limb by constrictions.

• Within each plate, the mesenchyme condenses into digital rays
• Apoptosis occurs between the rays

Question 14

Where do the myoblasts that form the muscles of the limb originate from?

Answer 14

hypaxial domain of the myotome

Question 15

The myoblasts (which come from the hypaxial domain) organize into 2 masses (on either side of the developing limb) once they are in the limbs, which are called:

Answer 15

1. dorsal muscle mass

2. ventral muscle mass

Question 16

What innervates the muscles of the upper limb?

Answer 16

Ventral rami of spinal nerves C5-T1

because the upper limb bud forms near the C5-T1 somites

Question 17

What innervates the muscles of the lower limb?

Answer 17

Ventral rami of spinal nerves L2-S3

b/c the lower limb bud forms near the L2-S3 somites

Question 18

Limb flexion: The long axis of the limb moves from ____ to ____ orientation.

Answer 18

From coronal to sagittal orientation

Question 19

The upper limb rotates ______ while the lower limb rotates ______.

Answer 19

The upper limb rotates LATERALLY.
-The dorsal muscle mass and elbow move to a POSTERIOR location; the ventral muscle mass moves ANTERIORLY.

The lower limb rotates MEDIALLY.
-Muscles derived from dorsal muscle mass are ANTERIORly found. Muscles derived from ventral muscle mass are located POSTERIORLY.

Question 20

Why is rotation of the limbs responsible for distortion of dermatome pattern in adults?

Answer 20

When the limbs elongate, the spinal nerves are still distributed and migrate along the limbs. But the most cranial nerves (C4-C5 in upper limb; L2-L3 in lower limb) and most caudal (T1 in upper limb; S2-S3 in lower limb bud) do not reach the most distal part of the limbs. So the original dermatome pattern changes somewhat as the limbs grow, but there is still a sequence.

Question 21

What is syndactyly?

Answer 21

fusion of digits

Question 22

What is polydactyly?

Answer 22

extra digits

Question 23

What is amelia?

Answer 23

absence of 1 or more limbs

Question 24

The hypaxial muscle group gives rise to what?

Answer 24

Muscles of the trunk and limbs

Question 25

What does the epaxial muscle group give rise to?

Answer 25

Intrinsic back muscles innervated by dorsal rami

Question 26

T/F: Dorsal muscle mass is innervated by dorsal rami, ventral muscle mass is inervated by ventral rami.

Answer 26

FALSE. Both are innervated by ventral rami. Both are derived from hypaxial myoblasts.