Anatomie Prufung1 Flashcards
(26 cards)
What are the segments that are formed by paraxial mesoderm called?
somites
What does each somite differentiate to form?
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
What does a sclerotome differentiate into?
Vertebrae, ribs, parts of intervertebral discs
What does a myotome differentiate into?
skeletal muscle of back, body wall, limbs
What does a dermatome differentiate into?
dermis of back
The myotome further develops into 2 regions, which are: ?
- Epaxial group (dorsally located)
2. Hypaxial group (ventro-laterally located)
Muscles of the limbs are derived from which group and are innervated by which ramus?
Hypaxial muscle group
Innervated by branches of the ventral ramus
When do limb buds first become visible, and where?
- Time: End of 4th week
- Where? They become visible on the ventrolateral body wall of the embryo.
What does a limb bud consist of?
- Outer layer of surface ectoderm –> gives rise to epidermis
- Underlying core of mesenchyme (derived from somatic layer of lateral plate mesoderm) –> gives rise to bones and connective tissue of the limbs
At the distal tip of each limb, what is the thickened ridge of ectoderm called and what does it do?
- AER: apical ectodermal ridge - thickened ridge of ectoderm along the distal edge of the limb bud.
- What does the AER do? It induces proliferation of the underlying mesenchyme –> causes the limb to grow in LENGTH
What direction does the limb grow in and why?
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).
What are bones derived from?
Somatic layer of lateral plate mesoderm
The mesenchymal cells differentiate into chondroblasts –> endochondral ossification –> bones.
What do the terminal portions of the limb buds form?
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
Where do the myoblasts that form the muscles of the limb originate from?
hypaxial domain of the myotome
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:
- dorsal muscle mass
2. ventral muscle mass
What innervates the muscles of the upper limb?
Ventral rami of spinal nerves C5-T1
because the upper limb bud forms near the C5-T1 somites
What innervates the muscles of the lower limb?
Ventral rami of spinal nerves L2-S3
b/c the lower limb bud forms near the L2-S3 somites
Limb flexion: The long axis of the limb moves from ____ to ____ orientation.
From coronal to sagittal orientation
The upper limb rotates ______ while the lower limb rotates ______.
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.
Why is rotation of the limbs responsible for distortion of dermatome pattern in adults?
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.
What is syndactyly?
fusion of digits
What is polydactyly?
extra digits
What is amelia?
absence of 1 or more limbs
The hypaxial muscle group gives rise to what?
Muscles of the trunk and limbs
