Question 1

________ Type of meromelia&#10;A)Dermatome&#10;B)Phocomelia&#10;C)Digital rays&#10;D)End of fourth week&#10;E)Amelia

Accepted Answer

Phocomelia is a type of meromelia (partial absence of the limbs).In this type of meromelia,the limbs have a flipper-like appearance.The term "phocomelia" is not commonly used;meromelia is the preferred term for all defects involving partial absence of a limb(s).

Question 2

________ Condensations of mesenchyme&#10;A)Dermatome&#10;B)Phocomelia&#10;C)Digital rays&#10;D)End of fourth week&#10;E)Amelia

Accepted Answer

The digital rays are condensations of mesenchyme in the hand and foot plates that indicate where the digits are developing.

Question 3

________ Exerts an inductive influence&#10;A)Upper limb&#10;B)Apical ectodermal ridge&#10;C)Somites&#10;D)Meromelia&#10;E)Lower limb

Accepted Answer

The apical ectodermal ridge (AER)is a thickened,epithelial plaque at the distal end of each limb bud.The AER exerts an inductive influence on the limb mesenchyme that initiates growth and development of the limbs.There is no further elaboration of distal structures (hands and fingers)if the ridge is removed experimentally.

Question 4

________ Area of skin supplied by a spinal nerve&#10;A)Dermatome&#10;B)Phocomelia&#10;C)Digital rays&#10;D)End of fourth week&#10;E)Amelia

Accepted Answer

A dermatome is the area of skin supplied by a single spinal nerve and its spinal ganglion (dorsal root ganglion).

Question 5

________ Rotates medially&#10;A)Upper limb&#10;B)Apical ectodermal ridge&#10;C)Somites&#10;D)Meromelia&#10;E)Lower limb

Accepted Answer

The developing lower limbs rotate medially through almost 90 degrees.As a result,the knees face anterolaterally.

Question 6

________ Partial absence of a limb&#10;A)Upper limb&#10;B)Apical ectodermal ridge&#10;C)Somites&#10;D)Meromelia&#10;E)Lower limb

Accepted Answer

Meromelia (from Greek meros,part,and melos,extremity)is the term now used to classify all limb defects that involve partial absence of a limb or limbs-including hemimelia (absence of all or part of the distal half of a limb)and phocomelia (absence of the proximal part of a limb or limbs).

Question 7

________ Limb muscles&#10;A)Upper limb&#10;B)Apical ectodermal ridge&#10;C)Somites&#10;D)Meromelia&#10;E)Lower limb

Accepted Answer

The limb muscles develop from mesenchyme that is derived from mesenchyme in the myotome regions of the somites.Following mesenchymal-epithelial transformation,the muscle-forming cells-myoblasts-migrate into the primordia of the limbs.

Question 8

________ Rotates laterally&#10;A)Upper limb&#10;B)Apical ectodermal ridge&#10;C)Somites&#10;D)Meromelia&#10;E)Lower limb

Accepted Answer

The developing upper limbs rotate laterally through 90 degrees on their longitudinal axes;as a result,the elbows face dorsally or posteriorly in an embryo at the end of the eighth week.

Question 9

________ Lower limb bud&#10;A)Dermatome&#10;B)Phocomelia&#10;C)Digital rays&#10;D)End of fourth week&#10;E)Amelia

Accepted Answer

The lower limb buds appear at the end of the fourth week as ventrolateral outgrowths of the body wall.

Question 10

________ Absence of the limbs&#10;A)Dermatome&#10;B)Phocomelia&#10;C)Digital rays&#10;D)End of fourth week&#10;E)Amelia

Accepted Answer

Amelia refers to absence of a limb(s).This condition resulted when thalidomide was ingested by pregnant women early in the fourth week after fertilization.

Deck 14: Limbs