LEA - Embryology

Question 1

at what week does the limb bud appear?

Answer 1

week 4

Question 2

during which week of gestation do the limb buds flatten?

Answer 2

week 5

Question 3

at what week do the lower limb buds undergo their first rotation?

Answer 3

week 6;

• in this first rotation, the limbs move horizontally from the CORONAL to the SAGITTAL plane with the soles of the feet facing each other;*
• This is the first of two lower limb bud rotations. The second occurs in the following weeks*

Question 4

during which week of gestation do the lower limbs undergo their second rotation?

Answer 4

week 7-8

• the limb buds internally rotate 90 degrees during this time so that the knees and extensor compartment of the leg face anteriorly,*
• (in contrast, the upper limbs externally rotate 90 degrees)*

Question 5

what is meant by “pre-axial” and “post-axial”?

Answer 5

• pre-axial:
  
  • developmentally ventral muscles or the anterior condensation of mesoderm
  • innervated by anterior divisions of ventral rami
• post-axial:
  
  • developmentally dorsal muscles or the posterior condensation of mesoderm
  • innervated by posterior divisions of ventral rami

Question 6

what two embryological tissues make up the limbs?

what do they each give rise to?

Answer 6

mesoderm & ectoderm

• mesoderm gives rise to bones, ligaments, tendons, and dermis.*
• ectoderm gives rise to nerves, epidermis, nails, hair, and apical ectodermal ridge (AER)*

Question 7

failure of apoptosis between toe rays during limb bud development leads to what congenital condition?

Answer 7

syndactyly

Question 8

by week 8 of gestation, the foot is in what position?

Answer 8

plantarflexed & adducted

(or the equinus-supinated position)

Question 9

all bones of the lower limb form from ________ precursors

Answer 9

cartilaginous,

• the process is known as endochondral ossification.*
• All bones originate from mesenchyme. However, flat bones of the skull skip the cartilaginous step and become osseous (intramembranous ossification).*
• All lower extremity bones form by endochondral ossification.*

Question 10

what are the developmentally ventral muscle compartments of the hip and thigh?

Answer 10

posterior & medial muscle compartments.

• (hamstrings & aDductors)*
• Remember: Ve**ntral = Pr**e-axial*

Question 11

what are the developmentally dorsal muscle compartments of the hip and thigh?

Answer 11

anterior & lateral muscle compartments

(quadriceps & aBductors)

Remember: D_orsal = Po_st-axial

Question 12

what are the developmentally ventral muscle compartments of the leg and foot?

Answer 12

posterior (superficial and deep) muscle compartments of the leg,

and plantar intrinsic muscles of the foot

Question 13

what are the developmentally dorsal muscle compartments of the leg and foot?

Answer 13

anterior & lateral muscle compartments of the leg,

and dorsal intrinsic muscles of the foot

Question 14

Pre-axial muscles are innervated by which divisions of ventral rami?

Answer 14

anterior divisions innervate developmentally ventral (pre-axial) muscles

Question 15

post-axial muscles are innervated by which divisions of the ventral rami?

Answer 15

posterior divisions innervate developmentally dorsal (post-axial) muscles

Question 16

hip and thigh muscles that are developmentally ventral arise from what two skeletal landmarks?

Answer 16

ischium & pubis

Question 17

name the anterior divisions of the lumbar and sacral plexuses

Answer 17

Question 18

hip and thigh muscles that are developmentally dorsal arise from what two skeletal landmarks?

Answer 18

vertebral column & ilium

Question 19

name the posterior divisions of the lumbar and sacral plexuses

Answer 19

Question 20

what muscles, due to their innervations, have both developmentally ventral and dorsal compartments?

Answer 20

1. biceps femoris: long head (tibial n.); short head (common peroneal n.)
2. pectineus: femoral n. and obturator n.*

*innervation is variable

Question 21

a club foot deformity, seen in about 1/1000 births, is characterized by a foot in what position related to the three cardinal planes?

Answer 21

1. Plantarflexed/equinus (sagittal plane)
2. Adducted (transverse plane)
3. Inverted/varus (frontal plane)

Known as “talipes equinovarus.” The term “talipes” is derived from “Talus” meaning “ankle”, and “pes” meaning “foot”. It makes sense that it’s a condition affecting the ankle and foot!