Embryology Flashcards
When do limb buds begin to develop
End of the 4th week
What type of cells are limb buds made up of
Mesenchymal stem cells with ectoderm covering
True or false; the lower limb development lags behind the development of the upper limb
True. It lags behind by 2 days
How does the limb bud elongated
Proliferation of mesenchymal cells
What are the 3 axes for asymmetrical limb development
- Shoulder to fingertips (proximal to distal axis)
- Palmar surface to dorsal surface (dorsal to ventral axis)
- Side to side (anterior to posterior axis)
What controls the development to anterior - posterior axis asymmetry
Cone of polarising activity (ZPA)
What controls the asymmetrical development in the proximal - distal axis
Apical ectodermal ridge (AER)
What controls the development of dorsal - ventral development
Dorsal Ectoderm
What is syndactyly
Fusion of digits, may involve just connective tissue or bones may be fused
What is polydactyly
Extra digits
True or false; polydactyly is a genetic dominant trait
False; it’s actually recessive
What is Amelia
Complete absence of a limb
What is meromelia
Partial absence of on or more limbs
What is phocomelia
Where the hands and feet are directly attached to the trunk of the body
Which direction does the upper limb rotate in development
Laterally (thumb ends up lateral)
What direction does the lower limb rotate during development
Medially
Where is the Apical Ectodermal Ridge located
Dense region at the apex of the limb bud
What does the AER do?
Prevents differentiation of mesenchymal cells in the limb bud. Causes proliferation of these cells to extend the limb in the proximal to distal direction
Where are the cells of the ZPA located
Posterior base of the limb bud
True of false; the ZPA also controls patterning and maintenance of the AER
True
How do the digits form?
Mesenchymal cells of the paddle condense forming notches. Cartilaginous models of the bones then forms. Apoptosis then occurs of the AER to separate the digits.
Give 2 examples of an external agents which causes limb disruption
Thalidomide and infections (e.g. Rubella)
What does thalidomide do
Disrupts the AER to stop elongation
What are constriction bands
When strands come off from mesenchymal tissue to form bands which restrict limb buds cutting part of the limb off
What causes deformation
Contraction bands
What causes malformation
Intrinsic error (e.g. Wrong signalling due to mutation) in coordinating morphogenesis
Why does the AER regress
To ensure separation of the digits
What appear in the final stages growth from the AER
Paddles
Which cells do the AER exert an effect on
The immediately underlying mesenchymal cells
Why does the proximal mesenchymal cells to the AER begin to differentiate
They are too far away from the AER so don’t have the AER’s influence
What process progressively sculpts the interdigital spaces
Apoptosis
What happens to the limbs before they rotate
Extend ventrally
Which spinal segments does the upper limb appear opposite to
Caudal cervical spinal segments
What spinal segments does the lower limb appear opposite to
Lumbar and sacral spinal segments
What type of tissue migrates to the limbs from the somites
Myogenic (precursor to muscle)
What happens to the myogenic tissue as it enters the limb bud
Splits into 2 muscle masses around the newly forming skeletal structures
What are the names of the 2 muscle masses formed in the limb bud when the myogenic muscle migrates into the limb bud
Ventral (flexor) and dorsal (extensor) compartments
what will the sclerotome develop into
vertebrae and ribs
what will the dermatomyotome separate into
dermatome and myotome
what type of nerve fibres do the dorsal roots contain
afferent / sensory fibres
what type of nerve fibres do the ventral roots contain
efferent / motor and autonomic fibres
what is true about the nerve supply to skin and muscle derived from a single dermatomyotome
they have a common spinal nerve supply
what type of neurones are found in the spinal cord
a mix of sensory and motor neurones
where do the spinal nerves pass out of
the intervertebral foramina
how many pairs of spinal nerves are there
31
what does the spinal cord run down
the vertebral foramen
what is the spinal canal
multiple vertebral foramina
what do the vertebral segments differentiate from
sclerotomes
where does the spinal cord start and end
starts at the inferior margin of the medulla oblongata and ends as the conus medullaris at L2
true or false: most spinal cord segments are vertically aligned with their corresponding vertebrae
false
where do long roots from the inferior segments to L2 descend into
cauda equina
which pairs of spinal nerves emerge above their corresponding vertebrae
C1-C7
where does the spinal nerve C8 exit from
above the T1 vertebra but below the C7 vertebra
where do the spinal nerves T1-L5 exit
below their corresponding vertebra
what are rami
divisions of the spinal cord after it exits through the intervertebral foramina
what are the 2 rami that the spinal nerve divides into
posterior and anterior rami
what does the posterior rami divide into
medial and lateral branches
where does the posterior rami innervate
deep muscles and skin of the back
where does the anterior rami innervate
muscles and skin of the front, upper limbs and lower limbs
what are meningeal branches
branches of spinal nerve that re-enter the spinal canal through the intervertebral foramen to supply the vertebrae, ligaments, blood vessels and meninges
what are rami communicantes
components of the ANS
true of false: the segments of muscle and skin supplied by the dorsal rami are in line with the intervertebral foramina
true
true of false: the segments of muscle and skin supplied by the anterior rami are in line with the intervertebral foramina
false
as the dermatomyotome spreads out what happens to the spinal nerve supplying it
it spreads out too
what is a myotome
a group of muscles supplied by a single spinal nerve
what Is a dermatome
area of skin supplied by a single spinal nerve
what is a motor unit
a motor neurone and the skeletal muscle fibres it innervates
what is an axial line
junction of 2 dermatomes supplied from discontinuous spinal levels
what do axial line mark
the centre of either the ventral or dorsal compartments of the limb
what marks the pre-axial and post-axial boundaries
veins
what veins mark the pre and post axial boundaries in the arm
pre = cephalic post = basilic
what veins mark the pre and post axial boundaries in the lower limb
pre = long saphenous post = short saphenous
true or false: within a peripheral nerve territory there may be fibres from more than 1 spinal nerve
true
true or false: fibres from one spinal nerve can only enter 1 peripheral nerve territory
false
what is herpes zoster
a viral infection affecting a single dermatome. it remains dormant in the dorsal root ganglion until the host is immunosuppressed then it reactivates and travels to a single dermatome
