How is the neural tube formed?
Notochord in the mesoderm directs the conversion of overlying ectoderm to neuroectoderm
Notochord signals the overlying ectoderm to thicken and form the key shaped neural plate
The edges of the neural plate elevate out of the plate of the ectoderm and curl towards each other, creating the neural tube
What are somites and how do they develop?
How many somites are there at the end of their development and what is the significance of this?
Somites are segments of paraxial (either side of axis) mesoderm.
The first pair forms on day 20 in the occipital region. MOre then appear in craniocaudal sequence at a rate of 3 pairs a day
There are 42-44 pairs by the end of week 5
Some then dissapear, leaving 31 pairs in total that correspond to the 31 pairs of spinal nerves/levels
What is the significance of the organisation of the somites?
The organisation of the mesoderm into somites gives rise to repeating structures
E.g. Vertebae, ribs, intercostal muscles
This guides innervation
Label this diagram
Labels from top right clockwise:
Describe the formation of the Coelom
When mesoderm differentiates the intraembryonic coelom is formed
When the embryo undergoes lateral folding the lateral branches of the mesoderm connect to form the coelom within (the intraembryonic coelom join)
What is derived from the paraxial mesoderm?
Axial skeleton (vertebral column and ribs)
Muscles of the axial body wall
Some limb muscles
What is derived from the somatic mesoderm?
Connective tissues of the limbs
Connective tissues of the axial body wall
What is derived from the splanchnic mesoderm?
Connective tissues and vasculature of the gut
What is derived from the intermediate mesoderm?
E.g. Kidneys, ureters, gonads
Describe the differentiation of somites into the dermomyotome and sclerotome
1. Somites appear as regular blocks of mesoderm arranged around a small cavity.
2. This is followed by organised degeneration of the ventral wall of the somite, which breaks down to form the sclerotome.
3. Further organisation of the dorsal portion forms the dermomyotome.
4. Myotome proliferates and migrates. Dermatome disperses.
What 3 structures arise from the somites and what is derived from these structures?
Dermatome - Skin
Myotome - Muscle
Sclerotome - Bones
These are the functional precursors of the musculo-skeletal system
Label this diagram
What process it showing?
Top left figure, from top clockwise:
Top right figure:
Bottom left figure, left to right:
Bottom right figure, top to bottom:
Showing the differentiation of somites into dermatomes, myotomes and sclerotomes
What is the differnece between the develpomental and clinical definitions of 'dermatome'?
For a given segment, a dermatome is a part of a somite that gives rise to the dermis
A dermatome is a strip of skin supplied by a single spinal nerve. Can be examined clinically
What's the difference between the developmental and clinical definitions of 'Myotome'?
The mytome is part of a somite that gives rise to muscles
The muyotome is a muscle/muscle group supplied by a single spinal nerve. Can be examined clinically
What nerves are derived from the neural tube?
Neural tube produces the nerves that innervate the dermomyotome
Describe the formation of the head/tail fold
Describe the movement of key structures in the embryo that occurs during this folding
Along what othe axes does folding occur?
Cephalocaudal folding occurs
Heart lies at the cranial end and moves inward until it lies in the future chest
The yolk sac extends out of the embryo to form a connection between the yolk sac and the gut
There is also lateral folding
What is the result of embryo folding?
Achieves 3D structure
Creates the ventral body wall
Pulls the amniotic membrane around the disk so the embryo becomes suspended in the amniotic sac
Pulls the connecting stalk ventrally
Lateral folding creates a new cavity within the embryo, the coelom
What three major processes occur during week 4 of development?
Organisation of the mesoderm E.g. Somite formation/segmentation