What is somite formation?

Somites are precursor populations of cells that give rise to important structures associated with the vertebrate body plan and will eventually differentiate into dermis, skeletal muscle, cartilage, tendons, and vertebrae. Formation begins as paraxial mesoderm cells organize into whorls of cells called somitomeres.

What are the somite layers that form?

In the developing vertebrate embryo, somites split to form dermatomes, skeletal muscle (myotomes), tendons and cartilage (syndetomes) and bone (sclerotomes).

What direction do somites form?

During somitogenesis, the unsegmented paraxial or presomitic mesoderm (PSM) progressively segments into bilaterally symmetrical epithelial somites in an anterior to posterior direction.

What is somite segmentation?

Somites are segmental axial structures of vertebrate embryos that give rise to vertebral column, ribs, skeletal muscles, and subcutaneous tissues. A bilateral pair of somites forms periodically at the anterior ends of the presomitic mesoderm (PSM), located at the caudal part of embryos (Fig. 10.2A).

What is the function of occipital somites?

Occipital somites (1-5 in human) fuse at an early stage of embryonic development and do not contribute to segmented skeletal structures. They incorporate into the occipital area of embryonic skull, give rise to the tongue muscles and also condense to contribute to the basi-occipital and exo-occipital cartilages.

What general features of vertebrates are associated with somites?

Segmented structures composed of repetitive units, called somites, that arise transiently during embryogenesis are a key feature of the vertebrate body plan. The somites lie laterally to the notochord, and a spinal nerve forms a segmental unit assigned to somitic derivatives in the trunk [1, 2].

Do somites form posterior to anterior?

Somitogenesis is the process by which somites form. Somites are bilaterally paired blocks of paraxial mesoderm that form along the anterior-posterior axis of the developing embryo in segmented animals.

Why do snakes have more somites?

In each tick of the clock, one additional somite is produced. So there are more segments in the snake not because its PSM cells multiply more quickly or for many more cell-division cycles than in the chick or mouse, but because they grow more slowly relative to the rate at which the segmentation clock ticks.

What does paraxial mesoderm give rise to?

The paraxial mesoderm gives rise to the axial skeleton. The lateral plate mesoderm gives rise to the appendicular skeleton.

Do humans have somites?

In the human embryo, somitic segmentation takes place between stage 9 and 13, that is from 19-21 days to 28-32 days of age. Somites are initially formed of clusters of elongated epithelial cells.