Paul McMenamin; Week 7 MED1011; Anatomy
PNS has 12 pairs of cranial nerves and 31 pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal). Notochord induces formation of neural ectoderm from surface epiblast cells. Neural crest cells form the dorsal root ganglia, Schwann cells, sympathetic and parasympathetic ganglia, melanocytes, parts of head and neck and the adrenal medulla. Sensory neurons are in dorsal root ganglia, surrounded by glial satellite cells, pseudounipolar, send information towards the spinal cord, peripheral processes to body walls (skin, muscles, joints). DRG joins to developing alar plate of the spinal cord which becomes the dorsal horn.
Neural plate folds to create neural tube, folds close in midsection (zip up and down), anterior and posterior neuropore
Somites are blocks of mesoderm that appear early in development. They form the schlerotomes, myotomes and dermatomes. Sclerotome gives rise to connective tissue, cartilage and bone of the axial skeleton. Each myotome forms dorsal epimere (post vertebral musculature), ventral hypomere (muscles of body wall and limbs). This determines dorsal and ventral primary rami fate. Somitic mesoderm disperses and mesodermal cells contribute to muscles and dermis. Lateral plate mesoderm forms bones, tendons, ligaments and connective tissue in limbs.
Brain development is from tube, flexures between 3 primitive parts: prosencephalon, mesencephalon, rhombencephalon (fore, mid and hindbrain). Secondary swellings make 5 parts- flexures to accomodate growth, especially in humans with forward pointing eyes. Lumen of tube becomes ventricular system