Human Neurobiology Prof Stuart Bunt Development of the CNS Prof. Stuart Bunt Semester

Human Neurobiology Prof Stuart Bunt Make yourself a brain The brain is probably the most complex structure in the universe for its size (putting little green men aside). However, not only is it an amazing structure, it is also self assembling. When development goes wrong it causes great problems as, unlike for example cardiac problems it does not always lead to death. (1.3% of total births have some abnormality)

Human Neurobiology Prof Stuart Bunt Formation of Ectoderm The environment of a cell plus its genes and developmental history determine what a cell will become Cells on the “inside” form the embryo Cells next to the blastoceol form the endoderm Cells next to the amniotic cavity form the ectoderm

Human Neurobiology Prof Stuart Bunt Neural plate One of the first signs of polarity is the blostopore This may be laid down by polarity in the egg following fertilisation Much of developmental complexity results from two tissues getting together induce the formation of a third This gives rise to the notocord The notocord induces formation of the neural plate

Human Neurobiology Prof Stuart Bunt Species Variations Much experimental neuroembryology done on other species The invertebrates develop differently Their neural cords are ventral Blastopore at their mouths

Human Neurobiology Prof Stuart Bunt Determinate vs regulative development Development determinate, not regulative Half the cells leads to half an embryo in invertebrates Not mammals Not man

Human Neurobiology Prof Stuart Bunt Neural plate forms the neural tube Cell movement and contraction makes it form a tube

Human Neurobiology Prof Stuart Bunt Anterior neuropore These close over time If anterior pore does not close leads to anencephaly (1:1000 births)

Human Neurobiology Prof Stuart Bunt Posterior neuropore Closure of this is complex partially due to “rolling” addition of a solid cord posteriorly problems can occur if these two parts do not join problems occur if the neural tube fails to close problems if the surrounding mesoderm does not form complete vertebrae.

Human Neurobiology Prof Stuart Bunt Lumbar cistern At 3 months cord runs the length of the vertebrae As the vertebrae grow and the spinal cord does not At birth stops at L3 In the adult at L2 use this space for epidural anaesthesia lumbar puncture

Human Neurobiology Prof Stuart Bunt Spina bifida All these problems can lead to varying severities of spina bifida –rachischisis –spina bifida 1-4/1000 occulta meningocele meningomyelocele from some hair over the base of the spine to open spinal cord with total paralysis below that point

Human Neurobiology Prof Stuart Bunt Arnold-Chiari malformation when the cord is tethered by spinal bifida it can be pulled down through the foramen magnum as the vertebrae lengthen. More common in the UK. In US isolated so drain CSF in utero

Human Neurobiology Prof Stuart Bunt Detection can be detected by ultrasound samples of amniotic fluid can confirm this looking for alpha fetal protein released by the spinal cord older mothers - higher risk all pregnant women in Australia given folic acid reduces incidence

Human Neurobiology Prof Stuart Bunt Neural Crest derivatives cells migrate out follow set paths differentiate into many tissues dorsal root ganglia schwann cells (peripheral nerve glia) facial muscles adrenal medulla

Human Neurobiology Prof Stuart Bunt Neuroepithelial cells “bounce” up and down

Human Neurobiology Prof Stuart Bunt Neural tube formation of basal and alar plates

Human Neurobiology Prof Stuart Bunt Brain section from spinal cord

Human Neurobiology Prof Stuart Bunt Formation of dilations forebrain - prosencephalon midbrain - mesencephalon –cephalic flexure hindbrain - rhombencephalon –cervical flexure spinal cord

Human Neurobiology Prof Stuart Bunt Telencephalon vesicles cortex and contents in a “C” shape basal ganglia shaped growth (not a simple folded sheet) diencephalon –thalami –hypothalamus half from endoderm Rathke’s pouch from roof of mouth

Human Neurobiology Prof Stuart Bunt Mesencephalon tectum (superior and inferior colliculi) cerebral peduncles

Human Neurobiology Prof Stuart Bunt Brain section from mesencephalon

Human Neurobiology Prof Stuart Bunt Rhombic flexure fourth ventricle somatic and visceral nuclei

Human Neurobiology Prof Stuart Bunt metencephalon –pons and cerebellum myelencephalon –brainstem/SC junction Rhombencephalon

Human Neurobiology Prof Stuart Bunt Brain section from rhombencephalon