University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

318

Pages:

3
Author:

Mariam A.

Proencephalon (forebrain) Diencephalon  epithalamus, thalamus, subthalamus and hypothalamus  Rostral neuropore closes day 22. o The first diverticula formed is the optic vesicles. o Then, a more dorsal rostral diverticulum forms, the telecephalon. o The caudal forebrain remnant is the diencephalon.  The diencephalon is developed within the walls of the primitive 3rd ventricle.  There are roof and alar plates, however SHH is expressed.  Roof plate. o Ependymal cells covered by vascular mesenchyme. o Forms choroid plexus of the 3rd ventricle.  Alar plate. o Form the lateral walls. o The hypothalamic sulcus divides the plate into a dorsal and a ventral region; the thalamus and the hypothalamus, respectively.  Epithalamus. o Most caudal part of roof and alar plate. o Initially large, but shrinks into numerous structures, most notably the pineal gland (channel which light and darkness affects endocrine and behavioural rhythms). o Habenular commissure forms roof of 3rd ventricle and forms choroid plexus.  Thalamus. o Sends cells into sensory cortex  neothalamus. o The two medial walls join at interthalamic adhesive.  Hypothalamus. o Develops from neuroblasts in ventricle zone of alar plate and floor plate ventral to hypothalamic sulcus. o Neuroblasts differentiate into a number of nuclei that regulate visceral functions. o The mammary bodies are a protuberance on the ventral surface on each side of the midline.  Subthalamus. o From the alar plate. o Neuroblasts migrate into a region of basal ganglion to form globus pallidus. o Subthalamus includes subthalamic nucleus, zona incerta, lenticular and thalamic fasiculi. Telencephalon  hemispheres, caudate, putamen, amygdaloid, claustrum, lamina terminales, olfactory bulbs and hippocampus  Two lateral out pockets (cerebral hemispheres) and medial lamina terminales.        Communicates with 3rd ventricle through the foramen of Monro. Hemispheres arise 5th week. By the 6th – 7th week, basal hemispheres are just extensions of thalamus. Region where hemispheres attached to roof of diencephalon fails to develop. Instead, it is engulfed by vascular mesenchyme with ependymal cells  choroid plexus. The hippocampus then forms, and the corpus striatum becomes split by internal capsule into 2. Continual growth gives rise to 4 lobes that overlie insula and brain stem. Between 6th – 8th month, lissencephalic structure becomes a convoluted gyrencephalic structure  gyri and sulci. Commisures  Fibre bundles that interconnect the two cerebral hemispheres.  Anterior commissure. o First to appear. o Connects olfactory structures to middle and inferior temporal gyri.  Hippocampal (fornical) commissure. o Second to appear. o Connects the two hippocampi.  Corpus callosum. o Third to appear, and is the largest. o Interconnects neocortical areas of the two cerebral hemispheres. Cerebral cortex  Consists of neuroepithelium in the three zone layers.  A transient cortical plate layer within the marginal layer forms from neuroblast in ventricular and mantle zones.  Ventricular proliferates and forms a subzone, the subventricular zone  cells migrate peripherally to subplate zone.  Cortical subplate + subplate zone = neocortex.  Intermediate zone loses neurons (white matter).  Marginal zone becomes molecular layer.