Development of Brain Stem, Cerebellum and Cerebrum

Transcription

1 Development of Brain Stem, Cerebellum and Cerebrum

2 The neural tube cranial to the 4th pair of somites develop into the brain. 3 dilatations and 2 flexures form at the cephalic end of the neural tube during the 4th week. primary brain vesicles 1) Prosencephalon (forebrain) 2) Mesencephalon (midbrain) 3) Rhombencephalon (hindbrain) flexures: 1) Cephalic flexure (midbrain region) 2) Cervical flexure (hindbrain-sc)

3 Secondary brain vesicles (5th week) and their derivatives

4 Brain flexures Midbrain flexure-cervical flexure. Unequal growth of the brain between flexures produces the pontine flexure in the opposite direction (5 th week). This flexure results in thinning of the roof of the hindbrain.

5 Initially, the primordial brain has the same basic structure as the developing spinal cord. However, the brain flexures produce variations in the position of white and gray matter.

6 Hindbrain Spinal cord-servical flexure-hindbrain

7 Myelencephalon The caudal part of the myelencephalon (future closed part of medulla) resembles the spinal cord. Central canal Neuroblasts from the alar plates migrate into the marginal zonenucleus gracilis, nucleus cuneatus Pyramids

8 The rostral part of the myelencephalon (future open part of medulla) is wide and rather flat. Roof plate is streched and thinned. Neural canal (future 4 th ventricle) becomes rhomboidal-diamond shape. As the alar plates come to lie lateral, the sensory nuclei develop lateral to the motor nuclei. Neuroblasts in the basal plates develop into motor nuclei. Neuroblasts in the alar plates develop into sensory nuclei.

9 Metencephalon Walls form the pons and cerebellum. Cavity forms the superior part of the 4 th ventricle.

10 Pons Pontine flexure causes divergence of the lateral walls. Neuroblasts of each basal plate develop into motor nuclei. Some neuroblasts from the alar plate.pontine nuclei Cerebellum Develops from thickenings of dorsal parts of the alar plates (cerebellar swellings). The swellings enlarge and fuse in the median plane, cerebellar vermis and hemispheres forms.

11 The primary fissure forms and divides the cerebellum into anterior and middle lobes. Continued fissuration subdivides the expanding cerebellum into further lobes and then, starting in the 3rd month, into lobules and folia.

12 The structure of cerebellum reflects its evolutionary development; 1. Archicerebellum (flocculonodular lobe) 2. Paleocerebellum (anterior lobe and vermis) 3. Neocerebellum (posterior lobe)

13 Neuroblasts of the mantle zone of the alar plate migrate to the marginal zone, differentiate into the neurons of the cerebellar cortex. Other neuroblasts of the alar plates give rise to central nuclei (e.g. dentate nucleus)

14 Choroid plexuses Thin ependymal roof is covered by piamater with numerous blood vessels. This vascular membrane together with the ependymal cells forms the tela choroidea of the 4 th ventricle. Pia mater proliferates and tela choroidea invaginates the 4 th ventricle and differentiates into choroid plexus. Similar plexuses develop in the roof of the third ventricle and the medial walls of the lateral ventricles.

15 Midbrain Neural canal.. Cerebral aquaduct Neuroblast from the alar plates migrate to form sup/inf colliculi at tectum. Neuroblast from the basal plates give rise to groups of neurons in tegmentum. Substantia nigra; gray matter Fibers growing from the cerebrum form the crus cerebri.

16 Forebrain Rostral part- telencephalon- primordia of the cerebral hemispheres Caudal part- diencephalon Alar and basal plates and sulcus limitans are recognizable until the junction of midbrain and forebrain!!!

17 Diencephalon In the lateral walls of the 3 rd ventricle 3 swellings develop Epithalamus Thalamus Hypothalamus

18 Epithalamus- pineal gland The growing thalami meet across the third ventricle, form the interthalamic adhesion. Hypothalamus

19 Pituitary gland

20 Telencephalon Consists of a median part and 2 lateral cerebral vesicles. The lateral ventricle in each hemisphere communicates with the third ventricle through an interventricular foramen (of Monro).

21 Developing cerebral hemispheres expand in all directions until they cover the diencephalon. The rostral wall of the forebrain, the lamina terminalis, is very thin.

22 The mesenchyme trapped in the longitudinal fissure between the cerebral hemispheres; falx cerebri The corpus striatum apppears during the 6 th week as a swelling in the future temporal lobe. The floor of each hemisphere expands slowly than the lateral walls; cerebral hemispheres become C-shaped.

23 Corpus striatum divides into the caudate and lentiform nuclei by the internal capsule (fiber pathway).

24 Caudal end of each hemisphere turns ventrally and then rostrally forming the temporal lobe; it carries the lateral ventricle.

25 The expansions of the neural canal in the brain vesicles and cerebral hemispheres give rise to the cerebral ventricles. lateral ventricles in the cerebral hemispheres, the 3rd ventricle in the diencephalon, the narrow cerebral aqueduct (of Sylvius) in the mesencephalon 4th ventricle in the rhombencephalon.

26 The telencephalon gives rise to commissural tracts that connect corresponding areas of the left and right cerebral hemispheres. These include the anterior and hippocampal commissures and the corpus callosum. The small posterior and habenular commissures arise from the epithalamus.

27 Initially the surface of the cerebral hemispheres is smooth As growth proceeds sulci and gyri develop

28 The walls of the developing cerebral hemispheres initially show the 3 typical zones of the neural tube (ventricular, mantle, marginal). Cells of the mantle zone migrate to the marginal zone and give rise to the cortical layers.

29 Morphogens and transcription factors play role in the development of nervous system. Dorsal to ventral gradient of sonic hedgehog (Shh) and bone morphogenetic proteins (BMPs) determine dorsal-ventral cell fates.

30 Shh ventralizes the neural tube, induces the floor and basal plates. BMPs increase the expression of dorsalizing genes; PAX3, 7 in the alar and roof plates.

31 References 1. The Developing Human: Clinically Oriented Embryology by Keith L. Moore, T. V. N. Persaud and Mark G. Torchia (2013). 9 th ed. Elsevier Saunders, Philadelphia. ISBN: Langman s Medical Embryology by T.W. Sadler (2012). 12 th ed. Lippincott Williams & Wilkins, Philadelphia. ISBN: Human Embryology by Larsen WJ (2001). 3rd ed. Churchill Livingstone, Philadelphia. ISBN: Netter s Atlas of Human Embryology by Larry R. Cochard (2002). 1 st ed. Icon Learning Systems, New Jersey. ISBN: Human Embryology and Developmental Biology by Bruce M. Carlson (2009). 4 th ed. Mosby, Elsevier, Philadelphia. ISBN: