Embryology: Key Terms

1. Embryology: Key Terms

2. Understanding the CNS Structure Through Development • Formation of the Tube • Differentiation of the Three Primary Vesicles • Organization of the Mammalian Nervous System

3. Formation of the Neural Tube: Neurulation • Key Terms: • Neural Plate • Neural Groove • Neural Tube • Neural Crest

4. From Blastocyst to Neural Tube

5. Neurulation • Neurulation occurs very early in embryonic development, about 22 days gestation. Anencephaly and Spina Bifida results from failure of the anterior and posterior ends of the tubes to close.

6. Brain Development • The nervous system develops from ectoderm (outer layer) which forms a plate (~day 18) • The edges of the plate curl and eventually fuse together forming a neural tube • By ~day 28, the rostral end of the neural tube has formed the ventricles and the tissue that surrounds these hollow chambers has formed three major divisions of the brain • Forebrain, midbrain, and hindbrain

7. Differentiation • Three Primary Vesicles • Forebrain • Midbrain • Hindbrain

8. Overview of Brain Development

9. Three Primary Brain Vesicles • The first step in differentiation of the brain is the development at the rostral end of the neural tube and three swellings creating what is referred to as the 3-segmented brain. • The three segments are proencephalon, mesencephalon and rhombencephalon. • The entire brain derives from the three primary vesicles of the neural tube.

10. Differentiation of the Forebrain • Secondary vesicles: optic and telencephalon. The unpaired structure that remains after secondary vesicles have sprouted off is the “between brain” or the diencephalon.

11. Differentiation of the Telencephalon • Telencephalic vesicles form the telencephalon, consisting of two cerebral hemispheres. • Continued development invloves: • Poterior growth of the telencephalic vesicles so that they lie over and lateral to the diencephalon • Olfactory bulbs sprout off the ventral surface • Cell divide and differentiate to form various structures • White matter systems develop, carrying axons to and from the telencephalon

12. Differentiation of the Diencephalon • Thalamus (Greek for “inner chamber”) • hypothalamus

13. Forebrain Structure-Function Relationships • The forebrain is the seat of perceptions, conscious awareness, cognition, and voluntary action. This all depends on interconnections with sensory, motor, stem and cord areas of the CNS.

14. Summarized Development of Forebrain

15. Differentiation of the Midbrain • Dorsal surface of mesencephalic vesicle becomes a structure called the tectum (Latin for “roof”). • Tegmentum develops from the floor of the midbrain. • The cerebral aqueduct connects rostrally with the third ventricle of the diencephalon.

16. Midbrain Structure-Function Relationships • Conduit for information passing from the spinal cord to the forebrain, and the reverse. • Contribute to sensory systems • Control of movement • Pain, mood, pleasure

17. Differentiation of Hindbrain • Important structures • Cerebellum-following the 3-vesicle stage, the tissue along the dorsal lateral side of the rostral hindbrain grow dorsally and medially until it fuses with its twin on the other side. • Pons-the ventral wall of this rostral segment swells to form the pons. • Medulla oblongata-ventral and lateral walls of caudal portion of the hindbrain swell forming this section • 4th ventricle-the residual central ventricle in the hindbrain

18. Hindbrain Structure-Function Relationships • Important conduit for information passing from the forebrain to the spinal cord and reverse, processing sensory information, voluntary movement, regulation of the autonomic nervous system

19. Overview of the CNS

20. Neuroanatomy Terms • The neuraxis is an imaginary line drawn through the spinal cord up to the front of the brain • Anatomical directions are understood relative to the neuraxis • Anterior (rostral): toward the head • Posterior (caudal): toward the tail • Ventral (inferior): toward the “belly” • Dorsal (superior): toward the back (top of head) • Location in brain: • Ipsilateral: same side of brain • Contralateral: opposite side of brain

21. Anatomical Directions Are Relative to the Neuraxis

22. Planes of Section • The brain can be sectioned in three planes • Each section provides a different view of the internal anatomy of the brain • Sagittal • Coronal (or transverse) • Horizontal

23. anteriorview human adult female cranium

24. posterior view

25. right lateral view

26. The Meninges • The brain and spinal cord are protected by a series of membranes termed meninges • Dura mater-outer (thick) layer • Arachnoid-middle layer • Overlies the arachnoid space (CSF) • Blood vessels run through the arachnoid layer • Pia mater- inner layer • Overlies every detail of the outer brain Source: Brain Tumor Foundation of Canada. http://www.btfc.org/

27. Cerebrospinal Fluid • The brain floats in a pool of cerebrospinal fluid (CSF) which reduces its net weight from 1400 g --> 80 g • CSF is also contained within four brain ventricles • CSF is produced by the choroid plexus of each ventricle • The brain ventricles are an access point for drug studies • The brain ventricles can expand when brain cells are lost (as in alcoholism or certain diseases)

28. The Corpus Callosum and the Anterior Commissure

29. Cerebral Cortex

30. Cerebral Cortex • The cerebral cortex forms the outer surface of the cerebral hemispheres • Cortex surface is convoluted by grooves • Sulci (small grooves) • Fissures (large grooves) • The bulges in cortex are termed gyri • The cortex is primarily composed of cells, giving it a gray appearance • The cortex is formed from 6 layers of cells • Cortex can be divided into 4 lobes: frontal, parietal, occipital, and temporal

31. CerebralCortex Numerical Data Total surface area: 1100 cm2 about 1/3 ------ surface area about 2/3 ------ hidden in the sulci Thickness: 1.5 mm - 4.5 mm Generally, thickest over the crest of the convolution and, thinnest in the depth of sulci Weight: 600 gm (40 % of total brain weight) 180 gm --------- neurons 420 gm --------- glial cells

32. Cerebral Cortex • The layer of gray matter covering • the entire surface of cerebral hemisphere • Accommodates enormous number of neurons - Large surface area accommodates more neurons than deep nuclei - Gyri and sulci also increase surface area - Laminar organization also accommodates enormous number of neurons

33. I. Molecular Layer II. External Granular Layer III. External Pyramidal Layer Line of Kaes-Bechterew IV. Internal Granular Layer Outer band of Baillarger - Line of Gennari in area 17 V. Internal Pyramidal Layer Giant pyramidal cell of Betz Inner Band of Baillarger VI. Polymorphic Layer Golgi NisslWeigert

34. Columnar Cortical Unit and Cortical Circuitary

35. lateral sulcus left cerebral hemisphere lateral view

36. central sulcus cingulate sulcus cingulate gyrus septum calcarine sulcus anterior commisure rhinal sulcus parietooccipital sulcus right cerebral hemisphere medial view

37. corpus callosum pineal body fornix medial surface of brain

38. Comparative Convolutions of the Cortex

39. Parietal Frontal Occipital Temporal

40. Lateral Central

41. Brodmann Areas

42. Cortex

44. Primary Sensory and Motor Cortex

45. Motor Homunculus

46. Sensory Homunculus

47. Sensory Homunculus

48. Limbic System • The limbic system is comprised of • Hippocampus: involved in learning and memory • Amygdala: involved in emotion • Mammillary Bodies • The fornix is a fiber bundle that interconnects the hippocampus with the mammillary bodies

49. Structures around the Limbic Lobe

50. Basal Ganglia • The basal ganglia are a collection of subcortical nuclei that lie just under the anterior aspect of the lateral ventricles • “Ganglia” is a misnomer (term refers to collections of cell bodies in periphery) • Basal ganglia consist of: • Globus pallidus • Caudate nucleus • Putamen • Basal ganglia are involved in the control of movement