Neuro

Development of the Nervous System

Outlines

  • Developmental Stages

  • Neural Tube

  • Regional Development

Developmental Stages

  • Zygote

    • Initial stage after fertilization

    • Undergoes mitosis to develop into a multicellular structure

  • Morula

    • Solid ball of cells formed after several divisions

  • Blastula

    • Two-layered structure formed after morula stage

  • Gastrula

    • Three-layered structure that marks the beginning of gastrulation

  • Neurula

    • Stage at which the nervous system starts to develop

Development from Ovulation to Implantation

  • DAY 1

    • Ovulation occurs, and sperm meets oocyte leading to fertilization and formation of zygote.

  • DAY 2

    • First cleavage division begins with the zygote.

  • DAY 5

    • Formation of morula (4 cell stage).

  • DAY 6

    • Formation of blastocyst from morula.

Detailed Study of the Blastula Formation

  • Blastula

    • Consists of two layers of cells:

    • Epiblast

      • Further differentiates into:

      • Primitive Ectoderm

      • Embryonic Disk

    • Hypoblast

      • Differentiates into the Primitive Endoderm.

  • Processes Involved:

    • Formation of Blastocoel (the cavity within the blastula).

Gastrulation - Gastrula Formation

  • Gastrula (Gastrulation)

    • Transitions to a three-layered ball of cells named Trilaminar Embryo.

    • Composed of:

    • Ectoderm (outer layer)

    • Mesoderm (middle layer; notochord forms)

    • Endoderm (inner layer)

Formation of the Trilaminar Embryo

  • Components:

    • Ectoderm: Future skin and nervous system structures.

    • Endoderm: Future gut and associated organs.

    • Mesoderm: Forms notochord, somites (precursors of skeletal muscles and axial skeleton).

Neurulation Process

  • Neurulation

    • The notochord (from mesoderm) stimulates the overlying ectoderm to thicken and form the neural plate.

    • Neural Tube:

    • Develops from the neural plate, giving rise to the central nervous system (CNS).

    • Neural Crest Cells:

    • Derived from neural plate border; contribute to the peripheral nervous system (PNS).

  • Neural Canal:

    • Future ventricles of the brain.

Maturation of Neural Tube

  • Neuroepithelium Migration:

    • Migrate to form the walls of the neural tube.

  • Layer Differentiation:

    • Forms three layers:

    • Mantle Layer: Develops into gray matter.

    • Ependymal Layer: Lines ventricles.

    • Marginal Layer: Forms white matter.

Functional Organization of the Neural Tube

  • Sulcus Limitans:

    • Divides the neural canal into dorsal (alar plate, sensory afferent) and ventral (basal plate, motor efferent) regions.

Formation of the Brain

  • Three Primary Brain Vesicles:

    • Prosencephalon (Forebrain)

    • Mesencephalon (Midbrain)

    • Rhombencephalon (Hindbrain)

  • Remaining Tube:

    • Develops into the spinal cord.

Development of Secondary Brain Vesicles

  • Stages of Brain Development:

    • Five secondary vesicles arise from the primary vesicles:

    • Telencephalon (from Prosencephalon)

    • Diencephalon (from Prosencephalon)

    • Mesencephalon (remains unchanged)

    • Metencephalon (from Rhombencephalon)

    • Myelencephalon (from Rhombencephalon)

Adult Structures Derived from the Brain Vesicles

  • Telencephalon:

    • Forms olfactory lobes, hippocampus, cerebrum, and retina.

    • Functions include smell, memory storage, association (intelligence), and vision.

  • Diencephalon:

    • Contains thalamus, hypothalamus, and epithalamus; functions in temperature regulation, sleep, breathing regulation, and connecting various brain regions.

  • Metencephalon:

    • Develops into pons and cerebellum, which coordinates complex muscular movements.

  • Myelencephalon:

    • Becomes medulla oblongata, controlling involuntary activities.

Formation and Functional Organization of the Spinal Cord

  • Layers in the Spinal Cord Formation:

    • Germinal, Alar, Mantle, Basal, and Marginal.

  • Functional Organization:

    • Gray columns throughout the spinal cord include dorsal, intermediate, and ventral horns. The dorsal median septum and ventral median fissure separate these areas.

Development of the Myelencephalon: Medulla

  • Sulcus limitans persists in the myelencephalon, delineating sensory (dorsal) and motor (ventral) systems.

Meninges Development

  • Origins:

    • Neural crest and mesodermal cells form the meninges.

  • Components:

    • Pia mater, ependymal cells, and capillaries. Contains the blood supply essential for the functioning of the nervous system.

Cerebellum Development

  • Mantle Layer Growth:

    • Involves thalamic nuclei and development of the rhombic lip which overgrows the roof plate of the fourth ventricle.

Organization of the Diencephalon

  • Key Structures:

    • Thalamus, hypothalamus, epithalamus, and components such as the interventricular foramen, anterior commissure, optic chiasm, and the roof of the third ventricle with choroid plexus.

Neuronal Organization

  • Axon Groups:

    • Based on their destination: axons that don't leave the hemisphere, axons leading to the brainstem, and commissural axons connecting hemispheres.

  • White Matter Components:

    • Corona Radiata and Centrum Semiovale are essential for processing and relaying information within the brain.

Final Developmental Stage of the Cortex

  • Neuronal Layers (I through VI):

    • Responsible for the organization and functionality of the cerebral cortex.

  • Basal Nuclei:

    • Originate from the mantle layer, involved in motor control and cognitive functions.

  • Choroid Plexus:

    • Formed in all ventricles, involved in the production of cerebrospinal fluid.