Embryology of Nervous System - Dr Najeeb Ullah -

Описание: Neuro Anatomy
Nervous System Overview
• CNS (Central Nervous System) = Brain + Spinal Cord
• PNS (Peripheral Nervous System) = Nerves, Ganglia, Plexuses
Embryological Development
• Sperm + Egg → Zygote → Morula (16 cells)
• At the end of 1st week → Blastula
• 2nd week: Formation of bilaminar disc (2 layers)• Epiblast
• Hypoblast
Gastrulation – 3rd Week
• Formation of 3 Germ Layers:
• Ectoderm
• Mesoderm
• Endoderm
Germ Layer Derivatives
• Endoderm → GIT
• Mesoderm → Heart, Reproductive System, Urinary System
• Ectoderm:
• Surface ectoderm → Skin
• Neuroectoderm → Brain & Spinal Cord
Notochord & Neural Plate
• Some mesoderm cells condense to form the Notochord
• Notochord sends signals to the overlying ectoderm, activating it
• Activated ectoderm forms the Neural Plate
Formation of Neural Groove & Neural Crest
• Cells of neural plate divide and invaginate downward, forming the Neural Groove
• Some ectodermal cells escape from the edges and become Neural Crest Cells, which surround the groove
Neural Tube Formation – Around 7th Week
• Neural folds close and fuse
• The fused structure detaches from the surface ectoderm → forms the Neural Tube
• Neural Tube → Brain + Spinal Cord
• Neural Crest Cells → PNS structures
Neuropores Closure Timeline
• Anterior Neuropore (cranial) closes on Day 25 of pregnancy
• Posterior Neuropore (caudal) closes on Day 28
• Failure to close → Neural Tube Defects (NTD)
Folic Acid Supplementation
• Needed for neural tube closure
• Give Vitamin B9 (Folic Acid) 5 mg/day to females
• Start 3 months before pregnancyBrain Vesicle Development
• After neural tube closure → it solidifies into vesicles
Primary Vesicles
1. Prosencephalon (Forebrain)
2. Mesencephalon (Midbrain)
3. Rhombencephalon (Hindbrain)
Cranial end grows faster than caudal endSecondary & Tertiary Vesicles
1. Prosencephalon →
• Telencephalon
• Cerebral Hemispheres
• 2 Lateral Ventricles
• Lobes of Forebrain
• Diencephalon
• Thalamus
• Hypothalamus
• Subthalamus
• Metathalamus
• Pineal Gland
• Optic Chiasm
• Pituitary Gland
• 3rd Ventricle
2. Mesencephalon (Midbrain) →
• Aqueduct of Sylvius
• 2 Superior Colliculi
• 2 Inferior Colliculi
3. Rhombencephalon →
• Metencephalon
• Pons
• Cerebellum
• Upper half of 4th Ventricle
• Myelencephalon
• Medulla Oblongata
• Lower half of 4th Ventricle
Ventricular System
• Foramen of Monro: Connects Lateral & 3rd Ventricles
• Aqueduct of Sylvius: Connects 3rd & 4th Ventricles
• Ventricles are lined by Ependymal Cells
CSF Production & Circulation
• Choroid Plexus produces Cerebrospinal Fluid (CSF)
• Total CSF = 500 mL/day
• 350 mL directly drains into venous system
• 150 mL enters the ventricles
• 25 mL remains in ventricles
• 125 mL enters Subarachnoid Space
• Ependymal cells help circulate CSF
• CSF drains into subarachnoid space via
• Foramen of Luschka
• Foramen of Magendie
• From subarachnoid space → drains into IJV and SVC
Meninges Around the Brain
1. Pia Mater
2. Arachnoid Mater
3. Dura Mater
Spaces Between Meninges
• Epidural Space
• Contains Middle Meningeal Artery
• Skull fracture rupture → Epidural Hematoma
• Subdural Space
• Contains veins
• Rupture → Subdural Hematoma
• Subarachnoid Space
• Contains Circle of Willis
• Berry Aneurysm rupture → Subarachnoid Hemorrhage
Hydrocephalus Types
• Non-communicating: Aqueduct of Sylvius blocked
• Communicating: Absorption defect at 4th ventricle
Brain Terminologies – Day 3
• Parenchyma (functional part) = Neurons
• Stroma (supportive cells) = Glial cells
• CNS: Oligodendrocytes, Astrocytes, Microglia
• PNS: Schwann Cells
Typical Neuron Structure
• Cell Body = Central Part
• Cytoplasmic Projections = Peripheral Parts
• Dendrites: Carry signals toward the cell body
• Axons: Carry signals away from the cell body
• Covered with Myelin Sheath
Gray vs White Matter
Gray Matter = Cell Bodies
• In CNS (brain): Cerebral Cortex, Cerebellar Cortex, Basal Ganglia, Dentate Gyrus, Amygdala, Thalamus, Hypothalamus, Red Nucleus, Cranial Nerve Nuclei• In Spinal Cord: Central Butterfly-Shaped Area
• In PNS: Ganglia
White Matter = Axons
• In CNS: Tracts
• Internal Capsule
• Corona Radiata
• Fornix
• Ascending & Descending Tracts
• Cerebellar Peduncles
• Cerebral Peduncles
• Optic Pathway
• Auditory Pathway
• Medial & Lateral Lemniscus
White/Gray Matter Relationships
• Cerebral Cortex = Outer gray matter
• Cerebellar Cortex = Outer gray matter
• Nuclei = Collection of gray matter within white matter
• Basal Ganglia = Gray matter surrounded by white matter at the base of brain
Tracts
• Axons moving:
• Downward = Descending tracts (e.g., Corticospinal)
• Upward = Ascending tracts (e.g., Spinothalamic)

Connections in the Brain
• Right & Left Hemispheres: Connected by Commissural Fibers
• Anterior & Posterior regions: Connected by Association Fibers