Lecture 2 2021

Overview of Neuroanatomy Lecture

Introduction

  • Course: Neuroanatomy at Western Sydney University

  • Lecturer: Assoc. Prof. Peter Shortland

  • Acknowledgement of copyright and traditional custodians of the lands.

Welcome to Country

  • Respect for the Eora, Darug, D'harawal, and Wiradjuri peoples.

  • Recognition of the contributions and knowledge of Aboriginal and Torres Strait Islander peoples.

Objectives for Development of the Nervous System

  1. Neurogenesis Stages

    • Understanding neurogenesis and its critical periods is essential for grasping how the nervous system develops.

  2. Formation Processes

    • Develop knowledge of the notochord, neural plate, neural folds, neural tube, and neural crest formation.

  3. Functional Regions

    • Identify major functional regions derived from the cephalic vesicles in adulthood.

  4. Neural Tube Organization

    • Describe the basic functions and organization within the neural tube.

  5. Peripheral Nervous System (PNS) Development

    • Study how PNS connections are formed.

  6. Developmental Conditions

    • Learn about major abnormalities in development, providing examples.

Importance of Nervous System Development

  • Provides a framework for understanding the anatomy of the nervous system.

  • Insight into developmental abnormalities categorized into:

    1. Genetic (inherited)

    2. Environmental (maternal/teratogen)

    3. Idiopathic (unknown causes)

  • Development categorized into major processes: induction, proliferation, migration, and maturation.

Neurogenesis in the Nervous System

  • Cell Lineage: Divided into self-renewing multipotent stem cells and specialized cells like neurons and glial cells.

  • These cells undergo stages including determination, proliferation, migration, and maturation influenced by various factors.

Timeline of Development in the Human Cortex

  • Development indicators:

    • Neurogenesis occurs predominantly between 6-20 weeks post-conception, finishing with neuron count at 25 weeks.

    • Migration occurs from approximately week 8 to week 29.

    • Maturation includes axon and dendrite growth starting at 20 weeks extending into postnatal life.

    • Brain development generally completes around age 20, while myelination can last until age 4.

Synaptogenesis in the Cortex

  • Illustrates synaptic pruning and cell death, which is significant during the first year after birth and through subsequent years leading to visual cortex development.

Critical Periods in Development

  • Defined as stages during which the nervous system is particularly sensitive to environmental stimuli; pivotal for functions to develop properly. Examples:

    • Prenatal: Neural tube defects, cerebral palsy.

    • Postnatal: Visual cortex development issues due to early deprivation.

  • CNS plasticity is highest in the early postnatal years, facilitating recovery from injury.

Neurulation: Formation of the Nervous System

  • Overview of processes during neurulation:

    • Gastrulation: Body plans formed with key germ layers: ectoderm, mesoderm, and endoderm emerging.

    • Neural Plate: The neural tube forms from the neural plate via thickening and folding processes.

    • Neural Crest: Cells that separate from the neural tube contribute to the PNS and other structures.

Neural Tube Differentiation

  • The rostral aspect develops into the forebrain via primary and secondary vesicles, while the rest forms the brainstem and spinal cord.

  • The closure of the neural tube is crucial, completing by week 4.

Early Differentiation of the Spinal Cord and Brainstem

  • Basic organization involves dorsal (sensory) and ventral (motor) differentiation, regulated by BMP and SHH signaling factors important for proper neuron fate specification.

Developmental Connections in the Spinal Cord

  • Involves orderly ingrowth of afferents regulated by guidance factors and growth factors leading to the maturation of synaptic connections.

Summary of Abnormal Developmental Conditions

  1. Neural tube defects like spina bifida and anencephaly outline failures in proper neural closure leading to varying degrees of clinical presentation.

  2. Other abnormalities include proliferation defects leading to microcephaly and lissencephaly due to failure in sufficient neuron migration.

  3. External factors like fetal alcohol syndrome illustrate environmental impacts on neurodevelopment, resulting in significant cognitive and physical disabilities.

Conclusion

  • This lecture series establishes foundational knowledge for understanding neuroanatomy, crucial for recognizing both normal and aberrant development of the nervous system.