EO

The Nervous System

Embryonic Brain Regions

  • Major Regions: Forebrain, Midbrain, Hindbrain
    • Forebrain: Includes Telencephalon (Cerebrum) and Diencephalon (Thalamus, Hypothalamus, Epithalamus)
    • Midbrain: Also called Mesencephalon, part of the brainstem
    • Hindbrain: Comprises Metencephalon (Pons, Cerebellum) and Myelencephalon (Medulla Oblongata)

Brain Development Phases

  • Phases of Development:
    1. Neural plate induction
    2. Neural proliferation
    3. Migration & Aggregation
    4. Axon growth & Synapse formation
    5. Cell death & Synapse rearrangement

Induction of the Neural Plate

  • Occurs 2-3 weeks after conception
  • A patch of tissue on the dorsal surface of the embryo that develops into the nervous system
  • Induced by chemical signals known as growth factors that stimulate neuron development and assist in response to injury

Neural Proliferation

  • The generation of new cells; 3 swellings at the anterior end form the forebrain, midbrain, and hindbrain.
  • Occurs in the ventricular zone at a rate of 250,000 cells per minute
  • Post mitosis, daughter cells become fixed (post mitotic)

Migration and Aggregation

  • Initially, cells are composed of only the soma and an immature axon; as they migrate, differentiation begins.
  • Radial glial cells serve as guides for migrating neurons.
  • Cells lacking dendrites migrate, aligning with others to form structures through aggregation.

Axon Growth & Synaptogenesis

  • Post-migration, axons and dendrites grow to their mature sizes; axons with growth cones form synapses.
  • Chemical cues from glial cells, particularly astrocytes, are crucial during synapse formation.

Cell Death & Synapse Rearrangement

  • Between 40-75% of the neurons die after migration; this is a normal and necessary occurrence due to competition for neurotrophins which promote growth and survival.

Postnatal Cerebral Development

  • Growth is a result of synaptogenesis, increased dendritic branches, and myelination; more synapses allow for greater "plasticity" in young brains compared to older ones.
  • Studies suggest that early environmental influences affect synaptic growth and development significantly.

Lateralization of Cortical Function

  • The brain's left hemisphere specializes in language, mathematics, and logic, while the right hemisphere focuses on pattern recognition and emotional processing.

Motor Cortex and Functional Areas

  • The cerebrum controls voluntary movement and cognitive functions; segments include:
    • Frontal lobe: Executive functions, voluntary movement
    • Temporal lobe: Auditory processing, language comprehension
    • Parietal lobe: Sensory integration
    • Occipital lobe: Visual processing

Neurotransmission: Events at the Synapse

  • Involving the presynaptic action potential, Ca2+ channels, and neurotransmitter release into the synaptic cleft, followed by binding to postsynaptic receptors.

Types of Neurons

  • Classified by shape:
    • Unipolar, Bipolar, Multipolar: Each varies in the number of processes extending from the soma.

Functional Regions of Neurons

  • Typical neurons consist of input, integrative, conductile, and output regions, facilitating complex signaling within the nervous system.

Neurotransmitter Inactivation & Astrocyte Role

  • Neurotransmitters can be returned for reuse, diffused, or inactivated by enzymes, indicating the vital role astrocytes play in neurotransmission management.

Nervous System Disorders

  • Disorders such as schizophrenia, Alzheimer’s disease, and addiction have molecular bases influenced by genetic and environmental factors.

Drug Addiction and the Brain

  • Addictive substances impact the brain's reward system and reward pathways, leading to compulsive behaviors and misuse.