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.