BRAIN DEVELOPMENT II

Development Stages

• Neurogenesis: Process of generating new neurons.

• Cell Migration: Movement of newly formed neurons to their final location.

• Cell Differentiation: Development of distinct cell types from undifferentiated stem cells.

• Synaptogenesis: Formation of synapses between neurons.

• Neuronal Cell Death: Natural process where excess neurons die off.

• Synapse Rearrangement: Continuous process throughout adulthood, shaped by experience.

SYNAPSE REARRANGEMENT

Overview

• Guided by Experience: Synapse rearrangement continues throughout adulthood.

• Synaptic Loss: Dependent on the loss of synapses, particularly in the cortex from late childhood to mid-adolescence.

• Caudal to Rostral Maturation: Synapse loss occurs from back (caudal) to front (rostral) of the brain, finishing in the prefrontal cortex, linked to teenage impulsivity.

Purpose

• Strengthening Connections: With some synapses lost, stronger synapses remain for enhanced functioning.

• Intellectual Development: Some inherited disorders retain early synapses, affecting overall intellectual growth.

FRAGILE X SYNDROME

Definition

• Genetic Disorder: Characterized by a mutation in the FMR1 gene on the X chromosome.

• Synaptic Impact: Results in retention of early synapses, hindering standard synapse rearrangement.

Symptoms

• Intellectual Disabilities: Individuals exhibit mild to moderate disabilities.

• Facial Characteristics: Specific facial features are associated with the syndrome.

GENOTYPE AND PHENOTYPE

Definitions

• Genotype: The individual’s genetic makeup, an intrinsic factor, a constant.

• Phenotype: The visible traits that change due to environmental and experiential influences.

FUNCTIONS OF GENES

• Gene Functionality: Genes are specific DNA regions coding for proteins involved in various bodily functions.

• Protein Formation: Proteins consist of amino acid chains, functioning as enzymes, channels, and transporters.

• Different proteins are made by expressing different genes.

GENETIC DISORDERS

Case Study: Phenylketonuria (PKU)

• Faulty Gene: Inherited gene defect causing an absence of the enzyme phenylalanine hydroxylase.

• Impact: Leads to the accumulation of phenylalanine, which is toxic to the brain.

• Symptoms: Can cause intellectual disabilities if not managed by diet from infancy.

Dietary Management

• Screening: Newborn screening prevents brain impairment by controlling dietary intake of phenylalanine until age 2.

• Restrictions: Failure to restrict leads to worsening cognitive disabilities.

AGING BRAIN

Physical Changes

• Atrophy: Specific areas, like the hippocampus, experience shrinkage with age. However, neurogenesis can still occur with active learning.

Mild Cognitive Decline

• Age Range: Normal aging processes bring mild cognitive decline, particularly in individuals aged 55-87.

• Cerebral Metabolism: Generally stable and does not change with normal aging but may reflect cognitive changes due to brain structure alterations.

ALZHEIMER’S DISEASE (AD)

Overview

• Cognitive Decline: This disorder increases with age, leading to severe memory loss and disorientation.

• Symptoms: Begins with memory loss, resulting in comprehensive cognitive decline and difficulties in conversation.

Brain Changes in AD

• Cortical Atrophy: Loss of cholinergic neurons results in a decline in cerebral metabolism, associated with formation of amyloid plaques and neurofibrillary tangles.

• Plaque Accumulation: More plaques correlate with increased cognitive decline.

Medications for AD

• Cholinesterase Inhibitors: Includes Donepezil, Galantamine, Rivastigmine for enhancing cognition.

• NMDA Receptor Antagonist: Memantine is used for moderate to severe cognitive impairment.