unit 4

UNIT 4 — Neuropathology & Neurodevelopment

(Full In-Depth Exam Notes)**

📍 Lecture 1 — Neurodevelopment: How the Nervous System Forms

1. Early Embryonic Development

  • Neural plate → neural tube (day 18–28)

  • Neural tube closes by ~4 weeks

    • Failure → neural tube defects (spina bifida, anencephaly)

2. Key Stages

Neurogenesis

  • Birth of neurons from neural progenitor cells

  • Mostly prenatal

  • Exceptions: adult hippocampus + olfactory bulb

Migration

  • Neurons move to final positions using:

    • Radial migration (glutamatergic cortex neurons)

    • Tangential migration (GABAergic interneurons)

  • Errors → cortical malformations (lissencephaly)

Differentiation

  • Neurons take on specific fates

  • Guided by chemical cues, genes, environment

Synaptogenesis

  • Rapid postnatal growth

  • Peak in childhood → way more synapses than adults

Apoptosis (Programmed Cell Death)

  • Eliminates unused neurons

  • Essential for efficient wiring

Myelination

  • Begins late fetal → continues into young adulthood

  • Last regions to myelinate: prefrontal cortex (executive function)

📍 Lecture 2 — Neurodevelopmental Disorders

1. Autism Spectrum Disorder (ASD)

Key Features

  • Social communication deficits

  • Restricted, repetitive behaviours

  • Sensory sensitivities

Neural Characteristics

  • Early brain overgrowth (esp. frontal/temporal lobes)

  • Excessive synapses (reduced pruning)

  • Atypical connectivity:

    • Hyperconnectivity locally

    • Hypoconnectivity between regions

Cognitive Features

  • Weak central coherence

  • Theory of mind difficulties

  • Strong systemising abilities (per Baron-Cohen)

2. ADHD

Key Features

  • Inattention, hyperactivity, impulsivity

Neurological Basis

  • Reduced volume in:

    • Prefrontal cortex

    • Basal ganglia

    • Cerebellum

  • Dopamine dysregulation

Cognitive Impact

  • Impaired executive function

  • Time perception differences

  • Reward-processing abnormalities

3. Schizophrenia (Neurodevelopmental hypothesis)

Evidence

  • Subtle brain abnormalities before onset

  • Synaptic pruning abnormalities in adolescence

  • Enlarged ventricles

  • Dopamine hyperactivity in striatum

📍 Lecture 3 — The Ageing Brain

Normal Ageing vs Pathological Ageing

Feature

Normal Ageing

Dementia

Memory

Mild decline

Severe, function-impairing

Cognition

Slower processing

Loss of basic functions

Brain volume

Gradual shrinkage

Accelerated atrophy

1. Cognitive Ageing

  • Processing speed ↓

  • Working memory ↓

  • Semantic memory preserved

  • Vocabulary preserved

  • Executive functions mildly decline

2. Structural Changes

  • Brain shrinkage, especially:

    • Prefrontal cortex

    • Hippocampus

  • White matter deterioration

  • Reduced dopamine receptors

3. Protective Factors

  • Physical exercise

  • Cognitive enrichment

  • Social engagement

  • Healthy diet

📍 Lecture 4 — Parkinson’s & Alzheimer’s Disease

Parkinson’s Disease (PD)

1. Core Symptoms

  • Resting tremor

  • Bradykinesia (slowness)

  • Rigidity

  • Postural instability

2. Neuropathology

  • Loss of dopamine neurons in substantia nigra pars compacta

  • Reduced dopamine in striatum

3. Cognitive Effects

  • Reduced executive function

  • Visuospatial deficits

Alzheimer’s Disease (AD)

1. Early Symptoms

  • Episodic memory loss

  • Mild confusion

  • Word-finding problems

2. Brain Pathology

  • Amyloid-β plaques

  • Tau neurofibrillary tangles

  • Hippocampal atrophy

  • Synaptic loss

Braak Stages

  1. Medial temporal lobe

  2. Limbic system

  3. Neocortex

3. Risk Factors

  • Age

  • APOE-ε4 gene

  • Cardiovascular health

📍 Lecture 5 — The Spinal Cord

1. Basic Organisation

  • White matter outside, grey matter inside

  • Dorsal horn = sensory

  • Ventral horn = motor

2. Reflexes

  • Stretch reflex (monosynaptic)

  • Withdrawal reflex (polysynaptic)

3. Spinal Cord Injury

Complete vs incomplete injury

  • Complete = no function below lesion

  • Incomplete = some sensory/motor preserved

Neuroplasticity

  • Reorganization possible

  • Central pattern generators (CPGs) can still drive walking with training

📍 Lecture 6 — Cerebellum

1. Main Functions

  • Motor coordination

  • Balance

  • Timing of movement

  • Motor learning

  • Error correction (predictive modelling)

2. Cerebellar Damage

  • Ataxia (clumsy movements)

  • Dysmetria (overshoot/undershoot)

  • Intention tremor

  • Hypotonia

  • Poor motor learning

3. Cognitive Role

  • Cerebellar cognitive affective syndrome:

    • Problems with planning

    • Language deficits

    • Dysregulation of emotion