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Basal Ganglia and Movement Disorders

Anatomy of Basal Ganglia

  • Putamen: Wraps around globus pallidus (internal and external).

    • Integral in motor pathways related to movement generation.

  • Globus Pallidus: Consists of:

    • Internal Segment: Inhibitory effect on thalamus.

    • External Segment: Involved in indirect pathways affecting movement.

  • Subthalamic Nucleus: Has connections with caudate and putamen; crucial for movement regulation.

Pathways of Movement

  • Direct Pathway:

    • Facilitates movement by inhibiting the globus pallidus internal, leading to thalamic excitation which promotes motor cortex activation.

  • Indirect Pathway:

    • Inhibits movement through activating the globus pallidus internal; increases inhibitory signals to the thalamus, reducing movement.

Movement Disorders

  • Movement disorders can be classified mainly into hyperkinetic (excessive movement) and hypokinetic (reduced movement).

Hyperkinetic Disorders:

  • Huntington's Chorea:

    • Genetic disorder (dominant) causing involuntary movements (chorea) resembling dancing.

  • Tourette Syndrome:

    • Characterized by motor and vocal tics.

Hypokinetic Disorders:

  • Parkinson's Disease:

    • Characterized by:

    • Resting Tremors: Tremors occurring when muscles are relaxed.

    • Rigidity: Increased muscle tone resulting from simultaneous firing of flexors and extensors.

    • Bradykinesia: Slow movement ability due to hypokinetic symptoms.

Understanding Symptoms

  • Tremors: Occur at rest; related to decreased dopamine affecting globus pallidus internal.

  • Muscular Rigidity: Hypertonic (too much muscle tone), leading to limited movement.

    • Dyskinesia: Involuntary movements, often seen in late stages of Parkinson's.

Neurotransmitters

  • Dopamine: Critical in regulating movement pathways; imbalances lead to various movement disorders (too little in Parkinson's, too much in certain types of schizophrenia).

Importance of the Cerebellum

  • Function:

    • Key for timing and accuracy of movements; intricately connected with movement feedback loops.

  • Role in Learning: Helps fine-tune movements based on sensory feedback (error correction).

Sensory and Motor Integration

  • Motor signals originate from the motor cortex:

    • Prefrontal Cortex: Planning movements.

    • Premotor Cortex: Organizing movements.

    • Primary Motor Cortex: Execution of movements.

Somatosensory System

  • Provides critical feedback on touch, position, pain, and temperature. Enables fine motor skills and sensory-motor feedback.

Receptors and Feedback Mechanism

  • Types of Receptors:

    • Nociceptors: Pain sensation.

    • Mechanoreceptors: Detect touch and pressure.

    • Thermoreceptors: Detect temperature changes.

Sensory Adaptation

  • The phenomenon where sensory receptors become less sensitive to constant stimuli.

    • Essential for focusing attention on important stimuli while ignoring constant background stimuli (e.g., feeling clothes).

Final Thoughts

  • Understanding the interplay between basal ganglia, cerebellum, and sensory systems offers insights into movement disorders and their management.