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.