Extrapyramidal system - anatomy, physiology, extrapyramidial syndromes
Extrapyramidal System
The extrapyramidal system is a network of nuclei and pathways that regulates muscle tone, posture, automatic movements, balance, and coordination of voluntary movements. It does not initiate movement but modulates and smooths it.
Anatomy
- Basal Ganglia Components
Caudate nucleus. Putamen. Globus pallidus. Subthalamic nucleus. Substantia nigra (midbrain)
- Main Connections
The basal ganglia communicate with: Motor cortex. Thalamus. Brainstem
- Neurotransmitters
- Dopamine (substantia nigra) → facilitates movement
- Acetylcholine → opposes dopamine effects
- GABA
- Glutamate
Physiology
Functions
- Regulation of muscle tone
- Maintenance of posture and balance
- Control of automatic and associated movements
- Coordination and smooth execution of voluntary movements
- Suppression of unwanted movements
A balance between dopamine and acetylcholine is essential for normal motor function.
Extrapyramidal Syndromes
Extrapyramidal disorders are characterized by abnormal involuntary movements, altered muscle tone, and postural disturbances without significant weakness.
1. Hypokinetic-Rigid Syndrome (Parkinsonian Syndrome)
Caused by dopamine deficiency in the basal ganglia.
- Clinical Features
Bradykinesia (slowness of movement). Resting tremor. Muscle rigidity ("lead-pipe" or "cogwheel"). Postural instability. Shuffling gait. Mask-like face (hypomimia). Reduced arm swing. Micrographia
- Causes
Parkinson disease. Drug-induced parkinsonism. Vascular parkinsonism
Mnemonic: TRAP ( Tremor. Rigidity. Akinesia/Bradykinesia.Postural instability)
2. Hyperkinetic Syndrome
Characterized by excessive involuntary movements.
- Tremor: Rhythmic oscillatory movement.
- Chorea: Rapid, irregular, jerky movements.. Example: Huntington disease
- Athetosis: Slow, writhing movements of distal limbs.
- Dystonia: Sustained involuntary muscle contractions causing abnormal postures.
- Hemiballismus: Violent flinging movements of one side of the body.
- Usually due to lesion of the subthalamic nucleus
- Tics: Sudden, repetitive, stereotyped movements or vocalizations.
Examination Findings in Extrapyramidal Disorders
Muscle Tone: Increased rigidity. Not velocity-dependent (unlike spasticity)
Reflexes: Usually normal
Muscle Strength: Usually preserved
Sensation: Normal
Involuntary Movements: Tremor. Chorea. Dystonia. Tics. Athetosis