Functions of basal ganglia & parkinsonism

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🧠 Summary Notes – Basal Ganglia & Thalamus

🟣 I. Basal Ganglia (BG)

🖇 Definition & Location:
Clusters of nerve cells located beneath the cerebral cortex, between the cortex and the brainstem.

📌 Main Components:
Caudate Nucleus – Putamen – Globus Pallidus – Subthalamic Nucleus – Substantia Nigra

🟠 A. Connectivity & Pathways

📌 Rules of Connection:

• BG receives input directly from the Cerebral Cortex.
• BG cannot send output directly to the cortex — it must pass through the Thalamus (the secretary).
• BG does not get input from the spinal cord; signals reach it via Extrapyramidal tracts.

🚨 Neurotransmitters:

• Cortex → BG: Excitatory (Glutamate)
• BG Output: Inhibitory (GABA)

📌 Pathways:

• Direct Pathway → Facilitates movement (stimulates cortex).
• Indirect Pathway → Inhibits movement (via Subthalamic Nuclei).

🟣 B. Functions of Basal Ganglia

🖇 Main Role: Ensures movements are correct, smooth, and well-timed.

📌 Functions include:

1. Regulation of Muscle Tone: Mostly inhibitory effect.
2. • Exception: Caudate Nucleus → stimulates muscle tone.
2. Control of Involuntary Movements: e.g., swinging of arms while walking.
3. Planning & Execution: Coordinates skillful actions (e.g., drinking water smoothly).
4. Trained/Automatic Movements: e.g., surgeon stitching, tailor cutting fabric.

🟠 C. Basal Ganglia Disorders

🚨 Defects lead to involuntary movements.

📌 1. Parkinsonism (Shaking Palsy):

• Affected nuclei: Substantia Nigra / Globus Pallidus
• Muscle tone: Hypertonia (rigidity)
• Tremor: Static tremor (present at rest, disappears in activity/sleep)
• Types of rigidity: Lead Pipe / Cogwheel
• Other features: Bradykinesia, monotone speech, masked face
• Treatment: Dopamine

📌 2. Chorea (Dancing Movements):

• Affected nucleus: Caudate Nucleus
• Muscle tone: Hypotonia
• Tremor: Present at rest, increases with activity, disappears during sleep

🟣 II. Thalamus

🖇 Definition: The “Secretary of the Cerebral Cortex” – an ovoid mass of gray matter composed of several nuclei.

🟠 A. Thalamic Functions

📌 1. Sensory Relay:
Main relay for most sensory signals to the cortex.

• VPL & VPM: For fine sensation & fast pain.

📌 2. Vision & Hearing:

• LGB: Vision
• MGB: Hearing

📌 3. Arousal & Sleep:

• Intralaminar Nuclei: Part of the Reticular Activating System (RAS); control consciousness and sleep–wake cycles.

📌 4. Memory:

• Part of Papez Circuit → controls recent memory.
• Damage may cause memory loss (e.g., Alzheimer’s).

📌 5. Personality & Behavior:

• Helps regulate emotional responses and behavior through cortical connections.

🟣 B. Thalamic Syndrome (Lesion)

🚨 Usually due to thrombosis or degeneration of the Thalamogeniculate Branch of the Posterior Cerebral Artery.

📌 Main Symptoms:

• Loss of all sensations.
• Astereognosis: Can’t identify objects by touch.
• Sensory Ataxia: Poor coordination of voluntary movements.
• Spontaneous Pain / Hyperalgesia: Mild touch causes severe pain.
• Possible visual or hearing defects (e.g., hemianopia).

📚 Key Points Emphasized by Lecturer

🟠 Basal Ganglia Highlights:

• Always remember: Input from Cortex → Output via Thalamus.
• Lesion–Tone Relationship:
• • Substantia Nigra lesion → Hypertonia (loss of inhibition).
  • Caudate lesion → Hypotonia (loss of stimulation).
• Tremor Patterns:
• • Parkinsonism → Tremor disappears with activity.
  • Chorea → Tremor worsens with activity.
• Functional Role: precise, well-timed, skillful movement.

🟣 Thalamus Highlights:

• “Secretary” concept: all signals pass through it before reaching the cortex.
• Nuclei functions: LGB (vision), MGB (hearing), VPL/VPM (sensation).
• Memory circuit: Papez circuit for recent memory.
• Thalamic Syndrome: Key feature = loss of sensation + spontaneous pain.