The Basal Ganglia: Structures, Function, and Disorders

• The basal ganglia's location, purpose, and function should be identified.
• Symptoms of dysfunction should be understood.
• Signs of disorders should be recognized.
• Diseases associated with disorders should be explored.
• Dopamine is a neurotransmitter responsible for reward and feelings of well-being.
• Dopamine is made in the basal ganglia.
• Damage to the basal ganglia results in damage to dopamine production.

Location

• Found deep within the cerebral hemispheres.
• The basal ganglia are a group of nuclei deep in the cerebrum.

Structures

• Include the caudate, putamen, accumbens, external globus pallidus, internal globus pallidus, subthalamic nucleus, and substantia nigra.

Key points

• Inputs come from structures outside the BG.
• Outputs go from the BG to motor centers elsewhere in the brain.
• Cerebrum information goes to the basal ganglia.
• The basal ganglia processes and fine-tunes information.
• Basal ganglia sends information back to the cerebrum.
• Cerebrum then sends information down the spinal cord to the muscles.

Big Picture

• It helps select the movements to make.
• It inhibits unwanted movements.
• It allows purposeful movements via inhibition/disinhibition.
• Enabling allows to happen.
• Impulse control is key for inhibition.
• Dysfunction in the basal ganglia can lead to OCD.
• Tics and Tourette's are examples of failure to inhibit movements.
• Modulation involves a process of allowing and not allowing movements.

Difference

• Differences exist in roles of the cerebrum, cerebellum, and basal ganglia.
• Decreased dopamine is a normal basal ganglia function.
• The basal ganglia inhibits and enables play, similar to a referee.
• Without a referee there are no rules, which inhibits movements
• The basal ganglia is able to stop or allow movement

Basal Ganglia Function

• Regulates the initiation of movement, balance, eye movements, and posture.
• Plays a role in cognition, emotional behaviors, addictive behaviors, and habit formation.
• Frontal lobe involvement is required for cognition.
• Dopamine is made in the basal ganglia, affecting emotional and addictive behaviors.

Lesion Symptoms

• Difficulty initiating, continuing, or stopping movement.
• Tone abnormalities, changes in tone.
• Involuntary, undesired movements due to lack of disinhibition.
• Akinesia is the absence of movement.
• Bradykinesia is slow movement.
• Dystonia is a state of muscle being contracted.
• Rigidity is stiffness and rigid tone.

Tone Involuntary

• Athetosis
• Ballismus
• Chorea
• Dyskinesia
• Tics
• Tremor

BG Motor Disorders

• Parkinson's Disease
• Huntington's Disease
• Tardive Dyskinesia (repetitive, rhythmic facial movements, tongue thrusting, lip smacking)
• Neuropsychiatric disorders can be associated with basal ganglia dysfunction, such as OCD, ADHD, Depression, Schizophrenia, Addiction, and Tourette Syndrome.

Parkinson's Disease

• Involves a resting tremor (rhythmic), rigidity, akinesia and bradykinesia, mask-like facial expressions, forward trunk flexion, shuffling gait patterns, and decreased gait initiation.
• Other functional changes: quiet speech patterns, cognitive changes, decreased balance, apathy or lack of motivation.
• Freezing gait often occurs with distractions or changes in floor.
• Decreased motivation is due to a lack of dopamine.
• Cerebellum is associated with intention tremor.
• The basal ganglia is associated with resting tremor.
• Provide focus, rhythms, and attention to high steps to help with this disorder.

Huntington's

• Involves chorea and athetosis (undesired, large movements).
• Larger and smaller tremors can occur.
• Progressive and genetic components.
• Muscles get er weak.