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Brainstem and Basal Ganglia

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Brainstem Motor Mechanism

• Motor – Pyramidal

• Corticospinal tract and corticobulbar tract

– Extrapyramidal• Facilitatory, inhibitory, and/or regulatory

– Red Nucleus• Part of midbrain

– Cranial Nerve Nuclei– Reticular Formation

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Brainstem Anatomy

• Red Nucleus– Rubrocerebellar Tract– Important for gait in animals

without significant corticospinal tract

– Humans: upper arm and shoulder

• Cranial Nerve Nuclei– Will Be Discussed With Cranial

Nerves

• Reticular Formation– Focus in This Chapter

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Reticular Formation

• Located between caudal diencephalon & spinal cord

• Network of Overlapping Dendrites and Axons

• Input From– Motor Cortex– Basal Ganglia– Cerebellum– Cranial Motor Neurons

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Reticular Formation Function

• Arousal• Tonal Modulation • Pain Processing• Regulation of

– Vomiting– Coughing– Cardiovascular Functions– Respiration– Speech Functions

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Reticular Nuclei• Reticularis Gigantocellular• Pontis Oralis and Cudalis• Lateral Reticular Nucleus• Ventral Reticular Nucleus• Paramedial Reticular

Nucleus• Interstitial• Raphe• Ceruleus

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Reticular Motor Functions (1)

• Examined in anencephalic children who have no cortex or cerebellum

- Expel food

- Eat - Suck - Cry - Yawn

- Breathe -Swallow - Vomit - Sleep - Awaken

Muscle Tone Regulation - Maintains Balance of Stimulation

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Reticular Motor Functions (2)

• Facilitatory Reticular Areas– Upper and Lateral Brainstem– Increases Muscle Tone in

Extremities

• Inhibitory Reticular Areas– Lower and Medial Region of

Medulla– Decreases Muscle Tone in

Extremities

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Clinical considerations

• Disconnection of cortex and basal ganglia from reticular formation– Decerebrate Rigidity

• Extensor posturing of all Limbs• Excessive facilitatory impulses

• Transection Below Vestibular Nucleus– Flaccid Paralysis – Similar to degeneration of the lower neuron

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Basal Ganglia

• Modify cortically initiated motor movements (speech)– Caudate Nucleus– Putamen– Globus Pallidus– Related Brainstem Structures– Substantia Nigra– Subthalamic Nucleus

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Results of Basal Ganglia Impairment

• Involuntary Motor Movements• Bradykinesia (slow) or Hypokinesia (slow or

diminished)• Altered Posture• Changes in Muscle Tone• Implicate Neurotransmitters• All Result in Dysarthria and Dysphagia• Parkinson’s Disease• Huntington’s Disease

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Basal Ganglia• rostral

– striatum• putamen• caudate nucleus• nucleus accumbens

– globus pallidus

• caudal– subthalamic nucleus (STN)– substantia nigra (SN)

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Aliases

• Lenticular Nucleus– Putamen and Globus Pallidus

• Neostriatum or Striatum– Caudate Nucleus and Putamen

• Pallidum– Globus Pallidus

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Structures

1. Caudate Nucleus Elongated C Shaped Mass With Head and Tail Bordered by Ventricles, Internal Capsule and

Temporal Lobe

2. Globus Pallidus Next to Putamen

3. Putamen Connected to Head of Caudate Nucleus

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The Basal Ganglia

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Neurotransmitters

• Dopamine– Inhibitory Neurotransmitter– Produced in the substantia nigra and secreted in the

striatum

• Acetylcholine– Facilitatory/Inhibitory Neurotransmitter

• Gamma-Aminobutyric Acid– GABA Regulates Adjacent Structures– e.g. thalamus

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Clinical Considerations• Athetosis

– Involuntary slow writhing (twisting) movement– Continuous stream of slow, sinuous, writhing movements, typically of

the hands and feet. – Varying degrees of hypertonia– Usually seen in lesions of the globus pallidus

• Ballism– Violent Forceful Flinging of Arms and Legs– Most violent form of dyskinesia (movement disorder)– Usually associated with lesions in the sub-thalamic nucleus (which

regulates the globus pallidus)– Hemiballism: unilateral ballism (e.g. unilateral stroke)– Can be treated with dopamine blockade or resection of GP.

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Clinical Considerations

• Chorea– Series of rhythmic involuntary movements– Predominantly in the distal extremities and muscles of the

face, tongue, and pharynx– Chorea is characterized by brief, irregular contractions that

are not repetitive or rhythmic, but appear to flow from one muscle to the next.

– These 'dance-like' movements of chorea (from the same root word as "choreography")

– often occur with athetosis and more severe cases present with ballism

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Forms of Chorea

• Sydenham’s Chorea (5& 13 years of age)– Secondary to streptococcal infection

• Huntington’s Chorea (aka Huntington’s Disease)– 1872, George Huntington– Treated families with same characteristics– Heredity, Adult Onset, Chorea, Cognitive Loss– Autosomal Dominant– 5 in 100,000 prevalence– Equal in Men and Women– Loss of Cholinergic and GABAnergic neurons in Caudate

Nucleus

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Clinical Considerations

• Dyskinesia– Generalized Disorder of Involuntary and Voluntary

Movement– Masked Face, Infrequent Blinking, Slow Movement,

Disturbed Equilibrium, Stooped Posture, Impaired Speech, Impaired Swallowing

• Tremors– Alternating Movement of Opposing Muscles– Resting Tremor

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Basal Ganglia Diseases• Parkinson’s Disease (1817, James Parkinson)

– Tremor at Rest– Cogwheel Muscular Rigidity– Bradykinesia (Slow execution of body movements)– Akinesia (Slow beginning or inability to initiate a movement) – Shuffling Gate– Expressionless Face– Flexed Posture– Dysarthria– 30% have Cognitive impairment

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Parkinson’s Disease Treatment

• Lack of Dopamine (Inhibitor)

• Tx: L-Dopa or Other Dopamine Enhancers

• Prolonged L-Dopa Tx can result in tardive dyskinesia (increased facial and lingual movements)

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Basal Ganglia Disease

• Parkinson's disease: loss of dopamine in the neostriatum– Treatment: increase dopamine

• Schizophrenia: Too much dopamine– Treatment: Block some (D2) dopamine receptors.– Problem: Prolonged treatment using Chlorpromazine and

Haloperidol leads to Parkinson's disease-like tremors (tardive dyskinesia)

Not enough DAParkinsons

Too much DASchizophrenia

‘Normal’