Basal Ganglia 1 Flashcards by Joel Glotfelty

a series of interconnected, subcortical nuclei, in telencephalon, diencephalon, and mesencephalon

Basal Ganglia

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The basal ganglia functions to control cortical functions such as

Cognitive, motor, and limbic function

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Cortical functions are initiated and enabled by the

Basal Ganglia

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Associted with several neurodegenerative and neuropsychiatric disorders

Basal Ganglia Disorders

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“Movement Disorders” or “Extrapyramidal disorders” are motor disorders that arise from

Basal Ganglia Dysfunction

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Neuropsychiatric Disorders of “habit” are also associated with basal ganglia. These include

Addictions, OCD, and Tics

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Basal ganglia loops facilitate

Motor Cortical areas

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Facilitate motor cortical areas including:

1-initiating movement
2-habit formation
3-“chunk” action sequences 4-terminate movements

Basal Ganglia Loops

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Basal Ganglia lesions produce either

Increased or decreased movement

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Forming motor habits enables movements to be executed without attention to the details of the

Movement

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The hallmark of basal ganglia diseases

Parkinson’s Disease

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Movements are slowed and labored and automaticity is lost

-There is an increased need for attention to movement

Parkinson’s Disease

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Made up of the caudate and putamen basal ganglia

Striatum

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The caudate ganglia and thalamus are medial to the

Internal Capsule

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What are the two basal ganglia structures outside of the cerebrum?

Subthalamic nucleus (diencephalon) and substantia nigra (Mesencephalon)

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The substantia Nigra is made up of the

Pars compacta and Pars Reticulata

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Tightly packed neurons contianing dopamine

Pars Compacta

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Less densely packed than pars compacta

Pars Reticulata

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Controls the movement in Parkinson’s Disease

Nigrostriatal Pathway

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Reward pathway for schizophrenia and depression

Mesolimbic Pathway

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Controls working memory and the negative signs of schizophrenia

Mesocortical Pathway

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Caudate and putamen receive

Cortical Inputs

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Substantia nigrapc DA projection modulates the

Circuit

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Receive Inputs from large areas of the entire cortex

Medium Spiny Neurons in the Striatum

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These medium spiny neurons then project to the

Globus pallidus (internal and external) and Substantia nigra pars reticulata (SNpr)

Have similar functions

Globus pallidus Internal (Gpi) and SNpr

SNpr is for

Eye movements

Internal globuspallidus (GPi) provides tonic inhibition to

VA/VL of thalamus (With SNpr)

Inhibitionof GPileads to more excitation of

VA/VL of thalamus and cortex

Excitationof GPileads to more inhibition of

VA/VL and cortex

Excites GPi, causing inhibition of the cortex (and movement)

Subthalamic Nucleus

Inhibits Gpi, causing more excitation of cortex (and movement), through disinhibition

Stiatum

Lesions of the subthalamicnucleus produce

Too much movement (Contralateral hemiballismus)

Facilitates movement through disinhibition

Basal Ganglia "Direct" Pathway

At rest, there is tonic inhibition by

GPi

However, during movement, Gpi is inhibited by

Striatum

Functions to inhibit movements

Basal Ganglia "Indirect" Pathway

The direct pathway is via the

Caudate/putamen ganglia

The indirect pathway is via the

Subthalamic Nucleus

The concept of activation of motor programs through Direct pathway with simultaneous inhibition of unwanted motor programs through Indirect pathway

Center-surround Organization

What are the receptor families for dopamine that are 1. ) Excitatory? 2. ) Inhibitory?

1. ) D1 receptor | 2. ) D2 receptor

NigrostriatalDopamine facilitates “Direct” pathway through

D1 receptors

Facilitates movement through the direct pathway

Dopamine

Nigrostriatal Dopamine inhibits “Indirect” pathway through

D2 Receptors

The neurotransmitter in 20% of striatal neurons

ACh

Preferentially excite the indirect pathway which increases movement inhibition

ACh in the 20% of striatal neurons

This is why anticholinergics provide benefit in

Parkinson's Disease

Characterized by too little movement -"Negative Symptoms"

Hypokinetic Disorders

Hypokinetic disorders are the result of either

Insufficient direct pathway output or excess indirect pathway output

Characterized by too much movement -Positive Symptoms

Hyperkinetic Disorders

Hyperkinetic disorders are the result of either

Excess direct pathway output or insufficient indirect pathway output

Abnormal movements caused by imbalanced activity in the basal ganglia

Dyskinesias

Hypokinetic disorders, hyperkinetic disorders, and dyskinesias all show symptoms that are

Contralateral to the lesion

What are the 5 hypokinetic or "negative" symptoms

Akinesia, bradykinesi, decreased postural adjustments, hypokineia, and rigidity

What are the three hyperkinetic or "positive symptoms"

Hemiballismus, chorea, and athetosis

The hyperkinetic or "positive symptoms" occur at

Rest

Spontaneous, involuntary movements usually caused by lacunar infarcts in the subthalamic nucleus

Hemiballismus

Hemiballismus is usually caused by

Lacunar infarcts in the subthalamic nucleus

Nearly continuous rapid movements of face, tongue, or limbs

Chorea

Chorea is most common in

Huntington's Disease

Slow, writhing movements, mostly in hands and fingers. Patients cannot maintain a fixed position

Athetosis

Often in children with cerebral hypoxia, affecting the basal ganglia

Athetosis

Slower than chorea, twisting postures Triggered by voluntary movements

Dystonia

The most common presentation of Dystonia

Writer's cramp

What are treatments for dystonia?

Botulinum toxin and DBS of the DP

Tics and tardive dyskinesia are also forms of

Hyperkinetic symptoms

Sudden brief action preceded by an urge to perform it

Tics

Characterized by persistent motor and vocal tics

Tourette's Syndrome

Dyskinesia resulting from drugs that have dopaminergic actions

Tardive Dyskinesia

Tardive diskenesia is caused by which classes of drugs?

Antipsychotics, anti-emetics, and manganese

Occurs in 70-80% of Parkinson's patients and is most common in hands and arms but can occur in legs and mouth

Parkinson's Tremor

Begins unilaterally and is 4-6 Hz at rest

Parkinson's Tremor

At rest, Parkinson's tumor is distinct from a

Cerebellar intention tremor

What are the 4 parallel basal ganglia pathways?

Motor, oculomotor, cognition, and emotions (limbic)

Many behaviors (motor, cognitive, emotional) begin with an impulse to act, followed by an

Action

Autosomal dominant neurodegenerative disorder with cell loss in caudate and putamen

Huntington Chorea

Progressive and Neurodegenerative. Eventually leads to akinetic/rigid form of the disease

Huntington's disease

In Huntington's the cell loss in caudate ganglia progresses to the

Putamen

Huntington's also affects the cortex, mainly the

Frontal and Temporal lobes

Treatments for Huntington's are drugs that decrease

Dopamine

The medium spiny neurons, containing GABA and Enkephalin, involved in Indirect pathway are affected in

Huntington's disease

A progressive and chronic neurodegenerative disease that does not go away and worsens with time

Parkinson's Disease

The mean onset of age for Parkinson's is? -Slightly higher prevalence in males than females

60 years old

Most causes of Parkinson's are

Sporadic

70% of young-onset of Parkinson's is due to

Autosomal recessive Parkin Mutation (PARK-2)

Common in familial cases of Parkinson's

Autosomal dominant Park-8 gene mutation

Pointed to a potential role of environmental toxins, or dopamine metabolism, leading to oxidative stress

MTPT

The 4 cardinal symptoms of Parkinson's disease begin unilaterally and are

Bradykinesia, Resting Tremor, Rigiity, and Postural Instability

Comes later in the disease

Postural Instability

A major motor sign of Parkinson's. Patients will take 2 steps back when pulled from behind

Retropulsion

An early sign of Parkinson's is

Hyposmia

What percentage of Parkinson's patients will have depression? -Most common psychiatric problem in PD

40%

To 1st diagnose Parkinson's, we need at least

Bradykinesia + one other symptom

Present in 70% of Parkinson's Cases -"Pill rolling"

Resting Tremor