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Neuro > Basal Ganglia > Flashcards

Basal Ganglia Flashcards

1
Q

4 Major Structures

A
  • Striatum = caudate + putamen (divided by internal capsule); input
  • Substantia nigra = pars compacta + pars reticulata
  • Subthalamiic nucleus = input nucleus
  • Globus Pallidus (GP) = internal (similar to pars reticulata) + external
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2
Q

Basic Loop Skeleton

A
  • Cortex —> input stage of striatum —> output stage in GPi or SNr —> special region in VL thalamus —> back to specific area of cortex
  • Also input from SNc to striatum
  • Also input from sub thalamic nucleus —> GP
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3
Q

Which neurotransmitters are secreted at each part of loop?

A
  • Cortex —> striatum is excitatory (glutamate)
  • Striatum —> GPi or SNr is inhibitory (GABA)
  • GPi or SNr —> thalamus is inhibitory (GABA)
  • SNc —> striatum is excitatory (dopamine)
  • Subthalamic nucleus —> GPi/SNr is excitatory (glutamate)
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4
Q

Rate Model of BG Dysfunction

A
  • Parkinsons
    • Removal of dopamine excitation from SNc —> dec stratal inhibition of GPi —> inc GPi inhibition of VL —> less motor output (hypokinesia)
  • Hemibalism
    • Removal of excitation from sub thalamic nucleus —> dec inhibition by GPi of VL thalamus —> inc motor output (hyperkinesia)
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5
Q

3 Ways Rate Model Fails to Explain BG Dysfunction

A
  • 1- does not explain rigidity and tremor in Parkinsons
    • 2- Pallidotomy (surgical removal of globes pallidus) helps Parkinsons while you would expect that no GPi would cause hyperkinesia
    • 3- Abnormal patterns of firing tends to correlate w/ severe disease not simple patterns
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6
Q

4 Reasons the BG is so easily damaged

A
  • High metabolic demand; needs oxygen
    • Vulnerable to hypoxia
    • CO
  • High conc of certain neuroTs (GABA, dopamine, Ach, Serotonin) so any problem in production, storage, metabolism or release of these causes problems
  • High conc of heavy metals (toxic accumulation)
    • Copper -
    • Iron - in GP and SNr (Hallervorden-Spatz disease - dystonia)
    • Manganese - in GP and subthalamic nucleus - Parkinson-like
  • Selective affinity for MPTP (contaminant in homemade heroin)
    • Akinesia and rigidity (Parkinson-like)
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7
Q

4 Hypothesis About Role of BG

A
  • Selection of desired movements and suppression of those that compete w/ them
  • Retention and recall of procedural knowledge
  • Linking cost and benefits to how behaviors are performed
  • Tutors or trains cortical circuits for certain skills or habits
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8
Q

3 Categories of BG Movement Disorders

A
  • Hypokinetic
    • Akinesia - problem w/ initiating movement
    • Bradykinesia - can initiate but then slow performance
  • Hyperkinetic
    • Involuntary movements
      • Chorea
      • Athetosis
      • Torsion spasm (torsion dystonia) - tonic contraction of proximal body
      • Resting tremor in Parkinsons
  • Change in muscle tone
    • Inc - rigidity in Parkinsons
    • Dec - Huntingtons
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9
Q

Chorea v Athetosis

A
  • Chorea - rapid, sporadic, fragmented dance-like movements (Huntingtons)
  • Athetosis - slow spreading contractions of closely related muscle groups
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10
Q

Rest v Action Tremors

A
  • Rest Tremor - when limb is supported against gravity not activated (Parkinsons); 4-6 Hz
  • Action Tremor - during voluntary movement
    • Postural - when limb is in set posture but not at rest
    • Kinetic -when limb is in motion (intention or terminal)
    • Task-specific
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11
Q

Essential Tremor

A
  • MOST COMMON (10% of those over 65 yo)
  • Autosomal dominant
  • Upper limbs > head > lower > voice & usually bilateral
  • Usually manifests in 20s or 60s
  • No visible pathology BUT think it is inferior olive —> cerebellum —> thalamus —> motor cortex pathway
  • Tx (all dec amp not frequency)
    • Beta blockers (esp propanolol b/c crosses BBB)
    • Primidone (anti-convulsant; metabolized to phenobarbital); somnolence
    • Deep Brain Stim - stimulate Vim thalamus so no permanent lesion
    • Gamma knife —> irreversible lesion to thalamus
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12
Q

Cerebellar Tremor

A
  • SLOW (2-4 Hz) and intention so at end of movement

- Tx same as essential but less effective overall

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13
Q

Psychogenic Tremor

A

VARIABLE (abrupt onset, distractable, spontaneous episodes)

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14
Q

2 Genetic Variations of Dystonia

A
  • DYT1 mutation - affects torsin A (chromosome 9); may be involved in protein folding/trafficking; high concentrations in SNc; usually childhood onset
  • DYT5 (Dopa-responsive dystonia) - generalized dystonia in early childhood w/ diurnal variation; marked improvement w/ L-dopa; caused by mutation in GTP cyclohydrolase (makes co-factor) or tyrosine hydroxyls (both needed for dopamine production)
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15
Q

Types of Primary Dystonia (5)

A
  • Primary
    • Only abnormal finding
    • Usually generalized/hereditary in kids & focal/random in adults

1- Cervical dystonia - co-contraction of neck and shoulder muscles
2- Blepharospasm - forced eye closures
3- Oromandibular dystonia - contraction of jaws, mouth, lower face
4- Laryngeal dystonia - vocal cords affected to hyper adduction during speech
5- Task - specific - writer’s cramp or athletes or musicians

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16
Q

What is the proposed pathology of dystonia?

A

Abnormal activation patterns from GP to thalamus —> inc in synchronous contraction of agonist/antagonist —> unwanted overflow movement

17
Q

Dystonia Tx

A
  • First line = botulinum toxin (prevents release of Ach at NMJ); repeat every 3-6 mo
  • May also try anticholinergics, benzodiazepines, dopamine-depleting drugs
  • Last resort = DBS to GPi not thalamus (need higher levels of stimulation)
18
Q

How does Parkinson’s affect both direct and indirect pathways?

A
  • Direct Path: Motor cortex –> putamen –> GPi/SNr –> thalamus –> motor cortex (GO)
    • D1 excitation on putamen
    • NO dopamine means … less inhibition of GPi by striatum so more GPi inhibition of thalamus/motor
  • Indirect Path: Motor cortex –> putamen –> GPe –> STN –> GPi –> thalamus –> motor cortex (INHIBITS)
    • D2 inhibition on putamen
    • NO dopamine means … less inhibition of putamen by dopamine – > more inhibition of GPe by putamen –> less inhibition of STN –> excites GPi so more GPi inhibition of thalamus/motor
19
Q

5 Intracellular Mechanisms of Parkinson’s Pathology

A
  • Mitochondria impairment
  • Oxidative stress
  • Protein misfolding and aggregation (Lewy bodies - cytoplasm inclusions - proteins aggregate)
    • Alpha - synuclein
  • Failure of ubiquitin-proteasome system to remove proteins
  • Inflammation
20
Q

Parkinson’s Epidemiology

A
  • Inc risk if male (2:1) and age; some monogenetic but very rare; usually combo of genetic and environmental factors
  • 2nd most common neurodegenerative disorder behind Alzheimer’s
  • 1-2% of those 65 yo +
21
Q

3 Categories of Parkinson’s Symptoms + Which are Cardinal?

A

1- Pre-motor (dec sense of smell, constipation, acting out dreams b/n no paralysis in REM)
2- 4 cardinal motor symptoms
3- non-motor (depression, anxiety, cognitive problems later in disease)

  • Bradykinesia (necessary for dx) + 1 other cardinal motor sign (rest tremor, rigidity, postural instability/gait imbalance/freezing/festination)
    • Festination = cannot stop once walking
    • Freezing = walking in place - cannot move forward
22
Q

Parkinson’s Differential Dx

A
  • Atypical parkinsonian syndromes - parkinson’s + extra signs (multiple system atrophy, supranuclear palsy w/ vertical gaze palsy, corticobasal degeneration, dementia w/ Lewy bodies)
  • If acute or step-wise probably vascular (mini-stroke or microvascular disease in brain)
  • Medication- induced (neuroleptics that block dopamine receptors, lithium)
  • CO, manganese, post-encephalitis
23
Q

Parkinson’s Tx

A
  • Pharm
    • L dopa + Carbidopa (sinemet) - L dopa crosses BBB while carbidopa does not so just prevents peripheral breakdown
    • D2 receptor agonists
    • MAO B inhibitors
    • COMT inhibitors (inchalf life of L dopa)
  • DBS
    • Used later when dyskinesia b/n L-dopa doses; persistent stimulation of the subthalamic nucleus –> normalize STN output to GPi
24
Q

Myoclonus + Classification + Tx

A
  • Myoclonus - brief, shock-like, rapid movements
    • Arise in CNS and cannot be suppressed by pt
    • Pos - sudden contraction (jerk)
    • Neg - sudden dec in tonic contraction; can no longer hold self up against gravity (“asterixis”)
  • Classification
    - Clinical/Descriptive - when (spontaneous, action, reflex) & where (generalized, segmental, focal, multi-focal)
    - Physiological - cortical, subcortical or spinal localization (may predict which drugs will work and know what imaging to order)
    - Etiology - cause
    - Physiological - NO BRAIN DISEASE (hiccups or hypnic jerks when falling asleep)
    - Essential - rare hereditary syndrome; myoclonus is only feature; resolves w/ alcohol
    - Symptomatic - secondary to underlying brin disease
    - Ex) Paraneoplastic, epilepsy, degenerative disease like Alzheimer’s or Lew bodies or prions, post hypoxia, drugs (SSRIs, narcotics, cocaine), metabolic
  • Tx - treat underlying cause; cortical myoclonus may respond to anticonvulsants (valproate, clonazepam, levetiracetam)
25
Q

Tics + Common Causes

A
  • recurrent, non-rhythmic, stereotyped movements or sounds
    • Can be simple or complex
    • “Unvoluntary” - b/c can be suppressed (but then rebound after) BUT preceded by pressure/unpleasant feeling that is only resolved by tic
  • Primary
    - Hereditary and childhood onset
    - Transient childhood tics, chronic motor tics, Tourettes
  • Secondary
    - Manifestation of other brain disease; adult onset
    - Drugs, post strep infection in kids (PANDAS), neurodegenerative disease
26
Q

Tourette’s

A
  • Hereditary
  • Dx - multiple motor tics + at least 1 vocal tic + distress/impairment + younger than 18 + not due to other brain problem
  • Tx - neuroleptics, dopamine depletor, benzo (clonazepam), alpha agonist (clonidine), atypical anti-psychotic
27
Q

What is Wilson’s disease?

A
  • Hereditary, autosomal recessive
  • Prob w/ copper metabolism; mutation —> loss of function of trans-golgi ATPase that normally transports copper so it can be excreted in bile
  • SO… copper accumulates in tissues (including basal ganglia)
28
Q

How does Wilson’s disease present?

A
  • Mixture of motor problems b/c basal ganglia is so widespread (cerebellar ataxia, tremor, dystonia, psych probs, bulbar/facial involvement)
  • Facial dystonia —> retracted upper lip (silly smile)
  • Brown rings in cornea b/c copper deposits
  • Liver disease, hepatitis, cirrhosis, hemolytic anemia, amino aciduria
  • Labs… LOW serum caeruloplasmin (normally binds copper but now misfolds instead), LOW serum copper, HIGH urine copper
29
Q

How do you treat Wilson’s Disease?

A
  • important b/c curable if early but fatal if not
  • Inc urinary copper excretion - penicillamine or trientene (bind copper in blood then excrete in urine)
  • Zinc salts - induce gut genes that encode proteins that bind dietary copper so not absorbed to begin with
  • Liver transplant may be needed

**Should test siblings + genetic counseling

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