Basal Ganglia anki deck

[Doctorcallyan]

Basal Ganglia

Intro

• Part of extrapyramidal system for movement (along with cerebellum)

• Contributes to behaviour, motor and cognition

• Related to movement and neuropsychiatric disorders - Thalamus is relay station for ascending info

Components

• • Striatum = caudate and putamen • Receiving station/input centre of basal ganglia
    • Caudate has a more extensive connection with cortex compared to putamen • Parkinsons
    • Cortico-striate pathway
• • Lentiform nucleus = globus pallidus and putamen
    • Target for Wilson’s disease
    • Lenticuostriatal artery (branch of MCA) blood supply
• • From lateral to medial: putamen —> GPE —> GPI
• • Substantia nigra: - Pars compacta = dopaminergic - Nigro-striate pathway Amygdala

• Tail of caudate is connected to amygdala and is involved with emotion

1

Outputs

• • Globus pallidum interna and substantia nigra reticulata are the 2 major output stations
• • Goes to VA & VL of thalamus Pathway
• • Glutamate activates inhibitory neurons in striatum which turn off the globus pallidus interna
• • Inhibiting the inhibitor globus pallidus interna so then the thalamus is active
• • indirect — reactivated globus pallidus inhibitory neurons to turn the thalamus back off again
• • When dopamine binds D1, it turns on the direct
• • When dopamine binds to D2, it turns off the indirect
• • Ach makes D2 less sensitive to dopamine to restore the inhibition on movement
• • Pars compacta is where the dopaminergic neurons are
• • Indirect overactive or direct underactive = hypokinetic; parkinsons
• • Direct overactive or indirect underactive = hyperkinetic; huntingtons, hemiballismus, wilsons disease Action/Motor Functions
• • Gatekeeper for movements and muscle tone
• • Suppresses unwanted movements (indirect) and only allows required movements (direct)
• • Secondary movements such as arm swing
• • Stereotyped movements such as laughing
• • Semiautomatic movements
• • Supporting movements

2

Behaviour Functions

• Lack of initiative to perform movements (akinesia); seen in parkinsons

• Manifests as hypokinesia and mask-like expressionless face Cognitive Functions

• • Caudate plays an important role in learning of sequential non-declarative motor skills (learning to ride a bike)
• • Hippocampus is involved in episodic/declarative memory
• • Loss of non-declarative memory in basal ganglia lesion = able to remember trying to do a mirror drawing before but difficulty in learning the skill
• • Loss of declarative memory in hippocampus lesion = cannot remember trying to draw before but is able to learn the skill of mirror drawing Neurons in CNS Most Vulnerable to Anoxic Death (Long Axons) - Pyramidal neocortical neurons

• Purkinje neurons of cerebellum
• Pyramidal neurons of hippocampal CA1 - Spiny neurons of striatum Parkinsons

• • TRAP: tremors (resting), rigidity, akinesia, postural (stooped) and gait disturbances (festinating)
• • Late dementia, usually subcortical
• • Lead-pipe rigidity/cog-wheel rigidity/plasticity = no loosening, resistance throughout, tremors superimposed on rigidity. SEEN IN PARKINSONS.
• • Clasp-knife rigidity/spasticity = resistance at first but tone loosens on extension. SEEN IN UMN LESIONS.

3

• • Signs are contralateral to the lesion and begin unilaterally. As it advances, will become bilateral.
• • Posture is last to be affected
• • Micrographia: diminished letter size with writing
• • Pathology: degeneration of dopamine neurons in substantia pars compacta • Replaced by eosinophilic lewy bodies that may contain synuclein, ubiquitin Huntington’s Disease
• • Caudate nucleus atrophy —> putamen —> cortex
• • MRI will show bilateral caudate atrophy with hydrocephalus ex vacuo
• • Death by 6th decade
• • CP: middle aged with signs of dementia, choreiform movements starting in fingers and toes, dysphagia, grimacing
• • Choreiform movements: rapid, jerky, non-repetitive pseudopurposive movements
• • Dementia, subcortical type. Difficulty learning skills.
• • Neuropsychiatric: forgetfulness, impulsivity, irritability, poor concentration and other emotional or behavioural disturbances at the beginning progressing to anxiety, depression, mania and suicide
• • AD, chromosome 4

• family hx of movement/psychiatric disorders

• • CAG repeats encoding for glutamine >36; turns its RNA in the HTT gene cytotoxic
• • Genetic anticipation
• • Abnormal huntingtin is apoptotic Sydenhams Chorea

• Autoimmune response to GAS beta-hemolytic - Girls aged 5-15 in developing countries

4

• • Pathophysiology: cross reactivity of strep antigens and membrane proteins of striatal neurons; host antibodies attack bacteria and striatal neurons —> transient chorea that causes inflammation but doesn’t kill the neurons
• • Initially presents as pharyngitis
• • ARF after 1-5 weeks (fever, joint pain, rash, cardiac)
• • 1-6 months after infection, will develop dance-like choreatic movements which disappear with sleep and worsen with stress
• • May be restless, aggressive or emotional
• • Self-limiting
• • Caudate nucleus is implicated but it is not long-lasting or degenerative
• • Chorea gravidarum: some with childhood sydenham’s chorea develop chorea during 2nd trimester of pregnancy Hemiballismus
• • High-amplitude rapid, flinging, flailing (ballet-like) unilateral involuntary movements
• • Lesion of contralateral subthalamic nucleus (lacunar infarct; lenticulostriate arteries from HTN or diabetes)
• • Causes exhaustion or injury Wilson’s Disease
• • Error in copper metabolism; deficiency of ceruloplasmin and decreased copper elimination
• • AR ATP7B mutations
• • Copper is used by dopaminergic neurons
• • Hepatolenticular degeneration: copper deposits in liver, lenticular nuclei (mostly putamen) and eyes
• • <30 age onset
• • Hepatic presentation: jaundice, hepatomegaly, edema, ascites

5

• Neuro presentation: dysarthria, dystonia, rigidity, wing-beating tremor, chorea, sardonic smile, gait abnormalities, ataxia

• Psychiatric: irritability, impulsivity, anxiety, depression, substance misuse - Ocular: Kaiser-Fleischer ring, sunflower cataracts

Tourette Syndrome

• • Premonitory urge followed by motor/phonic tics, coprolalia (explosive/vulgar swearing)
• • Increased dopamine activity
• • M:F = 3:1
• • 3-8 years
• • Tics must be present for >1 year and onset before age of 21 - Tics can be suppressed - Comorbid with ADHD, OCD, ASD Extrapyramidal Reactions
• • Akathisia: inner restlessness, inability to keep still (rocking, pacing, fidgeting) within 2 weeks of starting neuroleptics. May also present with anxiety and dysphoria.
• • Acute Dystonic Reaction: spasms of jaw, face, neck muscles within 5 days of starting neuroleptics. May also present with dysphagia.
• • Perioral Tremor (Rabbit syndrome): abnormal orofacial lips, mouth and jaw movement BUT NO TONGUE INVOLVEMENT after months-years of antipsychotics - Responds well to anti-parkinson drugs - Usually not permanent
• • Tardive Dyskinesia: choreiform movements of face and trunk, dystonia, tics - Mostly irreversible and persistent - TONGUE PROTRUSIONS - Worsened by anti-parkinson drugs

6

• D/t long term antipsychotic medications - Supersensitivity of dopamine receptors

Movement Disorders Overview

• Dyskinesia: abnormal movement usually due to lesions in basal ganglia

• Can be bradykinesia, hypokinesia, akinesia, or hyperkinesia

• • Lesions in basal ganglia present contralaterally
• • Rigidity
• • Dystonia = slow or sustained distorted positioning
• • Athetosis: proximal writhing or twisting
• • Chorea: continuous jerky “dance”
• • Choreoathetosis: merging chromatic and athetotic
• • Ballismus: high amplitude flinging
• • Tics: sudden, brief action preceded by an urge and followed by relief