Neuro 16 Basal Ganglia

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hyperkinetic movement disorders of the basal ganglia

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Huntington's-uncontrolled involuntary movements produce a random pattern of jerks and twists

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hypokinetic movement disorders of the basal ganglia

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Parkinson's-rigidity, slowness, and marked difficulty initiating movements

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fxns of basal ganglia

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movement, emotional control, cognition, and eye movements

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where are the basal ganglia located

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deep within white matter of cerebral hemispheres

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main components of the basal ganglia

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caudate nucleus, putamen, globus pallidus, subthalamic nucleus, and substantia nigra (sometimes nucleus accumbens and ventral pallidum included; amygdala primarily limbic system)

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neostriatum (or striatum)

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caudate and putamen thought of as single nucleus (histo and embryologically closely related); receives all inputs to the basal ganglia

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what separates the putamen and caudate

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penetrating fibers of internal capsule-remain joined in some places by cellular bridges

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caudate nucleus relationships

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C-shaped; constant relationship with lateral ventricles (like corpus callosum and fornix); 3 parts (head, body, tail)

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location of amygdala

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anterior to tip of caudate tail in temporal lobe

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putamen specs

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large nucleus forming lateral portion of basal ganglia; fuses with head of caudate anteriorly and ventrally

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most of central striatum consists of

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nucleus accumbebs

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globus pallidus (pallidum)

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pale globe' named due to many myelinated fibers traversing the region; medial to putamen

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lenticular (lentiform nucleus)

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putamen and globus pallidus together (resemble ice cream cone lying on side; putamen=icecream and globus pallidus = cone)

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internal capsule

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V-shaped collection of fibers going to and from the cortex

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what does the anterior limb of the internal capsule pass btwn

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lentiform nucleus (lateral) and head of caudate (medial)

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what does the posterior limb of the internal capsule pass btwn

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lentiform nucleus (lateral) and thalamus (medial)

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where in the internal capsule are the corticobulbar and corticospinal tracts

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posterior limb

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what is visible just dorsal to the cerebral peduncles

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substantia nigra

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what separates the internal segment of the globus pallidus and the substantia nigra pars reticulata

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internal capsule (similar to caudate and putamen separation)

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what does the substantia nigra pars reticulata contain

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cells very similar to internal segment of the globus pallidus

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substantia nigra pars compacta (dorsal) contains

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darkly pigmented dopaminergic neurons; degeneration important mechanism of Parkinson's

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what lies under the thalamus

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spindle/cigar-shaped subthalamic nucleus

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what is the subthalamic nucleus derived from

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midbrain (thalamus is from forebrain)

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blood supply to striatum and globus pallidus

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mainly from lenticulostriate branches of the MCA; medial globus pallidus often supplied by anterior choroidal artery (branch of internal carotid) and head of caudate and anterior portions of lentiform nucleus bu recurrent artery of Heubner (branch of ACA)

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outputs leave basal ganglia via

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internal segment of globus pallidus and closely related substantia nigra pars reticulata

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inputs to basal ganglia come from

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massive projections from cerebral cortex to striatum; substantia nigra pars compactal intralaminar nuclei; raphe nuclei of brainstem

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most important nucleus for motor control pathways in basal ganglia

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putamen

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neurotransmitter used in most cortical inputs to striatum

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excitatory glutamate

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neurotransmitter used in substantia nigra pars compacta inputs to striatum

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dopaminergic nigrostriatal pathway excitatory to some and inhibitory to others

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neurotransmitter used in intralaminar nuclei (within internal medullary lamina of the thalamus) inputs to striatum

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excitatory glutamatergic; especially centromedian and parafascicular nuclei

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neurotransmitter used in raphe nuclei of brainstem inputs to striatum

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serotonergic

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where do basal ganlia outputs arise

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from internal segment of globus pallidus and substantia nigra pars reticulata

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motor outputs for head and neck in basal ganglia

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substantia nigra pars reticulata (inhibitory via GABA)

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motor output for rest of body from basal ganglia

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internal segment of globus pallidus (inhibitory via GABA)

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where do the main outputs from basal ganglia go

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to the ventral lateral (VL) and ventral anterior (VA) nuclei of the thalamus via thalamic fasciculus (anterior portion)

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posterior parts of thalamic fasciculus carry what

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cerebellar outputs to posterior VL (Caudal part of VL receives inputs from Cerebellum)

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information from basal ganglia is relayed mainly to where from thalamus

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entire frontal lobe-mainly premotor cortex, supplementary motor area, and primary motor cortex

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intralaminar nuclei (in thalamus) receive input from basal ganglia and project where

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back to striatum

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where does mediodorsal nucleus of thalamus project inputs from basal ganglia

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primarily limbic pathways

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where do internal segment of gobus pallidus and substantia nigra pars reticulata project to

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pontomedullary reticular formation-influence descending reticulospinal tract

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whre else does the substantia nigra pars reticulata project

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superior colliculus-influences tectospinal pathways

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two predominant pathways from input to output nuclei through the basal ganglia

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1) direct 2) indirect

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direct pathway

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travels from striatum directly to internal segment of globus pallidus or substantia nigra pars reticulata

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indirect pathway

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detour from striatum-first to external segment of globus pallidus and then to subthalamic nucleus before reaching internal segment of globus pallidus or substantia nigra pars reticulata

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net effect of excitatory input from cortex via direct pathway

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excitation of thalamus-which then facilitates mavements through connections with motor and premotor cortex

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net effect of excitatory input from cortex via indirect pathway

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inhibition of thalamus-inhibition of movements through connections back to cortex (INdirect INhibits)

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direct pathway neutrotransmitters

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GABA and substance P

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indirect pathway neutotransmitters

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GABA and enkephalin (Enkephalin to External pallidum)

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Parkinson's cause

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dopamine-containing neurons in substantia nigra pars compacta degenerate

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dopamine affects on direct and indirect pathways

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excitatory on striatal neurons of direct; inhibitory on striatal neurons of indirect

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loss of dopamine net affect on thalamus

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net inhibition via both direct and indirect pathways = paucity of mvmnt in Parkinson's

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aspiny neurons

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large interneurons in striatum which contain acetylcholine; excitatory synapses onto striatal neurons of indirect pathway

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result of removal of cholinergic excitation of indirect pathway

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net decrease in inhibition of thalamus

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hemiballismus

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unilateral wild flinging movements of extremities contralateral to a lesion in the basal ganglia, typically with subthalamic nucleus

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how does damage to subthalamic nucleus cause hemiballismus

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decrease excitation of internal segment of globus pallidus, resulting in less inhibition of the thalamus casuing the hyperkinertic movement disorder

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Huntington's

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striatal neurons in caudate and putamen degenerate; initially enkephalin-containing striatal neurons most severely affected

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what does disruption of enkephalin-containing striatal neurons cause

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removal of inhibition from external segment of globus pallidus allowing it to inhibit the subthalamic nucleus

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advanced Huntington's

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both direct and indirect degenerate resulting in rigid hypokinetic parkinsonian state

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oculomotor channel of basal ganglia

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regulation of eye movements; input mainly via body of caudate and output to frontal eye fields and supplementary eye fields of frontal lobes

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prefrontal channel of basal ganglia

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important in cognitive processes involving frontal lobes; input from head of caudate and output reaches prefrontal cortex

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limbic channel of basal ganglia

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ventral pathway through basal ganglia involved in limbic regulation of emotion and motivational drives; inputs from major areas for limbic system and project to nucleus accumbens and other regions of ventral striatum

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two pathways the internal segment of the globus pallidus sends outputs to the thalamus through

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1) ansa lenticularis 2) lenticular fasciculus

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ansa lenticularis path

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looping course ventrally under internal capsule b4 passing dorsally to reach thalamus

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lenticular fasciculus path

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penetrate straight through internal capsule, then pass dorsal to subthalamic nucleus and ventral to zona incerta b4 turning superiorly and laterally to enter thalamus

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zona incerta

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inferior extension of reticular nucleus of the thalamus

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thalamic fasciculus is formed by

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fibers of ansa lenticularis and lenticular fasciculus join together

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H1 field of Forel

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thalamic fasciculus

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H2 field of Forel

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lenticular fasciculus-lies dorsal to subthalamic nucleus

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prerubal field (H field of Forel)

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region where ansa lenticularis and lenticular fasciculus join together

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subthalamic fasciculus

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carries fibers of indirect pathway from external segment of globus pallidus to subthalamic nucleus and from subthalamic nucleus to internal segment of globus pallidus

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movement disorders often refer to

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abnormal movements caused by basal ganglia pathology

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spasticity

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slow, clumsy, stiff movements and hyperreflexia resulting from corticospinal, upper motor neuron lesions

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ataxia

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irregular, uncoordinated movements caused by lesions of cerebellar circuitry

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dyskinesia

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abnormal movements caused by basal ganglia dysfunction; means 'abnormal movement'

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conversion disorder and abnormal movements

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occasionally occurs; psychological condition

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basal ganglia disorders often reffered to as

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extrapyrimidal syndromes (due to historical misguidance)

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unilateral movement disorders caused by focal basal ganglia lesions like infarct, hemorrhage, abscess, tumor or degeneration are

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contralateral to basal ganglia lesion

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what movement disorders do not cease during sleep

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palatal myoclonus and some tic disorders; although some aspects may persist

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bradykinesia vs hypokinesia

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slowed vs decreased amount of movement; terms only used for lesions higher than upper motor neurons

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what can cause bradykinesia

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increased inhibitory basal ganglia outflow to thalamus; loss of fxn of dopaminergic nigrostriatal system, loss of inhibitory pathways from striatum to substantia nigra and internal pallidum, or loss of inhibitory neurons projecting from the external pallidum to the subthalamic nucleus; in parkinson's along with hypokinesia

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decrease spontaneous movements without coma can be seen in

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diffuse lesions of frontal lobes, subcortical white matter, thalami, or brainstem reticular formation; psych disorders (advanced schizophrenia and depression)

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rigidity

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increase resistence to passive movement of a limb; often present with bradykinesia or dystonia

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rigidity along with spasiticty (upper motor neuron lesion)

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velocity dependent

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rigidity and corticospinal disorders

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initially increases as muscles stretched, but may then decrease; clasp-knife rigidity

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rigidity and basal ganglia disorders

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more continuous; called plastic, waxy, lead pipe rigidity

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cogwheel rigidity

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ratchetlike interruptions in tone that can be felt as limb bent; seen inparkinsonian disorders

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paratonia or gegenhalten

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actively resist movement of limbs

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dystonia

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assume abnormal, often distorted positions of limbs/trunk/face that are more sustained or slower than in athetosis; generalized, unilateral, or focal

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focal dystonias

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torticollis-neck muscles; blepharospasm-facial muscles around eyes; spasmodic dysphonia-laryngeal muscles; writer's cramp; presumed to be caused by basal ganglia dysfunction

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botulinum toxin MOA

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interferes with presynaptic acetylcholine release at NM jxn

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Primary idiopathic torsion dystonia

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uncommon hereditary disorder causing generalized dystonia

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when are dystonias or faster dyskinesias (athetosis or chorea) commonly seen

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acutely and after long term use of dopaminergic antagonists

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what are often used prophylactically with antipsychotic and anti-emetic dopaminergic antagonists

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antocholinergic medications to prevent tardive dyskinesia

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Wilson's disease

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autosomal recessive disorder of biliary copper excretion; progressive degeneration of liver and basal ganglia; 'wing beating' tremor=arms abducted with elbows flexed; wry smile (risus sardonicus)

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athetosis

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twisting movements of limbs, face, and trunk that sometimes merge with faster choreic movements = choreoathetosis

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chorea

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nearly continuous involuntary movements that have fluid or jerky, constantly varying quality

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major cause of chorea

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huntington's-autosomal dominant

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benign familial chorea

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autosomal dominant; chorea nonprogressive and not accompanied by cognitive or emotional decline

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sydenham's chorea or rheumatic chorea

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rare; onset adolescence, more common in females; 4 months after strep infection dvlp increased fidgetiness and emotional lability; apparent over weeks and gradually declines, but recurs in 1/5

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rheumatic fever and sydenham's

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up to 1/3 with sydenham's dvlp rheumatic fever

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Sydenham's vs lupus

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positive ANA or other positive rheumatilogic blood tests in SLE

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chorea as a side effect is common with

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levodopa use in parkinson's; early/delayed (tardive) in patients taking antipsychotic or anti-emetic meds

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ballismus

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movements of proximal limb muscles with larger-amplitude, more rotary or flinging quality than chorea; hemiballismus most common-contralateral to lesion

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classic cause of ballismus

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lacunar infarct of subthalamic nucleus-leads to decreased pallidal inhibition of thalamus

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what can imprive ballismus

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dopaminergic antagonists like haloperidol

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tics

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sudden brief action preceded by an urge to perform it and is followed by a sense of relief

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Tourette's syndrome

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persistent motor and vocal tics; autosomal dominant with incomplete penetrance; boys>girls; late childhood onset

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myoclonus

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sudden rapid muscular jerk that can be focal, unilateral, or bilateral

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palatal myoclonus

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persistence during sleep, rhythmicity; generally caused by lesions of central tegmental tract (brainstem infarcts can cause)

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asterixis ('lack of fixed position') or flapping tremor

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brief rapid movement that is often seen in toxic or metabolic encephalopathies (hepatic failure=liver flap)

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how does an examiner cause asterixis

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have patient hold out arms straight in front of chest with palms facing forward and wrists extended ('stopping traffic'); positive which brief flexion movements bilaterally as patient attempts to hold pose

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what causes asterixis

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not caused by muscle contractions, but brief interruptions in contraction of wrist extensors

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tremor

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rhythmic or semirhythmic oscillating movements; agonist and antagonist muscles activated resulting in bidirectional movement

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resting tremor

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most prominent when limbs relaxed; important feature of parkinson's; often asymmetric-mostly hands and upper limbs; aka pill-rolling tremor; 3-5 Hz frequency

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postural tremor

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most prominent when limbs actively held in a position and disappears at rest

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essential tremor frequency and what can help it

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5-8 Hz; beta-adrenergic antagonists like propranolol, also alcohol briefly

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intention tremor aka ataxic tremor

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feature of appendicular ataxia associated with cerebellar disorders; occurs as attempt to move limb toward a target-irregular, oscillating movement in multiple planes throughout trajectory; frequency 2-4 Hz

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action tremor

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either postural or intension tremor

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terminal tremor

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tremor increases toward the end of a movement

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rubral tremor

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caused by lesion of superior cerebellar peduncle or other cerebellar circuitry (not red nucleus); frequency 2-4 Hz; low amplitude at rest; MS or brainstem infarcts

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physiologic tremor

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frequency 8-13 Hz; enhanced with caffeine

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Parkinson's specs

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common idiopathic neurodegenerative condition caused by loss od dopaminergic neurons in the substantia nigra pars compacta; charcterized by asymmetrical resting tremen, bradykinesia, rigidity, and postural instability; onset 40-70; generally no familial tendency

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characteristics of remaining dopaminergic neruons in Parkinson's

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often contain Lewy bodies (eosinophilic cytoplasmic inclusions), which contain alpha-synuclein and ubiquitin and have a faint halo

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classic triad of parkinson's

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resting tremor, bradykinesia, and cogwheel rigidity (accompanied by postural instability that causes an unsteady gait)

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masked facies or hypomimia

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decrease in spontaneous blink rate and in facial expression

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hypophonic

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speech is hurried, with muttering quality

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retropulsion

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if pulled back slightly, person takes several steps backward to regain balance or they may fall

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festinating gait

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walk with small shuffling steps

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anteropulsion

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appear continually falling and ahuffling forward

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en bloc turning

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turns are executed without normal twists of the torso

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Myerson's sign

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inability to suppress blinking when center of glabella is tapped repeatedly; seen in neurodegenerative conditions

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dementia and Parkinson's

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not an early feature; later in course 15-40% or higher

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bradyphrenia

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responses to questions are slowed but may be accurate if enough time is allowed

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carbidopa

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decarboxylase inhibitor that cannot cross the blood-brain barrier; inhibits breakdown of lecodopa to dopamine in peripheral tissues

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most common peripheral side effects of dopamine

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GI disturbances and orthostatic hypotension-substantially reduced by carbidopa

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what can help on-off phenomena

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sustained release formulations and catechol O-methyltransferase (COMT) inhibitors

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Parkinson's and thalamus

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decreased dopaminergic input to striatum results in increased inhibition of the thalamus by basal ganglia outputs causing a hypokinetic movement disorder

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what meds can induce parkinsonian signs like rigidity, hypokinesia, and even resting tremor

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antipsychotic and anti-emetic sopaminergic antagonists like haloperidol and prochlorperazine; onset abrupt and symmetrical

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multisystem atropy examples

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striatonigral degeneration, Shy-Drager syndrome, and olivopontocerebellar atrophy; degeneration of striatal neurons projecting to globus pallidus and substantia nigra pars reticulata; insensitive to levodopa therapy

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Shy-Drager syndrome

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marked atrophy of intermediolateral cell colum of spinal cord plus parkinsonism; autonomic disturbances like marked orthostatic hypotension, impotence, and urinary incontinence

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Olivopontocerebellar atrophy

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parkinsonism with ataxia

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Progressive supranuclear palsy (PSP) aka Steele-Richardson-Olszewski syndrome

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degeneration of multiple structures around midbrain-diencephalic jxn (superior colliculus, red nucleus, dentate nucleus, subthalamic nucleus, globis pallidus)

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eye movements and PSP

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vertical eye movement markedly limited (upward and downward saccades) early in illness

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PSP vs Parkinsons

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wide-eyed stare; rigidity early in course and tends to be more proximal (neck not limbs) in PSP

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Dementia with Lewy bodies

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lewy bodies in substantia nigra and throughout cerebral cortex; prominent psychiatric symptoms early-episodic

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cortical basal ganglionic degeneration

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parkinsonism-asymmetric with marked cortical features like apraxia and corticospinal abnormalities

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Machado-Joseph disease and dentatorubropallidoluysian atrophy

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rare; both autosomal dominant via trinucleotide repeats

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Huntington's

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trinucleotide repeat disorder; onset childhood/early adult; autosomal dominant; progressive, choreiform movement, demenia, and psychiatric disturbances

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hallmark of huntington's

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progressive atrophy of striatum, especially caudate nucleus, putamen also involved and nucleus accumbens to a lesser extent

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what can make ventricles appear enlarged in huntington's

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atrophy of caudate and putamen-look for bulge of caudate on walls of lateral ventricles in coronal sections to distinguish from hydrocephalus

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pallidotomy location for parkinsons

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ventral posterior portion of globus pallidus-interupts inhibitory output pathway carried by the ansa lenticularis from medial globus pallidus to ventral lateral nucleus of thalamus (16.7 and 16.9)

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thalamotomy for debilitating tremor location

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posterior portion of ventral lateral nucleus of thalamus; mechanism for improvement unknown