sensorimotor impairments basal ganglia

what is the direct pathway?

focused selection of desired movement: disinhibition to thalamus

GOOOOOO!

what is the indirect pathway?

• inhibition of competing movement: strong inhibition to thalamus

• STOP the movement

what is the the nigrostriatal projections pathway?

modulation of the direct and indirect pathway to facilitate movement via dopamine release

what is D1?

to excite the direct pathway to facilitate movement via dopamine release

D1: DIRECT: EXCITE

what is D2?

inhibit the indirect pathway to facilitate movement via dopamine release

what is the primary neurotransmitter effected by basal ganglia disorders?

dopamine

what are symptoms of hyperkinetic disorders?

• athetosis

• ballismus

• chorea

• dystonia

what are symptoms of hypokinetic disorders?

TRAP

• tremor at rest

• rigidity

• akinesia/bradykinesia

• postural instability

what are hyperkinetic disorders characterized by?

characterized by an underactive indirect pathway resulting in reduced thalamic inhibition

what is huntington’s disease?

• hyperkinesia

• inherited disorder, appears in 30s or 40s

  • impacts motor, emotional and cognitive functions

what are key symptoms/signs of huntington’s?

• chorea

• irritability, depression, apathy

• attentional and memory deficits

• dementia

what is the mechanism of huntington’s disease?

characterized by loss of striatal in the indirect pathway

what is chorea?

• a sign of huntington’s disease

• irregular, involuntary, unpredictable movements (dance or worm like)

• worsens during voluntary movement

• voluntary movements are slowed and reaction times prolonged

what is hemiballismus?

• hyperkinesia

• violent, involuntary movement of the limbs on one half of the body

what is the cause of hemiballismus?

subthalamic nucleus lesion secondary to stroke

what muscles does hemiballismus impact?

proximal more than distal

when is hemiballismus worse?

worse during voluntary movements

what is the mechanism of hemiballismus?

characterized by lesion to the subthalamic nucleus

what is dystonia?

• hyperkinesia

• prolonged, unvoluntary muscle contraction resulting in abnormal posutes and movements

  • like constant cramps

what are the types of dystonia?

• primary (don’t know why), secondary to a disease

• generalized vs focal

• age of onset

what influences dystonia?

• stress makes it worse

• sleep makes it absent

• sensory tricks

what is the mechanism of dystonia?

• striatal dopamine deficiency?

• genetics - broad, heterogeneous basis

• treatment: botulinum injection

what is tourette syndrome?

• characterized by repetitive motor and vocal tics

what are tics?

involuntary, rapid, sudden movements that occur repeatedly in the same way

what is the diagnosis for tourettes?

multiple motor and one or more vocal tics for 1 year or more

what are tourette’s exacerbated by?

stress, disappear with sleep

what are other symptoms of tourettes"?

obsessions, compulsions and labile mood

what is the tourette/tic mechanism?

• numerous areas implicated both cortically and subcortically

• many genetic components identified that impact neuroveleopment

• reduced histamine production = lessened dopamine sesitivity

what is a hypokinetic disorder characterized by?

it is characterized by an OVERACTIVE indirect pathway which results in excessive thalamic inhibition

what is the mechanism of parkinsons disease?

it is characterized by degeneration of dopaminergic neurons in substantia nigra pars compacta

what are the cardinal features of parkinson disease?

TRAP

what is rest tremor in parkinson disease?

rest tremor only comes out when the patient is relaxed, and starts during movement

what is rigidity in PD?

• increased resistance to PASSIVE movement

• equal in all directions, velocity independent

what is akinesia in PD?

absence or lack of movement

what is bradykinesia in PD?

slowness of movement

what is postural instability in PD?

inability to maintain upright stance

what is the possible mechanism of rest tremor?

abnormal firing of thalamic neurons

what is the possible mechanism for rigidity in PD?

inability to inhibit subcortical stretch reflexes

what are possible mechanisms for bradykinesia and akinesia in PD?

• overactive indirect and underactive direct pathways

• co contraction

• inability to turn off antagonist vs turn on agonist

what are the possible mechanisms for postural instability in PD?

• related to brad/akinesia

• loss of postural reflexes

• visual input and processing

what are basal ganglia? KEY POINT

basal ganglia are collections of nuclei deeep within the brain that are involved in the focused selection of desired movement (direct pathway) and inhibition of competing movements (indirect pathway)

what happens with damage to basal ganglia ? KEY POINT

basal ganglia damage can result in hypokinetic or hyperkinetic movement disorders depending on the location of the lesion and the resulting neuronal firing patterns of the direct and indirect pathway components