basal ganglia
parkinson's disease
degenerative disorder of the cns; degeneration of the dopaminergic neurons in the substantia nigra; affects substantia nigra pars compacta, dopaminergic pathway; cause: unknown, some genetic links
huntington's disease
features: chorea, gradually worsening dementia and personality changes; affects: striatum; caudate nucleus; medium spiny neurons; cause: inherited; short arm of chromosome 4
athetosis "without position"
features: slow, writhing movements, most pronounced in the hands and fingers; affects: striatum; cause: lesions of striatum
hemiballismus "jumping about"
features: wild flailing movements of one arm and leg; affects: sub thalamic nucleus; cause: older people, stroke; small ganglionic branch of the posterior cerebral artery
what are hyperkinetic disorders?
huntington's disease; athetosis; hemiballismus
major connections of the external segment of the globes pallidus (GPe)
nucleus: GPe; input: striatum, subthalamic nuclei; output: wide spread, inhibitory to most basal ganglia including striatum, GPi and subthalamic nucleus; output is inhibitory
major afferents to and efferents from the internal segment of the globes pallidus (GPi)
nucleus: GPi; input: striatum, subthalamic nuclei, GPe; output: thalamus; output is inhibitory
connections of SNr
nucleus: SNr; input: striatum, sub thalamic nuclei, GPe; output: thalamus; output is inhibitory
major connections of the striatum
nucleus: striatum; input: cerebral cortex, substantia nigra and thalamus; output: globus pallidus (GPi and GPe) and the substantia nigra (SNr and SNc); output is inhibitory
connections of substantial nigra pars compacta (SNc)
nucleus: striatum; input: striatum; output: widespread; esp to striatum; output is modulatory
major connection of the subthalamic nucleus (STN)
nucleus: sub thalamic nuclei; input: GPe and cortex; output: GPi and SNr; output is excitatory
what are hypokinetic disorders?
parkinson's disease
what are the components of the lentiform nucleus?
putamen; globus pallidus (pallidum): external segment (GPe), internal segment (GPi);
what is the function of the basal ganglia?
role in motor control: initiates movements and stops any unwanted/unneeded movements; "brake hypothesis" - To sit still, you must put the brakes on all movements except those reflexes that maintain an upright posture. To move, you must apply a brake to some postural reflexes, and release the brake on voluntary movement.
what are other components of basal ganglia?
sub thalamic nuclei; substantia nigra (pars compacta (SNc) and pars reticulata (SNr))
describe parallel loops
1. association cortex > caudate > globus pallidus > DM (thalamus) > association cortex; 2. sensorimotor cortex > putamen > globus pallidus > VA/VL (thalamus) > sensorimotor cortex; 3. limbic cortex > nucleus accumbens > ventral pallidum > DM (thalamus) > limbic cortex; these loops all run parallel to each other
what are the components of the striatum?
caudate nucleus; nucleus accumbens; putamen
basal ganglia connectivity: normal
inputs: striatum, subthalamic nuclei; outputs: substantia nigra pars reticulata (SNr), globus pallidus interna (GPi); overall 2 pathways: direct (disinhibition of the thalamus): cortex > striatum > GPi > thalamus > cortex; indirect (inhibition of the thalamus): cortex > striatum > GP3 > STN > GPi > thalamus > cortex; figure: Connectivity diagram showing excitatory glutamatergic pathways as red, inhibitory GABAergic pathways as blue, and modulatory dopaminergic as magenta. Internal globus pallidus (GPi), external globus pallidus (GPe), substantia nigra pars reticulata (SNr), substantia nigra pars compacta (SNc), subthalamic nucleus (STN)
circuitry of basal ganglia
involves multiple parallel loops that modulate cortical output; interconnections of the basal ganglia determine the pattern of their outputs, principal inputs to and outputs from the basal ganglia
what is the tx for parkinson's disease?
loss of dopaminergic neurons in PD: A major target for symptomatic therapy; - Levodopa (l-dopa); - Carbidopap - Levodopa + carbidopa (Sinemet®)p - Dopamine (D2) agonist - Selective MAO-B inhibitor Drug: Selegiline (Eldepryl®)
anatomy of the basal ganglia
masses of gray matter within cerebral hemispheres; called the cerebral nuclei and basal nuclei; they lie within each hemisphere inferior to the floor of the lateral ventricle; they are embedded within the central white matter; radiating projection and commissural fibers travel around or between nuclei
what is the role of SNc on the direct and indirect pathways?
modulatory (dopamine) function via actions on direct and indirect pathways; SNc inhibits the indirect pathway and excites the direct pathway giving an overall net result of movement
what are the clinical features of parkinson's disease?
tremor, rigidity, bradykinesia, anteroflexed posture, postural instability, freezing/festiniating gait, poor balance, falls;
basal ganglia connectivity: pathological
with disease
