Neuroanatomy and Neuroscience at a Glance by Roger A. Barker

Author:Roger A. Barker
Language: eng
Format: epub
Published: 2017-07-29T00:00:00+00:00

Did you know?

Marijuana has actions at many sites in the central nervous system, and this includes the basal ganglia as they have high levels of the receptors for the active ingredient δ-9-tetrahydrocannabinol. Chronic use of this drug can cause long-term changes to the brain including the basal ganglia.

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Basal ganglia: diseases and their treatments

Parkinson’s disease

Parkinson’s disease is a degenerative disorder that typically affects people in the sixth and seventh decades of life. The primary pathological event is the loss of the dopaminergic nigrostriatal tract, with the formation of characteristic histological inclusion bodies, known as Lewy bodies. In the vast majority of cases the disease develops for reasons that are not clear (idiopathic Parkinson’s disease; see Chapter 60). However, in some cases clear aetiological agents are identified, such as vascular lesions in the region of the nigrostriatal pathway, administration of the antidopaminergic drugs in schizophrenia (see Chapter 58) or genetic abnormalities in young patients and some rare families.

Fifty to 60% of the dopaminergic nigrostriatal neurones need to be lost before the classic clinical features of idiopathic Parkinson’s disease are clearly manifest: slowness to move (bradykinesia); increased tone in the muscles (cogwheel rigidity); and rest tremor. However, most patients also display a range of cognitive, affective and autonomic abnormalities, which relates to pathological changes at other sites.

Neurophysiologically, these patients have increased activity of the neurones in the internal segment of the globus pallidus (GPi) with a disturbed pattern of discharge, which results from increased activity in the subthalamic nucleus (STN) secondary to the loss of the predominantly inhibitory dopaminergic input to the neostriatum (NS). The increased inhibitory output from the GPi and substantia nigra pars reticulata (SNr) to the ventroanterior–ventrolateral nuclei of the thalamus (VA–VL) results in reduced activation of the supplementary motor area (SMA) and other adjacent cortical areas. Thus, patients with Parkinson’s disease are unable to initiate movement because of their failure to activate the SMA.

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