What many of us might regard as ‘simple’ actions or movements (such as reaching out for an object or taking a step) actually involve intricate and complex interactions of the central nervous system and skeletal muscle.
Different brain regions are responsible for a variety of roles in movement. For example, situated behind the brainstem at the back of the skull, the cerebellum is understood to interact with the spinal cord and frontal lobes to guide balance, posture and motor skill learning. Containing the caudate nucleus, putamen and globus pallidus, the basal ganglia are subcortical structures which also interact with the frontal lobes and are involved in the control of voluntary movement. It is damage to this area in particular that most commonly gives rise to a variety of motor dysfunctions described as extrapyramidal disorders, characterised by either excessive or restricted movement.
Excessive and rapid involuntary movement (or hyerkinesia) is a prominent feature of Huntington’s disease. A rare and inherited degenerative motor disorder, patients with HD exhibit jerky, dance-like (choreiform) movements which they are unable to control. A significant loss of neurons is found in the globus pallidus whilst reduced glucose metabolism is evident in the caudate nucleus.
In contrast to HD, Parkinson’s disease is characterised by akinesia, a generalised reduction in - or lack of - movement. Also characteristic of PD is rigidity and tremor at rest. Patients with PD are found to have depleted levels of dopamine in the caudate nucleus, putamen, substantia nigra and globus pallidus.
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