5. Movement disorders

Movement disorder usually arises from damage to the central nervous system. It is commonly a result from degeneration of neurons in deep, subcortical structures, others from lesions to the cortex itself.
The subcortical structures most involved in motor dysfunction are the basal ganglia, which is a collection of structures in the forebrain.
Excessive or restricted motor activity are common symptoms of basal ganglia disporders which can also be known as extrapyramidal disoders.
The sensory motor transformation is the need to invoke a spatial reference frame that contains both information about the position of the body in space and the position of the object in space, in order to act towards an object. Complex behaviours, however, involve several motor and sensory areas.

The prefrontal cortex is part of the frontal lobe and lies in front of the premotor regions. It is involved in higher cognitive functions rather than action, whereas, the premotor cortex is involved in preparation for actions to internal and external events. The premotor cortex can be divided in to the lateral premotor cortex and the supplementary motor area.

NOTES

• Milner and Goodale suggest that there are two vision systems : visual perception and visuomotor control.
• as visual information exists two the occipital lobe, it follows two main neural streams : the ventral stream (associated with object recognition and form representation) and the dorsal stream, also known as the parietal stream (associated with where objects are in space).
• The dorsal stream ends in the posterior parietal cortex, and is the evolutionary older of the two cortical pathways.
• The Ventral stream ends in the inferotemporal cortex,and is the evolutionary newer of the two cortical pathways.
• There are two main subcortical loops involved in movement generation: The cerebellar loop and the Basil Ganglia loop.
• The cerebellar loop cooridnates timing of movement using sensory and motor information.
• The basil ganglia loop regulates the excitability of frontal motor structures.
• There are several extrapyrimidal disorders: Parkinson's disease, Huntington's disease, Sydenham's chorea, Dyskinesia, Gilles de la Tourette, Wilson's disease, Myoclonus, Ataxia and Apraxia.
• Parkinson's disease is a motor disorder characterized by a loss of movement (akinesia), resisiting passive movement (rigidity) and tremor at rest.
• Huntington's disease is an inherited motor disorder characterized by involuntary movements.
• Gilles de la Tourette syndrome describes motor and phonic tics that occur despite otherwise nomal motor behaviour.
• Apraxia is a motor disorder involving an inability to make voluntary actions to verbal commands. There are several types of Apraxia.