A motor action is a result of an interaction between cognitive, motor, and sensory processes. Volitional actions, in turn, arise schematically from a completed motor sequence. If, for example, paralysis occurs in a person or if his movements are uncontrolled, the voluntary motor action is disturbed. This is not due to damaged muscles, but to injury to the nerves.
What is voluntary motor function?
Volitional motor function is the movement of the body that is controlled by the will or consciousness. Volitional motor activity is the movement of the body that is controlled by the will or consciousness. This process takes place in the primary motor cortex, more specifically in the pyramidal system, which is located in the cerebral cortex and has the shape of a pyramid due to the fiber connections that run there. All the converging projections of the neurons and the central motor neurons form the skeletal muscles. In these association regions of the cerebrum the plan of a voluntary motor activity is formed. Here the movements are prepared, which are necessary for the execution. To be able to imagine the movement and execution, the supplementary motor area is needed. The movement plan is controlled by the cerebellum and the basal ganglia. The information passes through the thalamus and enters the motor cortex, where it then reaches the second motor neuron as impulses via the pyramidal tracts and extrapyramidal tracts, initiating muscle movement. The upper motor neuron is responsible for the voluntary motor activity, which also controls posture. All volitional actions are coordinated sequences of movements that are quite precise. For example, if a person moves his fingers, this occurs as voluntary motor activity via the pyramidal pathway, in order to subsequently perform a specific action corresponding to the will.
Function and task
Volitional motor activity is based on will movement, which is dependent on a situation and which can also take a different course. Will actions, in turn, are based on motives, intentions to act, goals, the decision or impulse of will, the planning of movement, the execution of action, the perception of it, and the evaluation of what has been achieved. The whole process happens arbitrarily, as it is determined by deliberation and decision possibilities. In contrast to this are the involuntary movements, which are mostly pure reflexes or simply unconsciously executed habitual actions. Reflexes are much more stereotyped reactions to stimuli. They proceed without consciousness. An example is the pupillary reflex. In contrast, the memorized action in voluntary movements improves through experience, whereas the reflex is not subject to change. Volitional motor actions do not arise from necessity, whereas reflexes are always stimulus responses and are generated by the central nervous system. The pyramidal system, in turn, can control the information content of stimuli without triggering a movement. In volitional actions, a distinction is made between intentions that lead to an action and those that proceed during one. These actions are strongly impaired by neuronal damage or fail completely. This in turn happens, for example, during a sleep attack. The seat of the will is the prefrontal cortex. It plays a crucial role in all decisions and movements. Impulses are made via the parietal lobe region, which controls all sensory information, as well as attention, memory and orientation in space. All motor memories are stored there. In this process, voluntary motor activity depends on complex neural control conditions of different brain regions.
Diseases and disorders
Many of the stimulations via the motor cortex activate different muscles simultaneously. External areas activate proximal muscles, and central areas activate both these and distal muscles. This results in complex movements that no longer interact with each other when disrupted. For example, if the pyramidal system is damaged, paralysis and failure of voluntary motor function may occur. A distinction is made between defects in the first or second neuron. In case of a disorder in the pyramidal system, the extrapyramidal one first takes over the control of some functions, therefore the paralysis does not have to be complete. Most often, in such conditions, voluntary and fine motor functions are disturbed. Not only the pathways in the pyramidal system are inhibited, but also others are affected.Neurological symptoms are then degenerating reflexes, including e.g. the Babinski reflex. Epilepsy can also trigger muscle twitches that follow the somatotopy of the motor cortex. In medicine, these neurological symptoms are called pyramidal pathway signs. This results in very specific reflexes in the extremities, which have different names. Disorders in the extrapyramidal system, in turn, trigger even more serious diseases. By “extrapyramidal” movement is always meant conditions in which the movement sequences are either not controlled by the pyramidal pathway or run outside of it. Voluntary motor activity occurs via both pyramidal and extrapyramidal pathways. Lesions result in movement disorders that are neurological or genetic. This results in diseases such as Parkinson’s or Huntington’s chorea. Diseases of this type disrupt muscle tone as lesions occur in the primitive subcortical nuclei. This results in abnormal or involuntary movements. Parkinson’s disease is a disorder of voluntary motor function and becomes a slow-moving, degenerative disease. Its symptoms mostly appear in old age. It causes hypokinetic movement disorders, which are based on the overactivity of the output nuclei. Inhibitions are then caused in the thalamus, and transmission to the various projection pathways then no longer takes place. Under these conditions, facial expressions are lost and arms and legs twitch uncontrollably. Also, disorders of consciousness or speech are manifestations of impaired voluntary motor activity associated with defective activity of the ascending reticular activating system.
