Final answer:
Postural tonus is the muscle's continuous and passive partial contraction that helps maintain posture. It is affected by the balance between autonomic inputs, integrity of the reticulospinal tract, and cerebellar function.
Step-by-step explanation:
Postural tonus, often referred to simply as muscle tone, is the continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state. It helps maintain posture and is governed by the brain, which sends electrical impulses to various muscle groups to control posture through alternate contraction and relaxation. These impulses are necessary to ensure no single muscle group becomes overly fatigued. When the muscle tone is disrupted, either by being too low (hypotonia) or too high (hypertonia), it can lead to various functional impairments and may be indicative of underlying neurological issues.
Factors that impact postural tonus include the balance between autonomic inputs (sympathetic and parasympathetic divisions), the integrity of the reticulospinal tract and extrapyramidal connections involving the brain stem and spinal cord, as well as the coordinated activity of the spinocerebellum and vestibulocerebellum, which are essential for maintaining balance and posture.