Final answer:
Tonus, or muscle tone, is the continuous and passive partial contraction of muscles, maintaining them in a state of readiness. Complete bed rest can lead to hypotonia, where muscles become flaccid and weak due to lack of regular stimulation and activity. Excessive muscle tone is known as hypertonia and indicates damage to motor neurons in the CNS.
Step-by-step explanation:
In a medical context, tonus, or muscle tone, refers to the continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state. It is the result of a complex interaction between the nervous system and skeletal muscles, involving cyclical activation of motor units, which prevents complete muscle fatigue.
Complete bed rest can significantly impact muscle tonus. When muscles are not regularly engaged in activity, they can lose their tone—a condition known as hypotonia. Hypotonic muscles appear flaccid and can display functional impairments like weak reflexes. This is because the usual stimulation to the muscles via motor neurons is reduced or absent, leading to a decline in muscle strength and function. Conversely, excessive muscle tone is known as hypertonia, characterized by conditions such as rigidity or spasticity and often indicates damage to motor neurons in the central nervous system.