Final answer:
Hypotonia is a decrease or absence of muscle tone leading to flaccid muscles and weak reflexes. Spasticity is a type of hypertonia with increased muscle contraction in response to stretch, causing limbs to 'snap' back after being passively moved.
Step-by-step explanation:
The terms hypotonia and spasticity relate to muscle tone, which is the resistance of muscle to passive stretch or its resting tension. Hypotonia is characterized by a reduction or absence of muscle tone, making muscles appear flaccid. It can stem from damage to the CNS such as the cerebellum, or loss of innervations to skeletal muscle, as seen in poliomyelitis. Weak reflexes are also a common feature of hypotonia.
In contrast, spasticity is a type of hypertonia where there's excessive muscle tone. It's a condition marked by an increased muscle contraction in response to stretch and is often associated with hyperflexia. Spasticity usually occurs from damage to the upper motor neurons in the CNS, as in certain strokes, and can present as a limb that resists passive stretching then 'snaps' back.