Atony

Atony is a loss or absence of normal muscle tone in skeletal or smooth muscle. Its effects depend on the affected muscles and underlying cause.

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Muscle tone: The continuous, low-level tension present in resting muscles. Atony is the loss or marked reduction of this resting tension.
Uterine atony: Failure of the uterus to contract effectively after childbirth. This is a specific form of smooth-muscle atony and a major cause of postpartum hemorrhage.
Muscle contraction: The generation of tension by muscle fibers, with or without a change in length. Atony describes diminished baseline tension, not simply the absence of every contraction.
Hypotonia: Abnormally low muscle tone, often assessed through resistance to passive movement. Hypotonia is a clinical finding that may be mild or partial, while atony denotes absent or near-absent tone.
Neuromuscular junction: The synapse where a motor neuron communicates with a skeletal muscle fiber. Disrupted signaling here can prevent skeletal muscles from maintaining normal tone.
Postpartum hemorrhage: Excessive bleeding after childbirth, commonly defined by blood loss or signs of circulatory compromise. Uterine atony is its leading cause worldwide.
Muscle strength: The maximum force a muscle or group of muscles can produce. Strength and tone are separate properties; weakness may accompany atony but is not its definition.
Atonic seizure: A seizure causing sudden loss of muscle tone, sometimes resulting in a fall. Despite the shared word, this is a brief seizure event rather than persistent muscle atony.
Lower motor neuron: A neuron that carries signals from the brainstem or spinal cord to skeletal muscle. Damage can reduce muscle activation and produce flaccid weakness or atony.
Atonic colon: Impaired colonic muscle activity that can cause severe constipation or fecal retention. It shows how reduced smooth-muscle activity can disrupt bowel function.