Final answer:
Bell's palsy, also known as peripheral facial palsy, is the clinical syndrome associated with a lower motor neurone facial nerve lesion, resulting in flaccid paralysis on one side of the face. It involves symptoms such as muscle weakness, fibrillation, and fasciculation, with a lack of muscle tone and reflexes.
Step-by-step explanation:
The clinical syndrome called when there is a lower motor neurone (LMN) facial nerve lesion is commonly referred to as Bell's palsy or peripheral facial palsy. This condition results in flaccid paralysis of the muscles on one side of the face, where affected individuals will experience a sudden weakness or paralysis, leading to drooping of the mouth, inability to close the eye, and a smooth or flattened forehead and eyebrow due to loss of muscle tone. This is in contrast to upper motor neuron (UMN) lesions, which may result in spastic paralysis but preserve some reflexes and muscle tone.
Lower motor neuron lesions can lead to several signs, such as muscle weakness, fibrillation, fasciculation, and decreased or lost reflexes due to the denervation of muscle fibers. In cases where muscle tone is retained, but voluntary movement is not possible, an upper motor neuron lesion is more likely implicated. However, in LMN lesions, there is often a complete lack of muscle tone leading to the presentation of flaccid paralysis.