Lower motor neurons are nerves that live outside the spinal cord or brain. These are the nerves that the upper motor neurons connect to.
When a lower motor neuron is damaged (e.g. a spinal cord injury below T12), the messages that would normally pass through the neuron aren’t able to connect to the muscles that they control.
Damage to the lower motor neurons mean that reflexes no longer work. This is because the messages that normally tell the spinal cord to make a reflex happen can’t get through the damaged nerve, and the reflex doesn’t happen.
A lower motor neuron lesion usually results in what’s called a flaccid bladder.
A flaccid bladder means that the bladder doesn’t respond as it fills up. The brain isn’t aware that the bladder is full and the bladder doesn’t try to empty itself like in the case of a reflex bladder.