Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Achalasia ?
    ### Response:
    What causes achalasia? The lower esophageal sphincter, the ring-shaped muscle at the bottom of the esophagus, normally relaxes during swallowing. In people with achalasia, this muscle ring does not relax as well. The reason for this problem is damage to the nerves of the esophagus.
    