eli5: why when your ears get cold and blood flow is slower you can’t feel them but can still hear
The part of the ear that helps in processing the hearing is inside the head. The outside ear helps to direct sound waves inside the ear and so the skin and nerves on the outside ear that gets cold are in a different spot than inside the ear where it is much warmer where the nerves and ear drums are sending signals to the brain.
The sensation of feeling your ears is due to the nerves in your skin sending signals to your brain, which interpret the signals as touch. When your ears get cold, the blood vessels in the skin constrict, reducing the amount of blood flow to the area. This reduces the amount of signals sent to the brain, so you can’t feel your ears, even though you can still hear.
Because your external ears are not really your ears at all. They are just flaps of skin and connective tissue. They help a little bit in that they direct sound into your actual ear, but that is it.
The bones in your middle ear vibrate and carry sound into your cochlea in your inner ear. It is in that organ that hairs vibrate and trigger the neurons that actually ultimately lead to your brain and calls you to hear things.
Even when your external ears are frozen solid or completely missing, you can still hear fairly well because all of the actual work is being done well inside your skull.