Which of the following statements is not correct?

An action potential in an axon does not move backward because the segment behind is in a refractory phase.

Depolarisation of hair cells of cochlea results in the opening of the mechanically gated potassium-ion channels.

Rods are very sensitive and contribute to daylight vision.

In the knee-jerk reflex, stimulus is the stretching of muscle and response is its contraction.