Sensory receptor located at the distal end of a neuron or an associated sensory structure. When stimulated it creates a receptor potential, when that reaches its threshold, it will trigger 1 or more nerve impulses in the sensory neuron.

Yes the sensory receptor is the first element.

the sensory receptors for the eyes are the cornea and the optic nerve

The first order sensory neuron can sometimes be a sensory receptor because it is what sends the signal to the brain from the receptor. The second order goes from the brainstem to the thalamus.

sensory receptor