_______ is defined as pressure disturbances, alternating areas of high and low pressure, which are produced by vibrating objects and propagated by air molecules. 

_______ are the long-distance chemical signals used by the endocrine system which can travel through either the blood or the  _______ to target cells. 

When light hyperpolarizes photoreceptors, what inhibitory neurotransmitter do they stop releasing? 

Visual pigments are differentiated based on the identity of what protein? 

What type of chemical messengers are locally acting and affect cells other than those which secrete them? 

The nervous system can adjust or override normal endocrine controls, for example when a person is under stress, the hypothalamus and sympathetic division can override the activities of insulin which allows blood glucose levels to increase. 

The hypothalamus contains  _______ which monitor solute concentration within the body. 

How does light react when passing through a convex lens? 

_______ is the key light-absorbing pigment.

What is it called when more than one hormone produces the same effects on a target cell?