Different types of extracellular signal allows cell to respond differently. The signal molecule acts as the primary messenger, bind with the membrane receptor, causing variation of cellular responds.
However, same types of signal molecule, sometimes, bind with differents receptors, triggers different responds. For example,
Nicotinic Ach receptor
It is a kind of ion-channel linked receptor. As the neurotransmitter-Ach binds to the receptor, it allows the Sodium ions to pass through the channel. Consequently, neuronal membrane is depolarised and muscle contraction occur
Muscarinic Ach receptor
<u</u>It is a type of G-protein linked receptor where Ach binds on the surface of the receptor. This activates the alpha subunits of G protein, causing the release of GDP, and binding with GTP. The secondary messenger triggers the potassium ion channel to open, K+ ions flow from the cell to the extracellular matrix. This results in membrane hyperpolarisation. Hence, the membrane will return back to its resting state.
Hardin, Bertoni,Kleinsmith 2010. Becker's World of the Cell Eighth Edition.p386