Module 1 - Cells

Cells communicate via cell signalling. The three main ways in which animal cells can do this are by; Neurones, hormones and local hormones.

Neurones

• Neurones transmit information electrically over long distances.
• At the end of each neurone is a swelling that contains vesicles of a chemical transmitter substance known as a neurotransmitter.
• When a nerve impulse reaches the end of the neurone, these vesicles travel to the membrane and release molecules of neurotransmitter by exocytosis across the synapse.
• On the next neurone, or on an effector (e.g. muscle cell or gland cell), there are receptor molecules that detect the neurotransmitter molecules.

• Endocrine cells secrete hormones into the bloodstream. Hormones have effects on their target cells, which are the only cells that detect the hormone and respond to it.
• Receptor molecules on the cell surface or inside the cell combine with the hormone, triggering a series of events inside the cell leading to the cell's response.

• Some cells release molecules that travel short distances to adjoining cells. examples of these local hormones are histamine and cytokines.
• During an immune response, some lymphocytes release cytokines that stimulate other lymphocytes to divide by mitosis and secrete antibodies.
• Cytokines also stimulate phagocytes to become more active.
• The hormones insulin and glucagon do not cross cell membranes to divide as they are large, water-soluble molecules. - So therefore, glycoprotein receptor molecules on the cell surface detect insulin.
• Steroids e.g. testosterone are fat-soluble, so they can cross phospholipid bilayers and interact with receptors inside cells.
• Many drugs are made to have a shape complementary to receptor molecules.
• Agonists - mimic the effect of the signalling molecule.
• Antagonists - block receptors to stop the signalling molecule having any effect.