Brain and quality of experience are important; for example, there is substantial evidence that animals raised in enriched environments have thicker cerebral cortices, indicating a higher density of synaptic connections, than animals whose levels of stimulation are restricted. The functions of the brain depend on the ability of neurons to transmit electrochemical signals to other cells, and their ability to respond appropriately to electrochemical signals received from other cells. The electrical properties of neurons are controlled by a wide variety of biochemical and metabolic processes, most notably the interactions between neurotransmitters and receptors that take place at synapses. Neurotransmitters are chemicals
Electrical conduction system of the heart Electrical conduction system of the heart The electrical conduction system of the heart transmits signals generated usually by the sinoatrial node to cause contraction of the heart muscle. The pacemaking signal generated in the sinoatrial node travels through the right atrium to the atrioventricular node, along the Bundle of His and through bundle branches to cause contraction of the heart muscle. This signal stimulates contraction first of the right and left atrium, and then the right and left ventricles. This process allows blood to be pumped throughout the body. The conduction system consists of specialised heart muscle cells, and is