66 Can you give a definition of homeostasis? If you can t, look for information about it on the web. There are 100 billion neurons in a human brain and up to 10,000 connections, more than the most advanced computer chip. Neurotransmitters travel unimaginably fast; in fact, they transmit information to their target cells within one millisecond. Information transmitted via the endocrine system is much slower. ONLINE RESOURCES Neurodegenerative disorders THE NERVOUS AND ENDOCRINE SYSTEMS The nervous and the endocrine systems control all body cells and are primarily responsible for maintaining homeostasis in the body; both transmit information from one part of the body to another, but in different ways. the autonomic nervous system, which controls the nerves of internal body organs over which humans have no conscious control, like heartbeat, digestion, and unconscious breathing. The nervous system The nervous system transmits information very quickly both electrically and chemically from a neuron (nerve cell) in one part of the body to another using neurotransmitters . The nervous system is also responsible for external and internal changes (stimuli) and helps the body to adapt to new conditions. It can be divided into: The endocrine system The endocrine system is a network of glands and organs that produce hormones. Hormones are chemicals that travel via the bloodstream throughout the body , where they bind to receptors on target cells and induce a certain response. Endocrine glands are responsible for almost every cell, organ, and function of the body, and they help control many body functions, including growth and development, metabolism, and fertility. They even transmit information about injuries, stress, and mood. the central nervous system (CNS), which includes the brain and the spinal cord; the peripheral nervous system (PNS), which includes the nerves connecting the brain and the spinal cord to other parts of the body, such as the skin surface and the skeletal muscles. It is divided into two parts: the somatic nervous system, which includes peripheral nerves that pick up sensory information from distant organs, like the limbs, and carry them to the CNS; Main endocrine glands The hypothalamus controls water balance as well as sleep, temperature, appetite, and blood pressure. The pineal gland produces melatonin, which is responsible for sleep. The hypophysis (or pituitary gland) regulates metabolic processes. The thyroid and parathyroid control the body s metabolism and regulate the balance of calcium. The thymus produces white blood cells. The pancreas makes the hormone insulin, which helps to control blood sugar levels. The adrenal glands are responsible for blood pressure and regulate metabolism and blood sugar levels. The female ovaries contain the egg cells for reproduction and produce oestrogen and progesterone. The male testes produce testosterone and sperm, necessary for reproduction. to bind: legarsi gland: ghiandola limb: arto spinal cord: midollo spinale 134 SCIENCE AND PHYSICS