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The Two Messenger Services of the Brain 1.Neurons (Nervous System) 2. Endocrine System What is a nerve? Bundles of neuron (axon and dendrites) fibers Can be seen by the unaided eye Can rejuvenate themselves is injured such as a severed finger. ( In fact you can expect feeling to return at a rate of about 1 millimeter a day!!!) The Nerves Nerves consist of neural “cables” containing many axons. They are part of the peripheral nervous system and connect muscles, glands, and sense organs to the central nervous system. What is a Neuron? Neurons are single cells in the nervous system They can NOT be replaced so they must last a lifetime!! If the body of a neuron dies, the whole cell will die (such as in polio) Each neuron has an axon, a cell body and dendrites. Spaces between neurons are called synapses. Parts of a Neuron Cell Body: Life support center of the neuron. Dendrites: Branching extensions at the cell body. Receive messages from other neurons. Axon: Long single extension of a neuron, covered with myelin [MY-uh-lin] sheath to insulate and speed up messages through neurons. Terminal Branches of axon: Branched endings of an axon that transmit messages to other neurons. What is a neurotransmitter? Any of a number of chemicals secreted by the NEURONS; which cross the synapse and alter activity in the receiving neuron Among the most important chemical messengers are adrenaline, histamine and various amino acids Neurotransmitters Neurotransmitters (chemicals) released from the sending neuron travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing it to generate an action potential. Lock & Key Mechanism Neurotransmitters bind to the receptors of the receiving neuron in a key-lock mechanism. Neurotransmitters The Nervous System Nervous System: Consists of all the nerve cells. It is the body’s speedy, electrochemical communication system. Central Nervous System (CNS): the brain and spinal cord. Peripheral Nervous System (PNS): the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body. Why is the spinal cord important? It connects the brain to all other parts of the body It along with the brain make up the CENTRAL NERVOUS SYSTEM Nerves which connect to the spinal cord are part of the Peripheral Nervous System The Nervous System What is the Endocrine System? Made up of a number of glands that pour chemicals into the bloodstream called Hormones It is the second messenger system in the body The Endocrine System The Endocrine System is the body’s “slow” chemical communication system. Communication is carried out by hormones synthesized by a set of glands. What are Hormones? Chemicals related to neurotransmitters. Like transmitters, hormones activate nerve cells Hormones Hormones are chemicals synthesized by the endocrine glands that are secreted in the bloodstream. Hormones affect the brain and many other tissues of the body. For example, epinephrine (adrenaline) increases heart rate, blood pressure, blood sugar and feelings of excitement during emergency situations. What are the major glands? Pituitary- (the master gland) controls the other glands through growth hormones Adrenal- adds adrenaline for emergencies Thyroid- controls metabolism Pancreas- helps fight infection Gonads (for both genders) –activated at puberty Pituitary Gland Is called the “master gland.” The anterior pituitary lobe releases hormones that regulate other glands. The posterior lobe regulates water and salt balance. Thyroid & Parathyroid Glands Regulate metabolic and calcium rate. Adrenal Glands Adrenal glands consist of the adrenal medulla and the cortex. The medulla secretes hormones (epinephrine and norepinephrine) during stressful and emotional situations, while the adrenal cortex regulates salt and carbohydrate metabolism. Gonads Sex glands are located in different places in men and women. They regulate bodily development and maintain reproductive organs in adults. What happens if the pituitary gland malfunctions? Too little growth hormone can cause dwarfism Too much growth hormone can cause giantism