Chapter 48 - Chapter 48 Neurons Synapses and signaling 1...

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Chapter 48: Neurons, Synapses, and signaling 1) 48.1 Sensory neurons transmit information from eyes and other sensors that detect external stimuli ( light, sound, touch, heat, smell, and taste) or internal conditions ( such as blood pressure, blood carbon dioxide level, and muscle tension). The vast majority of neurons in the brain are interneuron, which make only local connections Motor output relies on neurons that exit the processing centers in bundles called nerves and generate output by triggering muscle or gland activity. Motor neurons transmit signals to muscle cells, causing them to contact Central nervous system ( CNS), which includes the brain and a longitudinal nerve cord. The neurons that carry into and out of the CNS constitutes peripheral nervous system ( PNS). -------------------Neurons structure and function----------------------- Most of the neuron's organelles, including its nucleus, are located in the cell body a typical neuron has numerous dendrites ( greek for tree), highly branched extensions that receive signals from other neurons a neuron also has a signal axon, an extension that transmits signals to other cells The cone- shaped region of an axon where it joins the cell body is called the axon hillock- typically the region where the signals that travel down the axon are generated Each branched end of an axon transmit information to another cell at a junction called a synapse. The part of each axon branch that forms this specialized junction is a synaptic terminal at most synapses, chemical messengers called neurotransmitters pass information from the transmitting neuron to the receiving cell In describing a synapse, we refer to the transmitting neurons as the presynaptic cell and the post synaptic cell. To function normally, the neurons of vertebrates and most invertebrates require supporting cells called glial cells, or glia. Glia may nourish neurons, insulate the axons of neurons, or regulate the extracellular fluid surrounding neurons . Glia outnumbers neurons Page 1049 2) 48.2 : ion pumps and ion channels maintain the resting potential of a neuron all cells have membrane potential- a voltage ( difference in electrical charge ) across their plasma membrane. In neurons, inputs from other neurons or specific stimuli cause changes in this membrane potential that as signals, transmitting and processing information The membrane potential of a resting neuron - one that is not sending signals - is its resting potential ----------------formation of the resting potential-------------------- The concentration gradients of K+ and Na + across the plasma membrane represent a chemical form of potential energy. converting this chemical potential to an electrical potential involves ion channels, pores formed by clusters of specialized proteins that span the membrane. Ion channels allow ions to diffuse back and forth across the membrane
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any resulting net movement of positive or negative charge will generate a voltage, or potential, across the membrane.
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