ECOL 182 Nervous System Slides 2011

ECOL 182 Nervous System Slides 2011 -...

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Neurons and the nervous system
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Human development from infancy to adulthood involves dramatic  anatomical and physiological changes. In addition, our daily lives involve complex physiological and  behavioral responses to various stimuli. The question that we wish to address is: how are these anatomical,  physiological, and behavioral changes and responses  regulated  or  controlled?
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Regulation requires information. In humans, information is encoded as  electrical  signals in the  nervous  system and as  chemical  signals in the  endocrine   system. We begin by discussing the mechanisms by which electrical signals  are generated and propagated through the nervous system. In other words, we focus on the details of how the nervous system  works at the cellular level.
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The principal cells of the nervous system are  neurons . A key feature of neurons is that their plasma membranes can generate  and propagate electrical signals. As illustrated in Figure 44.3, neurons have four regions: the cell  body, dendrites, axon, and axon terminals.
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Cell body contains nucleus and most of the organelles Dendrites are bush-like projections that bring information  from other neurons.  Axons carry info away
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Glial cells: *nutrient suppliers *maintain ionic environment *do not generate action potentials
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Where an axon terminal comes close to another cell, the membranes of  both cells are modified to form a synapse. As we’ll see later, information transfer across the synapse usually  involves chemical signals. The human brain may contain 100 billion neurons, and each neuron  may make synapses with 1,000 or more other neurons.  This large  number of synapses helps to explain the brain’s exceptional ability to  process complex information.
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Ion pumps and channels The plasma membrane of a neuron contains protein molecules that act  as  pumps  to move ions against their concentration gradients. The key pump is the sodium-potassium pump, which moves sodium  (Na + ) ions from inside to outside the neuron, and moves potassium  (K + ) ions from outside to inside. The pump expels about 3 Na +  ions for every 2 K +  ions that it brings  in.
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channels  allowing ions to pass through by diffusion. The channels are selective, in that they may allow only a single type  of ion to pass through by diffusion. Some channels are always open.
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ECOL 182 Nervous System Slides 2011 -...

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