the nervous system ch 48 and 49 designed to sense an animal’s external environment, initiate a...
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THE NERVOUS SYSTEMCH 48 AND 49
• Designed to sense an animal’s external environment, initiate a response, and return the animal to HOMEOSTASIS
• Involves a series of cell-cell interactions
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I. Nervous systems consist of circuits of neurons and supporting cells
• Single celled organisms can respond to environment
• Most multicelled animals need neurons• Simplest nervous system is in cnidarians,
radially symmetrical animals with nerve net• All bilaterally symmetrical animals have
centralized nervous system
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What is the trend here? Importance?
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II. The vertebrate nervous systemA. Organization of the nervous system • Central nervous system (CNS)– Brain and spine– Where integration takes place
• Peripheral nervous system (PNS)– Neurons that send info to CNS and receive info
from CNS– Sensory neurons: send info to CNS– Motor neurons: receive info from CNS
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B. Neurons • Sensory (afferent) neurons – carry nerve impulses from the sensory receptors to the CNS – sensory receptors are located in: – skin, eyes, ears, mouth, nose
• Motor (efferent) neurons – Carry the nerve impulse from the CNS to effectors – Effectors are muscles and glands
• interneurons– Located in the CNS – link sensory and motor neurons
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Sense receptors send info to sense neurons which send info to interneurons which send info to motor neurons which send info to muscles or glands
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1. Neuron structure and function
• Cell body: contains organelles • Dendrites: short extensions off cell body that
receive signals • Axon: Long extension off of the cell body that
relays the stimulus • synaptic terminal: sends info from one cell to
another thru neurotransmitters• synapse: space between two cells
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• presynaptic cell sends info to postsynaptic cell
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C. How information is sent thru the nervous system
• all cells have a difference in charge on either side of plasma membrane called a membrane potential
• Rest membrane potential: Membrane potential of unstimulated neuron
• Change in resting membrane potential results in transmission of nerve impulse
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What do you notice about the resting membrane potential?
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1. Forming the resting membrane potential
• Uses energy in active transport• [ K+] is highest in cell, [Na+] is highest out • Na+/K+ pumps use NRG of ATP to maintain
these K+ and Na+ gradients across the plasma membrane (active transport: low to high concentration using NRG)
• These concentration gradients represent chemical potential energy
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2. Generating the action potential
• Stimulus from the environment causes the membrane of the nerve cell to depolarize: – Na+ diffuses into the nerve cell – K+ diffuses out
• As soon as this happens, the Na+/K+ pump restores the membrane potential
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3. Propagating the action potential
• The action potential travels down the nerve cell from dendrites to axon in a wave of depolarization and restoration of the membrane potential
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http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter8/animation__the_nerve_impulse.html http://www.blackwellpublishing.com/matthews/actionp.html http://wps.aw.com/bc_campbell_biology_8ap/
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D. How the nerve impulse moves from one cell to another
• The space between two nerve cells is called a synapse
• Two nerves communicate with each other by synaptic signaling
• How: – When the action potential reaches the end of the
axon, it stimulates the release of neurotransmitters into the synapse
– The neurotransmitters bind to receptors on the postsynaptic cell to transmit the nerve impulse
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http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter8/animation__chemical_synapse__quiz_2_.html
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E. What are neurotransmitters?
• Small molecules stored in vesicles in the presynaptic neuron
• Most are made in RER and golgi
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• Types:– Dopamine: the “reward” neurotransmitter,
cocaine and meth increase dopamine release– Serotonin: the “feel good” neurotransmitter.
MDMA either increases or prevents degradation of serotonin. Low serotonin is associated with depression
– Acetylcholine: involved in muscle contraction. Broken down by acetylcholinesterase to control muscle contraction
• http://www.youtube.com/watch?v=UabDiuTtU0M&list=PLFCE4D99C4124A27A&index=50