I cdnuolt blveiee that I cluod aulaclty uesdnatnrd what I was rdanieg The phaonmneal pweor of the hmuan mnid is icrebdinle. Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn’t mttaer in what odrer the ltteers in a wrod are, the only iprmoatnt thing is that the frist and lsat ltteer be in the rghit pclae. The rset can be a ttaol mses and you can still raed it wouthit a porbelm. This is bcuseae the hmuan mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Amzanig huh? Yaeh and I awlyas thought slpeling was ipmorantt! © 2016 Pearson Education, Inc.

Introduction to Information Processing Nervous systems process information in three stages Sensory input Integration Motor output © 2016 Pearson Education, Inc.

Siphon Sensory input Integration Sensor Motor output Processing center Figure 37.4 Siphon Sensory input Integration Sensor Motor output Proboscis Figure 37.4 Summary of information processing Processing center Effector © 2016 Pearson Education, Inc.

Sensory neurons transmit information about external stimuli or internal conditions (usually PNS) This information is sent to the processing center (usually CNS), where interneurons integrate (analyze and interpret) the sensory input Neurons that extend out of the processing centers trigger muscle or gland activity to elicit response. (usually PNS) For example, motor neurons transmit signals to muscle cells, causing them to contract © 2016 Pearson Education, Inc.

Concept 37.2: Ion pumps and ion channels establish the resting potential of a neuron The inside of a cell is negatively charged relative to the outside This difference is a source of potential energy, termed membrane potential The resting potential is the membrane potential of a neuron not sending signals Changes in membrane potential act as signals, transmitting and processing information © 2016 Pearson Education, Inc.

Functional Properties of Neurons Irritability – ability to respond to stimuli Conductivity – ability to transmit an impulse The plasma membrane at rest is polarized Fewer positive ions are inside the cell than outside the cell The resting potential of an actual neuron is about –60 to –80 mV

Concept 37.3: Action potentials are the signals conducted by axons Changes in membrane potential occur because neurons contain gated ion channels that open or close in response to stimuli A voltage-gated ion channel opens or closes in response to a shift in the voltage across the plasma membrane of the neuron Change in membrane potential (voltage) © 2016 Pearson Education, Inc.

Starting a Nerve Impulse Depolarization – a stimulus depolarizes the neuron’s membrane Gated Na+ channels open allowing sodium (Na+) to flow inside the membrane If a depolarization shifts the membrane potential sufficiently, (threshold) it results in a massive change in membrane voltage, called an action potential Figure 7.9a–c

Figure 37.11-3 (c) Action potential triggered by a depolarization that reaches the threshold Strong depolarizing stimulus +50 Action potential Membrane potential (mV) Threshold -50 Figure 37.11-3 Graded potentials and an action potential in a neuron (part 3: action potential) Resting potential -100 1 2 3 4 5 6 Time (msec) © 2016 Pearson Education, Inc.

When stimulus depolarizes the membrane Some gated Na+ channels open first, and Na flows into the cell During the rising phase, the threshold is crossed, and the membrane potential increases During the falling phase, voltage-gated Na channels become inactivated; voltage-gated K channels open, and K flows out of the cell During the undershoot, membrane permeability to K is at first higher than at rest, and then voltage-gated K channels close and resting potential is restored © 2016 Pearson Education, Inc.

The sodium-potassium pump restores the original configuration During the refractory period after an action potential, a second action potential cannot be initiated The refractory period is a result of a temporary inactivation of the Na channels The sodium-potassium pump restores the original configuration This action requires ATP © 2016 Pearson Education, Inc.

Continuation of the Nerve Impulse between Neurons Impulses are not able to cross the synapse to another nerve Neurotransmitter is released from a nerve’s axon terminal The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter An action potential is started in the dendrite

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containing neurotransmitter Figure 37.16 Presynaptic cell Postsynaptic cell Axon Synaptic vesicle containing neurotransmitter Synaptic cleft Postsynaptic membrane Presynaptic membrane Figure 37.16 A chemical synapse K+ Ca2+ Voltage-gated Ca2+ channel Ligand-gated ion channels Na+ © 2016 Pearson Education, Inc.