Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Objective 4 Outline the steps of a nerve impulse, and its conduction from one neuron to the next.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Action Potential  A nerve impulse, signal, electrical impulse…  Is correctly called an “Action Potential”  “Potential” is from the chemistry…the potential charges of the + and – ions involved  Are received from the dendrites…pass down an axon…to the axon terminals.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Starting a Nerve Impulse 1.Resting State – all ion gates closed… Na+ outside, K+ inside 2.Depolarizing - membrane allows sodium (Na + ) to flow inside the membrane Figure 7.9a–c

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nerve Impulse Propagation 3. Repolarizing – Na channels close. K+ channels open 4. “Undershoot” – K+ channels are open too long, there is a ‘dip’ in the charge 5. Sodium/Potassium Pump – energy is used to pump Na & K back to normal state Figure 7.9d–f

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Action Potential  If the action potential (nerve impulse) starts, it is passed over the entire axon (“all or none”)  Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane  The sodium-potassium pump restores the original configuration  This action requires ATP

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings How Neurons Communicate at Synapses Figure 7.10

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Continuation of the Nerve Impulse between Neurons  Impulses are able to cross the synapse to another nerve 1. Ca+ Gates open when action potential (nerve impulse) reaches the axon terminal

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings How Neurons Communicate at Synapses 2. Ca+ causes vesicles (vacuoles) to dump Neurotransmitters into the synapse (gap)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings How Neurons Communicate at Synapses (Ignore the numbers!)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings How Neurons Communicate at Synapses 3. Neurotransmitters bind to the receptors of the next cell (can be another neuron, a muscle, or a gland)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings How Neurons Communicate at Synapses

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings How Neurons Communicate at Synapses 4. Binding causes Na+ ion channels to open so … - (if neuron) action potential can continue - (if muscle/gland) trigger the appropriate response

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  The Neurotransmitter can “hang around” causing ‘after-effects’ after the stimulus is removed.  Some medications work on this process…  Pain killers can prevent neurotransmitters from binding to receptors  Depression medication can take the place of neurotransmitters

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Objective 5 List the main components of a reflex arc.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Reflex Arc  Reflex – rapid, predictable, and involuntary responses to stimuli  Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector Figure 7.11a

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Simple Reflex Arc Figure 7.11b–c

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Types of Reflexes and Regulation  Autonomic reflexes  Smooth muscle regulation  Heart and blood pressure regulation  Regulation of glands  Digestive system regulation  Somatic reflexes  Activation of skeletal muscles