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Tuesday, April 1, 2014 GOALS Learn about homeostasis from the webquest Learn how action potentials are propagated along a neuron Review action potentials using the webquest HOMEWORK: Work on Target Packet Read 48.2 and 48.3—take notes, etc. Remember—Quiz on Thursday 1 Neurons • Functional unit of nervous system • Bundles of neurons called nerves • Know parts & functions: – Cell body -Axon – Dendrite -Axon hillock – Synaptic terminal (figure 48.4) -Myelin sheath -Node of Ranvier -Schwann cell (glial) • Types of neurons: – Motor neurons – Sensory neurons – Interneuron 2 Neurons (figure 48.4) 3 Glial Cells (figure 48.12) • CNS has glial cells called astrocytes • Oligodendrocytes (of CNS) & Schwann cells (PNS) make myelin 4 Saltatory Conduction (figure 48.13) Glial cells allow electrical messages to travel faster along axon of neuron. 5 Human Nervous System Components • Central Nervous System Brain and spinal cord Process, associate, integrate Composed of interneurons With myelin = white matter Without myelin = grey matter • Peripheral Nervous System • Sense stimuli (receptors - dendrite of neuron) • Motor responses using effectors (muscles, organs, glands) • Transmit information to and from CNS • Sensory and motor neurons • Groups of cell bodies of PNS called ganglia 6 Summary of Information Processing (figure 48.3) 7 How Neurons Work: REVIEW • ION CHANNELS – Integral plasma membrane proteins – Neurons have K+ and Na+ channels – Allow specific ions to diffuse down chemical and electrical gradient – Can be gated or ungated ion channels: • UNGATED = open all the time, no gradient established across membrane • GATED = open (or close) in response to chemical or electrical stimulus *Chemically gated = channels open in response to binding of ligand, ion, hormone *Voltage gated = open in response to change in electrical charge across plasma membrane 8 Na+ and K + are voltage-gated ions channels How Neurons Work: Resting Potential • Lots of Na+ outside neuron • Lots of K+, anions, & proteins INSIDE neuron • Inside of neuron is less positive (negative) compared to outside of neuron (figure 48.6a,b) • Energy is required to maintain resting potential • Na+/K+ pump works (use ATP) to maintain 9 gradient of Na+ out and K+ inside (fig 8.15, 48.7b) How Neurons Work: Toilet Analogy • Little flush… subthreshhold stimulus • Normal flush… threshhold stimulus • BIG flush… threshhold stimulus, same threshhold regardless of stimulus strength All or NONE responses • Push down flusher when water is emptying or filling… refractory period • Push up on flusher (rather than down)… hyperpolarization 10 How Neurons Work: Changing Membrane Potential (figure 48.9) 11 How Neurons Work: Action Potential 1. Stimulus causes change in membrane voltage, Na+ channels open, and Na+ rushes into neuron 12 How Neurons Work: Action Potential 2. Nearby Na+ channels open along axon, causing more Na+ to rush into neuron 13 How Neurons Work: Action Potential 3. Voltage gated Na+ channels close, and K+ channels open, causing more negative change inside of neuron 14 How Neurons Work: Action Potential 4. Hyperpolarization occurs before the sodium / potassium pump restores resting potential 15 Neuron Circuits Presynaptic Neuron Postsynaptic Neuron a. b. c. Reflex Arc 16 Neuron Circuit: Reflex Arc (2) (3) • Involve two or all three types of neurons • Are automatic & innate; cannot be learned • Protect body from harmful stimuli *Name other examples of reflexes *Do other animals have reflexes? Provide an example... *What’s the selective advantage of reflexes? 17 Use graph to answer questions: 1. Neuron membrane is unable to respond to any further stimulation, regardless of intensity. 2. The Na+ gates (are) open. 3. Threshhold potential is achieved. 4. Repolarization occurs, Na+ gates close, K+ gates (are) open. 5. Hyperpolarization 6. Action potential 18(max. depolarization) A multiple guess for your CNS! 7. The threshhold potential of a membrane: A. Equals 70mV B. Opens voltage-gated channels that result in rapid outflow of Na+ ions C. Is the depolarization that is need to generate an action potential D. Is a graded potential that is proportional to the strength of a stimulus 19 Another multiple guess for your CNS! 8. A toxin that binds specifically to the voltagegated sodium channels of axons would: A. Block all sodium movement into or out of a neuron B. Block repolarization C. Prevent the axon from reaching the threshhold potential D. Ultimately block sodium and potassium movement 20 Another multiple guess for your CNS! 9. Action potentials are usually propagated in only one direction along an axon because: A. The node of Ranvier conducts in one direction B. The brief refractory period prevents opening of voltage gated Na+ channels C. The axon hillock has a higher membrane potential than the tips of the axon D. Ions can flow along a neuron in only one direction E. Both Na+ and K+ voltage-gated channels open 21 in one direction Saltatory Conduction (figure 48.13) Glial cells allow electrical messages to travel faster along axon of neuron. 22 Synaptic Transmission depolarization or hyperpolarization 1. If neurotransmitter causes Na+ channels to open, what will happen to postsynaptic neuron? Why? 2. If neurotransmitter causes K+ channels to open, what happens to postsynaptic neuron? Why? 3. If neurotransmitter causes Cl- channels to open, what happens to postsynaptic neuron? Why? Which situation(s) is (are) examples of excitatory postsynaptic potentials (EPSP)? Explain. Which situation(s) is(are) examples of inhibitory postsynaptic potentials (IPSP)? Explain. 23 Neural Integration What determines whether or not a postsynaptic neuron continues the action potential (message)? Amount of neurotransmitter binding to receptors Amount of neurons releasing neurotransmitters into synapse Distance of synapse, distance of receptor from axon hillock Frequency of neurotransmitter discharge (Summation) ALL OF THE ABOVE RELATE TO STRENGTH OF A STIMULUS! (and intensity of brain perception of stimulus) WARM VS. HOT PRESSURE VS. PAIN LIGHT VS. BLINDING SOUND VS. LOUD 24 Neural Integration - SUMMATION TWO TYPES OF SUMMATION: TEMPORAL: lots of chemical transmissions in small amount of time Spatial: lots of different pre-synaptic neurons stimulate post-synaptic cell (in a particular space) 25 Neural Integration - SUMMATION Figure 48.16a,b 26 Neural Integration - SUMMATION Figure 48.16c,d 27 Neuron Circuit: Reflex Arc (2) (3) • Involve two or all three types of neurons • Are automatic & innate; cannot be learned • Protect body from harmful stimuli Figure 49.3 *Name other examples of reflexes *Do other animals have reflexes? Provide an example... *What’s the selective advantage of reflexes? 28 Reflex Concept Generalization patellar reflex, stimulus (hammer), effector (upper quadriceps), sensory receptor, sensory neuron, motor neuron, spinal cord, brain, interneuron, inhibition, synapse(s) 29