Lecture Presentation by Lee Ann Frederick University of Texas at Arlington Chapter 12 Neural Tissue © 2015 Pearson Education, Inc. Capítulo 12 Tejido Nervioso V Biol 3791 UPR – Aguadilla JA Cardé, Ph. D.

An Introduction to the Nervous System Learning Outcomes 12-1 Describe the anatomical and functional divisions of the nervous system Sketch and label the structure of a typical neuron, describe the functions of each component, and classify neurons on the basis of their structure and function Describe the locations and functions of the various types of neuroglia. © 2015 Pearson Education, Inc.

An Introduction to the Nervous System Learning Outcomes 12-4 Explain how the resting membrane potential is created and maintained Describe the events involved in the generation and propagation of an action potential Discuss the factors that affect the speed with which action potentials are propagated. © 2015 Pearson Education, Inc.

An Introduction to the Nervous System Learning Outcomes 12-7 Describe the structure of a synapse, and explain the mechanism involved in synaptic activity Describe the major types of neurotransmitters and neuromodulators, and discuss their effects on postsynaptic membranes Discuss the interactions that enable information processing to occur in neural tissue. © 2015 Pearson Education, Inc.

12-8 Neurotransmitters and Neuromodulators Other Neurotransmitters At least 50 neurotransmitters other than ACh, including: Biogenic amines Amino acids Neuropeptides Dissolved gases © 2015 Pearson Education, Inc.

12-8 Neurotransmitters and Neuromodulators Important Neurotransmitters Other than acetylcholine Norepinephrine (NE) Dopamine Serotonin Gamma aminobutyric acid (GABA) © 2015 Pearson Education, Inc.

12-8 Neurotransmitters and Neuromodulators Norepinephrine (NE) Released by adrenergic synapses Excitatory and depolarizing effect Widely distributed in brain and portions of ANS Dopamine A CNS neurotransmitter May be excitatory or inhibitory Involved in Parkinson’s disease and cocaine use © 2015 Pearson Education, Inc.

12-8 Neurotransmitters and Neuromodulators Serotonin A CNS neurotransmitter Affects attention and emotional states Gamma Aminobutyric Acid (GABA) Inhibitory effect Functions in CNS Not well understood © 2015 Pearson Education, Inc.

12-8 Neurotransmitters and Neuromodulators Chemical Synapse The synaptic terminal releases a neurotransmitter that binds to the postsynaptic plasma membrane Produces temporary, localized change in permeability or function of postsynaptic cell Changes affect cell, depending on nature and number of stimulated receptors © 2015 Pearson Education, Inc.

12-8 Neurotransmitters and Neuromodulators Many Drugs Affect nervous system by stimulating receptors that respond to neurotransmitters Can have complex effects on perception, motor control, and emotional states © 2015 Pearson Education, Inc.

12-8 Neurotransmitters and Neuromodulators Neuromodulators Other chemicals released by synaptic terminals Similar in function to neurotransmitters Characteristics of neuromodulators Effects are long term, slow to appear Responses involve multiple steps, intermediary compounds Affect presynaptic membrane, postsynaptic membrane, or both Released alone or with a neurotransmitter © 2015 Pearson Education, Inc.

12-8 Neurotransmitters and Neuromodulators Neuropeptides Neuromodulators that bind to receptors and activate enzymes Opioids Neuromodulators in the CNS Bind to the same receptors as opium or morphine Relieve pain © 2015 Pearson Education, Inc.

12-8 Neurotransmitters and Neuromodulators Four Classes of Opioids 1. Endorphins 2. Enkephalins 3. Endomorphins 4. Dynorphins © 2015 Pearson Education, Inc.

12-8 Neurotransmitters and Neuromodulators How Neurotransmitters and Neuromodulators Work Direct effects on membrane channels For example, ACh, glycine, aspartate Indirect effects via G proteins For example, E, NE, dopamine, histamine, GABA Indirect effects via intracellular enzymes For example, lipid-soluble gases (NO, CO) © 2015 Pearson Education, Inc.

12-8 Neurotransmitters and Neuromodulators Direct Effects Ionotropic effects Open/close gated ion channels © 2015 Pearson Education, Inc.

Figure 12-17a Mechanisms of Neurotransmitter Function. a + Binding site Chemically gated channel Direct effects ACh Examples: ACh, glutamate, aspartate

12-8 Neurotransmitters and Neuromodulators Indirect Effects – G Proteins Work through second messengers Enzyme complex that binds GTP Link between neurotransmitter (first messenger) and second messenger Activate enzyme adenylyl cyclase Which produces second messenger cyclic-AMP (cAMP) © 2015 Pearson Education, Inc.

b Neurotransmitter Indirect effects by G proteins Examples: E, NE, dopamine, histamine, GABA Activates enzymes that change cell metabolism and activity G protein (inactive) Receptor Opens ion channels cAMP ATP G protein (active) Adenylate cyclase Figure 12-17b Mechanisms of Neurotransmitter Function.

12-8 Neurotransmitters and Neuromodulators Indirect Effects – Intracellular Receptors Lipid-soluble gases (NO, CO) Bind to enzymes in brain cells © 2015 Pearson Education, Inc.

Figure 12-17c Mechanisms of Neurotransmitter Function. c Nitric oxide Indirect effects by intracellular enzymes Examples: Nitric oxide, carbon monoxide Opens ion channels Production of secondary messengers Activation of enzymes Changes in cell metabolism and activity

© 2015 Pearson Education, Inc. Table 12-4 Representative Neurotransmitters and Neuromodulators.

© 2015 Pearson Education, Inc. Table 12-4 Representative Neurotransmitters and Neuromodulators (Part 1 of 5).

© 2015 Pearson Education, Inc. Table 12-4 Representative Neurotransmitters and Neuromodulators (Part 2 of 5).

© 2015 Pearson Education, Inc. Table 12-4 Representative Neurotransmitters and Neuromodulators (Part 3 of 5).

© 2015 Pearson Education, Inc. Table 12-4 Representative Neurotransmitters and Neuromodulators (Part 4 of 5).

© 2015 Pearson Education, Inc. Table 12-4 Representative Neurotransmitters and Neuromodulators (Part 5 of 5).

12-9 Information Processing Information Processing At the simplest level (individual neurons) Many dendrites receive neurotransmitter messages simultaneously Some excitatory, some inhibitory Net effect on axon hillock determines if action potential is produced © 2015 Pearson Education, Inc.

12-9 Information Processing Postsynaptic Potentials Graded potentials developed in a postsynaptic cell In response to neurotransmitters Two Types of Postsynaptic Potentials 1. Excitatory postsynaptic potential (EPSP) Graded depolarization of postsynaptic membrane 2. Inhibitory postsynaptic potential (IPSP) Graded hyperpolarization of postsynaptic membrane © 2015 Pearson Education, Inc.

12-9 Information Processing Inhibition A neuron that receives many IPSPs: Is inhibited from producing an action potential Because the stimulation needed to reach threshold is increased Summation To trigger an action potential: One EPSP is not enough EPSPs (and IPSPs) combine through summation 1. Temporal summation 2. Spatial summation © 2015 Pearson Education, Inc.

12-9 Information Processing Temporal Summation Multiple times Rapid, repeated stimuli at one synapse Spatial Summation Multiple locations Many stimuli, arrive at multiple synapses © 2015 Pearson Education, Inc.

Figure 12-18a Temporal and Spatial Summation. a Temporal Summation. Temporal summation occurs on a membrane that receives two depolarizing stimuli from the same source in rapid succession. The effects of the second stimulus are added to those on the first. Initial segment Threshold reached FIRST STIMULUS SECOND STIMULUS ACTION POTENTIAL PROPAGATION Action potential is generated Second stimulus arrives and is added to the first stimulus First stimulus arrives 3 2 1

© 2015 Pearson Education, Inc. Figure 12-18b Temporal and Spatial Summation. b Spatial Summation. Spatial summation occurs when sources of stimulation arrive simultaneously, but at different locations. Local currents spread the depolarizing effects, and areas of overlap experience the combined effects. TWO SIMULTANEOUS STIMULI Two stimuli arrive simultaneously 12 Action potential is generated ACTION POTENTIAL PROPAGATION Threshold reached

12-9 Information Processing Facilitation A neuron becomes facilitated As EPSPs accumulate Raising membrane potential closer to threshold Until a small stimulus can trigger action potential © 2015 Pearson Education, Inc.

12-9 Information Processing Summation of EPSPs and IPSPs Neuromodulators and hormones Can change membrane sensitivity to neurotransmitters Shifting balance between EPSPs and IPSPs © 2015 Pearson Education, Inc.

Figure Interactions between EPSPs and IPSPs. Membrane potential (mV) –60 mV –70 mV –80 mV Time 1: Depolarizing stimulus applied Stimulus removed Resting membrane potential Time 2: Hyperpolarizing stimulus applied Time Stimulus removed Resting membrane potential Time 3: Hyperpolarizing stimulus applied Time 3: Depolarizing stimulus applied Stimuli removed EPSP IPSP EPSP

12-9 Information Processing Axoaxonic Synapses Synapses between the axons of two neurons Presynaptic inhibition Action of an axoaxonic synapse at a synaptic terminal that decreases the neurotransmitter released by presynaptic membrane Presynaptic facilitation Action of an axoaxonic synapse at a synaptic terminal that increases the neurotransmitter released by presynaptic membrane © 2015 Pearson Education, Inc.

Figure 12-20a Presynaptic Inhibition and Presynaptic Facilitation. Action potential arrives GABA release Inactivation of calcium channels Ca Less calcium enters 1. Action potential arrives 3. Less neurotransmitter released 4. Reduced effect on postsynaptic membrane Presynaptic inhibition a

© 2015 Pearson Education, Inc. Figure 12-20b Presynaptic Inhibition and Presynaptic Facilitation. 2. More calcium enters 1. Action potential arrives 3. More neurotransmitter released Presynaptic facilitation b Ca Increased effect on postsynaptic membrane Activation of calcium channels Serotonin release Action potential arrives

12-9 Information Processing Frequency of Action Potentials Information received by a postsynaptic cell may be simply the frequency of action potentials received Rate of Generation of Action Potentials Frequency of action potentials depends on degree of depolarization above threshold Holding membrane above threshold level Has same effect as a second, larger stimulus Reduces relative refractory period © 2015 Pearson Education, Inc.

12-9 Information Processing In the Nervous System A change in membrane potential that determines whether or not action potentials are generated is the simplest form of information processing © 2015 Pearson Education, Inc.

12-9 Information Processing Summary Information is relayed in the form of action potentials In general, the degree of sensory stimulation or the strength of the motor response is proportional to the frequency of action potentials The neurotransmitters released at a synapse may have either excitatory or inhibitory effects The effect on the axon’s initial segment reflects a summation of the stimuli that arrive at any moment The frequency of generation of action potentials is an indication of the degree of sustained depolarization at the axon hillock © 2015 Pearson Education, Inc.

12-9 Information Processing Summary Neuromodulators Can alter either the rate of neurotransmitter release or the response of a postsynaptic neuron to specific neurotransmitters Neurons May be facilitated or inhibited by extracellular chemicals other than neurotransmitters or neuromodulators © 2015 Pearson Education, Inc.

12-9 Information Processing Summary The response of a postsynaptic neuron to the activation of a presynaptic neuron can be altered by: 1.The presence of neuromodulators or other chemicals that cause facilitation or inhibition at the synapse 2.Activity under way at other synapses affecting the postsynaptic cell 3.Modification of the rate of neurotransmitter release through presynaptic facilitation or presynaptic inhibition © 2015 Pearson Education, Inc.