Human Anatomy & Physiology Lecture Slides PDF

Elaine N. Marieb PowerPoint® Lecture Slides prepared by Vince Austin, Katja Hoehn...

Elaine N. Marieb PowerPoint® Lecture Slides prepared by Vince Austin, Katja Hoehn Bluegrass Technical 11 and Community College CHAPTER PART A Human Fundamentals Anatomy of the Nervous & Physiology SEVENTH EDITION System and Nervous Tissue Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Nervous System  The master controlling and communicating system of the body  Functions  Sensory input – monitoring stimuli  Integration – interpretation of sensory input  Motor output – response to stimuli Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Nervous System Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.1  Organization of the Nervous System  Central nervous system (CNS)  Brain and spinal cord  Integration and command center  Peripheral nervous system (PNS)  Paired spinal and cranial nerves  Carries messages to and from the spinal cord and brain Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Peripheral Nervous System (PNS): Two Functional Divisions  Sensory (afferent) division  Sensory afferent fibers – carry impulses from skin, skeletal muscles, and joints to the brain  Visceral afferent fibers – transmit impulses from visceral organs to the brain  Motor (efferent) division  Transmits impulses from the CNS to effector organs Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Motor Division: Two Main Parts  Somatic nervous system  Conscious control of skeletal muscles  Autonomic nervous system (ANS)  Regulates smooth muscle, cardiac muscle, and glands  Divisions – sympathetic and parasympathetic Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Histology of Nerve Tissue  The two principal cell types of the nervous system are:  Neurons – excitable cells that transmit electrical signals  Supporting cells – cells that surround and wrap neurons Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Supporting Cells: Neuroglia  The supporting cells (neuroglia or glial cells):  Provide a supportive scaffolding for neurons  Segregate and insulate neurons  Guide young neurons to the proper connections  Promote health and growth Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Astrocytes  Most abundant, versatile, and highly branched glial cells  They cling to neurons and their synaptic endings, and cover capillaries Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Astrocytes  Functionally, they:  Support and brace neurons  Anchor neurons to their nutrient supplies  Guide migration of young neurons  Control the chemical environment Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Astrocytes Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.3a  Microglia and Ependymal Cells  Microglia – small, ovoid cells with spiny processes  Phagocytes that monitor the health of neurons  Ependymal cells – range in shape from squamous to columnar  They line the central cavities of the brain and spinal column Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Microglia and Ependymal Cells Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.3b, c  Oligodendrocytes, Schwann Cells, and Satellite Cells  Oligodendrocytes – branched cells that wrap CNS nerve fibers  Schwann cells (neurolemmocytes) – surround fibers of the PNS  Satellite cells surround neuron cell bodies with ganglia Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Oligodendrocytes, Schwann Cells, and Satellite Cells Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.3d, e  Neurons (Nerve Cells)  Structural units of the nervous system  Composed of a body, axon, and dendrites  Long-lived, amitotic, and have a high metabolic rate  Their plasma membrane function in:  Electrical signaling  Cell-to-cell signaling during development PLAY InterActive Physiology ®: Nervous System I, Anatomy Review, page 4 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neurons (Nerve Cells) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.4b  Nerve Cell Body (Perikaryon or Soma)  Contains the nucleus and a nucleolus  Is the major biosynthetic center  Is the focal point for the outgrowth of neuronal processes  Has no centrioles (hence its amitotic nature)  Has well-developed Nissl bodies (rough ER)  Contains an axon hillock – cone-shaped area from which axons arise Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Processes  Armlike extensions from the soma  Called tracts in the CNS and nerves in the PNS  There are two types: axons and dendrites Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Dendrites of Motor Neurons  Short, tapering, and diffusely branched processes  They are the receptive, or input, regions of the neuron  Electrical signals are conveyed as graded potentials (not action potentials) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Axons: Structure  Slender processes of uniform diameter arising from the hillock  Long axons are called nerve fibers  Usually there is only one unbranched axon per neuron  Rare branches, if present, are called axon collaterals  Axonal terminal – branched terminus of an axon Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Axons: Function  Generate and transmit action potentials  Secrete neurotransmitters from the axonal terminals  Movement along axons occurs in two ways  Anterograde — toward axonal terminal  Retrograde — away from axonal terminal Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Myelin Sheath  Whitish, fatty (protein-lipoid), segmented sheath around most long axons  It functions to:  Protect the axon  Electrically insulate fibers from one another  Increase the speed of nerve impulse transmission Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Myelin Sheath and Neurilemma: Formation  Formed by Schwann cells in the PNS  A Schwann cell:  Envelopes an axon in a trough  Encloses the axon with its plasma membrane  Has concentric layers of membrane that make up the myelin sheath  Neurilemma – remaining nucleus and cytoplasm of a Schwann cell Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Myelin Sheath and Neurilemma: Formation PLAY InterActive Physiology ®: Nervous System I, Anatomy Review, page 10 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.5a–c  Nodes of Ranvier (Neurofibral Nodes)  Gaps in the myelin sheath between adjacent Schwann cells  They are the sites where axon collaterals can emerge PLAY InterActive Physiology ®: Nervous System I, Anatomy Review, page 11 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Unmyelinated Axons  A Schwann cell surrounds nerve fibers but coiling does not take place  Schwann cells partially enclose 15 or more axons Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Axons of the CNS  Both myelinated and unmyelinated fibers are present  Myelin sheaths are formed by oligodendrocytes  Nodes of Ranvier are widely spaced  There is no neurilemma Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Regions of the Brain and Spinal Cord  White matter – dense collections of myelinated fibers  Gray matter – mostly soma and unmyelinated fibers Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neuron Classification  Structural:  Multipolar — three or more processes  Bipolar — two processes (axon and dendrite)  Unipolar — single, short process Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neuron Classification  Functional:  Sensory (afferent) — transmit impulses toward the CNS  Motor (efferent) — carry impulses away from the CNS  Interneurons (association neurons) — shuttle signals through CNS pathways Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Comparison of Structural Classes of Neurons Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 11.1.1  Comparison of Structural Classes of Neurons Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 11.1.2  Comparison of Structural Classes of Neurons Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 11.1.3  Neurophysiology  Neurons are highly irritable  Action potentials, or nerve impulses, are:  Electrical impulses carried along the length of axons  Always the same regardless of stimulus  The underlying functional feature of the nervous system Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Electricity Definitions  Voltage (V) – measure of potential energy generated by separated charge  Potential difference – voltage measured between two points  Current (I) – the flow of electrical charge between two points  Resistance (R) – hindrance to charge flow  Insulator – substance with high electrical resistance  Conductor – substance with low electrical resistance Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Electrical Current and the Body  Reflects the flow of ions rather than electrons  There is a potential on either side of membranes when:  The number of ions is different across the membrane  The membrane provides a resistance to ion flow Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Role of Ion Channels  Types of plasma membrane ion channels:  Passive, or leakage, channels – always open  Chemically gated channels – open with binding of a specific neurotransmitter  Voltage-gated channels – open and close in response to membrane potential  Mechanically gated channels – open and close in response to physical deformation of receptors PLAY InterActive Physiology ®: Nervous System I: Ion Channels Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Operation of a Gated Channel  Example: Na+-K+ gated channel  Closed when a neurotransmitter is not bound to the extracellular receptor  Na+ cannot enter the cell and K+ cannot exit the cell  Open when a neurotransmitter is attached to the receptor  Na+ enters the cell and K+ exits the cell Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Operation of a Gated Channel Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.6a  Operation of a Voltage-Gated Channel  Example: Na+ channel  Closed when the intracellular environment is negative  Na+ cannot enter the cell  Open when the intracellular environment is positive  Na+ can enter the cell Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Operation of a Voltage-Gated Channel Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.6b  Gated Channels  When gated channels are open:  Ions move quickly across the membrane  Movement is along their electrochemical gradients  An electrical current is created  Voltage changes across the membrane Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Electrochemical Gradient  Ions flow along their chemical gradient when they move from an area of high concentration to an area of low concentration  Ions flow along their electrical gradient when they move toward an area of opposite charge  Electrochemical gradient – the electrical and chemical gradients taken together Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Resting Membrane Potential (Vr)  The potential difference (–70 mV) across the membrane of a resting neuron  It is generated by different concentrations of Na+, K+, Cl, and protein anions (A)  Ionic differences are the consequence of:  Differential permeability of the neurilemma to Na+ and K+  Operation of the sodium-potassium pump PLAY InterActive Physiology ®: Nervous System I: Membrane Potential Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Measuring Mebrane Potential Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.7  Resting Membrane Potential (Vr) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.8  Membrane Potentials: Signals  Used to integrate, send, and receive information  Membrane potential changes are produced by:  Changes in membrane permeability to ions  Alterations of ion concentrations across the membrane  Types of signals – graded potentials and action potentials Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Changes in Membrane Potential  Changes are caused by three events  Depolarization – the inside of the membrane becomes less negative  Repolarization – the membrane returns to its resting membrane potential  Hyperpolarization – the inside of the membrane becomes more negative than the resting potential Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Changes in Membrane Potential Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.9  Graded Potentials  Short-lived, local changes in membrane potential  Decrease in intensity with distance  Magnitude varies directly with the strength of the stimulus  Sufficiently strong graded potentials can initiate action potentials Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Graded Potentials Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.10  Graded Potentials  Voltage changes are decremental  Current is quickly dissipated due to the leaky plasma membrane  Only travel over short distances Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Graded Potentials Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.11  Action Potentials (APs)  A brief reversal of membrane potential with a total amplitude of 100 mV  Action potentials are only generated by muscle cells and neurons  They do not decrease in strength over distance  They are the principal means of neural communication  An action potential in the axon of a neuron is a nerve impulse PLAY InterActive Physiology ®: Nervous System I: The Action Potential Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Action Potential: Resting State  Na+ and K+ channels are closed  Leakage accounts for small movements of Na+ and K+  Each Na+ channel has two voltage-regulated gates  Activation gates – closed in the resting state  Inactivation gates – open in the resting state Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.12.1  Action Potential: Depolarization Phase  Na+ permeability increases; membrane potential reverses  Na+ gates are opened; K+ gates are closed  Threshold – a critical level of depolarization (-55 to -50 mV)  At threshold, depolarization becomes self-generating Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.12.2  Action Potential: Repolarization Phase  Sodium inactivation gates close  Membrane permeability to Na+ declines to resting levels  As sodium gates close, voltage-sensitive K+ gates open  K+ exits the cell and internal negativity of the resting neuron is restored Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.12.3  Action Potential: Hyperpolarization  Potassium gates remain open, causing an excessive efflux of K+  This efflux causes hyperpolarization of the membrane (undershoot)  The neuron is insensitive to stimulus and depolarization during this time Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.12.4  Action Potential: Role of the Sodium-Potassium Pump  Repolarization  Restores the resting electrical conditions of the neuron  Does not restore the resting ionic conditions  Ionic redistribution back to resting conditions is restored by the sodium-potassium pump Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Phases of the Action Potential  1 – resting state  2 – depolarization phase  3 – repolarization phase  4 – hyperpolarization Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.12  Propagation of an Action Potential (Time = 0ms)  Na+ influx causes a patch of the axonal membrane to depolarize  Positive ions in the axoplasm move toward the polarized (negative) portion of the membrane  Sodium gates are shown as closing, open, or closed Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Propagation of an Action Potential (Time = 0ms) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.13a  Propagation of an Action Potential (Time = 2ms)  Ions of the extracellular fluid move toward the area of greatest negative charge  A current is created that depolarizes the adjacent membrane in a forward direction  The impulse propagates away from its point of origin Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Propagation of an Action Potential (Time = 2ms) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.13b  Propagation of an Action Potential (Time = 4ms)  The action potential moves away from the stimulus  Where sodium gates are closing, potassium gates are open and create a current flow Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Propagation of an Action Potential (Time = 4ms) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.13c  Threshold and Action Potentials  Threshold – membrane is depolarized by 15 to 20 mV  Established by the total amount of current flowing through the membrane  Weak (subthreshold) stimuli are not relayed into action potentials  Strong (threshold) stimuli are relayed into action potentials  All-or-none phenomenon – action potentials either happen completely, or not at all Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Coding for Stimulus Intensity  All action potentials are alike and are independent of stimulus intensity  Strong stimuli can generate an action potential more often than weaker stimuli  The CNS determines stimulus intensity by the frequency of impulse transmission Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Stimulus Strength and AP Frequency Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.14  Absolute Refractory Period  Time from the opening of the Na+ activation gates until the closing of inactivation gates  The absolute refractory period:  Prevents the neuron from generating an action potential  Ensures that each action potential is separate  Enforces one-way transmission of nerve impulses PLAY InterActive Physiology ®: Nervous System I: The Action Potential, page 14 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Absolute and Relative Refractory Periods Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.15  Relative Refractory Period  The interval following the absolute refractory period when:  Sodium gates are closed  Potassium gates are open  Repolarization is occurring  The threshold level is elevated, allowing strong stimuli to increase the frequency of action potential events PLAY InterActive Physiology ®: Nervous System I: The Action Potential, page 15 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Conduction Velocities of Axons  Conduction velocities vary widely among neurons  Rate of impulse propagation is determined by:  Axon diameter – the larger the diameter, the faster the impulse  Presence of a myelin sheath – myelination dramatically increases impulse speed PLAY InterActive Physiology ®: Nervous System I: Action Potential, page 17 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Saltatory Conduction  Current passes through a myelinated axon only at the nodes of Ranvier  Voltage-gated Na+ channels are concentrated at these nodes  Action potentials are triggered only at the nodes and jump from one node to the next  Much faster than conduction along unmyelinated axons Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Saltatory Conduction Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.16  Multiple Sclerosis (MS)  An autoimmune disease that mainly affects young adults  Symptoms: visual disturbances, weakness, loss of muscular control, and urinary incontinence  Nerve fibers are severed and myelin sheaths in the CNS become nonfunctional scleroses  Shunting and short-circuiting of nerve impulses occurs Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Multiple Sclerosis: Treatment  The advent of disease-modifying drugs including interferon beta-1a and -1b, Avonex, Betaseran, and Copazone:  Hold symptoms at bay  Reduce complications  Reduce disability Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Nerve Fiber Classification  Nerve fibers are classified according to:  Diameter  Degree of myelination  Speed of conduction Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Synapses  A junction that mediates information transfer from one neuron:  To another neuron  To an effector cell  Presynaptic neuron – conducts impulses toward the synapse  Postsynaptic neuron – transmits impulses away from the synapse Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Synapses Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.17  Types of Synapses  Axodendritic – synapses between the axon of one neuron and the dendrite of another  Axosomatic – synapses between the axon of one neuron and the soma of another  Other types of synapses include:  Axoaxonic (axon to axon)  Dendrodendritic (dendrite to dendrite)  Dendrosomatic (dendrites to soma) PLAY InterActive Physiology ®: Nervous System II: Anatomy Review, page 5 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Electrical Synapses  Electrical synapses:  Are less common than chemical synapses  Correspond to gap junctions found in other cell types  Are important in the CNS in:  Arousal from sleep  Mental attention  Emotions and memory  Ion and water homeostasis PLAY InterActive Physiology ®: Nervous System II: Anatomy Review, page 6 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Chemical Synapses  Specialized for the release and reception of neurotransmitters  Typically composed of two parts:  Axonal terminal of the presynaptic neuron, which contains synaptic vesicles  Receptor region on the dendrite(s) or soma of the postsynaptic neuron PLAY InterActive Physiology ®: Nervous System II: Anatomy Review, page 7 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Synaptic Cleft  Fluid-filled space separating the presynaptic and postsynaptic neurons  Prevents nerve impulses from directly passing from one neuron to the next  Transmission across the synaptic cleft:  Is a chemical event (as opposed to an electrical one)  Ensures unidirectional communication between neurons PLAY InterActive Physiology ®: Nervous System II: Anatomy Review, page 8 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Synaptic Cleft: Information Transfer  Nerve impulses reach the axonal terminal of the presynaptic neuron and open Ca2+ channels  Neurotransmitter is released into the synaptic cleft via exocytosis in response to synaptotagmin  Neurotransmitter crosses the synaptic cleft and binds to receptors on the postsynaptic neuron  Postsynaptic membrane permeability changes, causing an excitatory or inhibitory effect PLAY InterActive Physiology ®: Nervous System II: Synaptic Transmission, pages 3–6 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Synaptic Cleft: Information Transfer Neurotransmitter Ac tent Ca2+ Na+ po tio ial Axon terminal of Receptor n 1 presynaptic neuron Postsynaptic Mitochondrion membrane Postsynaptic Axon of membrane presynaptic neuron Ion channel open Synaptic vesicles 5 containing neurotransmitter molecules Degraded 2 neurotransmitter Synaptic cleft 3 4 Ion channel closed Ion channel Ion channel (open) (closed) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.18  Termination of Neurotransmitter Effects  Neurotransmitter bound to a postsynaptic neuron:  Produces a continuous postsynaptic effect  Blocks reception of additional “messages”  Must be removed from its receptor  Removal of neurotransmitters occurs when they:  Are degraded by enzymes  Are reabsorbed by astrocytes or the presynaptic terminals  Diffuse from the synaptic cleft Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Synaptic Delay  Neurotransmitter must be released, diffuse across the synapse, and bind to receptors  Synaptic delay – time needed to do this (0.3-5.0 ms)  Synaptic delay is the rate-limiting step of neural transmission Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Postsynaptic Potentials  Neurotransmitter receptors mediate changes in membrane potential according to:  The amount of neurotransmitter released  The amount of time the neurotransmitter is bound to receptors  The two types of postsynaptic potentials are:  EPSP – excitatory postsynaptic potentials  IPSP – inhibitory postsynaptic potentials PLAY InterActive Physiology ®: Nervous System II: Synaptic Transmission, pages 7–12 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Excitatory Postsynaptic Potentials  EPSPs are graded potentials that can initiate an action potential in an axon  Use only chemically gated channels  Na+ and K+ flow in opposite directions at the same time  Postsynaptic membranes do not generate action potentials Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Excitatory Postsynaptic Potential (EPSP) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.19a  Inhibitory Synapses and IPSPs  Neurotransmitter binding to a receptor at inhibitory synapses:  Causes the membrane to become more permeable to potassium and chloride ions  Leaves the charge on the inner surface negative  Reduces the postsynaptic neuron’s ability to produce an action potential Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Inhibitory Postsynaptic (IPSP) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.19b  Summation  A single EPSP cannot induce an action potential  EPSPs must summate temporally or spatially to induce an action potential  Temporal summation – presynaptic neurons transmit impulses in rapid-fire order Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Summation  Spatial summation – postsynaptic neuron is stimulated by a large number of terminals at the same time  IPSPs can also summate with EPSPs, canceling each other out PLAY InterActive Physiology ®: Nervous System II: Synaptic Potentials Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Summation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.20  Neurotransmitters  Chemicals used for neuronal communication with the body and the brain  50 different neurotransmitters have been identified  Classified chemically and functionally Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Chemical Neurotransmitters  Acetylcholine (ACh)  Biogenic amines  Amino acids  Peptides  Novel messengers: ATP and dissolved gases NO and CO Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neurotransmitters: Acetylcholine  First neurotransmitter identified, and best understood  Released at the neuromuscular junction  Synthesized and enclosed in synaptic vesicles Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neurotransmitters: Acetylcholine  Degraded by the enzyme acetylcholinesterase (AChE)  Released by:  All neurons that stimulate skeletal muscle  Some neurons in the autonomic nervous system Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neurotransmitters: Biogenic Amines  Include:  Catecholamines – dopamine, norepinephrine (NE), and epinephrine  Indolamines – serotonin and histamine  Broadly distributed in the brain  Play roles in emotional behaviors and our biological clock Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Synthesis of Catecholamines  Enzymes present in the cell determine length of biosynthetic pathway  Norepinephrine and dopamine are synthesized in axonal terminals  Epinephrine is released by the adrenal medulla Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.21  Neurotransmitters: Amino Acids  Include:  GABA – Gamma ()-aminobutyric acid  Glycine  Aspartate  Glutamate  Found only in the CNS Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neurotransmitters: Peptides  Include:  Substance P – mediator of pain signals  Beta endorphin, dynorphin, and enkephalins  Act as natural opiates; reduce pain perception  Bind to the same receptors as opiates and morphine  Gut-brain peptides – somatostatin, and cholecystokinin Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neurotransmitters: Novel Messengers  ATP  Is found in both the CNS and PNS  Produces excitatory or inhibitory responses depending on receptor type  Induces Ca2+ wave propagation in astrocytes  Provokes pain sensation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neurotransmitters: Novel Messengers  Nitric oxide (NO)  Activates the intracellular receptor guanylyl cyclase  Is involved in learning and memory  Carbon monoxide (CO) is a main regulator of cGMP in the brain Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Functional Classification of Neurotransmitters  Two classifications: excitatory and inhibitory  Excitatory neurotransmitters cause depolarizations (e.g., glutamate)  Inhibitory neurotransmitters cause hyperpolarizations (e.g., GABA and glycine) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Functional Classification of Neurotransmitters  Some neurotransmitters have both excitatory and inhibitory effects  Determined by the receptor type of the postsynaptic neuron  Example: acetylcholine  Excitatory at neuromuscular junctions with skeletal muscle  Inhibitory in cardiac muscle Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neurotransmitter Receptor Mechanisms  Direct: neurotransmitters that open ion channels  Promote rapid responses  Examples: ACh and amino acids  Indirect: neurotransmitters that act through second messengers  Promote long-lasting effects  Examples: biogenic amines, peptides, and dissolved gases PLAY InterActive Physiology ®: Nervous System II: Synaptic Transmission Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Channel-Linked Receptors  Composed of integral membrane protein  Mediate direct neurotransmitter action  Action is immediate, brief, simple, and highly localized  Ligand binds the receptor, and ions enter the cells  Excitatory receptors depolarize membranes  Inhibitory receptors hyperpolarize membranes Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Channel-Linked Receptors Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.22a  G Protein-Linked Receptors  Responses are indirect, slow, complex, prolonged, and often diffuse  These receptors are transmembrane protein complexes  Examples: muscarinic ACh receptors, neuropeptides, and those that bind biogenic amines Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  G Protein-Linked Receptors: Mechanism  Neurotransmitter binds to G protein-linked receptor  G protein is activated and GTP is hydrolyzed to GDP  The activated G protein complex activates adenylate cyclase Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  G Protein-Linked Receptors: Mechanism  Adenylate cyclase catalyzes the formation of cAMP from ATP  cAMP, a second messenger, brings about various cellular responses Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neurotransmitter Receptor Mechanism Ions flow Blocked ion flow Adenylate Ion channel Channel closed Channel open cyclase (a) Neurotransmitter (ligand) released from axon terminal PPi of presynaptic neuron GTP 4 5 Changes in 3 membrane 1 cAMP ATP permeability 5 and potential 3 GTP 2 Enzyme Protein activation synthesis GDP GTP Receptor G protein Activation of specific genes (b) Nucleus Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.22b  G Protein-Linked Receptors: Effects  G protein-linked receptors activate intracellular second messengers including Ca2+, cGMP, diacylglycerol, as well as cAMP  Second messengers:  Open or close ion channels  Activate kinase enzymes  Phosphorylate channel proteins  Activate genes and induce protein synthesis Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neural Integration: Neuronal Pools  Functional groups of neurons that:  Integrate incoming information  Forward the processed information to its appropriate destination Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Neural Integration: Neuronal Pools  Simple neuronal pool  Input fiber – presynaptic fiber  Discharge zone – neurons most closely associated with the incoming fiber  Facilitated zone – neurons farther away from incoming fiber Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Simple Neuronal Pool Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.23  Types of Circuits in Neuronal Pools  Divergent – one incoming fiber stimulates ever increasing number of fibers, often amplifying circuits Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.24a, b  Types of Circuits in Neuronal Pools  Convergent – opposite of divergent circuits, resulting in either strong stimulation or inhibition Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.24c, d  Types of Circuits in Neuronal Pools  Reverberating – chain of neurons containing collateral synapses with previous neurons in the chain Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.24e  Types of Circuits in Neuronal Pools  Parallel after-discharge – incoming neurons stimulate several neurons in parallel arrays Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.24f  Patterns of Neural Processing  Serial Processing  Input travels along one pathway to a specific destination  Works in an all-or-none manner  Example: spinal reflexes Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Patterns of Neural Processing  Parallel Processing  Input travels along several pathways  Pathways are integrated in different CNS systems  One stimulus promotes numerous responses  Example: a smell may remind one of the odor and associated experiences Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Development of Neurons  The nervous system originates from the neural tube and neural crest  The neural tube becomes the CNS  There is a three-phase process of differentiation:  Proliferation of cells needed for development  Migration – cells become amitotic and move externally  Differentiation into neuroblasts Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Axonal Growth  Guided by:  Scaffold laid down by older neurons  Orienting glial fibers  Release of nerve growth factor by astrocytes  Neurotropins released by other neurons  Repulsion guiding molecules  Attractants released by target cells Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  N-CAMs  N-CAM – nerve cell adhesion molecule  Important in establishing neural pathways  Without N-CAM, neural function is impaired  Found in the membrane of the growth cone Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings