1. © 2012 Pearson Education, Inc. An Introduction to the Nervous System Organs of the Nervous System Brain and spinal cord (Processing incoming info and creating motor commands) Sensory receptors of sense organs (eyes, ears, pressure, pain, chemicals, etc.) Nerves connect nervous system with other systems( a nerve is a bundle of axons)

2. © 2012 Pearson Education, Inc. Anatomical Divisions of the Nervous System The Central Nervous System (CNS) Consists of the spinal cord and brain Contains neural tissue, connective tissues, and blood vessels Functions of the CNS are to process and coordinate: Sensory data from inside and outside body Motor commands control activities of peripheral organs (e.g., skeletal muscles) Higher functions of brain intelligence, memory, learning, emotion

3. © 2012 Pearson Education, Inc. Anatomical Divisions of the Nervous System The Peripheral Nervous System (PNS) Includes all neural tissue outside the CNS Functions of the PNS Deliver sensory information to the CNS Carry motor commands to peripheral tissues and systems

4. © 2012 Pearson Education, Inc. 12-1 Divisions of the Nervous System The Peripheral Nervous System (PNS) Nerves (also called peripheral nerves) Bundles of axons with connective tissues and blood vessels Carry sensory information and motor commands in PNS Cranial nerves — connect to brain Spinal nerves — attach to spinal cord

5. © 2012 Pearson Education, Inc. 12-1 Divisions of the Nervous System Functional Divisions of the PNS Afferent division (means “entrance”) Carries sensory information From PNS sensory receptors to CNS Efferent division (means “exit”) Carries motor commands From CNS to PNS muscles and glands

6. © 2012 Pearson Education, Inc. 12-1 Divisions of the Nervous System Functional Divisions of the PNS Receptors and effectors of afferent division Receptors Detect changes or respond to stimuli Neurons and specialized cells Complex sensory organs (e.g., eyes, ears) Effectors Respond to efferent signals Cells and organs

7. © 2012 Pearson Education, Inc. Functional Divisions of the PNS Somatic nervous system (SNS) Controls voluntary and involuntary (reflexes) muscle skeletal contractions Autonomic nervous system (ANS) Controls subconscious actions, contractions of smooth muscle and cardiac muscle, and glandular secretions Sympathetic division has a stimulating effect Parasympathetic division has a relaxing effect

8. © 2012 Pearson Education, Inc. Figure 12-1a The Anatomy of a Multipolar Neuron Dendrites Perikaryon Nucleus Cell body Telodendria Axon This color-coded figure shows the four general regions of a neuron.

9. © 2012 Pearson Education, Inc. Figure 12-1b The Anatomy of a Multipolar Neuron Axolemma Dendritic branches Nissl bodies (RER and free ribosomes) Mitochondrion Axon hillock Initial segment of axon Golgi apparatus Neurofilament Nucleus Nucleolus Dendrite PRESYNAPTIC CELL Telodendria Axon Synaptic terminals See Figure 12–2 POSTSYNAPTIC CELL An understanding of neuron function requires knowing its structural components.

10. © 2012 Pearson Education, Inc. 12-2 Neurons The Structure of Neurons The synapse Presynaptic cell Neuron that sends message Postsynaptic cell Cell that receives message The synaptic cleft The small gap that separates the presynaptic membrane and the postsynaptic membrane

11. © 2012 Pearson Education, Inc. Neurotransmitters Are chemical messengers Are released at presynaptic membrane Affect receptors of postsynaptic membrane Are broken down by enzymes (like AChE) Are reassembled at synaptic terminal

12. © 2012 Pearson Education, Inc. 12-2 Neurons Types of Synapses Neuromuscular junction Synapse between neuron and muscle Neuroglandular junction Synapse between neuron and gland

13. © 2012 Pearson Education, Inc. Figure 12-2 The Structure of a Typical Synapse Telodendrion Synaptic terminal Mitochondrion Synaptic vesicles Presynaptic membrane Postsynaptic membrane Synaptic cleft Endoplasmic reticulum

14. © 2012 Pearson Education, Inc. 12-2 Neurons Functions of Sensory Neurons Monitor internal environment (visceral sensory neurons) Monitor effects of external environment (somatic sensory neurons) Structures of Sensory Neurons Unipolar Cell bodies grouped in sensory ganglia Processes (afferent fibers) extend from sensory receptors to CNS

15. © 2012 Pearson Education, Inc. 12-2 Neurons Three Types of Sensory Receptors 1.Interoceptors Monitor internal systems (digestive, respiratory, cardiovascular, urinary, reproductive) Internal senses (taste, deep pressure, pain) 2.Exteroceptors External senses (touch, temperature, pressure) Distance senses (sight, smell, hearing) 3.Proprioceptors Monitor position and movement (skeletal muscles and joints)

16. © 2012 Pearson Education, Inc. 12-2 Neurons Motor Neurons Carry instructions from CNS to peripheral effectors Via efferent fibers (axons)

17. © 2012 Pearson Education, Inc. 12-2 Neurons Motor Neurons Two major efferent systems 1.Somatic nervous system (SNS) Includes all somatic motor neurons that innervate skeletal muscles 2.Autonomic (visceral) nervous system (ANS) Visceral motor neurons innervate all other peripheral (like internal organs) effectors Smooth muscle, cardiac muscle, glands, adipose tissue

18. © 2012 Pearson Education, Inc. 12-2 Neurons Interneurons Most are located in brain, spinal cord, and autonomic ganglia Between sensory and motor neurons Are responsible for: Distribution of sensory information Coordination of motor activity Are involved in higher functions Memory, planning, learning

19. © 2012 Pearson Education, Inc. 12-6 Axon Diameter and Speed Information “Information” travels within the nervous system As propagated electrical signals (action potentials) The most important information (vision, balance, motor commands) Is carried by large-diameter, myelinated axons

20. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Ion Movements and Electrical Signals All plasma (cell) membranes produce electrical signals by ion movements Transmembrane potential is particularly important to neurons

21. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Five Main Membrane Processes in Neural Activities 1.Resting potential The transmembrane potential of resting cell 2.Graded potential Temporary, localized change in resting potential Caused by stimulus

22. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Five Main Membrane Processes in Neural Activities 3.Action potential Is an electrical impulse Produced by graded potential Propagates along surface of axon to synapse

23. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Five Main Membrane Processes in Neural Activities 4.Synaptic activity Releases neurotransmitters at presynaptic membrane Produces graded potentials in postsynaptic membrane 5.Information processing Response (integration of stimuli) of postsynaptic cell

24. © 2012 Pearson Education, Inc. Figure 12-8 An Overview of Neural Activities Presynaptic neuron Resting potential stimulus produces Graded potential may produce Action potential

25. © 2012 Pearson Education, Inc. Figure 12-8 An Overview of Neural Activities Action potential triggers Synaptic activity Information processing Postsynaptic cell

26. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential The Transmembrane Potential Three important concepts 1.The extracellular fluid (ECF) and intracellular fluid (cytosol) differ greatly in ionic composition Concentration gradient of ions (Na +, K + ) 2.Cells have selectively permeable membranes 3.Membrane permeability varies by ion A&P FLIX Resting Membrane Potential

27. © 2012 Pearson Education, Inc. Figure 12-9 The Resting Potential is the Transmembrane Potential of an Undisturbed Cell CYTOSOL Na + leak channel EXTRACELLULAR FLUID Sodium– potassium exchange pump 0 +30 –70 Plasma membrane Protein –30 K + leak channel 2 K + 3 Na + Cl – Protein mV

28. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Changes in the Transmembrane Potential Transmembrane potential rises or falls In response to temporary changes in membrane permeability Resulting from opening or closing specific membrane channels

29. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Sodium and Potassium Channels Membrane permeability to Na + and K + determines transmembrane potential They are either passive or active

30. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Passive Channels (Leak Channels) Are always open Permeability changes with conditions Active Channels (Gated Channels) Open and close in response to stimuli At resting potential, most gated channels are closed

31. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Three Classes of Gated Channels 1.Chemically gated channels 2.Voltage-gated channels 3.Mechanically gated channels

32. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Chemically Gated Channels Open in presence of specific chemicals (e.g., ACh) at a binding site Found on neuron cell body and dendrites Voltage-gated Channels Respond to changes in transmembrane potential Have activation gates (open) and inactivation gates (close) Characteristic of excitable membrane Found in neural axons, skeletal muscle sarcolemma, cardiac muscle Mechanically Gated Channels Respond to membrane distortion Found in sensory receptors (touch, pressure, vibration)

33. © 2012 Pearson Education, Inc. Figure 12-11a Gated Channels Resting state Presence of ACh Binding site ACh Gated channel Channel closed Channel open A chemically gated Na + channel that opens in response to the presence of ACh at a binding site. Chemically gated channel

34. © 2012 Pearson Education, Inc. Figure 12-11b Gated Channels Voltage-gated channel Channel closed Channel open Channel inactivated +30 mV –60 mV –70 mV Inactivation gate

35. © 2012 Pearson Education, Inc. Figure 12-11c Gated Channels Mechanically gated channel Channel closed Channel open Channel closed Applied pressure Pressure removed

36. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Transmembrane Potential Exists Across Plasma Membrane Because: Cytosol and extracellular fluid have different chemical/ionic balance The plasma membrane is selectively permeable Transmembrane Potential Changes with plasma membrane permeability In response to chemical or physical stimuli

37. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Graded Potentials Also called local potentials Changes in transmembrane potential That cannot spread far from site of stimulation Any stimulus that opens a gated channel Produces a graded potential

38. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Graded Potentials The resting state Opening sodium channel produces graded potential Resting membrane exposed to chemical Sodium channel opens Sodium ions enter the cell Transmembrane potential rises Depolarization occurs

39. © 2012 Pearson Education, Inc. Figure 12-12 Graded Potentials Initial segment Resting State –70 mV EXTRA- CELLULAR FLUID CYTOSOL Resting membrane with closed chemically gated sodium ion channels

40. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Graded Potentials Depolarization A shift in transmembrane potential toward 0 mV Movement of Na + through channel Produces local current Depolarizes nearby plasma membrane (graded potential) Change in potential is proportional to stimulus

41. © 2012 Pearson Education, Inc. Figure 12-12 Graded Potentials Membrane exposed to chemical that opens the sodium ion channels Stimulus applied here Stimulation –65 mV

42. © 2012 Pearson Education, Inc. Figure 12-12 Graded Potentials Graded Potential Spread of sodium ions inside plasma membrane produces a local current that depolarizes adjacent portions of the plasma membrane –60 mV –65 mV –70 mV Local current Local current

43. © 2012 Pearson Education, Inc. 12-4 Transmembrane Potential Graded Potentials Repolarization When the stimulus is removed, transmembrane potential returns to normal Hyperpolarization Increasing the negativity of the resting potential Result of opening a potassium channel Opposite effect of opening a sodium channel Positive ions move out, not into cell

44. © 2012 Pearson Education, Inc. 12-5 Action Potential Action Potentials Propagated changes in transmembrane potential Affect an entire excitable membrane Link graded potentials at cell body with motor end plate actions

45. © 2012 Pearson Education, Inc. 12-5 Action Potential Initiating Action Potential All-or-none principle If a stimulus exceeds threshold amount The action potential is the same No matter how large the stimulus Action potential is either triggered, or not

46. © 2012 Pearson Education, Inc. Figure 12-14 Generation of an Action Potential Resting Potential –70 mV KEY The axolemma contains both voltage- gated sodium channels and voltage- gated potassium channels that are closed when the membrane is at the resting potential. = Sodium ion = Potassium ion

47. © 2012 Pearson Education, Inc. 12-5 Action Potential Four Steps in the Generation of Action Potentials Step 1: Depolarization to threshold Step 2: Activation of Na  channels Step 3: Inactivation of Na  channels and activation of K  channels Step 4: Return to normal permeability

48. © 2012 Pearson Education, Inc. 12-5 Action Potential Step 1: Depolarization to threshold Step 2: Activation of Na  channels Rapid depolarization Na + ions rush into cytoplasm Inner membrane changes from negative to positive

49. © 2012 Pearson Education, Inc. Figure 12-14 Generation of an Action Potential –60 mV KEY = Sodium ion = Potassium ion Local current Depolarization to Threshold

50. © 2012 Pearson Education, Inc. Figure 12-14 Generation of an Action Potential KEY = Sodium ion = Potassium ion +10 mV Activation of Sodium Channels and Rapid Depolarization

51. © 2012 Pearson Education, Inc. 12-5 Action Potential Step 3: Inactivation of Na  channels and activation of K  channels At +30 mV Inactivation gates close (Na  channel inactivation) K  channels open Repolarization begins

52. © 2012 Pearson Education, Inc. Figure 12-14 Generation of an Action Potential KEY = Sodium ion = Potassium ion +30 mV Inactivation of Sodium Channels and Activation of Potassium Channels

53. © 2012 Pearson Education, Inc. 12-5 Action Potential Step 4: Return to normal permeability K + channels begin to close When membrane reaches normal resting potential (–70 mV) K + channels finish closing Membrane is hyperpolarized to –90 mV Transmembrane potential returns to resting level Action potential is over

54. © 2012 Pearson Education, Inc. Figure 12-14 Generation of an Action Potential KEY = Sodium ion = Potassium ion –90 mV Closing of Potassium Channels

55. © 2012 Pearson Education, Inc. Figure 12-14 Generation of an Action Potential Graded potential causes threshold Sodium channels close, voltage- gated potassium channels open Threshold Resting potential Transmembrane potential (mV) D E P O L A R I Z A T I O NR E P O L A R I Z A T I O N Time (msec) Voltage-gated sodium ion channels open All channels closed Cannot respond Responds only to a larger than normal stimulus RELATIVE REFRACTORY PERIOD ABSOLUTE REFRACTORY PERIOD

56. © 2012 Pearson Education, Inc. 12-5 Action Potential Propagation of Action Potentials Propagation Moves action potentials generated in axon hillock Along entire length of axon Two methods of propagating action potentials 1.Continuous propagation (unmyelinated axons) 2.Saltatory propagation (myelinated axons)

57. © 2012 Pearson Education, Inc. 12-5 Action Potential Continuous Propagation Of action potentials along an unmyelinated axon Affects one segment of axon at a time Steps in propagation Step 1: Action potential in segment 1 Depolarizes membrane to +30 mV Local current Step 2: Depolarizes second segment to threshold Second segment develops action potential

58. © 2012 Pearson Education, Inc. Figure 12-15 Continuous Propagation of an Action Potential along an Unmyelinated Axon Action potential Extracellular Fluid Cell membrane Cytosol As an action potential develops at the initial segment , the transmembrane potential at this site depolarizes to +30 mV. –70 mV +30 mV Na + –70 mV

59. © 2012 Pearson Education, Inc. Figure 12-15 Continuous Propagation of an Action Potential along an Unmyelinated Axon As the sodium ions entering at  spread away from the open voltage-gated channels, a graded depolarization quickly brings the membrane in segment  to threshold. Local Graded depolarization current –60 mV –70 mV

60. © 2012 Pearson Education, Inc. 12-5 Action Potential Continuous Propagation Steps in propagation Step 3: First segment enters refractory period Step 4: Local current depolarizes next segment Cycle repeats Action potential travels in one direction (1 m/sec)

61. © 2012 Pearson Education, Inc. Figure 12-15 Continuous Propagation of an Action Potential along an Unmyelinated Axon An action potential now occurs in segment  while segment  beings repolarization. Repolarization (refractory) –70 mV +30 mV Na +

62. © 2012 Pearson Education, Inc. Figure 12-15 Continuous Propagation of an Action Potential along an Unmyelinated Axon As the sodium ions entering at segment  spread laterally, a graded depolarization quickly brings the membrane in segment to threshold, and the cycle is repeated. –60 mV Local current

63. © 2012 Pearson Education, Inc. 12-5 Action Potential Saltatory Propagation Action potential along myelinated axon Faster and uses less energy than continuous propagation Myelin insulates axon, prevents continuous propagation Local current “jumps” from node to node Depolarization occurs only at nodes

64. © 2012 Pearson Education, Inc. Figure 12-16 Saltatory Propagation along a Myelinated Axon –70 mV +30 mV –70 mV An action potential has occurred at the initial segment . Extracellular Fluid Myelinated internode Myelinated internode Myelinated internode Plasma membrane Cytosol Na +

65. © 2012 Pearson Education, Inc. Figure 12-16 Saltatory Propagation along a Myelinated Axon –60 mV–70 mV Local current A local current produces a graded depolarization that brings the axolemma at the next node to threshold.

66. © 2012 Pearson Education, Inc. Figure 12-16 Saltatory Propagation along a Myelinated Axon –70 mV +30 mV An action potential develops at node . Na + Repolarization (refractory)

67. © 2012 Pearson Education, Inc. Figure 12-16 Saltatory Propagation along a Myelinated Axon –60 mV A local current produces a graded depolarization that brings the axolemma at node to threshold. Local current A&P FLIX Propagation of an Action Potential

68. © 2012 Pearson Education, Inc. 12-6 Axon Diameter and Speed Axon Diameter and Propagation Speed Ion movement is related to cytoplasm concentration Axon diameter affects action potential speed The larger the diameter, the lower the resistance

69. © 2012 Pearson Education, Inc. 12-7 Synapses Synaptic Activity Action potentials (nerve impulses) Are transmitted from presynaptic neuron To postsynaptic neuron (or other postsynaptic cell) Across a synapse

70. © 2012 Pearson Education, Inc. 12-7 Synapses Two Types of Synapses 1.Electrical synapses Direct physical contact between cells 2.Chemical synapses Signal transmitted across a gap by chemical neurotransmitters

71. © 2012 Pearson Education, Inc. 12-7 Synapses Electrical Synapses Are locked together at gap junctions (connexons) Allow ions to pass between cells Produce continuous local current and action potential propagation Are found in areas of brain, eye, ciliary ganglia

72. © 2012 Pearson Education, Inc. 12-7 Synapses Chemical Synapses Are found in most synapses between neurons and all synapses between neurons and other cells Cells not in direct contact Action potential may or may not be propagated to postsynaptic cell, depending on: Amount of neurotransmitter released Sensitivity of postsynaptic cell

73. © 2012 Pearson Education, Inc. 12-7 Synapses Two Classes of Neurotransmitters 1.Excitatory neurotransmitters Cause depolarization of postsynaptic membranes Promote action potentials 2.Inhibitory neurotransmitters Cause hyperpolarization of postsynaptic membranes Suppress action potentials

74. © 2012 Pearson Education, Inc. 12-7 Synapses The Effect of a Neurotransmitter On a postsynaptic membrane Depends on the receptor Not on the neurotransmitter For example, acetylcholine (ACh) Usually promotes action potentials But inhibits cardiac neuromuscular junctions

75. © 2012 Pearson Education, Inc. 12-7 Synapses Cholinergic Synapses Any synapse that releases ACh at: 1.All neuromuscular junctions with skeletal muscle fibers 2.Many synapses in CNS 3.All neuron-to-neuron synapses in PNS 4.All neuromuscular and neuroglandular junctions of ANS parasympathetic division

76. © 2012 Pearson Education, Inc. 12-7 Synapses Events at a Cholinergic Synapse 1.Action potential arrives, depolarizes synaptic terminal 2.Calcium ions enter synaptic terminal, trigger exocytosis of ACh 3.ACh binds to receptors, depolarizes postsynaptic membrane 4.ACh removed by AChE AChE breaks ACh into acetate and choline

77. © 2012 Pearson Education, Inc. Figure 12-17 Events in the Functioning of a Cholinergic Synapse POSTSYNAPTIC NEURON An action potential arrives and depolarizes the synaptic terminal Presynaptic neuron Synaptic vesicles ER Action potential EXTRACELLULAR FLUID Synaptic terminal Initial segment AChE

78. © 2012 Pearson Education, Inc. Figure 12-17 Events in the Functioning of a Cholinergic Synapse Extracellular Ca 2+ enters the synaptic terminal, triggering the exocytosis of ACh Ca 2+ ACh Synaptic cleft Chemically gated sodium ion channels

79. © 2012 Pearson Education, Inc. Figure 12-17 Events in the Functioning of a Cholinergic Synapse Na + ACh binds to receptors and depolarizes the postsynaptic membrane Initiation of action potential if threshold is reached at the initial segment

80. © 2012 Pearson Education, Inc. Figure 12-17 Events in the Functioning of a Cholinergic Synapse ACh is removed by AChE Propagation of action potential (if generated)

81. © 2012 Pearson Education, Inc. Table 12-4 Synaptic Activity Mitochondrion Acetylcholine Synaptic vesicle SYNAPTIC TERMINAL SYNAPTIC CLEFT ACh receptor (AChE) Acetylcholinesterase Choline Acetate POSTSYNAPTIC MEMBRANE

82. © 2012 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

83. © 2012 Pearson Education, Inc. 12-8 Neurotransmitters and Neuromodulators Important Neurotransmitters Other than acetylcholine Norepinephrine (NE) Dopamine Serotonin Gamma aminobutyric acid (GABA)

84. © 2012 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

85. © 2012 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

86. © 2012 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

87. © 2012 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

88. © 2012 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

89. © 2012 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

90. © 2012 Pearson Education, Inc. 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

91. © 2012 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

92. © 2012 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

93. © 2012 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

94. © 2012 Pearson Education, Inc. Figure 12-19a Temporal and Spatial Summation First stimulus arrives FIRST STIMULUS Initial segment Second stimulus arrives and is added to the first stimulus SECOND STIMULUS Threshold reached Action potential is generated ACTION POTENTIAL PROPAGATION 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 of the first.

95. © 2012 Pearson Education, Inc. Figure 12-19b Temporal and Spatial Summation Two stimuli arrive simultaneously Action potential is generated TWO SIMULTANEOUS STIMULI ACTION POTENTIAL PROPAGATION Threshold reached 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.

96. © 2012 Pearson Education, Inc. Figure 12-21a Presynaptic Inhibition and Presynaptic Facilitation GABA release Action potential arrives Inactivation of calcium channels 4. Reduced effect on postsynaptic membrane 2. Less calcium enters Ca 2+ 3. Less neurotransmitter released 1. Action potential arrives Presynaptic inhibition

97. © 2012 Pearson Education, Inc. Figure 12-21b Presynaptic Inhibition and Presynaptic Facilitation Ca 2+ Action potential arrives Serotonin release Activation of calcium channels 2. More calcium enters 1. Action potential arrives 3. More neurotransmitter released 4. Increased effect on postsynaptic membrane Presynaptic facilitation