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48 49
- 1. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Neurons, Synapses, and Signaling Chapter 48 授課老師: 曾昭能 第一教學大樓 N914 分機2692 cntseng@kmu.edu.tw
- 2. Overview: Lines of Communication • The cone snail kills prey with venom that disables neurons • Neurons are nerve cells that transfer information within the body • Neurons use two types of .: 1. electrical signals (long-distance) 2. chemical signals (short-distance) © 2011 Pearson Education, Inc.
- 3. Topics • Flow of information in nervous system and neuron • Membrane potential • Synapse • Neurotransmitter
- 4. Concept 48.1: Neuron organization and structure reflect function in information transfer • Information Processing • Nervous systems process information in three stages: – sensory input – integration – motor output © 2011 Pearson Education, Inc.
- 5. Fig. 48-3 Sensor Sensory input Integration Effector Motor output Peripheral nervous system (PNS) Central nervous system (CNS) Sensory neuron Motor neuron Interneuron
- 6. Neuron Structure and Function • Most of a neuron’s organelles are in the cell body • Most neurons have dendrites, highly branched extensions that receive signals from other neurons • The axon is typically a much longer extension that transmits signals to other cells at synapses • The cone-shaped base of an axon is called the axon hillock 軸突坵 © 2011 Pearson Education, Inc.
- 7. Fig. 48-4 Dendrites 接收訊息 Stimulus Nucleus Cell body 代謝 訊息整合 Axon hillock 軸突丘 動作電位發起處 Presynaptic cell Axon 傳出訊息 Synaptic terminals Synapse Postsynaptic cell Neurotransmitter
- 8. Concept 48.2: Ion pumps and ion channels maintain the resting potential of a neuron • Every cell has a voltage (difference in electrical charge) across its plasma membrane called a membrane potential (potential=電壓,電位) • Messages are transmitted as changes in membrane potential • The resting potential is the membrane potential of a neuron not sending signals –The inside of a cell is negative relative to the outside
- 9. OUTSIDE CELL [K+] 5 mM [Na+] 150 mM [Cl–] 120 mM INSIDE CELL [K+] 140 mM [Na+] 15 mM [Cl–] 10 mM [A–] 100 mM (a) (b) OUTSIDE CELL Na+ Key K+ Sodium- potassium pump Potassium channel Sodium channel INSIDE CELL Membrane potential is established by 1. uneven distribution of ions across membrane 2. opening of ion-specific channel
- 10. Ion transport across membrane • ATPase pump • Na+/K+ pump • Ion channels • Leak K+ channel • Voltage-gated ion channel • Voltage-gated Na+ channel • Voltage-gated K+ channel
- 11. Resting membrane potential 靜止膜電位 • Caused by 1. Na+/K+ pump • Na+ → out • K+ → in • 膜內外電價仍相等 2. Leak K+ channel • 使部分K+漏出 • 細胞內損失正電價而帶負 電 Na+ Na+ Na+ Na+ Na+ Na+ K+ K+ K+ K+ K+ K+ K+ Na+
- 12. 靜止膜電位是一種平衡電位 Equilibrium potential • 在造成靜止膜電位時 K+的移動會達到平衡 因為下列兩者的 作用力方向相反且互相抗衡 – 擴散 • Chemical gradient • 驅使K+往細胞外流 – 電價堆積 • Electrical gradient • 逐漸變強 使K+不易外流 • 因此靜止膜電位最後會維持一穩定值 – 可以Nernst equation 計算
- 13. NERNST EQUATION (參考用) ► Chemical gradient Free energy change per mole of solute moved across the plasma membrane (moving out) △Gconc = - RTln(Co/Ci) ► Electrical gradient Free energy change per mole of ion with charge z moved across the plasma membrane with inside relative voltage V △Gvolt = zFV ► There is no free energy change at equilibrium; △Gconc + △Gvolt = 0 (zFV) + (-RTln(Co/Ci)) = 0 (zFV) = RTln(Co/Ci) V = 2.3(RT/zF)．log(Co/Ci) ► For a univalent ion at 37 C, 2.3(RT/zF) = 61.5 (mV) V = log(Co/Ci) × 61.5 (mV) ► Typical cell Vm=-89mV, [K+]o=5mM [K+]i=140mM
- 15. Figure 48.8 Inner chamber 90 mV 62 mVOuter chamber Inner chamber Outer chamber 140 mM KCl 150 mM NaCl 5 mM KCl 15 mM NaCl Potassium channel Sodium channel Artificial membrane K Na Cl Cl (a) Membrane selectively permeable to K (b) Membrane selectively permeable to Na EK 62 mV 90 mV ENa 62 mV 62 mV
- 16. 觀念回顧 • 膜電位的產生 – 因為 1.膜內外離子分佈不均 2.打開特定離子通道 – 離子移動會達成平衡,產生穩定的電壓 • 單一離子通道造成的膜電位可以 Nernst equation 計算 出 • 由Co/Ci比值決定 (10/1 與100/10產生相同膜電位) – 交替打開不同的離子通道就可使膜電位在不同值之間跳 動 • 打開K+ channel: -90 mV • 打開Na+ channel: +60 mV
- 17. 觀念補充 • 細胞的靜止膜電位(-70mV)的實際值比K+的平 衡電位理埨值(-90mV)稍高 – 雖然主要由K+離子通道造成但平常仍有相對少數 的Na+通道是開著 • 計算單一離子通道產生之平衡電位 – 與通道數目無關 • 實際會受相對通道數目影響
- 18. Concept 48.3: Action potentials are the signals conducted by axons • Changes in membrane potential occur because neurons contain gated ion channels that open or close in response to stimuli © 2011 Pearson Education, Inc. Microelectrode Voltage recorder Reference electrode TECHNIQUE
- 19. • 過極化 – When gated K+ channels open, K+ diffuses out, making the inside of the cell more negative – This is hyperpolarization過極化, an increase in magnitude of the membrane potential © 2011 Pearson Education, Inc. Hyperpolarization and Depolarization
- 20. • Opening other types of ion channels triggers a depolarization去極化, a reduction in the magnitude of the membrane potential • For example, depolarization occurs if gated Na+ channels open and Na+ diffuses into the cell © 2011 Pearson Education, Inc.
- 21. Stimulus Threshold Resting potential Hyperpolarizations Time (msec) 50 0 50 100 10 2 3 4 5 50 0 50 100 50 0 50 100 Time (msec) 10 2 3 4 5 Time (msec) 10 2 3 4 5 6 Threshold Resting potential Threshold Resting potential Stimulus Strong depolarizing stimulus Action potential Depolarizations Membranepotential(mV) Membranepotential(mV) Membranepotential(mV) (a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K (b) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to Na (c) Action potential triggered by a depolarization that reaches the threshold Figure 48.10
- 22. • 神經細胞受足夠刺激,使其興奮,且膜電位超過閾 值後,才會產生動作電位 • Graded potential 階梯電位 – 動作電位產生前的膜電位變化 – 發生於樹突及細胞本體 – 刺激造成特定離子通道打開 – 大小與刺激程度成比例‚可加成 – 被動擴散‚會耗損
- 23. • Neurons contain gated ion channels that open or close in response to stimuli • Gated(看管,控制) ion channels open or close in response to – membrane stretch • Mechanoreceptors – the binding of a specific ligand 配體 • Ligand-gated ion channels – a change in the membrane potential • Voltage-gated ion channels
- 24. ACTION POTENTIAL • Two kinds of voltage-gated channels open during action potential – voltage-gated Na+ channel: 開得快 關得快 – voltage-gated K+ channel: 開得慢 關得慢 • Voltage-gated Na+ channel – 因受刺激→去極化→打開 – Na+進入→造成更大去極化→形成連鎖反應 1. 最後所有Na+通道都打開 • 每次AP時所有Na+ 通道都打開 • 所以AP 大小都一樣 2. 在鄰近區域引發去極化並產生AP
- 25. 動作電位中離子通道之開關 鈉離子電位閘門通道: 開--------塞住(inactivation) 鉀離子電位閘門通道: 開------------------關 鈉離子流入膜電位偏正 更多鉀離子流出 膜電位比平常更負
- 26. OUTSIDE OF CELL INSIDE OF CELL Inactivation loop Sodium channel Potassium channel Action potential Threshold Resting potential Time Membranepotential (mV) 50 100 50 0 Na K Key 2 1 3 4 5 1 2 3 4 5 1 Resting state Undershoot Depolarization Rising phase of the action potential Falling phase of the action potential Figure 48.11-5
- 27. Refractory Period不反應期 • Absolute refractory period: – Axon membrane is incapable of producing another AP. – VG Na + channel inactivated • Relative refractory period: – More K+ channels are open (VG + leak K+ channels). – Hyperpolarization – Axon membrane can produce another action potential, but requires stronger stimulus.
- 28. Conduction of Action Potentials • An action potential travel by regenerating itself along the axon – action potential is generated at the axon hillock, • Refractory period prevents the action potential from traveling backwards • Conduction speed is increased by – Larger diameter – Myelination
- 29. Fig. 48-12 Axon Schwann cell Myelin sheath Nodes of Ranvier Node of Ranvier Schwann cell Nucleus of Schwann cell Layers of myelin Axon 0.1 µm Myelin sheaths are made by glia— oligodendrocytes in the CNS and Schwann cells in the PNS
- 30. Saltatory Conduction • Action potentials in myelinated axons – Jump between the nodes of Ranvier in a process called saltatory(跳躍)conduction Cell body Schwann cell Myelin sheath Axon Depolarized region (node of Ranvier) + + + + + + + + + + + – – – – – – – –– – – – Figure 48.15
- 31. Concept 48.4: Neurons communicate with other cells at synapses • At electrical synapses, – the electrical current flows from one neuron to another • At chemical synapses, – a chemical neurotransmitter carries information across the gap junction • Most synapses in human brain are chemical synapses © 2011 Pearson Education, Inc.
- 32. Chemical synapse • Synaptic vesicle突觸小泡 • Neurotransmitter • Voltage-gated calcium channel 因去極化而打 開 • Synaptic cleft 突觸溝 • Ligand-gated ion channel 與神經傳導物質結 合而打開
- 33. Presynaptic cell Postsynaptic cell Axon Presynaptic membrane Synaptic vesicle containing neurotransmitter Postsynaptic membrane Synaptic cleft Voltage-gated Ca2 channel Ligand-gated ion channels Ca2 Na K 2 1 3 4 Figure 48.15
- 34. Generation of Postsynaptic Potentials • Postsynaptic potential – 神經傳導物質釋放後，在突觸後細胞造成的局部 膜電位變化 • Direct synaptic transmission – 打開 ligand-gated ion channels, ionotropic receptor • Indirect synaptic transmission – Metabotropic receptor – 經由活化G蛋白與second messenger間接影響後 突觸端的離子通道/膜電位 – slower onset but last longer
- 35. • Postsynaptic potentials fall into two categories: – Excitatory postsynaptic potentials (EPSPs) 興奮性 更容易產生動作電位 – Inhibitory postsynaptic potentials (IPSPs)抑制性 更 不容易產生動作電位 • After release, the neurotransmitter – May diffuse out of the synaptic cleft – May be taken up by surrounding cells – May be degraded by enzymes
- 36. Summation總和, 神經細胞的訊息處理 • Through summation, an IPSP can counter the effect of an EPSP • The summed effect of EPSPs and IPSPs determines whether an axon hillock will reach threshold and generate an action potential © 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
- 37. Figure 48.17 Terminal branch of presynaptic neuron Postsynaptic neuron Axon hillock E1 E2 E1 E2 E1 E2 E1 E2 I I I I 0 70 Membranepotential(mV) Threshold of axon of postsynaptic neuron Resting potential Action potential Action potential IE1 E1 E1 E1 E1 E2 E1 I Subthreshold, no summation (a) (b) Temporal summation (c) Spatial summation Spatial summation of EPSP and IPSP (d) E1
- 38. Neurotransmitters • There are more than 100 neurotransmitters, belonging to five groups: acetylcholine, biogenic amines, amino acids, neuropeptides, and gases • A single neurotransmitter may have more than a dozen different receptors © 2011 Pearson Education, Inc.
- 39. Table 48.2
- 40. Acetylcholine • Acetylcholine is a common neurotransmitter in vertebrates and invertebrates • In vertebrates it is usually an excitatory transmitter
- 41. Biogenic Amines • Biogenic amines include epinephrine, norepinephrine, dopamine, and serotonin • They are active in the CNS and PNS
- 42. Amino Acids • Two amino acids are known to function as major neurotransmitters in the CNS: gamma- aminobutyric acid (GABA, -氨基丁酸) and glutamate谷氨酸
- 43. Neuropeptides • Several neuropeptides, relatively short chains of amino acids, also function as neurotransmitters • Neuropeptides include substance P (物質P) and endorphins腦內啡, which both affect our perception of pain • Opiates鴉片類bind to the same receptors as endorphins and can be used as painkillers
- 44. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Nervous Systems Chapter 49 授課老師: 曾昭能 第一教學大樓 N914 分機2692 cntseng@kmu.edu.tw
- 45. Topics • Evolution of nervous system – Vertebrate nervous system – PNS • Brain – Sleep & arousal, Biological clock – Emotion, Language, Learning & Memory – Neurological Disease
- 46. • Each single-celled organism can respond to stimuli in its environment • Animals are multicellular and most groups respond to stimuli using systems of neurons © 2011 Pearson Education, Inc. Concept 49.1: Nervous systems consist of circuits of neurons and supporting cells
- 47. Nerve net (a) Hydra (cnidarian) Radial nerve Nerve ring (b) Sea star (echinoderm) Nerve net: a series of interconnected nerve cells, no nerve Nerves: bundles of nerve fibers Radially symmetrical
- 48. Eyespot Brain Nerve cords Transverse nerve Brain Ventral nerve cord Segmental ganglia (c) Planarian (flatworm) (d) Leech (annelid) flatworms have a central nervous system (CNS) consists of a brain and longitudinal nerve cords Bilaterally symmetrical Ganglia segmentally arranged clusters of neurons Cephalization & Centralization
- 49. (e) Insect (arthropod) Segmental ganglia Ventral nerve cord Brain Anterior nerve ring Longitudinal nerve cords (f) Chiton (mollusc) (g) Squid (mollusc) Ganglia Brain Ganglia Brain Spinal cord (dorsal nerve cord) Sensory ganglia (h) Salamander (vertebrate) Nervous system organization correlates with lifestyle Sessile molluscs (e.g., clams and chitons) have simple systems, More complex molluscs (e.g., octopuses and squids) have more sophisticated systems In vertebrates CNS: brain and spinal cord Peripheral nervous system (PNS): nerves and ganglia
- 50. Organization of the Vertebrate Nervous System • The spinal cord – conveys information from and to the brain – produces reflexes independently of the brain • A reflex is the body’s automatic response to a stimulus – For example, a doctor uses a mallet to trigger a knee-jerk reflex © 2011 Pearson Education, Inc.
- 51. Quadriceps muscle Cell body of sensory neuron in dorsal root ganglion Gray matter White matter Hamstring muscle Spinal cord (cross section) Sensory neuron Motor neuron Interneuron Figure 49.3
- 52. • Invertebrates – Ventral腹 nerve cord • Vertebrates – Dorsal背 spinal cord • The spinal cord and brain develop from the embryonic nerve cord • The nerve cord gives rise to the central canal and ventricles of the brain © 2011 Pearson Education, Inc.
- 53. Figure 49.4 Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Cranial nerves Ganglia outside CNS Spinal nerves 骨 頭 包 覆
- 54. • Cerebrospinal fluid, CSF – Filtered from blood – Cushion the brain and spinal cord – central canal of the spinal cord – ventricles of the brain • Gray matter – neuron cell bodies, dendrites, and unmyelinated axons • White matter – bundles of myelinated axons
- 55. Glia in the CNS • Ependymal cells室管膜細胞 promote circulation of cerebrospinal fluid • Microglia微膠細胞 protect the nervous system from microorganisms • Oligodendrocytes寡突細胞 and Schwann cells form the myelin sheaths around axons Oligodendrocyte Microglial cell Schwann cells Ependy- mal cell Neuron Astrocyte CNS PNS Capillary VENTRICLE
- 56. • Astrocytes 星狀細胞 – structural support for neurons – regulate extracellular ions and neurotransmitters – induce the formation of a blood- brain barrier that regulates the chemical environment of the CNS • Radial glia play a role in the embryonic development of the nervous system
- 57. The Peripheral Nervous System • Transmits information to and from CNS • afferent neurons transmit information to the CNS • efferent neurons transmit information away from the CNS • Cranial nerves • Spinal nerves
- 58. • The PNS has two efferent components – The motor system • carries signals to skeletal muscles and is voluntary – The autonomic nervous system • regulates smooth and cardiac muscles and is generally involuntary • The sympathetic regulates arousal and energy generation (―fight-or-flight‖ response) • The parasympathetic system has antagonistic effects on target organs and promotes calming and a return to ―rest and digest‖ functions • The enteric division controls activity of the digestive tract, pancreas, and gallbladder © 2011 Pearson Education, Inc.
- 59. Efferent neuronsAfferent neurons Central Nervous System (information processing) Peripheral Nervous System Sensory receptors Internal and external stimuli Autonomic nervous system Motor system Control of skeletal muscle Sympathetic division Parasympathetic division Enteric division Control of smooth muscles, cardiac muscles, glands Figure 49.7
- 60. Parasympathetic division Action on target organs: Constricts pupil of eye Stimulates salivary gland secretion Constricts bronchi in lungs Slows heart Stimulates activity of stomach and intestines Stimulates activity of pancreas Stimulates gallbladder Promotes emptying of bladder Promotes erection of genitalia Cervical Thoracic Lumbar Synapse Sacral Sympathetic ganglia Sympathetic division Action on target organs: Dilates pupil of eye Accelerates heart Inhibits salivary gland secretion Relaxes bronchi in lungs Inhibits activity of stomach and intestines Inhibits activity of pancreas Stimulates glucose release from liver; inhibits gallbladder Stimulates adrenal medulla Inhibits emptying of bladder Promotes ejaculation and vaginal contractions
- 61. Table 49-1
- 62. Concept 49.2: The vertebrate brain is regionally specialized • Specific brain structures are particularly specialized for diverse functions • These structures arise during embryonic development © 2011 Pearson Education, Inc.
- 63. Embryonic brain regions Brain structures in child and adult Forebrain Midbrain Hindbrain Telencephalon Diencephalon Mesencephalon Metencephalon Myelencephalon Cerebrum (includes cerebral cortex, white matter, basal nuclei) Diencephalon (thalamus, hypothalamus, epithalamus) Midbrain (part of brainstem) Pons (part of brainstem), cerebellum Medulla oblongata (part of brainstem) Midbrain Forebrain Hindbrain Telencephalon Diencephalon Mesencephalon Metencephalon Myelencephalon Spinal cord Cerebrum Diencephalon Midbrain Pons Medulla oblongata Cerebellum Spinal cord ChildEmbryo at 5 weeksEmbryo at 1 month Figure 49.9b
- 64. Figure 49.9d Diencephalon Thalamus Pineal gland Hypothalamus Pituitary gland Spinal cord Brainstem Midbrain Pons Medulla oblongata
- 65. Figure 49.9c Adult brain viewed from the rear Cerebellum Basal nucleiCerebrum Left cerebral hemisphere Right cerebral hemisphere Cerebral cortex Corpus callosum
- 68. Arousal and Sleep • The brainstem and cerebrum control arousal and sleep • The core of the brainstem has a diffuse network of neurons called the reticular formation • This regulates the amount and type of information that reaches the cerebral cortex and affects alertness • The hormone melatonin is released by the pineal gland and plays a role in bird and mammal sleep cycles © 2011 Pearson Education, Inc.
- 69. Figure 49.10 Eye Reticular formation Input from touch, pain, and temperature receptors Input from nerves of ears suprachiasmatic nucleus (SCN)
- 70. • Sleep is essential and may play a role in the consolidation of learning and memory • Dolphins sleep with one brain hemisphere at a time and are therefore able to swim while ―asleep‖ © 2011 Pearson Education, Inc.
- 71. Figure 49.11 Low-frequency waves characteristic of sleep High-frequency waves characteristic of wakefulness Key Location Time: 0 hours Time: 1 hour Left hemisphere Right hemisphere
- 72. Biological Clock Regulation • Cycles of sleep and wakefulness are examples of circardian rhythms, daily cycles of biological activity • Mammalian circadian rhythms rely on a biological clock, molecular mechanism that directs periodic gene expression • Biological clocks are typically synchronized to light and dark cycles © 2011 Pearson Education, Inc.
- 73. • In mammals, circadian rhythms are coordinated by a group of neurons in the hypothalamus called the suprachiasmatic nucleus (視交叉上 核SCN) • The SCN acts as a pacemaker, synchronizing the biological clock © 2011 Pearson Education, Inc.
- 74. Emotions • Generation and experience of emotions involves many brain structures including the amygdala, hippocampus, and parts of the thalamus • The structure most important to the storage of emotion in the memory is the amygdala, a mass of nuclei near the base of the cerebrum • The limbic system also functions in motivation, olfaction, behavior, and memory © 2011 Pearson Education, Inc.
- 76. Concept 49.3: The cerebral cortex controls voluntary movement and cognitive functions • The cerebrum, the largest structure in the human brain, is essential for awareness 察覺 , language, cognition, memory, and consciousness 意識 • Four regions, or lobes (frontal, temporal, occipital, and parietal) are landmarks for particular functions © 2011 Pearson Education, Inc.
- 77. Figure 49.15 Motor cortex (control of skeletal muscles) Frontal lobe Prefrontal cortex (decision making, planning) Broca’s area (forming speech) Temporal lobe Auditory cortex (hearing) Wernicke’s area (comprehending language) Somatosensory cortex (sense of touch) Parietal lobe Sensory association cortex (integration of sensory information) Visual association cortex (combining images and object recognition) Occipital lobe Cerebellum Visual cortex (processing visual stimuli and pattern recognition)
- 78. Language and Speech • Broca’s area – in the frontal lobe – is active when speech is generated • Wernicke’s area – in the temporal lobe – is active when speech is heard • These areas belong to a larger network of regions involved in language • All in the left brain © 2011 Pearson Education, Inc.
- 80. Lateralization of Cortical Function • The two hemispheres make distinct contributions to brain function • The differences in hemisphere function are called lateralization • Lateralization is partly linked to handedness • The two hemispheres work together by communicating through the fibers of the corpus callosum 胼胝體 © 2011 Pearson Education, Inc.
- 81. • The left hemisphere is more adept at – language, math, logic, and processing of serial sequences – dominant • The right hemisphere is stronger at – pattern recognition, nonverbal thinking, and emotional processing © 2011 Pearson Education, Inc.
- 82. Information Processing • Somatosensory receptors provide information about touch, pain, pressure, temperature, and the position of muscles and limbs • The thalamus 丘腦 directs different types of input to distinct locations © 2011 Pearson Education, Inc.
- 83. Figure 49.17 Frontal lobe Parietal lobe Primary motor cortex Primary somatosensory cortex GenitaliaToes Abdominal organs Tongue Jaw Hip Knee Tongue Pharynx Head Neck Trunk Hip Leg
- 84. Information Processing in the Cerebral Cortex • Input and processing of sensory information in the brain 1. sensory organs 2. somatosensory receptors 3. specific primary sensory areas of the brain 4. adjacent association areas process and integrate information from different sensory areas • In the primary cortices, neurons are distributed according to the body part that generates sensory input or receives motor input
- 85. Frontal Lobe Function • Frontal lobe damage may impair decision making and emotional responses but leave intellect and memory intact • The frontal lobes have a substantial effect on ―executive functions‖ • 執行功能是一系列高層次的認知 過程，可以控制、整合、組織和 維持其他認知能力 © 2011 Pearson Education, Inc.
- 86. Evolution of Cognition in Vertebrates • Previous ideas that a highly convoluted neocortex is required for advanced cognition may be incorrect • The anatomical basis for sophisticated information processing in birds (without a highly convoluted neocortex) appears to be the clustering of nuclei in the top or outer portion of the brain (pallium) © 2011 Pearson Education, Inc.
- 87. Human brain Avian brain Thalamus Midbrain Hindbrain Cerebellum Avian brain to scale Thalamus Midbrain Hindbrain Cerebellum Cerebrum (including cerebral cortex) Cerebrum (including pallium) Figure 49.18
- 88. Concept 49.4 Changes in synaptic connections underlie memory and learning • Two processes dominate embryonic development of the nervous system(連結形成 時) – Neurons compete for growth-supporting factors in order to survive – Only half the synapses that form during embryo development survive into adulthood © 2011 Pearson Education, Inc.
- 89. Neural Plasticity可塑性 • Neural plasticity describes the ability of the nervous system to be modified after birth • Changes can strengthen or weaken signaling at a synapse © 2011 Pearson Education, Inc.
- 90. Figure 49.19 N2 N1 N2 N1 (a) Synapses are strengthened or weakened in response to activity. (b) If two synapses are often active at the same time, the strength of the postsynaptic response may increase at both synapses.
- 91. Memory and Learning • The formation of memories is an example of neural plasticity • Short-term memory is accessed via the hippocampus • The hippocampus also plays a role in forming long-term memory, which is stored in the cerebral cortex • Some consolidation of memory is thought to occur during sleep © 2011 Pearson Education, Inc.
- 92. Long-Term Potentiation (LTP) • As a form of learning, LTP increases the strength of synaptic transmission • If the presynaptic and postsynaptic neurons are stimulated at the same time, the set of receptors present on the postsynaptic membranes changes © 2011 Pearson Education, Inc.
- 93. Long-Term Potentiation (LTP) • LTP involves glutamate receptors – AMPA receptor: mostly internalized – NMDA receptor: needs depolarization to remove Mg2+ block, permeable to Ca2+ (gated by both ligand and voltage) – Ca2+ signaling enhances synapse strength by targeting AMPA receptors to membrane © 2011 Pearson Education, Inc.
- 94. Figure 49.20a PRESYNAPTIC NEURON Glutamate Mg2 Ca2 Na NMDA receptor (closed) Stored AMPA receptor NMDA receptor (open) POSTSYNAPTIC NEURON (a) Synapse prior to long-term potentiation (LTP)
- 95. Figure 49.20b (b) Establishing LTP 1 2 3 AMPA receptor NMDA receptor Mg2 Ca2 Na
- 96. Figure 49.20c (c) Synapse exhibiting LTP Depolarization Action potential AMPA receptor NMDA receptor 1 3 42
- 97. • 同時活化的神經元之間的連結會被強化 – 同時滿足打開NMDA receptor 的條件 • 作用頻繁的突觸也會被強化 – 突觸溝充滿glutamate, 藉由少數可活化的 AMPA或NMDA receptor 產生去極化, 進而 活化其他 receptor
- 98. Stem Cells in the Brain • The adult human brain contains neural stem cells • In mice, stem cells in the brain can give rise to neurons that mature and become incorporated into the adult nervous system • Such neurons play an essential role in learning and memory © 2011 Pearson Education, Inc.
- 99. Concept 49.5: Nervous system disorders can be explained in molecular terms • Disorders of the nervous system include – Schizophrenia – Depression – Addiction – Alzheimer’s disease – Parkinson’s disease • Genetic and environmental factors contribute to diseases of the nervous system © 2011 Pearson Education, Inc.
- 100. Schizophrenia • About 1% of the world’s population suffers from schizophrenia • Schizophrenia is characterized by hallucinations, delusions, and other symptoms • Available treatments focus on brain pathways that use dopamine as a neurotransmitter © 2011 Pearson Education, Inc.
- 101. Figure 49.22 Genes shared with relatives of person with schizophrenia 12.5% (3rd-degree relative) 25% (2nd-degree relative) 50% (1st-degree relative) 100% 50 40 30 20 10 0 Relationship to person with schizophrenia Riskofdevelopingschizophrenia(%) Individual, general population Firstcousin Uncle/aunt Nephew/ niece Fraternal twin Identical twin Grandchild Halfsibling Parent Fullsibling Child
- 102. Depression • Two broad forms of depressive illness are known: major depressive disorder and bipolar disorder • In major depressive disorder, patients have a persistent lack of interest or pleasure in most activities • Bipolar disorder is characterized by manic (high-mood) and depressive (low-mood) phases • Treatments for these types of depression include drugs such as Prozac (enhances serotonin activity) © 2011 Pearson Education, Inc.
- 103. Drug Addiction and the Brain’s Reward System • The brain’s reward system rewards motivation with pleasure (where dopamine is the major transmitter) • Some drugs are addictive because they increase activity of the brain’s reward system • These drugs include cocaine, amphetamine, heroin, alcohol, and tobacco • Drug addiction is characterized by compulsive consumption and an inability to control intake © 2011 Pearson Education, Inc.
- 104. • Addictive drugs enhance the activity of the dopamine pathway • Drug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drug © 2011 Pearson Education, Inc.
- 105. Figure 49.23 Nicotine stimulates dopamine- releasing VTA neuron. Inhibitory neuron Dopamine- releasing VTA neuron Cerebral neuron of reward pathway Opium and heroin decrease activity of inhibitory neuron. Cocaine and amphetamines block removal of dopamine from synaptic cleft. Reward system response
- 106. Alzheimer’s Disease • Alzheimer’s disease is a mental deterioration characterized by confusion and memory loss • Alzheimer’s disease is caused by the formation of neurofibrillary tangles and amyloid plaques in the brain • There is no cure for this disease though some drugs are effective at relieving symptoms © 2011 Pearson Education, Inc. Amyloid plaque Neurofibrillary tangle 20 m
- 107. Parkinson’s Disease • Parkinson’s disease is a motor disorder caused by the death of dopamine-secreting neurons in the midbrain • It is characterized by muscle tremors, flexed posture, and a shuffling gait • There is no cure, although drugs and various other approaches are used to manage symptoms © 2011 Pearson Education, Inc.