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Chapter 24 Nervous Systems Nervous System Structure and Function Nerve Signals and Their Transmission Neurons receive and process inputs and communicate responses. Nerve signals are electrical messages generated by the movement of ions across membranes. An Overview of Animal Nervous Systems The vertebrate nervous system can be understood as a structural and functional hierarchy. The Human Brain Modern research techniques are illuminating how the interplay of brain regions controls our actions and behavior. Nervous systems receive sensory input, interpret it, and send out appropriate commands Sensory input Integration 感受器 Sensory receptor Motor output Brain and spinal cord 作用細胞 Effector cells Muscle Gland cells Peripheral nervous system (PNS) 周邊神經系統 Central nervous system (CNS) 中樞神經系統 Organization of a nervous system Analysis Interpretation Nervous systems 12 pairs 31 pairs 神經元 星狀神經膠細胞 寡突膠細胞 Nerve & Ganglia in the PNS 神經節 Ganglia (ganglion): clusters of neuron cell bodies. 神經 Nerve: a bundle of neurons tightly wrapped in connective tissue. Sensory neurons 感覺神經元 - convey signals from sensory receptors to the CNS. Interneurons 連絡神經元 - are located entirely in the CNS. - integrate information, and send it to other interneurons/motor neurons. Motor neurons 運動神經元 - convey signals to effector cells. The knee-jerk reflex 膝躍反射 1 Sensory receptor 2 Sensory neuron Brain Ganglion Motor neuron Spinal cord 3 Quadriceps muscles 4 Interneuron Nerve Flexor muscles PNS CNS Neurons are the functional units of nervous systems 神經元 Neurons are - cells specialized for carrying signals. - the functional units of the nervous system. A neuron consists of - a cell body. 細胞本體 - two types of extensions (fibers) that conduct signals: - numerous dendrites. 樹突 - single axon. 軸突 Myelin sheaths 髓鞘 - enclose axons. - form a cellular insulation. - speed up signal transmission. Structure of a myelinated motor neuron Signal direction Cell body Nucleus 蘭氏結 Signal pathway Node of Ranvier Layers of myelin Nodes of Ranvier Myelin sheath Dendrites Cell body 許旺細胞 突觸末(端)稍 Schwann cell Synaptic terminals Nucleus Axon 突觸 Schwann cell Transmission of the action potential 動作電位 150 m/sec Glia cells 神經膠細胞 Glia supporting cells: (1) noruish neoruns (2) insulate the axons of neurons (3) maintain homeostasis of the extracellular fluid surrounding neurons. 微膠細胞 星狀神經膠細胞 寡突膠細胞 管膜細胞 Multiple sclerosis (MS) 多發性硬化症 Autoimmune disease by Tc cells Nerve function depends on charge differences across neuron membranes At rest, a neuron’s plasma membrane has potential energy, 膜電位 the membrane potential: exists as an electrical charge difference across the neuron’s plasma membrance. in which - just inside the cell is slightly negative. - just outside the cell is slightly positive. 靜止電位 The resting potential is the voltage across the plasma membrane of a resting neuron. (about -70 mV). The membrane potential can change from its resting value if the membrane’s permeability to particular ion changes. How the resting potential is generated Neuron Axon Plasma membrane Outside of neuron Na Na Na Na K K Na channel Na Na Na Na K Na Na Na Na-K pump K K Plasma membrane Na Na Na Na Na Na+ is high k+ is low ATP K channel K Na K K Na Na K K Inside of neuron K K K K K K K K+ is high Na+ is low How stimuli trigger signals in a living neuron? A nerve signal begins as a change in the membrane potential A stimulus is any factor that causes a nerve signal to be generated. A stimulus - alters the permeability of a portion of the membrane. - allows ions to pass through. - changes the membrane’s voltage. 動作電位 A nerve signal, called an action potential, is -a change in the membrane voltage. 動作電位 -from the resting potential to a maximum level. -back to the resting potential. Hyperpolarization 過極化 The action potential Na Na Na Na K Additional Na channels open, K channels are closed; interior of cell becomes more positive. Na 50 Membrane potential (mV) 3 Na K 2 Na Sodium Potassium channel channel Action potential 3 0 閥值 4 Na channels close and inactivate; K channels open, and K rushes out; interior of cell is more negative than outside. 5 The K channels close relatively slowly, causing a brief undershoot. 4 2 50 Threshold 1 100 Resting potential 5 1 Time (msec) A stimulus opens some Na channels; if threshold is reached, an action potential is triggered. Na K Outside of neuron Na Na Plasma membrane K 1 Resting state: Voltage-gated Na and K channels are closed; resting potential is maintained by ungated channels (not shown). K Inside of neuron 1 Return to resting state. Action potentials are all-or-none events 全有全無律 絕對不反應期 相對不反應期 去極化 再極化 過極化 The action potential propagates itself along the axon Action potentials are - self-propagated in a one-way chain reaction along a neuron. - all-or-none events. The frequency of action potentials (but not their strength) changes with the strength of the stimulus. Propagation of the action potential along the axon Axon Na Plasma membrane Action potential Axon segment 1 Na Action potential Na K 2 K Na Action potential Na K 3 K Na Neurons communicate at synapses 突觸 Synapses are junctions where signals are transmitted between two neurons or between neurons and effector cells. 電位突觸 Electrical signals pass between cells at electrical synapses. 化學突觸 At chemical synapses - the ending (presynaptic) cell secretes a chemical signal, a neurotransmitter. 神經傳遞物質 - the neurotransmitter crosses the synaptic cleft. 突觸間隙 - the neurotransmitter binds to a specific receptor on the surface of the receiving (postsynaptic) cell. Electrical synapses Two types of synapses Chemical synapses Neuron communication at a typical chemical synapse (1) 1 Sending cell Axon of sending cell Synaptic terminal of sending cell Action potential arrives Synaptic vesicles Synaptic terminal 2 Vesicle fuses with plasma membrane Dendrite of receiving cell 3 Neurotransmitter is released into synaptic cleft Synaptic cleft 4 Receiving cell Neurotransmitter binds to receptor Ion channels Neurotransmitter molecules Neuron communication at a typical chemical synapse (2) Neurotransmitter Receptor Neurotransmitter broken down and released Ions 5 Ion channel opens 6 Ion channel closes Chemical synapses enable complex information to be processed Some neurotransmitters excite a receiving cell, and others inhibit a receiving cell’s activity by decreasing its ability to develop action potentials. A receiving neuron’s membrane may receive signals - that are both excitatory and inhibitory. - from many different sending neurons. The summation of excitation and inhibition determines if a neuron will transmit a nerve signal. A neuron’s multiple synaptic inputs Synaptic terminals Dendrites Inhibitory Excitatory Myelin sheath Receiving cell body Axon Hillock Synaptic terminals Synaptic intergration Na+ channels (in) Excitatory postsynaptic potential 興奮性突觸後電位 抑制性突觸後電位 Inhibitory postsynaptic potential K+ channels (out) Cl- channels (in) A variety of small molecules function as neurotransmitters 乙醯膽鹼 Acetylcholine is a neurotransmitter in the brain and at synapses between motor neurons and muscle cells. (Excitatory in skeletal muscles contraction; inhibitory in cardiac muscles contraction) 谷氨酸 -丁氨基酪酸(Gama-aminobutyric acid) 甘氨酸 Amino acids glutamate (+), glycine (-), and GABA (-) in CNS. 生物胺 Biogenic amines - norepinephrine, serotonin, and dopamine in 血清素 多巴胺 正腎上腺素 CNS. Serotonin and dopamine affect sleep, mood, attention, and learning. (Lack of dopamine Parkinson’s disease; Lack of serotonin and noerpinephrine depression) 神經胜肽 Many neuropeptides - consist of relatively short chains of amino acids important in the CNS and include 腦內啡 endorphins, decreasing our perception of pain. Nitric oxide is a dissolved gas and triggers erections during sexual arousal in men. The erectile dysfunction drug Viagra promotes release NO into blood vessels in the erectile tissue of the penis. Classes of neurotransmitters 兒茶酚胺激素 吲哚胺 Botulinum toxin inhibits the release of ACh 肉毒桿菌素 Many drugs act at chemical synapses Many psychoactive drugs act at synapses and affect neurotransmitter action. - Caffeine counters the effect of inhibitory neurotransmitters. - Nicotine acts as a stimulant by binding to acetylcholine receptors. - Alcohol is a depressant. (increase the inhibitory effects of the neurotransmitter GABA) Selective serotonin reuptake inhibitors (SSRIs) 選擇性血清素回收抑制劑 Tranquilizers activate the receptors for GABA 鎮靜劑 Benzodiazepine increasing GABA’s effect at inhibitory synapses 安眠藥:苯重氮基鹽 Adderall = “study drug” Block the reuptake of dopamine and norepinephrine, which can increase alertness. Illegal drugs Opiates Stimulants Amphetamines, cocaine Bind to endorphin receptors Reducing pain & Producing euphoria Increase the release and availability of norepinephrine and dopamine at synapses The evolution of animal nervous systems reflects changes in body symmetry 輻射對稱 Radially symmetrical animals have a nervous system arranged in a diffuse, weblike system of neurons called a nerve net. 兩側對稱 Most bilaterally symmetrical animals evolved - cephalization, the concentration of the nervous system at the head end (sense organs, brain). 頭部集中(專)化 - centralization, the presence of a central nervous system distinct from a peripheral nervous system. 集中管理 Invertebrate nervous systems Eyespot Brain Nerve cord Nerve net Transverse nerve Neuron Hydra (cnidarian) Brain Ventral nerve cord Segmental ganglion Leech (annelid) Flatworm (planarian) Brain Ventral nerve cord Brain Giant axon Ganglia Insect (arthropod) Squid (mollusc) Vertebrate nervous systems are highly centralized In the vertebrates, the central nervous system (CNS) - consists of the brain and spinal cord. 腦脊液 - includes spaces filled with cerebrospinal fluid. - forming ventricles of the brain. 腦室 中央管 - forming the central canal of the spinal cord. - surrounding the brain. The vertebrate peripheral nervous system (PNS) consists of - cranial nerves (12 pairs). - spinal nerves (31 pairs). - ganglia. A vertebrate nervous system Central nervous system (CNS) Brain Spinal cord Cranial nerves Ganglia outside CNS Spinal nerves Peripheral nervous system (PNS) Fluid-filled spaces of the vertebrate CNS (nerve cell bodies & dendrites) Gray matter Brain Cerebrospinal fluid Meninges (axons) White matter Central canal Ventricles Central canal of spinal cord Spinal cord 背根神經結 Dorsal root ganglion (part of PNS) Spinal nerve (part of PNS) Spinal cord (cross section) Blood-brain barrier (BBB) 血腦障壁 The peripheral nervous system of vertebrates is a functional hierarchy The PNS can be divided into two functional components: - the motor system, mostly voluntary. - the autonomic nervous system, mostly involuntary. 自主神經系統 The motor nervous system - carries signals to and from skeletal muscles. - mainly responds to external stimuli. The autonomic nervous system - regulates the internal environment. - controls smooth and cardiac muscle and organs and glands of the digestive, cardiovascular, excretory, and endocrine systems. The autonomic nervous system is composed of three divisions “rest and digest” 1. The parasympathetic division primes the body for activities that gain and conserve energy for the body. 交感神經系“fight-or-flight” 2. The sympathetic division prepares the body for intense, energy-consuming activities. 副交感神經系 腸道神經系 3. The enteric division consists of networks of neurons in the digestive tract, pancreas, and gallbladder that control secretion and peristalsis. Cooperate to maintain homeostasis. Functional divisions of the vertebrate PNS Brain Peripheral nervous system (to and from the central nervous system) Motor system (voluntary and involuntary; to and from skeletal muscles) Autonomic nervous system (involuntary; smooth and cardiac muscles, various glands) Spinal cord Parasympathetic division (“Rest and digest”) Sympathetic division (“Fight and flight”) Enteric division (muscles and glands of the digestive system) Antagonistic opposite effects Sympathetic division Parasympathetic division norepinephrine acetylcholine Brain Eye Dilates pupil Constricts pupil Salivary glands Stimulates saliva secretion Inhibits saliva secretion Lung Relaxes bronchi Constricts bronchi Slows heart Accelerates heart Heart Adrenal gland Spinal cord Liver Stomach Stimulates stomach, pancreas, and intestines Pancreas Stimulates epinephrine and norepinephrine release Stimulates glucose release Inhibits stomach, pancreas, and intestines Intestines Bladder Stimulates urination Inhibits urination Promotes erection of genitalia Promotes ejaculation and vaginal contractions Genitalia Cooperation The vertebrate brain develops from three anterior bulges of the neural tube 大腦 Cerebrum Midbrain Hindbrain Diencephalon 間腦 Midbrain 中腦 Pons 橋腦 Cerebellum 小腦 Medulla 延腦 oblongata Forebrain Embryo (1 month old) Spinal cord 脊髓 Fetus (3 months old) In the course of vertebrate evolution, the forebrain and hindbrain gradually become subdivided both structurally and functionally. Embryonic development of the human brain Embryonic Brain Regions Brain Structures Present in Adult Cerebrum (cerebral hemispheres; includes cerebral cortex, white matter, basal ganglia) Forebrain Diencephalon (thalamus, hypothalamus, posterior pituitary, pineal gland) Midbrain Midbrain (part of brainstem) Pons (part of brainstem), cerebellum Hindbrain Medulla oblongata (part of brainstem) The main parts of the human brain Cerebral cortex (outer region of cerebrum) Cerebrum Forebrain Thalamus Hypothalamus pituitary gland body temperature blood pressure hunger thirst sex drive fight-or-flight responses emotions Pituitary gland Midbrain Hindbrain Brainstem Pons Medulla oblongata Cerebellum Spinal cord The rear view of the brain - the largest and most complex part of the brain. - most of the cerebrum’s integrative power resides in the cerebral cortex of the two cerebral hemispheres. each responsible for the opposite side of the body Left cerebral hemisphere Right cerebral hemisphere Thalamus Cerebrum contains most of the cell bodies of neurons that relay information to the cerebral cortex Cerebellum a planning center fir body movement facilitates communication between the hemispheres Corpus callosum 胼胝體 Basal nuclei 基底核 motor coordination Medulla (Parkinson’s disease ) oblongata Major structures of the human brain The cerebral cortex is a mosaic of specialized, interactive regions The cerebral cortex - is less than 5 mm thick. - accounts for 80% of the total human brain mass. Specialized integrative regions of the cerebral cortex include the somatosensory cortex and centers for vision, hearing, taste, and smell. 體感覺皮質區 The motor cortex directs responses. 運動皮質區 Association areas 聯合區 make up most of the cerebrum and are concerned with higher mental activities such as reasoning and language. 偏側化 In a phenomenon known as lateralization, right and left cerebral hemispheres tend to specialize in different mental tasks. Functional areas on the left cerebral hemisphere 頂葉 額葉 Frontal lobe Parietal lobe Frontal association area Speech Somatosensory association area Reading Speech Hearing Smell Auditory association area Visual association area Vision 顳葉 Temporal lobe Occipital lobe 枕葉 Einstein’s Brain Injuries and brain operations provide insight into brain function Broken brains Computer model of Phineas Gage’s injury X-ray of hemispherectomy patient after surgery fMRI scans provide insight into brain structure and function 功能性核磁造影 Functional magnetic resonance imaging (fMRI) is - a scanning and imaging technology used to study brain functions. - used on conscious patients, - monitors changes in blood oxygen usage in the brain. - correlates to regions of intense brain function. Comparative human fMRI images showing regions of brain activity in healthy veterans (left) and veterans with Gulf War syndrome (right) when performing the same task Several parts of the brain regulate sleep and arousal Sleep and arousal involve activity by the - hypothalamus. - medulla oblongata. - pons. - neurons of the reticular formation. EEG (electroencephalogram) Sleep - is essential for survival. - is an active state (REM sleep).rapid eye movement - may be involved in consolidating learning and memory. The reticular system 網狀結構 The reticular formation is a diffuse network of neurons containing over 90 separate clusters of cell bodies, that is present in the brainstem. Acting as a sensory filter. 邊緣系統 The limbic system is involved in emotions, memory, and learning 下視丘 視丘 Thalamus Hypothalamus Cerebrum Prefrontal cortex Smell Olfactory bulb Amygdala 杏仁核 Hippocampus 海馬迴 The limbic system (shown in shades of gold) Memory Changes in brain physiology can produce neurological disorders - Schizophrenia 精神分裂症 Schizophrenia is (1% of the population) - a severe mental disturbance. - characterized by psychotic episodes in which patients lose the ability to distinguish reality. 妄想症 幻覺 語無倫次 緊張性情神分裂症 情感平淡 Mechanism unknown. Strong genetic component. Changes in brain physiology can produce neurological disorders - Depression憂鬱症 (2/3 are women) Two broad forms of depressive illness have been identified: 重鬱症- major depression. 躁鬱症 (1% of the population) 雙相障礙- bipolar disorder (manic-depressive disorder). Treatments may include selective serotonin reuptake inhibitors (SSRIs), which increase the amount of time serotonin is available to stimulate certain neurons in the brain. PET scans showing brain activity in a depressed person (top) and healthy person (bottom). SSRI prescriptions in the United States. Changes in brain physiology can produce neurological disorders - Alzheimer’s Disease 阿茲海默症(老年痴呆症) Alzheimer’s disease is - characterized by confusion, memory loss, and personality change. - difficult to diagnose. - neurons die in huge areas of the brain, and brain tissue often shrinks. - 10% at age 65 to about 35% at age 85. Two features 神經纖維糾結 - neurofibrillary tangles (NFTs) are bundles of a protein called tau. - senile plaques are aggregates of beta-amyloid, an insoluble 老化斑塊 peptide of 40 to 42 amino acids. 類澱粉胜肽 Changes in brain physiology can produce neurological disorders - Parkinson’s Disease 帕金森氏症 Parkinson’s disease is - a motor disorder. - 1% at age 65 to about 5% at age 85. - characterized by (1) difficulty in initiating movements. (2) slowness of movement. (3) rigidity. - death of neuron (dopamine release) in the basal nuclei (substantia nigra). - environmental and genetic factors.