Chapter 11 The nervous system: autonomic and motor systems The autonomic nervous systems 自律神經系統 The somatic nervous system 體神經系統

I. The Autonomic Nervous System The autonomic nervous system (ANS) innervates all effector organs and tissues in the body except the skeletal muscles, including cardiac muscles, smooth muscles, glands, and adipose tissue 除了骨骼肌外，自律神經系統幾乎支配了所有的器官及組織，包括心肌、平滑肌、腺體及脂肪組織等 It is called ‘autonomic’ because its functions occur at a subconscious level  also referred to as the involuntary nervous system 它之所以稱為「自律的」，是因他的功能是在下意識或無意識下產生的，因此也稱為不隨意神經系統 P303

Dual Innervation of the Autonomic Nervous System Primary function—regulate organs to maintain homeostasis 主要功能在調控器官維持在一恆定狀態 Parasympathetic and sympathetic activities tend to oppose each other 副交感神經及交感神經的活性常常是彼此相反的 Parasympathetic nervous system—rest 休息 Sympathetic nervous system—fight or flight response 戰鬥或逃跑反應 P303

P304 Figure 11.1 Dual innervation in the autonomic nervous system. In this detailed schematic diagram of the ANS, parasympathetic pathways 副交感神經路徑 are shown in purple, and sympathetic pathways 交感神經路徑 in green Both branches of the ANS generally innervate the same organs 自律神經系統分支通常支配相同的器官 Only one side of the body is shown for each system; thus there are actually two sympathetic chains, two of each cranial nerve, and so on 此圖只秀出其中一邊，事實上有兩條交感神經鏈 Figure 11.1 Dual innervation in the autonomic nervous system. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P304

Anatomy of Autonomic Pathways Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. P303-305 In autonomic nervous system consists of efferent pathways containing two neurons arranged in series that communicate between the CNS and the effector organ 自律神經系統由兩條傳出神經路徑以連續排列方式所組成，可溝通中樞與作用器官 The neurons communicate with each other through synapses located in peripheral structures called autonomic ganglia 突觸末梢與神經元互相溝通的結構稱為自律神經節 The preganglionic neuron originates in the CNS and travels to a ganglion in the periphery, where it synapses with a postganglionic neuron that innervates one of several types of effector organ 節前神經的神經元位於中樞，神經纖維中止於末梢的神經節；在神經節，節前神經纖維與節後纖維形成突觸，節後纖維的軸突末梢則支配許多不同的器官 A single preganglionic neuron generally synapses with several postsynaptic neurons; in addition, other neurons located entirely within each other ganglion, called intrinsic neurons 通常一條節前神經的軸突末梢會與許多節後神經形成突觸；此外會有一些神經完全位於神經節內，稱為內生性神經

Anatomy of the Sympathetic Nervous System Preganglionic neurons in the sympathetic nervous system originate in thoracolumbar spinal cord  the sympathetic nervous system is sometimes called thoracolumbar system 交感神經的節前神經起源於脊髓的胸腰椎系統，因此 交感神經系統有時也稱為胸腰椎系統 General anatomy 一般的解剖構造 Short preganglionic neurons to sympathetic chain 節前神經較短 Long postganglionic neurons from chain to effector organs 節後神經較長 Ganglia linked together in sympathetic chain 神經節連結在一起形成交感神經鏈 P305

Anatomy of the Sympathetic Nervous System 交感神經鏈 外側角 節後神經元 作用者器官 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. 嗜鉻性細胞 腎上腺髓質 脊髓的胸椎及腰椎 旁系的(附屬的)神經節 Figure 11.3 Anatomical pathways of preganglionic and postgenglionic neurons in the sympathetic nervous system. Most sympathetic preganglionic neurons synapse with postganglionic neurons in ganglion in the sympathetic chain (1) 大部分交感神經的節前神經都在交感神經鏈的神經節內與節後神經形成突觸 Some sympathetic preganglionic neurons innervate secretory cells of the adrenal medulla (2) 有些交感神經的節前神經則是在腎上腺髓質內支配分泌性細胞 Still other sympathetic preganglionic neurons synapse in collateral ganglia that are independent of the sympathetic chain (3) 也有一些交感神經的節前神經在一些與交感神經鏈不相關的附屬神經節形成突觸 P305

Anatomy of the Sympathetic Nervous System 背根 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings. 腹根 P306 Figure 11.4 The most common pathway of sympathetic fibers. The sympathetic preganglionic neurons exits the spinal cord as part of the ventral root and travels to the spinal nerve Shortly after entering the spinal nerve the preganglionic neuron exits the nerve and travels via a white ramus 白枝 to a ganglion in the sympathetic chain, where the neuron synapses with a postganglionic neuron The postganglionic neuron then returns to the spinal nerve via a gray ramus 灰枝

Anatomy of the Sympathetic Nervous System Figure 11.5 Sympathetic innervation of the adrenal gland. P306 The various sympathetic ganglia are linked together to form sympathetic chains (1) A very important exception to the arrangement is a group of long preganglionic neurons that innervate endocrine tissue--the adrenal medulla--instead of synapsing on postganglionic neurons (2) The adrenal glands, located within fat pads on top of each kidney, consist of an outer cortex and inner medulla Sympathetic preganglionic neurons innervate chromaffin cells of the adrenal medulla, stimulating the release of epinephrine (and a small amount of norepinephrine) into the blood Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Anatomy of the Parasympathetic Nervous System Preganglionic neurons of the parasympathetic nervous system originate in brainstem or sacral spinal cord  is sometimes called craniosacral system 顱薦椎系統 Anatomy Long preganglionic neurons to ganglia near effector organ Preganglionic neuron communicates with postganglionic neuron in ganglia Short postganglionic neurons from ganglia to effector organs P307

Anatomy of the Parasympathetic Nervous System Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 11.6 Parasympathetic nervous system pathways. Parasympathetic preganglionic neurons originate in either the brainstem or the sacral spinal cord, and their axons are found in cranial and pelvic nerves, respectively These axons from synapses with postganglionic neurons in ganglia close to or within the effector organs One important cranial nerves is the vagus nerve (cranial nerve X), which originates in the medulla oblongata and innervates much of the viscera, including the lung, heart, stomach, small intestines, and liver P307

Anatomy of the Parasympathetic Nervous System Cranial Nerves 腦神經 Cranial nerve X = vagus nerve 迷走神經 Cranial nerve III = oculomotor 動眼神經 Cranial nerve VII = facial nerve 顏面神經 Cranial nerve IX = glossopharyngeal nerve 舌咽神經 Spinal Nerves 脊神經 Pelvic nerves distinct from somatic spinal nerves P307

The Mixed Composition of Autonomic Nerves Efferent fibers Autonomic nervous system Afferent fibers Transmit information from visceral receptors to CNS Important in maintaining homeostasis P307

Autonomic Neurotransmitters and Receptors The two neurotransmitters in the PNS are acetylcholine and norepinephrine Neurons that release the acetylcholine are referred to to as cholinergic All the preganglionic neurons of sympathetic and parasympathetic nerves & postganglionic neurons of parasympathetic nerves are cholinergic The somatic neuron of the efferent nervous system is also cholinergic Neurons that release the norepinephrine are referred to to as adrenergic Almost all sympathetic postganglionic neurons are adrenergic Some sympathetic postganglionic neurons release acetylcholine, specifically those innervate the sweat glands P307-308

Autonomic Neurotransmitters and Receptors Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 11.7 Neurotransmitters and receptors in the autonomic nervous system. (a) Neurotransmitters and receptors for the three distinct anatomical pathways of the sympathetic nervous system. In all cases, the preganglionic neuron releases acetylcholine (Ach), which then binds to nicotinic cholinergic receptors on either postganglionic neurons or endocrine cells in the adrenal medulla. The postganglionic neurons release (NE), which binds to adrenergic receptors on the effector organs. P308

Autonomic Neurotransmitters and Receptors Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 11.7 Neurotransmitters and receptors in the autonomic nervous system. (b) Neurotransmitters and receptors in the parasympathetic pathway. Acetylcholine is released from both preganglionic and postganglionic neurons; it binds to nicotinic cholinergic receptors on the postganglionic neuron, and to muscarinic cholinergic receptors at the effector organ. P308

Types of Cholinergic Receptors Nicotinic 尼古丁的 cholinergic receptors are located on the cell bodies and dendrites of sympathetic and parasympathetic postganglionic neurons, on chromaffin cells of the adrenal medulla, and on skeletal muscle cells Open channels for cations (Na+ and K+) Result = depolarization Muscarinic 蕈毒鹼的 cholinergic receptors are found on effector organs of the parasympathetic nervous system, such as the heart, smooth muscles controlling the contraction of the eye or the digestive tract G protein coupled Effect depends on target cell P308-309

Types of Adrenergic Receptors There are two major classes of adrenergic receptors located in effector organs of the sympathetic nervous system: alpha () and beta () Each of these is further divided into sub-classes: 1 and 2, and 1, 2, and 3 Adrenergic receptors are coupled to G proteins that either activate or inhibit second messenger systems The a receptors have a greater affinity for norepinephrine than epinephrine and are generally excitatory b1 and b3 receptors have approximately equal affinities for norepinephrine and epinephrine, and tend to be excitatory b2 receptors have a much greater affinity for epinephrine than norepinephrine, and are generally inhibitory P309-310

Copyright © 2008 Pearson Education, Inc Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 11.7 Signal transduction mechanism at effector organs of the sympathetic nervous system P309-310 Binding of norepinephrine or epinephrine to an a1 adrenergic receptor triggers activation of the phosphatidylinositol second messenger system Alpha 1 adrenergic receptors are most located in vascular smooth muscle  a1 agonist can be used to treat congestion 充血

Copyright © 2005 Pearson Education, Inc Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 11.7 Signal transduction mechanism at effector organs of the sympathetic nervous system P309-310 Binding of norepinephrine or epinephrine to an a2 adrenergic receptor triggers inhibition of the cAMP second messenger system, whereas binding to a b adrenergic receptor triggers excitation of the cAMP second messenger system

Summary of Adrenergic Receptors

Autonomic Neuroeffector Junctions The synapse between an efferent neuron and its effector organ is called a neuroeffector junction 神經-作用者聯合 Near the effector organ the axon of a postganglionic neuron splits into branches bearing swellings called varicosities 囊節 Whereas voltage-gated Na+ and K+ channels are present thought the axon to support propagation of action potentials, voltage-gated Ca2+ channels are concentrated at the varicosity Neurotransmitter is stored in synaptic vesicles 突觸小泡 in the varicosity Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 11.9 Neuroeffector junctions of the autonomic nervous system. P310-311

Autonomic Neuroeffector Junctions Copyright © 2008Pearson Education, Inc., publishing as Benjamin Cummings. When an action potential depolarizes a varicosity, voltage-gated Ca2+ channels open, allowing Ca2+ to enter the cell and triggering the release of acetylcholine by exocytosis 胞吐 Acetylcholine binds to muscarinic receptors on the effector organ membrane, thereby activating a G protein Once acetylcholine is degraded by acetylcholinesterase located on the effector organ, choline is actively transported back into the postganglionic varicosity and used to synthesize more acetylcholine Figure 11.10 Neurotransmitter release from varicosities. P311-312

Autonomic Neuroeffector Junctions Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. When an action potential depolarizes a varicosity, voltage-gated Ca2+ channels open, allowing Ca2+ to enter the cell and triggering the release of norepinephrine by exocytosis Norepinephrine binds to adrenergic receptors on the effector organ membrane, thereby activating a G protein Some norepinephrine is actively transported back into the postganglionic neuron’s varicosity, where it is degraded by monoamine oxidase (MAO) in mitochondria Figure 11.10 Neurotransmitter release from varicosities. P311-312

Regulation of Autonomic Function Dual innervation of organs Balance between parasympathetic and sympathetic activity Parasympathetic—rest, quiet, relaxed states, increase gastrointestinal activities; decrease heart rate and blood pressure Sympathetic—excitation; fight-or-flight response; prepare for emergency/stress/exercise; increase heart rate and blood pressure; mobilize energy stores; pupillary dilation; decrease gastrointestinal/urinary functions Most changes in the activity of the ANS are accomplished through the operation of visceral reflexes Increases in parasympathetic activity coupled with decreases in sympathetic activity Increases in sympathetic activity coupled with decreases in parasympathetic activity P311

Figure 11.11 Autonomic reflex response that controls blood pressure when a person stands up.

Regulation of Autonomic Function Hypothalamus下視丘, pons 橋腦, medulla 延腦  Maintenance of homeostasis Cerebral cortex 大腦皮質, limbic system邊緣系統  Emotions Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 11.12 Area of the brain that regulate autonomic function. This midsagittal section of the brain reveals the pons 橋腦 and medulla oblongata 延腦 of the brainstem 腦幹 and the hypothalamus 下視丘, all of which regulate autonomic function. P313

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II. Somatic Nervous System The somatic nervous system 體神經系統 controls only one type of effector organ—skeletal muscle 骨骼肌, which are connected to bones and thus function in support and movement of the body The somatic nervous system has only a single type of efferent neuron: motor neurons 運動神經 Most skeletal muscle is under voluntary control  the somatic nervous system is also referred to as the voluntary nervous system 隨意神經系統 P314

Anatomy of the Somatic Nervous System Figure 11.13 Anatomy of somatic nervous system pathway. The somatic nervous system consists of motor neurons, which originate in the ventral horns of the spinal cord and terminate on skeletal muscle fibers throughout the body. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. In the somatic nervous system, a single motor neurons travels from the central nervous system to a skeletal muscle cell 骨骼肌細胞 Motor neurons originate in the ventral horn 腹根 of the spinal cord 脊髓 and receive input from multiple sources, including afferents (for spinal reflexes), the brainstem 腦幹 extrapyramidal tracts 錐體外路徑, and the cerebral cortex 大腦皮質 pyramidal tract 錐體路徑 P314-315

Anatomy of the Somatic Nervous System Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. A single motor neuron innervates many muscle cells (called muscle fibers), but each muscle fiber is innervated by only one motor neuron A motor neuron plus all the muscle fibers it innervates is called a motor unit 運動單位 When a motor neuron is activated, it stimulates all the muscle fibers in its unit to contract 收縮 Note that the muscle fibers within a given motor unit are scattered 分散 throughout the muscle Figure 11.14 Motor units. P314,316

Neuromuscular Junction Synapse between a motor neuron and a muscle fiber Each branch of a motor neuron synapses with a skeletal muscle fiber at a single highly specialized central region of the fiber called the neuromuscular junction 神經肌肉聯合 The axon terminals of the motor neuron, called terminal boutons 終末 膨大, store and release acetylcholine, the only neurotransmitter in the somatic nervous system Opposite these terminal boutons is a specialized region of the muscle fiber’s plasma membrane called the motor end plate 運動終板, which has containing large numbers of nicotinic receptors 尼古丁接受器 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 11.15 Functional anatomy of the neuromuscular junction. P315-317

Neuromuscular Junction When an action potential arrives at the axon terminal of a motor neuron (), voltage-gated calcium channels open and Ca2+ enters the cytosol ()  triggers the release by exocytosis of acetylcholine () Acetylcholine diffuses to and binds to nicotinic receptors at the motor end plate, opening cation channels  Na+ enters the cell (), producing and end -plate potential (EPP) that generates currents throughout the plasma membrane of the skeletal muscle cell (), depolarizing the membrane to threshold to generate an action potential () The action potential spreads along the skeletal muscle cell membrane, ultimately stimulating contraction Acetylcholinesterase degrades acetylcholine to produce acetate and choline ()  choline is actively transported into the terminal bouton (), where it can be used to synthesize more acetylcholine Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 11.15 Functional anatomy of the neuromuscular junction. P316-317

Myasthenia Gravis Myasthenia gravis 重症肌無力 is a disease affecting transmission at neuromuscular junction Because the muscles most frequently affected are those of the head, difficulties in speaking (dysarthria) 發音困難 and in swallowing (dysphagia) 吞嚥困難 are common symptoms; dropping of the eyelids (ptosis) 眼瞼下垂 is also a common sign We now know that myasthenia gravis is an autoimmune disease 自體免疫疾病— a disease in which the immune system 免疫系統 attacks proteins that are normal components of body tissues In myasthenia gravis, the immune system produces antibodies 抗體 against acetylcholine receptors at the neuromuscular junctions  decrease in the number of functional receptors on the cell surface impairs the ability of these muscle cell to respond to acetylcholine P318

Curare Curare 劍毒 is an extract of a plant (Chondrodendron tomentosum) found in South America When an animal was struck by a curare-laced arrow or dart, it would become paralyzed and eventually die from respiratory failure 呼吸衰竭 The effective component of curare is a compound called tubocurarine, which blocks communication at the neuromuscular junction  tubocurarine binds to nicotinic receptors, thereby preventing acetylcholine from binding (antagonism 拮抗作用) When this occurs, skeletal muscles are unable to contract even when action potentials are transmitted by the motor neurons that innervate them Curare was first used as a skeletal muscle relaxant 骨骼肌鬆弛劑 to supplement general anesthesia 全身麻醉劑 in the 1930s P318

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