《医学生理学 Medical Physiology》参考教材资料（PDF电子书籍）Neuroscience, Third Edition, 2004

14 Chapter One Figure 1.9 Intracellularly recorded Microelectro (A) Sensory neuron responses underlying the myotatic to measur reflex. (A) Action potential measured in membrane potential a sensory neuron.(B)Postsynaptic trig- Action gering potential recorded in an extensor motor neuron.( C)Postsynaptic trigge ing potential in an interneuron. D) Postsynaptic inhibitory potential in a flexor motor neuron Such intracellula recon are the bas ing the cellular mechanisms of action potential generation, and the sensor receptor and synaptic potentials that Moto (extensor trigger these conducted signal Action potential Activate excitatory (C)Interneuron Motor neuron Activate excitatory D)Motor neuron(flexor Overall Organization of the Human Nervous System When considered together, circuits that process similar types of information comprise neural systems that serve broader behavioral purposes. The most general functional distinction divides such collections into sensory systems that acquire and process information from the environment( e.g., the visual ystem or the auditory system, see Unit ID), and motor systems that respond to such information by generating movements and other behavior(see Unit III). There are, however, large numbers of cells and circuits that lie between these relatively well-defined input and output systems. These are collec- tively referred to as associational systems, and they mediate the most com- plex and least well-characterized brain functions(see Unit V) In addition to these broad functional distinctions, neuroscientists and neurologists have conventionally divided the vertebrate nervous system anatomically into central and peripheral components(Figure 1.10). The cen- tral nervous system, typically referred to as the CNS, comprises the brain ( cerebral hemispheres, diencephalon, cerebellum, and brainstem) and the spinal cord (see Appendix A for more information about the gross anatomi- cal features of the CNS). The peripheral nervous system(PNS)includes the sensory neurons that link sensory receptors on the body surface or deeper within it with relevant processing circuits in the central nervous system. The motor portion of the peripheral nervous system in turn consists of two com- ponents. The motor axons that connect the brain and spinal cord to skeletal

14 Chapter One Overall Organization of the Human Nervous System When considered together, circuits that process similar types of information comprise neural systems that serve broader behavioral purposes. The most general functional distinction divides such collections into sensory systems that acquire and process information from the environment (e.g., the visual system or the auditory system, see Unit II), and motor systems that respond to such information by generating movements and other behavior (see Unit III). There are, however, large numbers of cells and circuits that lie between these relatively well-defined input and output systems. These are collec￾tively referred to as associational systems, and they mediate the most com￾plex and least well-characterized brain functions (see Unit V). In addition to these broad functional distinctions, neuroscientists and neurologists have conventionally divided the vertebrate nervous system anatomically into central and peripheral components (Figure 1.10). The cen￾tral nervous system, typically referred to as the CNS, comprises the brain (cerebral hemispheres, diencephalon, cerebellum, and brainstem) and the spinal cord (see Appendix A for more information about the gross anatomi￾cal features of the CNS). The peripheral nervous system (PNS) includes the sensory neurons that link sensory receptors on the body surface or deeper within it with relevant processing circuits in the central nervous system. The motor portion of the peripheral nervous system in turn consists of two com￾ponents. The motor axons that connect the brain and spinal cord to skeletal (C) Interneuron Interneuron Sensory neuron (A) Sensory neuron Motor neuron (flexor) (D) Motor neuron (flexor) Motor neuron (extensor) (B) Motor neuron (extensor) Microelectrode to measure membrane potential Record Record Record Record Membrane potential (mV) Membrane potential (mV) Membrane potential (mV) Membrane potential (mV) Time (ms) Activate excitatory synapse Activate excitatory synapse Activate inhibitory synapse Action potential Action potential Synaptic potential Action potential Synaptic potential Figure 1.9 Intracellularly recorded responses underlying the myotatic reflex. (A) Action potential measured in a sensory neuron. (B) Postsynaptic trig￾gering potential recorded in an extensor motor neuron. (C) Postsynaptic trigger￾ing potential in an interneuron. (D) Postsynaptic inhibitory potential in a flexor motor neuron. Such intracellular recordings are the basis for understand￾ing the cellular mechanisms of action potential generation, and the sensory receptor and synaptic potentials that trigger these conducted signals. Purves01 5/13/04 1:03 PM Page 14

Studying the Nervous Systems of Humans and Other Animals 15 (A) (B) Centra Peripheral nervous system nervous sy (analysis and integration of ord cerebellum, brainstem, and spinal Brain Cranial nerves sensory and motor information SENSORY MOTOR COMPONENTS COMPONENTS MOTOR MOTOR Sensory ganglia YSTEM SYSTEM parasympathetic nd enteric divisions) Motor nerv Sensory receptors (at surface and Autonomic within the body) and nerves EFFECTORS Smooth EXTERNAL Skeletal (striated) ENVIRONMENT cardiac Figure 1.10 The major components of muscles make up the somatic motor division of the peripheral nervous sys- the nervous system and their functional tem, whereas the cells and axons that innervate smooth muscles, cardiac relationships. (A)The CNS(brain and pinal cord)and PNS(spinal and cranial Those nerve cell bodies that reside in the peripheral nervous system are nerves).(B) Diagram of the major com- located in ganglia, which are simply local accumulations of nerve cell bodies ponents of the central and periphera nervous systems and their functional and supporting cells). Peripheral axons are gathered into bundles called relationships. Stimuli from the environ- nerves, many of which are enveloped by the glial cells of the peripheral ner- ment convey information to processing vous system called Schwann cells. In the central nervous system, nerve cells circuits within the brain and spinal cord, are arranged in two different ways. Nuclei are local accumulations of neu- which in turn interpret their significance rons having roughly similar connections and functions; such collections are and send signals to peripheral effectors found throughout the cerebrum, brainstem and spinal cord. In contrast, cor- that move the body and adjust the tex(plural, cortices) describes sheet-like arrays of nerve cells(again, consult workings of its internal organs Appendix A for additional information and illustrations). The cortices of the cerebral hemispheres and of the cerebellum provide the clearest example of this organizational principle Axons in the central nervous system are gathered into tracts that are more or less analogous to nerves in the periphery. Tracts that cross the midline of the brain are referred to as commissures. Two gross histological terms dis- tinguish regions rich in neuronal cell bodies versus regions rich in axons Gray matter refers to any accumulation of cell bodies and neuropil in the brain and spinal cord (e. g, nuclei or cortices), whereas white matter, named for its relatively light appearance resulting from the lipid content of myelin, refers to axon tracts and commissures

muscles make up the somatic motor division of the peripheral nervous sys￾tem, whereas the cells and axons that innervate smooth muscles, cardiac muscle, and glands make up the visceral or autonomic motor division. Those nerve cell bodies that reside in the peripheral nervous system are located in ganglia, which are simply local accumulations of nerve cell bodies (and supporting cells). Peripheral axons are gathered into bundles called nerves, many of which are enveloped by the glial cells of the peripheral ner￾vous system called Schwann cells. In the central nervous system, nerve cells are arranged in two different ways. Nuclei are local accumulations of neu￾rons having roughly similar connections and functions; such collections are found throughout the cerebrum, brainstem and spinal cord. In contrast, cor￾tex (plural, cortices) describes sheet-like arrays of nerve cells (again, consult Appendix A for additional information and illustrations). The cortices of the cerebral hemispheres and of the cerebellum provide the clearest example of this organizational principle. Axons in the central nervous system are gathered into tracts that are more or less analogous to nerves in the periphery. Tracts that cross the midline of the brain are referred to as commissures. Two gross histological terms dis￾tinguish regions rich in neuronal cell bodies versus regions rich in axons. Gray matter refers to any accumulation of cell bodies and neuropil in the brain and spinal cord (e.g., nuclei or cortices), whereas white matter, named for its relatively light appearance resulting from the lipid content of myelin, refers to axon tracts and commissures. Studying the Nervous Systems of Humans and Other Animals 15 SENSORY COMPONENTS Cerebral hemispheres, diencephalon, cerebellum, brainstem, and spinal cord (analysis and integration of sensory and motor information) (A) (B) MOTOR COMPONENTS INTERNAL AND EXTERNAL ENVIRONMENT Sensory ganglia and nerves (sympathetic, parasympathetic, and enteric divisions) VISCERAL MOTOR SYSTEM SOMATIC MOTOR SYSTEM Sensory receptors (at surface and within the body) Autonomic ganglia and nerves Motor nerves Smooth muscles, cardiac muscles, and glands Skeletal (striated) muscles EFFECTORS Central nervous system Peripheral nervous system Central nervous system Peripheral nervous system Cranial nerves Spinal nerves Brain Spinal cord Figure 1.10 The major components of the nervous system and their functional relationships. (A) The CNS (brain and spinal cord) and PNS (spinal and cranial nerves). (B) Diagram of the major com￾ponents of the central and peripheral nervous systems and their functional relationships. Stimuli from the environ￾ment convey information to processing circuits within the brain and spinal cord, which in turn interpret their significance and send signals to peripheral effectors that move the body and adjust the workings of its internal organs. Purves01 5/13/04 1:03 PM Page 15

16 Chapter One The organization of the visceral motor division of the peripheral nervous system is a bit more complicated (see Chapter 20). Visceral motor neurons in the brainstem and spinal cord, the so-called preganglionic neurons, form synapses with peripheral motor neurons that lie in the autonomic ganglia The motor neurons in autonomic ganglia innervate smooth muscle, gland nd cardiac muscle, thus controlling most involuntary(visceral)behavior. In the sympathetic division of the autonomic motor system, the ganglia lie along or in front of the vertebral column and send their axons to a variety of peripheral targets. In the parasympathetic division, the ganglia are found within the organs they innervate. Another component of the visceral motor system, called the enteric system, is made up of small ganglia as well a individual neurons scattered throughout the wall of the gut. These neurons influence gastric motility and secretion Neuroanatomical Terminology Describing the organization of any neural system requires a rudimentary understanding of anatomical terminology. The terms used to specify location in the central nervous system are the same as those used for the gross anatomical description of the rest of the body(Figure 1.11). Thus, anterior nd posterior indicate front and back (head and tail); rostral and caudal toward the head and tail; dorsal and ventral, top and bottom(back and belly) and medial and lateral, at the midline or to the side. Nevertheless the com parison between these coordinates in the body versus the brain can be con- fusing. For the entire body these anatomical terms refer to the long axis, which is straight. The long axis of the central nervous system, however, has bend in it. In humans and other bipeds, a compensatory tilting of the ros- tral-caudal axis for the brain is necessary to properly compare body axes to brain axes. Once this adjustment has been made, the other axes for the brain be easily assigned The proper assignment of the anatomical axes then dictates the standard planes for histological sections or live images(see Box A)used to study the internal anatomy of the brain(see Figure 1.11B). Horizontal sections(also referred to as axial or transverse sections) are taken parallel to the rostral- caudal axis of the brain; thus, in an individual standing upright, such sections are parallel to the ground. Sections taken in the plane dividing the two hemi pheres are sagittal, and can be further categorized as midsagittal and parasagittal, according to whether the section is near the midline(midsagittal) Figure 1.11 A flexure in the long axis of the nervous system arose as humans evolved upright posture, leading to an approximately 120 angle between the long sylvius axis of the brainstem and that of the forebrain The consequences of this flexure for anatomical terminology are indicated in(A). The terms anterior, posterior, superior, and inferior refer to the long axis of the body, which is straight. Therefore, these terms terms dorsaL, ventral, rostral, and caudal refer to the long axis of the central nervous system. The dorsal direction is toward the back for the brainstem and spinal cord, but toward the top of the head for the forebrain. The opposite direction is ventral. The rostral direction is toward the top of the head for the brainstem and spinal cord, but toward the face for the forebrain. The opposite direction is caudal. (B)The major planes of section used in cutting or imaging the brain.(C) The subdivisions and com- ponents of the central nervous system. ( Note that the position of the brackets on the left side of the figure refers to the vertebrae, not the spinal segments

16 Chapter One The organization of the visceral motor division of the peripheral nervous system is a bit more complicated (see Chapter 20). Visceral motor neurons in the brainstem and spinal cord, the so-called preganglionic neurons, form synapses with peripheral motor neurons that lie in the autonomic ganglia. The motor neurons in autonomic ganglia innervate smooth muscle, glands, and cardiac muscle, thus controlling most involuntary (visceral) behavior. In the sympathetic division of the autonomic motor system, the ganglia lie along or in front of the vertebral column and send their axons to a variety of peripheral targets. In the parasympathetic division, the ganglia are found within the organs they innervate. Another component of the visceral motor system, called the enteric system, is made up of small ganglia as well as individual neurons scattered throughout the wall of the gut. These neurons influence gastric motility and secretion. Neuroanatomical Terminology Describing the organization of any neural system requires a rudimentary understanding of anatomical terminology. The terms used to specify location in the central nervous system are the same as those used for the gross anatomical description of the rest of the body (Figure 1.11). Thus, anterior and posterior indicate front and back (head and tail); rostral and caudal, toward the head and tail; dorsal and ventral, top and bottom (back and belly); and medial and lateral, at the midline or to the side. Nevertheless, the com￾parison between these coordinates in the body versus the brain can be con￾fusing. For the entire body these anatomical terms refer to the long axis, which is straight. The long axis of the central nervous system, however, has a bend in it. In humans and other bipeds, a compensatory tilting of the ros￾tral–caudal axis for the brain is necessary to properly compare body axes to brain axes. Once this adjustment has been made, the other axes for the brain can be easily assigned. The proper assignment of the anatomical axes then dictates the standard planes for histological sections or live images (see Box A) used to study the internal anatomy of the brain (see Figure 1.11B). Horizontal sections (also referred to as axial or transverse sections) are taken parallel to the rostral– caudal axis of the brain; thus, in an individual standing upright, such sections are parallel to the ground. Sections taken in the plane dividing the two hemi￾spheres are sagittal, and can be further categorized as midsagittal and parasagittal, according to whether the section is near the midline (midsagittal) Figure 1.11 A flexure in the long axis of the nervous system arose as humans evolved upright posture, leading to an approximately 120° angle between the long axis of the brainstem and that of the forebrain The consequences of this flexure for anatomical terminology are indicated in (A). The terms anterior, posterior, superior, and inferior refer to the long axis of the body, which is straight. Therefore, these terms indicate the same direction for both the forebrain and the brainstem. In contrast, the terms dorsal, ventral, rostral, and caudal refer to the long axis of the central nervous system. The dorsal direction is toward the back for the brainstem and spinal cord, but toward the top of the head for the forebrain. The opposite direction is ventral. The rostral direction is toward the top of the head for the brainstem and spinal cord, but toward the face for the forebrain. The opposite direction is caudal. (B) The major planes of section used in cutting or imaging the brain. (C) The subdivisions and com￾ponents of the central nervous system. (Note that the position of the brackets on the left side of the figure refers to the vertebrae, not the spinal segments.) ▲ Purves01 5/13/04 1:03 PM Page 16

Studying the Nervous Systems of Humans and Other Animals 17 or more lateral (parasagittal). Sections in the plane of the face are called coro- nal or frontal. Different terms are usually used to refer to sections of the spinal cord. The plane of section orthogonal to the long axis of the cord is called transverse, whereas sections parallel to the long axis of the cord are called longitudinal. In a transverse section through the human spinal cord, the dorsal and ventral axes and the anterior and posterior axes indicate the same directions(see Figure 1. 11). Tedious though this terminology may be, it (A) Superior Cerebrum ongitudinal xis of the Midbrain Cerebellum 2 (in front of Caudal Posterior nerves (behind) Cervical enlargement ongitudinal axis T1 of the brainstem and spinal cord Thoracic Coronal enlargement Horizontal Cauda equina S1 Sacral erves Coc 1

or more lateral (parasagittal). Sections in the plane of the face are called coro￾nal or frontal. Different terms are usually used to refer to sections of the spinal cord. The plane of section orthogonal to the long axis of the cord is called transverse, whereas sections parallel to the long axis of the cord are called longitudinal. In a transverse section through the human spinal cord, the dorsal and ventral axes and the anterior and posterior axes indicate the same directions (see Figure 1.11). Tedious though this terminology may be, it Studying the Nervous Systems of Humans and Other Animals 17 (B) Posterior (behind) Superior (above) Anterior (in front of) Inferior (below) Caudal Longitudinal axis of the forebrain Longitudinal axis of the brainstem and spinal cord (A) Rostral Caudal Horizontal Coronal Sagittal Dorsal Ventral Dorsal Ventral Dorsal Ventral Dorsal Ventral Spinal cord Cervical enlargement Lumbar enlargement Cauda equina C 1 2 3 4 5 6 7 8 T 1 Cervical nerves Thoracic nerves Lumbar nerves (C) Sacral nerves Coccygeal nerve T 1 2 3 4 5 6 7 8 9 10 11 12 L 1 2 3 4 5 S 1 3 4 5 Coc 1 2 Medulla Pons Midbrain Diencephalon Cerebrum Cerebellum Purves01 5/13/04 1:03 PM Page 17

18 Chapter One is essential for understanding the basic subdivisions of the nervous system (Figure 1.11C) The Subdivisions of the Central Nervous System The central nervous system(defined as the brain and spinal cord)is usually considered to have seven basic parts: the spinal cord, the medulla, the pon the cerebellum, the midbrain, the diencephalon, and the cerebral hemi spheres(see Figures 1.10 and 1.11C). Running through all of these subdivi- sons are fluid-filled spaces called ventricles(a detailed account of the ven tricular system can be found in Appendix B). These ventricles are the remnants of the continuous lumen initially enclosed by the neural plate as it rounded to become the neural tube during early development(see Chapter 21). Variations in the shape and size of the mature ventricular space are char- acteristic of each adult brain region. The medulla, pons, and midbrain are collectively called the brainstem and they surround the 4th ventricle (medulla and pons)and cerebral aqueduct(midbrain). The diencephalon and cerebral hemispheres are collectively called the forebrain, and they enclose the 3rd and lateral ventricles, respectively. Within the brainstem are the cranial nerve nuclei that either receive input from the cranial sensory ganglia mentioned earlier via the cranial sensory nerves, or give rise to axons that constitute the cranial motor nerves(see Appendix A) The brainstem is also a conduit for several major tracts in the central ner vous system that relay sensory information from the spinal cord and brain- stem to the forebrain, or relay motor commands from forebrain back to motor neurons in the brainstem and spinal cord. Accordingly, detailed d other a sequences of damage to the brainstem provides neu- rologists and other clinicians an essential tool in the localization and diagno- sis of brain injury. The brainstem contains numerous additional nuclei that re involved in a myriad of important functions including the control of heart rate, respiration, blood pressure, and level of consciousness. Finally, one of the most prominent features of the brainstem is the cerebellum which extends over much of its dorsal aspect. The cerebellum is essential for the coordination and planning of movements(see Chapter 18)as well as learning motor tasks and storing that information(see Chapter 30) There are several anatomical subdivisions of the forebrain The most obvi- ous anatomical structures are the prominent cerebral hemispheres(Figure 12). In humans, the cerebral hemispheres(the outermost portions of which are continuous, highly folded sheets of cortex) are proportionally larger than in any other mammal, and are characterized by the gyri(singular, gyrus)or crests of folded cortical tissue, and sulci(singular, sulcus)the grooves th divide gyri from one another(as pictured on the cover of this book, for example). Although gyral and sulcal patterns vary from individual to indi- vidual, there are some fairly consistent landmarks that help divide the hemi- pheres into four lobes. The names of the lobes are derived from the cranial bones that overlie them: occipital, temporal, parietal, and frontal. A key fea- ture of the surface anatomy of the cerebrum is the central sulcus located Figure 1.12 Gross anatomy of the forebrain(A)Cerebral hemisphere surface anatomy, showing the four lobes of the brain and the major sulci and gyri. The ven- sylvius tricular system and basal ganglia can also be seen in this phantom view.(B)Mid- sagittal view showing the location of the hippocampus, amygdala, thalamus and hypothalamus

18 Chapter One is essential for understanding the basic subdivisions of the nervous system (Figure 1.11C). The Subdivisions of the Central Nervous System The central nervous system (defined as the brain and spinal cord) is usually considered to have seven basic parts: the spinal cord, the medulla, the pons, the cerebellum, the midbrain, the diencephalon, and the cerebral hemi￾spheres (see Figures 1.10 and 1.11C). Running through all of these subdivi￾sons are fluid-filled spaces called ventricles (a detailed account of the ven￾tricular system can be found in Appendix B). These ventricles are the remnants of the continuous lumen initially enclosed by the neural plate as it rounded to become the neural tube during early development (see Chapter 21). Variations in the shape and size of the mature ventricular space are char￾acteristic of each adult brain region. The medulla, pons, and midbrain are collectively called the brainstem and they surround the 4th ventricle (medulla and pons) and cerebral aqueduct (midbrain). The diencephalon and cerebral hemispheres are collectively called the forebrain, and they enclose the 3rd and lateral ventricles, respectively. Within the brainstem are the cranial nerve nuclei that either receive input from the cranial sensory ganglia mentioned earlier via the cranial sensory nerves, or give rise to axons that constitute the cranial motor nerves (see Appendix A). The brainstem is also a conduit for several major tracts in the central ner￾vous system that relay sensory information from the spinal cord and brain￾stem to the forebrain, or relay motor commands from forebrain back to motor neurons in the brainstem and spinal cord. Accordingly, detailed knowledge of the consequences of damage to the brainstem provides neu￾rologists and other clinicians an essential tool in the localization and diagno￾sis of brain injury. The brainstem contains numerous additional nuclei that are involved in a myriad of important functions including the control of heart rate, respiration, blood pressure, and level of consciousness. Finally, one of the most prominent features of the brainstem is the cerebellum, which extends over much of its dorsal aspect. The cerebellum is essential for the coordination and planning of movements (see Chapter 18) as well as learning motor tasks and storing that information (see Chapter 30). There are several anatomical subdivisions of the forebrain. The most obvi￾ous anatomical structures are the prominent cerebral hemispheres (Figure 1.12). In humans, the cerebral hemispheres (the outermost portions of which are continuous, highly folded sheets of cortex) are proportionally larger than in any other mammal, and are characterized by the gyri (singular, gyrus) or crests of folded cortical tissue, and sulci (singular, sulcus) the grooves that divide gyri from one another (as pictured on the cover of this book, for example). Although gyral and sulcal patterns vary from individual to indi￾vidual, there are some fairly consistent landmarks that help divide the hemi￾spheres into four lobes. The names of the lobes are derived from the cranial bones that overlie them: occipital, temporal, parietal, and frontal. A key fea￾ture of the surface anatomy of the cerebrum is the central sulcus located Figure 1.12 Gross anatomy of the forebrain (A) Cerebral hemisphere surface anatomy, showing the four lobes of the brain and the major sulci and gyri. The ven￾tricular system and basal ganglia can also be seen in this phantom view. (B) Mid￾sagittal view showing the location of the hippocampus, amygdala, thalamus and hypothalamus. Purves01 5/13/04 1:03 PM Page 18