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THE NERVOUS SYSTEM 95 Learning Objectives distribute or The Nervouspost, System Chapter Contentscopy, Introduction 4.2.2 The Structures and Functions of the 4.1 Central Nervous notSystem Development Forebrain: The Diencephalon 4.2.3 The Midbrain and the Hindbrain 4.1.1 Gastrulation 4.2.4 The Spinal Cord 4.1.2 Neurulation 4.2.5 The Protected Brain 4.1.3Do Differentiation of the Neural Tube Into the Primary Brain Vesicles 4.2.6 Hemispheric Specialization 4.2 The Fully Developed Brain 4.3 The Peripheral Nervous System 4.2.1 The Structures and Functions of the 4.3.1 The Somatic Nervous System Forebrain: The Telencephalon 4.3.2 The Autonomic Nervous System Copyright ©2021 by SAGE Publications, Inc. This work may not be reproduced or distributed in any form or by any means without express written permission of the publisher. CHAPTER 4 THE NERVOUS SYSTEM 95 Learning Objectives 4.1.1 Describe the process of gastrulation. 4.2.4 Describe the structure of the spinal cord and how 4.1.2 Describe the process of neurulation. it transmits information to and from the brain. 4.1.3 Explain how the neural tube differentiatesinto 4.2.5 Describe the different protective layers of the the brain's primary vesicles. brain and how they work. 4.2.1 Identify the major structures of the 4.2.6 Explain how each hemisphere of the brain is telencephalon and some of their functions. associated with different functions. 4.2.2 Identify the major structures of the 4.3.1 Explain the functions of the somatic nervous diencephalon and some of their functions. system. 4.2.3 Identify the major structures of the midbrain 4.3.2 Explain the functions of the somatic nervous and the hindbrain and some of their functions. system. Carolyn Pioro: From INTRODUCTION Trapeze Artist to Figure 4.1 shows thedistribute divisions of the nervous system. The nervous system is subdivided into the central ner­ Quadriplegic vous system (CNS) and the peripheral nervous sys­ tem (PNS). The CNS consists of the brain and spinal cord. Theor PNS is subdivided into the somatic nervous September 20. 2005, marked the day of a dramatic change system (SNS) and the autonomic nervous system in trapeze artist Carolyn Pioro's life. Her "big act" consisted (ANS). The SNS consists of the nerve fibers that con­ of swinging through the air while hanging onto a bar. letting nect to your skin, muscles, and joints. The ANS regu­ go and flipping for a revolution, and then being caught by lates the functions of your organs and glands. These are the functions that you never have to think about, the wrists by a catcher, hanging upside down from his own like breathing, your heartbeat, or the dilation of your bar. On that day. however. instead of Pioro being post,caught. pupils. The ANS is subdivided further into the sym­ her body collided with the catcher's. This sent her spinning pathetic and parasympathetic nervous systems. The as she fell head first into a safety net below, breaking her sympathetic nervous system activates your body neck and severing her spinal cord, the bundle of nerve by interacting with your various organs and glands, whereas the parasympathetic nervous system calms fibers that run up and down the middle of the back. The your body back down. In this chapter, we will take a fall left her paralyzedfrom the shoulders down. closer look at each one of these systems. We begin, however, with an overview of how the CNS develops Sensations coming from your body and motor com­ after conception. mands from your brain tocopy, your body make their way through your spinal cord. It follows that damage to the spinal cord impairs sensory and motor function in the body below the point at which the spinal cord has been Central Nervous damaged. Thenot extent of the paralysis depends on the 4.1 amount of damage done to the nerves of the spinal cord. System Development For Pioro, damage to her spinal cord was almost total. But because of an early intervention, she retained the ability Module Contents Doto breathe on her own, speak, and shrug her shoulders. The condition in which Pioro found herself is known as quadriplegia, also known as tetraplegia. When damage 4.1.1 Gastrulation occurs lower in the spinal cord, only the lower body may 4.1.2 Neurulation be affected,a condition known as paraplegia. Pioro is now 4.1.3 Differentiationof the Neural Tube Into the a journalist who writes about body image and the media. Primary Brain Vesicles Copyright ©2021 by SAGE Publications, Inc. This work may not be reproduced or distributed in any form or by any means without express written permission of the publisher. 96 BEHAVIORAL NEUROSCIENCE IIB·Miii 4.1.1 GASTRULATION Divisions of the nervous system. » LO 4.:1.:1 Describe the process of The Nervous System gastrulation. Key Terms Central Peripheral • Blastocyst: A fluid-filled ball that contains � I a mass of cells. Brain Spinal cord Somatic Autonomic • The mass of cells that I Embryonic disk: I develop within the blastocyst. Sympathetic Parasympathetic • Gastrula: The structure that develops from the blastocyst and forms the germ layers. • Gastrulation: The process by which the blastocyst develops into the gastrula. • Germ layers: Three layers of cells that develop into the different tissues of the Central body. Spinal nervous distribute cord system • Ectoderm: The germ layer that develops into the nervous system and the skin. or • Mesoderm: The germ layer that gives rise to the muscles. skeleton. some of the internal organs. and the circulatory system. • Endoderm: The germ layer that gives rise to the digestive system, lungs, and post,glands. ---� Nerves of peripheral nervous system Shortly after fertilization, about five days in humans, a fluid-filled ball known as the blastocyst begins to form (Figures 4.2a and 4.2b). Inside this ball, a mass of cells known as the embryonic disk becomes a new organism. Next, the blastocyst develops into copy, what is known as the gastrula, through the process of gastrulation. The gastrula forms three layers of cells, known as germ layers (Figure 4.2c). The germ layers are known as the ectoderm, mesoderm, and endoderm. Each of these layers develops into a dif­ Biological Foundations of Human Behavior, Source: Adapted from by J. Wilson. 2003. ferent type of tissue, giving rise to the different parts Belmont, CA: Wadsworth. not of the body. As shown in Figure 4.2d, the ectoderm gives rise to the nervous system and the skin; the meso­ Learning Objectives derm gives rise to the muscles, skeleton, some of the Do internal organs, and the circulatory system; and the endoderm gives rise to the digestive system, lungs, 4.1.1 Describe the processes of gastrulation. and glands (Moore, Persaud, & Torchia, 2016). For obvious reasons (because this book is mainly about 4.1.2 Describe the process of neurulation. the brain), we will focus mostly on the ectoderm, 4.1.3 Explain how the neural tube differentiatesinto which is responsible for the development of the ner­ the brain's primary vesicles. vous system. Copyright ©2021 by SAGE Publications, Inc. This work may not be reproduced or distributed in any form or by any means without express written permission of the publisher. CHAPTER 4 THE NERVOUS SYSTEM 97 IIB·Mif! Gastrulation. The process by which a hollow ball of cells called the blastocyst is transformed into the gastrula. which contains the germ layers that are to become the differenttissues of the body. (a) Artist conception of the blastocyst (the mass of cells at the bottom is the embryonic disk). (bl Light micrograph of a human blastocyst. (cl Gastrula with its germ layers. consisting of the endoderm. mesoderm. and ectoderm (also shown is the blastopore. which is the opening by which the cavity of the gastrula communicates with the exterior). (d) The three germ layers with the corresponding types of tissue to which they each give rise. (b) (c) Ectoderm distribute Blastopore or Mesoderm Lung cells Thyroid Digestive Cardiac Skeletal Tubule Red blood Smooth Skin cells Neuron Pigment (alveolar cells cells muscle muscle cells of cells muscle of on brain cells cell) (pancreatic cells cells post,the kidney cells epidermis cell) (in gut) (al Science Source SS2879407 (bl Science Source SS2119762 (c) "Gastrulation." Veterian Key. 2017. https://veteriankey.com/gastrulation/ Figure 6.1E. (di "Fertilization and Early Embryonic Development." OpenStax College. October 17. 2013, https://cnx.org/resources/cdd4d14foc1cde804e5a84495390806c/Figure_43_05_04jpg, • Notochord: A flexible. rodlike structure made out 4.1.2 NEURULATIONcopy, of cells from the mesoderm. which serves as the skeleton of the embryo until the formation of the » LO 4.1.2 Describe the process of neurulation. vertebrae. Key Terms • Neural crest: Made from migratingcells of the ectoderm; gives rise to the peripheralnervous system • Neurulation:not The process by which the neural • Somites: Protrusions on either side of the neural tube is formed. which gives rise to the central tube formed by the mesoderm. which give rise to nervous system. the vertebrae and associated skeletal muscles. • Neural folds: Risen edges of the ectoderm. which Dofuse together to form the neural tube. The central nervous system arises from the neural tube. The developmental process by which the neural • Neural groove: The depression in the central tube is formed is known as neurulation (Darnell & region of the ectoderm caused by the neural Gilbert, 2017). Shortly after the formation of the gas­ folds. trula (described in the preceding unit), the edges of • Neural plate: The region that spans the neural the ectoderm rise and become what are known as the folds along with the neural groove.
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