This chapter focuses on the nervous system. This includes motor control and the basis of sensation. It outlines the organization of the nervous system and the nature of its constituent cells. The nervous system may be divided into five main parts: the brain, the spinal cord, peripheral nerves, the autonomic nervous system, and the enteric nervous system. The chapter discusses how the brain and spinal cord constitute the central nervous system (CNS), while the peripheral nerves, autonomic nervous system, and enteric nervous system make up the peripheral nervous system. The autonomic nervous system is the part of the nervous system that is concerned with the innervation of blood vessels and the internal organs, which includes the autonomic ganglia that run parallel to the spinal column and their associated nerves.
Chapter
Introduction to the nervous system
Chapter
The somatosensory system
This chapter explains that skin is the interface between the body and the outside world. Skin is not uniformly sensitive over its surface. The chapter analyses the punctate distribution of various sensations: specific points of the skin are sensitive to touch, others are sensitive to cooling, warming, or noxious stimuli. The muscles and joints possess sensory receptors that provide information concerning the disposition and movement of the limbs, which is relayed to the spinal cord and brain by the afferent nerves of the somatosensory system. The chapter talks about nerve endings and encapsulated receptors. This prompts three key questions. Why are there so many different kinds of receptor? What are their functions? How do the various receptors convert the different kinds of stimuli into nerve impulses? To answer these questions, it is necessary to examine the responses of particular receptors to specific stimuli.
Chapter
Lower Motor Neuron Circuits and Motor Control
Edited by George J. Augustine, Jennifer Groh, Scott Huettel, Anthony-Samuel LaMantia, Leonard E. White, and Dale Purves,
This chapter investigates how skeletal muscle contraction is initiated by “lower” motor neurons in the spinal cord and brainstem. The cell bodies of the lower neurons are located in the ventral horn of the spinal cord gray matter and in the motor nuclei of the cranial nerves in the brainstem. These neurons send axons directly to skeletal muscles via the ventral roots and spinal peripheral nerves or, in the case of brainstem motor nuclei, via cranial nerves. The spatial and temporal patterns of activation of lower motor neurons are determined primarily by local circuits located within the spinal cord and brainstem. The local circuit neurons receive direct input from sensory neurons and mediate sensorimotor reflexes. They also maintain precise interconnections that enable the coordination of a rich repertoire of rhythmical and stereotyped behaviors.
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Upper Motor Neuron Control of the Brainstem and Spinal Cord
Edited by George J. Augustine, Jennifer Groh, Scott Huettel, Anthony-Samuel LaMantia, Leonard E. White, and Dale Purves,
This chapter evaluates how the axons of upper motor neurons arise from cell bodies in higher centers and descend to influence the local circuits in the brainstem and spinal cord. The sources of these upper motor neuron pathways include several brainstem centers and multiple cortical areas in the frontal lobe. The motor control centers in the brainstem are important in postural control, orientation toward sensory stimuli, locomotion, and orofacial behavior, with each center having a distinct influence. The mesencephalic locomotor region initiates locomotion. Two other centers, the vestibular nuclear complex and the reticular formation, make widespread contributions to the maintenance of body posture and position. The reticular formation also contributes to a variety of somatic and visceral motor circuits that govern the expression of autonomic and stereotyped somatic motor behavior. Also in the brainstem, the superior colliculus contains upper motor neurons that initiate orienting movements of the head and eyes.
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Vertebrate development III: chick and mouse—completing the body plan
This chapter explores some features of vertebrate development involved in completing the body plan, using the chick and the mouse as model organisms. It focuses on the development of the spinal cord, somites, antero-posterior axis of the body, neural crest cells, and left-right asymmetry in the body. The chapter acknowledges the striking differences seen between birds, mammals, and amphibians, in terms of early development. It notes the significance of nourishment in relation to the early development of the chick and mouse. Moreover, the chapter mentions the similarities in how germ layers are specific and patterned among all vertebrates despite the different topologies of embryos.
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Neuronal control of motor output
This chapter looks at different model systems that try to explain how coordinated contractions of muscles are controlled at the neural level. These muscle activities are associated with simple reflexes and rhythmic behaviors that often persist over long periods. The chapter reviews the model proposed by Charles Scott at the beginning of the twentieth century, which states that such coordinated activities are the result of a chain of reflexes, coordinated by proprioceptive information, in the spinal cord. The discussion also covers another major model proposed by Thomas Graham Brown, which assumes the existence of an intrinsic oscillator in the spinal cord that drives the coordinated activity of the muscles. Furthermore, the chapter tackles in detail the escape swimming behavior of Xenopus tadpoles relevant to the study of neural mechanisms involved in generating locomotor behavior.
