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  1. Splash

  2. Chapter Introduction Organization of the Nervous System 21.1 Sensory Systems 21.2 Motor Systems 21.3 The Peripheral Nervous System 21.4 The Central Nervous System 21.5 Cells of the Nervous System Cellular Communication 21.6 Transmission of Impulses 21.7 Synapses 21.8 Integration 21.9 Drugs and the Brain Evolution of Nervous Systems 21.10 Evolutionary Trends 21.11 Molecular Evolution of Nervous Systems Chapter Highlights Chapter Animations Chapter Menu Contents

  3. Learning Outcomes By the end of this chapter you will be able to: A Distinguish between sensory and motor systems. BDistinguish between the peripheral and central nervous systems. C Describe the cells of the nervous system. D Describe how impulses are transmitted and processed. E Describe the effects of drugs on the brain. F Discuss trends that characterize vertebrate brain evolution. G Describe the molecular evolution of the nervous system. Learning Outcomes

  4. This photo shows a runner moving away from the starting blocks. Nervous Systems • How does the runner translate the sound of the starting gun into action? • What organ systems are involved in the runner’s movement? Chapter Introduction 1

  5. This photo shows a runner moving away from the starting blocks. Nervous Systems • The components that make up the human nervous system are very similar to those of simpler animals. • Evolution has acted on how these components are arranged, enabling a person to react to sensory information, to think, to feel, and to remember. Chapter Introduction 2

  6. End of the Introduction

  7. Organization of the Nervous System 21.1 Sensory Systems • Nervous systems make it possible for animals to know and react to the world around them. • A change in the environment that causes an organism to respond is called a stimulus(plural: stimuli). • A stimulus and the response can be either internal or external. 21.1 Sensory Systems 1

  8. Organization of the Nervous System 21.1 Sensory Systems (cont.) • The nervous system gathers and interprets stimuli through sensory receptors. • Sensory receptors are made up of sensory nerve cells and support cells and can be single nerve cells or complex organs such as eyes. 21.1 Sensory Systems 2

  9. Organization of the Nervous System 21.1 Sensory Systems (cont.) Each type of receptor is specialized to detect one type of stimulus, which may include pressure, touch, pain, and high or low temperature. Other types of receptors are found in other organs. Among these are light receptors in the eye and stretch or movement receptors in the muscles and inner ear, which detect body position, muscle tension, and sound. 21.1 Sensory Systems 3

  10. The dendrites can receive stimuli from sensory receptors or from the axons of other neurons. In response, an electrical impulse travels from the dendrite through the neuron to the tip of its axon. From there, the impulse stimulates another neuron or cell. Organization of the Nervous System 21.1 Sensory Systems (cont.) • Sensory nerve cells, called sensory neurons, transmit impulses from the sensory receptors to the central nervous system. 21.1 Sensory Systems 4

  11. This micrograph clearly shows cell bodies, dendrites, and axons from the human brain. Organization of the Nervous System 21.1 Sensory Systems (cont.) • A typical neuron has three main parts: • The cell body contains the nucleus and other organelles. • Dendrites receive stimuli and conduct impulses toward the cell body. • The axon carries impulses away from the cell body. 21.1 Sensory Systems 5

  12. Organization of the Nervous System 21.1 Sensory Systems (cont.) • A nerve is a bundle of fibers consisting of both axons and dendrites. • The structure of neurons is similar in most types of animals, but the shape can vary. 21.1 Sensory Systems 6

  13. Organization of the Nervous System 21.1 Sensory Systems (cont.) • The dendrites of sensory neurons are specialized to collect and transmit information about environmental stimuli. • Dendrites translate the energy of specific stimuli into electrical energy, the language of the nervous system. 21.1 Sensory Systems 7

  14. Organization of the Nervous System 21.1 Sensory Systems (cont.) • The electrical electrical impulses travel through the axons of sensory neurons to the brain. • Groups of neurons in your brain receive these electrical impulses and comparison the pattern to others stored in your memory to identify the stimuli. • Other parts of your brain then signal your muscles to begin the appropriate response. • Perception happens in the brain, not in the sensory organs. 21.1 Sensory Systems 8

  15. Organization of the Nervous System 21.1 Sensory Systems (cont.) • Different animals depend on various types of sensory receptors. • Our sensory receptors convert sound, light, electrical, and magnetic energy into electrical impulses that the brain can interpret. • The brain can process many kinds of signals simultaneously. 21.1 Sensory Systems 9

  16. Organization of the Nervous System 21.2 Motor Systems • Once the nervous system receives and processes sensory information, the motor system enables an organism to react to stimuli. • The motor system made up of effectors, such as muscles and glands, that carry out responses. • Motor neurons have cell bodies within the brain and spinal cord and carry the instructions from the nervous system to the effectors over long axons. 21.2 Motor Systems 1

  17. Organization of the Nervous System 21.2 Motor Systems (cont.) • Effectors may be under either voluntary or involuntary control: • Voluntary control involves a conscious decision to act in response to a stimulus. • Involuntary control does not involve a conscious decision. 21.2 Motor Systems 2

  18. Organization of the Nervous System 21.2 Motor Systems (cont.) • Complex acts involve activation and inhibition of many responses. • Complex circuits of neurons that operate without conscious choice make smooth, efficient voluntary movement possible. 21.2 Motor Systems 3

  19. Organization of the Nervous System 21.3 The Peripheral Nervous System • A vertebrate nervous system is divided into two main parts: • The central nervous system (CNS) consists of the brain and spinal cord. • The peripheral nervous system (PNS) carries information between the CNS and the other organs. 21.3 The Peripheral Nervous System 1

  20. Organization of the Nervous System 21.3 The Peripheral Nervous System (cont.) • The PNS consists of all nerve tissue except the brain and spinal cord. • Sensory neurons of the PNS help maintain homeostasis by coordinating the functions of internal organs and providing the CNS with sensory information. • Motor neurons of the PNS enable an organism to respond to its environment by stimulating muscle contraction and the activities of glands. 21.3 The Peripheral Nervous System 2

  21. The PNS consists of bundles of axons, or nerves, that connect the CNS to the rest of the body. These nerves contain sensory neurons that carry impulses from the skin and internal organs to the CNS. Motor neurons in these same nerves carry impulses from the CNS to effector organs. These motor neurons control both voluntary responses, such as skeletal muscle contraction, and involuntary responses, such as changes in breathing, production of digestive juices, and the release of hormones into the bloodstream. 21.3 The Peripheral Nervous System 3

  22. Organization of the Nervous System 21.3 The Peripheral Nervous System (cont.) • The motor neurons of the PNS make up two subsystems: • The somatic nervous system is responsible for skeletal muscle contraction, which is usually voluntary. • The autonomic nervous system is responsible for involuntary responses, such as changes in the activities of glands and the digestive system. 21.3 The Peripheral Nervous System 4

  23. The main division of a vertebrate nervous system is between the CNS and the PNS. The autonomic nervous system regulates involuntary responses. Its sympathetic and parasympathetic divisions have opposite effects on effector organs. Although the somatic nervous system controls voluntary contraction of the skeletal muscles, it can also produce involuntary movements of those muscles, such as shivering. 21.3 The Peripheral Nervous System 5

  24. Organization of the Nervous System 21.3 The Peripheral Nervous System (cont.) • The somatic and autonomic nervous systems often work together. • The autonomic nervous system and the glands of the endocrine system work together to regulate many involuntary functions, such as sleep, appetite, and digestion. 21.3 The Peripheral Nervous System 6

  25. Organization of the Nervous System 21.3 The Peripheral Nervous System (cont.) • The autonomic nervous system has two systems: • The sympathetic system, often called the fight-or-flight system, prepares an animal for quick action. • The parasympathetic system reduces an animal’s readiness for action. • The sympathetic and parasympathetic nerves often have opposite effects on the same organ. 21.3 The Peripheral Nervous System 7

  26. Organization of the Nervous System 21.3 The Peripheral Nervous System (cont.) 21.3 The Peripheral Nervous System 8

  27. Organization of the Nervous System 21.4 The Central Nervous System • The vertebrate CNS forms the bridge between the sensory and motor functions of the PNS. • The CNS also can store experiences in memory and learn by establishing patterns of responses based on previous experiences. 21.4 The Central Nervous System 1

  28. Organization of the Nervous System 21.4 The Central Nervous System (cont.) The human CNS consists of the brain and spinal cord. The brain is divided into several major regions. The most prominent parts are the cerebellum, which coordinates movement and maintains balance, and the cerebrum, which is responsible for sense perception, voluntary movement, and thought. The medulla regulates basic homeostatic functions, such as the activities of the circulatory and respiratory systems. 21.4 The Central Nervous System 2

  29. Organization of the Nervous System 21.4 The Central Nervous System (cont.) • The brain and spinal cord are covered by protective membranes called the meninges. • Cerebrospinal fluid, which circulates around the CNS, provides shock protection. • The entire CNS is encased in protective bone. 21.4 The Central Nervous System 3

  30. Organization of the Nervous System 21.4 The Central Nervous System (cont.) • The brain of an adult human weighs about 1.5 kg and is composed of an estimated 100 billion neurons. • The senses of sight, hearing, taste, smell, and touch are experienced in the part of the brain called the cerebrum. 21.4 The Central Nervous System 4

  31. Organization of the Nervous System 21.4 The Central Nervous System (cont.) Specific regions of the brain serve specific functions. Some regions are responsible for certain kinds of sensory information, such as touch, sight, and hearing. Other regions initiate voluntary movement, memory, language skills, and other activities. 21.4 The Central Nervous System 5

  32. Organization of the Nervous System 21.4 The Central Nervous System (cont.) • The cerebrum is divided into left and right hemispheres, each having different functions. • The left hemisphere is associated with verbal and analytical skills. • The right hemisphere is responsible for the ability to judge spatial relationships and is involved in imaginative or creative thinking. 21.4 The Central Nervous System 6

  33. Organization of the Nervous System 21.4 The Central Nervous System (cont.) • Each hemisphere also controls the sensory and motor functions of the opposite side of the body. • Many functions of the right and left hemispheres are reversed in left-handed people. • The cortex (outer layers) of the human cerebrum has distinct specialized areas that control the sensory and motor functions of each body part. 21.4 The Central Nervous System 7

  34. Organization of the Nervous System 21.4 The Central Nervous System (cont.) The cartoon drawings show the body parts served by each part of the cerebrum. Note the distorted sizes of the cartoons; some body parts are served by disproportionately large or small brain regions. 21.4 The Central Nervous System 8

  35. Organization of the Nervous System 21.4 The Central Nervous System (cont.) • The cerebellum mainly coordinates contractions of the skeletal muscles. • The brain stem, also called the medulla, regulates vital involuntary functions, such as heart rate, contractions of blood vessels, and the depth and rate of breathing. 21.4 The Central Nervous System 9

  36. Organization of the Nervous System 21.5 Cells of the Nervous System • There are two major classes of cells in vertebrate nervous systems—neurons and glial cells. • Neurons can be divided into three general types: sensory neurons, motor neurons and interneurons. • Interneurons, the most abundant type of neuron in vertebrate nervous systems, transmit signals from one neuron to another within the CNS. 21.5 Cells of the Nervous System 1

  37. Glial cells provide physical support for neurons in the spinal cord, x766. Organization of the Nervous System 21.5 Cells of the Nervous System (cont.) • Glial cells, or glia, are generally smaller than neurons, but they are 10–50 times as numerous and make up more than half the weight of the nervous system. 21.5 Cells of the Nervous System 2

  38. Organization of the Nervous System 21.5 Cells of the Nervous System (cont.) • Glial cells have various functions including: • supporting the neurons by filling the spaces between their cell bodies and coating the surfaces of the CNS and blood vessels in the brain • providing nutrients and growth factors to neurons • waste removal 21.5 Cells of the Nervous System 3

  39. Schwann cells wrap themselves around axons in vertebrates, forming an insulating myelin sheath, x57,000. Organization of the Nervous System 21.5 Cells of the Nervous System (cont.) • Glial cells known as Schwann cells wrap themselves around the axons of neurons in the PNS to form the myelin sheath, that serves as insulation. • The gaps between neighboring Schwann cells are known as nodes of Ranvier. 21.5 Cells of the Nervous System 4

  40. Organization of the Nervous System 21.5 Cells of the Nervous System (cont.) • Cell bodies of neurons form aggregations called ganglia in the PNS and nuclei in the CNS. • The CNS also has layered groups of connected neurons calledlamina. 21.5 Cells of the Nervous System 5

  41. Organization of the Nervous System 21.5 Cells of the Nervous System (cont.) • Neurons perform three major functions: • they respond to chemical and physical stimuli • they conduct impulses • they release chemical regulators • Combinations of these three functions enable the nervous system to store your memories, help you analyze situations and make decisions, and regulate your organs and glands. 21.5 Cells of the Nervous System 6

  42. End of Section 1

  43. Note that the inside of the cell has a negative charge with respect to the outside. Most of the excess negative charges in the cytoplasm are due to proteins and phosphate ions. Sodium ions (Na+) are more concentrated outside the cell, and potassium ions (K+) are more concentrated in the cytoplasm. Cellular Communication 21.6 Transmission of Impulses • Like all cells, a neuron’s plasma membrane is electrically charged because ions are distributed unequally on the outside and inside of the cell. 21.6 Transmission of Impulses 1

  44. Cellular Communication 21.6 Transmission of Impulses (cont.) • The unequal distribution is due to three factors: 1. Cells contain many negatively charged molecules, such as phosphates and proteins, that cannot diffuse through the plasma membrane. 2. An active transport protein in the neuron plasma membrane pumps potassium into the cell and sodium out of the cell. 3. Potassium ions easily diffuse back out of the neuron though protein channels in the plasma membrane that facilitate diffusion. 21.6 Transmission of Impulses 2

  45. Cellular Communication 21.6 Transmission of Impulses (cont.) • Unequal diffusion creates a negative charge in the cell and more positive charge outside, a difference called an electric potential. • A membrane with a positive side and a negative side is also said to be polarized. • The potential of the membrane when it is not transmitting an impulse is called the neuron’s resting potential. 21.6 Transmission of Impulses 3

  46. How the plasma membrane of a neuron becomes charged: In step (a), negative ions trapped inside the cell attract positive ions. In step (b), an active-transport protein takes potassium ions (K+) into the cell and removes sodium ions (Na+). This process keeps the sodium concentration low and the potassium concentration high in the cytoplasm. These concentrations are reversed outside the cell. 21.6 Transmission of Impulses 4

  47. How the plasma membrane of a neuron becomes charged: In step (c), the concentrated potassium ions leak out through potassium channels in the cell membrane, leaving the negative charges in the cytoplasm partly unbalanced. The result is a relatively negative cytoplasm and a relatively positive exterior. In step (d), this electrical difference changes the tertiary structure of the sodium-channel proteins, which keeps the sodium-channels closed. They can open in response to a stimulus that depolarizes the membrane. 21.6 Transmission of Impulses 5

  48. Cellular Communication 21.6 Transmission of Impulses (cont.) • Stimulation of a neuron results in a sudden change in permeability causing a brief depolarization and repolarization, also known as an action potential. • The number of action potentials a neuron can experience per second depends on the time required for active transport to restore the resting potential. 21.6 Transmission of Impulses 6

  49. Cellular Communication 21.6 Transmission of Impulses (cont.) • Depolarization at one point in a neuron membrane sets up an electric current, called a nerve impulse, that spreads rapidly along the axon. • The nerve impulse moves away from the point of stimulation because sodium ion channels on the axon behind the area of depolarization temporarily close. 21.6 Transmission of Impulses 7

  50. How an action potential occurs 21.6 Transmission of Impulses 8