29.4. Central and Peripheral Nervous Systems. The nervous system s two parts work together. > Virginia standards

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1 29.4 Central and Peripheral Nervous Systems VOCABULARY cerebrum cerebral cortex cerebellum brain stem reflex arc somatic nervous system autonomic nervous system sympathetic nervous system parasympathetic nervous system > Virginia standards BIO.1.e The student will demonstrate an understanding of scientific reasoning, logic, and the nature of science by planning and conducting investigations in which conclusions are formed based on recorded quantitative and qualitative data. BIO.4.d The student will investigate and understand life functions of Archaea, Bacteria and Eukarya. Key concepts include human health issues, human anatomy, and body systems. BIO.1.EKS-20; BIO.4.EKS-5 KEY CONCEPT The central nervous system interprets information, and the peripheral nervous system gathers and transmits information. MAIN IDEAS The nervous system s two parts work together. The CNS processes information. The PNS links the CNS to muscles and other organs. Connect to Your World Imagine that you re watching television, and you want to turn up the volume. Without taking your eyes off the screen, you reach for the remote control on a table next to you. When you touch a glass of water or your homework that is sitting on the table, you will not pick it up because you know that it does not feel like the remote. Your brain is interpreting the stimuli gathered by your sense of touch. If you had no way to interpret each stimulus, you might pick up every item on the table before finding the remote. Main Idea The nervous system s two parts work together. Figure 4.1 Your central nervous system (orange) and peripheral nervous system (yellow) are connected. Earlier in this chapter you read that your nervous system is divided into two parts the central nervous system and the peripheral nervous system which are shown in figure 4.1. The central nervous system (CNS) includes the brain and spinal cord. The CNS is composed of interneurons that interact with other nerves in the body. The CNS receives, interprets, and sends signals to the PNS. The peripheral nervous system (PNS) is the collection of nerves that connects the CNS to all of your organ systems. The PNS uses sensory neurons to detect stimuli from inside and outside your body, and it uses motor neurons to carry signals from the CNS to other parts of the body and stimulate your muscles or other target organs. Both the CNS and the PNS are made of several smaller parts. For example, the brain has several areas that control different functions. Divisions of the PNS influence voluntary responses, such as muscle contractions that occur while you walk, and involuntary responses, such as those that occur during digestion. Summarize How do the neurons of the CNS and PNS work together to produce responses to stimuli? Chapter 29: Nervous and Endocrine Systems 829

2 QUICK LAB INFeRring The Primary Sensory Cortex The primary sensory cortex is the part of your cerebrum that receives information about your sense of touch from different parts of your body. Each body part sends information to a different place in your primary sensory cortex. In this lab, you will determine the relationship between different body parts and the amount of space the brain devotes to receiving touch information from those body parts. Materials 3 toothpicks soft blindfold/bandana Problem Does your finger or your forearm have more space devoted to it in the primary sensory cortex? Procedure 1. Hypothesize which area will be more sensitive. Make a data table to record the information you gather during the lab. 2. Have your partner close his or her eyes. Gently, touch the tip of your partner s index finger with the tip(s) of one, two, or three toothpicks at the same time. 3. Ask your partner how many points he or she feels. Write down the number your partner says next to the number of toothpicks you used. Repeat three more times, varying the number of toothpicks used. 4. Repeat steps 2 and 3 on your partner s forearm. Analyze and Conclude 1. Analyze Did your partner s finger or forearm receive more sensory information? Do your data support your hypothesis? Why or why not? 2. Infer Which area likely has more space in the primary sensory cortex? Table 1. Primary Sensory Cortex Data Area Tested Number of Toothpicks Used Reported Main Idea The CNS processes information. READING TOOLBox TAKING NOTES Use a main idea diagram to study the parts of the brain. brain cerebrum: interprets signals... The interneurons of the brain and spinal cord are arranged in a particular way. All of the neuron cell bodies are clustered together, and all of the axons are clustered together. The collection of neuron cell bodies is called gray matter because of its dark gray color. The collection of axons is called white matter because the myelin sheath on the axons give them a white appearance. In the brain, the gray matter is on the outside, and the white matter is on the inside. The spinal cord has the opposite arrangement. The Brain The entire brain weighs about half as much as a textbook and has more than 100 billion neurons. The brain is protected by three layers of connective tissue, called meninges (muh-nihn-jeez), that surround it. Between the layers of meninges is a fluid. The fluid cushions the brain so that the brain will not bang up against the skull. The brain itself has three main structures: the cerebrum, the cerebellum, and the brainstem. The cerebrum (SEHR-uh-bruhm) is the part of the brain that interprets signals from your body and forms responses such as hunger, thirst, emotions, motion, and pain. The cerebrum has right and left halves, or hemispheres. 830 Unit 9: Human Biology

3 (bl) Wellcome Dept. of Cognitive Neurology/Photo Researchers, Inc.; (bc) WDCN/Univ. College London/Photo Researchers, Inc.; (br) Wellcome Dept. of Cognitive Neurology/Photo Researchers, Inc. Each hemisphere controls the opposite side of the body. For example, the right hemisphere of your brain processes all of the stimuli received by your left hand. Similarly, the left side of your brain controls the muscles that kick your right leg. When the spinal cord brings a signal from the body, the signal crosses over to the opposite hemisphere in the corpus callosum. The corpus callosum is a thick band of nerves that connects the two hemispheres. The outer layer of the cerebrum, called the cerebral cortex, interprets information from your sensory organs and generates responses. The cerebral cortex is about as thick as a pencil. Yet its size is deceptive because its folds give it a larger surface area than you might expect. If the cerebral cortex were unfolded, it would cover a typical classroom desk. This surface area is large enough to hold more than 10 billion neurons. The neurons in the cerebral cortex are arranged in groups that work together to perform specific tasks. For example, movement is initiated by an area of the brain called the motor cortex, and the sense of touch is received by the sensory cortex. Scientists divide the cerebral cortex into different areas, or lobes, based on function. Each hemisphere of the human brain can be divided into four lobes frontal, parietal, occipital, and temporal. The lobes and the cortical areas they contain are shown in Figure 4.2. FIGURE 4.2 Lobes of the Brain The various areas of the cerebral cortex process different types of information. Frontal lobe Personality, reasoning, and judgment are controlled in the frontal lobe. It also coordinates voluntary movement and speech production. planning speech production These scans of an actual brain (right) show which part of the brain is most active while a person does different activities. motor cortex (movement) hearing Temporal lobe Speech interpretation and hearing are functions carried out by the temporal lobe. It also plays a role in memory. sensory cortex (touch) speech interpretation Parietal lobe The sensory cortex, which interprets and coordinates information regarding the sense of touch, is contained in this lobe. multisensory information vision (entire lobe) Occipital lobe Visual information is processed in this lobe. Apply Using the illustration as a guide, determine what type of information each scanned brain is processing. Chapter 29: Nervous and Endocrine Systems 831

4 midbrain medulla oblongata Figure 4.3 The structures of the brain stem connect the brain to the spinal cord. spinal cord pons Underneath the cerebral cortex are many smaller areas with different functions. The limbic system, for example, is involved in learning and emotions and includes the hippocampus and the amygdala. The thalamus sorts information from your sensory organs and passes signals between the spinal cord and other parts of the brain. The hypothalamus gathers information about body temperature, hunger, and thirst. Then it sends signals that help the body adjust and maintain homeostasis, as you will see in Section 6. The cerebellum (sehr-uh-behluhm) is the part of the brain that coordinates your movements. It helps you maintain your posture and balance, and it automatically adjusts your body to help you move smoothly. For example, when you brush your teeth, your cerebellum gets information about where your arm is positioned compared with the rest of your body. Your cerebellum plans how much your arm would need to move in order to brush your teeth. It sends this information to the motor cortex in your cerebrum, which signals your arm to move. VISUAL VOCAB cerebrum cerebellum You can learn the location of the cerebellum by remembering that it hangs below the large part of the brain, just as a bell hangs from the ceiling. The brain stem connects the brain to the spinal cord and controls the most basic activities required for life, such as breathing and heartbeat. The brain stem has three major parts midbrain, pons, and medulla oblongata which are shown in figure 4.3. The midbrain controls some reflexes, such as changing the size of the pupil to control the amount of light entering the eye. The pons regulates breathing and passes signals between the brain and the spinal cord. The medulla oblongata connects the brain to the spinal cord. It controls basic life-sustaining functions, such as heart function, vomiting, swallowing, and coughing. CONNECT TO Chordates The spinal cord is one anatomical feature that defines the phylum Chordata, which includes humans and many other animals. You can read more about chordates in Vertebrate Diversity. The Spinal Cord The spinal column consists of vertebrae, fluid, meninges, and the spinal cord. The spinal cord is a ropelike bundle of neurons that is about as wide as your thumb. It connects the brain to the nerves that are found throughout the body. All signals that go to or from the brain pass through the spinal cord. Although movement is controlled by your cerebrum and cerebellum, your brain depends on your spinal cord to deliver messages to the proper muscles. When you are brushing your teeth, and you want to move your arm, the cerebrum sends an impulse down the spinal cord. The impulse is directed by an interneuron to the motor neuron that connects to the arm muscles. The motor neuron then carries the impulse to receptors in the arm muscle. When the receptors are stimulated by the impulse, your arm moves. If the spinal cord (tr) Fotolistic/ShutterStock; (tc), (tr) Dr. Fred Hossler/Getty Images 832 Unit 9: Human Biology

5 is damaged, messages cannot move between the brain and the rest of the body. This results in paralysis. The spinal cord also controls involuntary movements called reflexes. Reflex arcs, as shown in Figure 4.4, are nerve pathways that need to cross only two synapses before producing a response. Because the signal never has to travel up the spinal cord to the brain, you react quickly. For example, when the doctor taps your knee, tissues that connect your kneecap to your leg muscles stretch and stimulate a sensory neuron in your leg. The sensory neuron sends an impulse to your spinal cord. An interneuron in the spinal cord directs the impulse into motor neurons that cause your leg to jerk. Reflex arcs play an important role in protecting your body from injury. When you put your hand on a hot stove, for example, you will jerk your hand away before you even have the chance to say Ouch! You do not feel the pain until moments after you jerk your hand away. If you did not have reflex arcs, your hand would remain on the stove until your brain interpreted the heat detected by thermoreceptors in your skin. Your hand would be badly burned before you ever reacted. Summarize How is a muscle movement caused by a reflex arc different from a voluntary muscle movement? Main Idea The PNS links the CNS to muscles and other organs. interneuron sensory neuron motor neurons Biology HMDScience.com Premium Content Reflex Arc Figure 4.4 Reflex arcs allow your body to respond quickly and without thinking, as when your leg jerks after your doctor taps your knee with a mallet. The peripheral nervous system (PNS) includes 12 pairs of nerves in the head, such as the facial and olfactory nerves, and 31 pairs of spinal nerves. Most nerves contain axons from both sensory and motor neurons that carry information to and from the CNS. In general, the PNS is made up of a sensory system and a motor system. The system of sensory nerves collects information about the body and its surroundings. The system of motor nerves triggers voluntary and involuntary responses within the body. When you are running, walking, or even sitting, you rely on your somatic nervous system to stimulate your muscles to maintain your movement, posture, and balance. The somatic nervous system is the division of the PNS that regulates all of the movements over which you have voluntary control. It connects the CNS to target organs. Chapter 29: Nervous and Endocrine Systems 833

6 Central nervous system (CNS) Somatic nervous system (voluntary) Sympathetic nervous system (action and stress) Nervous System Figure 4.5 The nervous system can be divided into subsystems based on their functions. Peripheral nervous system (PNS) Autonomic nervous system (involuntary) Parasympathetic nervous system (calm and relaxation) The autonomic nervous system is the division of the PNS that controls automatic functions that you do not have to think about. For example, involuntary muscles help you to digest food by pushing it through your intestines. The autonomic nervous system is also important in maintaining homeostasis. It takes messages from the hypothalamus to organs in the circulatory, digestive, and endocrine systems. Within the autonomic nervous system are two subdivisions: the sympathetic nervous system and the parasympathetic nervous system. Figure 4.5 shows how these two systems relate to the rest of the nervous system. Although the two systems have opposite effects on the body, they both function continuously. If something happens to cause one system to produce more signals, the other system will become more active to balance the effects of the first. Together, the sympathetic and parasympathetic nervous systems help your body to maintain homeostasis. The sympathetic nervous system is the part of the autonomic nervous system that prepares the body for action and stress. This is called the fight or flight response. When you become frightened or you are preparing to compete in a sport, your sympathetic nervous system is stimulated. Blood vessels going to the skin and internal organs contract, which reduces blood flow to those areas. Meanwhile, blood vessels going to the heart, brain, lungs, and skeletal muscles expand, increasing the blood supply in those areas. Heart rate increases. Airways enlarge, and breathing becomes more efficient. These changes improve your physical abilities and allow you to think quickly. If something frightens you, your sympathetic nervous system activates. When the danger passes, the parasympathetic nervous system takes over to bring your body back to normal. The parasympathetic nervous system is the division of the autonomic nervous system that calms the body and helps the body to conserve energy. It does this by lowering blood pressure and heart rate. It is active when the body is relaxed. Analyze Are reflex arcs part of the somatic or autonomic nervous system? Explain Reviewing Formative Assessment Main Ideas 1. How do the types of neurons found in the CNS and PNS differ in their functions? 2. How does the cerebral cortex differ from the rest of the cerebrum? 3. What are some similarities and differences between the somatic nervous system and autonomic nervous system? Critical thinking 4. Apply Why might a person with a brain injury be able to understand the speech of others but not be able to speak? 5. Synthesize You step on a sharp rock, your leg jerks upward, and a moment later you feel pain in your foot. Use the words motor neuron, sensory neuron, and interneuron to explain what happened. Self-check Online HMDScience.com Premium Content CONNECT TO Evolution 6. Which part of the brain the cerebrum, cerebellum, or brain stem probably evolved first? (Hint: Consider which part is most important for basic life processes.) 834 Unit 9: Human Biology