Chapter 37: Neurons and Nervous Systems AP Curriculum Alignment Chapter 37 presents a comparative and evolutionary analysis of the gradual increase in complexity of the nervous system. This information adds to the students understanding of evolutionary trends but is not part of the curriculum framework. Chapter 37 explains in detail how the structure of the neuron allows for the passage of signaling information from one neuron to the next in order for the information to be integrated and acted upon. The detection, integration, and transmission of signals occur in order t-for the animal to produce responses to internal and external signals. Different areas of the brain integrate and send response signals for received signals that vary according to the functions of that part of the brain. These areas of the brain are illustrative examples in Big Idea 3. Chapter 37 explains the reflex arc which is an example of neuron/muscle interaction. Other neuron/muscle interactions are explained in Chapter 37 and are illustrative examples in Big Idea 4. ALIGNMENT OF CONTENT TO THE CURRICULUM FRAMEWORK Big Idea 3: Living systems store, retrieve, transmit, and respond to information essential to life processes. Enduring understanding (EU) 3.D: Cells communicate by generating, transmitting and receiving chemical signals. Essential knowledge (EK) 3.D.2: Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling. b. Cells communicate over short distances by using local regulators that target cells in the vicinity of the emitting cell. To foster student understanding of this concept, instructors can choose an illustrative example such as: Neurotransmitters Plant immune response Quorum sensing in bacteria Morphogens in embryonic development Enduring understanding (EU) 3.E: Transmission of information results in changes within and between biological systems. Essential knowledge (EK) 3.E.2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses. a. The neuron is the basic structure of the nervous system that reflects function. Evidence of student learning is a demonstrated understanding of each of the following: 1. A typical neuron has a cell body, axon and dendrites. Many axons have a myelin sheath that acts as an electrical insulator. 2. The structure of the neuron allows for the detection, generation, transmission and integration of signal information. Mader, Biology, 12 th Edition, Chapter 37 521
3. Schwann cells, which form the myelin sheath, are separated by gaps of unsheathed axon over which the impulse travels as the signal propagates along the neuron. b. Action potentials propagate impulses along neurons. Evidence of student learning is a demonstrated understanding of each of the following: 1. Membranes of neurons are polarized by the establishment of electrical potentials across the membranes. 2. In response to a stimulus, Na+ and K+ gated channels sequentially open and cause the membrane to become locally depolarized. 3. Na+/K+ pumps, powered by ATP, work to maintain membrane potential. c. Transmission of information between neurons occurs across synapses. Evidence of student learning is a demonstrated understanding of each of the following: 1. In most animals, transmission across synapses involves chemical messengers called neurotransmitters. To foster student understanding of this concept, instructors can choose an illustrative example such as: Acetylcholine Epinephrine Norepinephrine Dopamine Serotonin GABA 2. Transmission of information along neurons and synapses results in a response. 3. The response can be stimulatory or inhibitory. d. Different regions of the vertebrate brain have different functions. To foster student understanding of this concept, instructors can choose an illustrative example such as: Vision Hearing Muscle movement Abstract thought and emotions Neuro-hormone production Forebrain (cerebrum), midbrain (brainstem) and hindbrain (cerebellum) Right and left cerebral hemispheres in humans The types of nervous systems, development of the human nervous system, details of the various structures and features of the brain parts, and details of specific neurologic processes are beyond the scope of the course and the AP Exam. Big Idea 4: Biological systems interact, and these systems and their interactions possess complex properties. Enduring understanding (EU) 4.A: Interactions within biological systems lead to complex properties. 522 Mader, Biology, 12 th Edition, Chapter 37
Essential knowledge (EK) 4.A.4: Organisms exhibit complex properties due to interactions between their constituent parts. b. Interactions and coordination between systems provide essential biological activities. To foster student understanding of this concept, instructors can choose an illustrative example such as: Respiratory and circulatory Nervous and muscular Plant vascular and leaf Concepts covered in Chapter 37 also align to the learning objectives that provide a foundation for the course, an inquiry-based laboratory experience, class activities, and AP exam questions. Each learning objective (LO) merges required content with one or more of the seven science practices (SP), and one activity or lab can encompass several learning objectives. The learning objectives and science practices from the Curriculum Framework that pertain to neurons and nervous systems are shown in the table below. Note that other learning objectives may apply as well. LO 3.34 The student is able to construct explanations of cell communication through cell-to-cell direct contact or through chemical signaling. LO 3.39 The student is able to construct an explanation of how certain drugs affect signal reception and, consequently, signal transduction pathways. LO 3.43 The student is able to construct an explanation, based on scientific theories and models, about how nervous systems detect external and internal signals, transmit and integrate information, and produce responses. LO 3.44 The student is able to describe how nervous systems detect external and internal signals. LO 3.45 The student is able to describe how nervous systems transmit information. LO 3.46 The student is able to describe how the vertebrate brain integrates information to produce a response. LO 3.47 The student is able to create a visual representation of complex nervous systems to describe/explain how these systems detect external and internal signals, transmit and integrate information, and produce responses. LO 3.48 The student is able to create a visual representation to describe how nervous systems detect external and internal signals. LO 3.49 The student is able to create a visual representation to describe how nervous systems transmit information. LO 3.50 The student is able to create a visual representation to describe how the vertebrate brain integrates information to produce a response. LO 4.8 The student is able to evaluate scientific questions concerning organisms that exhibit complex properties due to the interaction of their constituent parts. LO 4.9 The student is able to predict the effects of a change in a component(s) of a biological system on the functionality of an organism(s). LO 4.10 The student is able to refine representations and models to illustrate biocomplexity due to interactions of the constituent parts. Mader, Biology, 12 th Edition, Chapter 37 523
Key Concepts Summary Nervous system evolution The nervous system is vital in complex animals, enabling them to seek food and mates and to avoid danger. It monitors internal and external conditions and makes appropriate changes to maintain homeostasis. Sponges lack specialized cells so they have no nervous system. Cnidarians have a nerve net associated with contractile cells. Planarians have longitudinal and transverse nerves and ganglia that receive sensory input. The typical invertebrate nervous system includes a brain and a ventral nerve cord. Cephalopods have marked cephalization the anterior end has a well-defined brain and well-developed sense organs, such as eyes. All vertebrates have a brain that controls the nervous system. Parts of the nervous system The central nervous system (CNS) consists of the brain and spinal cord. The peripheral nervous system (PNS) consists of all the nerves and ganglia that lie outside the central nervous system. The peripheral nervous system (PNS) lies outside the central nervous system and contains nerves that carry impulses to and from the brain. o Voluntary control of skeletal muscles always originates in the brain. o Involuntary responses to stimuli, called reflex actions, can involve only the spinal cord. The nervous system is composed of two types of cells, neurons that send and receive signals and neuroglia that provide support and nourishment for the neurons. o A neuron consists of dendrites, a cell body and an axon. The cell body contains the nucleus and other organelles. The dendrites are highly branched and receive signals from sensory input and other neurons and pass this signal on to the cell body. The axon conveys information to other neurons or cells. Many axons are covered with insulating glial cells (neuroglia) called the myelin sheath. o Glial cells (neuroglia) are the most numerous type of nerve cell in the brain. Their functions in the nervous system include maintaining and nourishing neurons, insulating axons, removing bacteria and other b=debris, participating in response to injury and inflammation, secretin cerebrospinal fluid. Motor neurons take nerve impulses from the CNS to muscles or glands. Sensory (afferent) neurons take nerve impulses from sensory receptors to the CNS. 524 Mader, Biology, 12 th Edition, Chapter 37
Interneurons convey nerve impulses between various parts of the CNS. Some lie between sensory neurons and motor neurons; some take messages from one side of the spinal cord to the other or from the brain to the cord, and vice versa. Nerve impulses A signal is send down an action via an action potential. Neurons have an electrical potential difference across a membrane is called a membrane potential. o The resting potential of a neuron is about 70 mv (millivolts), indicating that the inside of the neuron is more negative than the outside. o This is caused by a difference in ion distribution, mainly potassium and sodium, on either side of the axonal membrane. An action potential is a rapid change in polarity across a portion of an axonal membrane as the nerve impulse occurs. This occurs when the threshold has been reached and the axon potential increases from 70 to 55. After the threshold is reached, depolarization continues as Na + gates open and Na + moves inside the axon. The action potential has begun and the signal will be sent down the axon to stimulate the release of neurotransmitters at the axon terminal. Action potential ends when K + gates open and K + moves to outside the axon. The sodium-potassium pump returns the ions to their resting positions. Many drugs affecting the nervous system act by interfering with or potentiating the action of neurotransmitters. Such drugs can enhance or block the release of a neurotransmitter, mimic the action of a neurotransmitter or block the receptor, or interfere with the removal of a neurotransmitter from a synaptic cleft. Diseases of the nervous system Alzheimer s disease (AD) is the most common cause of dementia, AD patients have abnormal neurons throughout the brain. Parkinson s disease (PD) is a brain disorder characterized by tremors, speech difficulties, and difficulty standing and walking. PD results from a loss of the cells in the basal nuclei that normally produce the neurotransmitter dopamine. Mader, Biology, 12 th Edition, Chapter 37 525
Key Terms action potential Alzheimer disease (AD) amygdala astrocyte autonomic system axon basal nuclei brain stem cell body central nervous system (CNS) cephalization dendrites dorsal root ganglion effector ependymal cells ganglion interneurons multiple sclerosis (MS) myelin sheath nerve fibers nerve net nerves neuroglia neurons neurotransmitters nodes of Ranvier oligodendrocytes parasympathetic division Parkinson disease (PD) peripheral nervous system (PNS) reflex actions reflex arc refractory period resting potential saltatory conduction satellite cells Schwann cells Sensory (afferent) neurons sensory receptors stroke sympathetic division synapse synaptic cleft synaptic integration Teaching Strategies Class time: Three 45-minute class periods Day 1: Lecture on neuron structure, sending/ receiving signals, and action potential 25 minutes Activity 1 on actin potentials 20 minutes Day 2: Lecture on the brain integration of signals and the reflex arc 15 minutes Activity 2 on brain activity 30 minutes Day 3: Lecture on neurotransmitter and disease conditions of the brain 20 minutes Activity 3on drugs and the brain 25 minutes 526 Mader, Biology, 12 th Edition, Chapter 37
Suggested Approaches The brain may be viewed as a frontier for research. The current Brainbow Project is attempting to map every circuit within our brain and other research is continually illuminating new information about the human brain. While the details about the parts of the nervous system, including the brain, are interesting, memorization of these compartments within the nervous system is not part of the AP curriculum. An exclusion statement in the AP Curriculum clearly states: The types of nervous systems, development of the human nervous system, details of the various structures and features of the brain parts, and details of specific neurologic processes are beyond the scope of the course and the AP Exam. The focus for this unit should be on the structure of the neuron and details of how the neuron sends and receives signals. How different areas of the brain integrate information is also important student knowledge. Activity 2 below provides an interactive format for learning this information. The action potential should be clearly understood and the use of models can reinforce the understanding of this mechanism. Activity 1 below will be helpful and can serve as a formative assessment of your students understanding of this process. Students should be able to explain how certain drugs affect reception, integration, and transmission of signals. Activity 3 below will provide students with that information. Students may feel that they have to memorize all of the structures and divisions within the nervous system but that is not the important focus of Chapter 37. Student Misconceptions and Pitfalls Some students may believe that w only use 10% of our brain while research has shown that we use our entire brain. While most students have heard of neurons before, many students have never encountered glial cells and all of their supportive functions. Mader, Biology, 12 th Edition, Chapter 37 527
Suggested Activities Activity One Action Potential Cards Print 15 sets of the cards below, cut out each piece within the sets. Place an entire set of cut out pieces into 15 separate baggies. Give each pair of students a baggie and ask them to place the pictures in order of an action potential and match the description with each picture. 528 Mader, Biology, 12 th Edition, Chapter 37
Stimulus causes the axon to reach its threshold; the axon potential increases from -70 to -55. The action potential has begun. Resting potential: Na+ outside the axon, K+ and large anions inside the axon. Separation of charges polarizes the cell and causes the resting potential. Depolarization continues as Na+ gates open and Na+ moves inside the axon. Action potential ends: Repolarization occurs when K+ gates open and K+ moves to outside the axon. The sodium-potassium pump returns the ions to their resting positions. An action potential can be visualized if voltage changes are graphed over time. Mader, Biology, 12 th Edition, Chapter 37 529
Activity 2: Understanding Neurobiology This NIH website is rich with student activities that fit with the AP Biology curriculum framework. http://science.education.nih.gov/supplements/nih2/addiction/guide/guide_toc.htm Select the student activities and determine which activities you will want to have your students complete. Analysis of the PET images can help students be able to create a visual representation to describe how the vertebrate brain integrates information to produce a response (LO 3.50). Activity 3: The Mouse Party The Mouse Party is an interactive site that provides detailed information on how various drugs affect the brain. Students should observe the various drug actions. The student should construct an explanation of how certain drugs affect signal reception and, consequently, signal transduction pathways. (LO 3.39). Have student go to the website http://learn.genetics.utah.edu/content/addiction/mouse/ 530 Mader, Biology, 12 th Edition, Chapter 37
Student Edition Chapter Review Answers Answers to Assess Questions 1. a; 2. c; 3. c; 4. a; 5. a; 6. c; 7. c; 8. c; 9. c; 10. c; 11. b; 12. d; 13. b; 14. c; 15. d; 16. d; 17. c Answers to Applying the Big Ideas Questions 1. Organisms must be able to respond to their environments for survival. Explain how the nervous system of animals does each of the following: (a) detect external and internal signals, (b) transmit and integrate information, and (c) produce responses. Essential Knowledge Science Practice Learning Objective 3.E.2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses. 6.2: The student can construct explanations of phenomena based on evidence produced through scientific practices. 3.43: The student is able to construct an explanation, based on scientific theories and models, about how nervous systems detect external and internal signals, transmit and integrate information, and produce responses. 3 points maximum. Explanations for mechanisms of the nervous system may include (1 point each): (a) detect external and internal signals The neuron is the basic structure of the nervous system that reflects function. A typical neuron has a cell body, axon, and dendrites. Its structure allows for the detection, generation, transmission and integration of signal formation. Examples might include pain receptors, which are naked nerve endings near the skin. There are also complex organs that detect external signals, such as the eye and ear. (b) transmit and integrate information Many axons have a myelin sheath that acts as an electrical insulator. Schwann cells, which form the myelin sheath, are separated by gaps of unsheathed axon over which the impulse travels as the signal propagates along the neuron. Action potentials propagate impulses along neurons. Membranes of neurons are polarized by the establishment of electrical potentials across the membranes. In response to a stimulus, sodium ion and potassium ion gated channels sequentially open and cause the membrane to become locally depolarized. Sodium/potassium pumps, powered by ATP, work to maintain membrane potential. Mader, Biology, 12 th Edition, Chapter 37 531
Transmission of information the short distance between neurons occurs across synapses. In most animals, transmission across synapses involves chemical messengers called neurotransmitters (examples include acetylcholine, epinephrine, norepinephrine, dopamine, serotonin, and GABA). (c) produce responses Transmission of information along neurons and synapses results in a response that can stimulate or inhibit. The brain could, for example, be stimulated to produce hormones and to send a response signal to muscles for movement away from danger. 2. Interactions and coordination between systems provide essential biological activities for the body. The nervous system provides information upon which the other body systems rely upon for their operation. Predict the effects each of the following changes upon the functionality of an organism: (a) Damage to the circulatory system decreases blood flow to the brain (b) Demyelination of axons (c) Inhibition of neurotransmitters Essential Knowledge Science Practice Learning Objective 4.A.4: Organisms exhibit complex properties due to interactions between their constituent parts. 6.4: The student can make claims and predictions about natural phenomena based on scientific theories and models. 4.9: The student is able to predict the effects of a change in a component(s) of a biological system on the functionality of an organism(s). 2 points maximum. Predictions for effects as the result of changes in the nervous system may include (1 point each): (a) Damage to the circulatory system decreases blood flow to the brain. (as seen in a stroke) If blood flow is decreased or cut off completely, the brain suffers from a lack of oxygen. Cells that do not receive oxygen will not be able to carry out their normal metabolic processes and will begin to die. The area(s) of the brain affected by a lack of oxygen will determine what type of symptoms arise. For example, if oxygen does not get to the motor areas of the brain, then muscles will not receive signals to induce movement and may become paralyzed. In this particular example, damage to the circulatory system has impacted both brains and muscles as a result. (b) Demyelination of axons (as seen in Multiple Sclerosis) 532 Mader, Biology, 12 th Edition, Chapter 37
Because myelin helps action potentials move quickly through salutatory conduction from node to node along an axon, one effect will be the slowing of signals along the nerve fiber. This slows the ability for instantaneous responses, as well as lessens the intensity of responses. The area of demyelination of axons will determine the types of symptoms that result from the slowing or stopping of nerve signal transmission. Some symptoms could include a weakness in motor abilities, causing muscles to spasm or become paralyzed, and sensory organs would not be able to communicate with the brain in the same way, impacting numbness or pain in the skin, vision in the eyes, or other symptoms. If the student recognizes that MS results from the demyelination of axons, they might also predict that the cause of demyelination was autoimmune, bringing another body system into their response. (c) Inhibition of neurotransmitters (as seen in Parkinson s disease or depression) Technically, inhibition of neurotransmitters could occur in the release of the molecule from the first nerve cell, in the synapse, or in the receiving cell. In any of these cases, the chemical message will not be completely transferred between the cells. If the neurotransmitter is serotonin, then mood, appetite and sleep cycles may be impacted. If dopamine, then the reward system in the brain (as seen with drug abuse) will be impacted, or movement of the body will be affected, as seen with Parkinson s disease where people lose control over some movement. The overall efficiency of the nervous system and neurons firing would be affected if the neurotransmitter problem is with glutamate. Answers to Applying the Science Practices Questions Think Critically 1. The amount of brain activity is lower in the heavy drinkers than in the nondrinkers. 2. There could be long-term damage to areas of the brain that involve memory. Mader, Biology, 12 th Edition, Chapter 37 533
Additional Questions for AP Practice 1. Describe the process that occurs at the axon terminal that sends a signal from one neuron to another neuron. 2. Explain the functioning of the reflex arc. 534 Mader, Biology, 12 th Edition, Chapter 37
Answers to Additional Questions for AP Practice 1. After an action potential arrives at an axon terminal, calcium binds to neurotransmitter vesicles and stimulates the fusing of these vesicles with the outer axon terminal membrane. Neuro- transmitter molecules are released and bind to receptors on the postsynaptic membrane (dendritic membrane of the receiving neuron). When an excitatory neuro- transmitter binds to a receptor, Na+ diffuses into the postsynaptic neuron, and an action potential begins. 2. A stimulus (e.g., a sharp pin) causes sensory receptors in the skin to generate nerve impulses that travel in sensory axons to the spinal cord. Interneurons integrate data from sensory neurons and then relay signals to motor axons. Motor axons convey nerve impulses from the spinal cord to a skeletal muscle, which contracts. Movement of the hand away from the pin is the response to the stimulus. Mader, Biology, 12 th Edition, Chapter 37 535