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UNIT B: Human Body Systems Chapter 8: Human Organization Chapter 9: Digestive System Chapter 10: Circulatory System and Lymphatic System Chapter 11: Respiratory System Chapter 12: Nervous System: Section 12.1 Chapter 13: Urinary System Chapter 14: Reproductive System UNIT B Chapter 12: Nervous System Chapter 12: Nervous System In this chapter, you will learn about the structure and function of the nervous system. How might a researcher study the effects of frequent head trauma? Sport-Related Head Trauma and Brain Function. Neurosurgeon Dr. Robert Cantu has studied the brains of many deceased athletes, including hockey and football players. He has found that these players often suffered from chronic traumatic encephalopathy (CTE), a degenerative brain disease caused by repeated blunt impact to the head. TO PREVIOUS SLIDE How might one determine which part of the brain has been affected by repeated blunt impacts? Given the available information about CTE, what steps do you feel should be taken to prevent its occurrence (if any)? UNIT B Chapter 12: Nervous System 12.1 Nervous Tissue The nervous system coordinates and regulates the functioning of the body’s other systems. The nervous system consists of two major systems that work together: • Central nervous system (CNS): brain and spinal cord • Peripheral nervous system (PNS): nerves that carry sensory messages to the CNS and motor commands from the CNS to the muscles and glands TO PREVIOUS SLIDE Section 12.1 UNIT B Chapter 12: Nervous System TO PREVIOUS SLIDE Figure 12.1 Organization of the nervous system. The sensory neurons of the peripheral nervous system take nerve impulses from sensory receptors to the central nervous system (CNS), and motor neurons take nerve impulses from the CNS to muscles and glands. Section 12.1 UNIT B Chapter 12: Nervous System Section 12.1 The nervous system contains two types of cells: • Neurons: cells that transmit nerve impulses between parts of the nervous system • Neuroglia: support and nourish neurons, maintain homeostasis, form myelin that surrounds neurons, and aid in signal transmission TO PREVIOUS SLIDE UNIT B Chapter 12: Nervous System Section 12.1 Types of Neurons and Neuron Structure There are three classes of neurons: • Sensory neurons: take messages to the CNS; have sensory receptors that detect changes in the environment • Interneurons: receive input from sensory neurons and other interneurons in the CNS • Motor neurons: take messages away from the CNS to an effector (an organ, muscle fibre, or gland); o Effectors carry out responses to environmental changes TO PREVIOUS SLIDE Figure 12.2 Types of neurons. UNIT B Chapter 12: Nervous System Section 12.1 Neurons vary in appearance, but most of them have three parts: • Cell body: contains the nucleus and other organelles • Dendrites: extensions leading toward the cell body that receive signals from other neurons and send them to the cell body • Axon: conducts nerve impulses away from the cell body toward other neurons or effectors TO PREVIOUS SLIDE Figure 12.2 Types of neurons. UNIT B Chapter 12: Nervous System Section 12.1 Myelin Sheath Some axons are covered by a protective myelin sheath. • In the PNS, a myelin sheath is formed by Schwann cells, a type of neuroglia that contains myelin in the plasma membranes • Schwann cells wrap around an axon and lay down many layers of plasma membrane • Each Schwann cell myelinates only part of an axon, leaving gaps called nodes of Ranvier TO PREVIOUS SLIDE Figure 12.3 Myelin sheath. a. In the PNS, a myelin sheath forms when Schwann cells wrap themselves around an axon. b. Electron micrograph of a cross section of an axon surrounded by a myelin sheath. UNIT B Chapter 12: Nervous System Section 12.1 Myelin in the PNS • The myelin sheath plays an important role in nerve generation in the PNS • If an axon is severed, the myelin sheath remains and serves as a passageway for new fibre growth Myelin in the CNS • In the CNS, myelin is produced by oligodendrocytes, a type of neuroglia • Nerve regeneration does not occur to any significant degree in the CNS TO PREVIOUS SLIDE UNIT B Chapter 12: Nervous System Section 12.1 Nervous tissue in the CNS The CNS is composed of two types of nervous tissue: • Grey matter o Contains neurons with short, nonmyelinated axons o Found in the surface layer of the brain and the central part of the spinal cord • White matter o Contains myelinated axons that run together in bundles called tracts o Found deep within the grey matter of the brain and surrounds the grey matter in the spinal cord TO PREVIOUS SLIDE UNIT B Chapter 12: Nervous System Check Your Progress 1. Identify the three classes of neurons, and describe their relationship to each other. 2. Describe the three parts of a neuron. 3. Distinguish the cell types that form the myelin in the PNS versus the CNS. 4. Review the structure of grey matter and white matter, and describe where each is found in the CNS and the PNS. TO PREVIOUS SLIDE Section 12.1 UNIT B Chapter 12: Nervous System TO PREVIOUS SLIDE Section 12.1 UNIT B Chapter 12: Nervous System TO PREVIOUS SLIDE Section 12.1