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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 Nervous Tissue The nervous system coordinates and regulates the functioning of the body’s other systems. The nervous system consists of two major systems: Central nervous system (CNS): brain and spinal cord Peripheral nervous system (PNS): • nerves that carry sensory messages CNS • Nerves that carry motor commands from the CNS to the muscles and glands TO PREVIOUS SLIDE Section 12.1 UNIT B Chapter 12: Nervous System Section 12.1 The nervous system contains two types of cells: Neurons (Nerve Cells): • transmit nerve impulses between parts of the nervous system Neuroglia (Glial Cells): 1. support and nourish neurons, 2. maintain homeostasis, 3. form myelin that surrounds neurons, 4. aid in signal transmission, 5. destroy and remove the carcasses of dead neurons (clean up). TO PREVIOUS SLIDE Neuronal Structure UNIT B Chapter 12: Nervous System Section 12.1 Most Neurons 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 3 Types of Neurons: • Sensory neurons: detect changes in the environment, take messages to the CNS; • 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. Flow of Information from Receptors to Effectors of Nervous System Reflex Arc: nerve pathway followed by a reflex action UNIT B Chapter 12: Nervous System TO PREVIOUS SLIDE Section 12.1 The nervous system contains two types of cells: Neurons: • transmit nerve impulses between parts of the nervous system Neuroglia (Glial Cells): 1. support and nourish neurons, 2. maintain homeostasis, 3. form myelin that surrounds neurons, 4. aid in signal transmission, 5. destroy and remove the carcasses of dead neurons (clean up). Neuroglia is found in both CNS and PNS Glial Cells in CNS Glial Cells in PNS Oligodendrocytes Astrocytes Microglia Ependymal Cells Satellite Cells Schwann cells Neuroglia Glial Cells of CNS Glia of CNS Oligodendrocytes - support and insulate axons Astrocytes -regulate transmission of electrical impulses in brain. Microglia -mediate immune responses in CNS by acting as macrophages, clearing cellular debris and dead neurons from nervous tissue through the process of phagocytosis Ependymal Cells - line the CSF-filled ventricles in the brain and the central canal of the spinal cord Glial Cells of PNS Glial Cells of PNS Satellite Cells – cover the surface of nerve cell bodies Schwann cells – produce myelin in PNS UNIT B Chapter 12: Nervous System Section 12.1 Myelin Sheath Some axons are covered by a protective myelin sheath. Myelin: • proteins and phospholipids forming a whitish insulating sheath around many nerve fibers, • increase the speed at which impulses are conducted. 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. Myelin Sheath UNIT B Chapter 12: Nervous System Section 12.1 Myelin in the PNS • produced by Schwann cells by wrapping around axon and laying down many layers of plasma membrane • Each Schwann cell myelinates only part of an axon, leaving gaps called nodes of Ranvier • 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 TO PREVIOUS SLIDE Myelin in the CNS: • produced by oligodendrocytes • Nerve regeneration does not occur to any significant degree in the CNS UNIT B Chapter 12: Nervous System Section 12.1 2 Types of Nervous tissue in the CNS: • Grey matter o Contains neurons with short, non-myelinated 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 Brain 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