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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

Chapter 12: Nervous 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? 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)? 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. Chapter opener figure background: Former NHL players Rick Rypien, Wade Belak, and Derek Boogaard had something in common; they were all “enforcers.” They were expected to fight during hockey games. There is another similarity among these men. They are all dead. Each died of causes that increasingly seem tied to their activities on the ice. 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. CTE seems to manifest itself in addiction, depression, and anxiety, conditions suffered by some or all of the deceased players. Dr. David Goldbloom, senior medical adviser at Toronto’s Centre for Addiction and Mental Health, thinks it is important not to assume that the deaths of the players were all the result of the same thing. Each was an individual and each had his own mental health history. Rypien and Belak had battled depression, and Boogaard was still recovering from previous concussions. Goldbloom feels that attributing the deaths to CTE is an oversimplification, but he does think further study in this area is worth pursuing. TO PREVIOUS SLIDE

UNIT B Chapter 12: Nervous System Section 12.1 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 nervous system: a type of organ system consisting of the brain, spinal cord, and associated nerves; allows us to respond to external and internal stimuli TO PREVIOUS SLIDE

UNIT B Chapter 12: Nervous System Section 12.1 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. TO PREVIOUS SLIDE

The nervous system contains two types of cells: 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 neurons: a specialized cell that transmits nerve impulses between parts of the nervous system; contained within nervous tissue neuroglia: cells that support and nourish neurons, maintain homeostasis, form myelin, and may aid in signal transmission TO PREVIOUS SLIDE

Types of Neurons and Neuron Structure 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); Effectors carry out responses to environmental changes sensory neuron: a type of neuron that takes messages to the central nervous system interneuron: a type of neuron that receives input from sensory neurons and other interneurons, and then communicates with motor neurons motor neuron: a type of neuron that takes messages away from the central nervous system to an effector such as an organ, muscle fibre, or gland Figure 12.2 Types of neurons. TO PREVIOUS SLIDE

Neurons vary in appearance, but most of them have three parts: 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 cell body: the part of a neuron that contains the nucleus, as well as other organelles dendrites: part of the neuron; extensions leading toward the cell body that receive signals from other neurons and send them on to the cell body axon: part of a neuron; conducts nerve impulses away from the cell body toward other neurons or effectors Figure 12.2 Types of neurons. TO PREVIOUS SLIDE

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 myelin sheath: a protective covering on axons Schwann cells: a type of neuroglia that forms a myelin sheath around axons in the peripheral nervous system nodes of Ranvier: gaps in the myelin sheath covering the axon 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. TO PREVIOUS SLIDE

Nerve regeneration does not occur to any significant degree in the CNS 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 oligodendrocytes: a type of neuroglia that produces myelin in the central nervous system TO PREVIOUS SLIDE

Nervous tissue in the CNS 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 Contains neurons with short, nonmyelinated axons Found in the surface layer of the brain and the central part of the spinal cord White matter Contains myelinated axons that run together in bundles called tracts Found deep within the grey matter of the brain and surrounds the grey matter in the spinal cord grey matter: a type of nervous tissue making up the central nervous system; contains neurons with short, nonmyelinated axons white matter: a type of nervous tissue making up the central nervous system; contains myelinated axons that run together in bundles called tracts tracts: bundles of myelinated axons in white matter in the central nervous system TO PREVIOUS SLIDE

Check Your Progress UNIT B Chapter 12: Nervous System Section 12.1 Check Your Progress Identify the three classes of neurons, and describe their relationship to each other. Describe the three parts of a neuron. Distinguish the cell types that form the myelin in the PNS versus the CNS. Review the structure of grey matter and white matter, and describe where each is found in the CNS and the PNS. ANSWERS 1. Sensory neuron: Take messages from a sensory receptor to the central nervous system Interneuron: Sum up messages from sensory neurons and other interneurons and communicate with motor neurons Motor neuron: Take messages away from the CNS to the effector organs, muscles, or glands 2. Most neurons contain dendrites (signal-receiving extensions leading to the cell body), a cell body containing a nucleus and other organelles, and an axon, which conducts nerve impulses from the cell body to other neurons or effectors. 3. Myelin is formed by Schwann cells in the PNS and by oligodendroglial cells in the CNS. 4. Grey matter contains nonmyelinated neurons; in the white matter the nerve fibres are myelinated. The brain (CNS) has grey matter on the surface and white matter in the deeper tissue. In the spinal cord (CNS) the grey matter forms a butterfly shape in the centre and the white matter surrounds this. In the PNS the long extensions of neurons (dendrites in the sensory neurons and axons in the motor neurons) are myelinated. TO PREVIOUS SLIDE

UNIT B Chapter 12: Nervous System Section 12.1 TO PREVIOUS SLIDE

UNIT B Chapter 12: Nervous System Section 12.1 TO PREVIOUS SLIDE