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Anatomy Physiology and Disease: An Interactive Journey for Health Professionals Chapter 9 The Nervous System: The Body's Control Center Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Figure 9-1 (refer to page 265) Organization of the nervous system. Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee The Parts and Basic Operations Central Nervous System (CNS) • Controls the total nervous system • “Sensory System” • Acts on sensory input it receives from the Peripheral Nervous System (PNS) • Transmits motor output to the PNS Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee The Parts and Basic Operations Peripheral Nervous System (PNS) • All nerves outside brain and spinal cord • “Motor System” • Transmits sensory input to the Central Nervous System (CNS) • Acts on motor output response from CNS Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee The Parts and Basic Operations Peripheral Nervous System (PNS) (continued) 2 DIVISIONS: 1)SOMATIC (Voluntary) • Controls skeletal muscles & voluntary movement 2)AUTONOMIC (Involuntary) • Controls cardiac muscle and smooth muscles of organs and several glands Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee The Parts and Basic Operations Autonomic Nervous System (Involuntary) 2 DIVISIONS: Parasympathetic “resting and digesting” • Sympathetic “fight-or-flight” deals with normal body • activated during times of functioning and maintenance stress of homeostasis elevates heart rate slows heart rate constricts blood vessels increases intestinal activity raises blood pressure Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Nervous Tissue Nervous Tissue if made up of 2 different types of cells: 1)Neuroglia (or glial cells) Perform specialized support activities for the nervous system ARE NOT capable of measuring the environment, making decisions, or sending orders 2)Neurons (or nerve cells) Carry out all the control functions of the nervous system Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Neuroglia (Glial Cells) CNS has 4 types of Neuroglia: Astrocytes: metabolic and structural support cells that hold neurons and blood vessels together Microglia: attack microbes and remove debris Ependymal cells: do the job of epithelial cells, covering and lining cavities of nervous system Oligodendrocytes: hold nerve cell fibers together & make myelin (lipid insulation) Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Neuroglia (Glial Cells) PNS has 2 types of Neuroglia: Schwann cells: make myelin for the PNS Satellite cells: support cells Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Neuroglia (Glial Cells) Figure 9-2 (refer to page 268) Glial cells and their functions. Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Neurons • All control functions of the nervous system must be carried out by a group of cells called neurons. main function is to transmit messages from one cell to another, throughout the body. Figure 9-3 (refer to page 269) A neuron connecting to a skeletal muscle. Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Neurons • Each part of a neuron has a specific function Cell Body: cell metabolism Dendrites: receive information from the environment or from other cells and carry information to the cell body Axon: generates and sends signals to other cells Axon terminal: where signal leaves cell Synapse: where axon terminal and receiving cell combine Example: Neuromuscular synapse/junction is where the receiving cell is a skeletal muscle cell Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Neurons direction of signal Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Neurons Neurons classifications: 1) Structure: (by how they look) Bipolar Multipolar Unipolar 2) Function: (what they do) Sensory or Afferent Neurons Motor or Efferent Neurons Interneurons or Association Neurons Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Neurons Structural Classification of Neurons: • Bipolar - 1 axon and 1 dendrite • Multipolar – 1 axon and many dendrites • Unipolar – one process that splits into a central and a peripheral projection Multipolar Bipolar Unipolar Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Neurons Functional Classification of Neurons: • Sensory Neurons or Afferent Neurons – input neurons that carry impulses for the skin and sensory organs to the spinal cord and the brain • Usually unipolar • Motor Neurons or Efferent Neurons – output neurons that carry messages from the brain and spinal cord to muscles and glands • Usually multipolar • Interneurons or Association Neurons – carry information between neurons • Usually bipolar Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Neurons (Unipolar) (Bipolar) (Multipolar) Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work • Neurons are called excitable cells – if cell is stimulated it can carry a small electrical charge – each time charged particles flow across a cell membrane, there is tiny charge generated (All three muscle types and many gland cells are also excitable cells) Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work A cell that is not stimulated or excited is called a resting cell; it is said to be polarized –It has a difference in charge across its membrane, being more negative inside than on the outside cell Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work 1) When cell is stimulated, sodium gates in the cell membrane spring open, allowing sodium ions (Na+) to travel across membrane –A cell that is more positive is called depolarized Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work 2) Sodium gates close after a few minutes and potassium gates open; potassium ions (K+) leaves cell, taking its positive charge with it – This is called repolarization 3) If cell becomes more negative than resting due to more potassium (K+) leaving than sodium (Na+) entering it is called hyperpolarization Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work • Action potential (AP) is cell moving through depolarization, repolarization, and hyperpolarization • Cell cannot accept another stimulus until it returns to its resting state, and this time period when it cannot accept another stimulus is called refractory period Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work Action potential – “All-or-none;” either the cell has one or it doesn't – Once it starts, will always finish and will always be same size Local potential – Size of stimulus determines excitement of cell; many sensory cells work via local potentials, which is how CNS determines size of environmental change Are additive – many may result in action potential Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Figure 9-4 (refer to page 271) The action potential. Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work • Neurons can use their ability to generate electricity to send, receive, and interpret signals If you hit your thumb with a hammer, dendrites in thumb are stimulated by blow and sodium gates open, sodium flows into dendrites and they become depolarized; number of cells affected depend on how hard you hit your thumb Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work • Dendrites carry depolarization to sensory neuron cell body, which takes information and generates action potential if stimulus is large enough • Speed of impulse conduction is determined by: 1. amount of myelin 2. diameter of axon Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work • Myelin is lipid insulation or sheath formed by oligodendrocytes in CNS and Schwann cells in PNS • Myelinated nerves are white; unmyelinated nerves are gray Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work Myelin is essential for speedy flow of Action Potentials (AP) down axons • in unmyelinated axon, AP can only flow down axon by depolarizing each and every millimeter of axon resulting in a relatively slow process • in myelinated axons there are Nodes of Ranvier located periodically, and only nodes must depolarize, allowing impulse to travel quickly as it skips from node to node Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work Myelinated axons results in quick response Figure 9-5 (refer to page 273) Impulse conduction via myelinated axon. Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work Unmyelinated vs. Myelinated Neurons Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Neurons Work Speed of Action Potential flow increases with: 1) Myelination 2) Diameter of axon Small-diameter unmyelinated axons have speeds as low as 0.5 meters/second Large-diameter myelinated axons have speeds as fast as 100 meters/second (200 times faster!) Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Pathology Connection: Action Potential Disorder Epilepsy Irregular electrical signals are suddenly discharged from neurons, causing the body to become overloaded with impulses Body reacts by going into a seizure Common Types of Seizures: (list is not inclusive) Tonic-Clonic (formerly known as grand mal) Severe convulsions Absence (formerly known as petit mal) Non-responsive staring Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Pathology Connection: Action Potential Disorder Epilepsy Some Causes: Most cases are idiopathic Earlier brain damage due to trauma Stroke Exposure to toxins Lack of oxygen during childbirth Treatments: (very patient specific) Anti-seizure medications Surgical treatments Various diets Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Synapses Work Chemical Synapse: -- the use of neurotransmitters to carry information from one cell to another The Process: • When the AP arrives at axon terminal, terminal depolarizes and calcium gates open allowing Calcium ions (Ca+2) to flow into cell Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Synapses Work • When Ca+2 flows in, it triggers tiny sacs in axon terminal called vesicles to release neurotransmitters • Neurotransmitters bind to the cell receiving signal, opening or closing gates: – some excite receiving cell – some calm it down • Last step in transfer of information is to cleanup by removing neurotransmitter from synapse with enzymes to prevent it from binding to the receiving cell for an extended period of time. Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee The Chemical Synapse: Figure 9-6 (refer to page 276) Step 1: The impulse travels down the axon. Step 2: Vesicles are stimulated to release neurotransmitter (exocytosis). Step 3: The neurotransmitter travels across the synapse and binds with the receptor site of post synaptic cell. Step 4: The impulse continues down the dendrite. Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Synapses Work • Our understanding of chemical synapses has led to several breakthroughs for treating mental illness • Many medications on the market today are designed to modify synapses by preventing the “cleanup” of the neurotransmitters and therefore extending the response. Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Synapses Work • Selective Serotonin Reuptake Inhibitors (SSRI) are good examples: – these medications prevent the cleanup of neurotransmitter serotonin from synapses, thus increasing effects of serotonin on receiving cell Serotonin maintains mood balance. Deficit of serotonin causes depression. • Many antidepressants and antianxiety drugs are SSRIs Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Refer to page 276 Table 9-1 Selected Common Neurotransmitters Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee How Synapses Work Electrical Synapses • These synapses transfer information freely because they have special connections called gap junctions • DO NOT use neurotransmitters • They are found in intercalated discs between cardiac muscle fibers • Helps to cause muscle fibers to “fire” causing heart contraction Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Pathology Connection: Myelin Disorders Multiple Sclerosis (MS): disorder where myelin in Central Nervous System (brain, spinal cord, & optic nerve) is destroyed – In areas without myelin, impulse conduction is slow or impossible – These areas of damaged myelin often have plaques or scarred areas – Cause is probably autoimmune attack – Symptoms vary depending on where patient's myelin has been damaged; possible symptoms include disturbances in vision, balance, speech, and movement Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Pathology Connection: Myelin Disorders • Types of MS – Relapsing-Remitting: characterized by symptomatic flare-ups (called relapses), followed by periods of time where patient has no symptoms (called remissions) – Chronic Progressive: has no remission periods; patients become steadily more disabled Most patients initially diagnosed with relapsingremitting, but at least 50% will progress to chronic progressive form. Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Pathology Connection: Myelin Disorders • Epidemiology of MS: more common in women diagnosed most often in people under age 50 • Diagnosis of MS: based upon history of symptoms flareups, and presence of plaques on MRI difficult to diagnosis Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Pathology Connection: Myelin Disorders Treatment of MS: no cure in acute flare, symptoms may be treated with steroid medication, plasma exchange, or intravenous Immunoglobulin G; immunosuppressant drugs can also be used to decrease frequency of relapses, prevent or slow conversion from relapsingremitting to chronic progressive Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Pathology Connection: Myelin Disorders Guillain-Barré Syndrome (ghee-YAN bah-RAY") – Disorder caused by autoimmune attack of myelin and/or axons in peripheral nervous system – Symptoms: weakness and ascending paralysis of a limb, face and diaphragm – Cause is unknown, although many patients develop Guillain-Barré syndrome after viral infection Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Pathology Connection: Myelin Disorders Guillain-Barré Syndrome Course of disease has three phases 1) Acute phase: initial onset of disease, in which patient becomes steadily worse 2) Plateau phase: period of days to weeks, in which patient's condition is stable Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Pathology Connection: Myelin Disorders • Guillain-Barré syndrome Course of disease has three phases 3) Recovery phase: period of time during which patients recover function – Some recover full function, over a period of up to two years – Significant portion of patients with severe cases have measurable disability two years after recovery Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Pathology Connection: Myelin Disorders • Guillain-Barré Syndrome – Diagnosis: based mostly on history of rapid-onset ascending paralysis after viral infection – Tests that may also be helpful include EMG and cerebrospinal fluid analysis showing high protein but no white blood cells Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee Pathology Connection: Myelin Disorders • Guillain-Barré Syndrome Treatment: supportive care until symptoms improve/resolve care may include: ventilation support prevention of blood clots and bed sores pain medication rehabilitation after their PNS recovers Anatomy, Physiology, & Disease: An Interactive Journey for Health Professionals, 2e Bruce J. Colbert • Jeff J. Ankney • Karen Lee