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6 The Nervous System Lesson 6.1: Overview of the Nervous System Lesson 6.2: Transmission of Nerve Impulses Lesson 6.3: Functional Anatomy of the Central Nervous System Lesson 6.4: Functional Anatomy of the Peripheral Nervous System Lesson 6.5: Injuries and Disorders of the Nervous System Chapter 6: The Nervous System Lesson 6.1 Overview of the Nervous System • The function of the nervous system is to coordinate all body systems! This is accomplished by the transmission of signals (electrochemical) from body parts to the brain and back to the body parts.. • The nervous system is composed of: • Neurons • Neuroglial cells (also known as neuroglia, glia, and glial cells) • Blood vessels • Connective tissue © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Two Major Divisions © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Organization of the Nervous System • two major divisions – central nervous system (CNS) – consists of the brain and spinal cord – peripheral nervous system (PNS) – consists of cranial nerves and spinal nerves • sensory receptors • afferent (sensory) nerves – transmit nerve impulses from the sensory receptors in the skin, muscles, and joints to the CNS • efferent (motor) nerves – transmit nerve impulses from the CNS to the muscles and glands © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. The Efferent Nerves • somatic nervous system – voluntary – carries information to skeletal muscle • autonomic nervous system – involuntary – carries information to smooth muscle, cardiac muscle, and glands – sympathetic – parasympathetic © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. brain spinal cord cranial nerves Central Nervous System (brain and spinal cord) Peripheral Nervous System (cranial and spinal nerves) Sensory division spinal nerves Sensory receptors Motor division Somatic Nervous System Autonomic Nervous System © Goodheart-Willcox Co., Inc. Skeletal muscle Smooth muscle Cardiac muscle Glands Permission granted to reproduce for educational use only. Nervous Tissues • neuroglia – also known as glial cells – support the neurons – protect the neurons • neurons – transmit nerve impulses © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Neuroglia • central nervous system – – – – astrocytes microglia ependymal oligodendrocytes © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Neuroglia - CNS • Astrocytes – most numerous - positioned between neurons and capillaries – protect neurons from harmful substances in the blood • Microglia – absorb and dispose of dead cells and bacteria • Ependymal – form a protective covering around the spinal cord and central cavities within the brain • Oligodendrocytes – produce myelin (fatty insulating material that surrounds nerve fibers) © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Neuroglia - PNS • peripheral nervous system – Schwann cells – form fatty myelin sheaths around nerve fibers • insulation from myelin sheath speeds up neurotransmission • a bundle of myelinated nerve fibers (axons) = “white matter” • a bundle of unmyelinated nerve fibers (cell bodies/dendrites) = “gray matter” • nodes of Ranvier – uninsulated gaps between sections of myelin where the axon is exposed – satellite cells – provide cushioning © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Neuroglia - PNS © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Parts of a Neuron • cell body (soma) - central portion of neuron - contains usual organelles • neuron processes (two types) - extensions from cell body • Dendrites – many per neuron; short & branched; receptive portion of neuron; carries impulse toward cell body • Axon - one per neuron; long, thin process; carries impulses away from cell body; terminations of axon branch = axon terminals © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Parts of a Neuron © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Neuron Types by Function • sensory neurons – send impulses toward CNS • motor neurons – send impulses away from CNS • interneurons – transport impulses between neurons © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Structural Types of Neurons • Due to structural differences, neurons can be classified into three (3) major groups: • Bipolar neurons – two extensions; one fused dendrite leads toward cell body and one axon leads away from cell body ex. Specialized parts of eyes, nose, & ears (sensory) • Unipolar neurons – one process from cell body; forms central & peripheral process; only distal ends are dendrites ex. Some sensory neurons in the PNS • Multipolar neurons – many extensions; many dendrites lead toward cell body and one axon leads away from cell body ex. All motor neurons and interneurons © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Neuron Structures • bipolar • unipolar © Goodheart-Willcox Co., Inc. • multipolar Permission granted to reproduce for educational use only. Review and Assessment Match these words with 1–4 below: sympathetic nervous system, myelin, synapse, axon. 1. high alert 2. transmits impulses away from cell body 3. fatty insulating material 4. gap between neurons © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Chapter 6: The Nervous System Lesson 6.2 Transmission of Nerve Impulses Transmission of Nerve Impulses Transmission of nerve impulses is an electrochemical process Creation of an action potential is electrical Neurotransmitters released at the synapse is chemical © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Transmission of Nerve Impulse When a neuron is inactive or at rest: Potassium ions are inside the cell and sodium ions are outside the cell membrane Inside of cell is more negatively charged than outside of cell Difference in electrical charge inside and outside of cell = cell membrane is polarized © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Transmission of Nerve Impulse Activation of a neuron: Stimulus causes the sodium channels to open Sodium ions enter the neuron causing the inside of the membrane to become more positive = cell membrane is depolarized Depolarization occurs only at the nodes of Ranvier Opening of sodium channels is like a domino effect creating more sodium channels to open along the membrane = action potential (electrical impulse) All-or-none concept – electrical charge of the action potential is always the same size and travels the full length of the axon © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Action Potential Direction of nerve impulse © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Transmission of Nerve Impulse Discharge of the action potential Membrane becomes permeable to potassium ions Potassium ions diffuse out of the cell Membrane is restored to its polarized state with a more negative charge inside the cell = repolarization Refractory period = time between the completion of the action potential and repolarization © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Transmission of Nerve Impulse © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Impulse Transmission Factors affecting speed of impulse transmission: – Faster in myelinated axons vs nonmyelinated axons where the myelin sheath acts as an insulator • Saltatory conduction – action potentials jump over myelinated regions of the axon – Faster in nonmyelinated axons with larger diameters vs. nonmyelinated axons with smaller diameters – Faster in warmer temps because of an increase in ions diffusion rates © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Impulse Transmission Transmission at synapses When an action potential reaches an axon terminal, calcium gates open and calcium ions flow into the terminal Influx of calcium causes the neurotransmitter vesicles to release the neurotransmitter into the synapse Neurotransmitters connect to a receptor site on a joining neuron or muscle fiber © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. • Introduction to Anatomy and Physiology Student Site Video.html © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Neurotransmitters 2 types of neurotransmitters: – Excitatory neurotransmitter – acetylcholine – activates muscle fibers – Inhibitory neurotransmitter – endorphins – inhibit nerve cells from discharging more pain signals © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Reflexes - simple, rapid, involuntary response to stimuli that follows a reflex arc involving both the PNS and CNS 2 types Somatic reflexes – involve the stimulation of skeletal muscles – when touching a hot surface, nerve impulses travel from a sensory nerve to an interneuron in the spinal cord to a motor neuron, bypassing the brain Reflex video.html Autonomic reflexes – send involuntary stimuli to the cardiac muscles of the heart and the smooth muscles of the organs – digestion, elimination, sweating © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Review and Assessment Fill in the blanks with: reflexes, saltatory conduction, neurotransmitter, or action potential. 1. A(n) _______________ is an all or none response. 2. _______________ occurs only in myelinated axons. 3. _______________ are rapid, involuntary responses. 4. The axon terminal has tiny vesicles filled with _______________. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Chapter 6: The Nervous System Lesson 6.3 Functional Anatomy of the Central Nervous System The Brain 4 Regions Cerebrum Diencephalon Brain stem Cerebellum © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Cerebrum • cerebral cortex Outer surface of cerebrum Contains nonmyelinated gray matter Gyrus – curved, raised area Sulcus – grooves between gyri Fissure – deep grooves © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Cerebrum © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Cerebrum • lobes – Frontal – memory, intelligence, behavior, emotions, motor function, smell – Parietal – pain, touch, hot/cold, speech – Occipital – vision, speech – Temporal – hearing, smell, memory, speech http://www.gwlearning.com/healthsciences/9781619604124/student/ch06_03/ident ify01/story.html • primary motor cortex – anterior side of central sulcus • primary somatic sensory cortex – posterior side of central sulcus • central sulcus – separates frontal lobes from parietal lobes © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Motor Cortex Somatosensory cortex © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Diencephalon • Thalamus – relays sensory impulses to the sensory cortex • Hypothalamus – autonomic center regulating metabolism, heart rate, blood pressure, hunger, thirst, energy level, and body temp • Epithalamus – regulates hormones secreted by the pineal gland © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Diencephalon © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Brain Stem • Midbrain – relays sensory and motor impulses • Pons – assists with regulation of breathing • Medulla oblongata – regulates heart rate, blood pressure, and breathing, and controls the reflexes of coughing, sneezing, and vomiting © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Brain Stem © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Cerebellum • Below the occipital lobe • Coordinates body movement and balance © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Blood Brain Barrier • Substances can pass less freely through capillaries in the brain compared to capillaries in other parts of the body • Protects the brain against surges in hormones, ions, and some nutrients © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Meninges • Membranes covering brain and spinal cord – dura mater (“hard mother”) – tough, outer doublelayered membrane – arachnoid mater – middle layer - web-like tissue subarachnoid space – contains cerebrospinal fluid which cushions the brain and spinal cord – pia mater (“gentle mother”) – innermost membrane of brain and spinal cord © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Meninges © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Spinal Cord • Major pathway for relaying sensory impulses to the brain and motor impulses from the brain • Exterior is myelinated white matter • Butterfly-shaped gray matter, composed of neuron cell bodies and interneurons, are centrally located • Dorsal, ventral, and lateral projections of gray matter are called horns © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Spinal Cord © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Review and Assessment True or False? 1. The gyri divide the brain into 4 regions. 2. The hypothalamus regulates blood pressure. 3. The meninges has 3 layers. 4. The cerebellum coordinates balance. 5. The pons is also called the interbrain. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Chapter 6: The Nervous System Lesson 6.4 Functional Anatomy of the Peripheral Nervous System Peripheral Nervous System - Nerve Structure • endoneurium – covers axons • perineurium – bundles fascicles • epineurium – encases fascicles and blood vessels © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Cranial Nerves • • • • • • 12 pairs Olfactory nerve – smell Optic nerve – sight Oculomotor – eye movement Vestibulocochlear – hearing, balance Glossopharyngeal – throat muscle movements, taste • Vagus – autonomic control of heart, lungs, digestion, taste, communication between brain and organs © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Cranial Nerves © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Spinal Nerves and Nerve Plexuses • 31 pairs • dorsal root (posterior) and ventral root (anterior) unite to form the left and right spinal nerves at each spinal level • dorsal ramus and ventral ramus split from the spinal nerves – carry nerve impulses to the muscle and skin of the trunk • Plexuses – interconnections of nerves formed from the ventral rami in the cervical and lumbar regions of the spinal cord – 4 plexuses – cervical, brachial, lumbar, and sacral © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Autonomic Nervous System • Involuntary nervous system that activates the heart, smooth muscles, and glands • Ganglion – enlarged junction of nerve tissue composed mainly of nerve cell bodies • Preganglionic neurons – originate in the lateral horn of the spinal cord and terminate in a ganglion • Postganglionic neurons – originate in a ganglion and terminate in a cardiac muscle, smooth muscle, or gland © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Autonomic Nervous System © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Autonomic Nervous System Sympathetic nervous system Fight-or-flight response Sympathetic nerves stimulate the adrenal gland to release epinephrine (adrenaline) – increases heart and breathing rates and sweating Parasympathetic nervous system Controls automatic day-in and day-out functions of the circulatory, respiratory, and digestive systems © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Review and Assessment Match these words with 1–4 below: efferent, ganglion, optic, perineurium. 1. wraps fascicles 2. motor 3. a cranial nerve 4. enlarged junction © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Chapter 6: The Nervous System Lesson 6.5 Injuries and Disorders of the Nervous System Injuries to the Brain and Spinal Cord • traumatic brain injury • cerebral palsy • spinal cord injury © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Traumatic Brain Injury • violent impact to head – mild – moderate – severe © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Spinal Cord Injuries • • • • C1–C3: usually fatal C1–C4: quadriplegia C5–C7: paralysis of lower extremities T1–L5: paraplegia Corepics/Shutterstock.com © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Common Diseases and Disorders of the CNS • meningitis – inflammation of the meninges around the brain or spinal cord – can be viral or bacterial • multiple sclerosis – autoimmune disease in which the body’s immune system destroys the myelin sheaths of nerve cell axons • epilepsy – abnormal electrical activity in the brain • Parkinson’s disease – slow but progressive destruction of the brain’s cells responsible for the production of the neurotransmitter dopamine which plays a role in motor functions • dementia and Alzheimer’s disease – loss of function in 2 or more areas of cognition including memory, thinking, judgment, behavior, perception, and language © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Review and Assessment Match these words with 1–4 below: quadriplegia, multiple sclerosis, dementia, cerebral palsy. 1. inflammation destroys myelin sheath 2. loss of memory and thinking 3. loss of function below the neck 4. may begin before birth © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.