Introduction to the Nervous System PDF

Introduction to the Nervous System Dr. Sean McWatt, PhD [email protected] Nervous System Central nervous system CNS Nervous System Brain Spinal Cord Nerves...

Introduction to the Nervous System Dr. Sean McWatt, PhD [email protected] Nervous System Central nervous system CNS Nervous System Brain Spinal Cord Nerves Peripheral nervous system Functions PNS Controls and integrates bodily activity Reacts to constant changes in external and internal environments The central nervous system is the main processing center and coordinator of all our body’s functions The central nervous system includes the brain and spinal cord, whereas the peripheral nervous system includes all of the nerves that extend out into the periphery Anterior view Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Cells of the Nervous System Neurons Basic unit of the nervous system Transmit electrical impulses to one another to communicate information Neuroglia Multipolar motor neuron Non-neuronal, non-excitable cells 5x as abundant as neurons Support for neurons Structural, nourishment, insulation, pathogen clearance There are several other types of neurons and neuroglia, but these will be our focus Myelin sheath Insulates axon to increase speed of signal Pseudounipolar sensory neuron Oligodendrocyte Schwann cell CNS PNS Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Multipolar Motor Neuron Cell body Nucleus Axon Transmits action potential Nodes of Ranvier Active sites Axon terminals Where synapse occurs with next neuron(s) in the chain or a target organ Myelin sheath Trigger zone Dendrites Axon hillock; where signals Collecting information summate to reach threshold and from other neurons/cells cause an action potential Motor neurons send signals from the CNS to target organs Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Pseudounipolar Sensory Neuron Trigger zone Axon hillock; where Cell body signals summate to reach Nucleus threshold and cause an action potential Myelin sheath Ganglion Nodes of Ranvier Collection of cell Active sites bodies from multiple Central Peripheral neurons within a nerve process process Part of axon proximal Part of axon distal to to the cell body the cell body Sensory neurons bring signals Dendrites from the periphery to the CNS Collecting information Axon terminals from other neurons/cells Where synapse occurs with next neuron(s) in the chain Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Neuroglia: Myelination Central Nervous System Peripheral Nervous System Multiple sclerosis Axons of CNS neurons Guillain-Barré Syndrome Motor Degradation of neuron Degradation of Schwann cells oligodendrocytes Episodes Weakness and paralysis Symptoms vary Myelin Myelin is sheaths white in appearance! Myelinated Unmyelinated axon axons Myelin sheath Schwann cell Forms one myelin sheath Oligodendrocyte around one section of an axon Forms several myelin sheaths around multiple axons Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone  White vs. Gray Matter Cell bodies Cell bodies Cortex and nuclei don’t have myelin Myelinated axons Appear white Consider gray matter as the buildings in a city that process and store information, whereas white matter Axons can represents the roads, transit lines, and have myelin bike lanes that connect the buildings to transmit information Rohen, Anatomy: A Photographic Atlas, 8th Ed., Copyright © 2016 by Wolters Kluwer Gilroy, Anatomy: An Essential Textbook, Copyright © 2013 by Thieme Myelination and Action Potentials Unmyelinated Neuron 0.5-2 m/s Unmyelinated neurons need to depolarize at every point along their axon, which Change in leads to a relatively slow polarization signal speed Threshold Myelinated neurons only need Myelinated Neuron to depolarize at the nodes of 3-120 m/s Nodes of Ranvier Active sites Ranvier, meaning the signal can jump from node to node, drastically increasing the speed of the signal Change in polarization Myelin sheaths Newton’s cradle Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Neuronal Synapse 1. Nerve impulse arrives at axon terminal end bulb of presynaptic neuron 2. Impulse causes calcium channels to open and calcium ions rush in 3. Neurotransmitter is released and crosses the synaptic cleft to trigger opening of sodium channels on postsynaptic neuron 4. Sodium ions flow into dendrite of postsynaptic neuron to initiate new nerve impulse Synapse Postsynaptic Presynaptic neuron neuron Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Nervous System Structure  Nervous System Central nervous system Brain and spinal cord Autonomic nervous system (ANS) Structural Peripheral innervation to Functional divisions visceral organs and glands divisions Peripheral nervous system Cranial nerves, spinal nerves, ganglia, enteric plexuses, and sensory receptors The nervous system is divided structurally into the central and peripheral nervous systems and Somatic nervous system functionally into the Peripheral innervation to all other autonomic and somatic tissues (e.g., muscles, skin, etc.) nervous systems Anterior view Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Autonomic Nervous System Brain …or sacral spine The autonomic nervous system (ANS) is a component of the peripheral nervous system (PNS) in charge of involuntary Parasympathetic control of viscera (organs and glands) nervous system (PSNS) “Feed and breed” or “rest and digest” system Parasympathetic signals come from cranial nerves and sacral spinal levels (craniosacral Sympathetic innervation), while sympathetic signals all chain/trunk come from spinal segments T1-L2 via the sympathetic chain/trunk Sympathetic nervous system (SNS) “Fight or flight” system Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins  Somatic Nervous System Spinal nerve The somatic nervous system is a component of the peripheral nervous system (PNS) in charge of voluntary motor control and peripheral sensation These motor and sensory components are spinal nerves associated with the level that they originate from, yielding patterned myotomes (motor) and dermatomes (sensory) Skin Muscle Dermatome Myotome Dermatomes and myotomes can be mapped to determine whether an injury is central or peripheral, and diagnose the level of injury (i.e., spinal level, brain region, nerve branch, etc.) American Spinal Injury Association Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Functional Overview Central nervous system Peripheral nervous system Sensory Motor Autonomic Somatic Somatic Autonomic Viscera and enteroceptors Body Skeletal muscle Organs and glands Voluntary control Involuntary control Our CNS receives sensory information from our external and internal environments via the PNS, which processes the information Parasympathetic Sympathetic Feed and breed Fight, flight, or fright and mounts a response via the motor system Rest and digest Adapted from Dr. Danielle Brewer-Deluce