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Ns3 Review Of The Organization Of The Nervous System

Ns3 Review Of The Organization Of The Nervous System




Lecture 3 of 63 in the Neuroscience Module

"Review Of The Organization Of The Nervous System" [Physiology]



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    Ns3 Review Of The Organization Of The Nervous System Ns3 Review Of The Organization Of The Nervous System Presentation Transcript

    • NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM A REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM I. OVERVIEW: A. Function: The nervous system consists of a group of organs and tissues that functions to control the body and respond to internal and external environmental changes by 1. gathering sensory information (SENSORY INPUT) 2. integrating the sensory information (INTERGRATION) 3. activating the appropriate glands or muscles (MOTOR OUTPUT) B. Structure: The nervous system is divided into two main components: 1. Central Nervous System (CNS) is composed of: a. brain b. spinal cord 2. Peripheral Nervous System (PNS) a. components: i. sensory receptors ii. nerves: sensory nerves & motor nerves iii. ganglia: dorsal root ganglia (sensory), parasympathetic ganglia (motor, autonomic), sympathetic ganglia (motor, autonomic) iv. motor endings b. divisions: i. sensory ii. motor • subdivided into - somatic (voluntary control) - autonomic (involuntary control) which is further subdivided into: * parasympathetic * sympathetic * enteric 1
    • NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM II. COMPONENTS OF NERVOUS TISSUE A. CLASSIFICATION OF GLIAL CELL TYPES Table 1: Classification and function of glial cells in the nervous system CLASS SUBDIVISION CELL TYPES FUNCTION Astrocyte i. nourishment (Macroglia) ii. guidance iii. synapse formation iv. regulation of extracellular environment (neurotransmitters, ions) Ependymal cell circulation of CSF CNS (Macroglia) Glia Oligodendrocyte myelination of neuronal axons (Macroglia) Microglia phagocytes Schwann cell myelination of neuronal axons PNS Satellite cell regulates extracellular environment B. NEURONAL SHAPE AND STRUCTURAL ELEMENTS 1. CELL BODY (Nucleus + Soma (everything but the nucleus)) a. SOMA: i. STRUCTURE: all organelles found in cells plus neurofilaments; plasma membrane (high levels of chemically gated ion channels) ii. FUNCTION: biosynthetic center; signal reception b. Description of clusters of cell bodies (gray matter) Clusters of cell bodies in the CNS = nuclei Clusters of cell bodies in the PNS = ganglia 2. PROCESSES: projections or extensions that function to receive and transmit signals (dendrites) or transmit and secrete neurotransmitters (axons) a. Description of clusters of axons (white matter) Clusters of axons in the CNS = tracts Clusters of axons in the PNS = nerves b. Classification and characteristics of neuron processes (Table 2) 2
    • NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM II. COMPONENTS OF NERVOUS TISSUE B. NEURONAL SHAPE AND STRUCTURAL ELEMENTS 2. PROCESSES Table 2: Classification and characterization of neuron processes TYPES CHARACTERISTICS ORGANELLES FUNCTION same as soma i. reception of neuronal signals Extensions: short Branching: diffuse branching plasma membranes ii. transmission of signals to cell contain chemically-gated body using short distance electrical Myelination: none ion channels signals (graded potentials) Dendrite DENDRITIC SPINES = terminal endings of dendrites conduction of electrical signals Extensions: variable in length Branching: variable Myelination: variable NERVE FIBERS = very long axons AXON HILLOCK: origin of axon from cell body; trigger generates long distance electrical signals (action potentials) zone for action potential AXON LENGTH: region same as soma except no conducts electrical signals away RER, Golgi apparatus from cell body after axon trigger zone to Axon terminal plasma membranes contain voltage-gated Na channels and voltage-gated potassium channels AXON TERMINAL: end of same as soma except no secretes neurotransmitters RER, Golgi apparatus and axons higher concentrations of BOUTONS = profusely vesicles and mitochondria branched terminals plasma membranes contain voltage-gated calcium channels 3
    • NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM II. COMPONENTS OF NERVOUS TISSUE B. NEURONAL SHAPE AND STRUCTURAL ELEMENTS 3. CELL CLASSIFICATION AND FUNCTION OF NEURONAL CELLS Table 3: Classification and function of neuronal cells in the nervous system CLASS SUBDIVISION CELL TYPES FUNCTION multipolar (multiple efferent, motor neurons (CNS  muscle); interneurons dendritic extensions; single axon) based on structure bipolar (fused specialized sensory neurons in retina or ear dendrite & axon) unipolar (single afferent, sensory neurons (receptor  CNS) axon) Neurons motor neurons efferent, multipolar neurons (CNS  muscle) (projection neuron) based on sensory neurons afferent, sensory unipolar neurons (receptor  CNS) function (projection neuron) interneurons association, multipolar neurons between neurons in CNS 4. MYELIN SHEATH a. STRUCTURE: a covering surrounding an axon that is formed by Schwann cells (PNS) or oligodendrocytes (CNS) i. in the PNS, the myelin sheath is segmented • each segment is composed of one Schwann cell that wraps around the axon • Nodes of Ranvier = uncovered axon membrane • neurilemma: outer surface of myelin sheath; contains nucleus of Schwann cell ii. in the CNS, the myelin sheath is continuous sheath • one oligodendrocyte covers multiple axons for greater lengths • Nodes of Ranvier are present but fewer in numbers • no neurilemma b. FUNCTION: provides insulation to promote faster conduction of electrical signals c. DISEASE: Multiple sclerosis i. autoimmune disease – inflammation and destruction of myelin sheaths ii. useful links http://www.bbc.co.uk/health/conditions/ms1.shtml http://www.bbc.co.uk/devon/community_life/features/living_with_ms.shtml http://www.allheadlinenews.com/articles/7004851125 http://news.bbc.co.uk/2/hi/health/4724414.stm http://www.findarticles.com/p/articles/mi_m0EIN/is_2005_Sept_28/ai_n15635911 http://www.fredericknewspost.com/sections/features/display.htm?storyid=51932 4
    • NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM III. LIFE AND DEATH IN THE NERVOUS SYSTEM A. Neural Stem Cells & Differentiation 1. Neural stem cells a. are present during prenatal development http://www.mpg.de/english/researchResults/researchPublications/researchReports/EEB/200414_01 3.shtml b. have been found in adult brains in two brain regions i. subventricular zone (SVZ) ii. hippocampus 2. Neural stem cells are pluripotent and can differentiate into macroglia and neurons. 3. Neural stem cells are under investigation as a possible therapy for neurodegenerative diseases such as Parkinson’s or Alzheimer’s or brain injury. http://www.sciencedaily.com/releases/2002/04/020415073115.htm http://www.sciencedaily.com/releases/2005/09/050920074831.htm http://www.ninds.nih.gov/news_and_events/news_articles/news_article_stroke_Notch.htm http://www.helpforheadaches.com/articles/nihsheets/life-neuron.htm B. Neuronal migration and axon guidance 1. Neurons migrate to site of final destination. 2. Glial cells and other neurons guide migrating neurons. 3. Neurons make connections with other neurons. http://apu.sfn.org/index.cfm?pagename=brainBriefings_axonGuidance C. Neuronal cell death 1. Neurons that make connections with other neurons integrate and mature. 2. Neurons that do not make connections die via apoptosis. IV. NEURON COMMUNICATION A. Synapses 1. Definition: junction between two neurons or a neuron and an effector cell 2. Structures: pre-synaptic membrane, post-synaptic membrane, synaptic cleft B. Types of communication 1. Electrical 2. Chemical (neurotransmitters) 5
    • NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM V. ORGANIZATION OF THE NERVOUS SYSTEM into regions that have discrete functions. Table 4: Overview of the organization of the nervous system SUB SUB-SUB- REGION DIVISION STRUCTURE FUNCTION DIVISION DIVISION brain consciousness, perception, thought, language, emotion, voluntary movement, maintaining homeostasis, Central Nervous System (CNS) memory, sleep spinal cord 1. connects brain with PNS 2. controls reflexes cranial nerves 1. sensation spinal nerves 2. coordination b/n CNS Peripheral Nervous System (PNS) sensory receptors and the body ganglia motor endings 3. conduction 1. somatic sensory nerve conduction of impulses from fibers receptors to CNS Sensory (Afferent) 2. visceral sensory nerve fibers motor nerve fibers conduction of nerve Motor (Efferent) impulses from CNS to: muscles & glands voluntary (somatic) motor conducts impulses from nerve fibers CNS to skeletal muscles Somatic Nervous System voluntary movement, coordination, reflexes involuntary (visceral) conducts impulses from motor nerve fibers CNS to: Autonomic Nervous System cardiac muscle autonomic ganglia smooth muscle glands Para- involuntary (visceral) maintenance – sympathetic motor nerve fibers “rest & digest” Sympathetic involuntary (visceral) emergency response – motor nerve fibers “fight or flight” involuntary (visceral) gut brain - regulation of digestion sensory and motor nerves; neurons connected to CNS via vagus nerve Enteric glial cells same developmental origin information processing as CNS circuits http://whyfiles.org/026fear/p all neurotransmitters hysio1.html 6
    • NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM Table 5: Structure and function of components of the CNS COMPONENT STRUCTURE FUNCTION Brain Gray matter (clusters of neuronal cell bodies and dendrites) - controls voluntary movement (cerebrum) White matter (clusters of myelinated fibers known as tracts) - interpretation and integration of sensation (cerebrum) Central cavity – filled with CSF and lined with ependymal - consciousness (cerebrum) cells - cognition (cerebrum) - maintains homeostasis Meninges – protective membranes between skull and brain (hypothalamus) - emotions - sleep - memory Spinal Cord Nervous tissue that runs from the brain to the first and third i. connects brain with PNS lumbar vertebrae ii. controls reflexes iii. Spinal cord injury Gray matter - H-shape gray area surrounding the central http://www.wingsforlife.com/?LN canal consisting of cell bodies of the motor neurons (ventral G=en&id=163&zid=78 horn), sensory neurons (dorsal horn) and interneurons (dor- sal horn). White matter – white area surrounding the gray matter which is composed of bundles of myelinated axons that ei- ther are ascending or descending nerve fiber tracts. Dorsal or ventral roots - bundles of afferent sensory neu- ron axons (dorsal root) or bundles of efferent motor fibers (ventral roots). Spinal nerve – the fusion of dorsal and ventral roots. Dorsal root ganglion -bundles of sensory neuron cell bodies adjacent to the spinal cord 7
    • NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM Table 6: Structure and function of components of the PNS COMPONENT STRUCTURE FUNCTION specialized nerve endings (dendrites) sense pain, touch, pressure, temperature skin, skeletal mus- cle, tendons and visceral organs Sensory receptors sense organs (sensory neurons and associated vision, hearing, taste, smell, cells) equilibrium bundle of nerve axons Nerves i. mostly mixed sensory and motor fibers; but some are purely sensory and purely motor Cranial ii. some also serve the parasympathetic division conduction of electrical signals of the autonomic nervous system to and from CNS/PNS i. mixed sensory and motor fibers; each nerve is a fusion of the dorsal and ventral root Spinal ii. 31 pairs of spinal nerves emerge form the spinal cord bundles of sensory neuron cell bodies transmission of signals Ganglia bundles of sensory neuron cell bodies adjacent transmission of sensory infor- Dorsal root to the spinal cord mation to the CNS bundles of motor neuron cell bodies of nerve maintains basal heart and respi- Parasympa- fibers of the parasympathetic division of the au- ratory rates; conserves body en- tonomic nervous system ergy thetic found adjacent to organ bundles of motor neuron cell bodies of nerve response to emergency situa- fibers of the sympathetic division of the auto- tions: responsible for dilated nomic nervous system pupils, ↑ heart and respiratory rates, ↑ blood pressure, bron- Sympathetic found adjacent to the spinal cord chio-dilation, ↑ blood glucose levels temperature control control of muscle contraction types of synapses between motor neuron and Motor endings target cell forms neuromuscular junction = synapse be- Skeletal tween motor neuron and motor endplate of muscle control muscle contraction and skeletal muscle fiber innervations relaxation forms varicosities = synapse between motor Visceral neuron and visceral muscle (heart, gut) or muscle and control muscle contraction or glands gland gland secretion innervations 8