CBIO 2200 1nd Edition Lecture 18 Outline of Last Lecture I ATP Sources II Cardiac Muscle III Smooth Muscle IV Neuromuscular Toxins and Paralysis V Tension Production by Muscle Contraction VI Behavior of Whole Muscles VII Contraction Strength of Twitches VIII Stimulus IX Isometric vs Isotonic Contraction Outline of Current Lecture I Overview of the Nervous System II Subdivisions of the Nervous System III Nervous Tissue IV Classes of Neurons V Types of CNS Neuroglia VI Types of PNS Neuroglia VII Myelin VIII Regeneration of PNS Nerve Fibers These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute IX Electrophysiology of Neurons Current Lecture CHAPTER 12 Nervous Tissue I II III Overview of the Nervous System a Nervous system carries out its task in three basic steps i Receives information through sensory receptors and coding it into a message ii Brain spinal cord processes that information iii Sends out information to the rest of the body Subdivisions of the Nervous System a Central i Brain ii Spinal cord b Peripheral Nerves and Ganglia i Sensory division afferent division receives info from receptors 1 Visceral sensory division info about internal environment 2 Somatic sensory division info about external environment ii Motor division efferent division send out commands to body 1 Visceral motor division info being sent to internal environment organs autonomic nervous system visceral reflexes a Sympathetic division arousing the body putting into action i Accelerated heart beat respiration etc b Parasympathetic division calming effect on body i Digestion 2 Somatic motor division info being sent to external environment Nervous Tissue a Two cell types in nervous tissue i Neurons basic cell of nervous system ii Glial cells support cells b Universal properties of nerves neurons i Excitability irritability ii Conductivity iii Secretion c Classes of neurons i Afferent Sensory synapse on interneurons ii Interneurons processing iii Motor efferent d Anatomy of neuron i Neuro soma cell body ii Nucleus IV V VI VII iii Neurofilament structural support iv Mitochondrion v Nissl bodies important in regeneration vi Dendrites vii Axon viii Axolemma cytoplasm of axon ix Axon hillock generate action potential e Nissl Bodies i Protein synthesis takes place here ii Many neurotransmitters are protein based molecules Classes of Neurons a Multiple neuron one axon and many dendrites b Bipolar neuron one axon and one dendrite found in eye ear and nose c Unipolar neuron one process leading off the soma and it then branches d Anaxonic neuron no axon just multiple dendrites seen in part of the visual pathway Types of CNS Neuroglia a Oligodendrocytes synthesize myelin in CNS b Ependymal line cavities in brain help make cerebrospinal fluid c Astrocyte most abundant responsible for malignant brain tumors help form the blood brain barrier i Send out projections called perivascular feet that wrap around blood vessels d Microglial macrophages of CNS make sure nothing is there that shouldn t be increased number in cerebrospinal fluid diagnosis meningitis Types of PNS Neuroglia a Schwann cells make the myelin b Satellite cells surround soma of the neuron providing protection Myelin a Myelin sheath i Formed by oligodendrocytes in CNS and Schwann cells in PNS b Myelination process of forming myelin i During this process the myelin coats the nerve in segments c Myelin sheath is segmented i Nodes of Ranvier spots on nerve that are not covered by myelin ii Internodes segments of myelin covered nerves d Speed up conduction of nerve signal e Diameter of nerve fiber affects conduction larger more rapid f Diseases of the myelin sheath i Multiple sclerosis 1 Autoimmune disease 2 Oligodendrocytes attacked by immune cells 3 Myelin replaced by hardened scar tissue sclerosis VIII IX a Reduces speed of conduction in nerves 4 No cure live 20 30 yrs after diagnosis ii Tay Sachs disease 1 Hereditary disorder need two recessive copied of the gene 2 Found mostly in people with eastern European Jewish ancestry 3 Abnormal accumulation of a glycolipid GM2 due to absence of lysosomal enzyme hexosaminidase A 4 Caused by defect on chromosome 15 5 No cure fatal by age 4 iii Guillain Barre syndrome 1 Loss of myelin from the peripheral nerves and spinal nerve roots 2 Ascending paralysis 3 Usually preceded by a flu like illness 4 Most people recover all neurologic function with little medical intervention Regeneration of PNS Nerve Fibers regeneration cannot occur in CNS a Regeneration can occur if i Its soma is in tact ii At least some neurilemma remains b Denervation atrophy Electrophysiology of Neurons a Establishing and maintaining the resting membrane potential RMP i Cytosol ICF high concentration of potassium ii ECF high concentration of sodium iii Sodium potassium pump corrects leaking of ions b Neuron response i Receptive segment receives information ii Initial segment action potential initiated iii Conductive segment axon propagation of action potential iv Transmissive segment dendrites releases neurotransmitters c Local potentials i Need enough local potentials to fire an action potential at the axon hillocks ii Differences in local potentials vs action potentials 1 Graded they can vary in magnitude the stronger the stimulus the more gates it can open 2 Decremental get weaker the farther away they are from the stimulus 3 Reversible if no action potential is initiated then the already open gates close stops local potential can t stop action potential once they ve started 4 Either excitatory or inhibitory some neurotransmitters make the membrane potential more negative depends on action of neurotransmitter that is released a Glycine GABA and chlorine are inhibitory neurotransmitters usually d Action Potentials in Neurons i Soma 50 75 gates per micron squared ii A rapid up and down shift in the membrane voltage iii Characteristics of action potentials vs local potentials 1 Follows all or none law 2 Nondecremental 3 Irreversible e In un myelinated fiber the nerve is polarized in segments that portions charges will be reversed of what is normal