Cells of the CNS: Neural Communication - Chapter 2 - PDF

Cells of the CNS: Neural communication Carlson Chapter 2 Cells of the CNS Neurons 1. Dendrite “tree” 2. Cell body (soma) 3. Axon Glia Astrocytes Oligodendrocytes Microglia Structural classification of neurons Process number Axon Dendri...

Cells of the CNS: Neural communication Carlson Chapter 2 Cells of the CNS Neurons 1. Dendrite “tree” 2. Cell body (soma) 3. Axon Glia Astrocytes Oligodendrocytes Microglia Structural classification of neurons Process number Axon Dendrites Types Unipolar -Sensory Bipolar - Rare (ear and eye) Multipolar Functional classification of neurons Motor neurons Efferent Sensory neurons Afferent Interneurons Local / relay  Soma Smooth ER Neuronal membrane Phospholipid bilayer Cytoplasm (cytosol) Intracellular fluid Organelles Rough ER Membrane-enclosed structures Nucleus  Organelles Ribosomes Protein production Endoplasmic reticulum (ER) Smooth – lipids Rough - proteins Golgi apparatus Package and direct Lysosomes Mitochondria Waste ATP (Adenosine triphosphate)  Nucleus Chromosome Double-stranded DNA (deoxyribonucleic acid) Nucleotides: adenine (A), thymine (T), cytosine (C), guanine (G) Gene Segment of DNA Alleles mRNA (messenger ribonucleic acid) adenine (A), cytosine (C), guanine (G), uracil (U) Protein synthesis Transcription DNA to RNA Translation RNA to protein Ribosomes Codon Amino acids Axon Hillock Initial segment Proper Axon terminal (synaptic boutons) Collaterals  Synapse Components: 1. Presynaptic element Vesicles Mitochondria 2. Postsynaptic element Receptors 3. Synaptic cleft Presynaptic & postsynaptic neurons  Postsynaptic element Synapse types: 1. Axodendritic Dendritic spines 2. Axosomatic 3. Axoaxonic Axon transport Cytoskeleton Microtubules Neurofilaments Motor proteins Kinesin Anterograde Dynein Retrograde Glia: Astrocytes Glia “glue” Functions: Structural support Development Protection – BBB Synaptic transmission Repair Metabolic support Chemical environment  Astrocytes provide energy to neurons Glucose  lactate and glycogen Chemical regulation Regulate extracellular glutamate Excitatory Amino Acid Transporter 2 (EAAT2) Glial scar Astrogliosis Glial fibrillary associated protein (GFAP) Sofroniew, 2009 Blood brain barrier (BBB) Tight junctions between endothelial cells Circumventricular organs (CVOs)  Myelinating glia Oligodendrocytes CNS Multiple axons Schwann cells PNS Single axon Myelin Nodes of Ranvier Saltatory conduction Trophic support Glia: Microglial cells Immune cells Activation Proinflammatory molecules Phagocytosis  Neural communication: Postsynaptic potentials & action potentials Ions Anion Cation Ion distribution Ions Sodium (Na+) Potassium (K+) Calcium (Ca2+) Chloride (Cl-) Organic anions/proteins (A-) Resting potential Voltage Intracellular Extracellular At rest Inside - negative Outside – positive -70 mV (-40 to -90 mV) Phospholipid bilayer (cell membrane) Hydrophobic tails Hydrophilic heads Resistance Selectively permeable K+ Movement of ions Diffusion Concentration gradient Electrostatic pressure Voltage Equilibrium potential Balance in the forces that drive ion movement across membrane Equilibrium potential K+ = -80mV Na+ = +40mV Ca2+ = +130mV Resting potential Voltage-gated ion channels Transmembrane proteins Selective Membrane potential Ligand-gated ion channels Neurotransmitter Receptors binding site and a pore (i.e., channel) Ionotropic receptor Ion pumps Sodium-Potassium pump Adenosine triphosphate (ATP) 40% of all ATP Resting potential Altering membrane potential Hyperpolarization More negative Depolarization Less negative Electrical communication Action potentials (AP) Postsynaptic/graded/loca l potentials Postsynaptic (local, graded) potentials Inhibitory postsynaptic potential (IPSP) Hyperpolarization Excitatory postsynaptic potential (EPSP) Depolarization Stimulus strength Threshold Ion movement during IPSPs and EPSPs Generation of AP Influx of ions Hillock (threshold) Integration: EPSPs and IPSPs Temporal summation Spatial summation Action potential (AP) All-or-none Rate law Threshold Subthreshold Threshold and depolarization (rising) Voltage-gated sodium channels Na+ influx Rest: 10% Open K+ Closed Na+ Overshoot Na+ (+40 mV) Threshold: Open Na+  Repolarization: Repolarization (falling) Open K+ Closed Na+ Voltage-gated K+ channels Efflux K+ Inactive Na+ channels  Afterpotential (undershoot) Hyperpolarized membrane K+ efflux -A intracellular Sodium potassium pumps Resting potential AP summary Threshold Na+ channels Na+ influx (depolarization) K+ channels open and Na+ inactive K+ efflux (repolarization) K+ channels close Na+/K+ pumps Restore resting Refractory periods Absolute Na+ channels Relative Hyperpolarization K+ efflux AP propagation Hillock (initial segment)  Proper  terminal Continuous conduction Saltatory conduction Nodes of Ranvier Velocity Unidirectional Absolute refractory period Synaptic transmission Electrical  chemical Exocytosis Voltage-gated Ca+ channels Exocytosis: SNARE complex Docking V-SNARE (synaptobrevins) T-SNARE (SNAP-25) 45 Neurotransmitter (NT) receptor: Ionotropic Components Binding site Pore Ligand-gated ion channels EPSP or IPSP Fast  NT receptor: Metabotropic receptor Guanyl-nucleotide-binding proteins (G-protein) subunit Guanine triphosphate (GTP) Alpha, beta, & gamma subunits Adenylate cyclase (enzyme) Second messenger Cyclic adenosine monophosphate (cyclic AMP) from ATP Signal amplification Neurotransmitter clearance 1. Reuptake Transporter proteins 2. Enzymatic degradation Acetylcholinesterase 3. Diffusion Astrocytes Vesicle formation Endocytosis  Presynaptic neuron Autoreceptors Presynaptic Negative feedback Postsynaptic neuron Botulism Neurotoxin produced by Clostridium botulinum Highly toxic Food borne (swollen cans) Wound borne – bloodstream Gut colonization – children (honey) Botulism Symptoms Nausea/vomiting Flaccid paralysis (loss of muscle tone) Facial weakness Difficulty speaking Drooping eyelids Difficulty breathing/swallowing Respiratory failure in severe cases 52 Mechanisms: Botulism toxin 53 Medical uses Botox & Neurobloc Uses: Wrinkles Migraines Muscle spasms Chronic pain 54