Alyssa Kwartler Kin 460 Exam 1 I Neural Signaling The Nervous System Fundamentals 1 What is the structure of neurons 2 What is the relation between neuronal form and function 3 How many neurons and connections does the CNS have Neural Signals Membrane Potentials and Transmission 1 What type of electrical signals do neurons exhibit Receptor potentials Characterized by receptors in the skin Amplitudes are graded in proportion to stimulus strength the more intense the stimulus the higher the response amplitude Synaptic potentials Action potentials These potentials enter through the dendrites of the neurons These are what allows for transmittance of signals throughout the entire body 2 How do nerve cells use ions to generate electrical potential Electrical potentials are generated across membranes of neurons because Differences in concentration of ions active transporters Selective permeability ion channels Active transporters move ions against their concentration gradient Ion channels selectively allow certain ions to pass through them along their concentration gradient Active transporters and ion channels Represented by different kinds of proteins They can work against each other Work to generate all known potentials including resting receptor synaptic and action potentials Electrochemical equilibrium balance between two opposing forces Concentration gradient that causes K efflux Electrical gradient that stops K efflux Can be predicted by the Nerst equation for a single ion Can be predicted by the Goldman equation for multiple ions Ex 58 z log X 2 X 1 where z valence or electrical charge x concentration Vm Pk K 2 PNa Na 2 Pk K 1 PNa Na 1 where Vm voltage across membrane K concentration P permeability Electrochemical equilibrium exists at resting potential 1 Efflux of K due to concentration gradient 2 This efflux creates an electrical gradient that stops further flow of K Resting potential 58 because K higher inside K flows our makes inside negative 3 How does long distance signaling occur through action potentials Passive flow Propagation 1 2mm Decays over distance leaks out and current disappears Action potential Propagation 1 meter Amplitude is constant but slows down Action potential propagation requires both active and passive current flow After AP the neuron is in a refractory period Prevents AP from flowing backwards Upper limit on frequency of firing in neuron 4 How does myelination increase conduction velocity If only passive flow occurs increasing the conduction velocity requires increasing axon Myelination electrical insulation that avoids leaking speaks up velocity reduces the amount diameter of action potentials 5 How does the break down of myelination affect people with Multiple Sclerosis MS MS causes T cells of the immune system to attack the myelin protein that makes up the myelin Nerves affected by MS have problems with the conduction of current in the nerves AND OR Cross talk wrong neurons are firing at the wrong times affects both voluntary and sheath demyelination cross talk happens involuntary nerve function Neural Signals Synaptic Transmission 1 What types of neuronal synapses exist Electrical neuronal synapses Current travels from presynaptic neuron to post synaptic neuron Neurons are connected through gap junctions ion channels which allow for very fast transmission AND bidirectional transmission from pre to post OR post to pre Extremely fast BUT cannot be modulated Chemical neuronal synapses Much more prevalent that electrical neuronal synapses Much larger gap between the pre and postsynaptic membranes Signals get transmitted by neurotransmitters that are held and carried in vesicles Slower than electrical neuronal synapses BUT can be modulated ability to change the propagation of the action potential due to different neurotransmitters being present 2 What kinds of neurotransmitters exist Different neurotransmitters have different functions excitatory vs inhibitory Co transmitters single neurons that contain two or more types of neurotransmitters Important neurotransmitters Acetylcholine Ach neuromuscular junction Excitatory neurotransmitter at neuromuscular junction Autonomic nervous system inhibitory for heart rate Myasthenia gravis grave muscle weakness Glutamate excitatory Found in majority of excitatory synapses in brain and spinal cord Involved in synaptic plasticity Plays role in neurodegeneration after brain cord damage overstimulation and cell death Gamma aminobutyric acid GABA inhibitory Spastic Diplegia Cerebral Palsy damage to upper motor neurons in cerebral cortex basal ganglia and brainstem reduced GABA absorption Result increased tone hypertonicity spacticity malformation Dopamine movement excitatory Stimulants such as cocaine and methamphetamines act directly on dopamine Reward system produced in brain Parkinsons lack of dopamine Schizophrenia elevated levels Serotonin sleep and wakefulness Norepinephrine arousal and attention Histamine arousal and attention Neural Signals The Neuromuscular Junction 1 Brief review of muscle structure Muscle structure Tendon connects muscle to bone Epimysium outer most membrane of muscle Perimysium membrane that surrounds fascicle bundles Fascicles bundles of muscle fibers Muscle fibers muscle cells the units responsible for contraction Endomysium membrane that surrounds each individual muscle fiber Myofibrils groups of these make up an individual muscle fiber composed of myofilaments Myofilaments make up each myofibril responsible for the banding patterns composed of thin filaments actin thick filaments myosin elastic filaments titin Z disc H zone I band A band and M line Sarcolemma membrane that surrounds each myofibril Sarcoplasm cytoplasm of a muscle cell contain large number of glycosomes and hemoglobin Sarcomere extends from Z disc to Z disc 1 Sarcomere shortens 2 I band shortens 3 H zone disappears 4 A band moves closer but length remains the same Sliding filament model during contraction myosin and actin slide past each other intermittently through cross bridges Muscle contraction is controlled by nerve initiated electrical impulses that travel along the sarcolemma Muscular contraction T tubules continuations of the sarcolemma the signal travels to the deepest part of the muscle Sarcoplasmic reticulum regulates intracellular calcium 2 Nerve stimulus and neuromuscular junction Phase one motor neuron stimulates muscle fiber at neuromuscular junction Action potential AP arrives at axon terminal at