UMass Amherst KIN 460 - Neural signals - communcation within neurons Handout (9 pages)

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Neural signals - communcation within neurons Handout



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Neural signals - communcation within neurons Handout

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Pages:
9
School:
University of Massachusetts Amherst
Course:
Kin 460 - Motor Control
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Questions Are neurons good conductors Neural signals membrane potentials and transmission Postural Control in Multiple Sclerosis Stability and Complexity Analyses University of Massachusetts Amherst Department of Kinesiology What type of electrical signals do neurons exhibit How do nerve cells use ions to generate electrical potential How does long distance signaling occur through action potentials How does myelination increase conduction velocity How does the breakdown of myelination affect people with Multiple Sclerosis Question 1 Are neurons good conductors Question 1 Are neurons good conductors is the space constant distance at which voltage drops 1 e to 37 Telephone wires hundreds of miles Nerves 4mm Axonal current depends on how good its insulation is the resistance of the axon membrane RM and how much resistance is offered to currents flowing longitudinally through the axoplasm the longitudinal resistance of the axoplasm RL Exponential decline in voltage as a function of distance along the axon 1 Types of neuronal electrical signals Figure 2 1 Types of neuronal electrical signals Part 1 Question 2 What type of electrical signals do neurons exhibit Receptor potentials Synaptic potentials Action potentials Resting membrane potential Resting potientials are negative less negative is receptor has been stimulated Hyperpolarization of cone stimulated with different amounts of light Types of neuronal electrical signals Part 2 Receptor potential amplitude graded in proportion to stimulus strength Hippocampus Spinal networks central pattern generators CPG 2 Summation of postsynaptic potentials Part 1 Types of neuronal electrical signals Part 3 Motor Neuron AP AP booster system neurons are poor conductors Recording passive and active electrical signals in a nerve cell Part 1 Recording passive and active electrical signals in a nerve cell Part 2 magnitude of stimulation is shown by the frequence of acton potential 3 Action Potential Features Arises when membrane potential exceeds threshold 50 mV Very brief 1 ms from to Magnitude the same all or none Frequency of AP encodes intensity of stimulus intensity then frequency AP Generation of electrical signals Question 3 How do nerve cells use ions to generate electrical potential Electrical potentials are generated across membranes of neurons because Differences in concentration of ions passive Active transport ATP sodium pump Selective permeability ion channels Active transport the sodium pump Sodium pump It swaps Na ions on the inside of a membrane with K ions on the outside of a membrane three Na ions for two K ions It is an active transport and uses adenosine triphosphate ATP Without it cell would draw water and swell burst Requires energy 20 resting energy Immediately available unlike glycogen fat 4 Membrane permeability Axonal membrane at at rest slightly permeable to K No permeability Electrochemical equilibrium balance between two opposing forces Permeable to K Concentration gradient that causes K Efflux Electrical gradient stops K efflux Predicted by Nernst Equation z valence or electrical charge x is concentration Ex 58 X 2 log z X 1 Permeability to multiple ions Permeability to multiple ions Electrochemical equilibrium resting potential 1 efflux of K due to concentration gradient 2 this efflux will create electrical gradient that impedes further flow of K Resting potential 58 because K higher inside flows out making inside negative 5 Resting and action potentials arise from differential permeability to ions Multiple ions Electrochemical equilibrium predicted by Goldman Equation Vm voltage across membrane k is concentration and P is permeability Vm Pk K 2 PNa Na 2 Pk K 1 PNa Na 1 Questions Top Permeability changes of sodium and potassium associated with action potential Bottom Membrane potential changes as a result of permeability changes of sodium and potassium Question 4 How does long distance signaling occur through action potentials Passive flow propagation 1 2 mm decays over distance leaks out Action potential propagation 1 meter amplitude constant but slows down 6 Passive current flow in an axon Part 1 Propagation of an action potential Action potential conduction requires both active and passive current flow Part 1 Action potential conduction requires both active and passive current flow Part 2 2 active passive 1 Action potential Na channels open 3 Some depolarizing current passively flows down axon Depolarization spreads 4 5 Upstream permeability changes AP stops refractory Repeat of process 7 Action Potential Questions Action potential AP propagation requires both active and passive current flow Question 5 How does myelination increase conduction velocity If only passive flow in conduction velocity through in diameter only After AP the neuron is refractory Prevents AP from flowing backwards Upper limit on frequency of firing in neuron Myelination electrical insulation unmyelinated 0 5 10 m s 3 mph myelinated 150 m s 340 mph Insulator avoids leaking speeds up reduces amount of AP s time consuming Saltatory action potential conduction along a myelinated axon Part 2 Questions Question 6 How does the breakdown of myelination affect people with Multiple Sclerosis 8 Symptoms of MS Multiple Systems Affected Multiple Sclerosis MS Auto immune disease Central Nervous System T cell attacking myelin protein Changes in cognitive function Depression Other emotional changes Bladder dysfunction Bowel dysfunction Sexual dysfunction Normal nerve Myelin sheath acts to insulate nerve conduction Nerve affected by MS Disruption of nerve conduction due to exposed axons Cross talk between affected neurons Canadian Network of MS Clinics Dizziness and vertigo Vision problems Muscle Weakness Spasticity Abnormal sensations Pain Symptomatic Fatigue Difficulty in walking Balance problems American Academy of Family Physicians Questions Are neurons good conductors What type of electrical signals do neurons exhibit How do nerve cells use ions to generate electrical potential How does long distance signaling occur through action potentials How does myelination increase conduction velocity How does the breakdown of myelination affect people with Multiple Sclerosis 9


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