Nerve Cell Action Potential PDF

Structure Function Relationship in Nerve Cells N EU F aculty of Medicine Dep of Biophysics Neurons ❖ Cell body (soma) contains the nucleus and other organelles ❖ Dendrites carry information from other neurons ❖ Axon carries information to other neurons transmits an action pot...

Structure Function Relationship in Nerve Cells N EU F aculty of Medicine Dep of Biophysics Neurons ❖ Cell body (soma) contains the nucleus and other organelles ❖ Dendrites carry information from other neurons ❖ Axon carries information to other neurons transmits an action potential Neuron  Cell Membrane, a selective barrier Sodium (Na+) and Potassium (K+) ions Pumps and gates Resting Potential: -70 mV  Cell Membrane Microelectrode: a very fine electrode, generally used to record activity of individual neurons. Inside of axon is negatively charged with Measuring electrical charge. respect to outside. The difference is 70mV, so the inside of the membrane is -70mV. This electrical charge is called the membrane potential. This electrical charge across the membrane is called resting potential. An axon is stimulated while its membrane potential is being recorded. Measuring Electrical Potentials of Axons – Membrane Potential – electrical charge across a cell membrane; the difference in electrical potential inside and outside the cell. – Resting Potential – membrane potential of a neuron when it is not being altered by excitatory or inhibitory postsynaptic potentials, normally about - 70 mV. – Depolarization – reduction (toward zero) of the membrane potential. Measuring Electrical Potentials of Axons – Hyperpolarization – increase in the membrane potential of a cell. – Action Potential – brief electrical impulse that provides the basis for conduction of information along an axon. – Threshold of Excitation – value of the membrane potential that must be reached to produce an action potential.  What Causes the Action Potential Why there is membrane potential? This electrical charge is the result of a balance between two opposing forces: The force of diffusion (Movement of molecules from regions of high concentration to regions of low concentration) The force of electrostatic pressure (Attractive force between atomic particles charged with opposite signs, or the repulsive force between atomic particles charged with the same sign) Action Potential (AP) 5 1.Resting potential 2.Start of depolarization 3.Opening of voltage-gated fast sodium channels 4 4.Influx of Na+ 6 5.Closure of Na+ channels, opening of voltage-gated slow K+ channels 3 9 6.Efflux of K+, repolarization 7.Hyperpolarization 1 2 8.Closure of K+ channels 8 7 9.Back to the resting potential! Some Concepts about Action Potentials All-or-none Law Refractory Period – Absolute – Relative Propagation of Action Potential Saltatory Conduction All-or-none Law Refractory Period Absolute Refractory Period Voltage gated Na+ channels are inactive. No AP can be generated Relative Refractory Period Voltage gated K+ channels are still open. Stronger stimulus is needed. Smaller AP is generated. Propagation of Action Potential Stimulus triggers AP V AP depolarizes a region V Charges diffuse to the next region V New AP starts V AP propagates further Information Flow in Neurons  Sensory Neurons INPUT from sensory organs to the brain and spinal cord. Drawing shows a somatosensory Brain Sensory neuron Neuron Spinal Vision, hearing, Cord taste and smell nerves are cranial, not spinal  Motor Neurons OUTPUT From the brain and spinal cord to the muscles and glands. Sensory Brain Neuron Spinal Cord Motor Neuron  Interneurons Interneurons carry information Sensory Brain Neuron between other neurons Spinal Cord Only found in the brain and spinal cord. Motor Neuron  EPSPs=Excitatory IPSPs=Inhibitory Neural Integration PostSynaptic Potentials PostSynaptic Potentials Neural integration. The effects of excitatory and inhibitory synapses on the production of Measurement of the depolarizations and hyperpolarizations action potentials in the postsynaptic neuron. produced by excitatory and inhibitory synapses.  Synaptic Transmission Transmission of messages from one neuron (presynaptic neuron) to another (postsynaptic neuron) through a synapse. Synapse types Axodendritic Axosomatic Axoaxonic Dendrodendritic  Synapse types Electrical Synapses Chemical Synapses Transmission via Transmission via direct ion transfer neurotransmitters Transmission is not Transmission is modulated. modulated. – Dendrodendritic Axodendritic Common in Axosomatic invertebrates Axoaxonic Dendrodendritic Common in vertebrates Release of Neurotransmitter Release zone of When the membrane the presynaptic of the terminal button membrane is depolarized by an contains voltage- arriving action dependent potential, the calcium calcium channels. channels open. Release of neurotransmitter. An action potential opens calcium channels. Ca+2 ions enter and bind with the protein embedded in the membrane of synaptic vesicles docked at the release zone. The fusion pores open and the transmitter substance is released into the synaptic cleft. The membrane of vesicles fuses with that of the terminal button.  Properties of Neurotransmitters: 1) Synthesized in the presynaptic neuron 2) Localized to vesicles in the presynaptic neuron 3) Released from the presynaptic neuron under physiological conditions 4) Rapidly removed from the synaptic cleft by uptake or degradation 5) Presence of receptor on the post-synaptic neuron 6) Binding to the receptor elicits a biological response 7) They can be used in other parts of the body with different functions (glutamate, epinehrine, etc.) NEUROTRANSMITTERS – Acetylcholine – Aspartate – Dopamine – Histamine – Norepinephrine – Epinephrine – Glutamate – Serotonin – GABA – Glycine