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Electrical excitability of Neurons and Chemical Messengers
- 1. { Electrical Excitability of Neurons & Chemical Messengers
- 2. Introduction Chemical Messengers -Neurotransmitters -Hormones -Neuropeptide -Pheromone Special Properties of Neurons -Excitability Action potential Electric excitability of a nerve impulse What creates an action potential Conclusion Index
- 5. { Special Properties of Neurons -Excitability--Action Potential in Axons. -Conduction--Action Potential in Axons. -Transmission--Synapses, Electrical & Chemical. -Integration--Postsynaptic Cell. -Plasticity--Pre-synaptic Terminal and Postsynaptic Membrane.
- 6. { Electrical Excitability of Neurons •The ability to create an action potential in response to a stimulus. • Two types of excitable cells in body: > Muscle > Nerve cells.
- 7. { What is an Action Potential? Action Potential – electrical signal carried by an axon in a nerve. • Caused by ions • Is an electrochemical response Result from the disturbance of the potential difference across the axon plasma membrane.
- 8. {
- 9. Resting Membrane Potential The concentration of these ions isn’t static, how does the cell maintain it’s fairly constant negative concentration?
- 10. { What creates the potential difference? Large negative proteins are trapped inside the cell. Sodium-potassium pump -Pumps 3 Na + out for every 2 K +it pumps into the cell.
- 12. { Constant negative concentration gradient (between -40 to -90 millivolts) The neuron cell membrane is super permeable to potassium ions, and so lots of potassium leaks out of the neuron through potassium leakage channels (holes in the cell wall). The neuron cell membrane is partially permeable to sodium ions, so sodium atoms slowly leak into the neuron through sodium leakage channels. The cell wants to maintain a negative resting membrane potential, so it has a pump that pumps potassium back into the cell and pumps sodium out of the cell at the same time.
- 13. ACTION POTENTIAL AND GRADED POTENTIAL
- 14. 1. Excitatory 2. Inhibitory Types of Synapses
- 16. How its is Relatable to Biomedical Engineering? Direct Neural Interface
- 17. Conclusion We’ve Briefly Discussed about: Chemical Messengers Excitability of Neurons Action Potential Resting Membrane Potential what created potential difference Types of synapses
- 18. {THANKYOU…
Editor's Notes
- A chemical messenger is any compound that serves to transmit a message. A chemical messenger may refer to: Hormone, Long range chemical messenger Neurotransmitter, communicates to adjacent cells Neuropeptide, a protein sequence which acts as a hormone or neurotransmitter Pheromone, a chemical factor that triggers a social response in members of the same species
- dendrites: receive signals from neighboring neurons (like a radio antenna) axon: transmit signals over a distance (like telephone wires) axon terminal: transmit signals to other neuron dendrites or tissues (like a radio transmitter) myelin sheath: speeds up signal transmission along the axon
- An action potential is a rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane with a characteristic pattern.
- Depolarization: A triggering event caused by signal comes from other cells connecting to the neuron, and it causes positively charged ions to flow into the cell body. Positive ions still flow into the cell to depolarize it, but these ions pass through channels that open when a specific chemical, known as a neurotransmitter, binds to the channel and tells it to open. Neurotransmitters are released by cells near the dendrites, often as the end result of their own action potential! These incoming ions bring the membrane potential closer to 0, which is known as depolarization. Repolarization - brings the cell back to resting potential. The inactivation gates of the sodium channels close, stopping the inward rush of positive ions. At the same time, the potassium channels open. There is much more potassium inside the cell than out, so when these channels open, more potassium exits than comes in. This means the cell loses positively charged ions, and returns back toward its resting state Hyperpolarization - makes the cell more negative than its typical resting membrane potential. As the action potential passes through, potassium channels stay open a little bit longer, and continue to let positive ions exit the neuron. This means that the cell temporarily hyperpolarizes, or gets even more negative than its resting state. As the potassium channels close, the sodium-potassium pump works to reestablish the resting state
- Voltage-gated sodium channels exist in one of three states: Deactivated (closed) - at rest, channels are deactivated. The m gate is closed, and does not let sodium ions through. Activated (open) - when a current passes through and changes the voltage difference across a membrane, the channel will activate and the m gate will open. Inactivated (closed) - as the neuron depolarizes, the h gate swings shut and blocks sodium ions from entering the cell. Voltage-gated potassium channels are either open or closed.
- Refrectory period is a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation. Absolute: Is the period of time during which a second action potential ABSOLUTELY cannot be initiated, no matter how large the applied stimulus is. Relative: Is the interval immediately following the Absolute Refractory Period during which initiation of a second action potential is INHIBITED, but not impossible. As voltage-gated potassium channels open to terminate the action potential by repolarizing the membrane, the potassium conductance of the membrane increases and the K+ ions move out of the cell and bring the membrane potential closer to the equilibrium potential for potassium and this can lead to membrane hyperpolarization.
- Synapse is junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter An inhibitory postsynaptic potential (IPSP) is a kind of synaptic potential that makes a postsynapticneuron less likely to generate an action potential. An excitatory synapse is a synapse in which an action potential in a presynaptic neuron increases the probability of an action potential occurring in a postsynaptic cell. Neurons form networks through which nerve impulses travel, each neuron often making numerous connections with other cells.
- Direct Neural Interface is another name of Brain computer Interface