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Understanding Neuron Function and Impulse Conduction: Dendrites, Axon Terminals, and Synapses

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18 diapositives · 311 Views · Jul 20, 2014

This journal entry explores the fundamental differences between dendrites and axon terminals, delves into how neurons and synapses function in the nervous system, and explains the process of impulse conduction down the axon. It covers important concepts, such as local potentials, action potentials, depolarization, repolarization, and the role of myelin sheaths in speeding up impulses. Additionally, it describes how neurotransmitters operate at chemical synapses, and highlights key neurotransmitters like acetylcholine and serotonin that influence muscle movement and mood regulation.

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Understanding Neuron Function and Impulse Conduction: Dendrites, Axon Terminals, and Synapses
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  1. January 15, 2014 • Journal: What is the difference between dendrites and the axon terminal?

  2. How Neurons and Synapses Work

  3. Excitable Cells • Neurons, glands, and muscle cells • Can carry an electrical charge when stimulated

  4. Local Potential • The size of the stimulus determines the excitement of the cell • Bigger stimulus causes a bigger response than a smaller stimulus • Allows your CNS to determine the size of the environmental change • Causes an action potential to occur, but only if the stimulus is big enough

  5. Action Potential • Occurs in response to an internal or external change • Series of permeability changes within the cell that carry the electrical impulse down the axon • Impulse Conduction: The movement of the action potential down the axon to the terminal

  6. How Action Potential Works • When a cell is not excited it is said to be at rest • A resting cell is considered to be polarized • Meaning that there is a difference in charge across the cell membrane with more negative charges inside the cell

  7. How Action Potential Works • When a cell becomes stimulated, sodium ion channels open and let Na+ ions to travel into the cell, making the cell more positive • This is called depolarization

  8. How Action Potential Works • Then K+ leaves the cell through potassium ion channels • These positive charges leaving the cell returns the cell back to a resting state called repolarization • When a cell accidently becomes more negative then when at rest it is called hyperpolarized *A cell is unable to accept another stimulus until it repolarizes. This period is called the refractory period

  9. Action Potentials

  10. Myelin Sheath Speeds up Impulse Conduction • If a myelin sheath is present around the axon the impulse conduction will move faster • In an unmyelinated axon, every single sodium ion channel must open in order for the action potential to flow down the axon • In a myelinated axon, only the channels at the nodes of ranvier must open in order for the action potential to flow down the axon. • Therefore, the action potential jumps down the axon from node to node rather than creeping along the entire axon

  11. Axon Diameter Speeds up Impulse Conduction • The wider the axon diameter the faster the ions will flow because there is more room for the ions to flow

  12. January 21, 2014 • Journal: Explain how an impulse is conducted down the axon of one neuron.

  13. Two Types of Synapses: • Chemical Synapses • Electrical Synapses

  14. Chemical Synapses • Step 1: Impulse arrives at the axon terminal • Step 2: The terminal depolarizes and calcium is released from calcium ion channels • Step 3: Neurotransmitters are released from vesicles via exocytosis and are released into the synapse • Step 4: Neurotransmitters bind to the cell receiving signal and causes gates to open or close, either exciting or calming down the receiving cell • Step 5: Neurotransmitter is taken away from the synapse by an inactivator, usually an enzyme, to stop the neurotransmitter from continuously binding to the receiving cell

  15. Important Neurotransmitters • Acetylcholine: Found in skeletal muscle • Norepinephrine: Found in visceral and cardiac muscle • Epinephrine: Found in pathways concerning behavior and mood • Serotonin: Found in pathways that regulate temperature, sensory perception, mood, and sleep • Endorphins: Decrease pain

  16. Synapse Video • http://www.youtube.com/watch?v=rWrnz-CiM7A

  17. Electrical Synapses • Electrical synapses transfer information freely across the synapse