January 15, 2014

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

16. 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

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

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