November 10, 2015 Journal: What is the difference between dendrites and the axon terminal? After completing today’s journal, hand in all of your journals.

How Neurons and Synapses Work

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

Local Potential A stimulus causes a response in a cell called a local potential The bigger the stimulus the bigger the response If the local potential is large enough it will cause an action potential

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

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

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

How Action Potential Works Then K+ leaves the cell through potassium ion channels These positive charges leaving the cell begin to return the cell back to a resting state. This is called repolarization.

How Action Potential Works Often a cell becomes more negative then when at rest This called hyperpolarized. When this happens the sodium-potassium pump must work to get the charges back to a resting state by sending out three Na+ ions for every two K+ ions it brings in The cell is unable to accept another stimulus until it repolarizes. This period is called the refractory period.

How Action Potential Moves Down the Axon As the Na+ comes into one section of the axon, it triggers the sodium ion channels in the neighboring section to open As each section becomes depolarized it signals the adjacent section to depolarize thus moving the action potential down the axon in a domino effect

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

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 Action Potential Video:

November 2015 Journal: Explain how an impulse is conducted down the axon of one neuron.

Chemical Synapses Step 1: Impulse arrives at the axon terminal

Chemical Synapses Step 2: The terminal depolarizes and calcium is released from calcium ion channels

Chemical Synapses Step 3: Neurotransmitters are released from vesicles via exocytosis and are released into the synapse

Chemical Synapses Step 4: Neurotransmitters bind to the cell receiving signal and causes gates to open or close, either exciting or calming down the receiving cell

Chemical Synapses 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

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

Synapse Video