January 15, 2014

November 10, 2015Journal: 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 CellsNeurons, glands, and muscle cellsCan carry an electrical charge when

stimulated

Local PotentialA stimulus causes a response in a cell called a local potentialThe bigger the stimulus the bigger the response

If the local potential is large enough it will cause an action potential

Action PotentialOccurs 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 WorksWhen a cell is not excited it is said to

be at restA resting cell is considered to be

polarizedMeaning that there is a difference in charge across the cell membrane with more negative charges inside the cell

How Action Potential WorksWhen a neuron becomes stimulated,

sodium ion channels open and let Na+ ions to travel into the neuron, making the cell more positiveThis is called depolarization

How Action Potential WorksThen K+ leaves the cell through potassium

ion channelsThese positive charges leaving the cell

begin to return the cell back to a resting state. This is called repolarization.

How Action Potential WorksOften 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 AxonAs 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 ConductionIf a myelin sheath is present around the

axon the impulse conduction will move fasterIn 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 ConductionThe wider the axon diameter the faster the ions will

flow because there is more room for the ions to flow

Action Potential Video: https://www.youtube.com/watch?v=OZG8M_ldA1M

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

Chemical SynapsesStep 1: Impulse arrives at the axon terminal

Chemical SynapsesStep 2: The terminal depolarizes and

calcium is released from calcium ion channels

Chemical SynapsesStep 3: Neurotransmitters are released

from vesicles via exocytosis and are released into the synapse

Chemical SynapsesStep 4: Neurotransmitters bind to the cell

receiving signal and causes gates to open or close, either exciting or calming down the receiving cell

Chemical SynapsesStep 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 NeurotransmittersAcetylcholine: Found in skeletal muscleNorepinephrine: Found in visceral and cardiac

muscleEpinephrine: Found in pathways concerning

behavior and moodSerotonin: Found in pathways that regulate

temperature, sensory perception, mood, and sleep

Endorphins: Decrease pain

Synapse Videohttps://www.youtube.com/watch?

v=p5zFgT4aofA