Neuron Poster; Cockroach Flow Chart w/ Rubric Attached Due Today Edible Neuron Bonus—explain & eat Neuron Quiz High Altitude Due on 11/15 Action Potential PPT Notes & Drawings! Homework: 2.2.2 The Secret to Signals (correct link on class website) http://outreach.mcb.harvard.edu/animations/actionpotential_short.swf What is an action potential & how does it happen?

Neurons - Sending a Message

The Neurons Sensory neurons receive information from the outside world (light, sound) Motor neurons convey messages to the muscles to move Inter-neurons receive messages from and send messages to other neurons

The Axon The axon is responsible for sending the message. Axons can be very long have to be to go down the spine Nerves are long bundles of axons in the body

Sending a Signal A signal begins by stimulating dendrites sound sight smell When a neuron is not being used to send a signal, it is considered “at rest”. It has a charge of -70 millivolts At rest, the neuron has a negative charge on the inside and a positive charge on the outside Even though there are + charged ions on inside, it is still - due to the proteins on inside. Sending a Signal

Stimuli - Skin Pacinian corpuscles are pressure receptors Located in the skin joints tendons tissue that lines organs and blood vessels Each is connected to a sensory neuron. Pressure, vibration - changes shape of the corpuscle - causing the “firing” of the neuron

Sensory Receptors

Action Potential Also known as a nervous impulse Is really a electrochemical message Chemical cause an electrical signal within the cell.

How Fast? Action potentials can travel along axons at speeds of 0.1-100 m/s. The speed is affected by 3 factors: temperature diameter of axon - larger the diameter, faster the signal myelin sheath

Threshold When not being stimulated, neurons are at rest at -70 mVolts An action potential is initiated by a stimulus above a certain intensity or threshold – around -50 mVolts Not all stimuli initiate an action potential. The stimulus could be a pin prick, light, heat, sound or an electrical disturbance in another part of the neuron. Some stimuli are more intense than others, causing more neurons to be involved.

Neurotransmitters Chemicals that are released causing a change in the potential of the cell = causes and action potential to occur

Neurotransmitters They are released from one axon to a neighboring dendrite – synaptic cleft or synapse Binds to receptors on dendrite If there are not enough that bind, no change in the cell = no action potential

Common Neurotransmitters Acetylcholine (Ach) Activates muscles Serotonin Helps in digestive tract Melatonin It helps regulate other hormones and maintains the body's circadian rhythm. Some are excitatory and some are inhibitory of a message

Synaptic Cleft A junction that mediates information from one neuron to the next Presynaptic neuron – conducts impulses toward the synapse Postsynaptic neuron – transmits impulses away from the synapse

Two Types of Synapse Chemical Synapse Electrical Synapse Neurotransmitters released This is the one we will focus on Electrical Synapse Found in cardiac tissue, smooth muscle –organs Allows for continued contraction of all muscles collectively Two cells are connected by a gap junctions and less space between each neuron.

Draw the Neuron

Action Potential What happens?

Action Potential - Firing Neurotransmitters have been received at dendrites Cell membrane has protein channels that allow ions in and out of the cell Neurotransmitters open these channels Some ions move in/out without the use of energy Some ions move in/out with the use of energy - Energy is ATP

At Rest -70 mV The sodium- potassium pump pumps out 3 sodium ions (Na+) for each 2 potassium ions (K+) pumped into the neuron. This results in more potassium ions inside and more sodium ions on the outside.

Na+ K+ Polarized http://www.mind.ilstu.edu/curriculum/neurons_intro/neurons_intro.php

Depolarization When a neuron has been stimulated by a neurotransmitter, the protein channels in the axon suddenly open and allow the Na+ that was on the outside of the membrane to go rushing into the cell. As this happens, the neuron goes from being polarized to being depolarized. Happens around -50mV

Depolarization Sodium channels open and sodium comes rushing in. The insides of the neuron becomes positive and the outside becomes negative http://www.mind.ilstu.edu/curriculum/neurons_intro/neurons_intro.php

This is An Action Potential!! Draw depolarization on your neuron.

Repolarization After the inside of the cell becomes flooded with Na+, the gated ion channels on the inside of the membrane open to allow the K+ to move to the outside of the membrane. Just after the K+ gates open, the Na+ gates close; otherwise, the membrane couldn't repolarize. http://www.mind.ilstu.edu/curriculum/neurons_intro/neurons_intro.php

Resting…Again The refractory period is when the Na+ and K+ are returned to their original sides: Na+ on the outside and K+ on the inside. While the neuron is busy returning everything to normal, it doesn't respond to any incoming stimuli. Hyperpolarization After the Na+/K+ pumps return the ions to their rightful side of the neuron's cell membrane, the neuron is back to its normal polarized state and stays in the resting potential until another impulse comes along.

http://www.youtube.com/watch?v=yQ-wQsEK21E

The Node of Ranvier The action potential and the change in charges occur at the Nodes. The myelin sheath does not allow all of the action to occur….good thing = faster travel

Indicate Repolarization on Your Picture

From One Neuron to Another Action potential causes voltage-gated calcium channels to open. Calcium causes vesicles of neurotransmitters to fuse with the cell membrane.

The neurotransmitters diffuse across the synaptic cleft. The neurotransmitter binds to the neuroreceptors in the post-synaptic membrane, causing the channels to open. This causes a depolarization of the post-synaptic cell membrane can initiate an action potential.

After the Action Potential Neurotransmitters can be reabsorbed into the axon ending But converted into a non-excitatory state Can diffuse into the blood and we can excrete them if needed.

Action Potential is like a toilet! Full Toilet – Resting Potential Push Flush Lever – Threshold Stimulus triggering Action Potential. Toilet Refilling/Can’t Flush – Repolarization/Refractory Period Sewer Pipes – One-way communication like action potential only goes from dendrite end to axon terminal end