1. 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: The Secret to Signals (correct link on class website)
What is an action potential & how does it happen?

2. Neurons - Sending a Message

3. 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

4. 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

5. 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

6. 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

7. Sensory Receptors

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

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

10. 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 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.

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

13. 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

15. 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

16. 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

18. 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.

20. Draw the Neuron

21. Action Potential
What happens?

22. 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

23. 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.

24. Na+ K+
Polarized

25. 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

26. Depolarization Sodium channels open and sodium comes rushing in.
The insides of the neuron becomes positive and the outside becomes negative

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

29. 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.

31. 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.

34. 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

36. Indicate Repolarization on Your Picture

37. 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.

38. 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.

40. 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.

41. 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