Me, you, & Neurons

Introduction to Neural Activity: Starting Instructions

• Form groups of 4.

• Person #1 will be a subject and should understand that this involves an experiment on their own feet.

• Person #2 will be the experimenter.

• People #3-4 will be data recorders.

• Subjects will leave the room as experimenters and recorders are debriefed.

• Subjects leave now!

Introduction to Neural Activity: Instructions to Experimenters and Recorders

• Experimenters will lightly touch the second, third, and fourth toe pads with a “stylus” (pencil eraser) in random orders.

• Touch the toe pad slightly to the side of the center line. Don’t touch the toes on the centers.

• Recorders will measure EACH trial, so get out a piece of paper. Measure which toe is touched (2, 3, or 4) and the subject’s response to which of their toes is being touched. Once subjects have their eyes shut, the experimenter will indicate to the recorders with their fingers which toe they are going to touch.

• When Mrs. H say, “It’s time for the next phase,” you should begin to include the 1st and 5th toes in your experiment.

• Experimenters may give a “yes/no” answer to subjects as to whether or not they guessed the right toes, but not anything more.

• Don’t tell subjects what’s going on! This is a single-blind experiment. Subjects may reenter now!

Introduction to Neural Activity: Instructions to Subjects

• Subjects, you will take off your shoes/socks and close your eyes. Follow the instructions of the experimenter! 5,4,3,2,1 1,2,3,4,5

Introduction to Neural Activity

• The point: Neurons communicate between different parts of the body and the brain. They form networks based on habits and environment – EX. 1st and 5th toes would yield different results, because

they’re more used to stimulation. Your brain therefore has those toes on its “cognitive map” because of regular stimulation (through neural networks, of course), and you’d be able to articulate during the experiment that those were the toes being stimulated.

• So, how do neurons work?

[Packet] How Neurons Work:• Go to http://faculty.washington.edu/chudler/ap.html • Answer the following questions:• What does the axon of the squid allow it to do?• What is a resting potential?• What is an action potential ?• What is a threshold?• Look at the chemical and action potential animated charts.

Which two chemicals are involved heavily in neurotransmission?

(You may also use pgs. 76-81 in your book to find the answers)

• Click on “BrainU Animations” at the bottom and then “Synapses Change” video. Interact with the media.

Other Simple Explanations of Neurons

• http://www.utexas.edu/research/asrec/synapse.html

• http://en.wikipedia.org/wiki/File:Action_potential_propagation_animation.gif

[Packet] Neurotransmitter Notes:How do neurons impact behavior?

• Key Points

• Neuron parts (not already named)

• Chemical reaction (NA+ and K+)

• Electrical reaction

• Rest and recovery

• Neurotransmitters

• Sending and Receiving Neurons (pre/post synaptic)

• Notes

Summary:

What Are Neurons?

• NEURONS = basic units of the human "biocomputer." Cells that deal with information.

• The Nervous System is made up of long chains of neurons. No two neurons are exactly alike in size or shape. Nerves are large bundles of neuron fibers. Nerve cells, arranged in long chains and dense networks. Alone, not very smart. Joined in vast networks, they produce intelligence and consciousness.

4 Basic Parts to Neuron

1. Dendrites = They look like roots and receive messages from other neurons

2. Soma = Cell body, it also accepts incoming information, which it collects and combines. Sometimes messages cause the soma to send a nerve impulse.

4 Basic Parts to Neuron

3. Axon = long, thin fiber down which impulses are sent. Carries messages from sensory organs to the brain.

4. Axon terminals = the branching at the end of axons. These branches link with dendrites and somas (cell bodies) of other neurons.

Body Analogy of Neurons

soma

dendrites

axons

What is the Nerve Impulse?

• THE NERVE IMPULSE (an electrical event):

Each neuron is like a tiny biological battery ready to be discharged. It takes about one-thousandth of a second for a neuron to fire an impulse and return to its resting level. A maximum of 1,000 nerve impulses per second is possible. However, firing rates of 1 per second to 300-400 per second are more typical.

A Neuron at Rest• Cell membrane = skin of cell. • Resting potential = inactive

state of neurons when they are negatively charged-- Must receive electrical message to activate it. When other neurons send enough neurotransmitters to the cell’s dendrites, it reaches it may reach its threshold.

• Ions = electrically charged molecules inside and outside each

neuron causing a tiny difference in electrical charge across the cell membrane.

NA+ andK+ ARE MAJOR PLAYERS!

Lots of NA + outside the cell at rest

An Active Neuron: from Chemical to Electrical

• Threshold = trigger point, for firing. The threshold for human neurons averages ca. -50 millivolts (a millivolt is one-thousandth of a volt.). At this point a nerve impulse or action potential sweeps down the axon.

• Action potential = nerve impulse caused by an exchange of ions (Na+ and K+) across the neuron membrane. A stimulus first causes sodium channels to open. The resulting current sweeps down the axon after being triggered by positive sodium ions opening gates in succession all the way down the axon.

Parts of Nerve Impulse: Electricity!

• Ion channels = tiny tunnels in the axon membrane that cause action potential. Normally “closed gates." The gates pop open during an action potential, allowing sodium ions to rush into the axon--happening near the soma, first, and then as action potential moves along, the gates open in sequence down the length of the axon.

• *** NOTE: An impulse occurs completely or not at all

NA+ flows into the axon during an impulse, raising its positive charge

After the Impulse:Negative After Potential

What will happen if he can’t rest before his next race?

Negative after-potential = the cell briefly drops below its resting level after each nerve impulse--caused by outward flow of positive potassium ions that occurs while the membrane gates are open. The neuron must recharge after each nerve impulse. It does this by shifting ions back across the cell membrane until the resting potential is restored.

To balance and be able to rest again, the cell moves 3 NA+ ions out for every 2 K+ ions it brings in

After “After Potential”The Great Balancing Act

• Positive sodium particles enter to cause action potential

• Positive potassium particles leave to rebalance the neuron to -70 millivolts

• The neuron returns to resting potential

+

Leaving the Axon: Neurotransmission between the Sending and Receiving Neurons

• NEUROTRANSMISSION: When the action potential impulse reaches the end of the axon, it stimulates tiny pouches of chemicals in the axon terminals. The pouches then release neurotransmitters such as dopamine, serotonin, and epinephrine.

• Communication between neurons, across the synapses, is molecular/chemical--in contrast to electrical event of nerve impulse.

Neurotransmitters

NOTE:• NA + (sodium) and K+ (potassium)

ARE NOT NEUROTRANSMITTERS! They are ions that dance in and out of the axon to stimulate the release of neurotransmitters at the ends of the axons.

• Neurotransmitters are chemicals held in the ends of the axons only that serve as the “chemical messengers” which communicate through the dendrites of other neurons.

NA+ and K+ zone

Neurotransmitter zone

Will the Neurotransmitters Fit the Receptor Site?

• If yes, and there are no inhibitory neurotransmitters in the same synapse, the receiving neuron will fire!

• If no, the sending neuron will reuptake (vacuum up) the neurotransmitters that it sent into the synapse!

Terms Regarding Neurotransmitters

• Neurotransmitters = Potent chemicals which are released when a nerve impulse reaches the tips of the axon terminals.

At any instant, a neuron receives messages from hundreds of thousands of other neurons.

If several "exciting" (+) messages arrive close in time, and they are not cancelled by "inhibiting" (-)messages, the neuron reaches its trigger point.

This means that chemical messages are combined before a neuron "decides" to fire its all-or- nothing action potential.

Terms Regarding Neurotransmitters

• Synapse = tiny gap between neurons. Neurotransmitters cross these gaps, attach to sites:

• Receptor sites = on the soma and dendrites of the next neuron. Transmitter molecules attach to these special sites. They also activate receptor sites on muscles and glands.

FYI: Neuro Regulators

• NEURO REGULATORS: A new class of brain transmitters. Neuropeptides or brain peptides. They do not carry messages directly. Instead, these Chemicals regulate the activity of other neurons. Doing so, they affect memory, pain, emotion, pleasure, mood, hunger, sexual behavior, and other basic processes

Summary

• You are learning to ride a bike. A neuron in your brain must communicate through your nervous system to reach your leg, balance systems, coordination systems, etc.

• Describe one neurotransmission that would be involved in this process from beginning to end.

• Use pgs. 76-80 to help you.