1. Neurons

2. (Spiral) Neurons Cornell Notes: How do neurons work?
Key Points
Notes
Summary:

3. 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. 4 Basic Parts to Neuron
Dendrites = They look like roots and receive messages from other neurons
Soma = Cell body, it also accepts incoming information, which it collects and combines. Sometimes messages cause the soma to send a nerve impulse.

5. 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.

6. Body Analogy of Neurons
soma
dendrites
axons

7. What is 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 per second are more typical.

8. 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.
Lots of NA + outside the cell at rest
NA+ and
K+ ARE MAJOR PLAYERS!

9. 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.

10. 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

11. After the Impulse: Negative After Potential
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.
What will happen if he can’t rest before his next race?
To balance and be able to rest again, the cell moves 3 NA+ ions out for every 2 K+ ions it brings in

12. 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 +

13. 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

14. 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

15. 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!

16. 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.

17. 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.

18. 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