Wednesday, December 5, 2007

The Nervous System

Today in class we continued to learn about the NERVOUS SYSTEM.

Voltage-Gated Channels
Changes in charge across the membrane causes ion channels to open and close.
In response to depolarization, Na+ channels open quickly and close slowly. While K+ channels open slowly and close slowly in response to depolarization.A neuron has to re-set itself after every reaction for the next reaction. Na+ is moved back out while K+ is moved back in. One protein pumps both potassium and sodium out with the use of energy because both are moving against the concentration gradients.
The nerve re-sets itself by pumping 3 Na+ out and 2 K+ in, which is not an equal exchange. Active transport proteins in the membrane are responsible for pumping Na+ out and K+ in. These proteins require a great deal of energy, or ATP.
Action Potential Graph
1. Resting potential- voltage-gated ion channels are closed but some K+ pass through 2. Threshold Potential- an action potential is produced
3. Depolarization- voltage-gated sodium channels open and allow Na+ to diffuse
4. Na+ channels close and K+ channels open
5. Repolarization- diffusion of K+ out of the axon; resets charge gradient
6. Undershoot- K+ channels start to close
Myelin Sheath

Axons are lined with Schwann cells which act as insulators to ensure that signals go far. Signals travel from node to node to reach their destination. A loss of signal can cause Multiple Sclerosis, when the immune system attacks myelin sheath.

Due to the gaps between neurons, impulses have to jump the synapse as quickly as possible to get to other cells. A chemical charge is needed to jump the gaps, so chemicals stored in the vesicles release neurotransmitters. The diffusion of chemicals across the synpases carry the chemcial signal across the synapse.


-Acetylcholine: help in the contraction of muscles, transmit signals to skeletal muscle

-Epinephrine & Norepinephrine: fight or flight response

-Dopamine: help in getting people out of comas but too much of it can cause schizophrenia

-Serotonin: affects sleep, learning and attention

Our next sherpa will be Ashley Scavo.

1 comment:

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