Nervous System:Group One

By: Cole Halpern, Michaela Freed, Meg Ruddy and Libby Alvin

Motor Neuron

In vertebrates, motor neurons are efferent neurons that originate in the spinal cord and synapse with muscle fibers to facilitate muscle contraction and with muscle spindles to modify proprioceptive sensitivity of muscles (1).

Ion Distribution Across the Neuron Membrane

• Sodium has a high concentration outside and a low concentration inside the membrane at rest (4).

• Potassium has a high concentration inside and a low concentration outside at rest (4).

• Crossing the membrane:o Channel Proteins:

Sodium leaks in (4). Potassium leaks in and out (4).

o Transport Proteins: Pump sodium out (4). Pump potassium in (4).

Action Potential

Defined as a fleeting reversal in the voltage difference across a neuron's plasma membrane (2).

Play a central role in cell to cell communication in neurons, is a passage of energy (2).

Action Potential Stages

1.) cell membrane is neutral, and is at its resting potential (or neural voltage) (1).

Action Potential Stages

2.) the cell becomes more positively charged inside the cell than outside the cell and there is a domino effect of other ions (1).

Action Potential Stages

3.) once the action potential passes through the cell however the neuron becomes more negatively charged inside the cell than outside the cell (1).

Action Potential Stages

4.) eventually returns to resting potential (1).

Myelin Sheath

Allows for fast and efficient transduction of electrical signals in the nervous system (2).

Myelin has two important advantages: fast conduction speed and energy efficiency (1).

Made up of Schwann Cells (2).

Multiple Sclerosis:

• Axons are wrapped in myelin,a fatty layer (3).• In multiple sclerosis the body attacks its own myelin on neurons in the brain and spinal cord (also known as "white matter") forming lesions (tears in the myelin)(5).• Scar like tissue is created and when electrical impulses travel along the tissue,the signals are slowed down and distorted (5).

• symptoms:      weakening of muscles     numbness

• Without signals being communicated correctly, muscle fibers cannot contract, weakening the muscle.  Also, numbness occurs as a result of brain and spinal cord neurons not receiving messages at the necessary speed or not getting any messages at all (3).

References:

1. Campbell. "Biology: Exploring Life." Login. 2004. Web. 16 Nov. 2010. <https://www.pearsonsuccessnet.com>

2. "Motor Neuron." Science Daily: News & Articles in Science, Health, Environment & Technology. Web. 16 Nov. 2010. <http://www.sciencedaily.com/articles/m/motor_neuron.htm>.

3. "Multiple Sclerosis Causes, Types, Symptoms, Diagnosis, Treatment, and Prognosis Information on MedicineNet.com." Web. 16 Nov. 2010. <http://www.medicinenet.com/multiple_sclerosis/article.htm>.

4. Starr, Cecie, and Ralph Taggart. Biology: The Unity and Diversity of Life. 9th ed. Pacific Grove: Brooks/Cole, 2001. Print.

5. "What Is Multiple Sclerosis?" All About Multiple Sclerosis : MS News and Information on Diagnosis, Symptoms & Treatments. Web. 16 Nov. 2010. <http://www.mult-sclerosis.org/whatisms.html>