1. { Nerve Stimulus and Action Potential Bella Veri Brandon Richter Haily Walker Deva Ramos Jenny Le Period 4

2.  Nerve Stimulus and Action Potential Question:

3.  For a skeletal muscle to move they must be stimulated by nerve impulses.  Depending on the muscle, one motor neuron can stimulate only a few muscle cell, or a few hundred muscle cells.

4.  Motor Unit- One neuron and all the skeletal muscle cells it stimulates.  Axon (nerve fiber)- A long, threadlike extension of the neuron.  Axon Terminal- distal terminations of branches of axon.  Neuromuscular Junctions- the region where a motor neuron comes into close contact with a skeletal muscle cells.  Synaptic cleft-the fluid filled space at a synapse between neurons.  Neurotransmitter- chemical released by neurons that may, upon binding to receptors of neurons or effector cells, stimulate or inhibit them.  Acetylcholine (Ach)- a chemical transmitter substance released by certain nerve endings  Action Potential- An electrical event occurring when a stimulus of sufficient intensity is applied to a neuron or muscle cell, allowing sodium ions to move into the cell and reverse the polarity. Vocabulary Page numbers: 189 190

5. 1. When nerve impulses reach the axon terminals, the chemical called neuromuscular is released. 2. Acetylcholine is the neurotrasmitter that stimulates a skeletal muscle cell. 3. Acetylcholine then diffuses across the synaptic cleft and attaches to receptors that are part of the sarcolemma. 4. When there is enough acetylcholine released, the sarcolemma at that point becomes temporarily more permeable to sodium ions which rush into the muscle cell, and to potassium ions, which diffuse out of the cell. However, more sodium ions enter when potassium ions leave. 5. This reverses the electrical conditions of the sarcolemma and opens more channels that allow sodium entry only. This generates an electrical current called an action potential. 6. After it begins it is unstoppable. The current travels over the entire surface of the sarcolemma, which conducts the electrical impulse from one end of the cell to the other. This causes the contraction of the muscle cell. Process

6. Images Page: 190 Motor Unit

7. Image Page: 190 Axon

8. Image Page: 191 Neuromuscular Junction