1. NEUROMUSCULAR JUNCTION & NERVE IMPULSES

2. Characteristics of Muscle Tissue 1)Irritability: ability to respond to a stimulus 2)Contractility: ability to shorten when an adequate stimulus is received

3. Nerve Stimulus & Action Potential Skeletal muscle cells require stimulation by nerve fibers to contract (one motor neuron may stimulate a few muscle cells or hundreds of them)

4. Nerve Stimulus & Action Potential Motor unit = a motor neuron and all the skeletal muscle cells it stimulates Neuromuscular junction = area where the nerve fiber(axon) and muscle cell are closest to each other (they don’t actually touch)

5. Nerve Stimulus & Action Potential Synaptic cleft = gap between a nerve fiber and muscle cell; filled with interstitial fluid Neurotransmitter = chemical that stimulates skeletal muscle cells (acetylcholine)

6. TRANSMISSION OF A NERVE IMPULSE (ACTION POTENTIAL) 1. A muscle cell that is in a resting state is polarized, which means there is a separation of + and - charges inside and outside of the cell. There is a greater concentration of sodium ions (Na+) outside the cell and a greater concentration of potassium ions (K+) and its associated negative ions inside the cell.

7. TRANSMISSION OF A NERVE IMPULSE (ACTION POTENTIAL) 1. So, in a resting state, a cell has a net negative charge while the outside of the cell is positively charged. This polarization, or separation of charges, has potential energy.

8. TRANSMISSION OF A NERVE IMPULSE (ACTION POTENTIAL) 2. When a nerve stimulus is delivered, acetylcholine is released. Acetylcholine changes the permeability of the membrane and allows its sodium ions to diffuse into the cell, initiating depolarization of the membrane = transmission of nerve impulse (charges are no longer separated)

9. TRANSMISSION OF A NERVE IMPULSE (ACTION POTENTIAL) 3. Almost as soon as the depolarization wave begins, a repolarization wave follows it across the cell membrane. This occurs as potassium and its associated negative ions diffuse out of the cell. Repolarization restores the electrical conditions of the cell membrane because Na+ is now inside the cell and the K+ with - ions are now outside the cell.

10. TRANSMISSION OF A NERVE IMPULSE (ACTION POTENTIAL) 3. Almost as soon as the depolarization wave begins, a repolarization wave follows it across the cell membrane. This occurs as potassium and its associated negative ions diffuse out of the cell. Repolarization restores the electrical conditions of the cell membrane because Na+ is now inside the cell and the K+ with - ions are now outside the cell.

11. TRANSMISSION OF A NERVE IMPULSE (ACTION POTENTIAL) 4. The relative ionic concentrations on the two sides of the membrane at rest are re- established by activation of the sodium- potassium pump, which moves K+ into the cell and Na+ back out of the cell.

12. SYNAPTIC TRANSMISSION Let's take a look!