Muscle Contractions

1. Muscle Contractions

2. Goal: • I will be able to explain how electrochemical impulses are brought to my skeletal muscles.

3. Electrochemical Impulses • Electrochemical impulses are sent from the Central Nervous System (brain and spinal cord) to muscles causing contractions called a muscle twitch. • The nervous system consists of nerve cells called neurons. • Nervous system

4. Nerve Cell – motor neuron

5. Motor Neurons • All animal cells have a separation of positive and negative charges across the plasma membrane called a membrane potential. • Motor neurons have a resting potential (-70 mV) and when excited undergo depolarization which creates an action potential (+40mV). • Depolarization occurs because there is an influx of sodium ions (Na+) into the cell. • An action potential reaches the axon terminal causing Ca2+ to enter the cell. • This causes the neurotransmitter acetylcholine to be released allowing the action potential to continue to the next motor neuron.

6. The process continues until the impulse reaches a muscle. • Electrical energy is converted into chemical energy and then mechanical energy causing the muscle to move.

7. Neurons • Neural Impulse Animation • Chemical Signals

8. Motor Unit (Fig. 3.3 on page 35)

9. Motor Units • Motor units are considered either small or large depending on the number of muscle fibers it stimulates. • Large muscles usually have large motor units.

10. All or None Principle • A motor unit that is stimulated to contract , will do so to its fullest potential. • This is referred to as the all-or-none principle.

11. Work • Read pages 34 - 35

12. In this synapse, which structure represents the synaptic cleft? • In this synapse, which structure represents the axon terminal of a presynaptic cell? • What is happening in structure B. • In structure D, neurotransmitter molecules diffuse across the cleft and bind to receptors in the plasma membrane of the postsynaptic cell. What happens next.