Unit 1 - Muscle Physiology and Contraction

What is the structure of muscle designed for?

Contraction and relaxation

What is the neuromuscular junction?

The neuromuscular junction is the site where a motor neuron communicates with a muscle fiber to stimulate muscle contraction

What is a motor unit?

A single motor neuron and all the muscle fibers it controls

Even during heavy lifting, what percentage of our motor units are working?

Only ~20%!

What is the purpose of Adenosine Triphosphate (ATP)?

To stimulate muscle contraction

What is the purpose of Creatine Phosphate?

To act as a short-term storage of energy within a muscle

• Can quickly turn ADP → ATP

What does Magnesium²⁺ do?

Needed to turn ATP → ADP for storage in the Creating Phosphate

What are the two pathways in the metabolism of glucose?

1. Anaerobic

2. Aerobic

What does the anerobic pathway of the metabolism of glucose entail?

• Occurs in the cytoplasm

• Requires little to no oxygen

• Only moderately efficient

What does the aerobic pathway of the metabolism of glucose entail?

• OIccurs in the mitochoindria

• Requires oxygen

• Greatest release of energy / most efficient

What pathway does Anaerobic metabolism use?

Glycolysis

• Little to no oxygen

• Consume 2 ATP per glucose

• Less efficient

What pathway does Aerobic metabolism use?

Krebs Cycle

• Requires oxygen

• Doesn’t consume ATP!

• More efficient

For each glucose that enters the muscle, how many ATPs can be generated?

36

• Both aerobic and anaerobic

Fat is a (bad/great) energy source.

Great

How is the nerve impulse from the brain transmitted to the muscle fiber?

Via transmembrane potentials

During the resting state of a nerve fiber, where are the charges located? What does this result in?

• Fluids inside the neuron are negatively charged

• Fluids outside the neuron are positively charged

• Results in a resting membrane potential

What causes a nerve fiber to depolarize and repolarize?

Action potentials (AP)

When an AP travels down a nerve, what happens?

Na⁺ floods in → inside becomes positive → K⁺ rushes out → inside becomes negative → recovery

Where does AP terminate at in the steps for muscle contraction?

The myoneural junction

What happens when AP reaches the myoneural junction?

Causes the release of the neurotransmitter acetlycholine, which crosses the synaptic cleft to bind to sites on the sarcolemma

What is acetlycholine responsible for?

Muscle contraction

What is acetlycholinesterase responsible for?

Muscle relaxation

How do APs communicated in a inner muscle cell?

Via the T-tubule system

Steps of Muscle Contraction

1. Begins with the resting state

2. AP travels down the motor neuron to the myoneural junction (motor end plate)

3. Acetlycholine is released; the sacrolemma and membranes depolarize (Na⁺ flux into fiber)

4. AP is transmittee via the T-Tubules to the sarcoplasmic reticulum (SR)

5. Calcium²⁺ is released from the terminal cisternae of the SR into the sarcoplasm

6. Ca²⁺ binds to troponin

7. Tropomyosin moves to expose myosin binding sites on actin

8. Actin-myosin bridges form (actomyosin)

9. Myostin ATPase activated, ATP is hydrolyzed and the myosin head rotates

10. Repeated over and over; filaments slide causing shortening of sarcomere

What is rigor mortis?

The stiffening of joints and muscles after death; permanent muscle contraction