Muscle Cell Structure and Function

This course describes the amazing structure and function of the skeletal muscle cell. The human body is comprised of 4 cell types; epithelial cells (e.g. skin), nerve cells (e.g. sciatic nerve), connective tissue cells (e.g. ligaments, tendons, and fascia), and muscle cells (e.g. biceps brachii). There are even 3 distinct types of muscle tissue:

• Smooth muscle tissue: involuntary and non-striated muscle tissue
• Cardiac muscle tissue: involuntary and striated muscle tissue
• Skeletal muscle tissue: voluntary and striated muscle tissue

Each cell type has components and attributes common to all cells, and unique modifications to components that give that cell type its unique characteristics. Muscle cells are specialized to maximize force production via "contraction", and have a unique combination of responsiveness, excitability, conductivity, contractility, extensibility, and elasticity.

This course details cell classifications, muscle cell organelles, muscle cell function, action potentials, sliding filament theory (actin and myosin), excitation-contraction coupling, motor unit recruitment, striation, fascial layers, and muscle structure and organization. By the time you complete this course, you will understand why the interaction of actin and myosin, and the sliding filament theory help us understand why muscles are weaker in a lengthened position; or, how excitation-contraction coupling and the organization of motor units explain why you cannot target or shape one part of a muscle. Movement professionals (personal trainers, fitness instructors, physical therapists, athletic trainers, massage therapists, chiropractors, occupational therapists, etc.) should consider this course to be foundational physiology content, which is essential for understanding future courses including acute variables, corrective exercise, strength training program design, physical rehabilitation, etc.

Additional Courses:

• Muscle Fiber Types
• Muscle Fiber Dysfunction and Trigger Points

Caption: Motor unit by electron microscope

Snippet From This Course:

Understanding this process should bring feelings of sheer amazement at the intricacy of the human body. Consider that all of the steps detailed above (and summarized below) happen every time you need to generate force. In fact, consider that this sequence happens many times per second, at every muscle cell, of every motor unit, of every muscle you recruit, at every joint, and every time you move or resist movement.

1. Stimulus (intent, reflex, motor program, etc)
2. Action potential at motor neuron
3. Conducted by axon to the synapse
4. ACh released into the neuromuscular junction
5. ACh binds to receptors on the motor endplate of the muscle cell
6. Sodium-ion channels open on the motor endplate
7. An action potential is propagated across the sarcolemma
8. Action potential conducts down T-tubules
9. Opens voltage-regulated calcium channels
10. Calcium is released and binds to troponin
11. The change in the shape of the troponin-tropomyosin complex exposes binding sites
12. ATP binds to Myosin
13. Hydrolyzed ATP becomes ADP and extends the myosin head
14. The myosin head binds to an available binding site on troponin
15. Release of ADP results in flexing of the myosin head
16. Flexing the myosin head pulls actin resulting in a power stroke
17. ATP binds to myosin releasing the head from troponin
18. The process starts over at a binding site further down actin.
19. This step is multiplied by the number of binding sites on each protein, the number of proteins in each sarcomere, the number of proteins in parallel in each myofibril, and the number of myofibrils in each muscle cell.
20. Force output is then multiplied again, and calibrated for function, by the number of cells in the motor unit recruited, and the number of motor units recruited.

Note: Even this step-by-step account is a simplified summary of this process. Understanding each step represents years of work from incredible minds. It is not necessary that you memorize this entire sequence today, (although, you may be able to write down most of these steps in your own words after studying this course). But, stop studying for a moment, and take the time to appreciate how amazing the muscle cell really is. This knowledge is the first step in understanding the human movement system.