NSCA CPT Chapter 1 - Structure and function of the muscular, nervous, and skeletal systems

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Chapter Objectives:

  • Discuss the function and the structures of skeletal muscles.
  • List the steps of the sliding filament theory.
  • Explain concepts of fiber type and its application to exercise performance.
  • Discuss the function and structure of the nervous system as it applies to skeletal muscle control.
  • Describe exercise’s role in bone health and the function of tendons and ligaments.

The Muscular System

Muscles generate force whenever they are activated. We call this muscle contraction or muscle action.

There are three muscle types: Skeletal, cardiac, and smooth. 

Skeletal muscles attach to bones and are used to rotate joints. These muscles allow us to run, jump, and lift daily.

 

Gross Anatomy of Skeletal Muscle

Each skeletal muscle has three levels of connective tissue.

Epimysium is the outer layer of connective tissue surrounding the whole muscle.

A bundle of muscle fibers is known as a fascicle. 

Perimysium covers these fascicles, the connective tissue covering this second layer.

The endomysium is the last layer of connective tissue. It surrounds the individual muscle fibers. 

Microscopic Anatomy of Skeletal Muscle

Each fiber is a cell; like any other cell, it has the same structural components. The skeletal muscle cells have more than one nucleus. 

Myofibrils

The myofibrils are bundles of myofilaments. His myofilaments are made of myosin and actin. Their arrangement gives muscle its striated appearance.

Two protein structures are associated with actin. Tropomyosin and Troponin. These are regulatory proteins that take care of regulating the interaction of both actin and myosin.    

Sarcomere

The most basic contractile unit of a muscle. 

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Consists of an M line, Z line, H zone, I band, and A band. 

Neuromuscular junction

This is the site where the muscle receives stimulus from the nervous system. 

The motor endplate, the space between the axon terminal and the motor endplate, also known as the synaptic cleft, are the other parts of this neuromuscular junction.

Sliding Filament Theory

This theory states that muscles shorten or lengthen when filaments slide past one another without any change in length in the filaments.

These are the steps for the sliding filament theory:

The Resting Phase: The myofibril has a lot of calcium within it, and because of this, we don’t have many myosin cross bridges that are bound to the actin.

The Excitation Contraction Coupling Phase: The SR, or sarcoplasmic reticulum, will release calcium in this stage when it becomes stimulated. These new calcium ions that are released will bond with the troponin. These events cause a shift in tropomyosin, and the myosin cross bridges will form much quicker to the actin in the cell.

The Contraction Phase: This is the third phase. Here we have the hydrolysis of ATP occurring and this causes the fibers to contract. 

The Recharge Phase: This fourth phase begins when the calcium is available in the cell. 

The Relaxation Phase: Here, the stimulation stops, and the calcium is now pumped into the SR for use at a later time. Thus, altogether actin and myosin cannot link together. 

ATP: Adenosine Triphosphate is the energy source of muscular actions. 

ATPase: Adenosine Triphosphatase causes the splitting of the ATP molecules. 

Types of Muscle Actions

Concentric Muscle Action: This occurs when the force produced in the muscle overcomes the external resistance in the opposing direction. In a bicep curl, this would bring the weight up.

Eccentric Muscle Action: This is the lengthening action. When the force produced by the muscle is less than the force opposing it, so, in a bicep curl, this would be the negative portion or the lowering of the weight.

Isometric (static) Muscle Action: This is when the muscle force equals the opposing force. These actions lead to no movement. A typical example is a plank, but with the bicep curl example, it would leave the weight at one spot in the movement.

Delayed-Onset Muscle Soreness (DOMS) and Eccentric Muscle Actions

This muscle pain lasts 24 – 48 hours following an exercise program or even some new movement patterns. It combines connective and muscle tissue damage and an inflammatory action activating the pain receptors.

Exercise is seen as the best way to reduce these pains.

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Muscle Fiber Types 

All fibers are not the same regarding contractile performance and their physiological characteristics. 

Type I fibers: Slow oxidative or slow twitch fibers. These have high oxidative capacities and are very resistant to fatigue. They also contract and relax more slowly.

Type IIa fibers: The fast oxidative glycolytic fibers. Large and powerful fibers with moderate to high anaerobic metabolic capabilities. These have moderate oxidative and anaerobic capacities.

Type IIx fibers: The fast glycolytic fibers. Large and powerful fibers with moderate to high anaerobic metabolic capabilities. These are purely anaerobic and fatigue very quickly. 

It is possible to transition some fibers.

The Nervous System:

In charge of directing and controlling voluntary movement.

Organization of the Nervous System:

The nervous system is broken down into the central and peripheral nervous systems. Also, the CNS and PNS.

The CNS is made up of the brain and the spinal cord.

The peripheral nervous system is the rest of the nervous system outside of the brain and the spinal cord.

Neurons:

The most basic unit of the nervous system is the nerve cell, also called a neuron.

Motor neurons conduct nerve impulses to the muscles from the central nervous system.

The Synapse is the communication site between two neurons or a neuron and a muscle or gland cell. This is the neuromuscular junction we talked about earlier, too.

The nerve cell comprises a cell body, dendrites, axon, and myelin sheath.

Two of the sensory structures that are most important in the exercise world are the muscle spindle and the Golgi’s tendon.

Muscle Spindle:

This stretch receptor is dispersed throughout most of the skeletal muscle within the body. They are specifically used to check changes in muscle length, particularly in rapid movements.

Muscle spindles contain specialized fibers that are known as intrafusal fibers.

Muscle spindles can inhibit a stretch reflex or myotatic.

Plyometric exercises take advantage of this reflex; using it will lead to more powerful concentric action.

Golgi Tendon Organ

This is located at the muscle junction and the tendon attaching the muscle to the bone. It is mainly used to prevent injuries.

Suppose the force of the muscle is great. In that case, it will lead to the Golgi tendon organ sending the information to the spinal cord, relaxing the acting muscle and stimulating the antagonistic muscle.

The Motor Unit

A motor unit consists of a motor neuron and all the muscle fibers it innervates.

The fibers in a motor unit are the same type.

Small muscles, like those of the fingers, have fewer fibers than large muscles, like the muscles in the thigh.

Gradation of Forces

The nervous system can vary produced forces of a muscle over a wide range of intensities.

Motor unit recruitment is used to do this. The nervous system can activate small, large, or multiple different motor units to provide the right intensity.

The size principle of motor unit recruitment states that the first motor units to be recruited are the smaller type I units. The next are type IIa and then type IIx.

The Skeletal System

Osteoporosis and Exercise

The bone is constantly being remodeled.

Osteoporosis means “porous bones.” This condition happens when the bones become weak and brittle, and the chance of breaking increases greatly. It can be prevented with proper nutrition.

Like our muscles, bone adapts to exercise by increasing mass and strength. Exercise-bearing weight and resistance exercise training are the best forms of exercise for increasing our bone mineral density.

Tendons and Ligaments

Both are made mainly from the inelastic protein collagen.

Ligaments are also formed from elastin. This allows them to stretch.

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Tyler Read - Certified Personal Trainer with PTPioneer

Tyler Read


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2 thoughts on “NSCA CPT Chapter 1 – Structure and function of the muscular, nervous, and skeletal systems”

  1. Hello Tyler

    I’ve been thinking about doing a personal training course for several years, but instead I studied biochemistry for 3 years. I didn’t make it through the 3rd year as I found the contents of the course were no longer suited to my ambitions for a career path. After I left, I have slowly gravitated back towards wanting to do personal training, but I have a lot of doubts. There are many organisations to choose from, and I don’t know which one would be suited for me. I’m also not sure how I to advance forward after obtaining the certification, and what potential in can lead onto in 5-10 years time.
    I get anxious and stressed when under a lot of pressure, especially with exams when I don’t feel prepared, and I find it easier to use visual studying materials along with text.
    I’m also worried that even if I do obtain the certification for becoming a personal trainer, that I may find that I don’t enjoy PT in the sense of a working environment. Do you have any good suggestions on how I can improve my confidence in choosing this career path? All I’ve got so far is looking at options for shadowing accomplished PT’s and observing their day-to-day work schedules.

    Thank you for taking the time to read this comment, and I hope to hear back from you soon

    Kind Regards
    Jordon Brown

    Reply
    • Hey Jordon,
      I definitely understand that changing career paths can be difficult. But if you are drawn towards personal training, that is definitely something that you should listen to. Personal training as a career is a fantastic option because you get to work in a very cool environment and help people at the same time. In terms of studying, I’d say just dive in. If you think about it too much you might never get right into the material. You won’t really know if you like personal training until you can work with clients. What I suggest you do is start studying, and ask your friends and family if they want free personal training session so that you can practice on them. This will give you a very good idea of whether or not you like the process of putting together a workout routine, teaching people and taking them through the routine etc. I really hope this helps and good luck with your career path, whatever it may be.

      Reply

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