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Chapter Goals:
- Outline the basic structure and function of the nervous system.
- Classify the bone and joint types and their associated functions.
- Make a summary of the structure and function of the muscular system.
- Be able to identify the effects exercise has on each of the components of the human movement system.
Introduction to the Human Movement System
Human movement is accomplished through the functional integration of the nervous, skeletal, and muscular systems. These systems work interdependently with each other and produce human movement altogether.
If one component is not working right, it will affect the other systems and ultimately affect movement in general.
Expectations for the Fitness Professional
The trainer must have a working knowledge of anatomy and physiology to give an accurate fitness assessment, program safe exercise, and answer clients’ questions about their fitness program.
Nervous System
This specialized network of nerves transmits information throughout the body. It provides sensory information, stimulates movement, and keeps the heart and organs working.
Anatomy of the Nervous System
This is one of the many organ systems in the body that is made of a network of specialized cells called neurons that will transmit and coordinate signals, giving a communication network in the body.
Neurons are made up of three parts:
- The cell body
- The axon
- Dendrites
Central and Peripheral Nervous Systems
The nervous system is made of two divisions: the central and the peripheral nervous systems. The central nervous system comprises the brain and the spinal cord. The rest of the nervous system is the peripheral nervous system.
The PNS can be divided further down into the somatic and the autonomic nervous systems.
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Functions of the Nervous System
The three main functions of the nervous system are sensory, integrative, and motor functions.
Mechanoreceptors are important to grasp for the sake of physical activity knowledge.
Muscle spindles are the sensory receptors in the muscles that run parallel to the muscle fibers and are sensitive to changes in the muscle length and the rate of those changes.
Golgi tendon organs are specialized sensory receptors that are in the area where the skeletal muscle fibers insert into the tendons of skeletal muscles.
Joint receptors are in the joint capsule and respond to the joint’s pressure, acceleration, and deceleration.
Nervous System Life Course
The nervous system is constantly developing from birth all the way to older adulthood. Humans also always learn throughout life, but our physical and cognitive abilities decline as we age.
Physical Activity and the Nervous System
The development of motor skills is understood best by considering a 3 step process:
- First, the client is learning a new skill. They understand the goals of the skill and develop strategies for developing movement and can perform the skill, but with inconsistent performance.
- Second, the client starts to understand the skill. Through practice, the skill is refined, and the skill is done with much less error.
- Third, we have the mastering the skill. It is done without error for the majority of attempts.
Skeletal System
The system serves many vital functions. It gives our bodies the shape it has, supports and protects the internal organs, creates movement, makes blood for the body, and stores necessary minerals to function.
Division of the Skeletal System
This is going to be divided into the axial and appendicular skeleton. The axial skeleton consists of the skull, rib cage, and vertebral column. The appendicular skeleton is made of around 126 bones in total.
Bones
These have two vital functions to perform. They act as levers where the muscles attach and give a place for the muscle to pull against and then produce movement. The second function is to provide support for the body.
The types of bones we have are long, short, flat, irregular, and sesamoid.
There are many important bone markings to note that have necessary functions for the movements we go through.
Joints
These joints are formed where one bone articulates with another. They are categorized based on shape, structure, and function.
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The movements that joints can produce are rolling, sliding, and spinning.
Joints are often classified as synovial, nonaxial, condyloid, hinge, saddle, pivot, ball-and-socket, and nonsynovial.
Synovial joints are the most common when discussing the human movement. Synovial joints are unique because they create synovial fluid.
Joints serve many functional requirements for the musculoskeletal system. One of the main functions is to allow for motion and movement of the body. They also work to provide stability.
Ligaments are fibrous tissues that connect the bones to other bones, providing stability both statically and dynamically. They also work to give sensory input and that aids our proprioception.
Skeletal System Life Course
In the course of a normal childhood and adolescence, the skeletal system will go through many changes. While aging, the bones get longer due to the growth plate.
Exercise plays a significant role in bone mass. Specifically, resistance and weight-bearing exercise give the greatest benefits to the bones.
Muscular System
The muscular system links the nervous and the skeletal systems, which generate forces to move the human body. Muscles will contract to create internal tensions, and the nervous system will manipulate the bones and move around the joints.
There are three types of muscles in the body. The types are skeletal, cardiac, and smooth.
The Structure of the Skeletal Muscle
Skeletal muscles are made up of muscle fibers that are held in by connective tissues. They are used for contracting and giving way to movement. They also assist with things like homeostasis by way of producing heat.
We can also break down the muscles into layers.
The first layer is the fascia. The fascicles make up this fascia. And then, the fascicles comprise individual muscle fibers, which are bundled together by the endomysium.
Muscle Fiber and Their Contractile Elements
In the endomysium of the fascicles, the individual fibers are closed in their own membrane, which is called the sarcolemma. It is important to know the breakdown of myofibrils as they are laid out in the figures throughout this chapter.
Skeletal muscles will not contract at all unless the motor neurons are stimulated to do so. This requires a link between the nervous system and the muscular system.
A motor unit is made up of a motor neuron and the muscle fibers that it innervates.
The action potential is a nerve impulse that is relayed from the central nervous system, through the peripheral nervous system and into the muscle across the neuromuscular junction.
Sliding Filament Theory
This theory describes muscle contractions through the shortening of the sarcomeres.
The steps here are:
- The nerve impulse begins in the CNS and travels down the motor neuron, which is facilitated by sodium and potassium electrolytes, to the neuromuscular junction.
- Acetylcholine is released into the neuromuscular junction, which then helps the nerve impulse across the synapse into the muscle.
- The nerve impulse travels into the muscle infrastructure, stimulating a small organ called the sarcoplasmic reticulum to release the electrolyte calcium.
- Calcium is then released into the muscle, stimulating a chain of events that results in the myosin heads binding to actin.
- The myosin heads then pull the actin toward the sarcomere center, which slides the overlapping filaments past each other, shortening the entire muscle.
The all or nothing principle describes how muscle contraction and force work. So, the theory shows that muscle fibers contract with all the force possible, or they do not contract at all.
Our muscles can be of different types.
Type one muscle fibers contract slowly and generate only a little force. This is important in times when we need to use the muscles for a long time, like running or just standing.
Type two muscle fibers are the fibers that generate force quicker and more powerfully than the small motor units of type one.
The type two muscle fibers are actually larger than the type one fiber.
Muscular System Life Course
From childhood to adolescence and then to adulthood, the muscular system is always growing and changing, with the peak in mass, strength, and power occurring around 20 and 30 years of age.
After age 50, we lose around 1 – 2 percent of our strength. Resistance training is ideal to pursue to slow down this process.
Tyler Read
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