This paper provides a structured overview of the anatomy and physiology of the human skeletal and muscular systems, along with selected disorders associated with each. The skeletal system is examined in terms of its structural components — including bones, cartilage, tendons, and ligaments — its physiological roles such as homeostasis and blood cell production, and the clinical significance of bone fractures. The muscular system is then analyzed through its three muscle types — skeletal, smooth, and cardiac — their respective functions, and amyotrophic lateral sclerosis (ALS) as a major muscular disorder. The paper concludes by emphasizing the inextricable interdependence of the two systems as a unified musculoskeletal framework.
Human health is being threatened on multiple fronts, and it is not surprising that there is growing interest in developing a better understanding of the human body's various systems and the respective roles they play in maintaining good health. Some people may intuitively recognize the importance of the skeletal and muscular systems to human health, but far too few understand the fundamental anatomy and physiology of these systems. The purpose of this paper is to provide a discussion of the anatomy and physiology of the skeletal and muscular systems in the human body, as well as selected disorders associated with those systems.
Although the human skeletal system is widely regarded as a static structure that provides the human body with structural support only, the bones that make up the skeletal system also function as organs. The other organs that comprise the skeletal system include cartilage, tendons, and ligaments (Cowen & Kahai, 2021). Comprised mainly of water and collagen, cartilage is a durable, smooth substance that prevents individual bones from rubbing against each other by coating the ends of bones (Anatomy of the joints, 2007). Similarly, tendons and ligaments are situated proximately to joints and support individual bones while facilitating the movement of joints (Anatomy of the joints, 2007). While tendons are comprised of fibrous cords that serve as connection points for bones and muscles, ligaments are strong tissues that connect bones to each other at joints (Anatomy of the joints, 2007).
The skeletal system provides a number of physiologically essential features for the human body. These critical features include defining the body's overall shape, maintaining homeostasis, facilitating breathing and locomotion, serving as a protective framework for internal vital organs, and generating the blood cells that are essential for life (Cowen & Kahai, 2021). It is also noteworthy that despite their rigid and static appearances, bones continue to grow and experience biological and structural changes throughout the human lifecycle in response to the demands placed on the body (Cowen & Kahai, 2021).
The human skeletal system is divided into two main parts: (1) the axial skeleton and (2) the appendicular skeleton (Docherty, 2007). The axial skeleton provides the physical structure for the human body's central axis, while the appendicular skeleton is comprised of the bones in the lower and upper limbs as well as the pelvis and shoulders (Human skeletal system, 2022). The 206 total bones contained in these two main parts of the skeletal system are not impervious to injury, however, as noted below.
Bone fractures exist along a continuum ranging from simple fractures that can be treated with supportive interventions — such as reduction (lining the fractured bones up so they heal properly) and placing the fracture in a splint or cast — to complicated fractures that may require surgical interventions in order to repair the damage to the maximum extent possible (Cowan & Kahai, 2022). In any event, bone fractures represent major disorders that can adversely affect the skeletal system in ways that diminish quality and length of human life (Cowan & Kahai, 2022).
Given the major impact that bone fractures can have on the entire body, orthopedists are keenly interested in identifying the most efficacious interventions. A retrospective study of 88 pediatric patients with bone fractures was conducted by Abdelgawad et al. (2013) to determine how long internal reductions were required, since casting for these patients was impracticable. The results showed that although all 20 fractures healed successfully, the average healing time varied depending on the number of fractures involved — ranging from 6.7 weeks for two fractures, 9.3 weeks for three fractures, and 13.3 weeks for four fractures (Abdelgawad et al., 2013). These findings indicate that not only does the severity of the fracture itself affect healing rates, but the number of fractures does as well.
The human skeletal system would be a purely static structural framework without the muscular system. Although they differ in their physiology, the fibrous tissues that comprise human muscles are generally strong and function in pairs through flexion and contraction to generate movement in joints (Anatomy of the joints, 2007). Because different muscles perform different functions in the human body, they do not share the same type of structures. The three kinds of muscles in the human muscular system are: (1) skeletal muscles, (2) smooth muscles, and (3) cardiac muscles (Robertson, 2015).
Skeletal muscles stretch and contract in order to support the human body and facilitate locomotion as well as other bodily movements; their operation is voluntary. However, they are vulnerable to easy fatigue, owing to the fact that skeletal muscles contain large numbers of blood vessels and nerves, which are only designed to function for comparatively short periods of time (Robertson, 2015). In other words, skeletal muscles help people walk, run, jump, reach for things, and generally navigate their surroundings.
In contrast to skeletal muscles, smooth muscles are located throughout the body in positions other than the heart and are termed "smooth" to differentiate them from skeletal muscles' striated appearance. Although smooth muscles are not as powerful as skeletal muscles, they do not require the same level of strength, since their primary function is to move foods and fluids through the digestive system (Robertson, 2015). In sharp contrast to both skeletal and smooth muscles, cardiac muscles never completely fatigue until death, when they cease powering the heart's blood-pumping action. In appearance, cardiac muscles resemble striated skeletal muscles (Robertson, 2015).
The malleability of skeletal muscle tissues is controlled by muscle protein synthesis and the corresponding rate of breakdown (Smeets et al., 2019). Research to date indicates that the balance of protein synthesis and breakdown rates of skeletal muscle plasticity ranges between 0.02 and 0.09% per hour, but there is a clear need for additional research in this area to more precisely define these breakdown rates (Smeets et al., 2019).
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease and motor neurone disease, is a neurodegenerative disease that results in the loss of control over the muscular system. The cause or causes of ALS remain undetermined, although genetics and various environmental factors are believed to be involved (Riancho et al., 2021). This disorder is essentially incurable at present, although there are some proven rehabilitative and palliative care steps that can help sufferers retain their quality of life for as long as possible (Riancho et al., 2021).
"How both systems work together"
The human body's skeletal and muscular systems are highly complex, mutually dependent systems. The muscular and skeletal systems would be essentially worthless without each other: the former provides the physical power needed for movement and for keeping the heart beating, while the latter provides the structural architecture that the muscular system requires to operate and that protects it and other internal organs. Although the integumentary and nervous systems are likewise essential components of the human body, the musculoskeletal system provides the framework that is needed for all of these systems to function in tandem to maintain homeostasis and human health.
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