Skeletal Muscles and Synovial Joints – Understanding Lever Systems in Human Movement

Skeletal Muscles and Synovial Joints – Understanding Lever Systems in Human Movement

Skeletal muscles, when acting across synovial joints, function as lever systems to facilitate movement. These systems are composed of three main components: the fulcrum (the joint), the effort (the force applied by the muscle), and the load (the resistance or weight to be moved). The arrangement of these components classifies levers into three types: first, second, and third-class levers.

First-Class Levers

First-class levers have a seesaw-like construction supporting the load and the fulcrum; thus, the effort is between those two points. The atlanto-occipital joint, located in the neck directly behind the skull, is one example in the human body. In this case, the force is applied at the joint, the load is the head’s weight, and the effort uses the neck muscles to apply the force. Additionally, it permits the head to move up and down, similar to this lever configuration. (McCuller et al., 2023).

Second-Class Levers

Comparable to a wheelbarrow, second-class levers place the burden between the fulcrum and the effort. The human body’s response to this is demonstrated by the way the calf muscles contract during plantar flexion, which is similar to tiptoeing. The gastrocnemius muscle exerts effort, the body’s weight acts as the load, and the foot’s ball acts as the fulcrum. With this arrangement, strong motions require less work.

Third-Class Levers

Third-class levers, with the effort positioned between the fulcrum and the load, are the most common type of levers found in the human body. A third-class lever, for instance, is the biceps brachii muscle, which contracts to flex the elbow. The forearm and hand carry the weight, the elbow joint acts as the fulcrum, and the biceps muscle exerts the effort. This arrangement enables quick and wide movement.

Nervous System Descriptions

Somatic Nervous System

Skeletal muscle is innervated by the somatic nervous system, which in turn regulates voluntary motions. It consists of motor neurons, which allow gestures like walking and speaking by sending information from the central nervous system to the muscles. (Waxenbaum et al., 2023). It also comprises sensory neurons that relay information from sensory receptors to the brain and spinal cord.

Autonomic Nervous System – Sympathetic

The sympathetic nervous system is responsible for the ‘fight or flight’ response, preparing the body to respond to stress by increasing heart rate, dilating airways, and inhibiting digestion. It mobilizes energy resources for rapid and intense physical activity.

Autonomic Nervous System – Parasympathetic

The parasympathetic nervous system promotes the ‘rest and digest’ state. It conserves energy by slowing the heart rate, stimulating digestion, and facilitating relaxation. This system helps maintain homeostasis during restful periods (Tindle & Tadi, 2022).

Enteric Nervous System

The second brain,’ the enteric nerve system, regulates digestion independently. It consists of a network of neurons buried in the walls of the gastrointestinal tract and controls blood flow, peristalsis, and the release of enzymes without the help of the central nervous system.

Autonomic Nervous System – Visceral

Internal organs are innervated by sympathetic and parasympathetic fibers, which are part of the visceral component of the autonomic nervous system. To preserve internal equilibrium, these fibers control involuntary processes like heart rate, breathing rate, and smooth muscle contraction.

References

McCuller, C., Jesus, R., & Callahan, A. L. (2023, July 30). Physiology, Skeletal Muscle. PubMed; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK537139/

Tindle, J., & Tadi, P. (2022, October 31). Neuroanatomy, Parasympathetic Nervous System. PubMed; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK553141/

Waxenbaum, J. A., Varacallo, M., & Reddy, V. (2023). Anatomy, Autonomic Nervous System. Nih.gov; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK539845/

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Describe how skeletal muscles acting across synovial joints function as a lever system. Discriminate between 1st-class, 2nd-class, and 3rd-class levers in the human body (provide an example of each)

please describe the following in your own words:

Somatic nervous system
Autonomic – sympathetic
Autonomic – parasympathetic
Enteric nervous system
Autonomic – visceral