Neuromuscular Junctions

An increase in the strength of a muscle’s contraction is necessary to perform a task. Subsequently, the brain increases the number of simultaneously active motor units within the muscle by a process known as the motor unit recruitment. Physical muscle movement in humans involves movement of fibers which are hundreds of cylindrically shaped cells bound together by connective tissue. It is essential for individuals, mainly professionals who work to promote health, to understand the mechanisms in the body. Resting skeletal muscles in vivo exhibit a phenomenon known as tonus, a constant state of slight tension that serves to maintain the muscle by motor centers in the brain and spinal cord. However, muscle

As we age, our brain and nervous system go through natural changes. An aging adult may experience memory loss, decreased touch sensation, change in the perception of pain, change in sleep pattern, decreased coordination and increased risk for infection (Ignatavicius, 2013, p. 912) .

Rationale, Significance and Hypothesis. An extrinsic factor, which exerts a dominant influence on skeletal muscle fiber phenotype, is the nervous system. Buller et al. (1960) elegantly demonstrated the plastic nature of skeletal muscle fibers in response to changes in innervation type. Later, Lφmo and Westgaard (Lφmo and Westgaard, 1974; Westgaard and Lφmo, 1988) demonstrated that depolarization of muscle with specific patterns and frequencies of electrical activity are sufficient to cause changes in mature muscle fiber phenotypes. However, how myofibrillar gene expression and structural organization is affected by the frequency of impulses during activity, the amount of activity over time, or other characteristics of patterned activity is essentially unknown. To answer these questions will require the isolation and study of subsets of muscle-specific proteins in relation to different electrical activation patterns in vivo, an issue that cannot be easily addressed in preparations currently used in the study of muscle development and maintenance. However, using novel in vivo approaches can, in part, circumvent this difficulty.

Each type of muscle fiber has a different power output. These fibers are fast-twitch, and slow-twitch muscle fibers. Fast-twitch fibers are used for explosive movements that are sustained for a short amount of time. While slow-twitch fibers are used for periods of time when movement is sustained for a long period. Slow-twitch fibers utilize aerobic beta-oxidation for energy. This means this type of muscle fiber uses fatty acids for energy and requires oxygen to break them down. This breakdown takes place within the mitochondria. Fast-twitch fibers get energy from anaerobic glycolysis. Meaning this fiber utilizes the breakdown of glucose without oxygen. Humans are born with these fibers in different proportions than others. Genetics determines the amount of each fiber a person will have, and these pre-genetically determined number of fibers will remain constant throughout a person’s life. Due to the different capabilities of each fiber, the amount of slow and fast-twitch fibers can determine the person’s capability. Therefore, those who have more fast-twitch fibers will jump higher than those with more slow-twitch fibers of the same stature. (BSC 228,

Motor Unit Recruitment - the successful activation of the same and more motor units with larger strength and voluntary muscle contraction

Within the last century, and even merely in the past decade, incredible advancements in technology have allowed modern medicine to rapidly progress to extraordinary levels, leaving scientists with unprecedented understanding of the human body, and of the aging process especially. While the field of gerontology has flourished as a result and knowledge of physiological changes in the aging body increased, scientists still only have a some-what fundamental understanding of the normal aging brain, and even less of abnormal age-related changes in the brain.

Actin and myosin filaments can be found in skeletal muscle and are the smallest units that form a sarcomere, which is the smallest contractile unit in muscle (Baechle, 2008). The Sliding Filament Theory states that the actin filaments slide inward on the myosin filaments, pulling on the boundaries of the sarcomere, causing it to shorten the muscle fiber, also known as a concentric muscular contraction (Baechle, 2008). The Sliding Filament Theory is composed of five steps: the “Resting Phase”, the “Excitation-Contraction Coupling Phase”, the “Contraction Phase”, the “Recharge Phase”, and the “Relaxation Phase” (Baechle, 2008). During the Resting Phase, the actin and myosin filaments are lined up with no cross-bridge binding of the two filaments. During the Excitation-Contraction Coupling Phase, Calcium is released from the sarcoplasmic reticulum and binds to troponin, causing a shift in tropomyosin where the binding cites are exposed (Baechle, 2008). When the binding cites are exposed, the myosin cross-bridge head attaches to actin. During the Contraction Phase, ATP bonds break, releasing energy that is used to allow the myosin head to flex, causing the actin filaments to move toward the M-bridge. During the Recharge Phase, there is a continuous repetition of the Excitation-Contraction Coupling Phase and the Contraction Phase in order to produce muscular

Under normal conditions, satellite cells are inactive, but become activated when there’s a serious injury, and when muscles lose their nerve supply. Satellite cells repair muscle fibres, but when they become old, they disrupt signals and skeletal muscle cannot be prepared and regenerated effectively. This results in muscle fibre degeneration, an increase in connective tissue between single muscle cells, and weakens the single muscle cell and neuromuscular junction connection (Tsitkanou, Della Gatta, Russell,

Our body has three muscle types, skeletal muscle , cardiac muscle, and smooth muscle. Each muscle has different functions within the body. Cardiac muscle is located in the heart and is responsible for pumping blood within the heart. Cardiac muscle is one of the two muscles with an activity that is non-voluntary meaning that signal from the motor neuron is not required for blood to pump through the heart. The second type of muscle is smooth muscle which is located in the intestines and responsible for moving food and regulating blood pressure(Freeman, 2011). Like cardiac muscle, smooth muscle also requires non-voluntary activity, where the signal from the motor neurons is not required for it to function properly. Lastly, the most important muscle in the neuromuscular junction, skeletal muscles. Skeletal muscle is attached to the bones through tendons composed of connective tissue and is responsible for moving the skeleton, however unlike the other two muscle types, skeletal muscle requires voluntary activity meaning that signal from the motor neurons is required (Ritchison, 2016). In this paper, I will be discussing the functions and parts of the neuromuscular

The muscle spindles and Golgi tendon organ are fundamental to the control of muscle length and tone. Any disturbance in the activity of these receptors may occur through shortened muscle length, intense work exercise and exercise to fatigue. This will likely result in an increase of motor neuron activity and motor unit recruitment. The relaxation phase of a muscle contraction is prolonged in a fatigued muscle, raising the likelihood of fused summation of action potentials if motor neuron activity muscle spindle and motor neuron activity by reflex inhabitation and afferent stimulation (Bentley, S, 1996). It has been documented that fatigue increases the afferent activity of the muscle spindle and decreases afferent activity of the Golgi tendon organ which, then may result in an increased alpha motor neuron activity. The uncontrolled firing of neurons on the muscle and the reduced relaxation of the muscle fibers leads to cramps (Schwellnus MP, 2010).

Aging is a part of life not everyone wants to accept. There are many theories on aging and I would like to focus on the Stochastic Theory. The Stochastic Theory is “based on random events that cause cellular damage that accumulates as the organism ages” (Grossman, S. & Lange, J., 2018, p. 55). Within this theory there are four categories but I am only going to focus on two: Wear and tear theory along with Connective tissue/cross-link theory.

The disease associated with aging of the muscles is called “Sarcopenia.” What this is according to, “Tae Nyun Kim and Kyung Mook,” Sarcopenia causes “Reductions in muscle mass and physical activity levels decrease total energy expenditures, which results in the accumulation of fat mass, especially visceral fat.” Which is the reduction of the muscle fibers.

Several cross-sectional, observational studies have related sarcopenia to decline of functional status, such as mobility performance, self-reported functional limitations, and disability, it is well established that the aging process itself is associated with numerous changes in the human body. One of the most significant age-related anatomical changes is that which happens to the skeletal muscle mass (Visser and Schaap, 2011).

According to our lecture, vision is restricted in old age. This is due to that fact that the lens becomes dull and thickens. The pupil becomes less reactive. Other medical issues can include cataracts and glaucoma. Cataracts is a medical condition in which the eye becomes progressively opaque, resulting in blurred vision. Glaucoma is an increase of pressure on the eyeball, causing gradual loss of sight. As for hearing, it can be damaged due to the small hairs within the cochlea. The elasticity of the tympanic membrane can also damage hearing. As for the sensory system, elderly often experience substantial decline in their ability to detect and discriminate touch stimuli. The age–related changed in prehension patterns (grip and pinch strength) and hand dexterity in the elderly population is most common. Deterioration in hand function is, to a large degree, secondary to degenerative changes in the musculoskeletal, vascular, and nervous systems. Deterioration of hand function is a combination of local structural changes (joint, muscle, tendon, bone, nerve receptors, blood supply, and skin) and more distant changes in neural

Craft, J Gordon, C 2011, ‘Alterations in neurological function across the life span’, in J Craft, C Gordon, A Tiziani (eds), Understanding pathophysiology, Elsevier Mosby, Chatswood, NSW, pp. 188-226.