We all know that calcium is essential for strong bones and teeth, but what else does it do? How about its critical roles in muscle contractions, nerve impulses, blood clotting, and cellular metabolism?
Recent research has even highlighted its role in weight management, controlling cholesterol and hypertension, along with reducing the risks of certain cancers. If you are a certified nutrition specialist , your clients will benefit wholeheartedly from more calcium in their diets.
Find out more of what calcium does, the recommended dietary intake, and the sources to get it below. Bones are continually remodeling, whether being broken down and going through resorption or being reformed with deposits of calcium Bone growth and density increases the most during childhood and adolescences when more bone is deposited than removed 1,2.
Most people have reached their bone mass peak by age 30, after that there is slightly more bone lost than gained during the remodeling process 1,2. Osteoporosis is when there is a decrease in bone mass and density, and the bones become porous and fragile This has a higher incidence in post menopausal women when estrogen and progesterone production declines, but can also be caused by low calcium and vitamin D intake, eating disorders, smoking, too much alcohol, and a lack of physical activity or bed-rest 1,3,4.
Developing and maintaining peak bone mass is key in preventing osteoporosis. Active women athletes should also be concerned with the female athlete triad, a syndrome of disordered eating, amenorrhea loss of normal menstrual cycle , and osteoporosis 1,2,5. It is not understood whether the physical opening of the L-type calcium channels or the presence of calcium causes the ryanodine receptors to open.
The outflow of calcium allows the myosin heads access to the actin cross-bridge binding sites, permitting muscle contraction. Excitation—contraction coupling is the connection between the electrical action potential and the mechanical muscle contraction. Excitation—contraction coupling is the physiological process of converting an electrical stimulus to a mechanical response. It is the link transduction between the action potential generated in the sarcolemma and the start of a muscle contraction.
Excitation-contraction coupling : This diagram shows excitation-contraction coupling in a skeletal muscle contraction. The sarcoplasmic reticulum is a specialized endoplasmic reticulum found in muscle cells. A neural signal is the electrical trigger for calcium release from the sarcoplasmic reticulum into the sarcoplasm. Each skeletal muscle fiber is controlled by a motor neuron, which conducts signals from the brain or spinal cord to the muscle. The area of the sarcolemma on the muscle fiber that interacts with the neuron is called the motor-end plate.
A small space called the synaptic cleft separates the synaptic terminal from the motor-end plate. Because neuron axons do not directly contact the motor-end plate, communication occurs between nerves and muscles through neurotransmitters.
Neuron action potentials cause the release of neurotransmitters from the synaptic terminal into the synaptic cleft, where they can then diffuse across the synaptic cleft and bind to a receptor molecule on the motor end plate. The motor end plate possesses junctional folds: folds in the sarcolemma that create a large surface area for the neurotransmitter to bind to receptors.
Acetylcholine ACh is a neurotransmitter released by motor neurons that binds to receptors in the motor end plate. Once released by the synaptic terminal, ACh diffuses across the synaptic cleft to the motor end plate, where it binds with ACh receptors. This reduces the voltage difference between the inside and outside of the cell, which is called depolarization. As ACh binds at the motor end plate, this depolarization is called an end-plate potential.
The depolarization then spreads along the sarcolemma and down the T tubules, creating an action potential. ACh is broken down by the enzyme acetylcholinesterase AChE into acetyl and choline. AChE resides in the synaptic cleft, breaking down ACh so that it does not remain bound to ACh receptors, which would cause unwanted extended muscle contraction.
Neural control initiates the formation of actin — myosin cross-bridges, leading to the sarcomere shortening involved in muscle contraction. These contractions extend from the muscle fiber through connective tissue to pull on bones, causing skeletal movement.
The pull exerted by a muscle is called tension. The amount of force created by this tension can vary, which enables the same muscles to move very light objects and very heavy objects. In individual muscle fibers, the amount of tension produced depends primarily on the amount of cross-bridges formed, which is influenced by the cross-sectional area of the muscle fiber and the frequency of neural stimulation.
Muscle tension : Muscle tension is produced when the maximum amount of cross-bridges are formed, either within a muscle with a large diameter or when the maximum number of muscle fibers are stimulated.
Muscle tone is residual muscle tension that resists passive stretching during the resting phase. The number of cross-bridges formed between actin and myosin determine the amount of tension that a muscle fiber can produce. Cross-bridges can only form where thick and thin filaments overlap, allowing myosin to bind to actin.
If more cross-bridges are formed, more myosin will pull on actin and more tension will be produced. Maximal tension occurs when thick and thin filaments overlap to the greatest degree within a sarcomere.
If a sarcomere at rest is stretched past an ideal resting length, thick and thin filaments do not overlap to the greatest degree so fewer cross-bridges can form. This results in fewer myosin heads pulling on actin and less muscle tension. As a sarcomere shortens, the zone of overlap reduces as the thin filaments reach the H zone, which is composed of myosin tails. Because myosin heads form cross-bridges, actin will not bind to myosin in this zone, reducing the tension produced by the myofiber.
If the sarcomere is shortened even more, thin filaments begin to overlap with each other, reducing cross-bridge formation even further, and producing even less tension. Conversely, if the sarcomere is stretched to the point at which thick and thin filaments do not overlap at all, no cross-bridges are formed and no tension is produced.
This amount of stretching does not usually occur because accessory proteins, internal sensory nerves, and connective tissue oppose extreme stretching. The primary variable determining force production is the number of myofibers long muscle cells within the muscle that receive an action potential from the neuron that controls that fiber. When using the biceps to pick up a pencil, for example, the motor cortex of the brain only signals a few neurons of the biceps so only a few myofibers respond.
In vertebrates, each myofiber responds fully if stimulated. On the other hand, when picking up a piano, the motor cortex signals all of the neurons in the biceps so that every myofiber participates.
This is close to the maximum force the muscle can produce. As mentioned above, increasing the frequency of action potentials the number of signals per second can increase the force a bit more because the tropomyosin is flooded with calcium.
Privacy Policy. Skip to main content. The Musculoskeletal System. Search for:. Muscle Contraction and Locomotion.
Structure and Function of the Muscular System The muscular system controls numerous functions, which is possible with the significant differentiation of muscle tissue morphology and ability. Learning Objectives Describe the three types of muscle tissue.
Key Takeaways Key Points The muscular system is responsible for functions such as maintenance of posture, locomotion, and control of various circulatory systems. We have selected 13 articles to present you with an overview of some noteworthy research of the year. A new model that describes the organization of organisms could lead to a better understanding of biological processes.
A new technique makes it possible to image the spatial structure of polysaccharides using a scanning tunnelling microscope. Homepage Newsroom From the Institutes Muscle cells need calcium ions.
Muscle cells need calcium ions Structural analysis for a ryanodine receptor 1 gain insight into calcium release during muscle contraction. March 13, Structural Biology. Importantly, compared to the previously reported structures of RyR1 which were extracted from the cells, current structures are determined in native membranes of sarcoplasmic reticulum making them more physiologically relevant.
Other Interesting Articles. Molecular mechanisms of corona drug candidate Molnupiravir unraveled August 16, Eukaryotic Cells. Cell Energy and Cell Functions.
Photosynthetic Cells. Cell Metabolism. The Origin of Mitochondria. Mitochondrial Fusion and Division. The Origin of Plastids. The Origins of Viruses. Discovery of the Giant Mimivirus. Volvox, Chlamydomonas, and the Evolution of Multicellularity. Yeast Fermentation and the Making of Beer and Wine. Dynamic Adaptation of Nutrient Utilization in Humans. Nutrient Utilization in Humans: Metabolism Pathways. An Evolutionary Perspective on Amino Acids.
Mitochondria and the Immune Response. Stem Cells in Plants and Animals. Promising Biofuel Resources: Lignocellulose and Algae. The Discovery of Lysosomes and Autophagy. The Mystery of Vitamin C. Krans, Ph. Citation: Krans, J. Nature Education 3 9 How do muscles contract? What molecules are necessary for a tissue to change its shape?
Aa Aa Aa. Muscle is a specialized contractile tissue that is a distinguishing characteristic of animals. Changes in muscle length support an exquisite array of animal movements, from the dexterity of octopus tentacles and peristaltic waves of Aplysia feet to the precise coordination of linebackers and ballerinas.
What molecular mechanisms give rise to muscle contraction? The process of contraction has several key steps, which have been conserved during evolution across the majority of animals. What Is a Sarcomere? Figure 1: A gastrocnemius muscle calf with striped pattern of sarcomeres. The view of a mouse gastrocnemius calf muscle under a microscope.
The Sliding Filament Theory. Figure 2: Comparison of a relaxed and contracted sarcomere. A The basic organization of a sarcomere subregion, showing the centralized location of myosin A band.
Figure 3: The power stroke of the swinging cross-bridge model, via myosin-actin cycling. Actin red interacts with myosin, shown in globular form pink and a filament form black line. Figure 4: Illustration of the cycle of changes in myosin shape during cross-bridge cycling 1, 2, 3, and 4. ATP hydrolysis releases the energy required for myosin to do its job. What Regulates Sarcomere Shortening? Figure 5: Troponin and tropomyosin regulate contraction via calcium binding.
Simplified schematic of actin backbones, shown as gray chains of actin molecules balls , covered with smooth tropomyosin filaments. Unresolved Questions. Muscle contraction provides animals with great flexibility, allowing them to move in exquisite ways. The molecular changes that result in muscle contraction have been conserved across evolution in the majority of animals.
By studying sarcomeres, the basic unit controlling changes in muscle length, scientists proposed the sliding filament theory to explain the molecular mechanisms behind muscle contraction. Within the sarcomere, myosin slides along actin to contract the muscle fiber in a process that requires ATP. Scientists have also identified many of the molecules involved in regulating muscle contractions and motor behaviors, including calcium, troponin, and tropomyosin.
This research helped us learn how muscles can change their shapes to produce movements. References and Recommended Reading Clark, M.
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