Most of the fibers will be sectioned at angles or will be difficult to get into a single plane of focus, but a little bit of searching can usually turn up some with all of the defining characteristics visible.
Skip to main content. Module 5: Microscopy II — Tissues. Search for:. Lab 5 Exercises 5. List the defining visual characteristics of that type of muscle, and draw arrows to features on the photograph that illustrate each characteristic. Licenses and Attributions. Content on this website is provided for information purposes only. Information about a therapy, service, product or treatment does not in any way endorse or support such therapy, service, product or treatment and is not intended to replace advice from your doctor or other registered health professional.
The information and materials contained on this website are not intended to constitute a comprehensive guide concerning all aspects of the therapy, product or treatment described on the website. All users are urged to always seek advice from a registered health care professional for diagnosis and answers to their medical questions and to ascertain whether the particular therapy, service, product or treatment described on the website is suitable in their circumstances.
The State of Victoria and the Department of Health shall not bear any liability for reliance by any user on the materials contained on this website. Skip to main content. Bones muscles and joints. Home Bones muscles and joints. Actions for this page Listen Print. Summary Read the full fact sheet. On this page. Different types of muscle Make-up of muscle The neuromuscular system Shapes of skeletal muscle Muscle disorders Where to get help Things to remember.
There are about muscles in the human body. Muscles have a range of functions from pumping blood and supporting movement to lifting heavy weights or giving birth.
Muscles work by either contracting or relaxing to cause movement. This movement may be voluntary meaning the movement is made consciously or done without our conscious awareness involuntary. Glucose from carbohydrates in our diet fuels our muscles. Shivering is an involuntary contraction of skeletal muscles in response to lower than normal body temperature. The muscle cell, or myocyte, develops from myoblasts derived from the mesoderm.
Myocytes and their numbers remain relatively constant throughout life. Skeletal muscle tissue is arranged in bundles surrounded by connective tissue.
Under the light microscope, muscle cells appear striated with many nuclei squeezed along the membranes. The striation is due to the regular alternation of the contractile proteins actin and myosin, along with the structural proteins that couple the contractile proteins to connective tissues. The cells are multinucleated as a result of the fusion of the many myoblasts that fuse to form each long muscle fiber.
Cardiac muscle forms the contractile walls of the heart. The cells of cardiac muscle, known as cardiomyocytes, also appear striated under the microscope. Unlike skeletal muscle fibers, cardiomyocytes are single cells with a single centrally located nucleus.
A principal characteristic of cardiomyocytes is that they contract on their own intrinsic rhythm without external stimulation. Cardiomyocytes attach to one another with specialized cell junctions called intercalated discs. Intercalated discs have both anchoring junctions and gap junctions. Attached cells form long, branching cardiac muscle fibers that act as a syncytium, allowing the cells to synchronize their actions.
The cardiac muscle pumps blood through the body and is under involuntary control. Smooth muscle tissue contraction is responsible for involuntary movements in the internal organs.
When a motor neuron receives a signal from the brain, it stimulates all of the muscles cells in its motor unit at the same time. The size of motor units varies throughout the body, depending on the function of a muscle. Muscles that need a lot of strength to perform their function—like leg or arm muscles—have many muscle cells in each motor unit.
One of the ways that the body can control the strength of each muscle is by determining how many motor units to activate for a given function. This explains why the same muscles that are used to pick up a pencil are also used to pick up a bowling ball. Muscles contract when stimulated by signals from their motor neurons.
Motor neurons release neurotransmitter chemicals at the NMJ that bond to a special part of the sarcolemma known as the motor end plate. The motor end plate contains many ion channels that open in response to neurotransmitters and allow positive ions to enter the muscle fiber.
The positive ions form an electrochemical gradient to form inside of the cell, which spreads throughout the sarcolemma and the T-tubules by opening even more ion channels. Tropomyosin is moved away from myosin binding sites on actin molecules, allowing actin and myosin to bind together. ATP molecules power myosin proteins in the thick filaments to bend and pull on actin molecules in the thin filaments. Myosin proteins act like oars on a boat, pulling the thin filaments closer to the center of a sarcomere.
As the thin filaments are pulled together, the sarcomere shortens and contracts. Myofibrils of muscle fibers are made of many sarcomeres in a row, so that when all of the sarcomeres contract, the muscle cells shortens with a great force relative to its size. Muscles continue contraction as long as they are stimulated by a neurotransmitter. When a motor neuron stops the release of the neurotransmitter, the process of contraction reverses itself.
Calcium returns to the sarcoplasmic reticulum; troponin and tropomyosin return to their resting positions; and actin and myosin are prevented from binding. Sarcomeres return to their elongated resting state once the force of myosin pulling on actin has stopped.
Certain conditions or disorders, such as myoclonus, can affect the normal contraction of muscles. You can learn about musculoskeletal health problems in our section devoted to diseases and conditions. Also, learn more about advances in DNA health testing that help us understand genetic risk of developing early-onset primary dystonia. A single nerve impulse of a motor neuron will cause a motor unit to contract briefly before relaxing.
This small contraction is known as a twitch contraction. If the motor neuron provides several signals within a short period of time, the strength and duration of the muscle contraction increases.
This phenomenon is known as temporal summation. If the motor neuron provides many nerve impulses in rapid succession, the muscle may enter the state of tetanus, or complete and lasting contraction. A muscle will remain in tetanus until the nerve signal rate slows or until the muscle becomes too fatigued to maintain the tetanus. Not all muscle contractions produce movement. Isometric contractions are light contractions that increase the tension in the muscle without exerting enough force to move a body part.
When people tense their bodies due to stress, they are performing an isometric contraction. Holding an object still and maintaining posture are also the result of isometric contractions. A contraction that does produce movement is an isotonic contraction.
Isotonic contractions are required to develop muscle mass through weight lifting. Muscle tone is a natural condition in which a skeletal muscle stays partially contracted at all times.
0コメント