Answer:
nucleus
Explanation:
The nucleus contains the cell 's DNA and directs the synthesis of ribosomes and proteins.
Unlike other dna, mitochondrial dna is circular
Sound waves enter the external ear and are funneled toward the tympanic membrane by the shape of the outer ear.Variation in air pressure due to sound waves causes the tympanic membrane to vibrate. The wave frequency will determine the vibration rate.Tympanic vibrations cause the malleus to move. Because the three ossicles are connected, this vibration is transduced to the stapes via the incus.Movement of the stapes vibrates the oval window. Significant amplification of sound waves occurs due to the small size of the window.Pressure changes transduced through the oval window vibrate the perilymph in the scala vestibuli which are transmitted across the vestibular membrane to the endolymph of the cochlear duct, and also up the scala vestibuli and down the scala tympani much the way <span>waves move through the ocean.</span>
Answer:
Technology that uses living organisms
Explanation:
<h3>By the end of this section, you will be able to:</h3><h3 /><h3>Classify the different types of muscle tissue</h3><h3>Explain the role of muscles in locomotion</h3><h3>Muscle cells are specialized for contraction. Muscles allow for motions such as walking, and they also facilitate bodily processes such as respiration and digestion. The body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle (Figure 19.33).</h3><h3>Figure_38_04_01</h3><h3>Figure 19.33. The body contains three types of muscle tissue: skeletal muscle, smooth muscle, and cardiac muscle, visualized here using light microscopy. Smooth muscle cells are short, tapered at each end, and have only one plump nucleus in each. Cardiac muscle cells are branched and striated, but short. The cytoplasm may branch, and they have one nucleus in the center of the cell. (credit: modification of work by NCI, NIH; scale-bar data from Matt Russell)</h3><h3>Skeletal muscle tissue forms skeletal muscles, which attach to bones or skin and control locomotion and any movement that can be consciously controlled. Because it can be controlled by thought, skeletal muscle is also called voluntary muscle. Skeletal muscles are long and cylindrical in appearance; when viewed under a microscope, skeletal muscle tissue has a striped or striated appearance. The striations are caused by the regular arrangement of contractile proteins (actin and myosin). Actin is a globular contractile protein that interacts with myosin for muscle contraction. Skeletal muscle also has multiple nuclei present in a single cell.</h3><h3>Smooth muscle tissue occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels. Smooth muscle has no striations, is not under voluntary control, has only one nucleus per cell, is tapered at both ends, and is called involuntary muscle.</h3><h3>Cardiac muscle tissue is only found in the heart, and cardiac contractions pump blood throughout the body and maintain blood pressure. Like skeletal muscle, cardiac muscle is striated, but unlike skeletal muscle, cardiac muscle cannot be consciously controlled and is called involuntary muscle. It has one nucleus per cell, is branched, and is distinguished by the presence of intercalated disks.</h3><h3>Skeletal Muscle Fiber Structure</h3><h3 /><h3>Each skeletal muscle fiber is a skeletal muscle cell. These cells are incredibly large, with diameters of up to 100 µm and lengths of up to 30 cm. The plasma membrane of a skeletal muscle fiber is called the sarcolemma. The sarcolemma is the site of action potential conduction, which triggers muscle contraction. Within each muscle fiber are myofibrils—long cylindrical structures that lie parallel to the muscle fiber. Myofibrils run the entire length of the muscle fiber, and because they are only approximately 1.2 µm in diameter, hundreds to thousands can be found inside one muscle fiber. They attach to the sarcolemma at their ends, so that as myofibrils shorten, the entire muscle cell contracts (Figure 19.34).</h3><h3>Figure_38_04_02</h3><h3>Figure 19.34. A skeletal muscle cell is surrounded by a plasma membrane called the sarcolemma with a cytoplasm called the sarcoplasm. A muscle fiber is composed of many fibrils, packaged into orderly units.</h3><h3>The striated appearance of skeletal muscle tissue is a result of repeating bands of the proteins actin and myosin that are present along the length of myofibrils. Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell causes the entire cell to appear striated or banded.</h3>