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Two Questions! The first image belongs to the first question, and the next three images belong to the second question.

FIG. 37.9 How does filament overlaD affect force generation in muscles? 100 BACKGROUND From the 1930s through the 1960s, British muscle physiologists studied the properties of striated frog muscle fibers In the first set of experiments, A. V. Hill examined how a muscles shortening velocity affects its force production. In the second set of studies, American physiologists Albert Gordon and Fred Julian, together with British physiologist Andrew Huxley, studied how a muscles length when it contracts affects the muscles force- generating ability 40 20 1.27 1.67 2.0 2.25 3.65 1.0 1.5 2.0 2.5 3.0 3.5 Sarcomere length (um) HYPOTHESIS Gordon, Huxley, and Julian hypothesized that changes in overlap between myosin and actin affect the number of cross-bridges and thus the force the muscle can produce 100 EXPERIMENT The three scientists isolated a single muscle fiber and used optical microscopy to measure sarcomere length. They kept this length constant while the fiber was stimulated to produce force. Measurements of force were then obtained at different sarcomere lengths. The length at which the muscle fiber generated maximum force is indicated on the graphs as 100%. Other lengths are expressed relative to this length 80 60 40 20 RESULTS The top graph shows the data obtained by Gordon, Huxley, and Julian, and the bottom graph reinterprets their data in terms of force and percent of muscle length. Their experiments showed that the muscle fiber produced maximal force at an intermediate sarcomere length (approximately 2.3 m). At this length, the greatest number of cross-bridges were hypothesized to form, generating maximal force. As the sarcomere length was decreased or stretched, and the sarcomere then stimulated to contract, force declined. These results were consistent with a decrease in the number of cross-bridges that could form as a result of decreased actin-myosin overlap 40 60 80 100 120 140 160 Percent of muscle length FOLLOW-UP WORK Other studies confirmed that changes in myosin cross-bridge formation are linked to changes in actin and myosin filament overlap at different sarcomere lengths, supporting the sliding filament model of muscle contraction SOURCE Gordon, A. M., A. F. Huxley, and F. J. Julian. 1966. The Variation in Isometric Tension with Sarcomere Length in Vertebrate Muscle Fibres. Journal of Physiology 184:170-192Question 8 of 9 A muscles force depends on the total cross-sectional area of all fibers within it that are activated to contract. As shown in Fig. 37.9, if maximum isometric force produced by a muscle (at 100%) is 25 N/mm2, how much force would a muscle produce that has 1 cm2 in cross-section of actively contracting fibers? O B. 250 N C. 2500 N D. 10 N E. None of the other answer options are correct. Submit

Background As discussed in Chapter 36, the somatosensory cortex is responsible for processing touch stimuli. If someone were tickling the bottom of your foot, mechanoreceptors in the skin of your foot would fire action potentials. These signal:s would ultimately be relayed to the somatosensory cortex portion of your brain, and then your motor cortex. Following this chain of events, you might quickly move your foot away from the tickler. If you were to take a cross section of the somatosensory cortex, you would find that neurons are arranged in six distinct layers; the first layer is composed of superficial neurons located near the brain surface, and the sixth layer is composed of the deepest neurons (that is, those closest to the white matter). How are neurons that respond to touch stimuli organized in the somatosensory cortex? Do neurons in the six different layers of the somatosensory cortex respond to different types of stimuli? Hypothesis Vernon Mountcastle hypothesized that researchers could create a diagram of the somatosensory cortex by tracking which neurons responded to different types of touch stimuli. Experiment Mountcastle exposed cats to two types of stimuli: (1) cutaneous or superficial stimuli, which included touching hairs or touching the skin, and (2) deep stimuli, which included bending and extending joints or touching the connective tissue surrounding muscles. He was able to track which neurons in the somatosensory cortex fired action potentials in response to these two types of stimuli, and measured their firing rates (Figure 1).

Cutaneous stimuli Deep stimuli Skin touched Hair touched Bend/unbend joint Electrode Sensorimotor cortex Record action potentials fired by different neurons Figure 1 Results Mountcastle determined that neurons involved in processing the same type of stimuli are organized in vertical columns (Figure 2). These columns are composed of cells belonging to the different layers of the somatosensory cortex. These results demonstrated that just because a neuron responds to deep stimuli does not mean that this neuron will be found deep within the brain; similarly, a neuron that responds to cutaneous stimuli will not necessarily be located near the brain surface. In addition to identifying vertical columns of neurons, Mountcastle also determined that these columns are arranged in a mosaic pattern in the somatosensory cortex. Columns composed of neurons responding to deep stimuli occur side-by-side with columns composed of neurons responding to cutaneous stimuli.

Source Mountcastle, V. B., 1957. Modality and topographic properties of single neurons of cats somatic sensory cortex. J Neurophysiol. 20: 408-34. Brain surface Brain interior Neurons responding to deep stimuli Neurons responding to cutaneous stimuli Figure 2

Mountcastle noted that within the somatosensory cortex, neurons that respond to the same type of stimulus (deep versus cutaneous) are arranged in vertical columns. One way Mountcastle discovered this vertical arrangement was by inserting a measuring device (to record action potentials) into the somatosensory cortex at different angles. This approach is depicted in Figure 3 below. Which of the following statements is true regarding measuring devices that were inserted into the brain at angles of 45° and 90°? Brain surface 45° Brain surface 90° Brain interior Brain interior Figure 3 A. The measuring device inserted into the brain at a 90° angle wil likely encounter neurons belonging to the same vertical column B. The measuring device inserted into the brain at a 45° angle will likely encounter neurons that belong to different vertical columns. C. All of the neurons encountered by the measuring device inserted into the brain at a 90% angle will likely respond to the same type of stimuli D. Neurons encountered by the measuring device inserted into the brain at a 45° angle will likely respond to different types of stimuli. OE. All of the choices are correct

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