2. Robert McNeil Alexander (British Zoologist, 1934-2016) described the crimp pattern (or zig zag pattern) for tendon in its unstressed state and related the appearance to the mechanical properties of tendon. Explain mathematically, with the help of suitably suited diagram, how a crimp angle of 15.4 for rat tail tendon would be compatible with a %3.7 axial strain before fiber straightening. Superimpose on Fig. b a plausible stress-strain curve for the same rat tail tendon which has the crimp angle of 15.4 (10 points) (a) (b) Stress (MPa) 50 0 0.01 0.02 0.03 Strain (a) A collagen fibril. (b) A graph of tensile stress against strain, from an experiment in which a sheep plantaris tendon was stretched in a tensile testing machine. (From Ker, 1981) Reconsider the tendon in Fig. b, assuming only half is collagen, with the remaining fibers being elastin running in parallel (assuming linearly elastic until failure at 200% strain and E = 0.9 MPa). Draw a new stress-strain graph for this hybrid tendon. NOTE: This is a concept experiment, recognizing that elastin is normally a very small fraction of tendon structure. Redraw the graph in Fig. b for a healing tendon 15 cm long with 2 mm healing section (completely across) modelled by 100% elastin only. Explain your reasoning.
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The crimp pattern of a tendon refers to the zigzag pattern of collagen fibers in the unstressed state. This pattern allows the tendon to stretch and absorb force before the fibers straighten and the tendon becomes taut. Show moreā¦
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This figure is from a study that looked at the effect of tension on the stability of the microtubule -kinetochore interaction. In this study they were looking at purified Kinetochores that did NOT have Aurora B. For this figure they attached a microtubule to a slide and then connected it to a kinetochore that was on a bead that they could pull on using a laser. In this figure they are graphing how much the microtubule grows over time before it looses its connection with the kinetochore. The line ends when the connection is lost a. In this figure there are three down arrows on the diagram and two up arrows. What do those arrows indicate? What might it mean that the higher tensions do not have any arrows? b. Many papers have suggested that tension is similarly important for actin stabilization at focal adhesions. i. What is a focal adhesion? ii. (3pts) What are the similarities between actin and microtubules that might cause them to both be stabilized by tension? iii. Given the roles of focal adhesions, why does it make sense that actin would be stabilized by moderate levels of tension at these sites?
Sri K.
Figure $12-85 a$ shows details of a finger in the crimp hold of the climber in Fig. $12-50 .$ A tendon that runs from muscles in the forearm is attached to the far bone in the finger. Along the way, the tendon runs through several guiding sheaths called pulleys. The A2 pulley is attached to the first finger bone; the A4 pulley is attached to the second finger bone. To pull the finger toward the palm, the forearm muscles pull the tendon through the pulleys, much like strings on a marionette can be pulled to move parts of the marionette. Figure $12-85 b$ is a simplified diagram of the second finger bone, which has length $d .$ The tendon's pull $\vec{F}_{t}$ on the bone acts at the point where the tendon enters the A4 pulley, at distance $d / 3$ along the bone. If the force components on each of the four crimped fingers in Fig. $12-50$ are $F_{h}=13.4 \mathrm{N}$ and $F_{v}=$ $162.4 \mathrm{N},$ what is the magnitude of $\vec{F}_{t} ?$ The result is probably tolerable, but if the climber hangs by only one or two fingers, the A2 and A4 pulleys can be ruptured, a common ailment among rock climbers.
Figure $12-85 a$ shows details of a finger in the crimp hold of the climber in Fig. 12-50. A tendon that runs from muscles in the forearm is attached to the far bone in the finger. Along the way, the tendon runs through several guiding sheaths called pulleys. The A2 pulley is attached to the first finger bone; the A4 pulley is attached to the second finger bone. To pull the finger toward the palm, the forearm muscles pull the tendon through the pulleys, much like strings on a marionette can be pulled to move parts of the marionette. Figure $12-85 b$ is a simplified diagram of the second finger bone, which has length $d$. The tendon's pull $\vec{F}_{t}$ on the bone acts at the point where the tendon enters the A4 pulley, at distance $d / 3$ along the bone. If the force components on each of the four crimped fingers in Fig. $12-50$ are $F_{h}=13.4 \mathrm{~N}$ and $F_{v}=$ $162.4 \mathrm{~N}$, what is the magnitude of $\vec{F}_{t} ?$ The result is probably tolerable, but if the climber hangs by only one or two fingers, the $\mathrm{A} 2$ and A4 pulleys can be ruptured, a common ailment among rock climbers.
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