User:Shawnbrookins/sandbox

Week 2: Comments/Review of Intervertebral Disc Article

Intervertebral Disc—

·       Provide a citation for disc composition

• lacking evolutionary perspective: why/when IV discs emerged phylogenetically (from what, etc.)

Structure—

·       Provide elaboration and citation for withstanding compressive forces

·       Provide citation for disc paragraph

·       Development section could benefit from some elaboration, perhaps shifts in composition during development windows, etc.

Function—

·       Provide some sort of image of either the constituent compounds in IV discs, or serial cross sections with labels

·       Elaborate on shock absorption function/provide citation for hydraulic function

Clinical Significance—

·       Demonstrates an avoidance of bias, favoring a neutral, objective viewpoint

·       Perhaps elaborate on Schmorl’s nodes and vertical herniation (image?)

• Provide definition and accompanying citation for condition of scoliosis

Synopsis: displays neutral viewpoint throughout (lack of bias for particular viewpoints, etc.); no obvious outdated information; citations provided are accessible and appear from reliable sources (i.e. 3 different peer reviewed medical journals); links are provided to auxiliary material; no overt instances of plagiarism; language is concise yet comprehensive for subject matter

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Week 3: Comment Draft for IV Disc Article (Post in-class collaboration 2/17/17)

I agree with the aforementioned suggestions that this article could benefit from the inclusion of a cited reference detailing how disc referencing in the human spine, as well as elaboration on disc morphology and biochemical constituents/processes pertinent to this structure. In my review of this article I noted the following areas for potential improvement. Namely, in the section titled "Intervertebral Disc", a citation could be provided for the mention of disc composition. Alternatively, a citation could be provided for the "crucial" function of the disc as a shock absorber.

With respect to the "Structure" section, the paragraph devoted to development of the IV discs could benefit from some elaboration (potential citation: Sivakamasundari and Lufkin 2012) on the exact developmental mechanism (i.e. key players, etc.). A citation could also be provided for the clause on withstanding compressive forces as well.

The "Function" section could likely be improved by including an image of the constituent compounds in IV discs for visual reference, or serial, labeled cross sections of IV discs to demonstrate the various regions.

Lastly, the "Clinical Significance" section could be revised to elaborate on the pathophysioloy of Schmorl's nodes on IV discs, or provide an accompanying link to another article. This revision could also be extended to the article's coverage of vertical herniation as well.

Concerning citations, I believe Panjabi's two-part article in the Journal of Spinal Disorder would be an apt citation for this topic, as it covers information that remains uncited in the article, in addition to being from a peer-reviewed academic medical source ( Panjabi 1992 ). Likewise, citation 7 (McGraw Hill) is linked to Launchpad--an academic supplement that is not universally accessible without a subscription. Therefore, an alternative reference to an article or other text based source would be ideal (Urban and Roberts 2003). Throughout the article, scientific jargon is used without accompanying citations or definitions which could be construed as plagiarism potentially.

Overall, the article displays an avoidance of biased perspectives (with the exception of focusing on IV discs in humans), favoring a neutral/objective viewpoint. It also excels in the area of concise, yet comprehensive coverage of the topic, merely requiring some elaboration on auxiliary topics and defining scientific jargon in a more accessible register (mentioned above).Shawnbrookins (talk) 18:00, 17 February 2017 (UTC)

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Week 4: Assignment to Group Dissections Assignment (3/3/17):

Selected Organisms/Page Edit Proposals--

1. Rat: I selected this organism because I had the opportunity to do a brief/crude dissection in AP Biology sophomore year of high school, however I would like a chance to revisit the organism in greater detail, and be able to simultaneously investigate a mammal's anatomy due to my vocational interest in becoming a surgeon. Pages to edit a. Masseter muscle b. Subsquamosal fenestra c. Zygomasseteric system d. Cheek pouch
2. Iguana: I selected the iguana because I would find it personally interesting to dissect an organism which I have only come in contact with on one or two occasions while I studied away in Trinidad and Tobago. Pages to edit: a. Iguania b. Tympanum (anatomy) c. Hemipenis d. Parietal eye
3. Garter Snake: I selected the garter snake, because I would enjoy the challenge associated with dissecting a smaller organism that requires a greater degree of dexterity and precision. Pages to edit: a. Vomeronasal organ b. Reptile (or the snake page itself, for elaboration on scales, musculature, etc.) c. Snake skeleton

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Week 5: Group Dissection Work (DUE 3/10/17):

Articles/Topics to Edit: (finalized discussions will appear in Shawn Brookins' sandbox.

1. Cheek Pouch (Lead = Shawn Brookins)
   1. Sources:
      1. http://jeb.biologists.org/content/210/17/3096: Kinematic analysis of an appetitive food-handling behavior: the functional morphology of Syrian hamster cheek pouches This source explicates muscles associated with the rodent cheek pouch and analyzes their individual functions.
      2. http://tru.uni-sz.bg/bjvm/BJVM-March%202015%20p.19-30.pdf: Morphology of the oral cavity of the African giant rat (C. Gambianus) This source explores the morphological and anatomical nature of the cheek pouch in rodents.
      3. Ryan. James. Comparative morphology and evolution of cheek pouches in rodents. J Morph. (190):1. October 1986. pp 27-41. This source investigates the selective pressures leading to and function of rodent cheek pouches.
      4. Ryan. James. Comparative Myology and Phylogenetic Systematics of the Heteromyidae. University of Michigan. 1989. https://deepblue.lib.umich.edu/bitstream/handle/2027.42/56420/MP176.pdf?sequence=1 Like sources 1 and 2, this paper focuses on the myology of the rodent cheek pouch.
      5. Ryan, J.M. 1989. Evolution of cheek pouches in African pouched rats (Rodentia: Cricetomyinae). Journal of Mammalogy. 70:(2). https://www.jstor.org/stable/1381507?seq=1#page_scan_tab_contents This source is similar in coverage to that of the aforementioned source #3, delineating the evolutionary pressures of the rodent cheek pouch in African rats.

For this particular article, we could go into further detail on the gross and microscopic morphology of the rat cheek pouch. For example, we could delineate the epithelial layers associated with this structure or the muscles that comprise it. We could also elaborate upon/compare the constituent structures among rodents similar to the rat.

1. Tail (section to be added to Rat page, if insufficient information/material acquired on cheek pouch)
   • We could include a section that elaborates on the anatomy of the rat/rodent tail, drawing on sources like the following journal article that explores the anatomy of this structure in rats
     • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1396070/pdf/jphysiol01041-0260.pdf
     • https://www.ncbi.nlm.nih.gov/pubmed/25346299
   • We could also discuss the thermoregulatory role of the rat's tail, as explored in the following journal studies (they focus on the rat thermoregulating during activity via tail flick activity, etc.):
     • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4844073/pdf/ktmp-02-04-1119615.pdf
     • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4126311/pdf/jssm-13-695.pdf
   • We could elaborate on the proprioceptive function of the tail in rats by gleaning the following kinesthetic studies wherein rat tails experienced various modifications:
     • https://www.ncbi.nlm.nih.gov/pubmed/25346299 (see above under anatomy bullet)
   • Lastly, we could elaborate on the rat tail's nocifensive function (defensive response to pain) function known as "degloving". The following study investigates associated pathologies and damages resulting from degloved tails:
     • http://www.scielo.br/scielo.php?pid=S1983-51752012000400006&script=sci_arttext&tlng=en

1. Teeth (Lead = Dalen)
   1. Sources:
      1. Cementogenesis reviewed: A comparison between human premolars and rodent molars
      2. Alistair. Evans. High-level similarity of dentitions in carnivorans and rodents. Nature. December 2006
      3. Croft. Darin. Incisor morphology reflects diet in caviomorph rodents. J Mammal. August 2011 Through this dissection project, we could elaborate on unique dental morphologies of the rat, comparing it to existing morphologies in other rodent species and humans as well. One example of the latter could be in investigating the vasculature associated with rat teeth relative to the aforementioned comparison groups. During our dissection of our rat we could add an image of its incisors/teeth in the rodent section of this article.
2. Aortic Arch (Lead = Riley)
   1. Sources:
      1. Monnereau, L., Carretero, A., Berges, S. et al. Anat Embryol (2005) 209: 357. doi:10.1007/s00429-004-0449-3. Morphometric study of the aortic arch and its major branches in rat fetuses on the 21st day of gestation. https://www.ncbi.nlm.nih.gov/pubmed/15864641
      2. Berry, C. The growth and development of the rat aorta. I. Morphological aspects. J. Anat. (1972) 113:1. pp 1-16. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1271363/
      3. Cizsek, B. The anatomy of the cardiac veins in mice. J. Anat. (2007) 211:1. pp 53-63.

Over the course of this dissection project, our group could edit sections on this particular page or in the cardiovascular morphology section of rodents, comparing it to humans, delineating unique structures, etc. https://www.ncbi.nlm.nih.gov/pubmed/17553104 We would like to include a section that compares the anatomical similarities and differences between the aortic arch of humans compared to rodents (specifically the rat). Here is a possible source that we would use to derive such information from, or follow as an example from our own dissection of the rat: Ciszek, B., Skubiszewska, D., and Ratajska, A. 2007. The anatomy of the cardiac veins in mice. Journal of Anatomy. 211:(1). 53-63. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2375793/ Dizzle32 (talk) 21:39, 10 March 2017 (UTC)

Week 6: Cheek Pouch & Tail Proposed Edits/Associated Sources (3/17/17)

Cheek Pouch

Under the "Examples" heading on Cheek pouch, I would suggest making the following addition:

• insert a heading for pouched rat
  • within this heading, elaborate on the muscles, nerves, and vessels associated with this structure
    • utilize previous morphological studies as references for this addition
      • https://deepblue.lib.umich.edu/bitstream/handle/2027.42/56420/MP176.pdf?sequence=1--This source looks specifically at the rodent cheek pouch myology
      • http://tru.uni-sz.bg/bjvm/BJVM-March%202015%20p.19-30.pdf
  • compare investigated rat pouch anatomy to that of the hamster, referencing aforementioned morphological studies:
    • http://jeb.biologists.org/content/210/17/3096--This source looks at individual muscles comprising the cheek pouch and their functions
    • https://deepblue.lib.umich.edu/bitstream/handle/2027.42/56420/MP176.pdf?sequence=1--[see in above bullet point]

Rat Tail

On the Rat or Rodent page, a new section heading could be inserted within "characteristics" to elaborate on the primary functions of the tail in rats:

• Functions
  • discuss the tail's thermoregulatory role: The two studies below analyze temperature flucuation during high activity periods and the associated anatomical features of the tail that facilitate this function
    • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4844073/pdf/ktmp-02-04-1119615.pdf
    • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4126311/pdf/jssm-13-695.pdf
  • discuss the tail's proprioceptive role: The following source describes the musculature, innervation, and vasculature associated with the rodent tail and how the collectively assist in orienting the rat in a three dimensional environment, perform their locomotive/proprioceptive functions
    • https://www.ncbi.nlm.nih.gov/pubmed/25346299
    • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3156064/
  • discuss the tail's nocifensive function: The following study explicates the pathologies associated with the degloving response/reflex
    • http://www.scielo.br/pdf/rbcp/v27n4/en_06.pdf

Week 6: Group Sandbox Site to Post Improvements--Edit Drafts (3/17/17)

Shawn

Draft-_Cheek Pouch Addition (to be added under examples heading):

While cheek pouches are more pronounced in certain rodents, such as hamsters, this structure is also distinguishable on certain species of rat, like the African pouched rat, of which extensive morphological investigations have been conducted. Aspects including rat pouch musculature, vascularization, and innervation were all explored and compiled through this and other studies.

Concerning the musculature, the cheek pouch is comprised primarily of a developed masseter (cheek) muscle that exhibits a high tensile ability. The pouch is clearly divided between a buccal (cheek) and sublingual (below the tongue) portion. The masseter muscle has been shown to insert into the pectoralis muscles, allowing for a higher degree of food retention. Volumetric analyses within this study attributed the differences in net cheek volume between male and female rats to the average size of the respective sexes.

Due muscle's high nutritional demand, this muscle exhibits vascularization that has been highly studied. Dissections at Boston University by Frank Brodie describe the various bifurcations (or splittings) of the common carotid. Namely, this artery splits into an internal and external branch, of which the latter extends dorsally and divides into five branches that supply the general cheek region. The branch that extends dorsally to the ear is known as the auricular branch.

As for innervation of this structure, the nerve branches associated with this structure were all found to originate from the facial (VII of XII) nerve which initiates at the medulla and passes into the facial canal via the stylomastoid foramen. The primary aformentioned muscle, the masseter, is supplied by two large neural branches known as the temporalis and zygomatic nerves. The buccal divisions of this nerve supply much of the masseter muscle, which ultimately facilitate the voluntary retention of food within the cheek pouch.

Rat Tail (to be added to Characteristics section of Rodent page as subheading):

The characteristic long tail of most rodents is a feature that has been extensively studied in rat models, which subsequently suggest three primary functions of this structure: thermoregulation, minor proprioception, and a nocifensive response. Rodent tails, particularly in rat models, has been implicated with a thermoregulation function that follows from its anatomical construction. Namely, the tail is hairless and thin-skinned, but highly vascularized, thus allowing for efficient counter-current heat exchange with the environment. The high muscular and connective tissue densities of the tail, along with ample muscle attachment sites along its plentiful caudal vertebrae facilitate specific proprioceptive senses to help orient the rat in a three dimensional environment. Lastly, rats have evolved a unique defense mechanism termed "degloving" which allows for escape from predation through the loss of the outermost integument layer on the tail. However, this mechanism is associated with multiple pathologies that have been the subject of investigation.

Multiple studies have explored the thermoregulatory capacity of rodent tails by subjecting test rodents to varying levels of physical activity and quantifying heat conduction via the animals' tails. One study demonstrated a significant disparity in heat dissipation from a rat's tail relative to its abdomen. This observation was attributed to the higher proportion of vascularity in the tail, as well as its higher surface area to volume ratio, which directly relates to heat's ability to dissipate via the skin. These findings were confirmed in a separate study analyzing the relationships of heat storage and mechanical efficiency in rats that exercise in warm environments. In this study, the tail was a focal point in measuring heat accumulation and modulation.

On the other hand, the tail's ability to function as a proprioceptive sensor/modulator has also been investigated. As aforementioned, the rat tail demonstrates a high degree of muscularization and subsequent innervation that ostensibly collaborate in orienting the organism. Specifically, this is accomplished by coordinated flexion and extension of tail muscles to produce slight shifts in the organism's center of mass, orientation, etc., which ultimately assists it with achieving a state of proprioceptive balance in its environment. Further mechanobiological investigations of the constituent tendons in the tail of the rat have identified multiple factors that influence how the organism navigates its environment with this structure. A particular example is that of a study in which the morphology of these tendons is explicated in detail. Specifically, cell viability tests of tendons of the rat's tail demonstrate a higher proportion of living fibroblasts that produce the collagen for these fibers. As in humans, these tendons contain a high density of golgi tendon organs that help the animal assess stretching of muscle in situ and adjust accordingly by relaying the information to higher cortical areas associated with balance, proprioception, and movement.

The tail of the rat also displays a unique defense mechanism known as "degloving" in which the outer layer of the integument can be detached in order to facilitate the animal's escape from a predator. Interestingly, however, this evolutionary selective pressure has persisted despite a multitude of pathologies that can manifest upon shedding part of the tail and exposing more interior elements to the environment. Paramount among these are bacterial and viral infection, as the high density of vascular tissue within the tail becomes exposed upon avulsion or similar injury to the structure.

Week 6 Work: Drafting Aortic Arch (Rat) Edits (Riley Manzo-Figgins)

Note: This edit should be added to the main Rat Wiki page, then linked to the general aortic arch page where appropriate (i.e., when emphasizing that the murine anatomical structure of the aorta is comparable to the human aorta, providing valuable insight concerning human cardiovascular conditions).

The aorta and the aortic arch are composed of three layers: The tunica intima, which surrounds the lumen and is composed of simple squamal epithelial cells; the tunica media, composed of smooth cell muscles and elastic fibers; and, the tunica adventitia, composed of loose collagen fibers. Innervated by barometric nerve terminals, the aortic arch is responsible for sensing changes in the dilation of the vascular walls, inducing changes in heart rate to compensate for changes in blood pressure. The aortic arch of the rat follows the classic model of branching, containing: 1) the brachiocephalic cephalic artery (branching into the right common carotid artery and right subclavian artery), supplying blood to the right side of the neck, the right shoulder and the right arm; 2) the left common carotid artery, supplying blood to the left side of the neck; and, 3) the left subclavian artery, supplying blood to the left shoulder and arm.

The aortic arches of the rat are among the most commonly studied in murine models due to marked anatomical homology (similarity) to the human cardiovascular system. Both rat and human aortic arches exhibit subsequent branching of brachiocephalic trunk, left common cartoid artery and left subclavian artery, as well as geometrically similar, non-planar curvature in the aortic branches. Aortic arches studied in rats exhibit abnormalities similar to those of humans, including altered pulmonary arteries and double or absent aortic arches. Despite exisiting anatomical analogy in the inthrathoracic position of the heart itself, the murine model of the heart and its structures remains a valuable tool for studies of human cardiovascular conditions.

Rat Incisors (to be added within Tooth article); Dalen E.

Though the information under the rodent section within the Tooth article contains the general characteristic of the rodent incisor, I would like to add more specificity - that is, add another terminology and the interior structure - to the teleological explanation as to why rodents can constantly gnaw on food/things. Later on during our dissection, I would like to add photos of our dissected rat's incisors into this sectional as well to better illustrate the structure of the rodent incisor. Here's an image that we could potentially use within the section as well:

Illustration of the rodent dental composition.

Proposed edit:

Rodents have upper and lower hypselodont incisors - that is, these teeth have the ability to constantly grow a crown (enamel) while not having properly formed roots. Therefore, the rate of wear and tooth growth are at equilibrium .

The microstructure of rodent incisor enamel has shown to be useful in studying the phylogeny and systematics of rodents because of its independent evolution from the other dental traits. The enamel on rodent incisors are composed of two layers: the inner portio interna (PI) with Hunter-Schreger bands (HSB) and an outer portio externa (PE) with radial enamel. The radial enamel contain prism-like structures that are parallel to each other and grow directed towards the occlusal surface. The HSB also contain prisms, though the layers may vary in thickness and orientation: some run parallel to each other, while others may intersect. In rodent incisors, there are three types of HSB that have been identified: pauciserial, uniserial, and multiserial

Week 9: Feedback Responses

Shawn:

Changes to be implemented:

• Cheek Pouch
  • links to relevant wikipedia pages
    • link to heteromyidae, geomyidae, and murids in distinguishing true cheek pouches (seen in Heteromyidae and Geomyidae) versus "stretchable cheeks" (seen in Murids)
    • specifically denote the misconception about cheek pouches (Murids vs Hetero and Geomyidae clades)
  • Acquire image to upload from PLU organism museum of gopher/hamster cheek pouches versus rat masseter muscle for comparison/contrast of the two mouth morphologies
• Rat Tail
  • Specify which rat species demonstrate this specific tail morphology (Murids) and contrast/provide links to other rodent families like the squirrel/Sciuridae family I will certainly incorporate the majority of peer feedback for my draft. Namely, I will include auxiliary links to relevant pages throughout the draft. Moreover, I can attempt to parse out some of the nonessential anatomy information in terms of the vasculature and innervation of the cheek pouch region, electing to focus more on the misconception of certain subfamilies of rodents possessing/not possessing a true cheek pouch (i.e. Heteromyidae and Geomyidae versus Muridae).

Shawn (Revised--Draft #2)

Draft-_Cheek Pouch Addition (to be added under "misconception" heading on cheek pouch page):

The cheek pouch is a specific morphological feature that is evident in particular subgroups of rodents (i.e. Heteromyidae and Geomyidae (or Gopher)), yet a common misconception is that certain families, like Muridae (including the common black and brown rats), contain this structure when, in actuality, their cheeks are merely elastic due to a high degree of musculature and innervation in the region. The true cheek pouch, however, is evident in the former Heteromyidae and Geomyidae groups.

Murid Lacking Cheek Pouches

Demonstration of Cheek Pouches in Geomyid

Cheek pouches are more pronounced in certain rodents, such as hamsters, yet this structure is also distinguishable on certain species of rat, like the Gambian pouched rat, of which extensive morphological investigations have been conducted. Aspects including rat pouch musculature, vascularization, and innervation were all explored and compiled through this and other studies. The widely distributed Rattus rattus is an example organism of the Muridae family of rodents that lack a true cheek pouch, rather, they exhibit more elastic cheeks (not true pouches) due to the organization of their cheek musculature.

Concerning the musculature, the cheek pouch is comprised primarily of a developed masseter (cheek) muscle that exhibits a high tensile ability. The masseter muscle has been shown to insert into the pectoralis muscles, allowing for a higher degree of food retention. The pouch is clearly divided between a buccal (cheek) and sublingual (below the tongue) portion. Volumetric analyses within this study attributed the differences in net cheek volume between male and female rats to the average size of the respective sexes.

Due to muscle's high nutritional demand, this muscle exhibits vascularization that has been highly studied. Dissections at Boston University by Frank Brodie describe the various bifurcations (or splittings) of the common carotid. This artery splits into an internal and external branch, of which the latter extends dorsally and divides into five branches that supply the general cheek region. The branch that extends dorsally to the ear is known as the auricular branch.

As for innervation of this structure, the associated nerve branches were all found to originate from the facial (CN VII of XII) nerve which initiates at the medulla and passes into the facial canal via the stylomastoid foramen. The primary aformentioned muscle, the masseter, is supplied by two large neural branches known as the temporalis and zygomatic nerves. The buccal divisions of this nerve supply much of the masseter muscle, which ultimately facilitate the voluntary retention of food within the cheek pouch.

R. rattus Tail (to be added to Rat page as subheading):

The characteristic long tail of most rodents is a feature that has been extensively studied in various rat species models, which subsequently suggest three primary functions of this structure: thermoregulation, minor proprioception, and a nocifensive-mediated degloving response. Rodent tails, particularly in rat models, has been implicated with a thermoregulation function that follows from its anatomical construction. This particular tail morphology is evident across the Muridae family (in contrast to the bushier tails of the Squirrel/Sciuridae family). The tail is hairless and thin-skinned, but highly vascularized, thus allowing for efficient counter-current heat exchange with the environment. The high muscular and connective tissue densities of the tail, along with ample muscle attachment sites along its plentiful caudal vertebrae facilitate specific proprioceptive senses to help orient the rodent in a three dimensional environment. Lastly, murids have evolved a unique defense mechanism termed "degloving" which allows for escape from predation through the loss of the outermost integument layer on the tail. However, this mechanism is associated with multiple pathologies that have been the subject of investigation.

Multiple studies have explored the thermoregulatory capacity of rodent tails by subjecting test organisms to varying levels of physical activity and quantifying heat conduction via the animals' tails. One study demonstrated a significant disparity in heat dissipation from a rat's tail relative to its abdomen. This observation was attributed to the higher proportion of vascularity in the tail, as well as its higher surface area to volume ratio, which directly relates to heat's ability to dissipate via the skin. These findings were confirmed in a separate study analyzing the relationships of heat storage and mechanical efficiency in rodents that exercise in warm environments. In this study, the tail was a focal point in measuring heat accumulation and modulation.

Coronal Cross Section of Histological Layers in Murid Tail

Murid Tail Microscopy Cross Section

On the other hand, the tail's ability to function as a proprioceptive sensor/modulator has also been investigated. As aforementioned, the tail demonstrates a high degree of muscularization and subsequent innervation that ostensibly collaborate in orienting the organism. Specifically, this is accomplished by coordinated flexion and extension of tail muscles to produce slight shifts in the organism's center of mass, orientation, etc., which ultimately assists it with achieving a state of proprioceptive balance in its environment. Further mechanobiological investigations of the constituent tendons in the tail of the rat have identified multiple factors that influence how the organism navigates its environment with this structure. A particular example is that of a study in which the morphology of these tendons is explicated in detail. Specifically, cell viability tests of tendons of the rat's tail demonstrate a higher proportion of living fibroblasts that produce the collagen for these fibers. As in humans, these tendons contain a high density of golgi tendon organs that help the animal assess stretching of muscle in situ and adjust accordingly by relaying the information to higher cortical areas associated with balance, proprioception, and movement.

Rattus rattus (Murid) Tail Dissected

Murid Tail Dissection (Lateral View)

The characteristic tail of Murids also displays a unique defense mechanism known as "degloving" in which the outer layer of the integument can be detached in order to facilitate the animal's escape from a predator. Interestingly, however, this evolutionary selective pressure has persisted despite a multitude of pathologies that can manifest upon shedding part of the tail and exposing more interior elements to the environment. Paramount among these are bacterial and viral infection, as the high density of vascular tissue within the tail becomes exposed upon avulsion or similar injury to the structure. The degloving response is a nocifensive response, meaning that it occurs when the animal is subjected to acute pain, such as when a predator snatches the organism by the tail.

Riley:

Changes to be implemented:

-The only large problem that was mentioned throughout all peer review was my phrase corresponding to the Vitamin A-deficient rats. I think that the point of the sentence is valuable, but throwing in "Vitamin A" threw readers off. I simply removed Vitamin A. This will read:

"Aortic arches studied in rats exhibit abnormalities similar to those of humans, including altered pulmonary arteries and double or absent aortic arches."

-After dissection, a picture of the aortic arch will be labeled in vivo noting all major arteries and where they lead relative to the heart (Will be using my own figure to avoid copyright issues..)

Dalen: Edits and Additions to Draft

Rodents have upper and lower hypselodont incisors - that is, these teeth have the ability to constantly grow a crown (enamel) while not having properly formed roots. Therefore, the rate of wear and tooth growth are at equilibrium .

The microstructure of rodent incisor enamel has shown to be useful in studying the phylogeny and systematics of rodents because of its independent evolution from the other dental traits. The enamel on rodent incisors are composed of two layers: the inner portio interna (PI) with Hunter-Schreger bands (HSB) and an outer portio externa (PE) with radial enamel (RE). The radial enamel contain prism-like structures that are parallel to each other and grow directed towards the occlusal surface. The HSB also contain prisms, though the layers may vary in thickness and orientation: some run parallel to each other, while others may intersect . It is believed then that the HSB strengthen enamel by distributing the stresses applied from chewing because of how their prism layers cross each other, oriented in the same direction of these forces to prevent the tooth from fractures .

For our next dissection, I actually want to get a more interior image of the incisors (a midsagittal view) to show how long they are in the interior compared to what is seen on the outside. But for now, here are some images with the relative/theoretical lengths of the top and bottom incisors:

Lower incisor of Rattus rattus. The lines indicate the theoretical extension of incisor inside the dentary.

Top incisors of Rattus rattus. Lines indicate the theoretical extension of incisor into the premaxilla.

Group Revision/Edit Comments:

Week 10

Notes on Riley's Additions:

-I have added briefly to existing sections in both the main Rat page, as well as to the aortic arch page

Week 11

Riley's Notes:

-Currently working on labeling rat arteries coming from the heart; Need to take a better picture with less tissue surrounding the heart for better clarity. On the upside, none of my additions to the aortic arch or rat pages have been contested, making me feel more confident to add.

-Notes on additions: Added information to the rat page under clinical significance of aortic arches.

-Remaining uncertainty: In my draft I listed the three major branches of the aortic arch and to which areas of the body they supply blood flow. I notice that the aortic arch page does not list these areas explicit, but each hyperlink to the corresponding branch covers this material. Should I add the areas of the body to the aortic arch page itself?