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BIO270 Pre-lab 2 assignment

Skeletal muscle contraction

Learning outcomes

Students will:

● develop an understanding of skeletal muscle structure and function.

● compile and present the appropriate information for an Introduction section of a scientific manuscript.

o become aware of the conventions of scientific writing.

o become aware (i.e. metacognition) of their individual writing process and improve writing through revision based upon formative feedback.

o practice writing clearly, concisely, and precisely.

Guidelines:

Consult the BIO270 Lab resources manual for a general summary of the contents and style. of an Introduction section of a scientific manuscript, transition words to use in an introduction section of a scientific manuscript, general guidelines for writing a title for a scientific manuscript. and Lab assignment tips in the General laboratory files folder on Quercus.

Completing this Pre-lab 2 assignment will provide you with an opportunity to have your work assessed by your TA (who will provide useful feedback) before the Lab 2 assignment is due.

Submit your assignment electronically following the instructions posted on Quercus or in the BIO270 Lab resources manual by the submission deadline. (29 points: mark recorded out of 6).

Assignment:

The Pre-lab 2 assignment consists of:

A. Questions regarding results of your motor unit recruitment experiment performed in the Pre-lab (3 marks).

B. Written Introduction section based upon the background scenario outlined below.

● Appropriate title. Refer to BIO270 Lab resources manual

● Your introduction should include relevant background information, identification of the ‘gap’ in the knowledge in the field, rationale for investigating this ‘gap’, presentation of a hypothesis or research question, rationale for your hypothesis or research question (prediction supported by a peer-reviewed citation), and a brief explanation of how you conducted the experiment.

● You must include at least these three cited (referenced) sources in the body of your introduction: 1) Pre-lab 2 manual, 2) chapter 6 of Moyes and Schulte, Principles of Animal Physiology, 3rd Edition, and 3) one peer-reviewed journal article (located and retrieved by you).

● Include a Literature Cited/References section that includes your three sources cited in the body of your introduction.

●Note that if it appears in the Literature Cited/References section, it must be cited in-text also.

●For assistance with your citations, please refer to the BIO270 Lab resources manual

● For a dissection of an introduction section of a manuscript, view the recording on Quercus ‘Deconstruction of an introduction’.

● To receive full marks, students must address the format and style. guidelines in the BIO270 Lab resources manual.

The primary categories in the marking rubric for this assignment are the following:

a) Title               2 marks

b) Format and style. 4 marks

c) Introduction specific. Refer to BIO270 Lab resources manual         16 marks

d) Citations: in-text and Literature Cited/References         4 marks

Submit this assignment online following the instructions posted on Quercus or in the BIO270 Lab resources manual. Refer to the Lab schedules for the specific due date for your assignment. The Introduction section should be a maximum of 1.5 pages, 12pt font, double spaced, standard margins. Assignments over the page limit will be subject to a 10% penalty.

Background scenario (this is a fabricated scenario and will require some imagination and creativity!)

At this time in the history of skeletal muscle physiology, the current state of knowledge is the following:

● We know that a nervous impulse is required to trigger skeletal muscle contraction (hence the latent period)

● We know the mechanics of the sliding filament theory, including knowledge of the mechanical components involved (myosin thick filaments, actin thin filaments, troponin, tropomyosin)

● We know that the sarcoplasmic reticulum stores Ca2+ in the sarcoplasm

● We know that Na+, K+, Mg2+, and Ca2+ are cations present in the sarcoplasm

● We know that ATP is the energy source required for muscle contraction

However, it is NOT known which cation is responsible for the initiation of contraction (i.e. it is not known what links excitation to contraction (excitation-contraction coupling)).

Consider yourself a muscle physiologist who would like to determine whether calcium ions are involved in the initiation of skeletal muscle contraction.

You decided to perform. an experiment that involved the microinjection of solutions of different ions into myofibres from the medial gastrocnemius muscle of the Eastern Cottontail rabbit, Sylvilagus floridanus. The experimental setup involved the use of a microdissection apparatus in which the muscle fibre was held in a hanging drop of isotonic ringer’s solution inside a moist chamber. The muscle fibre was pierced with the tip of a micropipette and then the solution to be tested was injected into the muscle fibre. Volumes injected were equivalent to 5% of the volume of each muscle fibre. Muscle fibres were measured prior to injection, where lengths varied from 90 mm to 150 mm, and then re-measured 1-minute post injection.

The results of your experiment are presented in Table 1. Note that in all cases ATP was present at levels sufficient to stimulate contraction of muscle fibers.

Table 1. Contraction of Sylvilagus floridanus medial gastrocnemius muscle fibers induced by ion injection.

Experiment	Experimental conditions#
	Na+, K+, Ca2+		Na+, K+, Mg2+		Na+, K+
	Pre*	Post*	Pre*	Post*	Pre*	Post*
1	1.50	0.90	1.50	1.45	1.45	1.45
2	1.25	1.05	1.45	1.50	1.20	1.15
3	1.30	0.75	1.30	1.25	1.25	1.30
4	1.05	0.60	1.15	1.20	1.40	1.40
5	0.90	0.55	1.25	1.25	1.15	1.15
6	1.35	0.95	1.50	1.50	1.35	1.25
7	1.40	0.80	1.35	1.30	1.35	1.30
8	1.50	0.95	1.25	1.20	1.45	1.50
9	1.15	0.75	1.45	1.25	1.50	1.50
10	1.10	0.65	1.35	1.35	1.30	1.25
Mean ± SEM1	1.25 ± 0.06	0.80 ± 0.05	1.36 ± 0.04	1.33 ± 0.04	1.34 ± 0.04	1.33 ± 0.04
Mean % change2	36.5 ± 2.6		2.18 ± 1.6		1.17 ± 1.1

# Ca2+ - 10 µM, Mg2+ (1 mM), Na+ (5 mM), K+ (140 mM). *Values expressed in cm. 1 SEM = standard error of the mean. ((pre-length – post-length)/pre-length) X 100.

Reflecting on this data, you should write an Introduction section to the scientific manuscript. in which you would be presenting this data. Use the Pre-lab 2 manual and chapter 6 of Moyes and Schulte, Principles of animal physiology, 3rd Edition as your primary sources of information (cited correctly: see the BIO270 Lab resources manual). In addition, you will be required to find one relevant and appropriate peer-reviewed article (for example, a peer reviewed article which indicates the role of calcium in some other physiological process – your goal is to provide rationale as to why you are investigating Ca2+ as the link between excitation and contraction in skeletal muscle fibres) that you must incorporate into your introduction and cite correctly. Consult the links provided on Quercus in the General laboratory information module under ‘Support Resources - for Research, Writing, and Academic Integrity’ for a refresher on how to find and evaluate peer-reviewed articles. In addition to in-text citations, you should include full citations in a ‘Literature cited’ section following your Introduction (consult the BIO270 Lab resources manual).

Note: Although the Pre-lab will be performed in pairs, you must write your own individual assignment to be handed in.

Please use the format below as your template for writing your Introduction.

A. Observe your motor unit recruitment data and answer the following questions [3 marks]:

a) List two factors that may affect the degree to which muscle fibers develop tension? [1 mark]

b) What is the relationship between the strength of the muscle contraction and the number of motor units stimulated? [1 mark]

c) Briefly explain why at maximum contraction there is no opportunity to prevent fatigue in a muscle? [1 mark]

B. Based only upon the background scenario described above and the Sylvilagus floridanus medial gastrocnemius muscle fiber data (Table 1).

Title [2 marks]

Introduction [20 marks]

Literature cited/References [4 marks]

For tips on how to write an introduction and use effective transitions words in scientific writing, please refer to ‘BIO270 Lab resources manual.’