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Report Lesson Skeletal Muscle Function – Lab

Types of contraction – Challenge Categorize the following exercises as isometric or isotonic. Isometric

Isotonic

Balancing on tiptoes

Balancing on tiptoes

Doing bicep curls

Doing a plank exercise (holding a

Doing a plank exercise (holding a

Pedaling a bicycle on a at

push-up position)

push-up position)

surface

Doing bicep curls

Holding a bench-press bar in the

Running up a hill

Holding a bench-press bar in the same position Pedaling a bicycle on a at

same position Pushing constantly against a concrete wall

surface Pushing constantly against a concrete wall Running up a hill Swimming freestyle

Types of contraction – Activity

Swimming freestyle

Label the type of muscle contraction illustrated by the images below. Concentric

Eccentric

Eccentric

Isometric

Isometric

De ne and describe isotonic contraction. Muscle contraction and shortening of muscle bers. (Ex: pedaling a bicycle).

De ne and describe isometric contraction. Muscle contraction, but no change in muscle length. (Ex: performing a plank).

Nerve stimulation – Activity

Concentric

1200 1000 800 600 400 200 0 6

Stimulus

7

8

9

10

Twitch response and recruitment – Activity

40

Force (mV)

20 0

Twitch from olecronon to phalanges.

-20 0.5

EMG (mV)

0

-0.5

0.6 1

Stimulus

0.4 0.2

0 0.04

Record

0.06

1

0.08

2

3

0.1

4

0.12

5

6

0.14

7

8

0.16

9

0.18





Now you have observed a muscle twitch, can you explain what you are seeing in the EMG and Force channels? The higher the MA, the more of a rise in EMG and Force

Twitch response and recruitment – Analysis Stimulus (mA)

Force (mV)

Complete the graph by labeling the title and axes

Untitled Graph

Unlabeled Axis

Incomplete data in table

Unlabeled Axis

Maximal Stimulus: the current at which the twitch response no longer increases. Maximal Stimulus (mA)

 Supramaximal Stimulus (mA)

20

25

What happened to the muscle contraction response as the current stimulus increased from 0 mA? What was the smallest current required to produce each of the following? a) a contraction (threshold current)  b) the maximum contraction (maximal stimulus)

When the current reached the following stages, what proportion of bers in the muscle were contracting? a) at threshold b) at the maximal stimulus c) above the maximal stimulus

Why does varying the stimulus strength a ect the twitch force?

Summation – Challenge Identify the physiological features of muscle contraction by matching the labels with the number shown on the graph. 

Action potential

Incomplete tetanus

Tetanus Incomplete tetanus Action potential

Summation Summation Tetanus Twitch Twitch

Summation – Activity

80 60

Force (mV)

40 20 0 -20 3

EMG (mV)

2 1 0 0.6 -1

Stimulus

0.4 0.2

6

0 0.5

Record

3

4

5

1

6

7

1.5

2

2.5

8

Summation – Analysis Frequency of nerve stimulation and muscle contraction Frequency (Hz)

Stimulus Interval (ms)

Force - First Response (mV)

Force - Second Response (mV)

1

1000

8.60

6.74

2

500

5.53

6.21

5

200

9.20

9.58

6.6

150

11.80

23.56

10

100

5.31

4.06

20

50

8.08

9.07

The stimulus interval has a profound e ect on the contraction force of the muscle. In your own words explain what happened when the muscle was stimulated in rapid succession. At which interval did the volunteer's muscle twitches begin to merge together (summate)? The muscle appeared as if it was tetanus. The volunteer's muscle twitches began to merge together at interval 1.

Tetanus – Activity

Force

EMG

Stimulus

Time

Record

Tetanus – Analysis

Muscle contraction with increasing numbers of nerve stimuli Stimulus Interval (ms)

Number of Pulses

Not applicable

1

50

2

50

3

50

4

50

5

Force (mV)

A short period of rapid electrical stimuli is used to observe muscle bers contracting continuously (tetanus). Chemical agents can cause tetanus by interfering with the motor neurons. These agents include a toxin produced by the soil bacterium Clostridium tetani. One of the symptoms of these agents is called "spastic paralysis".  Explain in your own words why these agents would have a negative e ect on you and your muscles.

Conduction velocity – Activity

EMG

Time

Record

Conduction velocity – Analysis

Site of Stimulation

Latency (ms)

Elbow Wrist

Wrist-elbow distance (mm) Conduction velocity (m/s)

Look at the latency for ulnar nerve stimulation at the wrist and at the elbow. How do these latencies di er? Why do you suppose this is?

Based on your results and calculations for nerve conduction velocity, how long would it take for a nerve impulse to travel from the spinal cord to the big toe? Assume that the distance traveled is 1 meter.

Popup - Re ection notebook Re ection notebook:

Popup - Convert inches to mm Inches (in)

Millimeters (mm)