Stimulation Strength Effect On Frog Muscles Biology Essay

Frogs are keystone species, an indispensable being to aquatic ecosystems. They have both tellurian and aquatic niches as marauders and quarry and service as index species to measure the response of ecosystems to environmental alteration. To put to death day-to-day motive power forms, toads use skeletal musculuss. We wanted to find the relationship between the strength of the stimulation and the response of the musculus. We besides wanted to mensurate the amplitude of contraction produced in a musculus that is stimulated with perennial pulsations delivered at increasingly higher frequences. We hypothesized that increasing stimulus electromotive force in the gastrocnemius musculus of a toad will ensue in an addition in stimulation amplitude and that an addition in stimulation frequence at a changeless electromotive force will ensue in an addition in force generated by the musculus up until a point where it plateaus. We found that our hypotheses were supported and that musculus ordinance was via temporal and spacial enlisting. This survey is of import because it serves as a theoretical account for understanding skeletal musculus mechanisms in other beings including worlds.

Frogs are widely distributed tellurian amphibious vehicles that inhabit highland and wetland parts, found on all continents of the universe except Antarctica. Many frog species, in both larval and big phases serve as of import quarry for larger marauders including fish, raccoons, serpents and birds of quarry ( Chalcraft and Resetarits 2003 ; Auniola and Kauhala 2001 ) . Additionally frogs serve an of import function as indexs of environmental emphasis ( King 2010 ) . A reappraisal of complex systems in impermanent pools by Wilbur ( 1997 ) makes the statement that toads have two distinguishable niches, one terrestrial and one aquatic. Wilbur states “ all toads with nonparasitic larvae alteration at metabolism from aquatic omnivorous polliwogs to amphibian carnivorous grownups. The function of such connexions among nutrient webs is a fruitful country for both theoretical and empirical research because the forage of animate beings across ectones may be an of import biological mechanism associating elements of the mosaics of home grounds that form landscapes. ”

One trait toads are most known for is motive power. Frogs typically display two type of motive power: jumping and swimming. Though toads are traditionally presented as “ leap specializers ” most species besides swim ( Navas et al. 1999 ) . Frogs exhibit these locomotor behaviours for a assortment of grounds including get awaying marauders, frequently times by a short set of speedy and powerful leaps ( Carvalho, Gomes and Navas 2007 ) . Frog motive power is dependent on musculuss, peculiarly skeletal musculuss, which are musculuss connected to the skeleton ( Marsh and Olson 1998 ) . Skeletal musculuss are organized get downing with units called sarcomeres. A sarcomere consists of two opposing perpendicular Z-line phonograph records each with actin fibrils attached. A myosin fibril floats between each horizontal actin subdivision. Sarcomeres are connected to each other by Z-lines. One mechanism of musculus contraction begins with the sliding of the actin and myosin fibrils. Partss of the myosin, known as myosin caputs, bind to the free terminal of the actin, the terminal non attached to the Z-line, and draw it one manner toward the centre of the mysosin, in an accordian-like mechanism. The musculus shortens or contracts because the sarcomeres shorten.

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The procedure by which the myosin binds to the actin is called the Cross-Bridge rhythm. The binding of the myosin to actin is the trigger for the myosin caput to joust and let go of an ADP and a P every bit good as a powerstroke. ATP binds to the myosin caput and the myosin releases the actin, in a “ softening ” consequence. The ATP is hydrolyzed and delivers energy to travel the mysosin caput back and it is ready for the following powerstroke. The sarcomeres move nearer together by many of these powerstrokes happening one after the other. In the Cross-Bridge rhythm myosin is usually prevented from adhering to the actin. Another protein called tropomyosin, which is wrapped around the actin, is in the manner to barricade the actin-myosin binding site. Another protein, troponin, is attached to the tropomyosin and when triggered, moves the troponin off to let the binding to happen. But what triggers the tropomyosin to travel the troponin? The simple reply is calcium and this occurs in a procedure called excitation-contraction yoke. In excitation-contraction matching an action potency or electrical stimulation, runs down a T-tubule in the musculus fibre. The stimulation reaches a ryanodyne receptor which opens ion channels in the sarcoplasmic Reticulum, a storage infinite for Ca in the musculus fibres. Once the ion channels are opened, Ca runs out into the cell.

For the musculus to loosen up or return to its original resting place, Ca must be moved back into the sarcoplasmic Reticulum by a SERCA pump. Because Ca is being moved against a concentration gradient, this relaxation requires ATP. The SERCA pump lowers Ca degrees in the cytosol or cell and when the Ca is taken up once more the musculus relaxes.

Since musculuss are non undertaking all the clip musculus contraction must be regulated. Regulating the musculuss allows toads to alter facets of locomotor behaviour, such as how far a toad is able to leap. Muscle contraction force can be regulated by Ca in three mechanisms: temporal enlisting, in which the fire rate at which single motor nerve cells fire is changed ; spacial enlisting, in which the figure of active motor units is changed ; and the length-tension relationship, in which the sarcomere length is changed to bring forth tenseness. This survey focuses on the force of musculus contraction via temporal and spacial enlisting.

In temporal enlisting, the frequence of the action potency is changed, normally increased, so that more Ca is released into the musculus cell. More Ca in the cell consequences in more tenseness generated. Another mechanism for the ordinance of musculus contraction force is centrifugal unit enlisting, besides known as spacial enlisting. A motor unit is comprised of musculus fibres and a motor nerve cell. There are different sums of fibres per motor unit. In spacial enlisting the figure of active motor units is increased to increase the strength of musculus contraction. More centrifugal units means that more musculus fibres can be stimulated. If lone half of the musculus fibres are stimulated, merely half the sum of force will be generated. If all of the musculus fibres are stimulated, the maximal sum of force will be generated.

We hypothesized that if we increase electromotive force of an electrical stimulation in a frog musculus we will see an addition in stimulation amplitude and if we increase stimulation frequence at a changeless electromotive force, we will see an addition in force generated by the musculus up until a point where it plateaus.

Materials & A ; Methods:

We used the gastrocnemius musculus of a toad in two experiments. In the first experiment we used a individual stimulation, altering the electromotive force of the stimulation from 0 Vs to 2.0 Vs. The force of the musculus was recorded. In the 2nd experiment we stimulated the musculus in series of 10 utilizing a changeless electromotive force identified in the first experiment. The frequence of the stimulation was increasingly increased get downing at 0.5 and stoping at 30 Hz.

Consequences:

Our consequences showed that as the stimulation increases the amplitude of the musculus vellications increases up until a point where it plateaus. Our consequences besides showed that as the stimulation frequence increases the inactive tenseness of the musculus addition up until a point where it plateaus.

Figure 1

Figure 1 shows a normalized graph for the effects of increasing stimulation on the amplitude of musculus vellications in the gastrocnemius musculus of a toad. The x-axis is the recorded stimulation in Vs and the y-axis is the amplitude of the vellications ( displayed as a per centum of the upper limit ) . The graph shows that as the stimulation increases the amplitude of the musculus vellications increases up until a point where it plateaus.

Table 1

Stimulation

Amplitude ( V )

Amplitude

( millivolt )

Contract Time

( millisecond )

Relaxation Time

( millisecond )

Rotational latency

( millisecond )

0.000

0

0

0

0

0.250

0.449

70.00

205.0

20.00

0.500

1.054

70.00

215.0

20.00

0.750

1.197

75.00

250.0

15.00

1.000

1.271

75.00

215.00

15.00

1.250

1.314

75.00

220.0

15.00

1.500

1.328

75.00

215.0

15.00

1.750

1.331

75.00

220.0

15.00

2.000

1.332

75.00

220.0

15.00

Table 1 shows a set of group informations from the first experiment, in which amplitude and times of musculus vellications were generated by stimulus pulsations of different amplitudes. As in Figure 1, Table 1 shows that as the stimulation increases the amplitude of the musculus vellications increases up until a point where it plateaus. The contraction clip and latency period remains mostly unchanged with altering stimulus amplitude.

Figure 2

Figure 2 shows a normalized graph for the effects of increasing stimulation frequence on the inactive tenseness in the gastrocnemius musculus of a toad. The x-axis is the stimulus frequence in Hz and the y-axis is the inactive tenseness in the musculus ( displayed as a per centum of the upper limit ) . The graph shows that as the stimulation frequence increases the inactive tenseness of the musculus addition up until a point where it plateaus.

Table 2

Stimulus Frequency ( Hz )

Amplitude 1st Twitch ( V )

Max. Amplitude ( V )

Change in Passive Tension ( V )

0.000

0

0

0

0.250

0.449

70.00

205.0

0.500

1.054

70.00

215.0

0.750

1.197

75.00

250.0

1.000

1.271

75.00

215.00

1.250

1.314

75.00

220.0

1.500

1.328

75.00

215.0

1.750

1.331

75.00

220.0

2.000

1.332

75.00

220.0

Table 2 shows a set of group informations from the 2nd experiment, in which the strength of musculus contraction was examined during mechanical summing up and lockjaw. As in Figure 2, Table 2 shows that as the stimulation increases the amplitude of the musculus vellications increases up until a point where it plateaus. The amplitude of the first vellication remains mostly unchanged with altering stimulus amplitude.

Discussion:

The information shows that the direct electrical stimulation produces contraction of the musculus via motor units. A small spot of force is generated when a few of these motor units are being used and a batch of force is generated when tonss of motor units are being used. The musculus does non react to the low stimulation electromotive forces because the electrical stimulation is non straight touching the musculus, it is touching the environing connective tissue. The low stimulation electromotive forces are non strong plenty to perforate the tissue. As celebrated in Figure 1 and Table 1 the amplitude of the musculus response increases with increasing stimulation electromotive forces. This is so because more and more of the musculus mass is stimulated as the electromotive forces addition. At high stimulation electromotive forces, the musculus response reaches maximal amplitude. The musculus response does non go on to increase with increasing stimulation electromotive forces because the musculus is already working at the best of its ability. The musculus cells have reached the point where all the troponins are activated by Ca. Let go ofing more Ca into the cell will non ensue in any more tenseness generated, as the system is already working at its maximal capacity.

Rotational latency is the interval between stimulation and a response to the stimulation, here intending musculus contraction. Over this period, the action possible expanses across the cell membrane of the musculus cell and the sarcoplasmic Reticulum releases calcium ions. The musculus fibre does non bring forth tenseness during the latent period, because the contraction rhythm has yet to get down. The latency period in this survey was changeless at 0.025 seconds.This consequence been found by anyone else and it seems does non vary among other species, since it is approximately the same for worlds ( Hamilton and Osborn 1977 ) .

Since contraction amplitude is dependent upon the additions in concentration and continuity of intracellular Ca, the inquiry of why the contraction amplitudes of individual vellications are the same is raised. This can be explained because the same sum of Ca is being put in for the same perennial event. As noted in Table 2, the amplitude of the first vellication seems to be changeless ( value ) . This can be explained because the musculus is using the same sum of Ca and is therefore bring forthing the same sum of force. Tetanus is the complete contraction of a musculus. Tetanus requires high stimulation frequences. This tells us that the Ca reuptake by the sarcoplasmic Reticulum is slower than the original release. The rate of musculus relaxation is much slower after lockjaw than after a individual vellication because more Ca needs to be re-taken up and it takes longer to acquire all the supernumerary added Ca back into the sarcoplasmic Reticulum.

A survey on leaping Rana catesbeianas by Marsh and Roberts reveals two points of involvement: foremost, toads jump farther than they should, sing merely the force their musculuss are able to bring forth. Second, musculuss are able to make the most work when they contract easy, nevertheless frog leaping involves a really rapid motion. They explain that by “ dividing the public presentation of muscular work from the application of mechanical work to the organic structure, ” a catapult-like mechanism, which works by lading elastic elements into the limbs prior to originating a leap, overcomes the restraints of skeletal musculus map ” ( Marsh and Roberts 2003 ) .

Another survey by Aerts and Nauwelaerts ( 2006 ) indicates that by taking more little leaps as opposed to fewer larger leaps, toads can increase their flexibleness in motion because they would be able to alter way during the forward motion portion jumping. Theoretically this means they would pass less clip in the same topographic point during landing and recovery of the jumping rhythm, which makes them more likely to be snatched by a marauder.

Frogs have physiological mechanisms that have enabled their musculuss to bring forth adequate force for jumping and swimming motive power including altering the frequence of the action potency and increasing the figure of active motor units. As mentioned before, toads are a anchor species, intending other beings rely on it and non ever straight in a predator-prey relationship. Without toads, nutrient webs would fall in and take to the death of many other species and potentially full ecosystems. This survey is of import because it serves as a theoretical account for understanding skeletal musculus mechanisms in other beings including worlds.