Robert K. Josephson

The effects of octopamine on contraction kinetics and power output of a locust flight muscle

Summary1.Perfusion with saline containing octopamine resulted in an increase in mechanical power output, and an increase in twitch and tetanic tension, from a flight muscle (metathoracic, second tergocoxal muscle) of the desert locust,Schistocerca americana gregaria.2.Mechanical power output was measured under conditions approximating those of flight. Power output increased upon exposure to 10−6M DL-octopamine by about 20% when the muscle was activated by 1 stimulus per cycle and by about 8% when the muscle was activated by paired stimuli.3.The increase in twitch tension was approximately proportional to the log of the octopamine concentration from 10−8M to 10−5M. At 10−6M, the twitch tension was about 19% greater than control values and the tetanic tension was about 8% above control values. The average twitch tension in control muscles was 17.0 N/cm2, and the average control tetanic tension was 27.9 N/cm2.4.The maximum shortening velocity was little affected by octopamine. In control muscles, the maximum shortening velocity was 8.3 muscle lengths/s (L/s) for slack-test measurements and 5.7 L/s by extrapolation of force-velocity curves. In octopamine, the corresponding maximum shortening velocities were 8.0 and 5.9 L/s, respectively.5.Octopamine perfusion resulted in a small increase in twitch duration (control mean = 40.5 ms at 30 °C). Both contraction and relaxation times increased by about 4%.

BODY TEMPERATURE AND SINGING IN THE KATYDID, NEOCONOCEPHALUS ROBUSTUS (ORTHOPTERA, TETTIGONIIDAE)

1. The katydid, Neoconocephalus robustus, produces a continuous song by rubbing its forewings together at frequencies of 150-200 per second. During singing the thoracic temperature is 5-15° C higher that that of the environment, the temperature gradient being greater the lower the ambient temperature.2. Singing is preceded by a warm-up period during which normally antagonistic forewing muscles contract synchronously. The result is heat production and a rising thoracic temperature (1.5° C/min) with little overt movement.3. The thoracic temperature at the onset of singing averages 33.5° C at ambient temperatures at 23.5°-29° C.4. The rate of heat loss at the cessation of singing indicates that the animal must produce 0.5 cal/min (3.6 cal/min/g thorax weight) to maintain a 15° C temperature gradient.5. This insect is immobilized by cooling to 11° C, but regains mobility when rewarmed to 21.5° C. It is reversibly immobilized at thoracic temperatures above 43.9° C.6. N. robustus basks readily, but moves to sha...

HIGH FREQUENCY MUSCLES USED IN SOUND PRODUCTION BY A KATYDID. I. ORGANIZATION OF THE MOTOR SYSTEM

1. During stridulation the forewings of Neoconocephalus robustus are rubbed against one another at a frequency of 145-212 per second. Despite the high frequency the forewing muscles are synchronous muscles; each contraction is preceded by a muscle action potential.2. The direct flight muscles of the mesothorax are wing openers during singing; the indirect flight muscles are wing closers. The sound pulse is produced on the closing stroke of the wings.3. Singing is preceded by warm-up during which all forewing muscles are activated synchronously. In early warm-up the muscles are activated in short bursts, often at a regular frequency. Later warm-up activity is continuous. Muscle activity stops briefly at the transition from warm-up to singing.4. Muscle activity patterns during singing indicate that the motor output results from an endogenous pacemaker which fires at the singing frequency. There are probably at least three neuronal elements in series between the pacemaker and the forewing muscles. The phasin...

Mechanical power output of locust flight muscle

Summary1.The mechanical work and power output of locust flight muscle were measured during cyclic contraction at normal flight frequency and operating temperature by subjecting muscle to sinusoidal length change and phasic stimulation at selected points in the length cycle.2.With a single stimulus per cycle, work output averaged 2.1 J/kg muscle inSchistocerca nitens and 2.4 J/kg muscle inS. americana gregaria (power output 52 and 49 W/kg respectively) (Table 1).3.Work was maximal at imposed length changes of about 4% of resting muscle length and at stimulus phases such that maximum tension occurred at the midpoint of the shortening phase of the length change (Table 1).4.With multiple stimulation, power output can be increased about 20% above that obtained with a single stimulus per cycle (up to about 73 W/kg muscle) (Fig. 2).

Mechanisms of sound-production and muscle contraction kinetics in cicadas

Summary1.The mechanisms of sound-production are described in 7 species of Australian cicadas:Abricta curvicosta, Arunta perulata, Chlorocysta viridis, Psaltoda argentata, P. claripennis, P. harrisii andTamasa tristigma. In all these species, sound is produced by a pair of tymbals, each of which is buckled by a large muscle (Figs. 1–7). The tymbal muscles are all of the synchronous (= neurogenic) type.2.There are great differences between species in the range of sound frequencies generated by their tymbal mechanisms and in the extent to which their songs are divided into pulses and subpulses. The most extreme case is the calling song ofChlorocysta viridis, in which there are no pulses and the sound produced is a modulated pure-tone (Fig. 3).3.In most species the left and right tymbal muscles contract alternately and so the muscle contraction frequencies during singing are half the observed pulse repetition frequencies. InT. tristigma, the two tymbal muscles contract only a few percent out of phase in calling but in full antiphase in protest song (Fig. 7). InA. perulata, there is some evidence that the two tymbal muscles contract in synchrony during calling even though they clearly alternate in protest song.4.Muscle contraction frequencies during calling songs vary from 56 Hz inC. viridis to 224 Hz inPsaltoda claripennis. Contraction frequencies during protest songs are somewhat lower than in calling.5.The tymbal muscle behaves as a single motor unit in all species, giving all-or-nothing twitches with a single, sharp threshold. The durations of isometric twitches are strongly correlated with the inferred cycle period (= reciprocal of contraction frequency) in a total of eleven species with synchronous tymbal muscles (Fig. 8).

How to Build Fast Muscles: Synchronous and Asynchronous Designs

Abstract In animals, muscles are the most common effectors that translate neuronal activity into behavior. Nowhere is behavior more restricted by the limits of muscle performance than at the upper range of high-frequency movements. Here, we see new and multiple designs to cope with the demands for speed. Extremely rapid oscillations in force are required to power cyclic activities such as flight in insects or to produce vibrations for sound. Such behaviors are seen in a variety of invertebrates and vertebrates, and are powered by both synchronous and asynchronous muscles. In synchronous muscles, each contraction/relaxation cycle is accompanied by membrane depolarization and subsequent repolarization, release of activator calcium, attachment of cross-bridges and muscle shortening, then removal of activator calcium and cross-bridge detachment. To enable all of these to occur at extremely high frequencies a suite of modifications are required, including precise neural control, hypertrophy of the calcium handling machinery, innovative mechanisms to bind calcium, and molecular modification of the cross-bridges and regulatory proteins. Side effects are low force and power output and low efficiency, but the benefit of direct, neural control is maintained. Asynchronous muscles, in which there is not a 1:1 correspondence between neural activation and contraction, are a radically different design. Rather than rapid calcium cycling, they rely on delayed activation and deactivation, and the resonant characteristics of the wings and exoskeleton to guide their extremely high-frequency contractions. They thus avoid many of the modifications and attendant trade-offs mentioned above, are more powerful and more efficient than high-frequency synchronous muscles, but are considerably more restricted in their application.

Comparative Physiology of Insect Flight Muscle

Insect flight is powered by muscles that attach more-or-less directly to the wings (direct flight muscles) and muscles that bring about wing movement by distorting the insect’s thorax (indirect flight muscles). Flight stability and steering are achieved by differential activation of power muscles and by the activity of control muscles that alter wing stroke amplitude and angle of attack. One evolutionary trend seen when comparing more advanced with less advanced fliers is a reduction in the number of power muscles and an increase in the number of control muscles. On the basis of the neural control of contraction, insect muscles may be divided into synchronous muscles and asynchronous muscles. In synchronous muscles there is neural input and evoked muscle action potentials associated with each contraction. Asynchronous muscles are turned on by neural input, but, when activated, they can contract in an oscillatory manner if attached to an appropriate, mechanically resonant load. The features of asynchronous muscles that allow oscillatory contraction are delayed stretch activation and delayed shortening deactivation. Because asynchronous muscles do not have to be turned on and off by neural input for each contraction, they are expected to be more efficient and more powerful than are synchronous muscles for high frequency operation.

Structural organization of two fast, rhythmically active crustacean muscles.

SummaryThe organization of the flagellum abductor muscle and of a scaphognathite levator muscle of the green crab, Carcinus maenas, has been compared quantitatively using light and electron microscopy. These muscles are rhythmically active at relatively high frequencies and for long durations. Fibers of both muscles are interconnected to form fascicles of 50 or more fibers within which there is cytoplasmic continuity. A single muscle is made up of 8–12 fascicles. Individual fibers consist of a peripheral rind of densely packed mitochondria, a thick region of glycogen granules, and myofibrils arranged into scattered central islands. Less than half the volume-density of these muscles is contractile material, the balance being largely mitochondria and glycogen. The fibers within a muscle are structurally similar. They have short sarcomeres (about 2 μm), thin to thick filament ratios of about 3:1, and junctions between the sarcoplasmic reticulum and the transverse tubules at the M line. Sarcoplasmic reticulum occupies about 10% of the myofibrillar volume-density. A well developed sarcoplasmic reticulum appears to underlie the capacities of these two muscles for high frequency contraction; extensive mitochondria and glycogen stores should confer fatigue resistance under both aerobic and anaerobic conditions.

Coding of acoustic information in cockroach giant fibers

Abstract Interneurons in the ventral nerve cord of Periplaneta americana are excited by sound stimuli to the cerci. The responsiveness of giant fibers in the nerve cord generally declines with increasing sound frequency but the frequency-response curve is complex with small sensitivity peaks along its course. The frequency-response curve for smaller interneurons differs from that of the largest giant fibers in having a pronounced sensitivity peak near 300 Hz. At sound frequencies below about 200 Hz, giant fiber spikes occur at the same frequency as impinging sound waves. Thus information about the frequency of sound stimuli is present in the nerve cord in the temporal pattern of activity in giant fibers at low sound frequencies, and in the spatial pattern of activity between large and small units of the nerve cord at higher sound frequencies.

Factors affecting muscle activation in the hydroid Tubularia.

1. Activating the distal opener system (DOS), one of the conducting systems of the hydroid Tubularia, causes synchronous opening of the distal tentacles. Simultaneously recorded potentials (DOS pulses = DOSPs) from the vicinity of the responding muscles have two components: (a) an initial, short, all-or-nothing pulse reflecting activity in the conducting system, and, after a brief delay; (b) a second, slower potential thought to be a muscle action potential because its amplitude varies monotonically with that of tentacle movement. The amplitude of the second component is here used as a measure of the intensity of muscle activation.2. The second DOSP component is depressed by preceding DOS activity (defacilitation); by spontaneous tentacle movement including but not restricted to spontaneous DOS firing; by firing of the HP sytsem, one of the pacemaker systems in the polyp; and during the mouth opening associated with defecation. In all instances the first DOSP component is unchanged, indicating that the d...