Sound produced by muscle tightening

Sound produced by muscle tightening

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If you are at some quiet place, you will hear some mild noise when you tighten your jaw. Why is this? Is this sound produced by face/jaw muscle?


The source of a sound vibrates, bumping into nearby air molecules which in turn bump into their neighbours, and so forth. This results in a wave of vibrations travelling through the air to the eardrum, which in turn also vibrates. What the sound wave will sound like when it reaches the ear depends on a number of things such as the medium it travels through and the strength of the initial vibration.

In the following activities, students will use simple materials to create, visualize and feel sound waves, investigate vibration and its role in producing sound, and make their own percussion instruments.

List of Activities:


Describe how sound is produced.

Understand how our inner ear contributes to hearing.

List some properties of sound.

Describe what pitch is and how it varies.


See individual activities for materials.


Sound is a type of energy made by vibrations. When an object vibrates, it causes movement in surrounding air molecules. These molecules bump into the molecules close to them, causing them to vibrate as well. This makes them bump into more nearby air molecules. This “chain reaction” movement, called sound waves, keeps going until the molecules run out of energy. As a result, there is a series of molecular collisions as the sound wave passes through the air, but the air molecules themselves don’t travel with the wave. As it is disturbed, each molecule just moves away from a resting point but then eventually returns to it.

Pitch and Frequency
If your ear is within range of such vibrations, you hear the sound. However, the vibrations need to be at a certain speed in order for us to hear them. For example, we would not be able to hear the slow vibrations that are made by waving our hands in the air. The slowest vibration human ears can hear is 20 vibrations per second. That would be a very low-pitched sound. The fastest vibration we can hear is 20,000 vibrations per second, which would be a very high-pitched sound. Cats can hear even higher pitches than dogs, and porpoises can hear the fastest vibrations of all (up to 150,000 times per second!). The number of vibrations per second is referred to as an object’s frequency, measured in Hertz (Hz).

Pitch is related to frequency, but they are not exactly the same. Frequency is the scientific measure of pitch. That is, while frequency is objective, pitch is completely subjective. Sound waves themselves do not have pitch their vibrations can be measured to obtain a frequency, but it takes a human brain to map them to that internal quality of pitch.

The pitch of a sound is largely determined by the mass (weight) of the vibrating object. Generally, the greater the mass, the more slowly it vibrates and the lower the pitch. However, the pitch can be altered by changing the tension or rigidity of the object. For example, a heavy E string on an instrument can be made to sound higher than a thin E string by tightening the tuning pegs, so that there is more tension on the string.

Nearly all objects, when hit, struck, plucked, strummed or somehow disturbed, will vibrate. When these objects vibrate, they tend to vibrate at a particular frequency or set of frequencies. This is known as the natural frequency of the object. For example, if you ‘ping’ a glass with your finger, the glass will produce a sound at a pitch that is its natural frequency. It will make this same sound every time. This sound can be changed, however, by altering the vibrating mass of the glass. For example, adding water causes the glass to get heavier (increase in mass) and thus harder to move, so it tends to vibrate more slowly and at a lower pitch.

What is Sound?
When we hear something, we are sensing the vibrations in the air. These vibrations enter the outer ear and cause our eardrums to vibrate (or oscillate). Attached to the eardrum are three tiny bones that also vibrate: the hammer, the anvil, and the stirrup. These bones make larger vibrations within the inner ear, essentially amplifying the incoming vibrations before they are picked up by the auditory nerve.

The properties of a sound wave change when it travels through different media: gas (e.g. air), liquid (e.g. water) or solid (e.g. bone). When a wave passes through a denser medium, it goes faster than it does through a less-dense medium. This means that sound travels faster through water than through air, and faster through bone than through water.

When molecules in a medium vibrate, they can move back and forth or up and down. Sound energy causes the molecules to move back and forth in the same direction that the sound is travelling. This is known as a longitudinal wave. (Transverse waves occur when the molecules vibrate up and down, perpendicular to the direction that the wave travels).

Speaking (as well as hearing) involves vibrations. To speak, we move air past our vocal cords, which makes them vibrate. We change the sounds we make by stretching those vocal cords. When the vocal cords are stretched we make high sounds and when they are loose we make lower sounds. This is known as the pitch of the sound.

The sounds we hear every day are actually collections of simpler sounds. A musical sound is called a tone. If we strike a tuning fork, it gives off a pure tone, which is the sound of a single frequency. But if we were to sing or play a note on a trumpet or violin, the result is a combination of one main frequency with other tones. This gives each musical instrument its characteristic sound.

Muscular system anatomy

Walking, talking, sitting, and standing are all controlled by muscles. We even have muscles that are not under our conscious control, like the ones controlling our posture and the contraction of blood vessels. Muscles are commonly only associated with strength, but there are numerous actions that muscles do behind the scenes that help keep us alive and healthy.

There are three recognized types of muscles within our body. Each has been specialized to be the best suited to a particular task, which makes them an important component of normal functioning bodies. However, all three types use the movement of actin against myosin to create a contraction.

  • Skeletal muscle: A form of striated muscle tissue that is the only type of muscle in the body under voluntary control. Most skeletal muscle is attached to bones by tendons, which are bundles of collagen fibers capable of withstanding tension.
  • Smooth muscle: A form of non-striated muscle tissue, this is involuntary or not under our direct control. This makes smooth muscle ideal for places such as the stomach and intestine as well as the blood vessels. Despite being the weakest of all the muscle tissues, smooth muscles perform all of the functions the body needs to maintain automatically without our direct input.
  • Cardiac muscle: An involuntary, striated muscle type found in the heart. These types of muscle tissue form the thick middle layer of the heart and are responsible for coordinated contractions, allowing blood to be efficiently pumped out of the atria and ventricles to the rest of the body. The heart is the only muscle in the body that never stops contracting.


Sounds were composed of short pulses (<20 ms) emitted alone or in series, and in a narrow band of low frequencies (<1 kHz). The sounds of 55–108 mm (SL) fish ranged in pulse period from 90.0 to 128.6 ms, and in number of pulses per train from 2.9 to 6.4 pulses (Table 1). Pulse duration was positively related to SL, increasing from 10.8 to 19.7 ms whereas dominant frequency was negatively related to SL, decreasing from 700 to 340 Hz (Table 1).

Effects of anaesthesia and swimbladder filling on acoustic features

The comparison of experimental conditions (i.e. before anaesthesia, after anaesthesia and after swimbladder filling) using Friedman's test revealed that experiments induce significant differences in some acoustic features such as pulse duration (χ 2 =13.56, d.f.=2, P=0.0003) and dominant frequency (χ 2 =13.56, d.f.=2, P=0.0003), but not in pulse period (χ 2 =4.667, d.f.=2, P=0.1066) or number of pulses per sound (χ 2 =1.556, d.f.=2, P=0.5690 Table 2). Pairwise comparisons showed that pulse duration (15.04 vs 15.01 ms, Dunn's test, P>0.05), dominant frequency (484.7 vs 483.1 Hz, Dunn's test, P>0.05), pulse period (110.8 vs 113.2 ms, Dunn's test, P>0.05) and number of pulses (4.7 vs 4.7, Dunn's test, P>0.05 Table 2) were not affected by anaesthesia. In contrast, the swimbladder filling induced a significant decrease in pulse duration of approximately 3 ms (2.93±0.07, N=9) from 15.0 to 12.1 ms (Dunn's test, P<0.001 Table 2), and a significant increase in dominant frequency of approximately 105 Hz (104.6±2.71, N=9) from 485 to 589 Hz (Dunn's test, P<0.001 Table 2). Overall, it clearly appears that the swimbladder filling specifically acted on size-related acoustic features.

Effects of anaesthesia and swimbladder (SWB) filling on the acoustic features in Amphiprion clarkii


Deeper attention to the oscillograms showed changes in the sound waveform after filling the swimbladder. Although the number of oscillation cycles did not vary (6.53 vs 6.55 Wilcoxon matched-pairs signed rank test, P=0.4961), all recorded pulses exhibited a waveform with a decrease in the period of oscillation cycles (Fig. 3B). This observation matched the upward shift observed in peak frequency (see white arrows in Fig. 3C,D). Such changes in acoustic features indicate that sound radiation appeared to be affected by the swimbladder filling. These results were also supported by the change in Q3dB, decreasing from 4.1 to 3.7 (Wilcoxon matched-pairs signed rank test, P=0.0039) after the swimbladder filling.

Swimbladder volume and resonant frequency

Swimbladder volume was exponentially related to fish size (r=0.99, P<0.0001 Fig. 4A): the more fish size increased, the more swimbladder volume increased. Natural dominant frequencies produced by fish decreased by an octave from 700 Hz in a 55 mm SL individual with a 0.49 cm 3 swimbladder volume to 340 Hz in a 108 mm SL individual with a 3.85 cm 3 swimbladder volume (Fig. 4A, Table 1). Frequencies emitted by fish were then compared with the resonant frequency calculated on the basis of the radius of a bubble-like swimbladder of equivalent volume (Fig. 4B). Although values were rather close and displayed the same scatter plot (ANCOVA, test for common slopes: F1,16=0.0059, P=0.9398), the calculated resonant frequency values were inferior to natural dominant frequencies emitted by fish. This finding strongly suggested that sound frequency is not determined by the natural resonant frequency of the swimbladder.

Oscillogram of one pulse illustrating the difference in sound waveform between an intact Amphiprion clarkii (A) and a fish with the swimbladder filled (B). The vertical lines delimit the pulse duration. Power spectra of the same pulses showing the peak frequency (see white arrows) in an intact fish (C) and a fish in which the swimbladder was filled (D).

Oscillogram of one pulse illustrating the difference in sound waveform between an intact Amphiprion clarkii (A) and a fish with the swimbladder filled (B). The vertical lines delimit the pulse duration. Power spectra of the same pulses showing the peak frequency (see white arrows) in an intact fish (C) and a fish in which the swimbladder was filled (D).

Morphological study

Generally speaking, the swimbladder of A. clarkii is a thin-walled sac located in the dorsal portion of the body cavity and surrounded by bony structures such as vertebrae and ribs. Amphiprion clarkii possesses 11 precaudal vertebrae (Fig. 5). The first two each possess a pair of epineural ribs, the second being the longest. From the third to the eleventh vertebrae, the vertebrae possess pairs of ribs and intermuscular bones as well. From the sixth to the eleventh vertebrae, there are pairs of ventral parapohyses on which ribs articulate (Fig. 5). These ribs are dorsally closely attached to the serosa of the abdominal cavity. The anterodorsal part of the swimbladder leans against the vertebral column. From the second to the seventh vertebrae, there is a groove at the midline that makes the swimbladder anteriorly bilobate (Fig. 6). Both lobes surround the ventral apophysis of the first vertebra (onto which the retractor dorsalis muscle inserts). The dorsocaudal part of the swimbladder is connected to the last four precaudal vertebrae via the ventral parapohyses that are more and more elongated (Fig. 5). The swimbladder is laterally delimited by the different pairs of ribs onto which the wall is attached (Fig. 6). The posterior part of the swimbladder presses against the second pterygiophore of the anal fin (Fig. 5). The swimbladder wall is very thin (∼20 μm) and histological cross-sections cannot clearly identify all of its layers (Fig. 7). The tunica interna of the swimbladder is a cuboidal epithelium. The tunica externa contains a thicker fibrous layer, which is more developed ventrally. At this level, the tunica externa is also doubled by the coelomic epithelium lining the abdominal cavity. Moreover, the tunica externa is also connected to a second fibrous layer lining the myosepta in relation with the ribs (Fig. 7C). As a result, the movements of the ribs have a direct influence on the whole fibrous layer.

(A) Relationship between swimbladder volume and fish size (SL) in Amphiprion clarkii. Fish (N=10) ranged in SL from 55 to 108 mm. (B) Comparison between dominant frequencies of natural sounds (filled circles) and calculated resonant frequencies (open triangles) in Amphiprion clarkii. Note that data were ln-transformed because they were exponentially related to SL. Resonant frequencies were calculated for a depth of 30 cm.

(A) Relationship between swimbladder volume and fish size (SL) in Amphiprion clarkii. Fish (N=10) ranged in SL from 55 to 108 mm. (B) Comparison between dominant frequencies of natural sounds (filled circles) and calculated resonant frequencies (open triangles) in Amphiprion clarkii. Note that data were ln-transformed because they were exponentially related to SL. Resonant frequencies were calculated for a depth of 30 cm.

Sound resonance experiments

Buccal jaws

Striking the buccal jaws using the impact hammer generated a waveform with an asymmetrical half-cycle with a shorter rise than fall time (6.3 and 8.5 ms, respectively, N=45 Fig. 8). The rise time represents the period during which the hammer was transferring energy to the jaws. It started with a relatively low force as pressure on the jaws increased and then continued with a steeper slope. The fall time represents the time when the hammer bounced back from the surface of the jaws. The slope of the fall time decreased just before return to the baseline.

The sound waveform induced by the hammer strike on buccal jaws displayed differences with that of natural sounds emitted by fish. It suddenly disappeared into the background noise without displaying decay (see Fig. 8). Comparison of hammer and sound traces indicated that the onset of the hammer trace and the sound waveform were closely aligned (Fig. 8). Generally speaking, hammer duration (rise and fall time) closely corresponded to sound duration.

Lateral view of the skull, axial skeleton ad hypural structure in Amphiprion clarkii showing the location of the swimbladder (in grey) in relation to the rib cage. Roman numerals refer to the first five vertebrae. Scale bar, 5 mm.

Lateral view of the skull, axial skeleton ad hypural structure in Amphiprion clarkii showing the location of the swimbladder (in grey) in relation to the rib cage. Roman numerals refer to the first five vertebrae. Scale bar, 5 mm.

Changes in hammer force (i.e. harder hits) caused significant changes in sound parameters (Fig. 9). Sound duration increased from 8.9 to 13.5 ms (r=0.87, P<0.0001, N=45), and sound amplitude increased from –64.6 to –58.1 dB rel. (r=0.87, P<0.0001, N=45) with harder hits. Inversely, peak frequency dropped from 1650 to 1100 Hz (r=–0.84, P<0.0001, N=45) and Q3dB decreased from 11.2 to 5.2 (r=–0.87, P<0.0001, N=45) with harder hits.

Comparisons of values calculated from regressions of variable force hammer strikes in three specimens of different size showed that hammer strikes had the same effects on sound duration (ANCOVA, test for common slopes: F2,39=0.1842, P=0.8325), sound amplitude (ANCOVA, test for common slopes: F2,39=0.3754, P=0.6894), sound frequency (ANCOVA, test for common slopes: F2,39=0.1678, P=0.8461) and Q3dB (ANCOVA, test for common slopes: F2,39=2.9250, P=0.0652), regardless of fish size. In addition, there were no significant differences between individuals of different size in sound duration (H=1.155, d.f.=2, P=0.5613), sound amplitude (H=1.140, d.f.=2, P=0.5656), sound frequency (H=1.754, d.f.=2, P=0.4161) or Q3dB (H=0.932, d.f.=2, P=0.6275), which suggests that buccal jaws may maintain similar acoustic properties as they increase in size.

Internal silicone cast of the swimbladder of Amphiprion clarkii. (A) Lateral view showing the imprints of the ribs. (B) Dorsal view with the imprints of the parapophyses and the first vertebrae. A midline groove is formed in the anterodorsal part because the swimbladder leans agaisnt the vertebral column. Scale bar, 5 mm.

Internal silicone cast of the swimbladder of Amphiprion clarkii. (A) Lateral view showing the imprints of the ribs. (B) Dorsal view with the imprints of the parapophyses and the first vertebrae. A midline groove is formed in the anterodorsal part because the swimbladder leans agaisnt the vertebral column. Scale bar, 5 mm.

Sources of ATP

ATP supplies the energy for muscle contraction to take place. In addition to its direct role in the cross-bridge cycle, ATP also provides the energy for the active-transport Ca ++ pumps in the SR. Muscle contraction does not occur without sufficient amounts of ATP. The amount of ATP stored in muscle is very low, only sufficient to power a few seconds worth of contractions. As it is broken down, ATP must therefore be regenerated and replaced quickly to allow for sustained contraction. There are three mechanisms by which ATP can be regenerated: creatine phosphate metabolism, anaerobic glycolysis, fermentation and aerobic respiration.

Creatine phosphate is a molecule that can store energy in its phosphate bonds. In a resting muscle, excess ATP transfers its energy to creatine, producing ADP and creatine phosphate. This acts as an energy reserve that can be used to quickly create more ATP. When the muscle starts to contract and needs energy, creatine phosphate transfers its phosphate back to ADP to form ATP and creatine. This reaction is catalyzed by the enzyme creatine kinase and occurs very quickly thus, creatine phosphate-derived ATP powers the first few seconds of muscle contraction. However, creatine phosphate can only provide approximately 15 seconds worth of energy, at which point another energy source has to be used (Figure 5).

Figure 5. Muscle Metabolism. Some ATP is stored in a resting muscle. As contraction starts, it is used up in seconds. More ATP is generated from creatine phosphate for about 15 seconds.

As the ATP produced by creatine phosphate is depleted, muscles turn to glycolysis as an ATP source. Glycolysis is an anaerobic (non-oxygen-dependent) process that breaks down glucose (sugar) to produce ATP however, glycolysis cannot generate ATP as quickly as creatine phosphate. Thus, the switch to glycolysis results in a slower rate of ATP availability to the muscle. The sugar used in glycolysis can be provided by blood glucose or by metabolizing glycogen that is stored in the muscle. The breakdown of one glucose molecule produces two ATP and two molecules of pyruvic acid, which can be used in aerobic respiration or when oxygen levels are low, converted to lactic acid (Figure 6).

Figure 6. Glycolysis and Aerobic Respiration. Each glucose molecule produces two ATP and two molecules of pyruvic acid, which can be used in aerobic respiration or converted to lactic acid. If oxygen is not available, pyruvic acid is converted to lactic acid, which may contribute to muscle fatigue. This occurs during strenuous exercise when high amounts of energy are needed but oxygen cannot be sufficiently delivered to muscle.

If oxygen is available, pyruvic acid is used in aerobic respiration. However, if oxygen is not available, pyruvic acid is converted to lactic acid, which may contribute to muscle fatigue. This conversion allows the recycling of the enzyme NAD + from NADH, which is needed for glycolysis to continue. This occurs during strenuous exercise when high amounts of energy are needed but oxygen cannot be sufficiently delivered to muscle. Glycolysis itself cannot be sustained for very long (approximately 1 minute of muscle activity), but it is useful in facilitating short bursts of high-intensity output. This is because glycolysis does not utilize glucose very efficiently, producing a net gain of two ATPs per molecule of glucose, and the end product of lactic acid, which may contribute to muscle fatigue as it accumulates.

Aerobic respiration is the breakdown of glucose or other nutrients in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP. Approximately 95 percent of the ATP required for resting or moderately active muscles is provided by aerobic respiration, which takes place in mitochondria. The inputs for aerobic respiration include glucose circulating in the bloodstream, pyruvic acid, and fatty acids. Aerobic respiration is much more efficient than anaerobic glycolysis, producing approximately 36 ATPs per molecule of glucose versus four from glycolysis. However, aerobic respiration cannot be sustained without a steady supply of O2 to the skeletal muscle and is much slower (Figure 7). To compensate, muscles store small amount of excess oxygen in proteins call myoglobin, allowing for more efficient muscle contractions and less fatigue. Aerobic training also increases the efficiency of the circulatory system so that O2 can be supplied to the muscles for longer periods of time.

Figure 7. Cellular Respiration. Aerobic respiration is the breakdown of glucose in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP. Approximately 95 percent of the ATP required for resting or moderately active muscles is provided by aerobic respiration, which takes place in mitochondria.

Muscle fatigue occurs when a muscle can no longer contract in response to signals from the nervous system. The exact causes of muscle fatigue are not fully known, although certain factors have been correlated with the decreased muscle contraction that occurs during fatigue. ATP is needed for normal muscle contraction, and as ATP reserves are reduced, muscle function may decline. This may be more of a factor in brief, intense muscle output rather than sustained, lower intensity efforts. Lactic acid buildup may lower intracellular pH, affecting enzyme and protein activity. Imbalances in Na + and K + levels as a result of membrane depolarization may disrupt Ca ++ flow out of the SR. Long periods of sustained exercise may damage the SR and the sarcolemma, resulting in impaired Ca ++ regulation.

Intense muscle activity results in an oxygen debt, which is the amount of oxygen needed to compensate for ATP produced without oxygen during muscle contraction. Oxygen is required to restore ATP and creatine phosphate levels, convert lactic acid to pyruvic acid, and, in the liver, to convert lactic acid into glucose or glycogen. Other systems used during exercise also require oxygen, and all of these combined processes result in the increased breathing rate that occurs after exercise. Until the oxygen debt has been met, oxygen intake is elevated, even after exercise has stopped.

Songbirds can control single vocal muscle fibers when singing

A male zebra finch from Australia. Credit: Jim Bendon/Wikipedia

The melodic and diverse songs of birds frequently inspire pop songs and poems, and have been for centuries, all the way back to Shakespeare's "Romeo and Juliet" or "The Nightingale" by H.C. Andersen.

Despite our fascination with birdsong, we are only beginning to figure out how this complicated behavior is being produced and which extraordinary specializations enabled songbirds to develop the diverse sound scape we can listen to every morning.

Songbirds produce their beautiful songs using a special vocal organ unique to birds, the syrinx. It is surrounded by muscles that contract with superfast speed, two orders of magnitude faster than, for example, human leg muscles.

"We found that songbirds have incredible fine control of their song, including frequency control below one Hertz," says Iris Adam, lead author on the study and Assistant Professor at Department of Biology, University of Southern Denmark.

A motor unit is the fundamental contraction unit of muscle and consists of a motor neuron and the number of muscle fibers it connects to and activates. Combining tissue preparations to count muscle and nerve fibers and mathematical models, the researchers could show that a large portion of the motor units must be very small and even as small as single muscle fiber.

"Motor units vary in size from several hundreds or thousands of muscle fibers in our leg muscles down to only 5-10 in the muscles controlling eye position and the muscles in the larynx," says Dr. Coen Elemans, senior author on the study and head of the Sound Communication and Behavior group at the University of Southern Denmark.

"In zebra finch song muscles our models predicted that 13-17% of the motor neurons innervates a single muscle fiber."

This was such an extraordinary claim that the researchers developed a new technique that can measure the activity of all muscle fibers within a small muscle.

"Our new method allowed us for the first time to activate single motor neurons and visualize and record the activity of all responding muscle fibers simultaneously," Adam says.

"Like this we were able to show that the song muscles of zebra finches indeed contain motor units as small as one muscle fiber.", Adam adds.

To be able to understand what effect such small motor units can have on song the researchers also measured the amount of stress the muscles can make and how such stress changes the frequency of the sound.

Adam: "Next to small motor units, we discovered that songbird vocal muscles have the lowest stress measured in any vertebrate."

"To be able to study how changes in muscle force alter the sound made by the birds' vocal organ, the syrinx, we had to invent a new setup" Elemans adds.

"This setup blows air through the syrinx while we can control the muscles with small motors."

Songbird vocal muscles certainly pack a lot of extremes. "They are among the fastest muscles known, and now we show that they are also the weakest, with the highest level of control possible," says Adam.

This fine control is important. Previous research has shown that females can detect these small changes and use it to decide whether they are attracted to a male or not.

Songbirds evolved about 40 million years ago and quickly radiated into the speciose group of birds we know today. Song is crucial for females to find and judge males and can even drive speciation. A few important special features are thought to have been important for their success. Just as humans, songbirds need to learn their song from a tutor by imitation.

Adam: "We think that next to a special syrinx and their amazing ability to imitate sounds, the fine gradation of the song features such as pitch has increased the amount of different sounds a bird can make."

"We suggest that the fine graduation of sound has contributed to the radiated of songbirds," Elemans concludes.

Anatomy of the Hip Muscles

Hip muscle anatomy is a complex topic. This is because there are so many different muscles that give our hip joints a full range of motion. The hip muscles are composed of multiple flexors, extensors, adductors, abductors, and rotators that work together. When we talk about the muscles of the hips, we are discussing a very broad group. This can seem quite intimidating. By practising some of the exercises described at the end of this article, you integrate theory with actually feeling the individual muscles contract and relax.

The hip muscles surround the hip joint – a ball and socket joint between the femur (thigh bone) and three fused (in adults) pelvic bones – the ilium, pubis, and ischium. At the top of the femur, an angled, rounded head is supported by the femur neck. The femus head is hidden by the ilio- and ischiofemoral ligaments in the next image.

To the other side is the bulge of the greater trochanter, a point for muscle and tendon attachment that you can usually feel through the skin. At the opposite side of the greater trochanter, a little lower so that it sits under the neck, is the lesser trochanter. The word trochanter refers to these bony outcrops. The lower end of the femur forms the top of the knee joint.

The femur head fits into a similarly rounded indentation in the pelvis, at the bottom of the wing-shaped ileum and the top of the ischium and pubis bones. As the above image is a back view, only the top edge of the ileum – the iliac crest – is indicated. By around eight years of age, the ischium and pubis have fused. The ileum fuses to the ischium and pubis – at the acetabulum – in the early teenage years. This fusion occurs earlier in females.

Synovial fluid is produced by the synovial membrane, the cells of which produce a thick, gooey byproduct of blood plasma combined with lubricants and thickeners such as hyaluronic acid and the aptly named lubricin. Tiny areas of cartilage damage can be smoothed over as this gel can run into shallow indentations, in the same way as a facial blur cream fills pores to produce smoother skin.

Our hip joints must withstand extremely high pressures. A study using artificial model joints based on human anatomy showed that these forces are much greater than previously thought – when landing after a vertical jump the hip joint must deal with compression forces of more than eight times the body weight the hips of a a one-hundred-and-sixty-pound man would need to support a force of nearly 1,300 lbs. Just standing still produces a compressive force of more than double the body weight.

You may think that this force would be shared equally between both hips however, joint compression in each hip can be anywhere from 75 to 100% of the total body weight. The surrounding ligaments and muscles also provide continuous forces, which may explain why each hip must deal with more than 50% of the load. Postural changes and joint degeneration can also change the load on one side.

If someone suffering from hip pain is quite short and weighs 250 lbs, losing fifty pounds could postpone hip replacement surgery – each hip joint will only need to support between 300 and 400 lbs when standing, instead of up to 500 lbs. And we tend to spend a lot of time on our feet.

Our hip muscles work in groups, some contracting and others relaxing as muscle agonists and antagonists. Some muscles have minor roles in particular movements where they support the prime movers (the primary agonists) – when they play a supporting role, muscles are known as synergists.

Each muscle group contributes to certain types of movement. It is simpler to look at the different ranges of motion and describe which muscles play a role rather than list each muscle as a separate entity. Different patterns of movement should be well understood, together with specific terminology. The hip muscle diagram below shows a number of the muscles we will be discussing in the next sections.

Hip Flexors

When you flex your hip, you move the leg forward. Hip flexion is maximal with a high, forward kick that brings the leg above the level of the waist. More commonly, our hips flex to a 90° angle when we sit in a chair the lower the seat of the chair, the greater the flexion. Walking also requires hip flexion. It does not matter whether the knee bends or not only flexion provided by the hip muscles is discussed in this article.

The prime mover (agonist) for hip flexion is the psoas major muscle. This is a long, tapering (fusiform) muscle that originates at either side of the spine and inserts at the lesser trochanter of the femur. The psoas muscle contracts when the hip is flexed.

The other prime mover is the iliacus muscle. The iliacus muscle is a triangular sheet that connects the iliac bone to the lesser trochanter.

As the iliacus is joined to the psoas major at the thigh, both are sometimes referred to as a single hip muscle – the iliopsoas muscle. The iliopsoas is the body’s most important hip flexor. If you spend the majority of the day sitting down, the muscle becomes shorter, tilting the pelvis, and can change how you walk.

The rectus femoris also contracts during hip flexion, especially if the knee bends. This muscle is part of a muscle group called the quadriceps.

The next important agonist is the pectineus muscle that extends from the pubis of the pelvis to a point under the lesser trochanter. The psoas major, iliacus, rectus femoris, and pectineus all contract to move the hip joint forward.

As these four muscles contract, others relax. A group of muscles that contributes to flexion is the hamstring. Although the hamstring muscles’ primary role is to flex the knee, it also assists during hip flexion. The hamstrings are a group of three muscles: the semitendinosus, semimembranosus, and biceps femoris (long head). As the psoas major and iliacus muscles contract, this group relaxes. The hamstrings are, therefore, antagonists.

The other antagonist for hip flexion is the gluteus maximus. This is a large, thick muscle that covers the buttocks and tapers around the hips to insert at two ridges located approximately halfway along the front of the femur.

Many other muscles contribute minor supporting actions to stabilize the joint when being flexed. These will prevent the joint from inward or outward rotation and help to keep the hip in a flexed position for long periods.

Hip Extensors

Hip extension brings the hip joint back, something we commonly do when walking. While flexion is a step forwards, extension describes the position of that hip after the other leg has taken a step. The angle of hip extension is important – a larger angle helps to prevent falls. While the average young adult extends the hip by approximately twenty degrees at a comfortable walking speed, elderly people have been reported to have an extension angle of as low as six degrees.

While the gluteus maximus is an antagonist for hip flexion, in hip extension it is the primary mover. It contracts to bring the leg back – you can feel the large muscle in the buttock area pull as you walk.

The hamstrings are agonists during both hip flexion and extension, but the most important antagonists are the psoas and iliacus muscles. This makes complete sense, as these muscles contract to bring the hip joint forward, and should, therefore, relax during the opposite movement. By learning the names of the prime movers and antagonists of one movement, you can usually swap them around to give the names of the agonists and antagonists of the opposite motion.

Hip Adduction

When the leg is brought back towards the midline or the opposite side of the body, for example, if you cross one leg in front of the other when line-dancing or if you kick a soccer ball with the inside of your foot, you are adducting your hip.

There are five primary movers for hip adduction but these are simply referred to as the adductor group. The adductor group consists of:

  • Pectineus muscle
  • Gracilis muscle
  • Adductor magnus
  • Adductor longus
  • Adductor brevis

The pectineus is a flat, wide ribbon of muscle that joins the pubic bone to just under the lesser trochanter of the femur. You may remember that it is also an important agonist in hip flexion. Many muscles of the hip play roles in multiple movement patterns. The muscle fibers of the pectineus run at angles to each other, meaning that when you adduct the thigh you automatically bring it a little forward (flexion).

The long gracilis muscle crosses both the hip and knee joints from a pelvis origin. In the hip, the gracilis contracts to bring the hip (and knee) towards the pelvis.

The adductor magnus is a wide, deep, almost triangular sheet of muscle that runs almost as far along the femur as the gracilis. Magnus, longus, and brevis give us an easy reference – the main adductor muscle is the longest of the three, the longus is a little shorter than the magnus, inserting about halfway along the femur, and the brevis is the shortest and inserts just under the lesser trochanter.

Hip Abduction

To abduct is to take away. When the hip moves horizontally away from the midline, it is being abducted. The fatter the horse you sit on, the more your hip joints need to abduct.

The prime mover for hip abduction is the gluteus minimus – a deep, small muscle within the buttocks that originates quite close to the crest of the ilium bone and extends to the greater trochanter (the part of the hip bone you can feel on the outer side of your hip). If you image the muscle as a half-open fan, the handle is at the trochanter and the fan spreads along the flat surface of the pelvic ilium.

The gluteus medius lies immediately above the gluteus minimus and is also fan-like in shape with similar origin and attachments. Both the medius and minimus contract to bring the greater trochanter up towards the iliac crest – abduction. Even though it is the largest of the gluteal muscles, the gluteus maximus only plays a synergist role during this movement.

Hip Internal Rotation

Internal rotation of the hip joint involves turning the hip inwards so that the greater trochanter comes towards the front of the body. The best way to do this is to twist one knee towards the other.

The gluteus minimus, as its name suggests, is the smallest of the three gluteal muscles and lies beneath the other two muscles in the buttock region. This is the prime mover of internal rotation of the hip. This joint can turn towards the pelvis at a maximum angle of approximately 45° and, as you will probably have realized, a certain degree of rotation also occurs during other hip movements. When we consider that the hip joint is a ball and socket joint, this is easy to explain – the rolling action of the joint means that a lot of rotation is involved. Many synergist muscles limit rotation during adduction, abduction, flexion, and extension.

Internal rotation has one prime mover but around nine other hip muscles assist in this movement. These include the gluteus medius, adductor muscles, and tensor fascia latae (TFL). The TFL is a fusiform (tapered) muscle of about fifteen centimeters in length that attaches the lower spine and iliac crest to the tibia (top of the lower leg bone), running over the hip and greater trochanter. This muscle acts as a synergist for multiple hip movements but is primarily a rotation muscle.

Hip impingement or femoroacetabular impingement can prevent internal rotation due to high levels of pain. When left untreated, this can lead to osteoarthritis of the joint. Hip impingement is common in all ages and especially in the athletic community. When bone at the edge of the acetabulum is misshapen, either as a congenital disorder or over time, the result may be pincer impingement. If it is the femur head that grows incorrectly, the result may be cam impingement. These bony outcrops mean smooth movement is not possible and, over time, the cartilage becomes damaged. It is no longer smooth and causes friction. Areas can become so thin that the femur head and acetabulum rub against each other.

Hip External Rotation

The primary mover for external rotation is the gluteus maximus. You can easily remember the prime rotators with “a small (minimus) internal rotation and a large (maximus) external rotation at the buttocks (gluteus)”.

There are six outward rotator muscles – the gluteus maximus, obturator internus, superior gemellus, inferior gemellus, quadratus femoris, and obturator externus.

The gemellus superior, gemellus inferior, and obturator internus muscles form a group called the triceps coxae. The triceps coxae are hip rotators and general hip stabilizers.

Muscles that assist in rotation include the iliopsoas, sartorius, and biceps femoris of the hamstrings. Finally, the piriformis – a flat and superficial muscle under the gluteal muscles – allows rotation when standing (when the hip is in extension) as well as pelvic tilting.

Knowing the names of every hip muscle is rarely necessary, but many athletes like to know exactly how to exercise and warm-up. By understanding how each muscle contributes to hip range of motion and how these muscles cross the hip joint, unnecessary injuries can be avoided. This Michigan State University list provides a quick overview of the various muscles involved in hip range of motion.

How To Use Tuning Forks For Chakras

First, what are the chakras?

The seven chakras of the body are circular vortexes of energy that are found in seven points along the spinal column.

All the seven chakras are linked to various glands and organs in the body.

To enable chakra healing with the use of tuning forks, it’s good to know what each of the seven chakras requires when it comes to healing sound.

The frequencies are measured in hertz (Hz). As the Pure Integrated Health Services Foundation reports, here are the frequencies commonly used to stimulate the different chakras:

  • 1 st chakra makes use of 396 Hz and it helps to release fear and guilt.
  • 2 nd chakra makes use of 417 Hz and it enables change.
  • 3 rd chakra makes use of 528 Hz and it enables transformation.
  • 4 th chakra makes use of 639 Hz and it helps one connect to others.
  • 5 th chakra makes use of 741 Hz and it encourages expression and solutions to problems.
  • 6 th chakra makes use of 852 Hz and it encourages the intuition to be awakened.
  • 7 th chakra makes use of the previous six frequencies as it connects one to the universe.

When your chakras are to be stimulated by tuning forks, you can expect to be asked to lie down on a massage table.

The practitioner will hold the tuning fork over the chakra (or all of them, one at a time) to create greater harmony in the body.

He or she will create an energy bridge from one chakra to the next, and two forks are usually used to track the energy channels all the way up the base of the spine.

Sound therapy is said to restore the chakra balance and help the energy to move better throughout the body.

Sound - Class 8 : Notes

(i) Sound is a form of energy like heat energy, light energy, potential energy and kinetic energy. It causes a sensation of hearing in our ears.
(ii) Sound helps us communicate with each other.

Production of Sound:
(i) Sound is produced due to the vibration of object.
(ii) The motion of materials or objects causes vibration.
(iii) Vibration is a kind of rapid to and fro motion of an object a central position. It is also referred to as oscillation.
(a) A stretched rubber band when plucked vibrates and produces sound.
(b) In the music room of your school you hear the sounds made by musical instruments like flute, tabla, harmonium, guitar etc. because of vibration.
(c) When a spoon is beaten on the plate, it starts vibrating and produces sound.

Sound Produced by Humans:
(i) In humans sound is produced because of vibration of his voice box or larynx.
(ii) It is situated at the upper end of windpipe. There are two stretched membranes called vocal cords attached in larynx with a narrow slit between them for passes air.

(iii) Muscles attached to the vocal cords can make the cords tight or loose. When the vocal cords are tight and thin, produce different type or quality of voice.

Propagation of Sound:
(i) The travelling of sound is called propagation of sound.
(ii) Sound is propagated by the to and fro motion of particles of the medium.

Sound needs a medium to propagate:
(i) A medium is necessary for the propagation of sound waves.
(ii) The matter or substance through which sound is transmitted is called a medium. The medium can be solid, liquid or gas.
(iii) Sound cannot travel in vacuum. A true vacuum refers to the complete absence of matter. Sound wave can travel only through matter. So, sound needs a physical medium in order to propagate anywhere.
(iv) We hear sound which comes to us through air medium particles.
(v)Aquatic animals communicate as sound travels through water.

We hear Sound through Our Ears:
(i) The funnel shaped outer ear collects the sound. The sound wave passes through the ear canal to thin and stretched membrane called eardrum or tympanum. The ear drum vibrates and produces vibrations.
(ii) The vibrations are amplified by the three bones of the middle ear called hammer, anvil and stirrup. The middle ear then transmits the sound wave to the inner ear.
(iii) In the inner ear the sound wave converted into electrical signals by cochlea and send to the brain through the auditory nerves. The brain interprets the signals as sound. That is how we hear.

Amplitude, Time Period and Frequency of a Sound:
(i) Sound is produced by to and fro motion of an object is known as vibration. This motion is also called oscillatory motion.
(ii) Sound propagates from one place to another in the form of waves, i.e. because of the disturbance of particles of the medium.
(iii) Wave is a phenomenon or disturbance in which energy is transferred from one point to another without any direct contact between the points. So, sound is considered as a wave.

1. Amplitude:
(i) In a sound wave, the maximum displacement associated with the particle constituting a wave is called its amplitude.
(ii) It is represented by ‘A’. SI unit is metre.

2. Frequency:
(i) The number of vibrations and osscillations completed by an object in one second is the frequency of the sound.
(ii) Frequency = Number of Oscillation/ Total time

ⱱ = 1/T
(iii) Frequency is expressed in hertz. It is represented by Hz.
(iv) A frequency of 20 Hz is twenty oscillation per second.
(v) If an object oscillates or vibrates 80 times in 1 second, then its frequency will be equal to 80 hertz.

From above figure waves have same amplitude but number of vibrations in one second are different. So their frequencies are different.

3. Time period:
(i) The time taken by object or the particle of the medium for completing one oscillation or vibration is called the time period.
(ii) It is represented by ‘T’. SI unit is Second.
(iii) Time period = Time/ Numbers of oscillation or vibration.

Loudness and Pitch:
1. Loudness:
(i) Loudness of sound is the measure of sound energy reaching the ear per second.
(ii) Loudness or softness of a sound depends upon its amplitude.
(iii) Loudness of sound is proportional to the square of the amplitude of the vibration producing the sound.

Loudness α (Amplitude) 2
If the amplitude becomes twice, the loudness increases by a factor of 4.

(iv) Loudness of sound is measured in decibel (dB).

The following table gives different types loudness of sound coming from various sources.

Normal breathing 10 dB
Soft whisper (at 5m) 30dB
Normal conversation 60dB
Busy traffic 70dB
Average factory 80dB

2. Pitch or Shrillness:
(i) Pitch is the sensation (Brain interpretation) of the frequency of an emitted sound.
(ii) The pitch of sound (Shrillness or flatness) depends on the frequency of vibration.
(iii) Sound with greater frequency is shriller and has higher pitch. Sound with lower frequency is less shrill and of lower pitch.

(i) Children and women produce high frequency sound so their sound is shriller or higher pitch. On the other hand, an adult male produces lower frequency sound so his sound is less shrill or lower pitch.
(ii) A drum produces lower frequency sound which is less shrill or lower pitch, while a whistle produces higher frequency sound which is shriller or higher pitch.

Audible and Inaudible Sound:
(i) Sounds of frequency range between 20 Hz to 20,000 Hz are called audible sound. The human beings can hear the sound range between 20 hertz to 20,000 hertz.
(ii) Sound of frequency below 20 hertz and above 20,000 hertz is called sound of inaudible range. Humans cannot hear the sound of inaudible range.
(iii) Many animals, such as dogs, cats, etc. can hear the sound with frequency above 20,000 hertz.

Noise and Music:
1. Noise: It is the sound that is unpleasant to hear. (E.g., Sound produced by vehicles)
2. Music: It is the sound that is pleasant to hear. (E.g., Sound coming out of musical instruments)

Noise Pollution:
(i) Presence of excessive, loud, unwanted or unbearable sound to our ears sounds in the environment is called noise pollution.
(ii) Examples: sounds of vehicles, explosions including bursting of crackers, machines, loudspeakers, television with high volume, loudspeakers etc

Problems due to Noise Pollution:
(i) Due to noise pollution many types of health related problems occurs, such as lack of sleep (insomnia), hypertension (High blood pressure), loss of hearing, anxiety, etc. Sound above 80 dB is very painful to hear.
(ii) A person who is exposed to loud sound continuously may get permanent or temporary impairment of hearing or loss of hearing.

Measures to Limit Noise Pollution:
Noise can be limited or controlled by controlling the noise source. Noise pollution can be controlled by taking following steps:
(i) TV, radio or loudspeakers should be played at low volume.
(ii) By installing high quality silencing devices in vehicles, air craft engines, industrial machines and home appliances.
(iii) We should not use loud vehicle horns.
(iv) Noise producing industries should be set up away from residential areas.
(v) Trees absorb sound. So plantation of trees should be done along the road sides and around buildings
(vi) Awareness campaign and noisy operations should be done to make people aware about the harmful effects of noise pollution and measures to control noise pollution.