vocal folds , also known as vocal cords or reeds , are composed of infolding twins of mucous membranes stretching horizontally, from back to back front, across the larynx. They vibrate, modulating the airflow released from the lungs during phonation.
Open while breathing and vibrating to speak or sing, the folds are controlled through the vagus nerve.
Video Vocal folds
Structure
The vocal folds are located in the larynx at the top of the trachea. They are attached posteriorly to the arytenoid cartilage, and anterior to the thyroid cartilage. They are part of a glottis that includes rima glottidis. The outer end is attached to the muscle in the larynx while the inner edge, or margin, is free to form an opening called rima glottidis. They are built from the epithelium, but they have several muscle fibers in them, namely the vocal muscles that tighten the front of the ligament near the thyroid cartilage. They are flat and pearly white triangular ribbons. On either side of the glottis are two vestibular folds or fake vocal folds that have a small sac between the two.
Located above the larynx, the epiglottis acts as a flap that closes the trachea during the swallowing action to direct the food to the esophagus. If food or fluid does not enter the trachea and contact the vocal cords it causes a coughing reflex to expel the problem to prevent lung aspiration.
Variations
Men and women have different sizes of vocal folds. Adult men's voice is usually low-pitched because of the longer and thicker folds. Male vocal folds are between 1.75 cm and 2.5 cm (approximately 0.75 "to 1.0") in length, while the female vocal cords are between 1.25 cm and 1.75 cm (approx. approximately 0.5 inches to 0.75 inches) in length. Children's vocal folds are much shorter than men and women. Differences in vocal band length and thickness between male and female cause differences in the vowel pitch. In addition, genetic factors cause variation between same-sex members, with male and female voices categorized into the type of sound.
Fake vocal folds
Vocal folds are sometimes called 'genuine vocal folds' to distinguish them from 'fake vocal folds' known as vestibular folds or ventricular folds . It is a pair of thick folds of mucous membrane that protects and sits slightly superior to the finer true folds. They have a minimal role in normal phonation, but are often used to produce loud tones in Tibetan songs and Tuvan throats, as well as in musical screams and vocal style of growl death.
Histology
The adult human vocal folds consist of very different layered structures at the histological level. The top layer consists of a stratified squamous epithelium bounded by a pseudo-ciliated epithelium. The surface of the inner layer of the squamous epithelium is covered by a layer of mucus (acting as a mucociliary clearance), which consists of two layers: the musinosum layer and the serous layer. Both layers of mucus provide a thick and watery environment for the posterior and superior cilia. Mucociliary clearance makes the vocal cords basically moist and lubricated. The epidermal layer is secured to deeper connective tissue by the basement membrane. Because fibrous and nonfibrous proteins are particularly amorphous in lamina propria, basement membranes apply strong retaining filaments such as collagen IV and VII to secure basal cell hemidesmosome to lamina propria. These attachments are strong enough to sustain beatings and stretching, in which VFs are imposed. The population density of some retaining fibers in the basement membrane, such as collagen VII, is genetically determined, and this genetics may affect the health and pathogenesis of the vocal cords.
The next three layers consist of lamina lipopolysaccharide (LP), which is grouped according to the histologic composition of elastin and collagen fibers, with fibroblasts, myofibroblasts and rarely intercalated macrophages. Superficial layer LP (SLLPs), also known as Reinke spaces, consists of amorphous and microfibril substances that allow this cover layer to "glide" over the inner layers with ease. The vibrational and viscoelastic characteristics of human VF are primarily associated with the molecular composition of SLLPs. In normal vocal folds, the jelly-like "reinke spaces" are very loose and abundant with interstitial proteins such as hyaluronic acid, fibronectin, proteoglycan such as fibromodulin, decoration and versicus. All these ECM components together regulate the water content of the vocal cords and create a thick shear property for it. The squamous epithelium and superficial lamina propria form a vocal mucosa that acts as a vibrational component in the phonation. The mucosal layer vibrates in the 100-1000 Hz frequency range and displaces at about 1mm. The middle layer of the phonograph record consists primarily of elastic fibers while the inner layer of LP consists of fewer elastin and more collagen fibers. Both of these layers have a bad distinction but are thicker than SLLP. The intermediate and inner layers of pear form a closed vowel ligament in the vocal fold and are responsible for the tension in the phonation. In the ECM community of vocal ligaments, fibrous proteins such as elastin and collagen are essential in maintaining proper elastic biomechanical properties of the vocal cords. Elastin fibers provide the flexibility and elasticity of vocal folds and, collagen is responsible for resistance and resiliece for tensile strength. The normal strain rate of vocal ligaments ranges from 0-15% during the phonation. These fibrous proteins exhibit spatial and temporal variation in distribution due to fibroblasts change during tissue maturation and aging. Each vowel ligament is a yellow elastic band tape attached to the front of the thyroid cartilage corner, and behind to the arytenoid cartilage vocal process.
Development
In the newborn
Newborns have uniform monolayered lamina propolis, which looks loose without vocal ligaments. The monolayered lamina propria consists of soil substances such as hyaluronic acid and fibronectin, fibroblasts, elastic fibers, and collagen fibers. While the fibrous component is rare, making the lamina propria structure loose, the content of hyaluronic acid (HA) is high.
HA is a large and negatively charged glycosaminoglycans, whose affinity is strong with water yielding viscoelastic absorbing HA properties and their shocks that are important for vocal biomechanics. Viscosity and elasticity are essential for sound production. Chan, Gray and Titze, measured the effect of HA on the viscosity and elasticity of the vocal cords (VF) by comparing the nature of tissue with and without HA. The results showed that HA removal decreased VF stiffness by an average of 35%, but increased their dynamic viscosity by an average of 70% at frequencies higher than 1 Hz. Newborns have proven to cry an average of 6.7 hours per day for the first 3 months, with a sustained tone of 400-600 Hz, and an average duration of 2 hours per day. A similar treatment in adult VF will rapidly produce edema, and then aphonia. Schweinfurth and al. presented the hypothesis that the high content and distribution of hyaluronic acid in the VF of the newborn is directly related to the survival of a newborn cry. The differences in the composition of newborn vocal tapes will also be responsible for the inability of newborns to articulate sound, in addition to the fact that their proprietary lamina is a uniform structure with no vocal ligaments. The layered structures required for the phonation will begin to develop during infancy and through adolescence.
Fibroblasts in the newborn Reinke room are not yet perfect, showing an oval shape, and large nucleotide-cytoplasmic ratios. Rough endoplasmic reticulum and Golgi apparatus, as demonstrated by electron micrographs, do not progress well, indicating that cells are in resting phase. Collagen and reticular fibers in the newborn VF are fewer than in adults, increasing the immaturity of the vocal band network.
In infants, many fibrous components appear to extend from macula flava to Reinke space. Fibronectin is very abundant in the Reinke room in newborns and infants. Fibronectin is a glycoprotein believed to serve as a template for collagen-oriented fibers deposition, stabilizing collagen fibrils. Fibronectin also acts as a framework for elastic tissue formation. Reticular fibers and collagen are seen running along the edge of VF throughout the lamina propria. Fibronectin in the Reinke space appears to guide the fibers and direct the fibrils deposition. Elastic fibers remain rare and immature during infancy, mostly made of microfibrils. Fibroblasts in the baby Reinke room are still sparse but spindle-shaped. The rough endoplasmic reticulum and their Golgi apparatus are still not well developed, suggesting that despite their altered shape, fibroblasts remain largely in the resting phase. Some of the newly released materials look adjacent to fibroblasts. The content of the soil substance in the baby Reinke room appears to decrease over time, as the fibrous component content increases, thus slowly changing the vocal fold structure.
In adult
The human VF is a paired structure located in the larynx, just above the trachea, which vibrates and is contacted during phonation. Human VF is about 12-24 mm, and 3-5 mm thick. Histologically, the human VF is a laminated structure consisting of five different layers. The vocal muscle, the main body of VF, is covered by the mucosa, which consists of epithelium and lamina propria. The latter is a flexible layer of connective tissue divided into three layers: superficial layer (SLP), intermediate layer (ILP), and inner layer (DLP). A good layer difference is made to see differences in cell content or extracellular matrix content (ECM). The most common way is to view ECM content. SLP has fewer elastic fibers and collagen than the other two layers, and thus is looser and more flexible. ILP is largely composed of elastic fibers, while DLP has fewer elastic fibers, and more collagen fibers. In the two layers, which form what is known as the vocal ligament, the elastic and collagenous solid fibers are packed as bundles that run almost parallel to the edges of the vocal cords.
The extracellular matrix of VF LP consists of fibrous proteins such as collagen and elastin, and interstitial molecules such as HA, non-sulphate glycosaminoglycans. While SLP is rather poor in elastic and collagen fibers, ILP and DLP are largely composed of it, with reduced elastic fiber concentration and increased collagen fiber concentration when the vocal muscle is approached. Fibrous proteins and interstitial molecules play different roles in ECM. While collagen (mostly type I) provides strength and structural support to the tissues, which are useful for resisting stress and resisting deformation when subjected to force, elastin fibers carry elasticity to the tissues, allowing it to return to its original form after deformation. Interstitial proteins, such as HA, play important biological and mechanical roles in VF networks. In the VF network, HA plays the role of shear thinners, affecting tissue viscosity, filler space, shock absorber, as well as wound healing and promoter cell migration. The distribution of proteins and interstitial molecules has been shown to be affected by age and sex, and is maintained by fibroblasts.
Maturation
The structure of the vocal folds in adults is very different from the newborn. Exactly how VF matures from an immature monolayer in newborns to adult three-layer tissue in adults is still unknown, but some studies have investigated the subject and brought some answers.
Hirano et al. previously found that the newborn did not have the actual lamina propria, but had a cellular region called maculae flavae, located at the anterior and posterior ends of the loose ribbon band tissue. Boseley and Hartnick were examined on the development and maturation of the human pediatric vocal lamina propria lamina. Hartnick was the first to define each layer by changing their cellular concentration. He also found that lamina propria monolayer at birth and soon afterwards was hypercellular, thus confirming Hirano's observations. At 2 months of age, the vocal cords begin to differentiate into bilaminar structures of different cell concentrations, with superficial layers less populous than deeper layers. At 11 months, a three-tier structure began to be recorded in several specimens, again with different cellular population densities. The superficial layer is still hypocellular, followed by a more intermediate hypercellular layer, and a deeper hypercellular layer, just above the vocalist muscle. Although VF seems to be regulating, this does not represent the visible trilaminar structures in adult tissue, where the layers are defined by the composition of elastin fibers and differential collagen. At the age of 7 years, all specimens showed a three-tier ribbed folding structure, based on cellular population density. At this point, the superficial layer is still hypocellular, the middle layer being hypercellual, with the greater elastin and collagen fibers, and the deeper layers of the less cellular populations. Again, the apparent differences between layers at this stage are not proportional to those seen in adult tissues. VF maturation does not appear before the age of 13 years, where layers can be defined by their differential fiber composition rather than by their differential cell population. This pattern now shows a hypocellular superficial layer, followed by a middle layer composed of elastin fibers, and a deeper layer composed primarily of collagen fibers. This pattern can be seen in older specimens up to 17 years, and above. While this study offers a great way to see the evolution from immature to mature VF, it still does not explain what the mechanism behind it.
Macula flavae
The maculae flavae is located at the anterior and posterior end of the membrane portion of the VF. The histologic structure of the macula flava is unique, and Sato and Hirano speculate that it could play an important role in the growth, development and aging of VF. Macula flava consists of fibroblasts, soil substances, elastic fibers and collagen. Fibroblasts are numerous and spindle or stellate. Fibroblast has been observed to be in an active phase, with some newly released amorphous materials present on its surface. From a biomechanical point of view, the role of macula flava is very important. Hirano and Sato's study suggest that the macula flava is responsible for the synthesis of fibrous components of VF. Fibroblasts have been found mostly parallel to the direction of the vocal ligaments, along with the fiber bundles. It is then suggested that mechanical pressure during the phonation stimulates fibroblasts to synthesize the fibers.
Impact of phonation
The viscoelastic properties of the human vocal folds of lamina propria are essential for their vibrations, and depend on the composition and structure of their extracellular matrix (ECM). Adult VF has a layered structure based on layer differences in the ECM distribution. Newborns on the other hand, do not have this layered structure. Their VF is uniform, and immature, making their viscoelastic properties most likely unsuitable for phonation. HA plays a very important role in the biomechanics of vocal folds. In fact, HA has been described as an ECM molecule that not only contributes to the maintenance of optimal tissue viscosity that allows phonation, but also optimal tissue stiffness that allows frequency control. CD44 is a cell surface receptor for HA. Cells such as fibroblasts are responsible for synthesizing ECM molecules. Cell surface matrix receptors returned, feedback to cells through cell-matrix interactions, allowing cells to regulate their metabolism.
Sato et al. undertake a non-disulfonated human histopathologic histopathological study. The vocal folding mucosa, which is not abused since birth, of three young adults (17, 24, and 28 years) is seen using light and electron microscopes. Interestingly, the results suggest that the folded vocal mucosa is hypoplastic, and imperfect, and like a newborn, it has no vocal ligaments, Reinke spaces, or layered structures. Like newborns, lamina propria emerges as a uniform structure. Some stellate cells are present in the macula flava, but begin to show some signs of degeneration. The stellate cells synthesize fewer ECM molecules, and the cytoplasmic process is shown to be short and shrunken, indicating decreased activity. These results confirm the hypothesis that the phonation stimulates stellate cells to produce more ECM.
Furthermore, using a specially designed bioreactor, Titze et al. shows that fibroblasts exposed to mechanical stimuli have different levels of ECM production from fibroblasts that are not exposed to mechanical stimulation. Levels of gene expression of ECM constituents such as fibronectin, MMP1, decorin, fibromodulin, HA synthase 2, and CD44 have been altered. All of these genes are involved in ECM remodeling, thus demonstrating that mechanical strength is applied to the tissues, altering the level of ECM-related gene expression, which in turn allows cells in the tissue to regulate ECM constituent synthesis, thus affecting tissue composition. , structure, and biomechanical properties. Ultimately, cell surface receptors close the loop by providing feedback on the surrounding ECM to the cell, affecting also the level of expression of their genes.
Impact of hormone
Other studies have shown that hormones also play an important role in maturation of vocal bands. Hormones are molecules that are secreted into the bloodstream to be sent to a variety of targeted sites. They usually promote growth, differentiation and functionality across multiple organs or tissues. The effect is due to their ability to bind intracellular receptors, modulate gene expression, and then regulate protein synthesis. The interactions between endocrine systems and tissues such as breast, brain, testicles, heart, bones, etc., are being studied extensively. It has been clearly seen that the larynx is somewhat affected by hormonal changes, but surprisingly, very little research works to explain this relationship. The effects of hormonal changes in sound are clearly visible when hearing the voices of men and women, or when listening to teenage voices change during puberty. In fact, it is believed that the number of hormonal receptors in the pre-pubertal phase is higher than in other ages. Menstruation has also been seen to affect sound. In fact, the singers are encouraged by their instructors not to perform during their pre-menstrual period, due to the deterioration of their sound quality.
The function of vocal folding vowels is known to change from birth to old age. The most significant changes occur in the development between birth and puberty, and in old age. Hirano et al. previously described some structural changes associated with aging, in a vocal fold network. Some of these changes are: the shortening of the male vocal folds, the thickening of the vocal mucosa and the female cover, and the development of edema in the shallow lamina propria layer in both sexes. Hammond et al. observed that the HA content in the folds of the lamina propria ribbons was significantly higher in males than in females. Although all of these studies show that there are marked structural and functional changes visible in human VF associated with sex and age, none of which really fully explains the underlying cause of the change. In fact, only a few recent studies are beginning to see the presence and role of hormone receptors in VF. Newman et al. found that hormone receptors did exist in VF, and showed differences in statistical distribution with respect to age and sex. They have identified the presence of androgen, estrogen, and progesterone receptors in epithelial cells, granular cells and VF fibroblasts, suggesting that some structural changes seen in VF may be due to hormonal influences. In this particular study, androgen and progesterone receptors are more common in men than in females. In another study, it has been suggested that the estrogen/androgen ratio is partly responsible for the sound changes observed during menopause. As said before, Hammond et al. show of HA content is higher in men than in female VF. Bentley et al. shows that the sex skin swelling seen in monkeys is due to an increase in HA content, which is actually mediated by estrogen receptors in dermal fibroblasts. An increase in the biosynthesis of collagen mediated by estrogen receptors from dermal fibroblasts was also observed. Connection between hormone levels, and ECM distribution in VF depending on age and sex can be made. More specifically the relationship between higher hormone levels and higher HA levels in men may exist in human vocal cord tissue. Although the relationship between hormone levels and ECM biosynthesis in the vocal cords can be established, the details of these relationships, and the mechanisms of influence have not been described.
Maps Vocal folds
Function
Oscillation
The larynx is the main (but not the only) voice source in speech, producing sound through the opening and closing of the rhythmic vocal cords. To oscillate, the vocal folds are brought close enough together in such a way that the air pressure builds up below the larynx. The folds are pushed apart by this increased subglotic pressure, with the inferior part of each fold leading the superior part. Movements such as waves cause the transfer of energy from the airflow to the tissue folds. Under the right conditions, the energy transferred to the network is large enough to overcome the losses with the dissipation and the oscillation pattern will defend itself. In essence, the sound is produced inside the larynx by cutting the constant airflow into the sound waves. (video)
The perceived tone of a person's voice is determined by a number of different factors, most importantly the fundamental frequency of the sound produced by the larynx. The basic frequency is affected by the length, size, and tone of the vocal cords. This frequency averages around 125 Hz in adult men, 210 Hz in adult women, and over 300 Hz in children. Depth-kymography is an imaging method for visualizing complex horizontal and vertical motions of the vocal cords.
Vocal folds produce rich harmonic sounds. Harmonics are generated by a vocal cord collision by themselves, by recirculating some air back through the trachea, or both. Some singers can isolate some of the harmonies in a way that is regarded as singing in more than one tone at the same time - a technique called tone chant or throat as in the tradition of Tuvan's throat song.
Clinical interests
Wound healing
Wound healing is a natural regeneration process of dermal and epidermal tissues involving the sequence of biochemical events. These events are complex and can be categorized into three stages: inflammation, proliferation, and tissue remodeling. The study of wound healing of vocal fold is not as large as that in animal models because of the limited availability of the human vocal cords. Vocal cords can have a number of causes including chronic, chemical, thermal and chronic trauma such as smoking, laryngeal cancer, and surgery. Other benign pathological phenomena such as polyps, vocal folding nodules, and edema will also introduce irregular fonations.
Any injury to the human vocal cords results in a wound healing process characterized by irregular collagen accumulation and, ultimately, scar tissue formation. Verdolini and his group sought to detect and describe the acute tissue response of the injured VF model of the rabbit. They measured the expression of two biochemical markers: interleukin 1 and prostaglandin E2, which were associated with acute wound healing. They found that the secretion of these inflammatory mediators increased significantly when collected from injured VF versus normal VF. These results are consistent with their previous research on the function of IL-1 and PGE-2 in wound healing. Investigations about the temporal and magnitude of the inflammatory response in VF can be useful for explaining subsequent pathological events in folds of vocal fold, which is good for clinicians to develop therapeutic targets to minimize scar formation. In the wound healing VFs proliferation phase, if HA and collagen production are unbalanced, which means lower than normal HA levels, collagen fibrosis can not be regulated. As a result, regenerative-type wound healing turns into scar formation. Scar tissue can cause vocal rib bending deformities, viscosity impairment and LP stiffness. Patients suffering from scar band tape complain about increased phonatory efforts, vocal fatigue, shortness of breath, and dysphonia. Ribbon bone scratches are one of the most challenging issues for otolaryngologists because it is difficult to diagnose at the germinal stage and the need for VF function is subtle.
History
Etymology
The sound string (often incorrectly written vocal cords ) is a term commonly used to refer to the vocal cords, or the vocal cords. The term was coined by the French anatomist Antoine Ferrein in 1741. In his violin analogue of human voices, he postulates that moving air acts like an arc on cordes vocales. The alternative spelling in English is 'vocal cords', probably because of the musical connotations or confusion with the geometric definition of the word "chord". While both spellings have historical precedents, the American standard spellings are 'vocal cords'. According to Oxford English Corpus, a 21st century text database containing everything from academic journal articles to unedited writing and blog posts, contemporary writers chose non-standard chords instead of 'ropes' of 49% of the time. Spellings 'vocal cords' are also standard in the UK and Australia.
See also
- Apple Adam
- Electroglotography
- Falsetto
- Vocal cords dysfunction
- Vocology
- Articulation phonetics
- Laryngospasm
Additional images
References
Bibliography
- Davids, Julia and Stephen A. LaTour. Vocal Techniques: A Guide for Conductors, Teachers, and Singers. Long Grove, IL: Waveland Press, 2012.
External links
- Official website of the Voice and Speech Center
- Lewcock, Ronald, et al. "Acoustics: The Voice." In Grove Music Online (by subscription)/http://www.oxfordmusiconline.com/subscriber/article/grove/music/00134pg6
Source of the article : Wikipedia
0 Comments