Larynx: Anatomy, Structure, Functions, Diseases

The larynx is an essential biological organ located between the pharynx and the trachea in the neck. It is a cartilaginous hollow tube that plays a significant role in the respiratory system and voice production (phonation).

It is also called the voice box, as it houses the vocal cords.

Anatomy and Structure of the Larynx

• The larynx is a triangular-shaped organ made up of cartilaginous tissues. 
• The ciliated columnar epithelial tissue forms the inner lining of the larynx, except for the vocal folds. 
• It is supported by 9 types of cartilages (3 paired and 3 unpaired), 2 types of ligaments, and 2 sets of muscles.

Anatomically, the larynx is divided into 3 parts: 

• Supraglottis 
• Glottis 
• Subglottis 

Supraglottis

• The supraglottis is the uppermost part of the larynx. 
• It includes the epiglottis, false vocal cords, aryepiglottic folds, and arytenoid cartilages. 
• It protects the airway, directs the food to the oesophagus, and prevents it from entering the tracheal region.

Glottis

• The gap between the two vocal folds is called the glottis. It is also referred to as the rima glottidis.
• It is the middle portion of the laryngeal anatomy, located between the supraglottis and subglottis.
• It is another significant part that prevents the entry of food/fluids into the windpipe (respiratory tract) and allows their passage to the food pipe (digestive organs).
• Since the glottis houses the vocal cords, it is essential to produce sounds. As the air flows through the vocal cords, it creates the vibration within the vocal folds, which allows the production of sound/voice. Therefore, the larynx is also called the voice box.

Subglottis

• It is the lowermost part of the larynx, situated above the trachea and below the glottis region.
• It is cylindrical in shape; however, it narrows down towards the vocal folds.
• It is also called Infraglottis.
• It acts as a significant section that protects the lower respiratory tract. It also assists in breathing, as it is involved in regulating the breathing temperature.

Larynx vs. Pharynx

Functions of the Larynx

Functions of the Larynx in Breathing

• The larynx regulates the flow of air within the respiratory tract.
• It protects the lower respiratory tract by directing the food into the alimentary canal route during swallowing and preventing its passage into the trachea.
• During inhalation, the vocal folds present on the larynx open (abduction), while during exhalation, they close (adduction).
• It also functions as the controller/operator to control the air pressure within the respiratory tract. It facilitates the adduction of the vocal cords. This causes the intra-thoracic pressure to increase, and in order to release the pressure, the body coughs and also removes the foreign particles from the body.

Functions of the Larynx in Voice Production (Phonation)

• Sound production: During respiration, when the air passes through the vocal cords, they vibrate within the larynx. The continuous vibration of the vocal folds generates the voice/sound.
• Pitch (high/low notes) control: As the cricothyroid muscles stretch, the vocal folds get thinner, and their tension rises. Eventually, it leads to an increase in the speed of the vibration. This process produces the sound of higher notes. Likewise, the larynx relaxes the vocal folds and makes them thicker and shorter. Hence, it generates the sound of lower notes. Usually, the vocal folds in the males are shorter and thicker; therefore, it produces the sound of higher pitch in males.

Vocal Cords and Mechanism of Sound Production

Vocal cords, also known as the vocal folds, are the soft, cylindrical-shaped cartilaginous tissues present in the throat.

There are two types of vocal folds, namely True vocal folds and false vocal folds.

True vocal folds (TVFs)

Generally called the vocal folds. Made of muscles and are more delicate, flexible, and resilient in comparison to the false vocal folds. Vibrate under normal circumstances and function to produce voices/sounds during regular phonation.

False vocal folds

Also called the vestibular folds or ventricular folds to distinguish them from the true vocal folds. They are the non-muscular structures, situated above the TVFs. They do not vibrate under normal conditions as they are responsible only for producing deep throat sounds and screams.

The shorter the vocal folds, the higher the sound frequencies. Therefore, the children tend to have the highest sound frequency, followed by the female voice and the male voice. 

Vocal folds are composed of 3 layers: mucosa, the vocal ligament, and the thyroarytenoid muscle. In addition to these vocal folds, the larynx also comprises the supportive cartilages, muscles, and ligaments that play a crucial role in generating sound. 

The mechanism of voice production includes the following subsystems: the air-pressure system, the vibratory system (vocal cords), the filter/resonating system, and the articulatory system.

Air-pressure system:

• First, the arytenoid muscles pull back the glottis during exhalation and close the glottic space within the vocal folds. 
• Consequently, the pressure in the subglottic region increases. When the subglottic pressure exceeds the glottis closure force, the air from the lungs passes through the vocal folds, resulting in the vibration.
• The diaphragm, chest muscles, and abdominal muscles coordinate together with the lungs in this system.
• The elasticity of the muscles and the Bernoulli effect play an essential role in bringing back the air pressure system.

Vibratory system:

• Afterwards, the airflow vibrates the vocal cords and generates a sequence of vibratory cycles. 
• The vibration of the vocal folds, together with the movement of the tongue and the mouth, produces a voiced sound (the ‘buzz’ sound). The speed of airflow determines the intensity of the vibration and the loudness of the sound produced.

Resonating system in the vocal tract:

• The vocal tract consists of the resonators, such as the throat, pharynx, oral cavity, and nasal cavity. 
• As the voiced sound propagates through them, they amplify/modify the quality of the sound. Thus, they are the modifiers that shape the buzz sound and produce the distinct perceptible characteristics of every linguistic sound.

Articulatory system:

• The lips, tongue, and soft palate help to articulate the voice produced. It helps in the formation of words during phonation and produces the recognizable voice.

Cartilages and Muscles of the Larynx

Laryngeal cartilages

• The larynx is composed of 2 sets of cartilages. Each set involves 3 types of cartilage. 
• The first set of cartilages occurs in pair, while another set is unpaired.
• The paired cartilages include the arytenoid cartilage, the corniculate cartilage, and the cuneiform cartilages.
• The unpaired cartilages include the thyroid cartilage, the cricoid cartilage, and the epiglottis.

Laryngeal Muscles

• The muscles present in the larynx can be divided into 2 types: extrinsic muscles and intrinsic muscles.

Blood supply and innervations of the larynx

Blood supply of the larynx:

• The blood is supplied to the larynx primarily by the superior and inferior laryngeal arteries, which form multiple branches bilaterally.
• The external carotid artery divides into several branches, one of which is the superior thyroid artery. The superior laryngeal artery originates from the superior thyroid artery and functions as the major blood supplier of the larynx. They supply blood to the structures between the top of the epiglottis and the glottis.
• The inferior laryngeal carotid artery originates from the inferior thyroid artery branch of the thyrocervical trunk. The thyrocervical trunk is one of the branches of the subclavian artery. They supply blood to the mucosal membrane and the muscles of the larynx.

Innervations of the Larynx:

• The vagus nerve (CN X) is the central point of origin of the innervations to the larynx. 
• It divides into superior and inferior laryngeal nerves.
• The superior laryngeal nerves further divide into external and internal nerves. External nerves transmit efferent nerve signals to the cricothyroid muscle, while the internal branch transmits the sensory afferent signals to the structures of the supraglottis and glottis (laryngeal vestibule and vocal cords).
• Inferior laryngeal nerves, also called the recurrent laryngeal nerves, provide the motor nerve innervations to the subglottis as well as the extrinsic and intrinsic laryngeal muscles (except for the cricothyroid muscle).

Common Diseases and Disorders of the Larynx

There are several causes that can halt the function of the larynx and produce acute to chronic symptoms.

• Acute laryngitis: It is the inflammation of the laryngeal tissues that results in the swelling of the larynx. It is commonly caused during a cold or as a consequence of excessive shouting.
• Chronic laryngitis: It is a serious condition in which the larynx becomes inflamed due to dust, smoking, yelling, or polluted air.
• Laryngeal carcinoma: Prolonged exposure to cigarettes or alcohol results in the development of tumor cells in the larynx. The common types of cancer in the larynx include squamous cell carcinoma and verrucous carcinoma.
• Laryngopharyngeal reflux (LPR): When the acid from the stomach burns and irritates the laryngeal tissues, the condition is termed “laryngopharyngeal reflux”.
• Vocal polyps and cysts: The appearance of the blisters or cysts on the vocal cords is called “vocal polyps”. They are non-cancerous.
• Muscle Tension Dysphonia (MTD): Excessive, inappropriate tension in the muscles of the throat consequently results in the voice disorder known as dysphonia.

Some of the common signs and symptoms of these disorders/diseases include: hoarseness of sound, changes in voice, dysphagia, noisy breathing, and a feeling of a lump in the throat region.

Diagnostic Procedures: Endoscopy and Laryngoscopy

• In order to diagnose the medical conditions of the internal organs, the clinical specialists insert a narrow, flexible tube (provided with a light and a camera) inside the body. This kind of non-surgical diagnostic procedure is called an endoscopy, and the device is called an endoscope.
• In laryngoscopy, the endoscope is passed through the nose or mouth to view the vocal cords/larynx during medical examinations.
• It is the best method to diagnose any kind of inflammation in the larynx. 

How to Keep the Larynx Healthy

In order to be able to speak clearly and produce different voices, we must take good care of our vocal cords and the larynx. Some of the ways to keep the larynx healthy are as follows:

• Drink water and stay hydrated.
• Avoid smoking, alcohol, and tobacco products, and also limit caffeine intake to reduce the risk of laryngeal tumors. 
• Avoid eating spicy foods.
• Eat the foods containing Vitamin A, E, and C. They help to keep the throat healthy.
• Take rest amidst the busy routine. Physical weakness affects the vocal cords and the voice.
• Avoid screaming/loud shouting, as they strain the laryngeal tissues.

Conclusion

The larynx is a biological organ in the throat, which is made up of cartilage. It plays a significant role in both the alimentary canal and the respiratory tract. They consist of the vocal cords, several cartilages, muscles, and ligaments, which play a primary role in sound production; while on the other hand, they are also significant to prevent the entry of food into the respiratory system.

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