喉頭（ボイスボックス）の説明

概要

The larynx or upper windpipe is the body’s organ for phonation or voice production. The larynx is a well-developed organ, it accounts for all verbal communications. The capabilities of the larynx tend to increase as we age. In addition, the larynx is a vital part of the respiratory system, which allows the two-way passage for gaseous flow. As a result, it allows us to speak or produce sounds during the expiratory phase of breathing.

構造

The larynx is located in front of the neck. It extends from the fourth to the sixth vertebrae.  In females and children, the location of the larynx is slightly higher. In males, the larynx lies exactly in front of the 3rd – 6th cervical vertebrae.

The approximate length or size of the larynx is 36 mm among females, 3mm in children, and 44 mm among males. In males, the larynx grows and develops rapidly to make a structure called Adam’s apple for low pitched and louder voice at puberty. The internal diameter of the larynx in an adult is 12mm.

Laryngeal cartilages

喉頭骨格として知られる、さまざまな軟骨の骨格が喉頭を構成しています。合計で、3つが対になっている9つの喉頭軟骨があり、残りの3つは次のように対になっていない：

• Paired cartilages include:
  • 楔形文字
  • 披裂軟骨
  • Corniculate

• 対になっていない軟骨：
  • 喉頭蓋
  • 甲状腺
  • クリコイド

Among these different cartilages, we shall look at the thyroid cartilage in more detail.

Thyroid cartilage

The thyroid cartilage is V-shaped cartilage consisting of left and right laminae. The thyroid cartilage sits as the uppermost and largest cartilage in the laryngeal cartilages. The laryngeal prominence (Adam’s apple) is the median projection of the left and right laminae of the anterior borders.

Cricothyroid joint forms as a result of articulation of cricoid cartilage and the thyroid. A ligament arises from the cricoid cartilage to attach to the thyroid. The cricothyroid ligament prevents the uncontrolled movement of each cartilage and in the case of upper airway obstruction, a surgery to excise this ligament may be required (emergency cricothyrotomy).

喉頭関節

輪状甲状関節と輪状甲状筋関節の2つの関節が喉頭で機能します

• 輪状甲状関節 – a joint between the cricoid cartilage and thyroid cartilage. It permits the rotatory movements leading to relaxation and contraction of vocal cords. A few gliding movements are also permissible in this joint.

• 輪状軟骨関節 – it is a joint between the cricoid cartilage and arytenoid cartilage. It permits rotatory movements of the vocal cords and multi-directional gliding movements.

喉頭の筋肉

内因性喉頭筋には以下が含まれます：

• 輪状甲状筋
• 後輪状披裂三角三角形
• 外側輪状披裂
• 横披裂軟骨
• 斜披裂軟骨および披裂喉頭蓋筋
• 甲状喉頭蓋筋および甲状披裂筋
• ボーカリス

The extrinsic muscles of the larynx are the ones that attach to the hyoid bone, thus enabling movement of the thyroid cartilage. 

These are a few muscles that act on the larynx to produce different movements such as;

• 声帯内転：
  • サイロアレテノイド
  • 横披裂軟骨
  • 外側輪状披裂
  • 輪状甲状腺

• Vocal cords contraction:
  • 輪状甲状腺

• Vocal cord relaxation:
  • ボーカリス
  • 甲状披裂筋

喉頭のひだ

The laryngeal folds are divided into vocal folds and vestibular folds. The folds are divided by a space between them, this is called the リマグロティデス.

声帯：

These folds are called true vocal folds because they form the inner walls of the larynx.

仮声帯：

Also known as false vocal cords because they sit on the vocal cords to protect the larynx. These folds have no contribution to the production of sound.

Both vocal fold and vestibular folds of the larynx divide the larynx into three parts:

• Supraglottis area
• 心室または洞
• Infraglottis area

喉頭の機能

Production of speech

There are four basic processes for speech production:

1. 空気の有効期限 – air forces out of the larynx and lungs to produce voice. The force of expiration determines the intensity or loudness of voice.
2. バイブレーター – vocal cord vibration is produced as a result of expired air. The rate of vocal cord vibration determines the pitch of the voice. Vibrators produce vowels.
3. 共鳴 –唇と鼻の間の空気の柱と声帯は、音声生成の共鳴器です。レゾネーターが音質を決定します。
4. 咬合器 –アーティキュレーターは、唇、歯、舌、口蓋を構成します。アーティキュレーターは、呼気を止めたり狭めたりする傾向があります。さらに、舌の内因性の筋肉は子音を出す傾向があります。

下気道の呼吸と保護

All the cartilages and membranes of the larynx help in protecting the lower respiratory tract. During swallowing, vestibular folds and epiglottis help in sealing the larynx to prevent the entry of food into the trachea.

神経血管供給

神経供給

Two nerves supply the muscles of the larynx:

• 反回神経（RLN） – also known as inferior laryngeal nerve, RLN is the principal motor nerve of the intrinsic laryngeal muscles. It is a branch of the vagus nerve, and also provides sensory innervation to the larynx. This nerve supplies all intrinsic muscles other than cricothyroid muscle.
• 上喉頭神経 – It also originates from the vagus nerve. The internal laryngeal nerve provides innervation to the mucous membrane of the glottis, including the laryngeal cavity and vocal folds. The external laryngeal nerve innervates the cricothyroid muscle.

静脈ドレナージと動脈供給

The blood supply for all the structures up to the vocal folds is by the superior laryngeal artery. The venous drainage at this point is via the superior laryngeal vein.

All the structures below vocal folds have their blood supply and venous drainage by the inferior laryngeal artery, and the inferior laryngeal vein respectively.

関連する病気

喉頭炎

Laryngitis is the infection and inflammation of the larynx on account of the trapping and lodging of foreign bodies. Laryngitis is characterized by hoarseness of voice and a dry cough. Acute laryngitis usually goes away on its own. With chronic laryngitis, treatment is targeted at the underlying condition, such as smoking or heartburn.

歌手の結節

Singer’s nodules or teacher’s nodules occur commonly occur in teachers, singers, or pastors. They result from repetitive vocal cords misuse or overuse. They cause callous-like growths that develop in the midpoint of the vocal folds. This leads to hoarseness of voice and a breathy sound when speaking or singing.

声帯麻痺

Vocal cord paralysis occurs when the nerve impulses to your voice box (larynx) are affected. This causes paralysis of the vocal cord muscles. Vocal cord paralysis can affect your ability to speak and even breathe because your vocal cords do more than just producing sound.

Vocal cord paralysis leads to inappropriate opening and closing of vocal cords and this causes various complications in swallowing, speaking, and breathing.

けいれん性発声障害

This is a lifelong condition where the muscles that generate a person’s voice go into periods of spasms affecting voice and speech. In some cases, the disorder is temporary or can be improved through treatment.

Laryngeal nerve injury

This usually follows neck surgery, a neck infection, or a tumor. External laryngeal nerve damage causes weakness in producing sound. In such an injury, the cricothyroid muscle’s tightening or contracting effect on vocal cords is lost.

In recurrent laryngeal nerve injury, phonation tends to completely vanish completely.

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