| Thyroid cartilage | |
|---|---|
 The cartilages of the larynx | |
| Details | |
| Precursor | 4th and 6th branchial arch |
| Identifiers | |
| Latin | cartilago thyroidea |
| MeSH | D013957 |
| TA98 | A06.2.02.002 |
| TA2 | 967 |
| FMA | 55099 |
| Anatomical terminology | |
The thyroid cartilage is the largest of the nine cartilages that make up the laryngeal skeleton, the cartilage structure in and around the trachea that contains the larynx. It does not completely encircle the larynx (only the cricoid cartilage encircles it).
The thyroid cartilage is a hyaline cartilage structure that sits in front of the larynx and above the thyroid gland. The cartilage is composed of two halves, which meet in the middle at a peak called the laryngeal prominence, also called the Adam's apple. [1] In the midline above the prominence is the superior thyroid notch. A counterpart notch at the bottom of the cartilage is called the inferior thyroid notch.
The two halves of the cartilage that make out the outer surfaces extend obliquely to cover the sides of the trachea. The posterior edge of each half articulates with the cricoid cartilage inferiorly at a joint called the cricothyroid joint. The most posterior part of the cartilage also has two projections upwards and downwards. The upper projection is called the superior horn (cornu), and the lower is called the inferior horn. The superior horn is long and narrow, backward, and medialward, and ends in a conical extremity, which gives attachment to the lateral thyrohyoid ligament. The inferior horn is short and thick; it is directed downward, with a slight inclination forward and medialward, and presents, on the medial side of its tip, a small oval articular facet for articulation with the side of the cricoid cartilage.
The entire superior edge of the thyroid cartilage is attached to the hyoid bone by the thyrohyoid membrane. The thyroid cartilage is found between the levels of the C4 to C5 vertebrae.
The oblique line is a line on the thyroid cartilage. It marks the upper lateral borders of the thyroid gland. Two muscles originate along the line, the thyrohyoid muscle and inferior pharyngeal constrictor. The sternothyroid inserts along the line.
Movement of the cartilage at this joint produces a change in tension at the vocal folds, which in turn produces variation in voice.
The thyroid cartilage may contain a variant foramen, known as thyroid foramen, in up to 39% of individuals. [2]
The thyroid cartilage forms the bulk of the front wall of the larynx. It protects the vocal folds ("vocal cords"), which are located directly behind it.
When the angle of the thyroid cartilage changes relative to the cricoid cartilage, this changes the pitch of voice.
The cartilage also serves as an attachment for several muscles.
The English term thyroid cartilage is derived from the Latin expression cartilago thyreoides. [3] [4] The latter is a translation of Ancient Greek χόνδρος θυρεοειδής, [5] attested in the writings of the Greek physician Galen. [5] The Latin word cartilago, as well as the Ancient Greek word χόνδρος, both mean cartilage, [5] [6] while the ancient Greek word θυρεοειδής means shield-like or shield-shaped. [3] [5] The latter compound is composed of Ancient Greek θυρεός, shield [3] [5] and εἶδος, form/shape. [5] The Greeks used εἶδος in compounds to indicate a resemblance with the first part of the word. [7]
The ancient Greek word θυρεός can be found in the Odyssey of Homer, [5] [8] and represented a large square stone that was put against the door to keep it shut. [5] [8] Those θυρεοί were eventually used by the Greek army as shields to protect themselves. [8] This shield was adapted by Roman legions and referred to by them as a scutum. [8] The Roman scutum was an oblong shield with an oval shape. [5] [8] Numerous shields were used by the Roman soldiers, such as the pelta, parma and clypeus. [8] In contrast to the scutum, these shields were round. [8] Despite these latter shields bearing a clear round shape, coinages like petalis cartilago, [9] cartilago parmalis, [8] and cartilago clypealis [10] were coined for the thyroid cartilage. In 16th-century Italian anatomist Realdo Colombo's De re anatomica, [9] besides the aforementioned incorrect petalis cartilago, correct forms like scutalis cartilago and scutiformis cartilago can be found, as the scutum is the real Roman pendant of the Greek θυρεός. The latter Latin expression can be found in its English form in medical dictionaries as scutiform cartilage, [11] while the name of the shield itself, i.e. scutum, is still being mentioned as a synonym for the thyroid cartilage. [12] [13]
In the various editions of the official Latin nomenclature ( Nomina Anatomica , in 1998 rebaptized as Terminologia Anatomica ), three different spellings can be found, i.e. cartilago thyreoidea. [14] cartilago thyroidea [15] [16] [17] [18] [19] [20] and the previously mentioned cartilago thyreoides. [4] [21] The variant with the adjective thyreoidea (with the ending -ea) would be a faulty rendering [7] [22] of Ancient Greek θυρεοειδής in Latin. Greek compounds ending in -ειδής, when imported into Latin as a loanword, ended in -ides. [7] [23] In the 17th-century the non-classical Latin form -ideus/-idea/ideum for Greek -ειδής/-ειδές came into use, mostly by French anatomist Jean Riolan the Younger. [8] No Greek loanwords (originally -ειδής/-ειδές) ending in -ideus/-idea/-ideum exist in classical Latin, [6] [23] thereby making the -ideus/-idea/-ideum form non-Latinate in character. [23] The first edition of the Jena Nomina Anatomica (JNA) contained the incorrect cartilago thyreoidea, [24] but after a list of recommendations/corrections was made [24] this was corrected in subsequent editions of the JNA. [4] [21]
The variant with thyroidea (omitting e after thyr) is a compromise for English-speaking anatomists, as they have difficulties pronouncing that specific combination of letters, [25] forcing a greater resemblance between Latin and English orthography. Dorland's medical dictionary from 1948 [12] already adopted this incorrect spelling with an erroneous reference to the official Basle Nomina Anatomica even before the nomenclature committee of the Nomina Anatomica officially approved this orthographic revision in its edition of 1961. [15] The spelling without an e is commonly accepted in English [13] [26] but earlier works preferred the etymologically correct thyreoid cartilage. [11] [27] The official Latin veterinary nomenclature, Nomina Anatomica Veterinaria , has the form cartilago thyroidea, [28] in common with the human Nomina Anatomica/Terminologia Anatomica, but allows (in contrast to the latter) cartilago thyreoidea [28] as an alternative spelling.
A mishap is the resemblance between Latin thyroidea and English thyroid on the one side and Ancient Greek θυροειδής on the other side, as the latter does not mean shield-like, but actually means like a door, [5] derived from θύρα, door. [5] Θυροειδής is however used in anatomic nomenclature in the expression θυροειδές τρῆμα (τρῆμα = hole, perforation, aperture [5] ), coined by the Greek physician Galen. [8] Ancient Greek θύρα can be translated, besides the aforementioned door, as gate, [5] [8] entrance [5] [8] and opening. [8] The Greek name θυροειδές τρῆμα for this opening between the os pubis and the os ischii, currently called obturator foramen, [13] clearly originates from its being an opening (θύρα), while bearing no resemblance to a shield (θυρεός). [8] The Latin translation foramen thyreoideum for θυροειδές τρῆμα by the 18th–19th-century German physician and anatomist Samuel Thomas von Sömmerring is clearly mistaken. [8] The current foramen thyroideum of the Terminologia Anatomica is not a Latin translation of Galen's θυροειδές τρῆμα, but an orthographic revision of what was previously known in the Nomina Anatomica as foramen thyreoideum, [4] [14] an inconstantly present opening in the lamina of the thyroid cartilage. [13]
The larynx, commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about 4–5 centimeters in diameter. The larynx houses the vocal cords, and manipulates pitch and volume, which is essential for phonation. It is situated just below where the tract of the pharynx splits into the trachea and the esophagus. The word 'larynx' comes from the Ancient Greek word lárunx ʻlarynx, gullet, throat.ʼ
The pituitary gland is an endocrine gland in vertebrates. In humans, the pituitary gland is located at the base of the brain, protruding off the bottom of the hypothalamus. The human pituitary gland is oval shaped, about the size of a chickpea, and weighs 0.5 grams (0.018 oz) on average.
The coccyx, commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates since Nacholapithecus, the coccyx is the remnant of a vestigial tail. In animals with bony tails, it is known as tailhead or dock, in bird anatomy as tailfan. It comprises three to five separate or fused coccygeal vertebrae below the sacrum, attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between the sacrum and the coccyx.
In human anatomy, the metacarpal bones or metacarpus, also known as the "palm bones", are the appendicular bones that form the intermediate part of the hand between the phalanges (fingers) and the carpal bones, which articulate with the forearm. The metacarpal bones are homologous to the metatarsal bones in the foot.
The Adam's apple is the protrusion in the neck formed by the angle of the thyroid cartilage surrounding the larynx, typically visible in men, less frequently in women. The prominence of the Adam's apple increases as a secondary male sex characteristic in puberty.
The raphe nuclei are a moderate-size cluster of nuclei found in the brain stem. They have 5-HT1 receptors which are coupled with Gi/Go-protein-inhibiting adenyl cyclase. They function as autoreceptors in the brain and decrease the release of serotonin. The anxiolytic drug Buspirone acts as partial agonist against these receptors. Selective serotonin reuptake inhibitor (SSRI) antidepressants are believed to act in these nuclei, as well as at their targets.
The locus coeruleus (LC), also spelled locus caeruleus or locus ceruleus, is a nucleus in the pons of the brainstem involved with physiological responses to stress and panic. It is a part of the reticular activating system.
The buccinator is a thin quadrilateral muscle occupying the interval between the maxilla and the mandible at the side of the face. It forms the anterior part of the cheek or the lateral wall of the oral cavity.
The recurrent laryngeal nerve (RLN) is a branch of the vagus nerve that supplies all the intrinsic muscles of the larynx, with the exception of the cricothyroid muscles. There are two recurrent laryngeal nerves, right and left. The right and left nerves are not symmetrical, with the left nerve looping under the aortic arch, and the right nerve looping under the right subclavian artery then traveling upwards. They both travel alongside the trachea. Additionally, the nerves are among the few nerves that follow a recurrent course, moving in the opposite direction to the nerve they branch from, a fact from which they gain their name.
The cricoid cartilage, or simply cricoid or cricoid ring, is the only complete ring of cartilage around the trachea. It forms the back part of the voice box and functions as an attachment site for muscles, cartilages, and ligaments involved in opening and closing the airway and in producing speech.
The arytenoid cartilages are a pair of small three-sided pyramids which form part of the larynx. They are the site of attachment of the vocal cords. Each is pyramidal or ladle-shaped and has three surfaces, a base, and an apex. The arytenoid cartilages allow for movement of the vocal cords by articulating with the cricoid cartilage. They may be affected by arthritis, dislocations, or sclerosis.
The iris dilator muscle, is a smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. The pupillary dilator consists of a spokelike arrangement of modified contractile cells called myoepithelial cells. These cells are stimulated by the sympathetic nervous system. When stimulated, the cells contract, widening the pupil and allowing more light to enter the eye.
The anconeus muscle is a small muscle on the posterior aspect of the elbow joint.
The ilium is the uppermost and largest region of the coxal bone, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.
Nomina Anatomica (NA) was the international standard on human anatomic terminology from 1895 until it was replaced by Terminologia Anatomica in 1998.
Terminologia Anatomica is the international standard for human anatomical terminology. It is developed by the Federative International Programme on Anatomical Terminology, a program of the International Federation of Associations of Anatomists (IFAA).
The lateral thyrohyoid ligament is a round elastic cord, which forms the posterior border of the thyrohyoid membrane and passes between the tip of the superior cornu of the thyroid cartilage and the extremity of the greater cornu of the hyoid bone. The internal branch of the superior laryngeal nerve typical lies lateral to this ligament.
The Terminologia Embryologica (TE) is a standardized list of words used in the description of human embryologic and fetal structures. It was produced by the Federative International Committee on Anatomical Terminology on behalf of the International Federation of Associations of Anatomists and posted on the Internet since 2010. It has been approved by the General Assembly of the IFAA during the seventeenth International Congress of Anatomy in Cape Town.
The Terminologia Histologica (TH) is the controlled vocabulary for use in cytology and histology. In April 2011, Terminologia Histologica was published online by the Federative International Programme on Anatomical Terminologies (FIPAT), the successor of FCAT.
The Federative International Programme for Anatomical Terminology (FIPAT) is a group of experts who review, analyze, and discuss the terms of the morphological structures of the human body. It was created by the International Federation of Associations of Anatomists (IFAA) and was previously known as the Federative Committee on Anatomical Terminology (FCAT) and the Federative International Committee on Anatomical Terminology (FICAT).
This article incorporates text in the public domain from page 1073 of the 20th edition of Gray's Anatomy (1918)
