Laryngeal Cartilage and Muscles of the Head and Neck: A Comprehensive Guide
Laryngeal Cartilage (Larynx)
Epiglottis
The epiglottis is a thin, flexible cartilage resembling an oval petal. It projects at an angle through the thyroid cartilage and extends above and beyond the upper edge of the thyroid cartilage via the thyroepiglottic ligament. Its posterior surface is convex above and concave below, directly covered by laryngeal mucosa. The epiglottis protects the laryngeal orifice during swallowing by directing food away from the airway.
Thyroid Cartilage
The thyroid cartilage forms the protective framework of the larynx. It consists of two quadrilateral plates (thyroid laminae) joined anteriorly at an angle of approximately 90 degrees. The prominent edge of this angle forms the laryngeal prominence (Adam’s apple), with the thyroid notch located above it.
Each quadrilateral plate has an oblique external surface facing downward and forward, providing attachment points for the thyrohyoid and sternothyroid muscles, which are involved in the suspensory apparatus of the larynx.
The posterior edge of each plate extends upwards as the superior horn and downwards as the inferior horn. The inferior horn articulates with the cricoid cartilage.
Cricoid Cartilage
The cricoid cartilage sits below the thyroid cartilage and articulates with it. It resembles a ring with a broad lamina posteriorly. The opposite side forms the cricoid arch, featuring a prominent tubercle. The cricothyroid muscles attach to the sides of this tubercle.
The lateral cricoarytenoid muscles attach to the upper edge of the ring. This edge connects to the lower edge of the thyroid cartilage via the cricothyroid ligament.
Articular facets on the upper edge of the cricoid lamina receive the inferior horns of the thyroid cartilage for articulation.
The cricoid lamina has two key features:
- A posterior surface with a median ridge and lateral depressions for the attachment of the posterior cricoarytenoid muscles.
- A superior edge that is continuous with the edges of the arch.
The superior edge features articular surfaces for the arytenoid cartilages (which support the vocal cords).
Arytenoid Cartilage
The arytenoid cartilages play a crucial role in vocal cord function. They are paired, symmetrical, pyramid-shaped cartilages with an apex. Each cartilage has a muscular process for the attachment of muscles responsible for rotation and a vocal process for the attachment of the thyroarytenoid muscle (which forms the vocal cord).
Corniculate Cartilage
The corniculate cartilages are accessory cartilages located on top of the arytenoid cartilages.
Muscles
Masticatory Muscles
The masticatory muscles control jaw movement, enabling elevation/depression, protrusion/retrusion, and lateralization.
Temporal Muscle
Originating from the temporal fascia between the superior temporal line and the inferior temporal line, the temporal muscle inserts onto the coronoid process of the mandible. It elevates the mandible (closes the jaw).
Masseter Muscle
The masseter muscle has two heads that originate from the zygomatic arch and insert onto the ramus and angle of the mandible. It also elevates the jaw.
Lateral Pterygoid Muscle
The lateral pterygoid muscle originates from the base of the skull and inserts onto the neck of the mandible. It protrudes the mandible and contributes to lateral movement.
Medial Pterygoid Muscle
The medial pterygoid muscle originates from the pterygoid process and inserts onto the angle of the mandible. It elevates the mandible.
Facial Muscles
Facial muscles share three characteristics: they insert into the skin, are innervated by the facial nerve (VII), and are located around facial orifices, controlling their dilation and constriction.
Respiratory Muscles
Respiratory muscles are grouped into five categories:
1. Chest Elevators
- Scalene Muscles: These muscles run obliquely between the cervical vertebrae and the first two ribs. They elevate the chest and flex the head, assisting in forced inspiration.
- Sternocleidomastoid Muscle: This muscle has three heads that attach to the mastoid process, clavicle, and sternum. It flexes the head, rotates the head laterally, and elevates the chest during inspiration.
2. Spinal Muscles (Accessory Muscles of Inspiration)
These muscles attach to the transverse processes, spinous processes, laminae of the vertebrae, and posterior angles of the ribs. They extend the spine and assist in rapid breathing.
3. Intercostal Muscles
The intercostal muscles are located between the ribs and are arranged in three layers: inner, middle, and outer. Their role in inspiration and expiration is complex and somewhat controversial.
4. Diaphragm (Principal Muscle of Inspiration)
The diaphragm is a dome-shaped muscle separating the thoracic and abdominal cavities. It has a central tendon and a peripheral muscular region. Contraction of the diaphragm increases thoracic volume in three dimensions, facilitating inspiration.
5. Abdominal Muscles
The abdominal muscles include the internal obliques, external obliques, and rectus abdominis. They act as antagonists to the diaphragm, compressing the abdominal cavity and pushing the diaphragm upwards during expiration. They are involved in forced expiration and vocalization.
Muscles of the Soft Palate
These muscles control the movement of the soft palate, enabling velopharyngeal closure and opening. This mechanism is crucial for the articulation of nasal and oral sounds. Velopharyngeal closure directs airflow through the mouth for oral sounds, while velopharyngeal opening allows air to escape through the nose for nasal sounds like /m/, /n/, and /ŋ/.
The soft palate extends from the hard palate and consists of an aponeurosis that provides structural support. Four key muscles contribute to its function:
Tensor Veli Palatini
This muscle originates from the sphenoid bone and inserts into the palatine aponeurosis. It tenses the soft palate and opens the Eustachian tube.
Levator Veli Palatini
Originating from the skull base, this muscle elevates the soft palate and opens the Eustachian tube, playing a vital role in speech production.
Palatoglossus
This muscle, also involved in tongue movement, originates from the palatine process and inserts into the anterior arch of the soft palate. It constricts the fauces, lowers the soft palate, and elevates the tongue base, contributing to speech articulation.
Musculus Uvulae
This muscle runs along the length of the soft palate and inserts into the uvula. Its exact function is not fully understood, but it is believed to be involved in velopharyngeal closure.
Muscles of the Tongue (Pending)
Muscles of the Pharynx
- Superior Constrictor
- Middle Constrictor
- Inferior Constrictor