Horses communicate primarily through vocalizations and body language. While their vocal apparatus is less complex than that of humans, they can produce various sounds using their larynx and associated muscles. Neighs, whinnies and nickers, the most common horse vocalizations, are primarily generated by the throat and larynx, along with a few other elements. Let’s explore the muscles behind their most common sounds:
1. Larynx and Vocal Cords: Muscles in and around the larynx manipulate the vocal cords, creating variations in pitch and intensity for distinctive sounds.
1.1. Thyrohyoideus Muscle: Crucial for regulating airflow during vocalization, this muscle controls the position of the larynx.
1.2. Vocalis Muscle: Located within the larynx, the vocalis muscle modulates pitch and sound production in horses.
1.3. Cricoarytenoideus Dorsalis Muscle: Responsible for controlling the tension and positioning of the vocal cords within the larynx.
1.4. Thyroarytenoideus Muscle: Fine-tuning the tension and length of the vocal cords, this muscle affects the pitch and tone of vocalizations.
1.5. Other Laryngeal Muscles: Various smaller laryngeal muscles work together to control the position and tension of the vocal cords during vocalization.
1.6. Extralaryngeal Muscles: Muscles around the larynx and throat area aid in controlling the tension and movement of the vocal cords.
2. Respiratory System: Airflow from the lungs through the larynx contributes to vocalization, with horses adjusting their breathing patterns for different sounds. Horses use several muscles to inhale and exhale. Key muscles involved in breathing are:
2.1. Diaphragm: The diaphragm is the primary muscle responsible for initiating inhalation. When it contracts, it creates a vacuum that draws air into the lungs. When the diaphragm relaxes, it moves back up into its dome-shaped resting position. This reduces the space in the chest cavity, increasing the pressure inside the lungs. As a result, the horse expels air from its lungs through the trachea and out of the nostrils.
2.2. External Intercostal Muscles: These muscles are located between the ribs and assist in expanding the ribcage during inhalation. They elevate the ribs, further increasing the thoracic cavity’s volume.
2.3. Internal Intercostal Muscles: These muscles are deeper and assist in exhalation by depressing the ribs, reducing the thoracic cavity’s volume during forced exhalation.
2.4. Serratus Dorsalis: The Serratus Dorsalis is divided into two parts: the serratus dorsalis cranialis and serratus dorsalis caudalis. These muscles assist in lifting and stabilizing the ribs during both inhalation and exhalation in horses.
2.5. Abdominal Muscles: The abdominal muscles play a role in exhalation by increasing intra-abdominal pressure, which assists in pushing air out of the lungs.
2.6. Accessory Muscles: Some smaller muscles in the neck and chest may also contribute to the horse’s breathing, particularly during strenuous activities like running or heavy breathing.
3. Oral Cavity: Horses shape and amplify sounds using their oral cavity. Lip, tongue, and nostril positions can affect the vocalization’s characteristics.
3.1. The tongue has several muscles that contribute to the tongue’s dexterity and vocalizations. Some of the key muscles involved in tongue movement in horses include:
3.1a. Hyoglossus Muscle: This muscle helps control the position and movement of the tongue, particularly during swallowing and vocalization.
3.1b. Palatoglossus Muscle: This muscle connects the tongue to the soft palate and plays a role in controlling the shape and position of the tongue.
3.1c. Genioglossus Muscle: This muscle is responsible for protruding the tongue forward and helps in grasping and manipulating food while eating.
3.1d. Styloglossus Muscle: It assists in retracting and moving the tongue backward into the oral cavity.
3.1e. Mylohyoid Muscle: It is involved in elevating the tongue during swallowing and maintaining its position.
3.2. Two main muscles are responsible for controlling the movement of the nostrils:
3.2a. Dilator Nares Muscle: This muscle, also known as the dilator muscle of the nostrils, runs horizontally across the nostrils. When it contracts, it widens or dilates the nostrils, allowing for increased airflow. This is especially important during strenuous exercise when the horse requires more oxygen.
3.2b. Levator Muscle: The levator muscle is responsible for elevating the upper lip and flaring the nostrils when the horse is investigating or sensing something in its environment. It aids in expanding the nasal passage to improve scent detection.
3.3. Some of the facial muscles responsible for lip movement:
3.3a. Levator Nasolabialis: This muscle is responsible for raising the upper lip, which is particularly important for certain vocalizations and for exposing the teeth, as seen in a horse’s characteristic “flehmen response.”
3.3b. Depressor Labii Inferioris: The depressor labii inferioris muscle lowers the bottom lip and contributes to various lip movements and expressions.
3.3c. Orbicularis Oris: This muscle encircles the mouth and is involved in controlling the opening and closing of the lips, allowing for different shapes and configurations of the mouth during vocalizations.
3.3d. Zygomaticus Muscles: These muscles are associated with the movement of the lips and are involved in facial expressions, including lip curling and other lip-related gestures during vocalizations.
Equine vocalizations result from a combination of factors, including the larynx, vocal cords, respiratory system, and oral cavity, allowing horses to produce expressive sounds. These vocalizations serve various social and communicative purposes among horses.