Anatomy & Neurophysiology
The 3D rotatable images below are derived from the Visible Human Female. Amira segmentation software (Version 6.3; Thermo Fisher Scientific) was used to trace lingual muscle fibres and group according to source and direction and then label the groups. See Wrench, A. A. (2024). The compartmental tongue. Journal of Speech, Language, and Hearing Research, 67(10S), 3887-3913. for more details of the segmentation process.
Selected groups of Neuromuscular compartments have been uploaded to SketchFab which allow the 3D image to be rotated and also has labels describing the compartments. Click the play button and then click and drag the 3D model.
Genioglossus comprises up to 10 neuromuscular compartments arranged as pairs in two rows. It is possible that in some individuals one or two of these pars are not independently innervated. The compartments originate from the short tendon which in turn attaches to the superior tubercle of the mandible.
Styloglossus comprises of eight neuromuscular compartments. Three of which blend with three transversus compartments to form three ‘slings’. Contraction of any of these transversus compartments stretches the extrinsic styloglossus compartment that it is connected to the styloid process of the cranium. The stretch reflex in this extrinsic compartment applies force to resist the stretch force. In this way, when the transversus compartment contracts, it does not narrow the tongue width but rather it extends the genioglossus fibres to dome that sector of the tongue root. Note that the styloglossus will likely generate EMG signals corresponding to the stretch reflex activation.
The hyoglossus comprises at least three neuromuscular compartments. Unusuallly, these compartments have names. Chondroglossus, ceratoglossus and basioglossus. The chondroglossus originates from the lesser cornu (small horn) of the hyoid. The ceratoglossus has its origin at along the greater cornu (large horn) of the hyoid. The basioglossus arises from the body of the hyoid.
The inferior longitudinal muscle comprises two neuromuscular compartments. A longitudinal compartment (dark blue) arises in the root of the tongue and inserts at the midsagittal underside of the tongue tip. The oblique compartment (light blue) arises at the tongue root, slightly inferior and more medial to the longitudinal part, then decussates with the longitudinal part and inserts into the tongue dorsum parasagittally, lateral to the most anterior genioglossus fibres and at 2/3 the distance from the root to the tip. Contraction of the inferior longitudinal, follows textbook descriptions for this muscle and will retract and ventroflex the tongue blade and tip. Contraction of the oblique longitudinal compartment will achieve tongue bunching by restricting the forward protrusion of the tongue body. It can do this without directly changing blade and tip position. Each compartment is connected to a compartment of the external Styloglossus which holds the posterior ends of the inferior longitudinal via the stretch reflex.
The superior longitudinal muscle is a flat muscular sheet that covers the dorsal surface of the tongue. There is some evidence (fibre type distribution) that this muscle has two compartments. A medial (bronze) and a lateral-blade-tip compartment (pink). The medial compartment blends with the chondroglossus (gold) . If the chondroglossus reflexively maintains its length then the medial compartment functions to retract the tongue body. The lateral compartment blends with the ceratoglossus (cerise). If the ceratoglossus reflexively maintains its length then the lateral compartment functions to retract and retroflex the lateral margin of the tongue, the blade, and the tip.
The Palatoglossus is functionally capable of consrticting the vocal tract in the velar region. Although it is often included as a tongue muscle and ascribed the function of raising the tongue, its size and lateral attachment means that this function is highly unlikely. Three compartments of the superior constrictor muscle are shown. The palatopharygeous and middle constrictor are missing from this model. The lingual tonsil sits between the chondroglossus and the mucosal surface of the parasagittal tongue root.
A subset of neuromuscular compartments of the styloglossus, hyoglossus inferior longitudinalis, superior longitudinalis, transversus, and verticalis plus all the genioglossus compartments control the tongue body without affecting the blade/tip/tongue margins.
A subset of neuromuscular compartments of the styloglossus, hyoglossus inferior longitudinalis, superior longitudinalis, transversus, and verticalis control the lateral margins, blade and tip of the tongue.