The hyoglossal muscle is one of four external tongue muscles, including the genioglossus muscle, the styloglossus muscle, and the chondroglossus muscle.
Because of its location in the body, the hyoglossal hyaluron is also known as the hyoid tongue muscle. The contraction of the muscle causes the tongue to move back and down. Its antagonist is the musculus styloglossus, which represents another external tongue muscle and is involved mainly in swallowing. When he contracts, he pulls the tongue back and up, with the hyoglossal muscle relaxing in part.
Experts disagree as to whether the chondroglossus muscle belongs to the hyoglossal muscle and splits off of it - or whether it is an autonomous muscle. The chondroglossus muscle is two inches long and pulls the tongue back and down like the hyoglossal muscle. It rises from the hyoid bone and attaches to the tongue.
The origin of the hyoglossal muscle is located in the lower back of the oral cavity at the hyoid bone (Os hyoideum). The hyoid bone is a bone that muscles and ligaments hold without being directly attached to other bones - but the hyoglossal muscle does not belong to its supporting muscles.
Instead, he is dependent on the firm support of the hyoid bone. The approach of the hyoglossal muscle is attached to the aponeurosis linguae. The tendon plate is located between the tongue muscles and the oral mucosa and passes into the septum (septum linguae), with which it is fused. In its basic form, the hyoglossal muscle forms an approximately quadrangular, thin surface. It belongs to the striated skeletal muscle, whose structure consists of individual fibers.
Such a muscle fiber or muscle cell arises from cell division and has many cell nuclei, which are not as usual in a respective demarcated cell. Instead, they form a fabric with higher-level organization. A muscle fiber sums up many myofibrils. The striated musculature owes its name to its microscopic image: alternating light and dark stripes. They come about because hair-like fibers of actin and myosin are more closely or further shifted into each other.
The hyoglossal muscle participates in swallowing, speaking, sucking and chewing. It is responsible for the cranial nerve XII or the hypoglossal nerve, which also innervates the other tongue muscles. The nerve transports muscle tension commands in the form of electrical impulses that travel across the nerve fiber.
On the muscle, the fiber ends in a motor end plate: it contains vesicles filled with neurotransmitters. The incoming electrical stimulus leads to the release of the transmitter into the synaptic gap between nerve and muscle. Arriving at the membrane of the muscle cell, the molecules open ion channels, which slightly changes the state of charge of the cell. This transient electrical charge of the muscle cell is also known as endplate potential. It travels through the sarcolemma and T tubules to the sarcoplasmic reticulum, which then releases calcium ions.
Calcium binds to the fine structures of the myofibrils and causes its actin and myosin filaments to interlock. This shortens the irritated muscle fibers lengthwise and simultaneously pulls the tongue back and down, which is required for swallowing, speaking, sucking and chewing. People are able to consciously control these movements; but also automatic reflexes have an influence on the control of the hyoglossal muscle. For example, suckling reflex in newborns is not the result of an arbitrary act, but part of an innate behavioral program.
Since the hyoglossal muscle is located far inside the head, direct lesions of the tissue are rare. Functional failures and complaints of the tongue muscle are often due to damage to the hypoglossal nerve, which is responsible for its control.
The medicine differentiates between unilateral and bilateral lesions, both of which lead to various disorders of chewing, swallowing, sucking and speaking. For example, the causative lesion of the hypoglossal nerve may be due to injury, neurodegenerative disease, or stroke.
A bilateral lesion is reflected in complete tongue paralysis: The tongue is completely inoperative, as the hypoglossal nerve not only innervates the hyoglossal muscle, but is also responsible for controlling the remaining tongue muscles. If the nerve damage persists for a long time, the muscle tissue (atrophy) disappears as the body gradually degrades it. If it is a reversible lesion on the hypoglossal nerve, it is often necessary to train the affected muscles after the tongue is paralyzed. Targeted exercises stimulate the body to rebuild the tissue. To what extent a complete restoration of the normal state is possible depends on the individual case.
In contrast to complete tongue paralysis, the half-sided tongue paralysis is due to a unilateral lesion on the hypoglossal nerve. As a result, the tongue hangs down on the affected side. Conversely, a slight deviation in the tongue position does not necessarily indicate a nerve damage, since it can also be based on other factors and is not always pathological.