Innervation of the Styloglossus Muscle
Yes, the styloglossus muscle is innervated by the hypoglossal nerve (CN XII). 1, 2
Hypoglossal Nerve Anatomy and Function
- The hypoglossal nerve (CN XII) is a purely motor nerve that originates from the dorsal medulla and provides somatic motor innervation to the intrinsic and extrinsic muscles of the tongue 3
- The nerve exits the brainstem in the preolivary sulcus, passes through the premedullary cistern, and exits the skull through the hypoglossal canal 1
- After exiting the skull, the extracranial hypoglossal nerve travels caudally within the carotid space and courses anteriorly inferior to the hyoid 4
Specific Tongue Muscles Innervated by CN XII
- The hypoglossal nerve innervates all intrinsic tongue muscles (superior longitudinal, inferior longitudinal, transverse, and vertical muscles) 1
- It also innervates three extrinsic tongue muscles: styloglossus, hyoglossus, and genioglossus 1
- The only tongue muscle not innervated by the hypoglossal nerve is the palatoglossus muscle 4
Embryological Development and Confirmation
- Embryological studies have confirmed that the styloglossus muscle is innervated by the hypoglossal nerve from early development 5
- The styloglossus muscle differentiates beyond the first lingual swellings in contact with a branch of the hypoglossal nerve 5
- In all examined cases, the styloglossus muscle was consistently innervated by the hypoglossal nerve 2
Clinical Significance
- Hypoglossal nerve palsy affects all muscles it innervates, including the styloglossus, resulting in dysarthria and deviation of the tongue to the side of the lesion upon protrusion 4, 3
- Common causes of hypoglossal nerve palsy include neoplasms (most common), brainstem infarct, demyelinating disease, vascular lesions, trauma, and infectious processes 3, 6
- MRI is the preferred imaging modality for evaluating hypoglossal nerve pathology, with CT providing complementary information on bony structures 4
Functional Anatomy
- The styloglossus muscle originates from Reichert's cartilage (which gives rise to the temporal styloid process) and inserts into the lateral aspect of the tongue 2
- It functions primarily to retract and elevate the tongue 7
- The hypoglossal nerve branches to the styloglossus muscle emanate from its lateral division 7
Common Pitfalls in Assessment
- Anatomical variations of the styloglossus muscle exist, including accessory muscle fascicles originating from the mandibular angle 2
- When evaluating hypoglossal nerve function, it's important to assess all innervated muscles, not just the more commonly examined genioglossus 1
- Isolated styloglossus dysfunction is rare; hypoglossal nerve pathology typically affects multiple tongue muscles simultaneously 6