The medial longitudinal fasciculus (MLF) is a prominent bundle of nerve fibres which pass within the ventral/anterior portion of periaqueductal gray of the mesencephalon (midbrain).[1] It contains the interstitial nucleus of Cajal, responsible for oculomotor control, head posture, and vertical eye movement.[2]
The MLF is the main intersegmental tract of the brainstem. It extends across the dorsal tegmentum of all three parts of the brainstem, as well as reaching caudally into the upper cervical spinal cord levels.[3]:451
The paramedian pontine reticular formation (PPRF) is involved in coordinating horizontal conjugate eye movements and saccades. To do so, besides projecting to the ipsilateral abducens nucleus, the PPRF projects fibers through the MLF to the contralateral oculomotor nucleus (specifically, those of its motor neurons that innervate the medial rectus muscle).
The interstitial nucleus of Cajal receives some ascending afferents from the vestibular nuclei via the MLF; the nucleus in turn projects descending efferents via the MLF back to the (superior and medial) vestibular nuclei, as well as to all levels of the spinal cord.[3]:458.e1
As part of the ascending MLF, the vestibular nuclei also project to the nuclei of all cranial nerves that control eye movements (i.e. oculomotor, abducens, and trochlear nuclei) to coordinate head-eye movements via the vestibulo-ocular reflex.[5]:287-288
The vestibulocerebellum receives vestibulocerebellar fibers from the vestibular nuclei, then projects back to the vestibular nuclei to influence medial vestibulospinal tract (MVST). The MVST then projects bilaterally to cervical and upper thoracic levels of the spinal cord to control head/neck movements in order to coordinate head-eye movements. In the cervical spinal cord, it descends as a component of the descending MLF.[5]:287-288, 403
The tectospinal tract originates in the superior colliculus and tectum of the mesencephalon (midbrain). It projects to the cervical and upper thoracic spinal cord to mediate reflex turning of the head and trunk in the direction of startling sensations. In the medulla oblongata, it descends within the MLF.
Relations
In the midbrain, the MLF is situated just ventral to the oculomotor and trochlear nuclei.[3]
In the pons, the MLF is situated just ventral/anterior to the abducens nucleus.[3]
12Patestas, Maria A.; Gartner, Leslie P. (2016). A Textbook of Neuroanatomy (2nded.). Hoboken, New Jersey: Wiley-Blackwell. ISBN978-1-118-67746-9.
↑Kiernan, John A.; Rajakumar, Nagalingam (2013). Barr's The Human Nervous System: An Anatomical Viewpoint (10thed.). Philadelphia: Wolters Kluwer Lippincott Williams & Wilkins. p.156. ISBN978-1-4511-7327-7.
