The midbrain represents the uppermost portion of the brainstem, containing numerous important nuclei and white matter tracts, most of which are involved in motor control, as well as the auditory and visual pathways. Its fibers course dorsally and decussate dorsal to the periaqueductal grey matter before exiting the brainstem immediately below the inferior colliculus . Isolated IIIrd nucleus lesion is rare, but can be seen in lacunar infarcts due to the occlusion of the long branches of paramedian perforators . Thus a lesion of the trochlear nucleus affects the contralateral eye. . Question 26.2 from the second paper of 2011 and Question 27 from the first paper of 2019 discussed the localisation of a midbrain lesion by a CN III palsy. The nerve fibers sweep dorsally around the If only saccades are affected, the lesion is in the PPRF, and is called lateral gaze palsy . Function See also: Superior oblique muscle Function . The trochlear nucleus, which rostrally overlaps the oculomotor nuclear complex, is for the greater part a comma-shaped cell group situated lateral, dorsal, and medial to the medial longitudinal fasciculus. Last Update: November 14, 2021. in the crude diagram above there must be a right midbrain lesion. The trochlear nucleus gives rise to nerves that cross (decussate) to the other side of the brainstem just prior to exiting the brainstem. Its fibers course dorsally and decussate dorsal to the periaqueductal grey matter before exiting the brainstem immediately below the inferior colliculus . With a slightly medial projection, the efferent motor fibres of the trochlear nerve cross over (decussate) and exit the brainstem just lateral to the . Description The trochlear nerve is the fourth Cranial Nerve (CNIV) with the longest intracranial course, but also the thinnest. Trochlear Nucleus and Fascicle. symptoms such as fever, malaise, and neck stiffness suggest meningitis. ; Fibres leaving the nucleus turn caudally in the periaqueductal grey. The trochlear nerve is the only cranial nerve with fibers that decussate and exit dorsally into the superior medullary velum before coursing around the midbrain to innervate the superior oblique muscle. Ninety days after lesion, 10 +/- 4 (6% of control) neurones were labelled in the ipsilateral trochlear nucleus; none were labelled in the contralateral nucleus or in any other part of the midbrain, pons, medulla, or cerebellum. Four types of boutons are found in the normal trochlear nucleus. This lesion suggests that there must be damage to the contralateral brainstem; i.e. ; Here, it indents the medial longitudinal fasciculus (MLF). Where is the 7th cranial nerve located? It is difficult to differentiate a trochlear nuclear lesion from a fascicular lesion because of the short course of the trochlear fascicle in the brainstem and the predecussation location of both structures. The trigeminal nerve, also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves.Its name ("trigeminal" = tri-, or three, and - geminus, or twin: so "three-born, triplet") derives from each of the two nerves (one on each side of the . my apologies. Lesions of the trochlear nerve (CN IV) Features of a Trochlear (Fourth) Nerve Palsy Failure to intort the eye (superior oblique): the affected eye cannot look down and in. a unilateral lesion may cause ipsilateral (rubrospinal tract) or contralateral (red nucleus) paresis/paralysis. Cranial nerve palsies can be congenital or acquired. The trochlear nerve is the only cranial nerve with fibers that decussate and exit dorsally into the superior medullary velum before coursing around the midbrain to innervate the superior oblique muscle. Oculomotor N., Trochlear N., & Abducens N. (CN III, IV, & VI) From Agur & Lee 1999 From Agur & Lee 1999 Oculomotor N. (CN III) . Un'eccezione il nucleo trocleare nel tronco cerebrale, che innerva il muscolo obliquo superiore dell'occhio sul lato opposto della faccia. Torun et al. Muscle Superior oblique . The trochlear nerve is a pure motor nerve that innervates the superior oblique muscle. Trochlear Nerve This supplies the superior oblique muscle. The trochlear nucleus is embedded within the MLF between the superior and inferior colliculi in the tegmentum of the midbrain. Lesions involving the trochlear nucleus or fascicles mostly give rise to contralesional superior oblique palsy (SOP). This presents as INO with a contralateral hyperdeviation because the loss of trochlear innervation affects the contralateral superior oblique muscle. If the onset is due to trauma, determine the mechanism of injury. Lesions of the trochlear nerve can either involve the nucleus or the nerve, but both virtually present with similar symptoms. The trochlear nerve is one of 12 sets of cranial nerves. Lesions of all other . The nucleus of the fourth (trochlear) nerve lies at the ventral border of the periaqueductal gray matter at the level of the inferior colliculus in the brainstem. One should suspect a lesion to the trochlear nucleus or fascicle when palsy is associated with a contralateral Horner syndrome or an ipsilateral relative afferent pupillary defect (RAPD . . sends its axons in the trochlear (IV cranial) nerve ; controls the superior oblique of the contralateral eye. The trochlear nerve is the longest intracranial nerve in . Neurologic findings can indicate a compressive lesion of the trochlear nucleus, fascicle . 3 Because the trochlear nucleus and fascicles are surrounded by the ascending trigeminothalamic tract, spinothalamic tract, medial longitudinal fasciculus, descending sympathetic tract and decussating fibres of the superior . Trochlear Nerve Palsy The fascicles of the trochlear . 30 This lesion produces an INO and contralateral hyperdeviation secondary to a IV nerve palsy (remember the trochlear nerve exits and decussates to innervate the opposite side superior . The trochlear nerve is uncommonly affected in isolation. Trochlear Nerve Lesions. In the oculomotor-trochlear nucleus, beta-calcitonin gene-related peptide messenger RNA was the sole isotype expressed. In. Excyclodeviation (outer rotation of globe) can be seen as . Run in the lateral wall of the cavernous sinus below the oculomotor nerve. . The trochlear nerve is the cranial nerve with the longest intracranial course (60 mm) but also the smallest diameter (0.75-1.0 mm) (Villain et al., 1993). In addition, white . The lesions that were visible on noncontrast MR scans (T1-, T2-, and proton density-weighted) had signal intensities that were . Pure unilateral nuclear lesions are very . Methods: The oculomotor nucleus emits nerve fibres, as does also the trochlear nucleus, which lies in the isthmic segment. It is the only cranial nerve to exit the brainstem posteriorly. With a slightly medial projection, the efferent motor fibres of the trochlear nerve cross over (decussate) and exit the brainstem just lateral to the . Head tilting away from the side of the lesion; Causes of Trochlear Nerve Palsy; . This nerve is the fourth set of cranial nerves (CN IV or cranial nerve 4). When looking down and in (medially) with the bad eye there will be DIPLOPIA. It is the only cranial nerve to exit the brainstem posteriorly. originates from the trochlear nerve nucleus, just ventrolateral to the cerebral aqueduct and caudad to the oculomotor nerve nucleus. The only difference is that a unilateral trochlear nuclear lesion affects the contralateral nerve and superior oblique muscle, while a fascicular lesion affects the ipsilateral nerve and muscle.

Trochlear nerve palsy is mentioned in ophthalmology texts dating to the mid nineteenth century. Name the nuclei, functional components and structures supplied by trochlear nerve. - corticospinal fibers run through the midbrain, prior to decussating in the medulla oblongata - cranial nerve nuclei and roots: oculomotor nerve (enables eye movement medially & pupil constriction) trochlear nerve (innervates dorsal . . The number of myelinated fibres in the IVth nerve had decreased to 21 +/- 5 (9% of control) so that the cell/axon . Patients with trochlear nerve palsy typically have worse diplopia on downgaze and gaze opposite the affected eye. Cortical Centre Primary motor cortex (frontal lobe) Trochlear Nucleus Tegmentum (midbrain) Decussation Upper medulla. Cranial nerve IV (trochlear nerve) is a somatic motor nerve that innervates the superior oblique muscle, which intorts, infraducts, and abducts the globe. Nuclear lesions will be more complicated because the . Lesions of all other cranial nuclei affect the ipsilateral side (except of course the optic nerve, cranial nerve II, which innervates both eyes). After exiting the pons, the nerve curves over the superior cerebellar peduncle and then runs between the SCA and the PCA. Foramen Superior orbital fissure . The trochlear nucleus contains somatic motor neuronal cell bodies that exit the nucleus posteriorly. A highly unusual syndrome involves a unilateral lesion of the MLF at the level of the caudal midbrain with extension into the trochlear nucleus on the same side. The calibration was performed on the trochlear nucleus in developing chicks. It innervates a muscle, the superior oblique muscle, on the opposite side (contralateral) from its nucleus.The trochlear nerve decussates within the brainstem before emerging on the contralateral side of the brainstem (at the level of the inferior colliculus). Other structures in this cistern include the great cerebral vein of Galen and the superior cerebellar and posterior cerebral arteries. Lesions affecting the CN IV nucleus can arise from hemorrhage, infarction/stroke . If the onset is due to trauma, determine the mechanism of injury. CN-III fasciculus lesions at the red nucleus present as oculomotor palsy with crossed hemitremor, Benedikt syndrome.

However, it received little more than a brief mention and was no doubt an underrecognized entity. Trochlear nucleus The trochlear nucleus (IVth cranial nerve) is located in the gray matter in the floor of the cerebral aqueduct just caudal to the oculomotor nuclear complex. I sometimes get carried away with the rule of thumb, yes CN IV is an exception for the decussation, .. however the rule of thumb stands, CN lesion (LMNs) will be ipsilateral, no matter what nerve it is. INTRODUCTION Only cranial nerve to cross completely to the other side (arises from the contralateral nucleus) Longest intracranial course (7.5cm) and thinnest of all cranial nerves Unprotected intracranial course of trochlear nerve is responsible for frequent involvement in intracranial lesions Superior oblique palsy is the most common type of . Thus a dorsal midbrain lesion may cause a combination of contralateral IV nerve palsy and ipsilateral INO (5). Thus, a lesion affecting both the MLF and ipsilateral trochlear nucleus presents clinically as INO with a contralateral globe hyperdeviation . Nuclear lesions are contralateral, since the superior oblique is innervated by the trochlear nucleus on the contralateral side of the midbrain. Nuclear lesions are contralateral, since the superior oblique is innervated by the trochlear nucleus on the contralateral side of the midbrain. The trochlear nerve innervates only the superior oblique muscle. Motor Pathway. Enter the orbit by passing through the superior orbital fissure. The trochlear nucleus. The trochlear nerves originate 1 on either side of frenulum veli, from the dorsal aspect of the midbrain.The nerve winds round the superior cerebellar peduncle and cerebral peduncle just above the pons, after appearing from the brain.It then enters between the posterior cerebral and superior cerebellar arteries to appear ventrally. Lesions involving the trochlear nucleus or fascicles mostly give rise to contralesional superior oblique palsy (SOP). While diagnosis can usually be made based on clinical features, further investigation . Corticobulbar innervation of the facial nerve [cranial nerve (CN) VIIJ nucleus. This muscle depresses, intorts, and abducts the eye. The trochlear nucleus contains somatic motor neuronal cell bodies that exit the nucleus posteriorly. It is located medial to and below the complimentary margin to . The nucleus of CN IV is located in the periaqueductal grey matter of the inferior part of the midbrain. This strabismus will be contralateral to a nuclear lesion in the mesencephalon and ipsilateral to a trochlear nerve lesion after it emerges from the rostral medullary velum. Notable midbrain nuclei include the superior and inferior colliculus nuclei, red nucleus, substantia nigra, oculomotor nuclear complex, and trochlear nucleus. MRI documented contralateral tegmental lesions of the trochlear nucleus and adjacent intraaxial trochlear nerve. An exception is the trochlear nucleus in the brainstem, which innervates the superior oblique muscle of the eye on the opposite side of the face. Figure 13-4. The tendon of the superior oblique is tethered by a fibrous structure known as the trochlea, giving the nerve its name. Oh, you're right, trochlear does arise from the contralateral nucleus. . Trochlear nucleus 301Brain stem A 4th nerve lesion causes atrophy of the superior oblique muscle.

Foville's syndrome is a unilateral lesion at or near the abducens nucleus (p. 323 in Zee) which causes conjugate gaze palsy, contralateral limb paralysis, and ipsilateral facial paralysis. For example, a right sided midbrain lesion causes damage to the right trochlear nucleus . A 63-year-old man is suddenly unable to speak or swallow and is tetraplegic. Lesions can affect the third nerve in the brainstem (nucleus or fascicular portion), in the subarachnoid space, in the cavernous sinus, at the superior orbital fissure, or in the orbit [138,547,549] (see Table 8.8). An isolated fourth nerve palsy is the most common presenting symptom in cases of fourth nerve schwannoma, occurring in about 75% of symptomatic cases. Thus, each superior oblique muscle is supplied by nerve fibers from the trochlear nucleus of the opposite side. Gross anatomy Nucleus and intraparenchymal portion. 22. Trochlear nucleus. Lesions in the midbrain tegmentum, ventral to the aqueduct of Sylvius and rostral to the third nerve nucleus, can cause selective paralysis of downward saccades by disrupting projections from the riMLF to the INC and oculomotor and trochlear nuclei. As the nerve bundle emerges from the brainstem, it enters the infratentorial part of the quadrigeminal cistern. Lesions of all other cranial nuclei affect the ipsilateral side. Morphological studies by Graybiel and Hartwiegl0 suggest that prepositus . . Axons emanating from the trochlear nucleus arc dorsally around the periaqueductal gray into the tectum of the midbrain, where they cross .

Overview. In cats, which have . Laboratoire de Physiologe du Travail,4l, Rue Gay-Recent evidence indicates that the prepositus hypoglossi nucleus subserves a role in eye movemel1'2'5'10,1i,18. Motor Function. The nucleus is located caudal to the oculomotor nucleus and the nerves pass dorsally to decussate before emerging from the dorsal brainstem just below the inferior colliculi. and lesions of the trochlear nucleus or fascicle may be accompanied by a Horner's syndrome. The trochlear nucleus is found immediately anterior to the cerebral aqueduct at the level of the inferior colliculus..

The trochlear nucleus is located in the dorsoventral midbrain, ventral to the periaqueductal grey matter . Figure 1c presents a schematic diagram of the relative location between the lesion site and the trochlear nucleus. Trochlear nerve The trochlear nerve (CN IV) is a paired cranial nerve that is responsible for innervating the superior oblique muscle. Score: 4.7/5 (46 votes) . Symptom #3 in this case indicates that the lesion affected the (A) nucleus ambig us (B) solitary nucleus (C) corticobulbar fibers to the nucleus ambiguus (D) accessory nucleus . Cranial nerve palsy is characterized by a decreased or complete loss of function of one or more cranial nerves. As a result, it causes the eyeball to move downward and inward. It is part of the autonomic nervous system, which supplies (innervates) many of your organs, including the eyes. Classically, this is the lesion which develops during uncal herneation, due to an ipsilateral cerebral injury. An attempted lateral gaze in a contralesional direction (away from the . A more comprehensive review of the clinical features of fourth nerve palsies due to all . Patients with trochlear nerve palsy typically have worse diplopia on downgaze and gaze opposite the affected eye. This trochlear nucleus is adjacent to the midline in the ventral portion of the central gray substance that surrounds the mesencephalic aqueduct. The trochlear nucleus is found immediately anterior to the cerebral aqueduct at the level of the inferior colliculus.. the medial rectus of the right eye (Figure 8.2), the failure to perform a lateral gaze to the left suggests an abducens nucleus lesion. Thus, each superior oblique muscle is supplied by nerve fibers from the trochlear nucleus of the opposite side. lesions of the trochlear nerve anatomical course arises from It is a pure general somatic efferent nerve that innervates the superior oblique muscle, which depresses, intorts, and abducts the eye. One should suspect a lesion to the trochlear nucleus or fascicle when palsy is associated with a contralateral Horner syndrome or an ipsilateral relative afferent pupillary defect (RAPD . A complete IIIrd nucleus lesion can lead to an ipsilateral IIIrd nerve palsy, contralateral superior rectus weakness, and bilateral mild ptosis. Both locations will result in paresis of the contralateral superior oblique muscle. 102, 104, 127 The riMLF itself can be spared when downward gaze is paralyzed. . The trochlear nerve innervates a single muscle - the superior oblique, which is a muscle of oculomotion.As the fibres from the trochlear nucleus cross in the midbrain before they exit, the trochlear neurones innervate the contralateral superior oblique.. These lesions can be congenital or acquired. If the lesion extends to the medial lemniscus, there is also contralateral hypesthesia. Trochlear nerve palsy may result from both peripheral - injury to nerve bundles or central - involvement of the trochlear nucleus, and lesions. Thus a lesion of the trochlear nucleus affects the contralateral eye. Monosynaptic excitation of stimulation of the prepositus trochlear motoneurons hypoglossi nucleus . The trochlear nucleus gives rise to nerves that cross (decussate) to the other side of the brainstem just prior to exiting the brainstem. The oculomotor nucleus lies in the midbrain anterior to the periaqueductal grey matter at the level of the superior colliculus anterior to the cerebral aqueduct.The fibers run through the tegmentum, red nucleus and medial aspect of the substantia nigra.

The trochlear nucleus is unique in that its axons run dorsally and cross the midline before emerging from the brainstemso a lesion of the trochlear nucleus affects the contralateral eye. The trochlear nucleus is unique in that its axons run dorsally and cross the midline before emerging from the brainstem posteriorly. A pure trochlear palsy is characterized by vertical or diagonal diplopia greatest on downward gaze directed to the opposite side. Neuroanatomy, Cranial Nerve 4 (Trochlear) - StatPearls - NCBI Bookshelf. Dysfunction of the fourth cranial nerve (trochlear nerve), which innervates the superior oblique muscle, is one cause of paralytic strabismus and can result from lesions anywhere along its path between the fourth nerve nucleus in the midbrain and the superior oblique muscle within the orbit. No obvious lesions were identified in the other magnetic Lesions of the trochlear nerve can either involve the nucleus or the nerve, but both virtually present with similar symptoms. found the average size of fourth nerve schwannomas causing diplopia to be 4.6mm [21].

The nucleus of CN IV lies at the level of the inferior colliculus in the tegmentum of the midbrain. Neurologic findings can indicate a compressive lesion of the trochlear nucleus, fascicle . IV cranial nerve - Trochlear nerve. The trochlear nucleus is located in the dorsoventral midbrain, ventral to the periaqueductal grey matter . Trochlear palsy is the most common cause of vertical strabismus. median plane, the location of the trochlear nucleus and intra-axial trochlear nerve (Figures 1a and 1b), which perfectly corre-lated with the clinical manifestations. Types I and II are large and demonstrate typical . A combination of ipsilateral III and contralateral IV nuclear palsies can also occur. INO and trochlear syndrome results from a lesion affecting the MLF at the caudal midbrain as well as the adjacent ipsilateral trochlear nucleus. The only difference is that a unilateral trochlear nuclear lesion affects the contralateral nerve and superior oblique muscle, while a fascicular lesion affects the ipsilateral nerve and muscle. The trochlear (fourth) nerve is the only cranial nerve that decussates before emerging from the posterior aspect of the brainstem. It has a general somatic efferent (somatic motor) nerve, which innervates a single muscle (superior oblique muscle) on the contralateral side of its origin. Acute symptoms may indicate trauma, while chronic symptoms are mostly congenital. cisternal segments of the trochlear nerves. . The two nerves decussate and wind around the cerebral peduncles to reach the ventral aspect of midbrain. Course Trochlear nerve illustration Ptosis; Down-and-out pupil; Mydriasis

The trochlear nucleus (IVth cranial nerve) is located in the gray matter in the floor of the cerebral aqueduct just caudal to the oculomotor nuclear complex. A combination of ipsilateral III and contralateral IV nuclear palsies can also occur.

Ultrastructural degeneration studies were carried out on the cat trochlear nucleus following lesion of the vestibulo-trochlear pathway in order to characterize the location and type of presynaptic endings involved in this pathway. The trochlear nucleus. Thus a dorsal midbrain lesion may cause a combination of contralateral IV nerve palsy and ipsilateral INO (5). Features of a Third Nerve Palsy. It is divided into brainstem, cisternal, tentorial .

128 Since one . symptoms such as fever, malaise, and neck stiffness suggest meningitis. ; They then arch dorsally to decussate and leave the brainstem at . It is the unique nerve with a root zone arising from the posterior brainstem where its nucleus lies . There are two cranial nerve nuclei whose neurons contribute axons to the oculomotor nerve:. The trochlear nerve (CN IV) is the only cranial nerve to exit the brainstem from its posterior surface. An upper motor neuron (UMN) lesion (e.g., stroke involving the internal capsule) results in contralateral . He can only move his eyes vertically and is able to blink . An intra-axial lesion is an uncommon aetiology in patients with trochlear palsy without other neurological deficits. The trochlear nucleus. This is a summary of some clinical conditions that I learnt for my anatomy exam in 2nd year. . The localization of lesions of the trochlear nerve to the nucleus or fascicles (or both), subarachnoid space, cavernous sinus and superior orbital fissure, or orbit depends on the associated damage to neighboring neurologic structures. ; Its cell bodies are located in the contralateral trochlear nucleus. It is a motor nerve that sends signals from the brain to the muscles. Methods: We report 2 patients with SOP on the side of intraaxial lesions with . The nucleus is located caudal to the oculomotor nucleus and the nerves pass dorsally to decussate before emerging from the dorsal brainstem just below the inferior colliculi. Lower Motor Neuron Lesions (LMNL) lesion of facial nucleus or more peripheral Ipsilateral effects on both upper and lower quadrants of face Upper Motor Neuron Lesion (UMNL) Multiple cranial neuropathies are commonly caused by tumors, trauma, ischemia, or infections. Etiologies of oculomotor nerve palsies, based on localization, are outlined in Table 8.9. ; This is a small nucleus located at the level of the inferior colliculus. The false image will lie below the true image (verticaldiplopia) and will be somewhat oblique (torsionaldiplopia).