where is the trochlear nerve

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Why trochlear nerve is called the pathetic nerve?

Trochlear nerve or the 4th cranial nerve is called pathetic nerve ! It is called so because the paralysis of this nerve causes deviation of eye making the patient do a head tilt to fuse two images (formed by the normal eye and the abnormally deviated eye) and thus giving the patient a “dejected” or “pathetic” look !

What function does the trochlear nerve have?

What function does the trochlear nerve have?

1. The Central Nervous System: It consists of the brain and the spinal cord. It is the central evaluating and commanding unit.
2. The Peripheral Nervous System: It consists of the following subdivisions. A. ...
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What are the 4 cranial nerves?

These Are the 12 Cranial Nerves and Their Functions The 12 Cranial Nerves I. Olfactory nerve II. Optic nerve III. Oculomotor nerve IV. Trochlear nerve V. Trigeminal nerve VI. Abducens nerve VII....

What does the trochlear do?

The trochlear nerve is a motor nerve, and it controls the superior oblique muscle of the eye. The superior oblique muscle controls the downward movement of the eyeball and, in part, keeps the eyeball from rolling upward into the orbit (eye socket).

Where are the Trochlear nerves located?

brainstemThe trochlear nerve emerges from the back (dorsal) brainstem, just below the inferior colliculus. It circles from behind around the brainstem and runs forward toward the eye in the subarachnoid space.

What are the function of trochlear nerve?

The trochlear nerve is the fourth cranial nerve. It's a motor nerve and provides movement to only one muscle—an eye muscle called the superior oblique, which connects to the top of the eyeball. The tendon of that muscle passes through a structure that's a lot like a pulley.

Where is the 4th cranial nerve located?

The fourth cranial nerve is the only cranial nerve that starts at the back of the brain. It has a longer path through the skull than any other cranial nerve. It enters the eye socket through an opening at the back and then travels to the superior oblique muscle.

Where does the trochlear nerve start?

medial midbrainThe trochlear nerve pair originates from a pair of symmetrical trochlear nuclei within the medial midbrain at the level of the inferior colliculus. The left and right nerves then travel dorsally surrounded by the periaqueductal gray matter, decussating before their exit in the dorsal midbrain.

What happens if the trochlear nerve is damaged?

Thus, a trochlear nerve palsy causes an ipsilateral higher eye (i.e., hypertropia) and excyclotorsion (the affected eye deviates upward and rotates outward). Patients may report vertical and/or torsional diplopia that is usually worse on downgaze and gaze away from the affected side.

How do you test for trochlear nerve damage?

To detect excyclotropia one must ask the patient whether there is a tilted double image in down gaze. Bilateral trochlear nerve palsy causes a change of vertical deviation between right and left gaze and between head-tilt to the right and to the left shoulder.

Is 4th nerve palsy serious?

People with fourth nerve palsy often have one iris that is higher than the other, tilt their head, and have double vision. Some types of fourth nerve palsy may go away on their own. You may need surgery if the palsy does not go away.

How long does it take for fourth nerve palsy to go away?

Most cases resolve within weeks to months, with the vast majority completely recovering by 6 months. Some cases may resolve slowly over the course of a year. Patients with head trauma were less likely to recover, yet 44% of these patients experienced gradual and spontaneous recovery.

What organs do the trochlear nerve control?

In each eye, the superior oblique muscle functions as the trochlea. The trochlear nerve innervates this muscle to lift the eyes so you can look down. The nerve also enables you to move your eyes toward your nose or away from it.

What eye movements does trochlear nerve control?

Cranial nerve 4, also called the trochlear nerve, controls the movement of the superior oblique muscle. This muscle moves the eye down and rotates the top of the toward the nose. It also helps pull the eye outward when the eye is looking downward.

What muscles does the trochlear nerve innervate?

The trochlear nerve is a purely motor nerve, responsible for providing general somatic efferent (GSE)/motor innervation to just one muscle, the superior oblique muscle of the eye, on the contralateral side of its associated nucleus.

How do you test the function of the trochlear nerve?

To assess the trochlear nerve, instruct the patient to follow your finger while you move it down toward his nose. Cranial nerve V covers most of the face. If a patient has a problem with this nerve, it usually involves the forehead, cheek, or jaw—the three areas of the trigeminal nerve.

What is the motor function of nerve IV?

Synonyms: Cranial nerve IV, CN IV , show more... The trochlear nerve is a purely motor nerve, responsible for providing general somatic efferent (GSE)/motor innervation to just one muscle, the superior oblique muscle of the eye, on the contralateral side of its associated nucleus.

Where is the nucleus of the trochlear nerve located?

The nucleus of the trochlear nerve is located in the caudal mesencephalon beneath the cerebral aqueduct. It is immediately below the nucleus of the oculomotor nerve (III) in the rostral mesencephalon.

Where does the trochlear nerve decussate?

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 ).

What is the effect of a trochlear nerve palsy on the eye?

Trochlear nerve palsy also affects torsion (rotation of the eyeball in the plane of the face). Torsion is a normal response to tilting the head sideways. The eyes automatically rotate in an equal and opposite direction, so that the orientation of the environment remains unchanged—vertical things remain vertical.

What nerve causes vertical diplopia?

Vertical diplopia. Injury to the trochlear nerve cause weakness of downward eye movement with consequent vertical diplopia (double vision). The affected eye drifts upward relative to the normal eye, due to the unopposed actions of the remaining extraocular muscles.

What is the difference between a trochlear injury and a trochlear injury?

An injury to the trochlear nucleus in the brainstem will result in an contralateral superior oblique muscle palsy, whereas an injury to the trochlear nerve (after it has emerged from the brainstem) results in an ipsilateral superior oblique muscle palsy. Homologous trochlear nerves are found in all jawed vertebrates.

How is the trochlear nerve tested?

The trochlear nerve is tested by examining the action of its muscle, the superior oblique. When acting on its own this muscle depresses and abducts the eyeball. However, movements of the eye by the extraocular muscles are synergistic (working together). Therefore, the trochlear nerve is tested by asking the patient to look 'down and in' as the contribution of the superior oblique is greatest in this motion. Common activities requiring this type of convergent gaze are reading the newspaper and walking down stairs. Diplopia associated with these activities may be the initial symptom of a fourth nerve palsy.

What is the name of the cranial nerve that curves around the brain?

The trochlear nerve ( CN IV) seen with other cranial nerves. It is the only cranial nerve to emerge from behind the brainstem, and curves around it to reach the front. Details. Innervates. Superior oblique muscle. Identifiers. Latin. nervus trochlearis. MeSH.

Where does the trochlear nerve go?

From the back of your head, the trochlear nerve curves around the brainstem and emerges between two arteries called the posterior cerebral and superior cerebellar arteries. It then goes inside the cavernous sinus and runs along one of its walls.

What is the function of the trochlear nerve?

Function. The trochlear nerve doesn't transmit sensory signals. It functions purely as a motor nerve. The one muscle it sends signals to—the superior oblique muscle—is one of six muscles that allow the eye to make precise movements for tracking or focusing on an object.

What causes trochlear nerve palsy?

Typically, trochlear nerve palsy is the result of head trauma. Motorcycle accidents are a common cause, but sometimes it can result from even minor head injuries. Less often, palsy is caused by: 5  3 . Diabetes.

Why is trochlear nerve palsy misdiagnosed?

Typically, trochlear nerve palsy is the result of head trauma.

How many cranial nerves are there in the human body?

You have twelve pairs of cranial nerves in your head. They're symmetrical—each one has a right side and left side (but each pair is generally referred to as a single nerve). The rest of the nerves in your body emerge from the spinal cord but all the cranial nerves, including the trochlear nerve, come from your brain.

Which cranial nerves are involved in the sinuses?

In the sinus, the trochlear nerve is joined by several other nerves, including the third and sixth cranial nerves (which also serve the eye) and two branches of the trigeminal (fifth cranial) nerve: the ophthalmic and maxillary nerves, which supply sensory innervation to much of the face. Finally, the trochlear nerve reaches ...

Which nerve runs farther on the inside of the skull than any other cranial nerve?

The trochlear nerve is one of these nerves, but it's unique in that it's the only one that comes from the rear of the brainstem. It also runs farther on the inside of the skull than any other cranial nerve and is the thinnest of them. 2 .

What is the trochlear nerve?

The trochlear nerve is also known as cranial nerve IV (CN-IV). It is the only cranial nerve that emerges dorsally from the brain (near the back ), giving it the longest pathway. It is the smallest nerve to service the eye.

Which nerve is responsible for the movement of the eye?

It is the smallest nerve to service the eye. CN-IV passes through the superior orbital fissure, and it provides motor function, or movement. It serves the superior oblique eye muscle and connects to the annular tendon. As a result, it processes brain signals to move the eyes up and down, and also outwards.

Where does the trochlear nerve originate?

The trochlear nerve arises from the trochlear nucleus of the brain, emerging from the posterior aspect of the midbrain (it is the only cranial nerve to exit from the posterior midbrain).

Which muscle is innervated by the trochlear nerve?

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.

What nerve is examined in conjunction with the oculomotor and abducens nerves?

Examination of the Trochlear Nerve. The trochlear nerve is examined in conjunction with the oculomotor and abducens nerves by testing the movements of the eye. The patient is asked to follow a point (commonly the tip of a pen) with their eyes without moving their head.

What is the name of the nerve that causes vertical diplopia?

Palsy of the Trochlear Nerve. Trochlear nerve palsy commonly presents with vertical diplopia, exacerbated when looking downwards and inwards (such as when reading or walking down the stairs). Patients can also develop a head tilt away from the affected side.

Which cranial nerve has the longest intracranial course?

The trochlear nerve is the fourth paired cranial nerve. It is the smallest cranial nerve (by number of axons), yet has the longest intracranial course. It has a purely somatic motor function. In this article, the anatomical course, motor functions and clinical relevance of the nerve will be examined.

Where does the trigeminal nerve enter the eye?

The nerve then moves along the lateral wall of the cavernous sinus (along with the oculomotor nerve, the abducens nerve, the ophthalmic and maxillary branches of the trigeminal nerve and the internal carotid artery) before entering the orbit of the eye via the superior orbital fissure.

Where does the sphenoid run?

It runs anteriorly and inferiorly within the subarachnoid space before piercing the dura mater adjacent to the posterior clinoid process of the sphenoid bone.

What is the trochlear nerve?

Moreover, the trochlear nerve is a somatic efferent (motor) nerve, and along with oculomotor (III) and abducens (VI) nuclei, it is responsible for eye movement. Through its innervation of the superior oblique, the trochlear nerve controls the abduction and intorsion of the eye. [1]

Why is the trochlear nerve so fragile?

Because of its fragility and extensive intracranial course, the trochlear nerve is especially vulnerable to trauma compared to most cranial nerves. Thus, the most common cause of an acquired defect of the trochlear nerve is trauma.[13]  Traumatic trochlear nerve palsies are associated with motor vehicle accidents and boxing, as they involve rapid deceleration of the head. Because the trochlear nerve is so fragile, this can occur in minor head injuries that do not involve loss of consciousness or skull fracture. Shearing forces can result in disruption particularly at the superior orbital fissure, where the trochlear nerve enters the orbit.

What is the clinical presentation of acquired fourth nerve palsy?

Clinical presentation of acquired fourth nerve palsy is similar to that of congenital palsy. Patients may present most commonly with diplopia but can also present with blurry vision or a minor vision problem when looking down like reading a book or going down the stairs. The diplopia presented in trochlear nerve palsy is either vertical or diagonal and is worse with a downward gaze. Compensation for the nerve palsy usually includes a head tilt to the opposing side and tucking in the chin, so the affected eye’s pupil can move up and extort, instead of downwards and intort. During clinical examination, the eyes will display hypertropia with the affected eye being slightly elevated relative to the other normal eye. Under cover, the affected eye will show an upward drift relative to the other eye. [15]

What causes a 4th nerve palsy?

The most common cause of an isolated fourth nerve palsy is congenital. [5][6][7][8] These patients may commonly present with eye deviation and complain of diplopia and postural head changes. This characteristic head tilt is towards the unaffected side to compensate for a lack of intorsion from the superior oblique muscle. Congenital trochlear nerve palsies are almost always unilateral. These nerve palsies in children can be initially mistaken for torticollis because of the head tilt many of these children display. [9][10] Most commonly, this can be corrected surgically or with prism. A more conservative approach for minor deviations involves patching of one eye that can alleviate diplopia. However, if patients defer or fail initial therapy, surgical approaches include tucking of the superior oblique tendon or inferior oblique weakening.[11]  Interestingly, there is evidence to suggest that congenital superior oblique palsy is more common in young males. [12]

What muscle elevates the posterior of the eye?

This “pulley” system afforded by the trochlea makes the superior oblique unique among the extraocular muscles and allows for its muscular functions of depression, abduction, and intorsion of the eye. Because of the muscle’s placement at the posterior portion of the eye, the muscle elevates the posterior of the eye, causing the front of the eye to become depressed. The muscle also causes abduction of the eye, moving the pupil away from the nose, and intorsion, rotating the eye such that the top of the eye moves toward the nose.

Which muscle innervates the superior oblique muscle?

The only muscle the trochlear nerve innervates, the superior oblique muscle, is the longest and thinnest muscle among the extraocular muscles. The muscle belly originates from the back of the roof of the orbit near the common tendinous ring, but it takes an unusual course to reach the eye. The tendon extends between the orbital roof and passes through a fibrous loop (known as the trochlea) located on the frontal bone. The tendon then reaches laterally and posteriorly prior to its insertion point on the posterior half of the eye.

Where does the trigeminal nerve enter the cavernous sinus?

It enters the cavernous sinus where it runs anteriorly above the abducens nerve and ophthalmic branch of the trigeminal nerve. Here in the cavernous sinus, a few sympathetic fibers join the trochlear nerve with the possibility of some sensory fibers from the trigeminal nerve. The nerve then enters the orbit through the superior orbital fissure and continues to extend anteriorly to the superior oblique muscle. [1][3]The superior orbital fissure is also the nerve pathway for cranial nerves III, VI, and V and is vulnerable to shearing forces in the setting of trauma.

Where is the nucleus of the trochlear nerve located?

The nucleus of the trochlear nerve (CN IV) is located within the ventral aspect of the periaqueductal grey matter of the midbrain. The cells are small and oval-shaped and are partially embedded within the dorsal aspect of the medial longitudinal fasciculus.

Where do trochlear nerves travel?

Both nerves will eventually travel towards the preoptic myotomes (embryonic origins of the extraocular muscles), where they will innervate their respective extraocular muscle. The cells of the trochlear nerve develop in the dorsal and most inferior aspect of the midbrain.

What are the CN IV and VI?

The trochlear (CN IV) and abducens (CN VI) nerves are derivatives of the somatic efferent column of the basal plates of the brainstem. As such, they are pure motor nerves that are responsible for carrying general somatic efferent impulses to their end target organs. Therefore they are similar to the nerves arising from the ventral spinal roots, which are also spinal basal plate derivatives. Both nerves will eventually travel towards the preoptic myotomes (embryonic origins of the extraocular muscles), where they will innervate their respective extraocular muscle.

What is the cistern of the trochlear nerve?

Cisternal portion of trochlear nerve. Recall that a cistern is a communicating subarachnoid dilatation within the brain that contains cerebrospinal fluid. The quadrigeminal cistern (also known as the superior or ambient cistern) is dorsal to the midbrain and is divided into supratentorial and infratentorial parts.

What nerves innervate the recti?

These six muscles (four recti and two obliques) are innervated by cranial nerves III, IV, and VI. This article, however, focuses on the embryology, anatomy, function, and clinical examination of the trochlear (CN IV) and abducens (CN VI) nerves. It is not uncommon to encounter an alternative spelling for CN VI (abducent nerve).

Which nerves provide somatic efferent innervation?

Both the trochlear and abducens nerves provide general somatic efferent (motor) innervation to their respective target muscles. Of note, general somatic efferent fibers are those that arise from lower motor neurons arising from either the ventral horn of the grey matter or an analogous area in the brainstem. Key facts.

Which cranial nerve exits the brainstem?

Subarachnoid cisterns (overview) The trochlear nerve (CN IV) is the only cranial nerve to exit the brainstem from its posterior surface. As the nerve bundle emerges from the brainstem, it enters the infratentorial part of the quadrigeminal cistern.

Where do trochlear nerves originate?

These nerves originate in the midbrain, passing through the superior orbital fissures of the sphenoid bone, to reach the superior oblique muscles. The trochlear nerves are the smallest of the cranial nerves. The trochlea is shaped like a pulley and is a sling of ligamentous tissue.

Where does the trochlear nerve enter the cavernous sinus?

The cisternal segment courses through the ambient cistern between the posterior cerebral and superior cerebellar arteries. The trochlear nerve enters the cavernous sinus superior to the petroclinoid ligament. The cavernous segment of the trochlear nerve courses through the lateral wall of cavernous sinus below the oculomotor nerve.

What is the trochlear nerve exiting the dorsal brainstem in close relation to the?

Figure 4.7. Axial T2 WI showing the trochlear nerve exiting the dorsal brainstem in close relation to the superior medullary velum.

Which nucleus is inferior to the oculomotor nucleus?

The trochlear nucleus is directly inferior to the oculomotor nucleus which is at the level of the superior colliculus (Fig. 3.12 ). Unlike other lower motor nerves ( Fig. 2.17), the lower motor neuron of CN IV decussates in the central nervous system.

Where does trochlear palsy occur?

Trochlear nerve palsy can occur in lesions involving the nucleus, central segment, cisternal segment, cavernous segment, and orbital segment. The nerve is most susceptible to pressure in the cisternal segment. View chapter Purchase book. Read full chapter.

Which nerve innervates the superior oblique muscle?

The trochlear nerve has only somatic motor fibers, which innervate the superior oblique muscle contralateral to its nucleus. The fourth nerve nucleus is located in the tegmentum of the midbrain at the level of the inferior colliculus, ventral to the periaqueductal gray matter, inferior to the oculomotor nucleus, ...

What nerves control the eye?

The oculomotor, trochlear, and abducens nerves control actions of the intraocular (pupillary sphincter) and extraocular muscles. These nerves are observed for symmetry of eye movement, globe position, asymmetry or drooping of the eyelid (ptosis), and twitching or fluttering of the lids or globes. With the lights dimmed, anisocoria or differences in the sizes of the pupils should be ruled out. Pupillary light response is evaluated for quickness and symmetry. Normally, the pupils average about 3 mm in diameter in a room with adequate light. They can range, however, from about 6 mm in children to < 2 mm in elderly patients. Also, one patient's pupils may be different from each other by about 1 mm in size. This is called physiologic anisocoria. The pupils are normally round and regularly shaped, constricting quickly from direct illumination, and slightly less to illumination of the pupils on the opposite side. This is called the consensual response. They dilate again quickly when illumination is removed. Normal pupils constrict when the eyes converge to focus on a closer object, such as the tip of the nose. This is known as accommodation.

Where does the trochlear nerve originate?

While the trochlear nerve is the shortest of all the cranial nerves, it has the longest cranial path through the brain stem. It originates in the inner ear and extends laterally and posteriorly to the inferior trapezius muscle and laterally to the premaxillary muscles.

What are the four parts of the trochlear nerve?

The trochlear nerve branches off into four parts: the main trunk, the branches that branch off into the arms or legs (the acromion), the posterolateral, iliotibial and iliopsoidal branches which each have their respective bones, cartilage and skin. Each branch of the trochlear nerve receives messages from the auditory nerve and from the fifth sensory nerve, which are located in the middle brain. The branches of the trochlear nerve that exits the body wall run along the top of the cervical spine, the backbone of the upper neck, and extend onto the shoulders, back, chest and head. When these branches link up with the other branches of the spinal cord, they form the large white area that you see when a person looks down.

What causes trochlear nerve palsy?

The most common cause of trochlear nerve palsy, the intracranial hearing syndrome, usually results from injuries to the temporal regions near the ear. In this case, there is a delay between the auditory stimulation caused by the outer and middle ear nerves and the processing of that information by the inner ear. The intracranial course usually follows a direct path through the cranial cavity to the auditory cortex and the inner ear. When this occurs, the brain must find a way to send the auditory impulses to the ear that are already receiving the information it needs.

Which part of the trochlear nerve is responsible for controlling eye movements?

The other part of the trochlear nerve, which is important in controlling eye movements is called the extrinsic ganglion. This part of the nerve supplies the muscles surrounding the oculomotor nerves. It is subdivided into four types: the internal mononeurosis, external carotid artery, internal jugular veins, and the internal peduncle. The internal mononeurosis is located inside the brain, external carotid artery branches off in the neck area, and the internal jugular veins are located in the neck and near the eye. The external peduncle branches off in the forehead area.

Which nerve is the branch that connects to the white area that you see when you look down?

The branches of the trochlear nerve that exits the body wall to connect to the large white area that you see when you look down, and this is called the somatic efferent. The branches that branch off into the legs connect to the large white area that you see when you look up, and this is called the plantar fascia. The largest of these branches is the superior piriformis, and it has two branches that branch off into the buttocks; the ethmoid region and the inguinal region.

What nerves are involved in eye movement?

The trochlear nerve’s role in regulating eye movement involves the processing of information from the oculomotor nerve. The nerve roots at the base of the middle ear, the rostrocaudal ganglion, and the IV point to the brain through branches of the superior cervical ganglion. These three branches of the nerve originate from a single central nucleus, which is present in all mammals and has direct connections with many other nervous tissues. The superior cervical ganglion and the base of the iris together form the spinal cord, which provides the connection between the central nervous system and the oculomotor nerves. When this cord is injured or destroyed as a result of an accident or trauma, the result is the loss of the messages it was used to relay.

Overview

Structure

Function

Clinical significance

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