Trochlear (iv) nerve

TROCHLEAR (IV) NERVE

Q. 1 Which of the following structure does not pass through Cavernous sinus:
 A Middle Cerebral artery
 B Internal Carotid artery
 C Abducens nerve
 D Trochlear nerve
Q. 1 Which of the following structure does not pass through Cavernous sinus:
 A Middle Cerebral artery
 B Internal Carotid artery
 C Abducens nerve
 D Trochlear nerve
Ans. A

Explanation:Middle Cerebral artery (Ref: B.D. Chaurasia, 3rd Ed, Vol lll/Pg 72, 73) Relation of Cavernous sinus:
A.   Structures outside the sinus:
(a)  Superiorly: Optic tract, internal carotid artery, & anterior perforated substance
(b)  Inferiorly: Foramen lacerum & junction of greater wing of sphenoid
(c)  Medially: Hypophysis cerebri & sphenoid sinus
(d)  Laterally: Temporal lobe with uncus
(e)  Anteriorly: Superior orbital fissure & apex of the orbit
(f) Posteriorly: Apex of petrous temporal bone & crus cerebri of midbrain
B. Structures in the lateral wall of sinus:

(a)  Occulomotor nerve (b) Trochlear nerve (c) Ophthalmic nerve
(d) Maxillary nerve (e) Trigeminal nerve  

C. Structures passing through the centre of sinus:
(a)  Internal carotid artery     (b)  Abducens nerve


Q. 2

Trochlear nerve all true except

 A

Longest intracranial course

 B

>Arises from dorsum of brainstem.

 C

>Supply ipsilateral superior oblique muscle

 D

Enters orbit through sup. orbital fissure outside 

Q. 2

Trochlear nerve all true except

 A

Longest intracranial course

 B

>Arises from dorsum of brainstem.

 C

>Supply ipsilateral superior oblique muscle

 D

Enters orbit through sup. orbital fissure outside 

Ans. C

Explanation:

Trochlear nerve is a crossed cranial nerve. The nucleus of the trochlear nerve supplies the contralateral superior oblique muscle.

The trochlear nerve has certain unique features:

  • It is the only cranial nerve whose fibers originate totally from the contralateral nucleus.
  • It is the only cranial nerve to emerge from the dorsal surface of the brain stem.
  • It is the smallest (thinnest) of the cranial nerves. (largest is trigeminal)
  • It has the longest intracranial course and is thus highly susceptible to increased intracranial pressure. (shortest cranial nerve is olfactory)
  • It supplies only one muscle- i.e. superior oblique (Abducent cranial nerve also supplies only one muscle i.e. Lateral rectus)

Course: As the trochlear nerve emerges from the brainstem, it curves around the cerebral peduncle and proceeds anteriorly within the lateral wall of cavernous sinus to pass into the orbit via the lateral part of superior orbital fissure.


Q. 3 Which of the following statement is not true about the Trochlear nerve?

 A

It has the longest intracranial course

 B

It supplies the ipsilateral superior oblique muscle

 C

It is the only cranial nerve that arises from the dorsal aspect of the brainstem

 D

It enters the orbit through the superior orbital fissure outside the annulus of Zinn

Q. 3

Which of the following statement is not true about the Trochlear nerve?

 A

It has the longest intracranial course

 B

It supplies the ipsilateral superior oblique muscle

 C

It is the only cranial nerve that arises from the dorsal aspect of the brainstem

 D

It enters the orbit through the superior orbital fissure outside the annulus of Zinn

Ans. B

Explanation:

Trochlear nerve is the fourth cranial nerve. It is a motor nerve ( somatic efferent nerve), which innervates superior oblique muscle, which depress the eye in adduction and incyclodeviates the eyeball. It is the smallest nerve in terms of the number of axons it contains. Other than the optic nerve (cranial nerve II), it is the only cranial nerve that decussates (crosses to the other side) before innervating its target.
Finally, it is the only cranial nerve that exits from the dorsal aspect of the brainstem.

Injury to the trochlear nerve cause weakness of downward eye movement with consequent vertical diplopia (double vision).

Q. 4 All statements regarding trochlear nerve are true, EXCEPT?

 A

Longest intracranial course

 B

Arises from dorsum of brainstem

 C

Supply ipsilateral superior oblique muscle

 D

Enters orbit through superior orbital fissure outside annulus of Zinn

Q. 4

All statements regarding trochlear nerve are true, EXCEPT?

 A

Longest intracranial course

 B

Arises from dorsum of brainstem

 C

Supply ipsilateral superior oblique muscle

 D

Enters orbit through superior orbital fissure outside annulus of Zinn

Ans. C

Explanation:

Trochlear nerve is a crossed cranial nerve. The nucleus of the trochlear nerve supplies the contralateral superior oblique muscle.The trochlear nerve emerges from dorsal surface of the brainstem near the midline, courses anteriorly around the cerebral peduncle and enters the orbit through superior orbital fissure.

The trochlear nerve has certain unique features:

  • It is the only cranial nerve whose fibers originate totally from the contralateral nucleus.
  • It is the only cranial nerve to emerge from the dorsal surface of the brain stem.
  • It is the most slender of all the cranial nerves.
  • It has the longest intradural course among the three extraocular motor nerves.
  • It supplies only one muscle i.e. superior oblique (Abducent cranial nerve also supplies only one muscle i.e. Lateral rectus).

Q. 5 All of the following cranial nerves contain Somatic Efferents, except?

 A

VII Nerve (Facial nerve)

 B

III Nerve (Occulomotor nerve)

 C

IV Nerve (Trochlear nerve)

 D

VI Nerve (Abducent nerve)

Q. 5

All of the following cranial nerves contain Somatic Efferents, except?

 A

VII Nerve (Facial nerve)

 B

III Nerve (Occulomotor nerve)

 C

IV Nerve (Trochlear nerve)

 D

VI Nerve (Abducent nerve)

Ans. A

Explanation:

Facial nerve does not contain Somatic Efferents.


Q. 6

Fibres of which of the following nerve decussate before emerging out from the brain stem?

 A

Facial nerve

 B

Abducent nerve

 C

Trochlear nerve

 D

Oculomotor nerve

Q. 6

Fibres of which of the following nerve decussate before emerging out from the brain stem?

 A

Facial nerve

 B

Abducent nerve

 C

Trochlear nerve

 D

Oculomotor nerve

Ans. C

Explanation:

The trochlear nucleus is located near the midline, just inferior to the motor nucleus of the occluomotor nerve and at the level of the inferior colliculus. The axons of the fourth cranial nerve leave the nucleus and actually decussates in the superior medullar velum. This is the only cranial nerve to decussate prior to exiting the brainstem.


Q. 7

The following are contents of the interpeduncular fossa except :

 A

Trochlear nerve

 B

Oculomotor nerve

 C

Oculomotor nerve

 D

None

Q. 7

The following are contents of the interpeduncular fossa except :

 A

Trochlear nerve

 B

Oculomotor nerve

 C

Oculomotor nerve

 D

None

Ans. D

Explanation:

D i.e. None

–  Corticopontine, corticospinal and corticonuclear fibres pass through crus cerebri.

–  Inter peduncular fossa contains posterior perforated substance, posterior cerebral & superior cerebellar arteries, optic chiasma (not nerve), occulomotor & trochlear nerve, tuber cinereum, tuberal eminences, infundibular stalk & mammilary body


Q. 8 Superior oblique muscle is supplied by :

 A

Occulomotor nerve

 B

Trochlear nerve

 C

Abducent nerve

 D

Trigeminal nerve

Q. 8

Superior oblique muscle is supplied by :

 A

Occulomotor nerve

 B

Trochlear nerve

 C

Abducent nerve

 D

Trigeminal nerve

Ans. B

Explanation:

B i.e. Trochlear


Q. 9

Structures passing through superior orbital fissure:

 A

Oculomotor nerve

 B

Trochlear nerve

 C

Lacrimal nerve

 D

All

Q. 9

Structures passing through superior orbital fissure:

 A

Oculomotor nerve

 B

Trochlear nerve

 C

Lacrimal nerve

 D

All

Ans. D

Explanation:

A. i.e. Oculomotor nerve; B i.e. Trochlear nerve; C i.e. Lacrimal nerve


Q. 10

The cranial nerve with the largest intra-cranial course is:

 A

Abducens- nerve

 B

Trochlear nerve

 C

Optic nerve

 D

Trigeminal nerve

Q. 10

The cranial nerve with the largest intra-cranial course is:

 A

Abducens- nerve

 B

Trochlear nerve

 C

Optic nerve

 D

Trigeminal nerve

Ans. B

Explanation:

B i.e. Trochlear nerve


Q. 11

Trochlear nerve all true except:

 A

Longest intracranial course

 B

Arises from dorsum of brainstem

 C

Supply ipsilateral superior oblique muscle

 D

Enter orbit through sup. 

Q. 11

Trochlear nerve all true except:

 A

Longest intracranial course

 B

Arises from dorsum of brainstem

 C

Supply ipsilateral superior oblique muscle

 D

Enter orbit through sup. 

Ans. C

Explanation:

C i.e. Supplies ipsilateral superior oblique muscle 

Trochlear nerve is thinnest nerve. It is the only nerve to emerge from dorsum of brain stemQ has longest intracranial course. It enters orbit through outer part of superior orbital fissure (ie lateral to annulus of Zinn)Q and supplies superior oblique muscle. Because it’s a crossed cranial nerve (with decussation in mid brain), the trochlear nerve nucleus supplies contralateral superior oblique muscle.


Q. 12

Which of the following is not true about the Trochlear nerve:

 A Has the longest intracranial course

 B

Supplies the ipsilateral superior oblique muscle

 C

Only cranial nerve that arises from the dorsal aspect of the brainstem

 D

Enters orbit through the superior orbital fissure outside the annulus of Zinn

Q. 12

Which of the following is not true about the Trochlear nerve:

 A

Has the longest intracranial course

 B

Supplies the ipsilateral superior oblique muscle

 C

Only cranial nerve that arises from the dorsal aspect of the brainstem

 D

Enters orbit through the superior orbital fissure outside the annulus of Zinn

Ans. B

Explanation:

B i.e. Supplies the ipsilateral superior oblique muscle



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