The trochlear nerve is unique
among the cranial nerves in several respects:
1. It is the
smallest nerve in terms of the number of axons it contains.
2. It has
the greatest intracranial length.
3. It is the only cranial nerve that exits from
the dorsal (rear) aspect of the brainstem.
4. It decussates
before emerging from the dorsal brainstem just below the inferior colliculi.
Course:
It is the only cranial nerve to
emerge on the dorsal aspect of the brainstem, appearing on the midbrain's
dorsal surface beneath the inferior colliculi.
Then it reaches the ventral side of the midbrain after decussate and loop
around the cerebral peduncles.
It runs in the cavernous sinus's lateral wall beneath the oculomotor nerve. It passes
through the superior orbital fissure to enter the orbit and supply the muscle of the contralateral side
Nuclei, functional
components and the structures supplied by trochlear nerve:
|
NUCLEUS |
FUNCTION COMPONENT |
STRUCTURES INNERVATED |
|
Trochlear nucleus (in
midbrain) |
GSE (General Somatic
Efferent) |
Superior oblique muscle
of eyeball |
Due to its lengthy path, the
nerve is more prone to damage. Trochlear nerve palsy is a frequently occurring
appearance in ophthalmology clinics.
Trochlear nerve lesion
The symptoms are:
Diplopia on looking downward: due
to paralysis of superior oblique muscle.
Patient faces difficulty while
going downstairs or reading a book.
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