Trochlear Nerve (CN IV)
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Cranial Nerves
- Olfactory Nerve (CN I)
- Optic Nerve (CN II)
- Oculomotor Nerve (CN III)
- Trochlear Nerve (CN IV)
- Trigeminal Nerve (CN V)
- Abducens Nerve (CN VI)
- Facial Nerve (CN VII)
- Vestibulocochlear Nerve (CN VIII)
- Glossopharyngeal Nerve (CN IX)
- Vagus Nerve (CN X)
- Accessory Nerve (CN XI)
- Hypoglossal Nerve (CN XII)
Summary
The trochlear nerve, also known as cranial nerve number 4 or the 4th cranial nerve, is a motor nerve that controls eye movement - specifically by innervating the superior oblique muscle. Since it controls eye movement, the trochlear nerve is also a major motor component of the vestibulo-ocular reflex, used to stabilize our gaze in response to head movements. The nerve originates in the midbrain and exits the skull to enter the eye socket through a cranial foramen called the superior orbital fissure.
Key Points
- Trochlear Nerve (Cranial Nerve IV)
- Nerve Type
- Motor
- Function
- Eye movement
- Innervates superior oblique muscle to abduct, depress, and internally rotate eye
- Test function via six cardinal positions of gaze test (tracking H-shape)
- Damage typically leads to vertical diplopia, which worsens when the patient looks down (compensated by tucking chin and tilting head away from affected side)
- Eye movement
- Nerve Entry/Exit
- Nerve exits the dorsal midbrain near the inferior colliculus
- Only cranial nerve that crosses over (decussates) before reaching its target (superior oblique)
- Nerve originates in nucleus of the trochlear nerve
- Nerve exits the dorsal midbrain near the inferior colliculus
- Cranial foramen
- Superior orbital fissure
- Reflexes
- Vestibulo-ocular reflex (efferent motor)
- Responsible for adjusting and stabilizing vision in response to vestibular balance
- Vestibulo-ocular reflex (efferent motor)
- Nerve Type