Third nerve palsy

Summary

This video explains the symptoms of complete third nerve palsy (oculomotor nerve palsy), highlighting its causes such as brainstem disease, multiple sclerosis, aneurysms, and more. It details the key symptoms, including ptosis (drooping eyelid), the 'down and out' position of the eye, and pupil dilation. The video also discusses the mechanisms behind these symptoms, such as unopposed muscle actions and sympathetic innervation. A mnemonic is provided to help remember the symptoms: 'Nobody loves you when you're down and out.' This concise explanation aims to help viewers understand this complex neurological condition.

Takeaways

• 😀 A complete third nerve palsy (oculomotor nerve palsy) can occur due to multiple causes such as brain stem disease, multiple sclerosis, vascular occlusion, meningitis, aneurysms, or expanding intracranial lesions.
• 😀 Symptoms of third nerve palsy are linked to the specific functions of the oculomotor nerve and its innervation to eye muscles.
• 😀 A drooping eyelid, known as ptosis, occurs due to the loss of innervation to the levator palpebrae superioris muscle, causing eyelid droop.
• 😀 Ptosis can also be worsened by the unopposed action of the orbicularis oculi muscle, which is innervated by the facial nerve.
• 😀 In third nerve palsy, the eye assumes a 'down and out' position due to the unopposed action of the lateral rectus and superior oblique muscles.
• 😀 The pupil may become dilated (mydriasis) in third nerve palsy because of unopposed sympathetic innervation, which causes pupil dilation.
• 😀 The loss of oculomotor nerve function leads to a lack of pupil response (no constriction) during a pupillary light reflex.
• 😀 The 'down and out' eye position is explained by the unopposed actions of the lateral rectus muscle (abducent nerve) and superior oblique muscle (trochlear nerve).
• 😀 The unopposed sympathetic innervation causes dilation of the pupil, as the oculomotor nerve is responsible for constriction of the pupil.
• 😀 A helpful mnemonic to remember the symptoms of third nerve palsy is 'nobody loves you when you're down and out,' referencing the typical eye position and pupil dilation associated with the condition.

Q & A

What is a third nerve palsy?

A third nerve palsy, also known as oculomotor nerve palsy, is a condition where the oculomotor nerve is damaged, leading to symptoms like drooping eyelids, pupil dilation, and eye movement abnormalities.

What are some causes of third nerve palsy?

Third nerve palsy can be caused by various factors such as brain stem diseases, multiple sclerosis, vascular occlusions, meningitis, aneurysms in the Circle of Willis, expanding intracranial lesions, and cavernous sinus issues (e.g., thrombosis or aneurysm of the internal carotid artery).

What symptoms are typically associated with a complete third nerve palsy?

The main symptoms of a complete third nerve palsy include ptosis (drooping eyelid), 'down and out' eye position, a dilated pupil, and an unresponsive pupil to light.

What causes ptosis in third nerve palsy?

Ptosis occurs in third nerve palsy due to the loss of innervation to the levator palpebrae superioris muscle, responsible for elevating the eyelid. Additionally, the unopposed action of the orbicularis oculi muscle (innervated by the facial nerve) may contribute to eyelid drooping.

What is the cause of the 'down and out' eye position in third nerve palsy?

The 'down and out' position occurs because of the unopposed actions of the lateral rectus muscle (innervated by the abducent nerve) causing lateral pull, and the superior oblique muscle (innervated by the trochlear nerve) which depresses the eye.

Why is the pupil dilated in third nerve palsy?

The pupil becomes dilated due to unopposed sympathetic innervation, as the oculomotor nerve normally innervates the constrictor pupillae muscle in the iris to constrict the pupil. In third nerve palsy, this function is lost, and the sympathetic action dominates, causing dilation.

What is the response of the pupil to light in third nerve palsy?

In third nerve palsy, the pupil does not constrict in response to light. This is because the oculomotor nerve's ability to control the constrictor pupillae muscle is impaired, leaving the pupil unresponsive and dilated.

How can the symptoms of third nerve palsy be remembered easily?

A mnemonic to remember the symptoms of third nerve palsy is 'Nobody loves you when you're down and out,' which refers to the drooping eyelid ('nobody'), the 'down and out' eye position, and the unopposed actions leading to pupil dilation ('loves you').

What is the significance of the oculomotor nerve in eye function?

The oculomotor nerve is crucial for controlling several eye muscles, including those that raise the eyelid, move the eye up, down, and medially, and constrict the pupil. Damage to this nerve disrupts these functions.

What is the relationship between third nerve palsy and sympathetic innervation?

In third nerve palsy, the loss of oculomotor nerve function leads to the unopposed action of sympathetic innervation, resulting in pupil dilation. Normally, the oculomotor nerve controls the constriction of the pupil, but its loss allows sympathetic innervation to dominate.