Which structure is purely motor

Significance: Acute compression of CN III is the most serious problem and pupillary dilation or loss of reactivity is the most important change. When CN III compression occurs, the pupil on the side of the lesion will become dilated and less reactive loses its ability to constrict to light.

This is a catastrophic finding and indicates herniation of the brain. In consious patients, eye movement is assessed by having the patient follow an object into the vertical, horizontal and diagonal directions. The object should be 2 or more feet away from the patient make the movement slow and large to allow time to focus. It is often difficult to identify ptsosis if the eyelid weakness is mild. It is easier to look at the whites of the eye and the distance between the upper and lower lids called the palbebral fissure.

Ptsosis causes the palbebral fissure to be narrowed less white of the eye on the affected side. The eyelid may have a puffy or thickened appearance. Critical Care Trauma Centre.

Where are the 3rd Cranial Nerves located? The two 3rd cranial nerves oculomotor nerves are located at the top of the brainstem - one to the right and one to the left. They sit at the level of the tentorium. The 3rd cranial nerves are pure motor nerves. They control eye muscles on the same side of the body ipsilateral.

See Diagram. Pupil Constriction Each one of the two 3rd cranial nerves controls the parasympathetic response of the pupil on the same side ipsilateral. The parasympathetic response of the pupil or "return to normal" is constriction. Eye Movement The 3rd cranial nerve also controls eye muscle movement. The ability to move the eye in all other directions is controlled by the 3rd cranial nerve.

It activated the medial rectus, superior rectus, inferior rectus and inferior oblique muscles to cause orbital rotation. You can remember this function because the Oculomotor nerve starts with the letter "O" for eye "O"pening. Acute loss of CN III function is an important sign of a raised intracranial pressure with expanding mass lession.

A new and sudden finding of pupillary dilation and loss of reactivity suggests supratentorial herniation. By contrast, the CN III control of eye movement and eyelid opening runs deep in the centre of the nerve.

Consequently, a mass that presses on the outside of CN III will usually impact the pupillary function first for example as a result of an aneurysm or raised ICP. This can lead to problems with eye movement or eyelid opening where pupil function is spared. Pupillary abnormalities can also be chronic.

Correlation of pupil abnormalities with clinical findings, history and trends is important. CN III dysfunction causes the eyelid on the affected side to become "droopy". This is called ptsosis. Allow the pupils to adjust to the room light for a few seconds. Once they have stabilized, determine the size of the pupils in milimeters by comparing them to the pupil size chart available on graphic record Assess pupil equality: While lids are held open, examine the eyes to determine symmetry and shape.

The pupils should be the same size and the should have a round shape. Reactivity: Begin with the eyelids closed. The assessment of reactivity is a 4 - step assessment using the "swinging flashlight" technique.

Begin by shining light into one eye we will begin with the right for ease of explanation. When pupillary dilation or loss of reactivity occurs as a result of CN III compression, both direct and indirect light reflex response is impaired in the same eye e.

If direct light reflex is lost but indirect light reflex is preserved, true CN III compression is less likley. This suggests an afferent defect is affecting the side with the loss of direct response. Example: the pupillary reflex is absent in the right eye when light is shone into the right eye, but the right pupil constricts in response to light directed into the left eye.

This suggests a problem with the sensory input to the right eye called an afferent defect. Diabetes, vascular conditions or eye diseases may cause afferent defects. Observe for the following: The eyes should move in the same direction in tandom. Your accessory nerve is a motor nerve that controls the muscles in your neck. These muscles allow you to rotate, flex, and extend your neck and shoulders.

The spinal portion originates in the upper part of your spinal cord. The cranial part starts in your medulla oblongata. These parts meet briefly before the spinal part of the nerve moves to supply the muscles of your neck while the cranial part follows the vagus nerve.

Your hypoglossal nerve is the 12th cranial nerve which is responsible for the movement of most of the muscles in your tongue. It starts in the medulla oblongata and moves down into the jaw, where it reaches the tongue.

Learn about its symptoms, diagnosis, and treatment. Have trouble blinking or closing your eyes to sleep? You might have lagophthalmos. Learn what causes this condition and how to treat it.

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