2015 Hearing & Balance

The reflex sequence begins with a turn of the head to the LEFT (top of diagram).

As described previously (and shown at the bottom of the diagram), head rotation to the LEFT causes:

• DEPOLARIZATION in the LEFT HORIZONTAL CANAL

• HYPERPOLARIZATION in the RIGHT HORIZONTAL CANAL.

This is followed by EXCITATION in the LEFT VESTIBULAR NUCLEI, and INHIBITION in the RIGHT VESTIBULAR NUCLEI.

Due to the organization of the pathway, at the level of the extraocular motor nuclei, there is:

• EXCITATION of cells in the LEFT OCULOMOTOR and RIGHT ABDUCENS nuclei

• INHIBITION of cells in the RIGHT OCULOMOTOR and LEFT ABDUCENS nuclei

This pattern of extraocular motor activity results in:

• CONTRACTION of the LEFT MEDIAL RECTUS and RIGHT LATERAL RECTUS muscles.

• RELAXATION of the RIGHT MEDIAL RECTUS and LEFT LATERAL RECTUS muscles.

Movement of the eyes to the RIGHT.