The trochlear nerve starts in the cerebellum and continues through the central nervous system to the auditory nerve and then back to the brain stem. The trochlear nerve is named so because it “tears” when squeezed. While the trochlear nerve is the shortest of all the cranial nerves, it has the longest cranial path through the brain stem. It originates in the inner ear and extends laterally and posteriorly to the inferior trapezius muscle and laterally to the premaxillary muscles.
The trochlear nerve branches off into four parts: the main trunk, the branches that branch off into the arms or legs (the acromion), the posterolateral, iliotibial and iliopsoidal branches which each have their respective bones, cartilage and skin. Each branch of the trochlear nerve receives messages from the auditory nerve and from the fifth sensory nerve, which are located in the middle brain. The branches of the trochlear nerve that exits the body wall run along the top of the cervical spine, the backbone of the upper neck, and extend onto the shoulders, back, chest and head. When these branches link up with the other branches of the spinal cord, they form the large white area that you see when a person looks down.
The branches of the trochlear nerve that exits the body wall to connect to the large white area that you see when you look down, and this is called the somatic efferent. The branches that branch off into the legs connect to the large white area that you see when you look up, and this is called the plantar fascia. The largest of these branches is the superior piriformis, and it has two branches that branch off into the buttocks; the ethmoid region and the inguinal region.
The branch of the trochlear nerve that exits the body at the sacrum is called the oculomotor muscles. These muscles are divided into three types: the superficial, deep and uvula muscles. The superficial muscles are the brachialis anterior, brachialis posterior and isthmic flexor muscles. The deep muscles are brachioradialis minor, brachioradialis parsus, and the uvula muscles. The third type, the uvula, contains twelve muscles, the vastus lateralis, the base of the skull, and twelve nerves.
The dominant function of the superior oblique muscles is controlling the lower part of the face. This part of the face is called the labia. The function of the superior oculomotor nerve is to control eye movement, particularly eye movement during gaze and looking. It controls gaze direction. One of its branches, the dorsal longitudinal incisors, inserts on the anterior of the glare above the eyelids. It inserts on the posterior side of the labia for controlling the upper part of the upper face.
The other part of the trochlear nerve, which is important in controlling eye movements is called the extrinsic ganglion. This part of the nerve supplies the muscles surrounding the oculomotor nerves. It is subdivided into four types: the internal mononeurosis, external carotid artery, internal jugular veins, and the internal peduncle. The internal mononeurosis is located inside the brain, external carotid artery branches off in the neck area, and the internal jugular veins are located in the neck and near the eye. The external peduncle branches off in the forehead area.
The trochlear nerve’s role in regulating eye movement involves the processing of information from the oculomotor nerve. The nerve roots at the base of the middle ear, the rostrocaudal ganglion, and the IV point to the brain through branches of the superior cervical ganglion. These three branches of the nerve originate from a single central nucleus, which is present in all mammals and has direct connections with many other nervous tissues. The superior cervical ganglion and the base of the iris together form the spinal cord, which provides the connection between the central nervous system and the oculomotor nerves. When this cord is injured or destroyed as a result of an accident or trauma, the result is the loss of the messages it was used to relay.
The most common cause of trochlear nerve palsy, the intracranial hearing syndrome, usually results from injuries to the temporal regions near the ear. In this case, there is a delay between the auditory stimulation caused by the outer and middle ear nerves and the processing of that information by the inner ear. The intracranial course usually follows a direct path through the cranial cavity to the auditory cortex and the inner ear. When this occurs, the brain must find a way to send the auditory impulses to the ear that are already receiving the information it needs.