Cranial+Nerves

//I – Olfactory Nerve// The olfactory nerve is not a cranial nerve, in the strictest sense, as it bypasses the brainstem. It is a complex axonal pathway that projects to many structures including the amygdala, entorhinal cortex, hypothalamus, orbital frontal lobes and dorsal medial cortex. It is, however, associated with many brainstem functions as it receives information regarding smell and taste. The nerve begins in the olfactory endothelium where cells turnover rapidly and a cells life is only about two days. It then passes through the cribriform plate where it is prone to injury or shearing before reaching the olfactory bulb then projecting to the amygdala, hippocampus, thalamus, orbital frontal lobes and insula. If an injury occurs the cribriform plate may fracture, the nerve may be severed, and the meninges may rupture. If this happens an individual may not only lose their loss of smell (asnosmia), but may also develop a cerebrospinal fistula in which cerebrospinal fluid drips or gushes into the nose. Is asnosmia is unilateral then the individual will likely not notice the loss and each nostril should be assessed individually. Dysosmia, or a perversion of the sense of smell may also occur due to partial injuries to the olfactory bulbs or a tumor. Olfactory hallucinations are associated with tumors, seizure activity, as well as head injuries involving the inferior temporal lobes.

//II - Optic Nerve// All visual impulses from the retina to the brain are transmitted via the optic nerves. Injuries to these pathways create visual defects. If these defects are restricted to either the right or left visual field only they are called homonymous, if bilateral, heteronymous. Heteroonymous defects suggest either an injury to both hemispheres or to the retina or optic nerve before reaching the optic chiasm. Homonymous symptoms indicate the injury can be localized to one side of the optic tract or radiations within one cerebral hemisphere. Complete destruction of the optic tract results in homonymous neglect to the left or right, whereas a partial injury may creat a quadratic homonymous defect. Temporal lobe injuries are associated with upper quadrant defects, while injuries to the superior parietal lobe is associated with lower quadrant defects.

//III – Oculomotor Nerve// Innervation of all ocular rotary muscles, with the exception of the lateral rectus and superior oblique muscles, is provided by the oculomotor nerve. This includes the medial, superior, inferior recti, inferior oblique muscles. The intraocular and smooth muscles of the pupil (ciliary and pupilloconstrictor muscles) are also innervated by this nerve, as is the levator palprebrae muscle which raises the eyelid. If damaged there may be an inability to rotate the eye upward downward, or inward. The pupil may also not respond to direct light and there may be ptosis (drooping) of the eyelid due to weakness of levator palpebrae.

//IV – Trochlear Nerve// Located just caudal to the inferior colliculi, the trochlear nerve innervates the superior oblique muscle of the eye. This allows for depression, abduction and intorsion of the eyeball so that an individual can look downward or inward. This is the most common cranial nerve to be damaged from head trauma.

//V – Trigeminal// The trigeminal nerve is the largest of the cranial nerves. It innervates the trigeminal nucleus within the medulla to control jaw closure, chewing, grinding, and lateral movement of the jaw. In concert with the facial nerve, it impacts muscles involved in facial expression. Pathology of this nerve tract can cause difficulty in chewing. In severe cases ipsilateral atrophy and complete paralysis of of the temporal or masseter muscle(s) may occur. Somatic afferent parts of the nerve mediate general sensory input such as temperature, touch, and pain from the face, teeth, mouth, and mucus membranes of the nose, cheek, tongue and sinuses. The sometimes intensely painful condition known as trigeminal neuralgia is an instance of this.

//VI -Abducens// Primarily concerned with horizontal eye movement, the abducens nerve ascend the brainstem to terminate at the oculomotor complex and innervate the lateral rectus muscle of the eye. This works alongside the pontine center for lateral gaze with eye movements outward to the right or left. It is also linked to the pontine/midbrain center for vertical gaze and is a part of a collection of fibers which form a loop tying into the facial nerve. An injury to the 6th cranial nerve can cause lateral gaze paralysis or paralysis of the lateral rectus muscle which results in horizontal diplopia (double vision)

//VII – Facial// The 7th cranial nerve controls motor control of the face. This includes the ability to raise eyebrows, movement of the lips, closure of the auditory canals and gustatory sensation. The facial nerve also innervates the taste buds of the anterior 2/3 of the tongue, which if injured, can cause a loss in taste sensation. The stapedius muscle, which inhibits the movement of the ossicles to dampen excessive sound. Should the stapedius become paralyzed an individual may experience sounds as too loud, intolerable or painful. Other symptoms associated with an injury to this nerve include lip retraction, eyebrow lifting, eyelid closure paralysis (Bell's Palsy), inability to wrinkle one's forehead, purse lips or show their teeth. There may be a drooping of the corner of the mouth.

//VIII – Vestibular// The vestibular portion of the 8th cranial nerve innervates the labyrinth and the macules of the saccule and urticle as well as the ampullae of the semicircular canals. The primary function of this nerve is to determine the body's position in visual-space in order to maintain equilibrium during movement. Changes in fluid balance in the semicircular canals allows the brain to determine changes in position. As a result, if there is an injury to the vestibular receptors or central connections an individual can experience abnormal sensations of movement, vertigo, nausea, tendencies to fall, dizziness, and motion sickness. Hearing problems including deafness or tinnitus which may be described as hearing buzzing, humming, whistling, roaring, hissing or clicking can also occur. They may feel as though they are being pulled to one side or lean/veer to one side when walking. In order to mediate postural reflexes, the vestibular nerve has rich interconnections with cranial nerves III, IV, and VI which subserve eye movement. Nystagmus or difficulty focussing when moving or when an object is moving can thus result from injury as well

//IX – Glossopharyngeal// Closely related to the vagus nerve, the 9th cranial nerve receives tactile, thermal, and pain sensations from the tongue and helps to form the gustatory nucleus. It also receives information about carotid artery pressure via fibers from the carotid sinus. All of this information is transmitted to the solitary nucleus which then contributes to the vagus nerve. Together the 9th and 10th cranial nerves can influence heart rate and arterial blood pressure. Lesions here will usually result in loss of taste and sensation in the posterior 1/3 of the tongue, a loss of gag reflex, and carotid sinus reflex. Swallow or coughing may become intensely painful.

//X – Vagus// Actually a complex mix of nerves, the vagus innervates a number of structures including the larynx, pharynx, trachea, esophagus, epiglottis, external auditory meatus, and viscera in the thoracic and abdominal cavities. As such, important bodily functions such as swallowing, breathing, speaking, movement of the palate, pharynx and larynx are all within its influence. It is also responsible for the swinging of the soft palate upward to seal off the oropharynx from the nasopharynx when swallowing, whistles, or talks. An injury can cause palate weakness and pseudobulbal palsy. Speech can be severely affected as well if fluids get into the nasal passages, in which case speech will becomes excessively nasal in nature. Due to it's long-reaching influence on a wide range of structures many other symptoms may develop from injury to the vagus nerve, incuding gastroparesis, hyperarousal, smooth muscle cramping, IBS, weight gain, depression, bradycardia, chronic inflammation, nutritional deficiencies and seizures.

//XI – Spinal Accessory Nerve// Two distinct segments of this nerve exist. The cranial portion, along with the vagus nerve, forms the inferior laryngeal nerve going to the larynx. The spinal portion of this nerve innervates the sternocleidomastoid (SCM) and upper trapezius muscles to help turn the head and elevate the shoulders. As a results, if this nerve becomes injured one's shoulders may sag on the affected side or the individual may show weakness in turning the head. This is particularly true against resistance.

//XII – Hypoglossal Nerve// Located in the caudal medulla, the hypoglossal nerve controls movement of the tongue by innervating the relevant skeletal muscle. If the nerve is damaged the skeletal musculature will not properly move the tongue and weakness or atrophy can result. Tongue strength can be tested by placing one's tongue on one side of the cheek and pressing against a practitioners finger when it is placed on the outside of the cheek. Lower motor neuron pathology may cause unilateral atrophy, fasciculation or fibrillation and paralysis that results in an obvious deviation toward the paralytic side when the tongue is protruded.

**The Cranial Nerves – Pathology and Symptoms**
 * I - Olfactory || Loss of smell/taste, risk of cerebrospinal fluid fistula ||
 * II - Optic || Visual defects including blindness, neglect, etc. ||
 * III - Oculomotor || Ptosis, pupil unresponsive to direct light, inability to move eye downward, upward, or inward ||
 * IV - Trochlear || Inability to move eye in order to look in downward or inward direction ||
 * V - Trigeminal || Face pain, difficulty chewing, atrophy or paralysis of temporal or masseter muscles ||
 * VI - Abducens || Lateral gaze paralysis, horizontal diplopia ||
 * VII -Facial || Bells' Palsy, facial paralysis or flaccidity, eyebrow raising, eyelid closure paralysis, taste loss in anterior 2/3 of tongue, sounds may seem too loud or painful ||
 * VIII -Vestibular || Vertigo, nauea, dizziness, leaning or veering to one side when walking, unsteadiness, abnormal sensations of movement, tinnitus, nystagmus, difficulty focusing on objects when they are moving or when walking ||
 * IX -Glossopharyngeal || Loss of taste/sensation in posterior 1/3 of tongue, loss of gag reflex and carotid sinus reflex, painful swallowing or cough ||
 * X - Vagus || Pseudobulbar palsy, difficulty swallowing/dysphagia, slurred speech, palate weakness, gastroparesis, hyperarousal, smooth muscle cramping, IBS, weight gain, depression, bradycardia, chronic inflammation, nutritional deficiencies, seizures ||
 * XI – Spinal Accessory || Ipsilateral sagging shoulder(s), weakness in turning head (esp. against resistance) ||
 * XII - Hypoglossal || Tongue weakness/atropy/deviation ||

**Acupuncture Considerations** A number of points have demonstrated by fMRI studies a correlation to brain activity in the temporal lobes 10

**Activating:** Pons: GB-34, GB-39 Caudate nucleus: GB-34, GB-39 Superior Collicus: GB-37

**Deactivating:** Basal Gyrus: ST-36

George Soulie De Morant 13 notes indications for brain regions according to his extensive studies of the medicine in Chinaprior to the communist revolution when much of the information was either politically streamlined or lost. According to hisstudies points had been found to influence brainstem structures. SP-6, SP-9 HT-6, HT-8 KI-6, KI-10, KI-17, KI-19, KI-20 PC-1 GB-20 LR-5 ||  ||
 * Pons ||
 * Tonifying || Dispersing ||
 * ST-11

LI-6 ST-4, ST-14, ST-16, ST-22, ST-32, ST-33, ST-42, ST-44 SP-21 HT-6 SI-8, SI-19 BL-11, BL-51, BL-52, BL-54, BL-66 KI-1, KI-7, KI-21, KI-25 PC-2 TW-19 GB-4, GB-5 (opposite), GB-20, GB-25, GB-26 GB-34, GB-35, GB-37 LR-4, LR-13 CV-9, CV-17 GV-1, GV-10, GV-13, GV-18 || KI-2 TW-10 LR-2 || Sympathetic Tonifying ST-41 PC-8 TW-5 GB-20 Parasympathetic Tonifying: ST-21 BL-10 CV-12 GV-20 Parasympathetic Dispersing: PC-8
 * Medulla Oblongata ||
 * Tonifying || Dispersing ||
 * LU-1, LU-7
 * Autonomic Nervous System **