Nerves Head

Trochlear Nerve

The trochlear nerve is also known as cranial nerve IV (CN-IV). It is the only cranial nerve that emerges dorsally from the brain (near the back), giving it the longest pathway. It is the smallest nerve to service the eye. CN-IV passes through the superior orbital fissure, and it provides motor function, or movement. It serves the superior oblique eye muscle and connects to the annular tendon. As a result, it processes brain signals to move the eyes up and down, and outwards. Whether due to a head injury or a complication of surgery, damage to this nerve will compromise some ability to use the superior oblique eye muscle. Without the use of the nerve, the superior oblique eye muscle will no longer function properly. The muscle, not the trochlear nerve, is what physically moves the eyeball. Double vision, otherwise known as diplopia, results from problems with either the muscle or the nerve. Complications from these issues will result in a diminished ability to walk, especially down stairs. Source

R Oculomotor Nerve

The oculomotor nerve is the third of 12 pairs of cranial nerves in the brain. This nerve is responsible for eyeball and eyelid movement. It follows the olfactory and optic nerves in terms of order. The oculomotor nerve involves two separate components, each of which has a distinct function. The somatic motor component supplies four extraocular muscles in the eye and the upper eyelid’s levator palpebrae superioris with motor (movement) fibers. It controls the muscles that allow for visual tracking and fixation by the eye. Visual tracking is the ability to follow an object as it moves across the field of vision. Fixation is the ability to focus on a stationary object. The visceral motor component controls parasympathetic innervation (nerves related to involuntary actions) of the ciliary muscles and constrictor papillae, aiding in accommodation and pupillary light reflexes. Accommodation is the ability of the eye to keep an object in focus as the object’s distance from the eye changes. Pupillary light reflexes are automatic changes in dilation (size) of the pupil, which regulate the amount of light that enters the eye, making sure the light is enough to see but not too bright. The oculomotor nerve can become paralyzed in a condition known as oculomotor nerve palsy. This condition can result from multiple sclerosis or other demyelinating diseases, direct trauma, space-occupying lesions (such as brain cancer), microvascular disease (such as diabetes), or spontaneous subarachnoid hemorrhage (bleeding into the space between two of the membranes that cover the brain). A berry aneurysm is a type of subarachnoid hemorrhage. The oculomotor nerve is responsible for the majority of eye and eyelid movements, although the trochlear nerve and abducens nerve also contribute to eye movements. Source

R Frontal Nerve

The frontal nerve is the largest branch of the ophthalmic division of the fifth cranial nerve. The ophthalmic nerve is responsible for conveying sensory information from the skin of the upper eyelids, forehead, and sides of the nose. It is formed by the union of the lacrimal, nasociliary, and frontal nerves. The frontal nerve splits into the supratrochlear and supraorbital nerves. The supratrochlear nerve conveys information from the medial portion of the upper eyelid, medial forehead, and bridge of the nose. The supraorbital nerve relays information from the forehead, upper eyelid, and scalp. Source

R Optic Nerve

The optic nerve is located in the back of the eye. It is also called the second cranial nerve or cranial nerve II. It is the second of several pairs of cranial nerves. The job of the optic nerve is to transfer visual information from the retina to the vision centers of the brain via electrical impulses. The optic nerve transmits all visual information including brightness perception, color perception and contrast (visual acuity). It also conducts the visual impulses that are responsible for two important neurological reflexes: the light reflex and the accommodation reflex. The light reflex refers to the constriction of both pupils that occurs when light is shone into either eye. The accommodation reflex refers to the swelling of the lens of eye that occurs when one looks at a near object as in reading (lens adjusts to near vision). The optic nerve is made of ganglionic cells or nerve cells. It consists of over one million nerve fibers. Our blind spot is caused by the absence of specialized photosensitive (light-sensitive) cells, or photoreceptors, in the part of the retina where the optic nerve exits the eye. Glaucoma is one of the most common illnesses affecting the optic nerve. Glaucoma is caused by high intraocular pressure, or high pressure in the fluid that is inside the eye (vitreous fluid). This high pressure compresses the optic nerve and causes cells to die. It is referred to as atrophy of the optic nerve. Although the optic nerve is part of the eye, it is considered part of the central nervous system. Source

R Olfactory Nerve Branches

Also known as CN1, the olfactory nerve is the first of 12 cranial nerves located within the head. It relays sensory data to the brain, and it is responsible for the sense of smell. The nerve’s olfactory receptors are located within the mucosa of the nasal cavity. Unlike many other nerves, CN1 does not possess two trunks. Rather, its sensory fibers extend through the ethmoid bone’s cribriform plate, a part of the skull located behind the nose. Once airborne chemicals and particles enter the nasal cavity, they interact with these neural receptors. While part of the nervous system, the CN1 does not join the brainstem. It and the optic nerve are the only cranial nerves for which this is true. CN1 is the shortest cranial nerve within the human head. It can be susceptible to lesions created by blunt trauma damage, which can result from complications of frontal brain lobe tumors, meningitis, and a few other factors. This will lead to a reduced or absent sense of smell. However, even if CN1 is damaged, nasal pain will still be transmitted via the trigeminal nerve.

L Olfactory Nerve Branches

R Maxillary Nerve V2

The maxillary nerve is a nerve located within the mid-facial region of on the human body. The nerve follows a pathway from the cavernous sinus (a blood-filled space behind each eye), through the head. At the origin of the nerve, it resembles a thin band, but the nerve becomes cylindrical and harder as it reaches its end. The nerve ends on the face, where it’s then known as the infraorbital nerve. The nerve consists of four different branches where the nerve branches off into different areas of the body. Maxillary nerve refers to the main portion of the nerve and every time it branches off, it becomes known as a different nerve. The four areas are the infraorbital canal (located below the eye), pterygopalatine fossa (a deep space in the skull located behind the jaw), the cranium (the part of the skull that holds the brain), and the face. Recent studies found that dental and facial surgeries may be complicated by injury to this nerve. Source

R Ophthalmic Nerve V1

The ophthalmic nerve divides into three branches, lacrimal, frontal, and nasociliary. The ophthalmic nerve supplies sensory branches to the cornea, ciliary body, iris, the lacrimal grand and the conjunctiva all the way to the part of the mucous membrane of the nasal cavity. The ophthalmic nerve also supplies to the skin of the eyelids, eyebrows, forehead, and nose. It carries sensory branches from the eyes, conjunctiva, lacrimal gland, nasal cavity, frontal sinus, ethmoidal cells, falx cerebri, dura mater in the anterior cranial fossa, superior parts of the tentorium cerebelli, upper eyelid, dorsum of the nose, and anterior part of the scalp.

Roughly speaking, the ophthalmic nerve supplies general somatic afferents to the upper face, skull, and eye.

Face: Upper eyelid and associated conjunctiva. Eyebrow, forehead, scalp all the way to the lambdoid suture.

Skull: Roof of orbit, frontal, ethmoid, and possibly sphenoid sinuses.

Eye: The eye itself (all the intraocular structures such as cornea) and the lacrimal gland and sac.

Compare this to the maxillary nerve, which supplies general somatic afferents to the mid-face and skull:

Face: Lower eyelid and associated conjunctiva. Cheek, upper lip.

Skull: Orbital floor, maxillary sinus, upper teeth, nasal cavity, and palate, cheekbone.

R Mandibular Nerve V3

The mandibular nerve (V3) is the largest of the three divisions of the trigeminal nerve, the fifth cranial nerve (CN V). The mandibular nerve (V3) is the largest of the three divisions of the trigeminal nerve, the fifth cranial nerve (CN V). the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The mandibular foramen (the upper side portion of the mandible) provides a nerve extension to the mylohyoid muscle that makes up the bottom of the oral cavity. The nerve supplies an additional extension to the small muscle just below the mandible known as the digastric. The inferior alveolar nerve is also located within the mandible in an area called the mandibular canal. Its entrance is made possible by the mandibular foramen, which is an opening in the lower jawbone. The bottom row of teeth receives sensory branches from the nerve. These inferior alveolar branches comprise the network of nerve fibers known as the inferior dental plexus, which then supplies the teeth with sensory information. The nerve also provides sensation to canines and incisors. Anesthesia that blocks the inferior alveolar nerve is often administered to patients undergoing dental procedures. They experience loss of sensation in their teeth, lower lip, and chin. Source

R Trigeminal Nerve V

The trigeminal nerve is the fifth cranial nerve located within the brain, and is primarily responsible for transmitting sensations from the face to the brain. It is composed of three branches: the ophthalmic, maxillary, and mandibular. Each branch connects nerves from the brain to different parts of the face. The trigeminal nerve is responsible for transmitting sensations to the mouth, teeth, face, and nasal cavity. It is also the nerve that controls the muscles used for chewing. Source

R Posterior Temporal Nerve

The right temporal lobe is specialized to process nonverbal memories such as memory for pictures, visual scenes, familiar faces, routes or directions and music, but may also contribute to verbal memory, which is a primary left temporal lobe function. The temporal lobes do not store all of these memories but instead encode new information and relay it to other systems of the brain to be stored. Thus, if the right temporal lobe is seriously damaged, the person may remember many previously learned scenes, pictures and music, but she will not be able to form new memories of these. The right temporal lobe is important in prosody, or the rhythm of one’s speech. People with damage to the right temporal lobe often produce meaningful sentences, but they are choppy and uneven. The right temporal lobe is also important in decoding speech intonations, the changes in the tone of speech that give it different meanings in different contexts, decoding others’ facial expressions and interpreting sequences of visual and verbal information. Thus, people with right temporal lobe damage often have difficulty picking up social cues, understanding facial expressions, following tunes and melodies, inhibiting comments that might be offensive to others and understanding aspects of nonverbal communication such as humor, expressed anger or sadness in others. The right temporal lobe is also involved in aspects of personality. The temporal lobe folds underneath each half of the brain on either side, below the frontal and parietal lobes. The temporal lobe houses our ability to receive and interpret auditory information from the ear. It also collects and interprets information from the nose. It is the primary area of the brain for dealing with sensory input. An important area within the temporal lobe, referred to as the Wernicke’s area, gives us the ability to recognize speech and interpret the meaning of words. Damage to this area, such as from trauma or a stroke, can lead to difficulty understanding speech and difficulty saying words that make sense. This area is highly important to language. Studies have shown that children begin understanding language they hear years before they can speak it, and this is largely due to the functioning of the temporal lobe. The temporal lobe is also believed to be part of long-term memory, such as remembering autobiographical information, dates, and places. Damage to this area can also cause anterograde amnesia, or the inability to create new memories. Sou rce

R Vestibulocochlear Nerve

The vestibulocochlear nerve (sometimes referred to as the auditory nerve) is the eighth of twelve cranial nerves. This group includes all the nerves that emerge from the cranium (skull), as opposed to those that emerge from the vertebral column (spinal cord). It is a paired set of nerves (one from each ear) and the nerve is located in the internal auditory canal, a part of the skull’s temporal bone. The vestibulocochlear nerve is responsible for both hearing and balance and brings information from the inner ear to the brain. A human’s sense of equilibrium is determined by this nerve. Two special organs help the nerve function properly: the cochlea and the vestibular apparatus. The cochlea transforms sound waves into electrical signals that the brain can interpret. The vestibular apparatus senses changes in the position of the head in relation to gravity. Problems with the vestibulocochlear nerve can result in vertigo, vomiting, ringing in the ears, a false sense of motion, motion sickness, or even hearing loss. Source

R Anterior Temporal Nerve

The anterior temporal lobe (ATL) is thought to be critical for semantic memory—our knowledge of objects, people, words, and facts. The temporal lobe folds underneath each half of the brain on either side, below the frontal and parietal lobes. The temporal lobe houses our ability to receive and interpret auditory information from the ear. It also collects and interprets information from the nose. It is the primary area of the brain for dealing with sensory input. An important area within the temporal lobe, referred to as the Wernicke’s area, gives us the ability to recognize speech and interpret the meaning of words. Damage to this area, such as from trauma or a stroke, can lead to difficulty understanding speech and difficulty saying words that make sense. This area is highly important to language. Studies have shown that children begin understanding language they hear years before they can speak it, and this is largely due to the functioning of the temporal lobe. The temporal lobe is also believed to be part of long-term memory, such as remembering autobiographical information, dates, and places. Damage to this area can also cause anterograde amnesia, or the inability to create new memories. Sou rce

R Auriculotemporal Nerve

Supplies nerves to several regions on the sides of the head. This nerve supplies the external acoustic meatus (ear canal), auricle (what people usually call the ear), external part of the tympanic membrane (eardrum), and the temporal skin, which is on the sides of the head. Several articular branches are also carried with the nerve, which supply blood to the temporomandibular joints (TMJ). The auriculotemporal nerve is the primary nerve to supply the TMJ, together with the masseteric nerve branches and the deep temporal. This nerve may suffer injury during TMJ surgery, which may cause parasthesia of the auricle and the ear region. Parathesia is a condition where a person feels unusual sensations, such as tingling, burning, or itching. Source

R Facial Nerve

The Facial Nerve is also known as the seventh cranial nerve (CN7). This nerve performs two major functions. It conveys some sensory information from the tongue and the interior of the mouth. Specifically, CN7 serves about two-thirds of the tongue’s tip. The nerve extends from the brain stem, at the pons and the medulla. Also, this nerve innervates facial muscles, controlling how to contract and produce facial expressions. During its course, CN7 splits into several branches. The greater petrosal nerve serves the lacrimal gland (the gland that produces tears) and the nasal cavity, as well sphenoid, frontal, maxillary, and ethmoid sinuses (cavities in the skull). One of the branches provides motor signals to the stapedius muscle, which is situated in the inner ear. The branch called the chorda tympani serves the sublingual glands (a major salivary gland) and the submandibular glands (glands that lie under the floor of the mouth). The chorda tympani also conveys taste sensations from the tip of the tongue. Most problems involving the facial nerve include paralysis, commonly with Bell’s palsy. This condition, as well as other forms of paralysis, is sometimes triggered by a viral infection or complications of Lyme disease. Source

R Vagus Nerve

The vagus nerve is one of 12 cranial nerves. It is the longest of the cranial nerves, extending from the brainstem to the abdomen by way of multiple organs including the heart, esophagus, and lungs. Also known as cranial nerve X, the vagus forms part of the involuntary nervous system and commands unconscious body procedures, such as keeping the heart rate constant and controlling food digestion. Electrical stimulation of the vagus nerve, called vagus nerve stimulation (VNS), is sometimes used to treat people with epilepsy or depression. The vagus nerve is involved in one of the most common causes of fainting, called vasovagal syncope. This is an overreaction of the body to certain stimuli, like the sight of blood, which involves the stimulation of the vagus nerve. This stimulation causes a drop-in blood pressure and heart rate. Less blood flows to brain, resulting in loss of consciousness. In most cases, vasovagal syncope does not require treatment. Source

R Accessory Nerve

The accessory nerve is a cranial nerve that controls the movement of certain neck muscles. It is coiled in appearance. It is divided into spinal and cranial divisions, but its cranial part is often disregarded. The spinal accessory nerve provides motor function to the sternocleidomastoid muscle, which extends the neck and the trapezius, as well as the upper back and shoulder. Dysfunction of the spinal accessory nerve can negatively affect the shoulder’s performance. Accessory nerve palsy is one complication that most often occurs after surgery has been performed on the neck’s posterior triangle, a triangle-shaped area that lies between the sternocleidomastoid and trapezius on each side of the neck. Additionally, there are three types of accessory nerve schwannoma tumors that occur in some people: intracisternal, spinal canal, and intrajugular; they can be removed with surgery from beneath the base of the skull. Schwannoma tumors are tumors that grow in the tissue that covers nerves, the nerve sheath. Source

R Lingual Nerve

The lingual nerve is located near the sides of the tongue (specifically below the lateral pterygoid muscle), and is responsible for its senses of taste and touch. The lingual nerve provides senses to the tongue’s front two-thirds, as well as to the underside that surrounds it. It branches off the mandibular nerve and twists around the submandibular duct to reach the tongue. The facial nerve’s chorda tympani is one of the nerve fibers the lingual nerve carries to the skull, a process by which the lingual nerve allows taste to be transmitted to the brain. This information is then returned to the front two-thirds of the tongue. A lingual tonsillectomy — an operation to remove extra tonsillar tissue, or the lingual tonsils, from the back of the tongue — is designed to enlarge the airway to assist with breathing; however, such an operation may damage the lingual nerve, causing the tongue to tingle or feel numb. Certain dental procedures, especially those requiring the use of local anaesthetics, can also damage the lingual nerve. Source

R Alveolar Nerve

Also called “inferior alveolar nerve” is a bundle of nerve fibers that stems from the mandibular nerve in the head. The inferior alveolar nerve is situated near the lower jawbone, known as the mandible. It crosses to the mandibular foramen (the upper side portion of the mandible) and provides a nerve extension to the mylohyoid muscle that makes up the bottom of the oral cavity. The nerve supplies an additional extension to the small muscle just below the mandible known as the digastric. The inferior alveolar nerve is also located within the mandible in an area called the mandibular canal. Its entrance is made possible by the mandibular foramen, which is an opening in the lower jawbone. The bottom row of teeth receives sensory branches from the nerve. These inferior alveolar branches comprise the network of nerve fibers known as the inferior dental plexus, which then supplies the teeth with sensory information. The nerve also provides sensation to canines and incisors. Anesthesia that blocks the inferior alveolar nerve is often administered to patients undergoing dental procedures. They experience loss of sensation in their teeth, lower lip, and chin. Source

R Glossopharyngeal Nerve

The glossopharyngeal nerve is a paired set of nerves, which is part of the 24 cranial nerves. These nerves are arranged in twelve pairs, of which the glossopharyngeal is the ninth. The pairs of cranial nerves, in order, are: the olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, and hypoglossal. The glossopharyngeal nerve connects to the brainstem at the upper medulla, travels through the base of the skull at the jugular foramen, and ends in the mouth in the mucous glands, palatine tonsil, and the base of the tongue. It splits into various branches: the tonsillar, tympanic, stylopharyngeal, carotid sinus nerve, lingual, communication branch to the vagus nerve, and a branch to the back third of the tongue. The glossopharyngeal nerve has many functions, including receiving various forms of sensory fibers from parts of the tongue, carotid body, the tonsils, the pharynx, and the middle ear. It also supplies parasympathetic fibers (those that aid the body with rest and digestion processes) to the parotid gland (a major salivary gland) and motor fibers to the stylopharyngeus muscle, which helps with swallowing. The glossopharyngeal nerve, along with the vagus nerve, forms part of the pharyngeal plexus, which supplies nerves to the palate and parts of the throat (larynx and pharynx). Source

R Hypoglossal Nerve

The hypoglossal nerve is the twelfth cranial nerve. This nerve is involved in controlling tongue movements required for speech and swallowing, including sticking out the tongue and moving it from side to side. If there are problems with the hypoglossal nerve, the tongue may become paralyzed. To test the nerve’s function, a patient would be asked to stick out their tongue. If paralysis were present, the tongue would point in the direction of the affected side. Another test monitors the strength of the tongue by having the patient press their tongue against the side of their cheek. The doctor can then tell how strongly the patient is pressing. Eventually, the tongue will begin to atrophy, or shrink, if the hypoglossal nerve is permanently damaged. The hypoglossal nerve may be impacted by several things, such as tumors at the base of the skull, strokes, infections, or neck injuries. Any of these can lead to a problem with speaking, chewing, or swallowing. Once the cause is determined, the doctor can look for suitable treatments to restore functionality to the nerve. Source

L Glossopharyngeal Nerve

The glossopharyngeal nerve, also known as cranial nerve pair number 9 (out of 12 pairs), coordinates information for the throat, salivary glands, sinuses and middle ear. Originating in the medulla oblongata in the brain stem, this is a mixed nerve in that it has both sensory and motor functions. The sensory division of the glossopharyngeal nerve receives information from the pharynx (part of the throat), the posterior third of the tongue, the parotid salivary gland and the middle ear. The motor division sends information to the parotid gland, muscles in the throat, nerve bundles (plexus) in the throat. The glossopharyngeal nerve’s main functions are initiating swallowing and the gag reflex, but it has other functions as well. These are broken into the five pathways the nerve has outside of the brain. One, the special sensory branch provides taste sensation form the taste buds located in the posterior third of the tongue. Two, he visceral sensory branch carries information from the sinuses in the face. Three, the general sensory branch brings information from the skin on the external ear, the tympanic membrane in the ear, the pharynx and the posterior third of the tongue. Four, the visceral motor branch sends parasympathetic signals to the parotid glands. Five, the branchial motor branch sends information to the stylopharyngeus muscle in the throat to facilitate swallowing. Damage to the glossopharyngeal nerve can happen if you have a stroke, also tumors or small cysts at the bas of the skull can possible put pressure on the nerve. Symptoms of the vary depending on which branch o the nerve is affected. The most common sensory symptom is trouble swallowing. Source

L Hypoglossal Nerve

L Optic Nerve

L Trochlear Nerve

L Oculomotor Nerve

R Abducens Nerve

The abducens nerve is also known as the abducent or sixth cranial nerve (CN6). It controls the eye’s lateral rectus muscle, which moves the eye sideways, away from the nose. This nerve is susceptible to a number of clinical conditions. If the abducens nerve is injured, double vision can result. The eye ends up pulled in toward the nose because the medial rectus muscle works without opposition. Damage to the abducens nerve can result from anything that stretches or compresses it, such as from the growth of tumors or blood vessels that bulge into aneurysms. Meningitis infections (serious infection of the brain’s covering tissues) may also develop and damage the nerve. Of all the possible conditions, diabetic neuropathy, related to prolonged issues with blood sugar, is the most frequently occurring. Source

L Frontal Nerve

L Abducens Nerve

L Opthalmic Nerve V1