There should be no noticeable asymmetry. In an upper motor neuron lesion, called central seven central facial palsy , only the lower part of the face on the contralateral side will be affected due to the bilateral control to the upper facial muscles frontalis and orbicularis oculi.
This can be tested with a swab dipped in a flavored solution, or with electronic stimulation similar to putting your tongue on a battery.
In regards to the corneal reflex, the afferent arc is mediated by the general sensory afferents of the trigeminal nerve. The efferent arc occurs via the facial nerve.
The reflex involves the consensual blinking of both eyes in response to stimulation of one eye. Thus, the corneal reflex effectively tests the proper functioning of both cranial nerves V and VII. The vestibulocochlear nerve also known as the auditory vestibular nerve and cranial nerve VIII has axons that carry the modalities of hearing and equilibrium. It consists of the cochlear nerve that carries information about hearing, and the vestibular nerve that carries information about balance.
This is the nerve along which the sensory cells the hair cells of the inner ear transmit information to the brain. It emerges from the pons and exits the inner skull via the internal acoustic meatus or internal auditory meatus in the temporal bone.
The vestibulocochlear nerve consists mostly of bipolar neurons and splits into two large divisions: the cochlear nerve and the vestibular nerve. The cochlear nerve travels away from the cochlea of the inner ear where it starts as the spiral ganglia. Processes from the organ of Corti the receptor organ for hearing conduct afferent transmission to the spiral ganglia.
It is the inner hair cells of the organ of Corti that are responsible for activating the afferent receptors in response to pressure waves reaching the basilar membrane through the transduction of sound.
The vestibular nerve travels from the vestibular system of the inner ear. The vestibular ganglion houses the cell bodies of the bipolar neurons and extends processes to five sensory organs. Three of these are the cristae, located in the ampullae of the semicircular canals. Hair cells of the cristae activate afferent receptors in response to rotational acceleration.
The other two sensory organs supplied by the vestibular neurons are the maculae of the saccule and utricle. Hair cells of the maculae activate afferent receptors in response to linear acceleration. The vestibulocochlear nerve has axons that carry the modalities of hearing and equilibrium. Damage to the vestibulocochlear nerve may cause hearing loss, vertigo, a false sense of motion, loss of equilibrium in dark places, nystagmus, motion sickness, and gaze-evoked tinnitus.
A benign primary intracranial tumor of vestibulocochlear nerve is called a vestibular schwannoma also called acoustic neuroma. The glossopharyngeal nerve cranial nerve IX serves many distinct functions, including providing sensory innervation to various head and neck structures. The glossopharyngeal nerve is the ninth of 12 pairs of cranial nerves. It exits the brainstem out from the sides of the upper medulla, just rostral closer to the nose to the vagus nerve. Glossopharyngeal nerve : Image of head structures including the glossopharyngeal nerve.
The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, while the sensory division originates from the cranial neural crest.
There are a number of functions of the glossopharyngeal nerve. It controls muscles in the oral cavity and upper throat, as well as part of the sense of taste and the production of saliva.
Along with taste, the glossopharyngeal nerve relays general sensations from the pharyngeal walls. The various functions of the glossopharyngeal nerve are that:. The vagus nerve cranial nerve X is responsible for parasympathetic output to the heart and visceral organs. The vagus nerve, also known as the pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves. Upon leaving the medulla between the medullary pyramid and the inferior cerebellar peduncle, it extends through the jugular foramen, then passes into the carotid sheath between the internal carotid artery and the internal jugular vein below the head, to the neck, chest and abdomen, where it contributes to the innervation of the viscera.
Vagus nerve : Diagram demonstrating the course of the vagus nerve. The vagus nerve supplies motor parasympathetic fibers to all the organs, except the suprarenal adrenal glands, from the neck down to the second segment of the transverse colon. The vagus also controls a few skeletal muscles, most notably:. This means that the vagus nerve is responsible for such varied tasks as heart rate, gastrointestinal peristalsis, sweating, and quite a few muscle movements in the mouth, including speech via the recurrent laryngeal nerve , swallowing, and keeping the larynx open for breathing via action of the posterior cricoarytenoid muscle, the only abductor of the vocal folds.
This explains why a person may cough when tickled on the ear such as when trying to remove ear wax with a cotton swab.
Afferent vagus nerve fibers that innervate the pharynx and back of the throat are responsible for the gag reflex. In addition, 5-HT3 receptor-mediated afferent vagus stimulation in the gut due to gastroenteritis and other insults is a cause of vomiting. Parasympathetic innervation of the heart is partially controlled by the vagus nerve and is shared by the thoracic ganglia.
This occurs commonly in cases of viral gastroenteritis, acute cholecystitis, or in response to stimuli such as the Valsalva maneuver or pain. Excessive activation of the vagal nerve during emotional stress can also cause vasovagal syncope due to a sudden drop in cardiac output, causing cerebral hypoperfusion.
The accessory nerve cranial nerve XI controls the sternocleidomastoid and trapezius muscles of the shoulder and neck. It begins in the central nervous system CNS and exits the cranium through a foramen. Unlike the other 11 cranial nerves, the accessory nerve begins outside the skull. In fact, most of the fibers of the nerve originate in neurons situated in the upper spinal cord. The accessory nerve : Upon exiting the skull via the jugular foramen, the spinal accessory nerve pierces the sternocleidomastoid muscle before terminating on the trapezius muscle.
The fibers that make up the accessory nerve enter the skull through the foramen magnum and proceed to exit the jugular foramen with cranial nerves IX and X. Due to its unusual course, the accessory nerve is the only nerve that enters and exits the skull. Traditional descriptions of the accessory nerve divide it into two components: a spinal component and a cranial component.
However, more modern characterizations of the nerve regard the cranial component as separate and part of the vagus nerve. Therefore, in contemporary discussions of the accessory nerve, it is common to disregard the cranial component when referencing the accessory nerve and assume reference to the spinal accessory nerve.
The accessory nerve provides motor innervation from the CNS to the sternocleidomastoid and trapezius muscles of the neck. The sternocleidomastoid muscle tilts and rotates the head, while the trapezius muscle has several actions on the scapula, including shoulder elevation and adduction of the scapula. During neurological examinations, the function of the spinal accessory nerve is often measured by testing the range of motion and strength of the aforementioned muscles.
Limited range of motion or diminished muscle strength often indicates injury of the accessory nerve. Patients with spinal accessory nerve palsy may exhibit signs of lower motor neuron disease, such as atrophy and fasciculations of both the sternocleidomastoid and trapezius muscles.
The hypoglossal nerve is the twelfth cranial nerve XII and innervates all extrinsic and intrinsic muscles of the tongue, except for the palatoglossus. The hypoglossal nerve emerges from the medulla oblongata in the preolivary sulcus where it separates the olive olivary body and the pyramid medullary pyramid.
It goes on to traverse the hypoglossal canal and, upon emerging, it branches and merges with a branch from the anterior ramus of C1. It passes behind the vagus nerve and between the internal carotid artery and internal jugular vein which lies on the carotid sheath.
After passing deep to the posterior belly of the digastric muscle it proceeds to the submandibular region to enter the tongue.
Hypoglossal nerve : Schematic image of the hypoglossal nerve and the structures it innervates. The hypoglossal nerve controls tongue movements of speech, food manipulation, and swallowing.
It supplies motor fibers to all of the muscles of the tongue, with the exception of the palatoglossus muscle, which is innervated by the vagus nerve cranial nerve X or, according to some classifications, by fibers from the glossopharyngeal nerve cranial nerve IX that hitchhike within the vagus. Proper function of the hypoglossal nerve is important for executing the tongue movements associated with speech.
Many languages require specific and sometimes unusual uses of the nerve to create unique speech sounds, which may contribute to the difficulties some adults encounter when learning a new language. Several corticonuclear-originating fibers supply innervation and aid in the unconscious movements required upon engaging in speech and articulation.
Progressive bulbar palsy is a neuromuscular atrophy associated with the combined lesions of the hypoglossal nucleus and the nucleus ambiguous, upon atrophy of the motor nerves of the pons and medulla. This condition causes dysfunctional tongue movements that lead to speech and chewing impairments and swallowing difficulties.
Tongue muscle atrophy may also occur. Privacy Policy. Skip to main content. Peripheral Nervous System. Search for:. Cranial Nerves. Brief Overview of Cranial Nerves The peripheral nervous system has 12 pairs of cranial nerves that control much of the motor and sensory functions of the head and neck. Learning Objectives Describe the function of the cranial nerves.
Key Takeaways Key Points The cranial nerves serve functions such as smell, sight, eye movement, and feeling in the face. The cranial nerves also control balance, hearing, and swallowing. The twelve cranial nerves, in order from I to XII are: olfactory nerve, optic nerve, oculomotor nerve, trochlear nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve, glossopharengeal nerve, vagus nerve, spinal accessory nerve, and hypoglossal nerve.
The vagus nerve X has many branches and is responsible for tasks including heart rate, gastrointestinal peristalsis, sweating, and muscle movements in the mouth, including speech and keeping the larynx open for breathing. Key Terms innervate : To supply an organ or other body part with nerves. Olfactory I Nerve The olfactory nerve, or cranial nerve I, is the first of 12 cranial nerves and is responsible for the sense of smell. Learning Objectives Describe the olfactory nerve cranial nerve I.
Key Takeaways Key Points The olfactory nerve consists of a collection of many sensory nerve fibers that extend from the olfactory epithelium to the olfactory bulb. Olfactory receptors within the olfactory mucosa in the nasal cavity receive information about smells that travel to the brain through the cranial nerve that extends from the olfactory epithelium to the olfactory bulb.
Key Terms olfactory receptors : Expressed in the cell membranes of olfactory receptor neurons, these are responsible for the detection of odor molecules. Activated olfactory receptors are the initial player in a signal transduction cascade that ultimately produces a nerve impulse that is transmitted to the brain. The olfactory nerve carries impulses for the sense of smell. The optic nerve carries impulses for the sense of sight. Optic nerve glioma. The occulomotor nerve is responsible for motor enervation of upper eyelid muscle , extraocular muscle and pupillary muscle.
The trochlear nerve controls an extraocular muscle. The trigeminal nerve is responsible for sensory enervation of the face and motor enervation to muscles of mastication chewing. The abducent nerve enervates a muscle, which moves the eyeball.
The facial nerve enervates the muscles of the face facial expression. The vestibulocochlear nerve is responsible for the sense of hearing and balance body position sense. Check for differences in the sizes of the right and left pupils. Trigeminal Nerve V The trigeminal nerve has both sensory and motor functions.
To test the motor part of the nerve, tell your partner to close his or her jaws as if he or she was biting down on a piece of gum. To test the sensory part of the trigeminal nerve, lightly touch various parts of your partner's face with piece of cotton or a blunt object. Be careful not to touch your partner's eyes. Although much of the mouth and teeth are innervated by the trigeminal nerve, don't put anything into your subject's mouth. Facial Nerve VII The motor part of the facial nerve can be tested by asking your partner to smile or frown or make funny faces.
The sensory part of the facial nerve is responsible for taste on the front part of the tongue. You could try a few drops of sweet or salty water on this part of the tongue and see if your partner can taste it.
Vestibulocochlear Nerve VIII Although the vestibulocochlear nerve is responsible for hearing and balance, we will only test the hearing portion of the nerve here. Have your partner close his or her eyes and determine the distance at which he or she can hear the ticking of a clock or stopwatch.
Also the glossopharyngeal nerve is responsible for taste on the back part of the tongue. You could try a few drops of salty or sugar water on this part of the tongue and see if your partner can taste it. Spinal Accessory Nerve XI To test the strength of the muscles used in head movement, put your hands on the sides of your partner's head.
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