How many cranial nerves do humans have

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 receptors form a multigene family consisting of over genes in humans and 1, genes in mice. Optic II Nerve The optic nerve cranial nerve II receives visual information from photoreceptors in the retina and transmits it to the brain.

Learning Objectives Describe the optic nerve cranial nerve II. Key Takeaways Key Points The optic nerve is considered part of the central nervous system. The myelin on the optic nerve is produced by oligodendrocytes rather than Schwann cells and it is encased in the meningeal layers instead of the standard endoneurium, perineurium, and epineurium of the peripheral nervous system. The optic nerve travels through the optic canal, partially decussates in the optic chiasm, and terminates in the lateral geniculate nucleus where information is transmitted to the visual cortex.

The axons responsible for reflexive eye movements terminate in the pretectal nucleus. Key Terms oligodendrocyte : A type of neuroglia that provides support and insulation to axons in the central nervous system. It is located in the occipital lobe, in the back of the brain. Key Takeaways Key Points The oculomotor nerve is the third paired cranial nerve. The oculomotor nerve contains two nuclei, including the Edinger-Westphal nucleus that supplies parasympathetic nerve fibers to the eye to control pupil constriction and accommodation.

The oculomotor nerve originates at the superior colliculus and enters through the superior orbital fissure to control the levator palpebrae superioris muscles that hold the eyelids open. Key Terms levator palpebrae superioris : A muscle that elevates the upper eyelid. Trochlear IV Nerve The trochlear nerve cranial nerve IV is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye.

Learning Objectives Describe the trochlear nerve cranial nerve IV. Key Takeaways Key Points The trochlear nerve innervates the superior oblique muscle of the eye. The trochlear nerve contains the smallest number of axons of all the cranial nerves and has the greatest intracranial length. The two major clinical syndromes that can arise from damage to the trochlear nerve are vertical and torsional diplopia. Key Terms contralateral : On the opposite side of the body.

Also called the aqueduct of Sylvius, it is surrounded by periaqueductal gray matter. The trochlear nerve is unique among the cranial nerves in several respects. It is the smallest nerve in terms of the number of axons it contains and it has the greatest intracranial length.

Other than the optic nerve cranial nerve II , it is the only cranial nerve that decussates crosses to the other side before innervating its target. It is the only cranial nerve that exits from the dorsal aspect of the brainstem. The human trochlear nerve is derived from the basal plate of the embryonic midbrain. Clinical Syndromes There are two major clinical syndromes that can manifest through damage to the trochlear nerve: Vertical diplopia: Injury to the trochlear nerve causes weakness of downward eye movement with consequent vertical diplopia double vision.

Torsional diplopia: Weakness of intorsion results in torsional diplopia, in which two different visual fields, tilted with respect to each other, are seen at the same time. To compensate for this, patients with trochlear nerve palsies tilt their heads to the opposite side, in order to fuse the two images into a single visual field. Trigeminal V Nerve The trigeminal nerve is the fifth cranial nerve and it is responsible for sensation and motor function in the face and mouth.

Learning Objectives Describe the trigeminal nerve cranial nerve V. Key Takeaways Key Points The sensory function of the trigeminal nerve is to provide tactile, motion, position, and pain sensations for the face and mouth; its motor function activates the muscles of the jaw, mouth, and inner ear. The trigeminal nerve has three major branches on each side—the opthalmic nerve, maxillary nerve, and mandibular nerve—that converge on the trigeminal ganglion.

Structure The trigeminal nerve is the largest of the cranial nerves. Abducens VI Nerve The abducens nerve cranial nerve VI controls the lateral movement of the eye through innervation of the lateral rectus muscle. Learning Objectives Describe the abducens nerve cranial nerve VI. Key Takeaways Key Points The abducens nerve exits the brainstem at the junction of the pons and the medulla and runs upward to reach the eye, traveling between the dura and the skull. In most mammals besides humans, it also innervates the musculus retractor bulbi, which can retract the eye for protection.

Key Terms abducens nerve : A nerve that controls the lateral rectus muscle in the eye. It forms a gradual sloping process at the anterior-most portion of the basilar occipital bone at its junction with the sphenoid bone. It is one of six extraocular muscles that control the movements of the eye abduction in this case and the only muscle innervated by the abducens nerve, cranial nerve VI, functioning to bring the pupil away from the midline of the body.

Key Takeaways Key Points The facial nerve cranial nerve VII is responsible for the muscles that determine facial expression, as well as the sensation of taste in the front of the tongue and oral cavity. The nerve then runs through the facial canal, passes through the parotid gland, and divides into five branches. Key Terms nervus intermedius : A part of the facial nerve cranial nerve VII located between the motor component of the facial nerve and the vestibulocochlear nerve cranial nerve VIII.

It contains the sensory and parasympathetic fibers of the facial nerve. Key Takeaways Key Points The vestibulocochlear nerve comprises the cochlear nerve that transmits hearing information, and the vestibular nerve that transmits balance information. Key Terms cochlear nerve : A sensory nerve that conducts information about the environment to the brain, in this case acoustic energy impinging on the tympanic membrane sound waves reaching the ear drum.

The cochlear nerve arises from within the cochlea and extends to the brainstem where its fibers make contact with the cochlear nucleus, the next stage of neural processing in the auditory system.

It connects to the semicircular canals via the vestibular ganglion and receives positional information. Glossopharyngeal IX Nerve The glossopharyngeal nerve cranial nerve IX serves many distinct functions, including providing sensory innervation to various head and neck structures.

Learning Objectives Describe the glossopharyngeal nerve cranial nerve IX. Key Takeaways Key Points The glossopharyngeal nerve cranial nerve IX is responsible for swallowing and the gag reflex, along with other functions. The glossopharyngeal nerve receives input from the general and special sensory fibers in the back of the throat. The glossopharyngeal nerve has five components: branchial motor, visceral motor, visceral sensory, general sensory, and special sensory components.

Key Terms otic ganglion : A small parasympathetic ganglion located immediately below the foramen ovale in the infratemporal fossa that is associated with the glossopharyngeal nerve. Function There are a number of functions of the glossopharyngeal nerve.

It receives visceral sensory fibers from the carotid bodies, carotid sinus. It supplies parasympathetic fibers to the parotid gland via the otic ganglion.

It supplies motor fibers to the stylopharyngeus muscle. It contributes to the pharyngeal plexus. Five Functional Components The glossopharyngeal nerve consists of five components with distinct functions: Branchial motor special visceral efferent : Supplies the stylopharyngeus muscle. Visceral motor general visceral efferent : Provides parasympathetic innervation of the parotid gland.

Visceral sensory general visceral afferent : Carries visceral sensory information from the carotid sinus and body. 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. Tell your partner to move his or her head from side to side.

Apply only light pressure when the head is moved. Try it! It is also involved with taste sensation for the back of your tongue. Doctors often use vagus nerve stimulation therapy to treat conditions such as epilepsy, depression, and anxiety. The vagus nerve is also the longest of all the cranial nerves because it begins in the medulla in the brain and extends all the way to the abdominal area.

This cranial nerve, the accessory nerve , provides motor function to some of the muscles in the neck. The last of the cranial nerves is the hypoglossal nerve. It provides necessary motor functions to the tongue muscles. The spinal cord is part of your central nervous system. It begins at the bottom of the brain stem and continues down to your lower back. There are 31 pairs of spinal nerves, and they control sensory, motor, and other functions of your body. They transmit messages between your spinal cord and the rest of the body, including skin, muscles, and internal organs.

Each spinal nerve is responsible for providing sensation to a different area of your body. Source: neuroxcel. Each group of spinal nerves is involved with movements in certain parts of your body, including your hands, fingers, arms, upper back, hips, and abdominal muscles. Some spinal nerves are even responsible for ensuring you can walk and run properly. Some nerves in the spinal cord are responsible for controlling automatic body functions, such as your heart rate, breathing, and other things your body does automatically.

For example, spinal nerves T1-L5, which are your thoracic and lumbar nerves, are partially responsible for controlling the functions of your:. The upper part of your sacral nerves, from L5-S3, are responsible for controlling bladder and bowel movements. At NorthEast Spine and Sports Medicine, we help our patients feel more comfortable in their everyday lives by addressing problems they might experience with nerves in their brain or spinal cord.

We offer treatments such as spinal decompression therapy , treatment for sciatica , and many other chiropractic services. If you have questions about cranial or spinal nerves or think you might be a good candidate for chiropractic care, give us a call at or book an appointment online.

View Videos. Learn More. Since the beginning, our doctors and staff have been committed to treating patients who suffer from several different types of painful spine, joint, and orthopedic conditions. Furthermore, our goal is not only to reduce pain through physical rehabilitation, therapy, or any of our procedures and treatment options, but to help all of our patients have their functionality and quality of life restored.

Furthermore, every service and treatment option we offer is available at each of our eleven offices. Furthermore, when patients come to one of our offices, they are always greeted with smiles and treated with kindness. Every member of a team is respectful and empathetic, and will go to great lengths to ensure your pain management needs are addressed. Lastly, our physicians and staff also make certain that patients have the knowledge they need to help them live pain-free lives.

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In the end, you will be provided with a comprehensive and customized care plan that will greatly improve the quality of your life. Aberdeen Barnegat Freehold Jackson. Lincroft Manchester Neptune Orthopedic Consultations. What Is the Nervous System?