How many cranial nerves and spinal nerves are there

It has both sensory and motor functions, including:. Out of all of the cranial nerves, the vagus nerve has the longest pathway. It extends from your head all the way into your abdomen. It originates in the part of your brainstem called the medulla. Your accessory nerve is a motor nerve that controls the muscles in your neck. These muscles allow you to rotate, flex, and extend your neck and shoulders. The spinal portion originates in the upper part of your spinal cord.

The cranial part starts in your medulla oblongata. These parts meet briefly before the spinal part of the nerve moves to supply the muscles of your neck while the cranial part follows the vagus nerve. Your hypoglossal nerve is the 12th cranial nerve which is responsible for the movement of most of the muscles in your tongue. It starts in the medulla oblongata and moves down into the jaw, where it reaches the tongue. Learn about its symptoms, diagnosis, and treatment. Have trouble blinking or closing your eyes to sleep?

You might have lagophthalmos. Learn what causes this condition and how to treat it. Isolated nerve dysfunction IND is a type of neuropathy nerve damage that occurs in a single nerve. Technically it is a mononeuropathy because it…. Several supplements may ease neuropathy symptoms, like vitamin B, fish oil, curcumin, and more.

The telltale symptoms of sciatic nerve pain are severe pain in your back, buttocks, and legs. Many people with sciatica pain find lying down painful. In general, some sleeping positions are better than others and put less stress on the sciatic…. Learn the average duration of a pinched nerve based on type, what treatments are available, and how to prevent pinched nerves in the first place.

With neuropathic pain, the body sends pain signals to your brain unprompted. Here's what causes it and what you can do. An occipital nerve block is one of the most common procedures to relieve the pain of migraines and chronic headaches. We review the procedure along…. Health Conditions Discover Plan Connect. The 12 Cranial Nerves. Medically reviewed by Deborah Weatherspoon, Ph. The membranes are wrapped tightly around the axon, forming a multilayered sheath.

This myelin sheath resembles insulation, such as that around an electrical wire. Nerve impulses travel much faster in nerves with a myelin sheath than in those without one. Nerves that directly connect the brain and the brain stem with the eyes, ears, nose, and throat and with various parts of the head, neck, and trunk are called cranial nerves. There are 12 pairs of them see Overview of the Cranial Nerves Overview of the Cranial Nerves Twelve pairs of nerves—the cranial nerves—lead directly from the brain to various parts of the head, neck, and trunk.

Some of the cranial nerves are involved in the special senses such as seeing Cranial nerves transmit sensory information, including touch, vision, taste, smell, and hearing. Nerves that connect the spinal cord with other parts of the body are called spinal nerves. The brain communicates with most of the body through the spinal nerves.

There are 31 pairs of them, located at intervals along the length of the spinal cord see Overview of Spinal Cord Disorders Overview of Spinal Cord Disorders Spinal cord disorders can cause permanent severe problems, such as paralysis or impaired bladder and bowel control urinary incontinence and fecal incontinence.

Sometimes these problems can Several cranial nerves and most spinal nerves are involved in both the somatic and autonomic parts of the peripheral nervous system. Spinal nerves emerge from the spinal cord through spaces between the vertebrae.

Each nerve emerges as two short branches called spinal nerve roots : one at the front of the spinal cord and one at the back. Motor nerve root anterior nerve root : The motor root emerges from the front of the spinal cord. Motor nerve fibers carry commands from the brain and spinal cord to other parts of the body, particularly to skeletal muscles. Sensory nerve root posterior nerve root : The sensory root enters the back of the spinal cord. It controls the sternocleidomastoid and trapezius muscles that allow a person to rotate, extend, and flex the neck and shoulders.

The spinal component starts in the spinal cord and travels into the skull through the foramen magnum. From there, it meets the cranial component of the accessory nerve and exits the skull along the internal carotid artery.

The hypoglossal nerve is a motor nerve that supplies the tongue muscles. Disorders of the hypoglossal nerve can cause paralysis of the tongue, most often occurring on one side. The twelve cranial nerves are a group of nerves that start in the brain and provide motor and sensory functions to the head and neck.

Trigeminal neuralgia is a nerve disorder that causes abrupt, searing pain in the face and jaw. It affects about one million people worldwide and is…. A nerve conduction velocity test measures how fast the nerves in the body send important signals. If they are too slow, this may indicate nerve damage….

Bell's palsy causes weakness or paralysis of the muscles on one side of the face. It tends to occur due to a malfunction of the facial nerve, usually…. The radial nerve is prone to injury, even from minor incidents, such as sleeping on the arm. Radial nerve injury is also common after breaking the arm. Epilepsy is a fairly common neurological condition characterized by recurrent seizures.

In this article, learn about the different types of epilepsy…. What are the 12 cranial nerves? Medically reviewed by Elaine K. Luo, M. Each cranial nerve is paired and is present on both sides. The numbering of the cranial nerves is based on the order in which they emerge from the brain, front to back brainstem. The terminal nerves, olfactory nerves I and optic nerves II emerge from the cerebrum or forebrain, and the remaining ten pairs arise from the brainstem, which is the lower part of the brain.

The cranial nerves are considered components of the peripheral nervous system. However, on a structural level, the olfactory, optic, and terminal nerves are more accurately considered part of the central nervous system. The cranial nerves : The locations of the cranial nerves within the brain.

There are many mnemonic devices to remember the cranial nerves. The olfactory nerve, or cranial nerve I, is the first of 12 cranial nerves and is responsible for the sense of smell. Olfactory bulb : Sagittal section of human head showing the olfactory bulb. The olfactory nerve, or cranial nerve I, is the first of the 12 cranial nerves.

It is instrumental in the sense of smell. The olfactory nerve is the shortest of the 12 cranial nerves and only one of two cranial nerves the other being the optic nerve that do not join with the brainstem. The specialized olfactory receptor neurons of the olfactory nerve are located in the olfactory mucosa of the upper parts of the nasal cavity.

The olfactory nerves consist of a collection of many sensory nerve fibers that extend from the olfactory epithelium to the olfactory bulb, passing through the many openings of the cribriform plate of the ethmoid bone. Olfactory receptor neurons continue to emerge throughout life and extend new axons to the olfactory bulb.

Olfactory-ensheathing glia wrap bundles of these axons and are thought to facilitate their passage into the central nervous system. The sense of smell olfaction arises from the stimulation of olfactory or odorant receptors by small molecules of different spatial, chemical, and electrical properties that pass over the nasal epithelium in the nasal cavity during inhalation. These interactions are transduced into electrical activity in the olfactory bulb, which then transmits the electrical activity to other parts of the olfactory system and the rest of the central nervous system via the olfactory tract.

The optic nerve cranial nerve II receives visual information from photoreceptors in the retina and transmits it to the brain. The optic nerve is also known as cranial nerve II. It transmits visual information from the retina to the brain. Each human optic nerve contains between , and 1.

Optic nerve : An illustration of the brain highlighting the optic nerve and optic tract. The optic nerve is the second of twelve paired cranial nerves. It is considered by physiologists to be part of the central nervous system, as it is derived from an outpouching of the diencephalon during embryonic development. As a consequence, the fibers are covered with myelin produced by oligodendrocytes, rather than Schwann cells that are found in the peripheral nervous system.

The optic nerve is ensheathed in all three meningeal layers dura, arachnoid, and pia mater rather than the epineurium, perineurium, and endoneurium found in the peripheral nerves. The fiber tracks of the mammalian central nervous system are incapable of regeneration.

As a consequence, optic nerve damage produces irreversible blindness. The optic nerve leaves the orbit, which is also known as an eye socket, via the optic canal, running posteromedially toward the optic chiasm, where there is a partial decussation crossing of fibers from the nasal visual fields of both eyes.

Most of the axons of the optic nerve terminate in the lateral geniculate nucleus where information is relayed to the visual cortex , while other axons terminate in the pretectal nucleus and are involved in reflexive eye movements.

The optic nerve transmits all visual information including brightness perception, color perception, and contrast. 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 the eye that occurs when one looks at a near object, as in reading. The oculomoter nerve cranial nerve III controls eye movement, such as constriction of the pupil and open eyelids. The oculomotor nerve is the third paired cranial nerve. The occulomotor nerve is derived from the basal plate of the embryonic midbrain.

Cranial nerves IV and VI also participate in control of eye movement. Sympathetic postganglionic fibers also join the nerve from the plexus on the internal carotid artery in the wall of the cavernous sinus and are distributed through the nerve, for example, to the smooth muscle of levator palpebrae superioris. On emerging from the brain, the oculomotor nerve is invested with a sheath of pia mater and enclosed in a prolongation from the arachnoid mater.

It passes between the superior cerebellar and posterior cerebral arteries, and then pierces the dura mater anterior and lateral to the posterior clinoid process to give attachment to the tectorium cerebella , passing between the free and attached borders of the tentorium cerebelli.

It then runs along the lateral wall of the cavernous sinus, above the other orbital nerves, receiving in its course one or two filaments from the cavernous plexus of the sympathetic nervous system, and a communicating branch from the ophthalmic division of the trigeminal nerve.

It then divides into two branches that enter the orbit through the superior orbital fissure, between the two heads of the lateral rectus a muscle on the lateral side of the eyeball in the orbit. Here the nerve is placed below the trochlear nerve and the frontal and lacrimal branches of the ophthalmic nerve, while the nasociliary nerve is placed between its two rami the superior and inferior branch of oculomotor nerve.

Cranial nerves : Image of cranial nerves showing the position of the oculomotor nerve. The trochlear nerve cranial nerve IV is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye. The trochlear nerve : The trocheal nerve and where it innervates. The nucleus of the trochlear nerve is located in the caudal mesencephalon beneath the cerebral aqueduct.

It is immediately below the nucleus of the oculomotor nerve III in the rostral mesencephalon. The trochlear nucleus is unique in that its axons run dorsally and cross the midline before emerging from the brainstem—so a lesion of the trochlear nucleus affects the contralateral eye.

Lesions of all other cranial nuclei affect the ipsilateral side except of course the optic nerve, cranial nerve II, which innervates both eyes. Homologous trochlear nerves are found in all jawed vertebrates. The unique features of the trochlear nerve, including its dorsal exit from the brainstem and its contralateral innervation, are seen in the primitive brains of sharks. The clinical syndromes can originate from both peripheral and central lesions. A peripheral lesion is damage to the bundle of nerves, in contrast to a central lesion, which is damage to the trochlear nucleus.

The trigeminal nerve is the fifth cranial nerve and it is responsible for sensation and motor function in the face and mouth.

The trigeminal nerve cranial nerve V , and it contains both sensory and motor fibers. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Trigeminal nerve : Schematic illustration of the trigeminal nerve labeled Sensory root above and the structures it innervates in the face and mouth. The sensory function of the trigeminal nerve is to provide the tactile, motion, position, and pain sensations of the face and mouth.

The motor function activates the muscles of the jaw, mouth, and inner ear. The trigeminal nerve is the largest of the cranial nerves. Its name, trigeminal, means three twins. It is derived from the fact that each nerve, one on each side of the pons, has three major branches: the ophthalmic nerve V1 in the illustration below , the maxillary nerve V2 , and the mandibular nerve V3. The ophthalmic and maxillary nerves are purely sensory.

The mandibular nerve has both sensory and motor functions. The three branches converge on the trigeminal ganglion that is located within the trigeminal cave in the brain; it contains the cell bodies of incoming sensory nerve fibers. The trigeminal ganglion is analogous to the dorsal root ganglia of the spinal cord, which contain the cell bodies of incoming sensory fibers from the rest of the body.

Areas of the face innervated by the trigeminal nerve : The ophthalmic nerve branch V1 innervates the bright red area, the maxillary nerve branch V2 innervates the light red area, and the mandibular nerve branch V3 innervates the yellow area.

From the trigeminal ganglion, a single large sensory root enters the brainstem at the level of the pons.