neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defi ...

, the trigeminal nerve ( lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a

cranial nerve Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...

responsible for

sensation Sensation (psychology) refers to the processing of the senses by the sensory system. Sensation or sensations may also refer to: In arts and entertainment In literature *Sensation (fiction), a fiction writing mode *Sensation novel, a British ...

in the

face The face is the front of the head that features the eyes, nose and mouth, and through which animals express many of their emotions. The face is crucial for human identity, and damage such as scarring or developmental deformities may affect th ...

and

motor functions Motor control is the regulation of movements in organisms that possess a nervous system. Motor control includes conscious voluntary movements, subconscious muscle memory and involuntary reflexes, as well as instinctual taxes. To control movem ...

such as

biting Biting is an action involving a set of teeth closing down on an object. It is a common zoological behavior, being found in toothed animals such as mammals, reptiles, amphibians, fishes, and arthropods. Biting is also an action humans participate ...

and

chewing Chewing or mastication is the process by which food is crushed and ground by the teeth. It is the first step in the process of digestion, allowing a greater surface area for digestive enzymes to break down the foods. During the mastication proc ...

; it is the most complex of the

cranial nerves Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...

. Its name (''trigeminal'', ) derives from each of the two nerves (one on each side of the

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other mammals, lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of ...

) having three major branches: the

ophthalmic nerve The ophthalmic nerve (CN V1) is a sensory nerve of the head. It is one of three divisions of the trigeminal nerve (CN V), a cranial nerve. It has three major branches which provide sensory innervation to the eye, and the skin of the upper face ...

(V), the

maxillary nerve In neuroanatomy, the maxillary nerve (V) is one of the three branches or divisions of the trigeminal nerve, the fifth (CN V) cranial nerve. It comprises the principal functions of Sense, sensation from the maxilla, nasal cavity, Sinus (anatomy ...

(V), and the

mandibular nerve In neuroanatomy, the mandibular nerve (V) is the largest of the three divisions of the trigeminal nerve, the fifth Cranial nerves, cranial nerve (CN V). Unlike the other divisions of the trigeminal nerve (ophthalmic nerve, maxillary nerve) which ...

(V). The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory (or "

cutaneous Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different d ...

") functions. Adding to the complexity of this nerve is that autonomic nerve fibers as well as special

sensory fibers A sensory nerve, or afferent nerve, is a nerve that contains exclusively afferent nerve fibers. Nerves containing also motor fibers are called mixed. Afferent nerve fibers in a sensory nerve carry sensory information toward the central nervous ...

(

taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth biochemistry, reacts chemically with taste receptor cells l ...

) are contained within it. The motor division of the trigeminal nerve derives from the basal plate of the

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

nic

, and the sensory division originates in the

cranial neural crest The cranial neural crest is one of the four regions of the neural crest. The cranial neural crest arises in the anterior and populates the face and the pharyngeal arches giving rise to bones, cartilage, nerves and connective tissue. The endocraniu ...

. Sensory information from the face and body is processed by parallel pathways in the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

Structure

Origin

From the trigeminal ganglion, a single, large sensory root enters the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...

at the level of the

. Immediately adjacent to the sensory root, a smaller motor root emerges from the pons slightly rostrally and medially to the sensory root. Motor fibers pass through the trigeminal ganglion without synapsing on their way to peripheral muscles, their cell bodies being located in the nucleus of the fifth nerve, deep within the pons.

Trigeminal ganglion

The three major branches of the trigeminal nerve—the

(V₁), the

(V₂) and the

(V₃)—converge on the

trigeminal ganglion The trigeminal ganglion (also known as: Gasserian ganglion, semilunar ganglion, or Gasser's ganglion) is the sensory ganglion of each trigeminal nerve (CN V). The trigeminal ganglion is located within the trigeminal cave (Meckel's cave), a cav ...

(also called the semilunar ganglion or gasserian ganglion), located within Meckel's cave and containing the cell bodies of incoming sensory-nerve fibers. The trigeminal ganglion is analogous to the

dorsal root The dorsal root of spinal nerve (or posterior root of spinal nerve or sensory root) is one of two "roots" which emerge from the spinal cord. It emerges directly from the spinal cord, and travels to the dorsal root ganglion. Nerve fibres with the v ...

ganglia of the spinal cord, which contain the cell bodies of incoming sensory fibers from the rest of the body. Gray784

Sensory branches

The ophthalmic, maxillary and mandibular branches leave the skull through three separate

foramina In anatomy and osteology, a foramen (; : foramina, or foramens ; ) is an opening or enclosed gap within the dense connective tissue (bones and deep fasciae) of extant and extinct amniote animals, typically to allow passage of nerves, arter ...

: the

superior orbital fissure The superior orbital fissure is a foramen or cleft of the skull between the lesser and greater wings of the sphenoid bone. It gives passage to multiple structures, including the oculomotor nerve, trochlear nerve, ophthalmic nerve, abducens nerve ...

, the

foramen rotundum The foramen rotundum is a circular hole in the sphenoid bone of the skull. It connects the middle cranial fossa and the pterygopalatine fossa. It allows for the passage of the maxillary nerve (V2), a branch of the trigeminal nerve. Structure T ...

and the foramen ovale, respectively. The ophthalmic nerve (V₁) carries sensory information from the scalp and forehead, the upper eyelid, the conjunctiva and cornea of the eye, the nose (including the tip of the nose, except alae nasi), the nasal mucosa, the frontal sinuses and parts of the

meninges In anatomy, the meninges (; meninx ; ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in the subarachnoid spac ...

(the dura and blood vessels). The maxillary nerve (V₂) carries sensory information from the lower eyelid and cheek, the nares and upper lip, the upper teeth and gums, the nasal mucosa, the palate and roof of the pharynx, the maxillary, ethmoid and sphenoid sinuses and parts of the meninges. The mandibular nerve (V₃) carries sensory information from the lower lip, the lower teeth and gums, the chin and jaw (except the angle of the jaw, which is supplied by C2-C3), parts of the external ear and parts of the meninges. The mandibular nerve carries touch-position and pain-temperature sensations from the mouth. Although it does not carry taste sensation (the

chorda tympani Chorda tympani is a branch of the facial nerve that carries gustatory (taste) sensory innervation from the front of the tongue and parasympathetic ( secretomotor) innervation to the submandibular and sublingual salivary glands. Chorda tymp ...

is responsible for taste), one of its branches—the

lingual nerve The lingual nerve carries sensory innervation from the anterior two-thirds of the tongue. It contains fibres from both the mandibular division of the trigeminal nerve (CN V) and from the facial nerve (CN VII). The fibres from the trigeminal nerve ...

—carries sensation from the tongue. The peripheral processes of mesencephalic nucleus of V neurons run in the motor root of the trigeminal nerve and terminate in the muscle spindles in the muscles of mastication. They are proprioceptive fibers, conveying information regarding the location of the masticatory muscles. The central processes of mesencephalic V neurons synapse in the motor nucleus V.

Dermatomes

The areas of cutaneous distribution (

dermatome Dermatome may refer to: * Dermatome (anatomy), an area of skin that is supplied by a single pair of dorsal roots * Dermatome (embryology), the portion of the embryonic paraxial mesoderm, the somite, which gives rise to dermis * Dermatome (instrument ...

s) of the three sensory branches of the trigeminal nerve have sharp borders with relatively little overlap (unlike dermatomes in the rest of the body, which have considerable overlap). The injection of a

local anesthetic A local anesthetic (LA) is a medication that causes absence of all sensation (including pain) in a specific body part without loss of consciousness, providing local anesthesia, as opposed to a general anesthetic, which eliminates all sensati ...

, such as

lidocaine Lidocaine, also known as lignocaine and sold under the brand name Xylocaine among others, is a local anesthetic of the amino amide type. It is also used to treat ventricular tachycardia and ventricular fibrillation. When used for local anae ...

, results in the complete loss of sensation from well-defined areas of the face and mouth. For example, teeth on one side of the jaw can be numbed by injecting the mandibular nerve. Occasionally, injury or disease processes may affect two (or all three) branches of the trigeminal nerve; in these cases, the involved branches may be termed: * V1/V2 distribution – Referring to the ophthalmic and maxillary branches * V2/V3 distribution – Referring to the maxillary and mandibular branches * V1-V3 distribution – Referring to all three branches Nerves on the left side of the jaw slightly outnumber the nerves on the right side of the jaw.

Function

The sensory function of the trigeminal nerve is to provide tactile,

proprioceptive Proprioception ( ) is the sense of self-movement, force, and body position. Proprioception is mediated by proprioceptors, a type of sensory receptor, located within muscles, tendons, and joints. Most animals possess multiple subtypes of propri ...

, and

nociceptive In physiology, nociception , also nocioception; ) is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, convert it to a molecular ...

afference to the face and mouth. Its motor function activates the

muscles of mastication The four classical muscles of mastication elevate the mandible (closing the jaw) and move it forward/backward and laterally, facilitating biting and chewing. Other muscles are responsible for opening the jaw, namely the geniohyoid, mylohyoid, an ...

, the

tensor tympani The tensor tympani is a muscle within the middle ear, located in the bony canal above the bony part of the auditory tube, and connects to the malleus bone. Its role is to dampen loud sounds, such as those produced from chewing, shouting, or thun ...

tensor veli palatini The tensor veli palatini muscle (tensor palati or tensor muscle of the velum palatinum) is a thin, triangular muscle of the head that tenses the soft palate and opens the Eustachian tube to equalise pressure in the middle ear. Structure The te ...

, mylohyoid and the anterior belly of the digastric. The trigeminal nerve carries

general somatic afferent fibers The general somatic afferent fibers (GSA or somatic sensory fibers) are afferent fibers that arise from neurons in sensory ganglia and are found in all the spinal nerves, except occasionally the first cervical. General somatic afferents conduct im ...

(GSA), which innervate the skin of the face via ophthalmic (V1), maxillary (V2) and mandibular (V3) divisions. The trigeminal nerve also carries

special visceral efferent Special visceral efferent fibers (SVE) are the efferent nerve fibers that provide motor innervation to the muscles of the pharyngeal arches in humans, and the branchial arches in fish. Some sources prefer the term "branchiomotor" or "branchial ef ...

(SVE)

axon An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

s, which innervate the muscles of mastication via the mandibular (V3) division.

Muscles

The motor component of the mandibular division (V3) of the trigeminal nerve controls the movement of eight muscles, including the four

: the

masseter In anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. The most obvious muscle of mastication is the masseter muscle, since it is the ...

, the

temporal muscle In anatomy, the temporalis muscle, also known as the temporal muscle, is one of the muscles of mastication (chewing). It is a broad, fan-shaped convergent muscle on each side of the head that fills the temporal fossa, superior to the zygomatic ...

, and the medial and lateral pterygoids. The other four muscles are the

, the mylohyoid, the anterior belly of the

digastric The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a bilaterally paired suprahyoid muscle located under the jaw. Its posterior belly is attached to the mastoid notch of temporal bone, and its anterior belly ...

and the

. With the exception of the tensor tympani, all these muscles are involved in biting, chewing and swallowing and all have bilateral cortical representation. A unilateral central lesion (for example, a

stroke Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...

), no matter how large, is unlikely to produce an observable deficit. Injury to a peripheral nerve can cause paralysis of muscles on one side of the jaw, with the jaw deviating towards the paralyzed side when it opens. This direction of the mandible is due to the action of the functioning pterygoids on the opposite side.

Sensation

The two basic types of sensation are touch-position and pain-temperature. Touch-position input comes to attention immediately, but pain-temperature input reaches the level of consciousness after a delay; when a person steps on a pin, the awareness of stepping on something is immediate but the pain associated with it is delayed. Touch-position information is generally carried by myelinated (fast-conducting) nerve fibers, and pain-temperature information by unmyelinated (slow-conducting) fibers. The primary sensory receptors for touch-position ( Meissner's corpuscles, Merkel's receptors,

Pacinian corpuscles The Pacinian corpuscle (also lamellar corpuscle, or Vater–Pacini corpuscle) is a low-threshold mechanoreceptor responsive to vibration or pressure, found in the skin and other internal organs. In the skin it is one of the four main types of cuta ...

, Ruffini's corpuscles, hair receptors, muscle spindle organs and

Golgi tendon organs The Golgi tendon organ (GTO) (also called Golgi organ, tendon organ, neurotendinous organ or neurotendinous spindle) is a proprioceptor – a type of sensory receptor that senses changes in muscle tension. It lies at the interface between a mus ...

) are structurally more complex than those for pain-temperature, which are nerve endings. Sensation in this context refers to the conscious perception of touch-position and pain-temperature information, rather than the

special senses In medicine and anatomy, the special senses are the senses that have specialized organs devoted to them: * vision (the eye) * hearing and balance (the ear, which includes the auditory system and vestibular system) * smell (the nose) * taste (th ...

(smell, sight, taste, hearing and balance) processed by different cranial nerves and sent to the cerebral cortex through different pathways. The perception of magnetic fields, electrical fields, low-frequency vibrations and infrared radiation by some nonhuman vertebrates is processed by their equivalent of the fifth cranial nerve. Touch in this context refers to the perception of detailed, localized tactile information, such as

two-point discrimination Two-point discrimination (2PD) is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one. It is often tested with two sharp points during a neurological examination and is assumed to reflect how fi ...

(the difference between touching one point and two closely spaced points) or the difference between coarse, medium or fine sandpaper. People without touch-position perception can feel the surface of their bodies and perceive touch in a broad sense, but they lack perceptual detail. Position, in this context, refers to conscious

proprioception Proprioception ( ) is the sense of self-movement, force, and body position. Proprioception is mediated by proprioceptors, a type of sensory receptor, located within muscles, tendons, and joints. Most animals possess multiple subtypes of propri ...

. Proprioceptors (muscle spindle and Golgi tendon organs) provide information about joint position and muscle movement. Although much of this information is processed at an unconscious level (primarily by the

cerebellum The cerebellum (: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or eve ...

and the

vestibular The Vestibular (from , "entrance hall") is a competitive examination and is the primary and widespread entrance system used by Brazilian universities to select the students admitted. The Vestibular usually takes place from November to January, ...

nuclei), some is available at a conscious level. Touch-position and pain-temperature sensations are processed by different pathways in the central nervous system. This hard-wired distinction is maintained up to the cerebral cortex. Within the cerebral cortex, sensations are linked with other cortical areas.

Sensory pathways

Sensory pathways from the periphery to the cortex are separate for touch-position and pain-temperature sensations. All sensory information is sent to specific nuclei in the

thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...

. Thalamic nuclei, in turn, send information to specific areas in the

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. It is the largest site of Neuron, neural integration in the central nervous system, and plays ...

. Each pathway consists of three bundles of nerve fibers connected in series: Sensory Pathways III

The secondary neurons in each pathway

decussate Decussation is used in biological contexts to describe a crossing (due to the shape of the Roman numeral for ten, an uppercase 'X' (), ). In Latin anatomical terms, the form is used, e.g. . Similarly, the anatomical term chiasma is named aft ...

(cross the spinal cord or brainstem), because the spinal cord develops in segments. Decussated fibers later reach and connect these segments with the higher centers. The

optic chiasm In neuroanatomy, the optic chiasm, or optic chiasma (; , ), is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. The optic chiasm is found in all vertebrates, ...

is the primary cause of decussation; nasal fibers of the optic nerve cross (so each cerebral hemisphere receives contralateral—opposite—vision) to keep the

interneuron Interneurons (also called internuncial neurons, association neurons, connector neurons, or intermediate neurons) are neurons that are not specifically motor neurons or sensory neurons. Interneurons are the central nodes of neural circuits, enab ...

al connections responsible for processing information short. All sensory and motor pathways converge and diverge to the contralateral hemisphere. Although sensory pathways are often depicted as chains of individual neurons connected in series, this is an oversimplification. Sensory information is processed and modified at each level in the chain by interneurons and input from other areas of the nervous system. For example, cells in the main trigeminal nucleus (Main V in the diagram below) receive input from the

reticular formation The reticular formation is a set of interconnected nuclei in the brainstem that spans from the lower end of the medulla oblongata to the upper end of the midbrain. The neurons of the reticular formation make up a complex set of neural networks ...

and cerebellar cortex. This information contributes to the final output of the cells in Main V to the thalamus. Touch Pain Pathways

Touch-position information from the body is carried to the thalamus by the

medial lemniscus The medial lemniscus, also known as Reil's band or Reil's ribbon (for German anatomist Johann Christian Reil), is a large ascending bundle of heavily myelinated axons that decussate in the brainstem The brainstem (or brain stem) is the pos ...

, and from the face by the

trigeminal lemniscus The trigeminal lemniscus or the trigeminothalamic tracts is a somatosensory tract containing second-order neuron fibers of the trigeminal system. It consists of the ventral and dorsal trigeminal tracts. Its second-order sensory axons convey ta ...

(both the anterior and posterior trigeminothalamic tracts). Pain-temperature information from the body is carried to the thalamus by the

spinothalamic tract The spinothalamic tract is a nerve tract in the anterolateral system in the spinal cord. This tract is an ascending sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upwar ...

, and from the face by the anterior division of the

(also called the

anterior trigeminothalamic tract The ventral trigeminal tract, ventral trigeminothalamic tract, anterior trigeminal tract, or anterior trigeminothalamic tract, is a nerve tract, tract composed of second-order neuron, second-order neuronal axons. These afferent fibers carry sensor ...

). Pathways for touch-position and pain-temperature sensations from the face and body merge in the brainstem, and touch-position and pain-temperature sensory maps of the entire body are projected onto the thalamus. From the thalamus, touch-position and pain-temperature information is projected onto the cerebral cortex.

Summary

The complex processing of pain-temperature information in the thalamus and cerebral cortex (as opposed to the relatively simple, straightforward processing of touch-position information) reflects a

phylogenetically In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

older, more primitive sensory system. The detailed information received from peripheral touch-position receptors is superimposed on a background of awareness, memory and emotions partially set by peripheral pain-temperature receptors. Although thresholds for touch-position perception are relatively easy to measure, those for pain-temperature perception are difficult to define and measure. "Touch" is an objective sensation, but "pain" is an individualized sensation which varies among different people and is conditioned by memory and emotion. Anatomical differences between the pathways for touch-position perception and pain-temperature sensation help explain why pain, especially chronic pain, is difficult to manage.

Trigeminal nuclei

All sensory information from the face, both touch-position and pain-temperature, is sent to the

trigeminal nucleus The sensory trigeminal nerve nuclei are the largest of the cranial nerve nuclei, and extend through the whole of the midbrain, pons and medulla, and into the upper cervical spinal cord. The nucleus is divided into three parts, from rostral to ...

. In classical anatomy most sensory information from the face is carried by the fifth nerve, but sensation from parts of the mouth, parts of the ear and parts of the

is carried by

in cranial nerves VII (the

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of ta ...

), IX (the

glossopharyngeal nerve The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper Medulla oblongata, medulla, just anterior (closer to the nose) to t ...

) and X (the

vagus nerve The vagus nerve, also known as the tenth cranial nerve (CN X), plays a crucial role in the autonomic nervous system, which is responsible for regulating involuntary functions within the human body. This nerve carries both sensory and motor fibe ...

). All sensory fibers from these nerves terminate in the trigeminal nucleus. On entering the brainstem, sensory fibers from V, VII, IX and X are sorted and sent to the trigeminal nucleus (which contains a sensory map of the face and mouth). The spinal counterparts of the trigeminal nucleus (cells in the dorsal horn and dorsal column nuclei of the spinal cord) contain a sensory map of the rest of the body. The trigeminal nucleus extends throughout the brainstem, from the midbrain to the medulla, continuing into the cervical cord (where it merges with the dorsal horn cells of the spinal cord). The nucleus is divided into three parts, visible in microscopic sections of the brainstem. From caudal to rostral (ascending from the medulla to the midbrain), they are the spinal trigeminal, the principal sensory and the

mesencephalic The midbrain or mesencephalon is the uppermost portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum. It is functionally associated with vision, hearing, mo ...

nuclei. The parts of the trigeminal nucleus receive different types of sensory information; the spinal trigeminal nucleus receives pain-temperature fibers, the principal sensory nucleus receives touch-position fibers and the mesencephalic nucleus receives proprioceptor and mechanoreceptor fibers from the jaws and teeth.

Spinal trigeminal nucleus

The

spinal trigeminal nucleus The spinal trigeminal nucleus is a nucleus in the medulla that receives information about deep/crude touch, pain, and temperature from the ipsilateral face. In addition to the trigeminal nerve (CN V), the facial (CN VII), glossopharyngeal (CN ...

represents pain-temperature sensation from the face. Pain-temperature fibers from peripheral

nociceptors A nociceptor (; ) is a sensory neuron that responds to damaging or potentially damaging stimuli by sending "possible threat" signals to the spinal cord and the brain. The brain creates the sensation of pain to direct attention to the body part, ...

are carried in cranial nerves V, VII, IX and X. On entering the brainstem, sensory fibers are grouped and sent to the spinal trigeminal nucleus. This bundle of incoming fibers can be identified in cross-sections of the pons and medulla as the spinal tract of the trigeminal nucleus, which parallels the spinal trigeminal nucleus. The spinal tract of V is analogous to, and continuous with,

Lissauer's tract The posterolateral tract (fasciculus of Lissauer, Lissauer's tract, tract of Lissauer, dorsolateral fasciculus, dorsolateral tract, zone of Lissauer) is a small strand situated in relation to the tip of the posterior column close to the entrance of ...

in the spinal cord. The spinal trigeminal nucleus contains a pain-temperature sensory map of the face and mouth. From the spinal trigeminal nucleus, secondary fibers cross the midline and ascend in the trigeminothalamic (quintothalamic) tract to the contralateral thalamus. Pain-temperature fibers are sent to multiple thalamic nuclei. The central processing of pain-temperature information differs from the processing of touch-position information.

Somatotopic representation

Exactly how pain-temperature fibers from the face are distributed to the spinal trigeminal nucleus is disputed. The present general understanding is that pain-temperature information from all areas of the human body is represented in the spinal cord and brainstem in an ascending, caudal-to-rostral fashion. Information from the lower extremities is represented in the lumbar cord, and that from the upper extremities in the thoracic cord. Information from the neck and the back of the head is represented in the cervical cord, and that from the face and mouth in the spinal trigeminal nucleus. Within the spinal trigeminal nucleus, information is represented in a layered, or "onion-skin" fashion. The lowest levels of the nucleus (in the upper cervical cord and lower medulla) represent peripheral areas of the face (the scalp, ears and chin). Higher levels (in the upper medulla) represent central areas (nose, cheeks and lips). The highest levels (in the pons) represent the mouth, teeth and pharyngeal cavity. The onion skin distribution differs from the dermatome distribution of the peripheral branches of the fifth nerve. Lesions which destroy lower areas of the spinal trigeminal nucleus (but spare higher areas) preserve pain-temperature sensation in the nose (V₁), upper lip (V₂) and mouth (V₃) and remove pain-temperature sensation from the forehead (V₁), cheeks (V₂) and chin (V₃). Although analgesia in this distribution is "nonphysiologic" in the traditional sense (because it crosses several dermatomes), this analgesia is found in humans after surgical sectioning of the spinal tract of the trigeminal nucleus. The spinal trigeminal nucleus sends pain-temperature information to the

and sends information to the

mesencephalon The midbrain or mesencephalon is the uppermost portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum. It is functionally associated with vision, hearing, mo ...

and the

of the brainstem. The latter pathways are analogous to the spinomesencephalic and spinoreticular tracts of the spinal cord, which send pain-temperature information from the rest of the body to the same areas. The mesencephalon modulates painful input before it reaches the level of consciousness. The reticular formation is responsible for the automatic (unconscious) orientation of the body to painful stimuli. Incidentally,

Sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

-containing compounds found in plants in the

onion An onion (''Allium cepa'' , from Latin ), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus '' Allium''. The shallot is a botanical variety of the onion which was classifie ...

family stimulate receptors found in trigeminal ganglia, bypassing the

olfactory system The olfactory system, is the sensory nervous system, sensory system used for the sense of smell (olfaction). Olfaction is one of the special senses directly associated with specific organs. Most mammals and reptiles have a main olfactory system ...

Principal nucleus

The principal nucleus represents touch-pressure sensation from the face. It is located in the pons, near the entrance for the fifth nerve. Fibers carrying touch-position information from the face and mouth via cranial nerves V, VII, IX, and X are sent to this nucleus when they enter the brainstem. The principal nucleus contains a touch-position sensory map of the face and mouth, just as the spinal trigeminal nucleus contains a complete pain-temperature map. This nucleus is analogous to the dorsal column nuclei (the gracile and cuneate nuclei) of the spinal cord, which contain a touch-position map of the rest of the body. From the principal nucleus, secondary fibers cross the midline and ascend in the ventral trigeminothalamic tract to the contralateral

. The ventral trigeminothalamic tract runs parallel to the

, which carries touch-position information from the rest of the body to the thalamus. Some sensory information from the teeth and jaws is sent from the principal nucleus to the

ipsilateral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

thalamus via the small

dorsal trigeminal tract The dorsal trigeminal tract (also dorsal trigeminothalamic tract, or posterior trigeminothalamic tract) are un crossed second-order sensory fibers conveying fine (discriminative) touch and pressure information from the dorsomedial division of pr ...

. Touch-position information from the teeth and jaws of one side of the face is represented bilaterally in the thalamus and cortex.

Mesencephalic nucleus

The

mesencephalic nucleus The mesencephalic nucleus of trigeminal nerve is one of the sensory nuclei of the trigeminal nerve (cranial nerve V). It is located in the brainstem. It receives proprioceptive sensory information from the muscles of mastication and other muscles ...

is not a true

nucleus Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

; it is a sensory

ganglion A ganglion (: ganglia) is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there are ...

(like the

) embedded in the brainstem and the sole exception to the rule that sensory information passes through peripheral sensory ganglia before entering the central nervous system. It has been found in all

vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

except

lampreys Lampreys (sometimes inaccurately called lamprey eels) are a group of Agnatha, jawless fish comprising the order (biology), order Petromyzontiformes , sole order in the Class (biology), class Petromyzontida. The adult lamprey is characterize ...

and hagfishes. They are the only vertebrates without jaws and have specific cells in their brainstems. These "internal ganglion" cells were discovered in the late 19th century by medical student

Sigmund Freud Sigmund Freud ( ; ; born Sigismund Schlomo Freud; 6 May 1856 – 23 September 1939) was an Austrian neurologist and the founder of psychoanalysis, a clinical method for evaluating and treating psychopathology, pathologies seen as originating fro ...

. Two types of sensory fibers have cell bodies in the mesencephalic nucleus: proprioceptor fibers from the jaw and mechanoreceptor fibers from the teeth. Some of these incoming fibers go to the motor nucleus of the trigeminal nerve (V), bypassing the pathways for conscious perception. The

jaw jerk reflex The jaw jerk reflex, or masseter reflex, is a stretch reflex used to test the status of a patient's trigeminal nerve (cranial nerve V) and to help distinguish an upper cervical cord compression from lesions that are above the foramen magnum. The ma ...

is an example; tapping the jaw elicits a reflex closure of the jaw in the same way that tapping the knee elicits a reflex kick of the lower leg. Other incoming fibers from the teeth and jaws go to the main nucleus of V. This information is projected bilaterally to the thalamus and available for conscious perception. Activities such as biting, chewing and swallowing require symmetrical, simultaneous coordination of both sides of the body. They are automatic activities, requiring little conscious attention and involving a sensory component (feedback about touch-position) processed at the unconscious level in the mesencephalic nucleus.

Pathways to the thalamus and cortex

Sensation has been defined as the conscious perception of touch-position and pain-temperature information. With the exception of smell, all sensory input (touch-position, pain-temperature, sight, taste, hearing and balance) is sent to the thalamus and then the cortex. The thalamus is anatomically subdivided into nuclei.

Touch-position sensation

Touch-position information from the body is sent to the

ventral posterolateral nucleus The ventral posterolateral nucleus (VPL) is one of the subdivisions of the ventral posterior nucleus in the ventral nuclear group of the thalamus. It relays sensory information from the second-order neurons of the neospinothalamic tract and me ...

(VPL) of the thalamus. Touch-position information from the face is sent to the

ventral posteromedial nucleus The ventral posteromedial nucleus (VPM) is a nucleus within the ventral posterior nucleus of the thalamus and serves an analogous somatosensory relay role for the ascending trigeminothalamic tracts as its lateral neighbour the ventral posterolat ...

(VPM) of the thalamus. From the VPL and VPM, information is projected to the

primary somatosensory cortex In neuroanatomy, the primary somatosensory cortex is located in the postcentral gyrus of the brain's parietal lobe, and is part of the somatosensory system. It was initially defined from surface stimulation studies of Wilder Penfield, and parallel ...

(SI) in the

parietal lobe The parietal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus. The parietal lobe integra ...

. The representation of sensory information in the postcentral gyrus is organized somatotopically. Adjacent areas of the body are represented by adjacent areas in the cortex. When body parts are drawn in proportion to the density of their innervation, the result is a "little man": the

cortical homunculus A cortical homunculus () is a distorted representation of the human body, based on a neurological "map" of the areas and portions of the human brain dedicated to processing motor functions, and/or sensory functions, for different parts of th ...

. Many textbooks have reproduced the outdated Penfield-Rasmussen diagram ef? with the toes and genitals on the

mesial This is a list of definitions of commonly used terms of location and direction in dentistry. This set of terms provides orientation within the oral cavity, much as anatomical terms of location provide orientation throughout the body. Terms ...

surface of the cortex when they are actually represented on the convexity. The classic diagram implies a single primary sensory map of the body, when there are multiple primary maps. At least four separate, anatomically distinct sensory homunculi have been identified in the postcentral gyrus. They represent combinations of input from surface and deep receptors and rapidly and slowly adapting peripheral receptors; smooth objects will activate certain cells, and rough objects will activate other cells. Information from all four maps in SI is sent to the secondary sensory cortex (SII) in the parietal lobe. SII contains two more sensory homunculi. Information from one side of the body is generally represented on the opposite side in SI, but on both sides in SII. Functional MRI imaging of a defined stimulus (for example, stroking the skin with a toothbrush) "lights up" a single focus in SI and two foci in SII.

Pain-temperature sensation

Pain-temperature information is sent to the VPL (body) and VPM (face) of the thalamus (the same nuclei which receive touch-position information). From the thalamus, pain-temperature and touch-position information is projected onto SI. Unlike touch-position information, however, pain-temperature information is also sent to other thalamic nuclei and projected onto additional areas of the cerebral cortex. Some pain-temperature fibers are sent to the

medial dorsal thalamic nucleus The medial dorsal nucleus (or mediodorsal nucleus of thalamus, dorsomedial nucleus, dorsal medial nucleus, or medial nucleus group) is a large nucleus in the thalamus. It is separated from the other thalamic nuclei by the internal medullary lam ...

(MD), which projects to the anterior

cingulate cortex The cingulate cortex is a part of the brain situated in the medial aspect of the cerebral cortex. The cingulate cortex includes the entire cingulate gyrus, which lies immediately above the corpus callosum, and the continuation of this in the cin ...

. Other fibers are sent to the ventromedial (VM) nucleus of the thalamus, which projects to the

insular cortex The insular cortex (also insula and insular lobe) is a portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal lobe, parietal and frontal lobes) within each brain hemisphere ...

. Finally, some fibers are sent to the intralaminar nucleus (IL) of the thalamus via the

. The IL projects diffusely to all parts of the cerebral cortex. The insular and cingulate cortices are parts of the brain which represent touch-position and pain-temperature in the context of other simultaneous perceptions (sight, smell, taste, hearing and balance) in the context of memory and emotional state. Peripheral pain-temperature information is channeled directly to the brain at a deep level, without prior processing. Touch-position information is handled differently. Diffuse thalamic projections from the IL and other thalamic nuclei are responsible for a given level of consciousness, with the thalamus and reticular formation "activating" the brain; peripheral pain-temperature information also feeds directly into this system.

Clinical significance

Trigeminal neuralgia Trigeminal neuralgia (TN or TGN), also called Fothergill disease, tic douloureux, trifacial neuralgia, is a chronic pain, long-term pain disorder that affects the trigeminal nerve, the nerve responsible for sensation in the face and motor funct ...

Cluster headache Cluster headache is a neurological disorder characterized by recurrent severe headaches on one side of the head, typically around the eye, eye(s). There is often accompanying eye watering, nasal congestion, or swelling around the eye on the aff ...

Migraine Migraine (, ) is a complex neurological disorder characterized by episodes of moderate-to-severe headache, most often unilateral and generally associated with nausea, and light and sound sensitivity. Other characterizing symptoms may includ ...

Lateral medullary syndrome

Lateral medullary syndrome (Wallenberg syndrome) is a clinical demonstration of the anatomy of the trigeminal nerve, summarizing how it processes sensory information. A stroke usually affects only one side of the body; loss of sensation due to a stroke will be lateralized to the right or the left side of the body. The only exceptions to this rule are certain spinal-cord lesions and the medullary syndromes, of which Wallenberg syndrome is the best-known example. In this syndrome, a stroke causes a loss of pain-temperature sensation from one side of the face and the other side of the body. This is explained by the anatomy of the brainstem. In the medulla, the ascending

(which carries pain-temperature information from the opposite side of the body) is adjacent to the ascending spinal tract of the trigeminal nerve (which carries pain-temperature information from the same side of the face). A stroke which cuts off the blood supply to this area (for example, a clot in the posterior inferior cerebellar artery) destroys both tracts simultaneously. The result is a loss of pain-temperature (but not touch-position) sensation in a "checkerboard" pattern (ipsilateral face, contralateral body), facilitating diagnosis.

Sensory neuronopathy

Sensory neuronopathy (also known as sensory ganglionopathy) is a type of peripheral neuropathy in which sensory nerve cell bodies in the

dorsal root ganglia A dorsal root ganglion (or spinal ganglion; also known as a posterior root ganglion) is a cluster of neurons (a ganglion) in a dorsal root of a spinal nerve. The cell bodies of sensory neurons known as first-order neurons are located in the dors ...

, commonly including the

of the trigeminal nerve, are damaged due to a variety of mechanisms leading to sensory symptoms such as parasthesias,

dysesthesia Dysesthesia is an unpleasant, abnormal sense of touch. Its etymology comes from the Greek word "dys," meaning "bad," and "aesthesis," which means "sensation" (abnormal sensation). It often presents as pain but may also present as an inappropriate, ...

s, or

hyperalgesia Hyperalgesia ( or ; ''hyper'' from Greek ὑπέρ (''huper'') 'over' + ''-algesia'' from Greek ἄλγος (algos) 'pain') is an abnormally increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves and ...

in the affected nerve distribution including the distribution of the trigeminal nerve.

Additional images

References

Sources

* * * * * * * * * *

External links

Pigeons Detect Magnetic Fields
An experiment indicating that the trigeminal nerve in ''Columba livia'' may be the mechanism through which "homing pigeons" detect magnetic fields * ()
Trigeminal nerve anatomy, part 1
an
part 2
on

YouTube YouTube is an American social media and online video sharing platform owned by Google. YouTube was founded on February 14, 2005, by Steve Chen, Chad Hurley, and Jawed Karim who were three former employees of PayPal. Headquartered in ...

Trigeminal neuralgia
{{Authority control Cranial nerves Innervation of the face Medical mnemonics Otorhinolaryngology Neurology Nervous system Nerves of the head and neck Human head and neck

Structure

Origin

Trigeminal ganglion

Sensory branches

Dermatomes

Function

Muscles

Sensation

Sensory pathways

Summary

Trigeminal nuclei

Spinal trigeminal nucleus

Somatotopic representation

Principal nucleus

Mesencephalic nucleus

Pathways to the thalamus and cortex

Touch-position sensation

Pain-temperature sensation

Clinical significance

Lateral medullary syndrome

Sensory neuronopathy

Additional images

See also

References

Sources

External links