File Name: cranial nerves anatomy and clinical comments .zip
- Cranial Nerves - Anatomy, Clinical Signs and Study
- Trigeminal nerve
- Cranial nerves
- Cranial Nerves: Anatomy and Clinical Comments
Cranial Nerves - Anatomy, Clinical Signs and Study
The trigeminal nerve the fifth cranial nerve , or simply CN V is a nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves. The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory or "cutaneous" functions.
The motor division of the trigeminal nerve derives from the basal plate of the embryonic pons , and the sensory division originates in the cranial neural crest. Sensory information from the face and body is processed by parallel pathways in the central nervous system. The three major branches of the trigeminal nerve—the ophthalmic nerve V 1 , the maxillary nerve V 2 and the mandibular nerve V 3 —converge on the trigeminal ganglion 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 ganglia of the spinal cord, which contain the cell bodies of incoming sensory fibers from the rest of the body. From the trigeminal ganglion, a single, large sensory root portio major enters the brainstem at the level of the pons.
Immediately adjacent to the sensory root, a smaller motor root portio minor emerges from the pons at the same level. Motor fibers pass through the trigeminal ganglion without synapsing on their way to peripheral muscles, but their cell bodies are located in the nucleus of the fifth nerve, deep within the pons.
The areas of cutaneous distribution dermatomes 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 , such as lidocaine , 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:.
The ophthalmic, maxillary and mandibular branches leave the skull through three separate foramina : the superior orbital fissure , the foramen rotundum and the foramen ovale , respectively. The ophthalmic nerve V 1 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 the dura and blood vessels.
The maxillary nerve V 2 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 V 3 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 is responsible for taste , one of its branches—the lingual 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. The sensory function of the trigeminal nerve is to provide tactile, proprioceptive , and nociceptive afference to the face and mouth.
Its motor function activates the muscles of mastication , the tensor tympani , tensor veli palatini , mylohyoid and the anterior belly of the digastric.
The trigeminal nerve carries general somatic afferent fibers 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 SVE axons , which innervate the muscles of mastication via the mandibular V3 division. The motor component of the mandibular division V3 of the trigeminal nerve controls the movement of eight muscles, including the four muscles of mastication : the masseter , the temporal muscle , and the medial and lateral pterygoids.
The other four muscles are the tensor veli palatini , the mylohyoid , the anterior belly of the digastric and the tensor tympani. 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 , 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. 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. Sensation in this context refers to the conscious perception of touch-position and pain-temperature information, rather than the special senses 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 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. 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 and the vestibular 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 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. Thalamic nuclei, in turn, send information to specific areas in the cerebral cortex. Each pathway consists of three bundles of nerve fibers connected in series:. The secondary neurons in each pathway decussate 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 is the primary cause of decussation; nasal fibers of the optic nerve cross so each cerebral hemisphere receives contralateral—opposite—vision to keep the interneuronal 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 and cerebral cortex. This information contributes to the final output of the cells in Main V to the thalamus.
Touch-position information from the body is carried to the thalamus by the medial lemniscus , and from the face by the trigeminal lemniscus both the anterior and posterior trigeminothalamic tracts. Pain-temperature information from the body is carried to the thalamus by the spinothalamic tract , and from the face by the anterior division of the trigeminal lemniscus also called the anterior trigeminothalamic tract.
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. 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 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. Anatomical differences between the pathways for touch-position perception and pain-temperature sensation help explain why pain, especially chronic pain, is difficult to manage.
All sensory information from the face, both touch-position and pain-temperature, is sent to the trigeminal nucleus. 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 meninges is carried by general somatic afferent fibers in cranial nerves VII the facial nerve , IX the glossopharyngeal nerve and X the vagus nerve.
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 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.
The spinal trigeminal nucleus represents pain-temperature sensation from the face. 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 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.
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 V 1 , upper lip V 2 and mouth V 3 and remove pain-temperature sensation from the forehead V 1 , cheeks V 2 and chin V 3. 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 thalamus and sends information to the mesencephalon and the reticular formation 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 -containing compounds found in plants in the onion family stimulate receptors found in trigeminal ganglia, bypassing the olfactory system. The principal nucleus represents touch-pressure sensation from the face.
Jennifer L. J Athl Train 1 July ; 45 4 : — To present the case of a National Collegiate Athletic Association Division I men's lacrosse athlete with fourth cranial nerve injury as the result of a minor traumatic blow. The athlete was struck on the right side of his head during a lacrosse game. On-field evaluation revealed no cervical spine involvement or loss of consciousness. He complained of headache and dizziness, with delayed reports of visual disturbance.
If your institution subscribes to this resource, and you don't have a MyAccess Profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus. Please consult the latest official manual style if you have any questions regarding the format accuracy. The olfactory nerves transmit smell information through the cribriform plate to the olfactory bulbs and tracts, which in turn transmit this information to the olfactory cortex in the medial temporal lobes.
Cranial nerve , in vertebrates, any of the paired nerves of the peripheral nervous system that connect the muscles and sense organs of the head and thoracic region directly to the brain. Lower vertebrates fishes, amphibians have 10 pairs. A 13th pair, a plexus branching network known as the terminal nerve CN 0 , is sometimes also recognized in humans, though whether it is a vestigial structure or a functioning nerve is unclear. Cranial nerves are made up of motor neurons , sensory neurons, or both. They are named for their function or structure; for example, the trigeminal nerve consists of three primary branches, while the vestibulocochlear nerve serves the organs of equilibrium and hearing.
Clinical Anatomy of the Cranial Nerves combines anatomical knowledge, pathology, clinical examination, and explanation of clinical findings, drawing together material typically scattered throughout anatomical textbooks. All of the pertinent anatomical topics are conveniently organized to instruct on anatomy, but also on how to examine the functioning of this anatomy in the patient.
Cranial Nerves: Anatomy and Clinical Comments
Diffusion imaging tractography caught the attention of the scientific community by describing the white matter architecture in vivo and noninvasively, but its application to small structures such as cranial nerves remains difficult. The few attempts to track cranial nerves presented highly variable acquisition and tracking settings. To conduct and present a targeted review collecting all technical details and pointing out challenges and solutions in cranial nerve tractography. We selected studies that reported how to perform the tractography of cranial nerves, and extracted the following: clinical context; imaging acquisition settings; tractography parameters; regions of interest ROIs design; and filtering methods. Twenty-one published articles were included. These studied the optic nerves in suprasellar tumors, the trigeminal nerve in neurovascular conflicts, the facial nerve position around vestibular schwannomas, or all cranial nerves.
The trigeminal nerve the fifth cranial nerve , or simply CN V is a nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves. The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory or "cutaneous" functions. The motor division of the trigeminal nerve derives from the basal plate of the embryonic pons , and the sensory division originates in the cranial neural crest. Sensory information from the face and body is processed by parallel pathways in the central nervous system.
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