Fiber Tractography

Fiber tractography is the neurological procedure to study neuron axons tracts in a human brain using magnetic resonance imaging techniques and computer-based image analysis. A fiber tractography test can be shown in either two dimensional or three dimensional images. In the cerebrum the myelinated neuron axons of the cerebral cortex cluster together to form fibers, and these get together to form thick bundles or tracts called fasciculus which connect one lobe or region of the cortex with another. Thus, there is a complicated three-dimensional network formed by short connections among different cortical and subcortical regions.


The existence of these bundles has been revealed by histochemistry and biological techniques on post-mortem specimens. Brain tracts are not identifiable by direct exam, CT, or MRI scans. This difficulty explains the paucity of their description in neuroanatomy atlases and the poor understanding of their functions. The magnetic resonance imaging (MRI) sequences used look at the symmetry of brain water diffusion. Bundles of fiber tracts make the water diffuse asymmetrically in a tensor, the major axis parallel to the direction of the fibers. The asymmetry here is called anisotropy. There is a direct relationship between the number of fibers and the degree of anisotropy.

Inferior Longitudinal fasciculus

The inferior longitudinal fasciculus is a bundle of myelinated axons which connects the occipital lobe with the temporal lobe in each hemisphere of the cerebrum. It runs parallel to the lateral walls of the inferior and posterior cornua of the lateral ventricle. Some anatomists call this bundle of fibers "occipitotemporal projection system." The function of the inferior longitudinal fasciculus is highly involved in visual memory as a 47-year-old woman with visual memory disturbance, demonstrated by the Wechsler Memory Scale-Revised, suffered from brain tumor in the right temporal lobe that disrupted the fibers bundle of the ILF. Disruption of white matter integrity in the inferior longitudinal fasciculus in teenagers with schizophrenia was also revealed by fiber tractography.

Superior Longitudinal Fasciculus

The superior longitudinal fasciculus is a thick and long bundle of myelinated axons which links the frontal lobe to the occipital, and part of the parietal and temporal lobes of each cerebral hemisphere. The association fibers that constitute the superior longitudinal fasciculus are bi-directional, which means that some axons originate in cortical neurons of the frontal lobe, while others in neurons located in the occipital and back regions of the temporal and parietal lobes, integrating motor and decision-making centers with visual and sensory ones. The superior longitudinal fasciculus sweeps along the superior margin of the claustrum in a great arc.

The superior longitudinal fasciculus consists of three distinct components: 1) SLF I is the dorsal component and originates in the superior and medial parietal cortex, passes around the cingulate sulcus and terminates in the dorsal and medial cortex of the frontal lobe and in the supplementary motor cortex; 2) SLF II is the major component of SLF and originates in the caudal-inferior parietal cortex and occipital lobe, ending in the dorsolateral prefrontal cortex (Brodmann 6, 8 and 46); 3) SLF III is the ventral component which begins in the supramarginal gyrus (rostral portion of the inferior parietal lobe) and ends in the ventral premotor and prefrontal cortex (Brodmann 6, 44, and 46).

Occipitofrontal Fasciculus

The occipitofrontal fasciculus is a bundle of association fibers which connects the frontal lobe with the occipital lobe of each brain hemisphere. The myelanated fibers that make up the occipitofrontal fasciculus radiate in a fan-like manner, extending into occipital and temporal lobes, lateral to the posterior and inferior cornua.

Uncinate Fasciculus

The uncinate fasciculus is a band of cortical neuron myelinated axons in the human brain that connects the inferior part of the frontal lobe with the anterior temporal lobe and parts of the limbic system, such as the hippocampus and amygdala that are located in this lobe. It is the last fasciculus to mature in the brain (beyond the age of 30). The average length of the uncinate fasciculus is 45 mm. It has three parts: a frontal extension, an intermediary segment, and a temporal segment. The uncinate fasciculus is a hook-shaped tract of fibers which go from the inferior frontal gyrus and the lower surfaces of the frontal lobe to the forward portions of the temporal lobe.

Uncinate Fasciculus and Schizophrenia

Evidence suggests that a disruption in connectivity between different brain regions, especially between the frontal and temporal lobes, linked up by the uncinate fasciculus, may partly explain some of the primary symptoms of schizophrenia. This idea, first proposed by Wernicke in 1906, posits a disturbance in functional connectivity between the frontal and temporal cortices in schizophrenia that might have as its basis a disruption in the white matter tracts connecting them. Abnormalities within the fiber bundles of the uncinate fasciculus associate with social anxiety, Alzheimer's disease, bipolar disorder, and depression in the elderly that had first had it in adolescence or early adulthood. Such abnormalities also link to schizophrenia.

Arcuate Fasciculus

The arcuate fasciculus is the thick bundle of myelinated axons which links the Broca's area to the Wernicke's area, which are the two language centers of the brain. Thus, the arcuate fasciculus fibers go from the inferior frontal gyrus of the frontal lobe to the back area of the superior temporal gyrus and a small area in the parietal lobe and vice versa. The function of this bundle of nerve fibers is to articulate or coordinate the motor verbal function of the Broca's area and the semantic and syntactic comprehension of the Wernicke's area. Damage to the arcuate fasciculus can cause a form of aphasia known as conduction aphasia, where auditory comprehension and speech articulation are preserved, but people find it difficult to repeat heard speech.

Hypoglossal Nerve (CN XII)

Also known as CN XII, the hypoglossal nerve is the twelfth of twelve paired cranial nerves. The CN XII innervates the muscles of the tongue. It is a somatomotor nerve whose fibers originate in the hypoglossal nucleus neurons situated in the dorsal medulla oblongata of the brainstem. The hypoglossal nucleus nerve cells send axons that exit as rootlets that emerge in the ventrolateral sulcus of the medulla between the olive and pyramid. Then, the rootlets come together to make up the hypoglossal nerve, exiting the cranium through the hypoglossal canal.

As the CN XII comes out of the hypoglossal canal, it gives off a small meningeal branch, picking up a branch from the anterior ramus of C1. Then, it spirals behind the vagus nerve and passes between the internal carotid artery and internal jugular vein lying on the carotid sheath. After passing deep to the posterior belly of the digastric muscle, the hypoglossal nerve passes to the submandibular region to enter the tongue.

Accessory Nerve (CN XI)

The accessory nerve is the eleventh of the twelve paired cranial nerves. It is also known as cranial nerve XI (CN XI). It is called accessory since it receives an accessory root from the upper part of the spinal cord as it emerges from the skull. The spinal fibers of the accessory nerve provides motor innervation from the central nervous system to two muscles of the neck: the sternocleidomastoid muscle and the trapezius muscle. The cranial part rapidly joins the vagus nerve and serves the same function as other vagal nerve fibers.

Although it originates in the central nervous system, the spinal accessory nerve begins outside the skull rather than inside, with its axonal fibers arising from neurons located in the upper spinal cord, near the medulla oblongata. These fibers coalesce to form the spinal accessory nerve, which enters the skull through the foramen magnum, the large opening at the base of the skull. Then the nerve runs along the inner wall of the skull towards the jugular foramen, through which it exits the skull together with the glossopharyngeal (CN IX) and vagus nerves (CN X). Thus, the accessory nerve is notable for being the only cranial nerve to both enter and exit the skull.

Vagus Nerve (CN X)

Also known as cranial nerve X (CN X), the vagus nerve is one of the twelve paired cranial nerves. Consisting of both motor and sensory fibers, the vagus nerve emerges from the medulla oblongata in the groove between the olive and the inferior peduncle. Then, it projects through the jugular foramen, passing into the carotid sheath between the internal carotid artery and the internal jugular vein down below the head, to the neck, chest and abdomen, where it contributes to the innervation of the viscera. Besides output to the various organs in the body the vagus nerve conveys sensory information about the state of the body's organs to the central nervous system. Between 80 and 90% of the fibers that make up the vagus nerve are sensory nerves communicating the state of the viscera to the brain.

The vagus nerve also supplies motor parasympathetic fibers to all the organs except the suprarenal glands, from the neck down to the second segment of the transverse colon. This means that the vagus nerve is responsible for such varied tasks as heart rate, gastrointestinal peristalsis, sweating, and quite a few muscle movements in the mouth, including speech (via the recurrent laryngeal nerve) and keeping the larynx open for breathing, via action of the posterior cricoarytenoid muscle, the only abductor of the vocal folds. It also has some afferent fibers that innervate the inner (canal) portion of the outer ear, via the Auricular branch, which also known as Alderman's nerve, and part of the meninges. This explains why a person may cough when tickled on their ear (such as when trying to remove ear wax with a cotton swab).

Glossopharyngeal Nerve (CN IX)

The Glossopharyngeal nerve is the ninth cranial nerve (CN IX). It consists of both motor and sensory fibers and emerges from the brain stem as the most rostral of a series of nerve rootlets that protrude between the olive and inferior cerebellar peduncle. The CN IX supplies the tongue, throat, and one of the salivary glands (the parotid gland). Problems with the glossopharyngeal nerve result in trouble taste and swallowing. Compared with other lower cranial nerves, the glossopharyngeal nerve (GPhN) is well hidden within the jugular foramen, at the infratemporal fossa, and in the deep layers of the neck. "Glosso-" comes from the Greek "glossa", the tongue and "pharynx" is the Greek for throat. So the glossopharyngeal nerve is the nerve that serves the tongue and throat.

Glossopharyngeal Nerve Overview.
 

The glossopharyngeal nerve consists of five components with distinct functions: Brancial motor (special visceral efferent) - supplies the stylopharyngeus muscle. Visceral motor (general visceral efferent) provides parasympathetic innervation of the smooth muscle and glands of the pharynx, larynx, and viscera of the thorax and abdomen. Visceral sensory (general visceral afferent) carries visceral sensory information from the carotid sinus and body. General sensory (general somatic afferent) provides general sensory information from the skin of the external ear, internal surface of the tympanic membrane, upper pharynx, and the posterior one-third of the tongue. Special sensory (special afferent) provides taste sensation from the posterior one-third of the tongue.

Glossopharyngeal Nerve (Video)

Privacy Policy

Privacy Policy for Science, Natural Phenomena & Medicine

If you require any more information or have any questions about our privacy policy, please feel free to contact us by email at ademecah@gmail.com.

At Science, Natural Phenomena & Medicine, the privacy of our visitors is of extreme importance to us. This privacy policy document outlines the types of personal information is received and collected by Science, Natural Phenomena & Medicine and how it is used.

Log Files
Like many other Web sites, Science, Natural Phenomena & Medicine makes use of log files. The information inside the log files includes internet protocol ( IP ) addresses, type of browser, Internet Service Provider ( ISP ), date/time stamp, referring/exit pages, and number of clicks to analyze trends, administer the site, track user’s movement around the site, and gather demographic information. IP addresses, and other such information are not linked to any information that is personally identifiable.

Cookies and Web Beacons
Science, Natural Phenomena & Medicine does use cookies to store information about visitors preferences, record user-specific information on which pages the user access or visit, customize Web page content based on visitors browser type or other information that the visitor sends via their browser.

DoubleClick DART Cookie
.:: Google, as a third party vendor, uses cookies to serve ads on Science, Natural Phenomena & Medicine.
.:: Google's use of the DART cookie enables it to serve ads to users based on their visit to Science, Natural Phenomena & Medicine and other sites on the Internet.
.:: Users may opt out of the use of the DART cookie by visiting the Google ad and content network privacy policy at the following URL - http://www.google.com/privacy_ads.html

Some of our advertising partners may use cookies and web beacons on our site. Our advertising partners include ....
Google Adsense


These third-party ad servers or ad networks use technology to the advertisements and links that appear on Science, Natural Phenomena & Medicine send directly to your browsers. They automatically receive your IP address when this occurs. Other technologies ( such as cookies, JavaScript, or Web Beacons ) may also be used by the third-party ad networks to measure the effectiveness of their advertisements and / or to personalize the advertising content that you see.

Science, Natural Phenomena & Medicine has no access to or control over these cookies that are used by third-party advertisers.

You should consult the respective privacy policies of these third-party ad servers for more detailed information on their practices as well as for instructions about how to opt-out of certain practices. Science, Natural Phenomena & Medicine's privacy policy does not apply to, and we cannot control the activities of, such other advertisers or web sites.

If you wish to disable cookies, you may do so through your individual browser options. More detailed information about cookie management with specific web browsers can be found at the browsers' respective websites.

Vestibulocochlear Nerve (CN VIII)

The vestibulocochlear nerve, also known as cranial nerve VIII (CN VIII), is composed of sensory fibers which carry two types of sensory information to the brain: balance and hearing. It is the 8th of the twelve cranial nerves. The vestibulocochlear nerve is made up of bipolar neuron axons and splits into two branches: 1) the vestibular nerve, which carryies sensory information about balance; 2) the cochlear nerve, carrying information about hearing. The CN VIII enters the brain stem at the junction of the pons and medulla, lateral to the facial nerve. The auditory component of the eighth nerve terminates in a sensory nucleus called the cochlear nucleus, which is located at the junction of the pons and medulla. The vestibular part of the CN VIII ends in the vestibular nuclear complex located in the floor of the fourth ventricle.

Facial Nerve (CN VII)

The facial nerve is the seventh cranial nerve (CN VII). It is a paired nerve with both motor and sensory functions, providing motor innervation to the muscles of facial expression and sensory information of taste sensations from the anterior two-thirds of the tongue and oral cavity. It also supplies preganglionic parasympathetic fibers to several head and neck ganglia. The CN VII originates in the facial nerve nucleus in the pons while the sensory part of it arises from the nervus intermedius. It emerges from the brainstem between the pons and the medulla.

The motor fibers of the facial nerve innervate all the facial musculature; the principal muscles are the frontalis, orbicularis oculi, buccinator, orbicularis oris, platysma, the posterior belly of the digastric, and the stapedius muscle. The sensory fibers has the following components: 1) taste to the anterior two-thirds of the tongue; 2) secretory and vasomotor fibers to the lacrimal gland, the mucous membranes of the nose and mouth, and the submandibular and sublingual salivary glands; 3) cutaneous sensory impulses from the external auditory meatus and region back of the ear.