What are commissural fibers of the brain?
Commissural fibers of the brain, also known as commissural tracts of the brain or commissures are a type of white matter tract that cross the midline, connecting the same cortical area in opposite hemispheres (right-left hemispheric connections 3 ).
What is the commissure between the brain and spinal cord?
Commissures of the Brain The two halves of the brain and spinal cord are interconnected by numerous fibres that cross the middle line. In some situations such fibres form recognisable bundles that are called commissures. The corpus callosum is the largest commissure connecting the right and left cerebral hemispheres.
What is the commissure that connects the two cerebral hemispheres?
If one hand is trained to perform an act the other hand may not be able to do so. Other commissures connecting the two cerebral hemispheres are the anterior commissurethe posterior commissure the hippocampal commissure or commissure of the fornixand thehabenular commissure.
How are commissural connections formed in the brain?
In the brain of vertebrates, formation of commissural connections begins soon after closure of the neural tube.
What are the commissures of the brain?
Commissural fibers of the brain, also known as commissural tracts of the brain or commissures are a type of white matter tract that cross the midline, connecting the same cortical area in opposite hemispheres (right-left hemispheric connections 3).
What is the name of the largest commissure structure?
The corpus callosumThe corpus callosum is the largest commissural tract in the human brain. It consists of about 200-300 million axons that connect the two cerebral hemispheres.
What is the largest commissural nerve tract in humans?
the corpus callosumThe great majority of commissural tracts pass through the largest commissure the corpus callosum. A few tracts pass through the much smaller anterior and posterior commissures.
How many types of commissures are there?
The five are the anterior commissure, posterior commissure, corpus callosum, commissure of fornix (hippocampal commissure), and habenular commissure. They consist of fibre tracts that connect the two cerebral hemispheres and span the longitudinal fissure.
What is the white commissure?
The anterior or ventral white commissure is a collection of nerve fibers that cross the midline of the spinal cord and transmit information from or to the contralateral side of the brain. It is present throughout the length of the spinal cord and lies behind the anterior median fissure.
What is the anterior commissure of the brain?
The anterior commissure (also labeled ac) is a large bundle of crossing fibers, which connects the olfactory bulb and parts of the cerebrum to the same areas on the opposite side.
Is corpus callosum white matter?
The corpus callosum is the largest white matter structure in the brain, consisting of 200–250 million contralateral axonal projections and the major commissural pathway connecting the hemispheres of the human brain.
What is white matter called?
White matter, or substantia alba, refers to neural tissue in the form of densely packed bundles of myelinated nerve fiberss, typically found in the brain and spinal cord. As the name suggests, white matter is white in color.
What are the 4 lobes of the cerebrum?
The cerebrum consists of two cerebral hemispheres the outer layer called the cortex (gray matter) and the inner layer (white matter). There are four lobes in the cortex, the frontal lobe, parietal lobe, temporal lobe, occipital lobe. This review article will focus on the functions of the cerebral cortex.
Where is the gray commissure?
central canal of the spinal cordThe term gray commissure refers to the bridge of gray matter that contains the central canal of the spinal cord and connects the gray columns on either side of the spinal cord ( Carpenter-1983 ).
What is the function of anterior commissure?
The anterior commissure works with the posterior commissure to link the two cerebral hemispheres of the brain and also interconnects the amygdalas and temporal lobes, contributing to the role of memory, emotion, speech and hearing. It also is involved in olfaction, instinct, and sexual behavior.
What is the difference between Connective and commissure?
“Commissure” is a noun, and it refers to a place where two parts of the body unite. For example, the “median commissure” of the brain is the collection of axons (white matter) where the two sides of the brain connect. “Connective” is an adjective, and it refers to something which attaches one thing to another.
Is the corpus callosum a commissure?
The corpus callosum is the largest set of commissural fibers in the brain and is a pathway of crucial importance to speech-language functions (Fig. 2-10, B). The corpus callosum serves as the major connection between the hemispheres and conveys neural information from one hemisphere to the other.
What is the fornix?
The fornix is a white matter bundle located in the mesial aspect of the cerebral hemispheres, which connects various nodes of a limbic circuitry and is believed to play a key role in cognition and episodic memory recall.
What is a commissure in medical terms?
1 : a point or line of union or junction especially between two anatomical parts (such as adjacent heart valves) 2 : a connecting band of nerve tissue in the brain or spinal cord.
Where is the gray commissure?
central canal of the spinal cordThe term gray commissure refers to the bridge of gray matter that contains the central canal of the spinal cord and connects the gray columns on either side of the spinal cord ( Carpenter-1983 ).
Which receptor is responsible for the selective recognition of synaptic partners?
Finally, recent analysis of the sensorimotor connectivity in mice deficient for Sema3E and its high-affinity receptor Plexin-D1 illustrates another original contribution of the Sema3 signaling in the selective recognition of synaptic partners ( Pecho-Vrieseling et al., 2009 ). This ligand receptor pair controls the targeting of subsets of sensory afferences from the dorsal root ganglia to precise motoneuron pools of the spinal cord. Given the expression profiles of Sema3's in specific pools of spinal motoneurons, this function could be shared by other Sema3 members ( Cohen et al., 2005 ).
What are the two interhemispheric circuits of tetrapods?
Tetrapods are characterized by having at least two distinct routes of interhemispheric telencephalic circuits, namely the anterior and the hippocampal commissures ( Fig. 2 ). However, precisely when in evolutionary time these commissural routes became anatomically distinct remains inconclusive, but most likely occurred before the origin of tetrapods. Interhemispheric circuits in the telencephalon of the spotted African lungfish ( Protopterus dolloi ), a distant relative of modern tetrapods, include an anterior commissure, which connects mostly olfactory-recipient and subpallial regions, and a more dorsal commissural bundle that connects both hemispheres of the medial pallium, a region considered putative homologue of the hippocampal formation ( Fig. 1; Northcutt, 2009; Northcutt and Westhoff, 2011 ). Teleost fish, a more distant group, are characterized by the developmental eversion of their telencephalic hemispheres, where the medial pallium out-folds during development to adopt a lateral position ( Meek and Nieuwenhuys, 1998; Northcutt, 2008; Nieuwenhuys, 2009 ). Interestingly, commissural fibers connecting the “lateralized” hippocampal homologue of goldfish cross the midline within the dorsalmost extent of the anterior commissure ( Northcutt, 2006 ), suggesting that fibers of the hippocampal commissure were originally present within the anterior commissure. Whether a distinct hippocampal commissure is present in older lineages, such as cartilaginous fish, remains unknown. Nevertheless, it is likely that early tetrapods underwent exaptation of developmental mechanisms regulating axon guidance and fasciculation within the anterior commissure, resulting in the dorsal separation of axons of the hippocampal commissure.
Do vertebrates have commissural connections?
All animals with a bilateral body plan have commissural connections between both sides of the nervous system. The cellular and molecular events involved in the formation of commissures share remarkable similarities across vertebrates and invertebrates, suggesting the conservation of axon guidance mechanisms for more than 600 million years ( Brose et al., 1999; Brose and Tessier-Lavigne, 2000; Hirth and Reichert, 2007; Round and Stein, 2007; Arendt et al., 2008; Semmler et al., 2010; Evans and Bashaw, 2012 ). However, which features of commissural formation were present in the common ancestors of all bilaterians and which originated independently in different lineages are not well understood. Elucidating this will require detailed comparisons combining molecular, developmental, anatomical, and functional features across species.
Do behavioral results indicate that subsystems are lateralized?
Note that, taken alone, such behavioral results do not suffice to indicate the extent to which the subsystems are lateralized or the degree to which they are modular. They only indicate that at least relatively independent subsystems are involved and that they are at least weakly lateralized. Further investigations utilizing additional methodologies are needed to clarify the unresolved issues. For example, further methods are needed to determine whether one subsystem operates in only one hemisphere, whether both subsystems operate with asymmetric efficiency in each hemisphere, etc.
Do axonal projections cross the midline?
Axonal projections from any particular area are not necessarily restricted to cross the midline through just one commis sural route. For example, commissural neurons from olfactory-recipient regions in the brain of sharks send axons that decussate through multiple routes, such as the anterior, the habenular, and the posterior commissures ( Smeets, 1998; Northcutt, 2011; Yáñez et al., 2011 ). Similarly, commissural projections from adjacent regions of the main and accessory olfactory bulbs cross the midline through the distant habenular and anterior commissures, respectively ( Halpern, 1976; Ulinski and Peterson, 1981; Martinez-Garcia et al., 1991; Lohman and Smeets, 1993; Lanuza and Halpern, 1997; Moreno et al., 2005; Patzke et al., 2011; Northcutt and Rink, 2012; Atoji and Wild, 2014 ). Therefore, one possible scenario for the differentiation of axonal routes is that both pathways were present in the ancestor and then became distinct in the daughter lineages. Alternatively, new routes could also arise de novo in a lineage-specific manner from nonmaladaptive modifications of developmental events. For example, a remarkable medial-to-lateral rerouting of axons has been described in the accessory olfactory system of South American caviomorph rodents, suggesting that axonal routes can be altered and established in a lineage-specific manner, without apparent functional detriment ( Suárez and Mpodozis, 2009; Suárez et al., 2011, 2012 ). Therefore, it is tempting to speculate that the routes taken by axons can be subjected to evolutionary variability as long as the functional circuits are conserved.
What is brain storm?
a kind of storm in the brain, which is caused by the excessive signaling of nerve cells, and in these patients, the brain storm was prevented from spreading to the other hemisphere when the corpus callosum was cut off.
Which hemisphere is specialized in different tasks?
The studies demonstrated that the left and right hemispheres are specialized in different tasks. The left side of the brain is normally specialized in taking care of the analytical and verbal tasks. The left side speaks much better than the right side, while the right half takes care of the space perception tasks and music
