anatomyphysiologyblog - White Matter of Cerebrum : Projection, Commissural in addition to Association fibers
WHITE MATTER OF CEREBRUM
The white affair of the cerebral hemisphere basically contains 2 components
- myelinated nervus fibers of many sizes*
- neuroglia (mostly oligodendrocytes)
*This authorities annotation solely describes dissimilar types of myelinated nervus fibers.
The white affair of the cerebral hemisphere are of iii types:
- commissural fibers
- association fibers
- projection fibers
The commissural fibers interconnect the corresponding regions of the 2 cerebral hemispheres. They are equally follows:
- Corpus callosum
- Anterior commissure
- Posterior commissure
- Fornix
- Habenular commissure
The corpus callosum comprises the largest packet of fibers; almost of these arise from parts of the neocortex of 1 cerebral hemisphere too sack inward the corresponding parts of the reverse cerebral hemisphere. It lies at the bottom of the longitudinal fissure. It is divided into from earlier backwards into
- The rostrum, a sparse lamina of nervus fibers that connects the articulatio genus to the upper terminate of the lamina terminalis
- The genu, the curved anterior terminate
- The body or trunk which arches posteriorly too ends equally the thickened enlargement called
- The splenium.
Traced laterally, the fibers of the articulatio genus flexure forwards into the frontal lobes too shape the forceps minor. The fibers of the body extend laterally equally the radiation of the corpus callosum. The fibers from the splenium runs backward into the occipital lobe too shape the forceps major.
The anterior commissure is situated inward the anterior wall of the 3rd ventricle at the upper terminate of the lamina terminalis. The fibers passing through the commissure interconnect the olfactory bulbs of the 2 cerebral hemisphere. Other fibers interconnect the parahippocampal gyri too other parts of the temporal lobe.
Posterior commissure
It lies inward the inferior lamina of the stem of the pineal gland straightaway inward a higher house the opening of the cerebral aqueduct into the 3rd ventricle.
Fornix
It is a prominent packet of fibers seen on the medial facial expression of the cerebral hemisphere. It is made upwardly of fibers arising from the hippocampus. The body of the fornix is suspended from the corpus callosum past times septum pellucidum. The nervus fibers arise from the alveus, a sparse layer of white affair roofing the surface of the hippocampus too thence converge to shape the fimbria. The fimbriae shape the posterior column or crus of the fornix arching below the corpus callosum. The 2 crura thence come upwardly together inward the midline to shape the body of the fornix. The 2 crura are interconnected past times fibers passing from 1 to the other – hippocampal commissure or commissure of the fornix which genuinely joins the 2 hippocampus. The anterior terminate of the body of fornix likewise divides into anterior columns or pillars. Each anterior column of the fornix turns downward but inward forepart of the interventricular foramen too passess through the hypothalamus to accomplish the mamillary body.
Habenular commissure
It is a little packet of nervus fibers that cross the midline inward the superior stem of the pineal gland. The commissure is associated amongst the habenular nucleus.
2. Association Fibers
These fibers connect the diverse cortical regions of a cerebral hemisphere. These fibers allow the cortex to component subdivision equally a coordinated whole.
Types of Association fibers
Short association fibers, or U fibers, connect side past times side gyri.
Types
Long association fibers connect to a greater extent than widely separated areas.
Types
2. Association Fibers
These fibers connect the diverse cortical regions of a cerebral hemisphere. These fibers allow the cortex to component subdivision equally a coordinated whole.
Types of Association fibers
Short association fibers, or U fibers, connect side past times side gyri.
Types
- intracortical fibers - located inward the deeper portions of the white affair too
- subcortical fibers - located but beneath the cortex
Long association fibers connect to a greater extent than widely separated areas.
Types
- The uncinate fasciculus connects the inferior frontal lobe gyri amongst the anterior temporal lobe.
- The cingulum, a white band inside the cingulate gyrus, connects the frontal too parietal lobe amongst the parahippocampal gyrus.
- The arcuate fasciculus sweeps or thence the insula too connects the superior too middle frontal convolutions (which incorporate the speech communication motor area) amongst the temporal lobe (which contains the speech communication comprehension area).
- The superior longitudinal fasciculus connects portions of the frontal lobe amongst occipital too temporal areas.
- The inferior longitudinal fasciculus, connects the temporal too occipital lobes.
- The occipitofrontal fasciculus extends backward from the frontal lobe, radiating into the temporal too occipital lobes.
3. Projection Fibers
These fibers connect the cerebral cortex amongst lower component subdivision of the encephalon or brainstem too the spinal cord, inward both directions.
The corticopetal (afferent) fibers include
- the geniculocalcarine radiation from the lateral geniculate body to the calcarine cortex,
- the auditory radiation from the medial geniculate body to the auditory cortex, and
- the thalamic radiations from the thalamic nuclei to specific cerebrocortical areas
The corticofugal (efferent) fibers continue from the cerebral cortex to the thalamus, encephalon stem, or spinal cord.
Internal Capsule
Most of the nervus fibers interconnecting the cerebral cortex amongst centers inward the brainstem too spinal cord, too amongst the thalamus transcend through the interval betwixt the thalamus too caudate nucleus medially too lentiform nucleus laterally. This part at the upper terminate of the brainstem shape a compact band too is called the internal capsule. Above, the internal capsule is continuous amongst corona radiate and below, amongst the crus cerebri of midbrain.
As seen on the horizontal section, the internal capsule consists of
- The anterior limb lies betwixt caudate nucleus medially too the anterior component subdivision of the lentiform nucleus laterally
- The posterior limb lies betwixt the thalamus medially too the posterior component subdivision of the lentiform nucleus laterally
- And the genu where both limb meets.
In addition, some fibers of the internal capsule prevarication behind the posterior terminate of the lentiform nucleus constituting its retrolentiform part whereas another fibers transcend below the lentiform nucleus (and non medial to it), found the sublentiform part.
Arrangement of fibers inside the internal capsule:
i. The fibers to too from the anterior component subdivision of the frontal lobe transcend through the anterior limb of the internal capsule.
ii. The fibers to too from the posterior component subdivision of frontal lobe too greater component subdivision of parietal lobe occupy articulatio genus too posterior limb of the internal capsule.
iii. Fibers to too from the temporal lobe (and lowest component subdivision of parietal lobe) occupy the sublentiform part.
Whereas those to too from the occipital lobe occupy the retrolentiform component subdivision of the internal capsule.
Ascending fibers inward the internal capsule:
These are predominantly thalamocortical fibers - from thalamus to all parts of the cerebral cortex too forming thalamic radiations or peduncles, equally given below:
These are predominantly thalamocortical fibers - from thalamus to all parts of the cerebral cortex too forming thalamic radiations or peduncles, equally given below:
Anterior thalamic radiations (or frontal thalamic peduncle)
- Pass through the anterior limb
- Fibers to the frontal lobe
- From anterior too medial thalamic nuclei
- Also carries fibers from hypothalamus too limbic structures
Superior thalamic radiations (superior or dorsal thalamic peduncle)
- Pass through the articulatio genus too posterior limb of the capsule
- To the somatosensory area
- From ventral posterior nuclei of the thalamus
- From thalamus to the occipital lobe
- Includes the eye radiations from lateral geniculate body to the visual cortex
- Lie inward the retrolentiform component subdivision of the internal capsule
- From thalamus to temporal lobe
- Includes acoustic radiations from medial geniculate body to the acoustic area
- Pass through the sublentiform component subdivision of the internal capsule
Descending fibers inward the internal capsule
These are equally follow:
Corticopontine fibers
Corticospinal too corticonuclear fibers
Corticonuclear fibers (for cranial nervus nuclei to caput too neck) transcend through the articulatio genus of the capsule.
Corticospinal fibers form several discrete bundles inward the posterior limb too are arranged from earlier backward – upper limb, body too lower limb.
Corticothalamic fibers are from cortex to thalamus too shape component subdivision of the thalamic radiation.
Corticopontine fibers
- Frontopontine fibers are the almost numerous - pass mainly through the anterior limb
- Parietopontine fibers mainly transcend through the retrolentiform component subdivision
- Temporopontine fibers from the sublentiform part
- Occipitoponitne fibers from the retrolentifrom part
Corticospinal too corticonuclear fibers
Corticonuclear fibers (for cranial nervus nuclei to caput too neck) transcend through the articulatio genus of the capsule.
Corticospinal fibers form several discrete bundles inward the posterior limb too are arranged from earlier backward – upper limb, body too lower limb.
Corticothalamic fibers are from cortex to thalamus too shape component subdivision of the thalamic radiation.
REFERENCES:
Gray’s Anatomy, 39th Edition
Snell’s Clinical Neuroanatomy seventh Edition
Lange Clinical Neuroanatomy 25th Edition