Projection fibers
Encyclopedia
The projection fibers consist of efferent and afferent fibers uniting the cortex
with the lower parts of the brain and with the spinal cord
.
strands are:
fibers are:
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
with the lower parts of the brain and with the spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
.
Efferent
The principal efferentEfferent
Efferent is an anatomical term with the following meanings:*Conveying away from a center, for example the efferent arterioles conveying blood away from the Bowman's capsule in the kidney. Opposite to afferent....
strands are:
- (1) the motor tract, occupying the genuGenuLatin for "knee", genu is a term commonly encountered in studies of anatomy. It is used to refer to several anatomical structures, including :* conditions affecting the knees, such as genu valgum and genu varum...
and anterior two-thirds of the occipital part of the internal capsuleInternal capsuleThe internal capsule is an area of white matter in the brain that separates the caudate nucleus and the thalamus from the lenticular nucleus. The internal capsule contains both ascending and descending axons....
, and consisting of- (a) the geniculate fibersGeniculate fibersThe geniculate fibers are the fibers in the region of the genu of the internal capsule; they originate in the motor part of the cerebral cortex, and, after passing downward through the base of the cerebral peduncle with the cerebrospinal fibers, undergo decussation and end in the motor nuclei of...
, which decussate and end in the motor nuclei of the cranial nervesCranial nervesCranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...
of the opposite side; and - (b) the cerebrospinal fibersCerebrospinal fibersThe cerebrospinal fibers, derived from the cells of the motor area of the cerebral cortex, occupy the middle three-fifths of the base; they are continued partly to the nuclei of the motor cranial nerves, but mainly into the pyramids of the medulla oblongata....
, which are prolonged through the pyramid of the medulla oblongata into the medulla spinalis:
- (a) the geniculate fibers
- (2) the corticopontine fibersCorticopontine fibersCorticopontine fibers are projections from the cerebral cortex to the pontine nuclei.Depending upon the lobe of origin, they can be classified as frontopontine fibers, parietopontine fibers, temporopontine fibers and occipitopontine fibers....
, ending in the nuclei pontis.
Afferent
The chief afferentAfferent
Afferent is an anatomical term with the following meanings:*Conveying towards a center, for example the afferent arterioles conveying blood towards the Bowman's capsule in the Kidney. Opposite to Efferent.*Something that so conducts, see Afferent nerve fiber...
fibers are:
- (1) those of the lemniscusLemniscusA lemniscus is an anatomic term. It can refer to:* In anatomy, a part of the brain, such as the medial lemniscus or lateral lemniscus...
which are not interrupted in the thalamusThalamusThe thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
; - (2) those of the superior cerebellar peduncle which are not interrupted in the red nucleusRed nucleusThe red nucleus is a structure in the rostral midbrain involved in motor coordination. It comprises a caudal magnocellular and a rostral parvocellular part.-Function:...
and thalamusThalamusThe thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
; - (3) numerous fibers arising within the thalamusThalamusThe thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
, and passing through its stalks to the different parts of the cortexCerebral cortexThe cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
; - (4) optic and acoustic fibers, the former passing to the occipitalOccipitalThe word occipital, in zoology, pertains to the occiput .Occipital is a descriptor for several areas of animal & human anatomy.*External occipital protuberance* Internal occipital crest* Greater occipital nerve...
, the latter to the temporal lobeTemporal lobeThe temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
.