



























Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community for help and clear up your study doubts
Discover the best universities in your country according to Docsity users
Free resources
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
An overview of the anatomy of the superior colliculus in various species, focusing on the distribution of optic tract fibers and their connections. It discusses the central nucleus, fiber connections, and the role of the lateral lemniscus. The text also mentions the optic nerve and tract reduction in insectivores, and the contribution of other cell layers to the efferent paths.
What you will learn
Typology: Study notes
1 / 35
This page cannot be seen from the preview
Don't miss anything!
THOMAS N. JOHNSON' Laboratory o f Comparative Neurology, Departmmt of Amtomy, Un&versity of hfiehigan, Ann Arbor
INTRODUCTION This investigation is a study of the afferent and efferent
a well-drained, loose soil. It usually frequents open fields
larvae and adult insects are the more usual fare. It has been
moles will eat vegetable matter. It seems not improbable
A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the University of Michigan. 1952. 765
The single annual litter suggests that moles have few enemies. Their fossorial habits prevent hawks and owls from taking any considerable numbers in spite of the fact that the moles are active at all hours. Nevertheless they do
est power is exerted by the mole when the forefeet are thrust
digging the shallow burrows in which the soil is thrust up in a ridge. The mole rotates in its burrow and, thrusiing from below with one forefoot, raises the roof of the burrow
or nearly so, and repeats the process. I n excavation of deeper burrows, in which the roof cannot be elevated, only one fore- foot is used at a time, while the other is braced against the side of the burrow. The earth is loosened by lateral strokes of first one forelimb and then the other, the earth being
of such activity the mole then turns around in the newly formed burrow, the diameter of which is scarcely more than
thorax bent to one side and locomotion achieved by use of
pushing dirt out onto the surface. Under such conditions the hind limbs are performing the major part of the locomotor
gressing awkwardly by running with its hind legs while trying to support the heavy front part of the body on its outstretched front legs, which are in contact with the ground only on the edge of the thumb. The microscopic study shows a poorly developed optic
perior than inferior colliculus. The other afferent and efferent fiber connections of the midbrain generally conform to those of other insectivores, rodents and marsupials.
768 THOMAS N. JOHNSON
NUCLEAR PATTERN O F THE TECTUM
duced, 8 layers (figs. 4 and 5) can be distinguished in the optic
(1882) did not demonstrate this layer in the mole. It corre-
external cortico-tectal fibers. It corresponds to the oberflach-
THE FIBER CONNECTIONS OF THE TECTUM
on the ventral surface of the diencephalon. It is not possible
ABBREVIATIONS AQ., aqueduct. BRACH. CONJ.. brachium con.juncti- vum. colliculus.
BRACH. I.C., brachium of the inferior BRACH. PONT., brachium pontis. CEREBR. PED., cerebral peduncle. COMM. INF. COL., commissure of the DEC. BRACH. CONJ., decussation of DEC. TRAP. FIB., decussation of trape- D. COCH. NUC., dorsal cochlear nucleus. D. NUC. LAT. LEMN., dorsal nucleus
D. NUC. RAPHE, dorsal nucleus of
D. TEG. DEC., dorsal tegmeiital decus-
EXT. CORT. TECT., external cortico.
HAB. PED. TR., habenulo-peduncular HYPOTHAL., hypothalamus. INF. COL., inferior colliculus. INF. THAL. RAD., inferior thalamic INT. CORT. TECT., internal cortico-
inferior colliculus. the brachium con junctivum. zoid fibers.
of the lateral lemniscus. raph6. sation. tectal tract. tract.
radiations. tectal tract. cleus.
INTERPED. NUC., interpeduncular nu- LAT. GEN. NUC., lateral geniculate nucleus. LAT. LEMN., lateral lemniscus. LAT. TECT.-SP., lateral tecto-spinal tract. nucleus.
MED. GEN. NUC., medial geniculate MED. LEMN.. medial lemniscus. MED. TECT.:SP., medial tecto-spinal M.L.F., medial longitudinal fasciculus. N1G.-TECT., nigro tectal tract. NUC., nucleus. NUC. DESC. RT. TRIG., nucleus of the descending root of the trigeminal. NUC. FAC., nucleus of facial nerve. NUC. TNF. COL., nucleus of the inferior colliculus. NUC. OCUL. N., nucleus of oculomotor nerve.
tract.
NUC. TROCH. N., nucleus of troehlear OP. CH., optic chiasm. OP. TR., optic tract. PERIV. GR., periveiitricular gray. PONS, pons. PONT. GR., pontine gray. PRETECT. AREA, preteetal area. PYR., pyramid. REST. BOD., restiform body. R. NUC., red nucleus. RT. FAC., root of the facial nerve. RT. TRIG. N., root of the trigeminal S. NIGRA, substantia nigra. SP.-TECT., spino-tectal tract. STR. ALB. PROF., stratum album pro- STR. ALB. INTERMED., stratum al-
nerve.
nerve.
fundum. bum intermediale. STR. GRIS. INTERMED.. stratum eri- seum intermediale. periventriculare.
STR. GRIS. PERIV., stratum griseum STR. GRIS. PROF., stratum griseuni prof undum. seum sunerficiale.
STR. GRIS. SUPERFIC., stratum gri- STR. OP+., stratum opticum. STR. ZON., stratum zonale. SUP. COL., superior colliculus. SUP. OL., superior olive. SUP. THAL. RAD., superior thalamic TECT.-NIGR., tecto-nigral tract. TECT.-PONT., tecto-pontine tract. TECT.-RUBR., tecto-rubral tract. TECT.-TEG., tecto-tegmental fibers. TRAP. FIB., trapezoid fibers. VENT. CAUD. NUC. LAT. LEMN., v&ntral caudal nucleus of lateral lem- V. COCH. NUC., ventral cochlear nu- cleus. VENT., ventricle. V. SEC. ASC. TR. TRIG., ventral sec- ondary ascending tract of trigeminal. V. TEG. DEC., ventral tegmental decus- sa tion. X. INC., zona ineerta.
radiations.
111scus.
connections with the ventral nucleus of the lateral geniculate body in the cat, although it is true that many of these fibers pass through this nucleus as they approach the dorsal nucleus.
contributed fibers to the nucleus of the basal optic root and to the lateral geniculate nucleus, continues dorsocaudad (figs.
INF. THAL. RAD.
VENT. HYPOTHAL. Fig. 2 Photomicrograph of a transverse section passing through the rostra portion of the dieneeplialoii of the mole at the level of the optic chiasm. Silver preparation. X 30.
minate in the superior colliculus. As the optic fibers approach the superior colliculus, they divide so that some of them enter the tectum laterally and the others enter it medially, to repeat the pattern of mammalian optic fiber terminations in the tectum. The number of fibers contributed to the su- perior colliculus is very slight, nevertheless the superior
the nasal quadrants to the posteromedial portions of the superior colliculus ; the upper quadrants are projected laterad to the lower quadrants. Brouwer and Zeeman ('26) were unable to establish the pattern of projection of the retina on the superior colliculus of the cat because, according to their own statement, their material was not adequate. How-
quadrants on the superior colliculus of the rabbit and found that the lower quadrants are projected to oral and medial
regions. He implied that the .superior colliculus is of much higher significance f o r sight in rabbits than in higher mam-
in these rodents.
prominent in the mole with large numbers of fibers passing by way of the lateral lemniscus to distribute to the inferior colliculus, where, after relay, they distribute by the peduncle of the inferior colliculus to the medial geniculate nucleus of the thalamus.
form body in the opossum but this is not their position in the mole where they occupy positions typical f o r most mammals.
to the inferior cerebellar peduncle. The fibers arising from this nucleus are both crossed and uncrossed. Some of the fibers curve around the dorsal border of the inferior cerebellar peduncle, others pass through the peduncle ; these fibers then turn ventromediad towards the raph6. Many of them accumu- late in the lateral lemniscus of the same side, which lies at
the facial nerve and the motor nucleus of that nerve ventrally. The decussating fibers cross the midline dorsal to the g e m of
servers (as Ariens Kappers, Huber and Crosby, '36) refer to the inferior colliculus as an auditory reflex center which receives auditory impulses and then discharges to the su- perior colliculus and the medial geniculate nucleus, a meta- thalamic auditory center mediating impulses to the cerebral cortex. Mettler ( '32) studied the effects of lesions in the
certain of the axis cylinders in the brachium of the inferior colliculus do not stop in the medial geniculate bodies but pass
lesions in the inferior colliculus of guinea pigs and cats and suggested that some fibers pass directly from the inferior colliculus to the cerebral cortex. The present material fur- nished no satisfactory evidence for direct colliculo-cortical fibers.
The spino-tectal tract occupies a position in the lateral funiculus of the spinal cord adjacent to the spino-thalamic
material. This tract ascends through the spinal cord to enter
which it maintains at lower medullar levels. At such levels in the mole it lies ventromedial to the spino-thalamic tract and to the nucleus of the descending root of the trigeminal.
through the medulla ventromedial to the nucleus of the de-
internal arcuate fibers as they swing into the sensory decus- sation. At the level of the inferior olivary nucleus it lies lateral to this olivary nucleus, ventromedial to the nucleus of the descending root of the trigeminal, and in proximity to the ventral secondary ascending tract of the latter. Cerebello- olivary and olivo-cerebellar fibers passing towards the resti- form body overlie the tract and the external arcuate fibers
oblongata. The spino-tectal tract continues its rostral course with the lateral spino-thalamic and ventral secondary ascend- ing tract of the trigeminal, along the dorsolateral portion of the olive, ventromedial to the secondary ascending tract
lateral region of the medulla throughout the level of the
ventrolateral to the descending root of the trigeminal. At the level of the g e m of the facial nerve and the decussating dorsal cochlear fibers, the spino-tectal tract lies lateral to the superior olivary nucleus, medial to the descending root of the trigeminal, and lateral to the root of the facial nerve
the pons, the medial lemniscus is horizontal in position but
these pathways. At the caudal levels of the superior colliculus the fibers of the spino-tectal tract course dorsad in the lateral
entering its stratum album intermediale. These fibers are mingled with fibers from the ventral secondary ascending tract of^ the trigeniinal in their passage towards the tectum.
medial lemniscus has turned dorsolateralward with the ventral secondary ascending tract of the trigeminal on its dorsomedial
tip of the medial lemniscus in the cat. Crosby and Henderson ('48) found that the spino-tectal fascicles form the uppermost
levels and that these fibers of the spino-tectal system swing
to the stratum album profundum.
to enter the tecturn (fig. 6 ) by the intermediate white layer
then continue forward to the thalamus, medial to the medial lemniscus. Woodburne ( '36) described the trigeminal com- plex in a series of vertebrates and found that in the rabbit
ascending tract of the trigeminal enter the tectum of the superior colliculus. Huber et al. ('43) also maintained that collaterals of the ventral secondary ascending tract of the
the spino-thalamic and the main fascicles of the ventral secondary ascending tract of the trigeminal terminate di- rectly in the ventral nucleus of the dorsal thalamus.
Two groups of fibers, the internal and the external cortico- tectal tracts, enter the superior colliculus from the cerebral cortex. Beevor and Horsley ( '02) described occipito-mes- encephalic fascicles in the monkey as composed of large fibers which stand out distinctly from the medium-sized, occipito- thalamic fibers and which pass to the entire extent of the stratum griseum profundum of the superior colliculus. They also demonstrated temporo-mesencephalic fibers in the cat passing primarily from the posterior limb of the ecto-Sylvian gyrus to distribute to the superior colliculus. They did not determine the termination of the latter fibers in the superior colliculus. Crosby and Henderson ( '48) identified external and internal cortico-tectal pathways in the macaque. These
mesencephalic tracts, respectively, of Beevor and Horsley ('02). Crosby and Henderson traced the external cortico- tectal fibers in their course along the optic pathways; they subdivided the internal system into a dorsal and a ventral division. I n the mole, the internal cortico-tectal fibers from the pre- occipital and occipital areas of the cerebral cortex enter the diencephalon as part of the superior thalamic radiations (fig.
the diencephalon the more dorsomedial fibers of the internal capsule are joined by more lateral bundles which swing across the other internal capsule fibers in a dorsomedial direction. Thus a common internal cortico-tectal system is maintained which proceeds dorsocaudalward. Behind the habenula the
EXT. CORT. TECT. PRETECT, AREA
Pig. 3 Photomicrograph of a transverse section through the posterior third of the diencephalon of the mole showing the optic tract fibers to the lateral geniculate nucleus and the lateral geniculate nucleus. Ailver preparation. X 30.
synapse, and to the tectum, which they enter by the inter- mediate white stratum (fig. 4). These fibers cannot be traced from their origin in the cerebrum; they can only be demon- strated from the region where they enter the diencephalon to the tectum. The external cortico-tectal fibers enter the diencephalon from the temporal lobe by a sublenticular path and join the
tract, toward the lateral geniculate nucleus where a large nnmber of the optic tract fibers enter this nucleus. Beyond
The chief nucleus of the inferior colliculus is directly con- tinuous with the periventridar gray of the superior collicu- lus. The acustico-optic fibers are short, thin, medullated and unmedullated fibers which are found in the nucleus of the inferior colliculus and extend rostralward in the periventricu- lar gray of the superior colliculus to synapse with the den- drites of the periventricular layer. These could not be photographed satisfactorily although they are demonstrable in the material.
The medial tecto-spinal fibers arise from the deep gray
by the stratum album profundum, pass ventrally around the periventricular gray to cross to the opposite side in the dorsal tegmental decussation and then to attain a position ventral to the medial longitudinal fasciculus (fig. 6). Rasmussen ('36), working with cats, produced lesions in the superior and inferior colliculi which caused degeneration of the medial
lesion below the dorsal tegmental decussation, indicating
plane of the nucleus of the lateral lemniscus and found no degeneration in the medial tecto-spinal tract. Papez and
('25b), working with the opossum, reported that the tecto- spinal tract (apparently the medial tecto-spinal of the present account) arises from the entire length of the tectum and that
arises from the entire length of the tectum in different animals
After its decussation, the medial tecto-spinal tract passes caudad through the tegmentum of the midbrain and the pons
in a position ventral to the medial longitudinal fasciculus
tecto-spinal tract is found near the midline on each side of the raph6 (fig. 10) and maintains this position in the medulla oblongata to a level through the caudal end of the inferior
it reaches the level of the motor decussation. At the upper levels of the spinal cord the tract enters the ventral funiculus medial to the ventral horns and ventral to the medial vestibu-
extent in the cord has not been determined.
Fig. 5 Photomicrograph of a transverse section through the anterior third of the superior colliculi and the medial geniculate nuclei of the mole. The hrachium of the inferior eolliculus should be noted. (^) Weil stain. X 30.