Cross references: Motor Neuron Evolution Corticospinal Tract
Medial Motor Column Wikipedia Extrapyramidal Revision
Extrapyramidal system (Wiki)
"In human anatomy , the extrapyramidal system is a neural network that is part of the motor system that causes involuntary reflexes and movement, and modulation of movement (i.e. coordination). The system is called "extrapyramidal" to distinguish it from the tracts of the motor cortex that reach their targets by traveling through the " pyramids " of the medulla . The pyramidal pathways ( corticospinal and some corticobulbar tracts) may directly innervate motor neurons of the spinal cord or brainstem ( anterior (ventral) horn cells or certain cranial nerve nuclei), whereas the extrapyramidal system centers around the modulation and regulation (indirect control) of anterior (ventral) horn cells.
Extrapyramidal tracts are chiefly found in the
and target neurons in the spinal cord involved in reflexes, locomotion,
complex movements, and postural control. These tracts are in turn
modulated by various parts of the central nervous system, including the
, and different sensory areas of the
All of these regulatory components can be considered part of the
extrapyramidal system, in that they modulate motor activity without
directly innervating motor neurons.
The extrapyramidal tracts include parts of the following:
I'm interested in correlating the tracts listed in Wikipedia, above, with the tracts identified by Herrick in Brain of the Tiger Salamander .
To start, there's no indication that salamanders have a rubrospinal tract . In fact, looking up "Nucleus" in the Index yields " - ruber, 45, 177". In the second paragraph of page 45, he says "No primordium of the nucleus ruber or of the inferior olive has been recognized. ", and, similarly, in the third paragraph of page 177, he says: "No evidence has been found of a concentration of cells related with it which could be regarded as a nucleus ruber.".
In contrast with Herrick's inability to find anything that could be called a rubrospinal tract , he was able to identify, not only a clearly defined tectospinal tract , but also numerous other tracts originating in the Tectum and terminating in structures which then project on to the spinal cord. The only figure illustrating his specifically named tectospinal tract (his notation: tr.t.sp.; tr.tec.sp., tractus tecto-spinalis) for which I have so far provided Figure Labels is :
BTS Fig 006 p. 329 .
However page 394 of Figure Abbreviations and page 408 of the Index list 15 other tracts originating in the Tectum , many of which may be considered indirect components of the tectospinal tract .
Page 408 of the Index also says " tecto-spinalis; see Tractus tecto-bulbaris", and the same page says
"tecto-bulbaris et spinalis, 186, 219, 224, 226, 277, 303 ;
tecto-bulbaris posterior, 165, 188, 214 ;
tecto-bulbaris rectus, 168, 188, 189, 225, 284" ,
so the existence of a tectospinal tract in the tiger salamander seems well established.
On page 402 of the Index , Herrick lists "Formatio reticularis, 44, 61, 64, 79, 126, 155, 156, 162, 206". However, the Index doesn't list any tracts originating in the Reticular Formation , and the Reticular Formation itself is not listed in Figure Abbreviations . Looking at the pages specified in the Index :
Page 44: "The motor field of the Medulla Oblongata and the intimately related Reticular Formation contain the complicated apparatus by which the nuclei of the motor nerves are so interconnected as to act in groups, each of which may execute a series of co-ordinated actions in patterns determined by these connections."
Page 61: "In the spinal cord and Medulla Oblongata the peripheral motor neurons are so mingled with the co-ordinating neurons of the tegmentum and Reticular Formation and they are so similar in form that it is often impossible to distinguish the peripheral neurons except in cases where their axons are seen to enter the nerve roots."
Page 64: "... throughout the length of the spinal cord and brain there is a band of tissue between the sensory and motor zones primarily concerned with these adjustments. At lower levels I have termed this tissue the " Reticular Formation " ..."
Although the above quotes are from only three of the nine pages on which Herrick discusses the Reticular Formation , They seem adequate to establish its location within the Medulla Oblongata .
So, where's the reticulospinal tract ?
Hiding in plain sight.
One might think that, since the Reticular Formation is located within the Medulla Oblongata , an alternative name might be the "medullospinal" tract, but it isn't. The Index says "Medulla oblongata, 22, 42, 118, 153", and on page 22 Herrick says "The medulla oblongata, on the other hand, is a stable structure, extending from the isthmus to the spinal cord, and for it the shorter name "bulb" is sometimes used, especially in compounds.". Sure enough, under "Tractus", the Index lists:
"bulbo-isthmialis, 164, 168, 187",
"bulbo-spinalis, 156, 162",
"bulbo-tectalis lateralis; see Lemniscus, lateral" and
So we've identified one direct and three indirect reticulospinal tracts in the salamander. This leaves the vestibulospinal tract as the last element of the Extrapyramidal System to be looked for.
The vestibulospinal tract was easy to find. The Index , under "Tractus" lists "vestibulo-spinalis, 161". On page 161, Herrick says "There is, accordingly, a dorsal vestibulo-spinal connection by both peripheral and secondary fibers, a connection which puts the vestibular apparatus into especially intimate relation with the neuropil of the nucleus funiculi."
Cholinergic vs. noncholinergic efferents from the mesopontine tegmentum to the extrapyramidal motor system nuclei. - 1988 (PubMed)
Characteristics of fast and slow corticobulbar fibre projections to reticulospinal neurones. - PubMed
No PubMed Abstract:
but there is a Google Abstract
"The brain stem reticular formation is an important structure transmitting extrapyramidal influences to the spinal cord. This transmission is realized predominantly through pontine reticular nuclei and nucleus reticularis gigantocellularis of the medulla; axons of many of the neurones of these nuclei project in a descending direction.
Morphological data have shown that the gigantocellular nucleus consists of large, medium and small reticular neurones. The variability of the size of the neurones is reflected in differences in axon diameter and conduction velocities.
In cats the conduction velocities of reticulospinal fibres are very different. Magni and Willis have shown that conduction velocities in 90% of reticulospinal neurones range from 90 to 130 m/sec, Wolstencroft showed their conduction velocity to be 20 to 138 m/sec and lto et al. found that the mean value was 100 m/sec.
Three functional groups of reticulospinal fibres in the thoracic ventral funiculus which responded to stimulation of the medullary reticular formation were found. The conduction velocities for these groups were 65-110, 45-60 and 20-40 m/sec, respectively.
Analysis of the EPSPs evoked in reticulospinal neurones of the nucleus reticularis gigantocellularis by stimulation of the cerebral cortex shows that the EPSPs appear through mono and polysynaptic corticoreticular pathways. Monosynaptic activation is due to both fast and slow corticobulbar fibres. Data concerning monosynaptic projections of different types of corticobulbar fibres to reticulospinal neurones in nucleus reticularis gigantocellularis with different axon conduction velocities are presented in this paper. Special attention was paid to the search for correlations between conduction velocities of reticulospinal neurones and of the corticobulbar fibres to these neurones.
Experiments were performed on cats anaesthetised with Nembutal (30 mg/kg) or chloralose (60 mg/kg). The head of the animal was fixed in a stereotaxic apparatus according to Horsley-Clarke coordinates. After fixation the cat was laminectomised at C2-C4; the cerebellum was ablated and the pericruciate regions of the cerebral cortex were exposed. Bipolar stimulating electrodes were implanted into the ipsilateral internal capsule and red nucleus. They were fixed to the cranium by wax. For cortical stimulation bipolar isolated electrodes with tips placed 1 mm apart were used."
The statement, "transmission is realized predominantly through pontine reticular nuclei and nucleus reticularis gigantocellularis", is very important to me. I need to follow this thread.
See also: Reticulospinal Transmission .
Although there was no PubMed Abstract, there were 120 PubMed Related citations:
CotA - Extrapyramidal System
130908 - 0844
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