692 



CONDITIONS AFFECTING THE MOTOR CENTRES. 



of these areas is influenced by the stimulation of afferent nerves (Bubnoff and 

 Heidenhain) It may be that these centres are acted upon by voluntary impulses in 

 the execution of voluntary movements. Hence, they have been called "psychomotor 

 centres" r-Vt any rate, these areas have a definite relation to certain motor acts, 

 rc//c*. L j ^ perhaps it is well to speak of them as 



"areas of representation " of the function to 

 which they are related.] The motor areas 

 of the cerebrum (dog, cat, sheep) are charac- 

 terised by the presence of specially large 

 pyramidal cells (Betz, Merzejewsky, Bevan 

 Lewis) ; while similar cells were found by 

 Obersteiner in the areas marked 4 and 8 (fig. 

 483), and Betz found them in the ascending 

 frontal convolution of man, in the third 

 frontal convolution, and in the island of 

 ReiL O. Soltmann found that stimulation 

 of the motor areas in newly-born animals is 

 without result, while only the deeper fibres 

 of the corona radiata are excitable. 



Modifying Conditions. In the condition of deep 

 narcosis produced by chloroform, ether, chloral, 

 morphia, or in apnoea, the excitability of the centres 

 is abolished (Schiff), whilst the subcortical con- 

 ducting paths still retain their excitability {Bubnoff 

 and Heidenhain). Small doses of these poisons 

 and also of atropin at first increase the excitability 

 of the centres. Moderate loss of blood excites 

 them, while a great loss of blood diminishes and 

 then abolishes the excitability {Munk and Orschan- 

 sky). Slight inflammation increases, while cooling 

 fmnt.,1 InhP iTi.l diminishes, the excitability. If the cortex cerebri 

 iionui looe ana removed in animals, the excitability of the 

 the island of Red, the tip of the tempore- ' completely abolished 



sphenoidal lobe removed to show the " ~_ ", . ,, , . . . +v no x n a __ 

 latter. 17, convolution of the margin of about the fourth day just as the case o a per - 

 the longitudinal fissure ; 0, olfactory fis- P n heral n * rve separated from its centre (Albertoni, 

 sure, with the olfactory lobe removed ; Du ^ &** ?^^'Li v*r+ x n,* Ah 

 TR, triradiate fissure ; 1" and 1"', con- Stimulation of Subcortical Parts.-As the fibres 

 volutions on the orbital surface ; 1,1, 1, 1, <* the corona radiata converge towards the ^centre 

 under surface of the in fero- frontal con^ f J hemisphere, it is .evident that, after removal 

 volution; 4, undersurface of the ascending f the cortex stimulation of these fibres in the 

 frontal, and 5 of the ascending parietal deeper parts of the hemisphere is followed by the 

 convolutions ; C, central lobe or island. same . tor ^ s <"* and , Eckhard) The 



stimulus is applied merely to a deeper part of the 

 motor path. If the stimulus be applied to parts situated still more deeply, as for example to 

 the internal capsule, general contraction of the muscles on the opposite side is the result. 



Time Relations of the Stimulation. According to Franck and Pitres, the time which elapses 

 between the moment of stimulation of the cortex and the resulting movement, after de- 

 ducting the period of latent stimulation for the muscles, and the time necessary for the con- 

 duction of the impulse through the cord and nerves of the extremities, is 0*045 second. 

 Heidenhain and Bubnoff found that, during moderate morphia narcosis, when the stimulating 

 current was increased in strength, the muscular contraction and the reaction-time became 

 shorter. After removal of the cortex, the occurrence of the muscular contraction from the 

 moment of stimulation of the white matter is diminished \ to . The form of the muscular 

 contraction is longer and more extended when the cortex, than when the subcortical paths, are 

 stimulated. If the animal (dog) be in a state of high reflex excitability, these differences dis- 

 appear ; in both cases the contraction follows very rapidly {Bubnoff and Heidenhain). If the 

 stimulus be very strong the muscles of the same side may contract, but somewhat later than 

 those of the opposite side. If the motor areas for the fore and hind limbs be stimulated 

 simultaneously, the latter contract somewhat after the former. 



Number of Stimuli. If 40 stimuli per second be applied to a motor area, then the corre- 

 sponding muscles yield 40 single contractions ; while with 46 single stimuli per second there 

 results a continued complete contraction {Franck and Pitres). In one and the same animal, 



Fig. 4S1. 

 Orbital surface of the left 



