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EFFECTS OF THE LABYRINTHS ON THE CERVICAL 

MUSCLE TONUS 



S. I. Stepanova 



Translation of "K Voprosu O Vliyanii Labirintov 
Na Tonus Sheynykh Myshts. " Voprosy Aviatsionnoy Medi- ^ 
tsiny, Narmal'noy i Patologicheskoy Fiziologii (Problems of Avia-^ 
tion Medicine, and of Normal and Pathological Physiology), "Tsentral'- 
nyy Institut Usovershenstvovaniya Vrachey" Press, Moscow, 1966, ppl20- 

129. 



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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 MAY 1968 



NASA TT F-11, 615 



EFFECTS OF THE LABYRINTHS ON THE CERVICAL 

MUSCLE TONUS 



S. I. Stepanova 



ABSTRACT. Demonstration that the electromyographic tonus 
of the sternocleidomastoid muscles of intact rabbits is equally 
strong on both sides and that it weakens considerably on the 
operated side and remains essentially unaffected on the intact 
side after unilateral labyrinthectomy. This observation is 
consistent with the findings of Magnus (1924). 



It has been known for a long time that the labyrinths influence the muscles 
of the limbs and neck and, in some animals, the trunk muscles. 

To express this relationship, Ewald (1892) introduced the concept of the 
^^labyrinthotonus^' (rf muscle& into^physiology and established^an experimental 
basis for it. Later Magnus (1924) examined the mechanisms of this influence 
in more detail. He performed numerous experiments on guinea pigs, rabbits, 
cats, dogs and monkeys, and also examined neurological patients. As a re- 
sult he showed that the labyrinths influence the tone of the limb and trunk 
muscles in two ways: directly and secondarily. 

The direct influence is mediated by tonic labyrinthine reflexes; reflexes 
from one labyrinth act with equal strength on the limbs of both sides. 

In rabbits and cats the labyrinths also have a direct influence on the 
trunk muscles. 

Magnus also observed that after unilateral labyrinthectomy a consider- 
able weakening of the tone of the limbs on the side of operation takes place 
in all species of animals, and this effect lasts from a few hours to a few 
weeks depending on the species of animal. He interpreted it as a direct re- 
sult of extirpation of the labyrinth, but could not connect it with the action of 
a definite labyrinthine reflex. 

The secondary (in Magnus's words, very intensive) effect is mediated by 
the direct action of the labyrinths on the cervical muscles which, in turn, regu- 
late the tone of the limb (and trunk in guinea pigs , dogs and monkeys) muscles 
through ceivical tonic and stato-kinetic reflexes. 

According to Magnus the labyrinths exert their influence on the neck mus- 
cles by means of tonic labyrinthine reflexes. One labyrinth influences only the 
ipsilateral cervical muscles. After removal of one labyrinth the tone of tlae 



/120* 



* Numbers in margin indicate pagination in foreign text. 



neck muscles which rotate the neck and incline it to the side of the intact 
labyrinth disappears, regardless of their anatomical position on either side of 
the neck. As a result the classical signs of unilateral labyrinthectomy appear: 
rotation and inclination of the head primarily toward the side of the absent 
labyrinth. 

Rotation of the head also takes place after exclusion of proprioceptive cer- 
vical reflexes, this being evidence of a direct influence of the labyrinths on the 
neck musculature. 

Later investigations have mainly confirmed the connection between the 
muscles of different parts of the bocfy and the labyrinths. 

Fulton, Liddell and Rioch (1930), for instance, showed that injury to the 
vestibular nuclei in cats lowers the tone of the quadriceps femoris muscle on 
the side of injury. As a result of subsequent decerebration of these animals /121 

the rigidity and the reflex of the quadriceps femoris muscle to stretching 
were much lower on the side of injury than on the intact side. 

Bach and Magoun (1947) confirmed the observations of the previous work- 
ers: in decerebrate cats unilateral destruction of Deiters' nucleus causes dis- 
appearance of rigidity of the limb muscles on the side of injury. 

According to the findings of Ward (1950), preliminary distruction of the 
vestibular nuclei on one side causes asymmetry of the subsequent decerebrate 
rigidity in a cat as follows: strong extension of the fore- and hind limbs on 
the side contralateral to the injury with rotation of the whole trunk to this 
side. Extensor rigidity on the homolateral side was much less marked. 

Kempinsky and Ward (1950) studied the effect of unilateral division of the 
vestibular nerve on motor responses of the flexor and extensor of the leg 
caused by stimulation of the motor cortex in cats. As a result a marked de- 
crease or, in many cases, disappearance of the bacl^round movements of the 
limbs was found on both sides. 

Gernandt and Thulin (1953) showed that each vestibular apparatus has an 
equally strong facilitatory influence on the spinal monosynaptic reflex of the 
leg flexors, the intensity of which diminishes appreciably on both sides after 
unilateral division of the vestibular nerve. 

Data obtained by all these authors confirm Ma^us's conclusion that the 
influence on each labyrinth on the limb muscles is equally strong on both 
sides. In their opinion, this influence is effected through the facilitatory 
region of the reticular formation along the Ireticulo- spinal tract. The vesti- 
bulospinal tracts are known to be uncrossed. The work of Ferraro, Pacella 
and Barrera (1940), of Lorente de No (1933) and others has proved the 
existence of numerous anatomical connections between the vestibular nuclei 
of both sides and the reticular formation. In addition, the work of Gernandt /122 

and Thulin has shown that local destruction of the funiculus ventralis in the 
lower thoracic or upper lumbar divisions, interrupting the vestibulospinal 
tract, has only a very slight action, and in many cases no action at all, on 
a tested spinal reflex. 



Gernandt and Thulin also showed that stimulation of the horizontal semi- 
circular canals in cats by rotation usually leads to a generalized strengthening 
of the tone of the limb muscles. Only in decerebrate cats in indiviudal cases 
is a marked reciprocal effect observed, disappearing after unilateral division 
of the vestibular nerve. These workers consider that the vestibular apparatus 
may also exercise reciprocal control over activity of the muscles through the 
reticular formation. 

Molnar (1 958) fully confirmed the findings of Gernandt and Thulin. He showed 
that as a result of stimulation of the semicircular canals of cats in a state of 
decerebrate rigidity by rotation, and also simultaneously with stimulation of 
the motor cortex, a generalized contraction of the muscles of the limbs and 
neck is observed. Only in "especially favorable conditions" did Molnar ob- 
serve reciprocal relationships between the flexors and extensors of the limbs, 
and also between the muscles on the right and left sides of the neck. Unilat- 
eral division of the vestibular nerve disturbed these reciprocal relationships 
and led to development of a generalized response from the muscles of the 
limbs and neck. I.Ya. KalinobskayaandYu. S. Yusevich (1963) studied the 
effect of unilateral caloric stimulation of the vestibular apparatus on the 
electrical activity of the limb and neck muscles in 8 healtiiy persons. As a 
result of stimulation the tone and electrical activity of the muscles increased 
on both sides, but in some cases to a greater degree on the side of stimula- 
tion. 

In most of the works cited above data relating to the influence of the 
labyrinths on the limb muscles are given. 

In the investigation now to be described, the influence of the vestibular 
apparatus on the tone of the sterno-cleido-mastoid muscles and the long 
spinal muscles was studied. The work was carried out on rabbits. As /123 

Magnus (1924) showed, rotation and inclination of the rabbit's head take 
place as a result of the activity of paired muscles: the sterno-cleido- 
mastoid, the longus colli muscle, and the six occipital muscles: the four 
recti and the two oblique. The long spinal muscles take part in rotation of 
the trunk in the lumbar region. 

Method . The animals were delabyrinthized unilaterally by Valentine's 
operation as described in Krause's monograph (1868). While the EMG was 
being recorded the rabbits wore a special overall and were fixed by its 
straps to a stationary support. The biopotentials of the muscles to be tested 
were recorded by leads applied to the skin surface (the "global" method of 
Yu. S. Yusevich, 1963). Yusevich states that "global" electromyography is 
a more adequate procedure for determining muscle function than the "local" 
method. The fact that in the global method no painful stimuli are applied to 
the animal, capable of producing reflex changes in the tone of the muscle to 
be tested, was important in our investigations. As Yusevich points out, 
electrophysiologists observe that even after a single insertion of a needle 
the reflex increase in tonic contraction of the muscle arising at the moment of 
puncture persists after removal of the needle. 

Circular silver electrodes 8 mm in diameter were used to record the bio- 
potentials. In the neck one electrode was applied to the point of attachment 
of the sterno-cleido-mastoid muscle to the mastoid process, and the other 2 



cm away from the first along the line of the muscle. To record the EMG of the 
long spinal muscles one electrode was applied at the level of the 12th rib, the 
other 2 cm posteriorly to the first. 

The skin at each point of application of the electrode was carefully shaved, 
leaving a hair-covered area between them. In this way the points of applica- 
tion of the electrodes were strictly standardized. When taking the EMG, the 
skin surface was coated with contact paste. 

To prevent possible changes in tone of the investigated muscles as a re- 
sult of application of the electrodes, we recorded the EMG 5 min after their 
application. 

The EMG was recorded on a "Galileo" ink-writing electrocardiograph with / . 

electroencephalographic attachment. ^ 

The winding speed of the paper tape during recording was 100 mm/sec, 
and the amplification used was from 100 to 25 jit V/ cm. The filters and time 
constant were chosen so as to reduce distortion to the minimum. 

We were of the opinion that an ink-writing oscillograph could be used for 
recording the EMG in this case, despite the fact that under these circum- 
stances the frequency of the muscle potentials as recorded by no means al- 
ways corresponds to their true frequency. 

There are definite indications in the literature (R. S. Person, 1962) that 
the frequency of the EMG should not be used to assess muscle function, for a 
relationship between muscle function and frequency of the EMG exists only 
in particularly rare cases. Moreover, under these conditions of recording, 
muscle function may be assessed from the amplitude of the waves on the 
electr omy ogr am . 

For the quantitative estimation of amplitude we used the method suggested 
by V. V. Usov (1961) for EEG analysis. The magnitude of the extreme am- 
plitude values is measured. The magnitude of the extreme amplitude values 
was taken to be the distance between two lines corresponding to the greatest 
positive and greatest negative values of the potentials in a time interval always 
of 0. 1 sec. 

It was impossible to choose the time interval in accordance with the 
frequency of the potentials, as Usov recommends, for the following reasons: 
a) as already mentioned, the true frequency of the muscle potentials could 
not be judged from the frequency recorded on the EMG; b) the frequency of 
the biopotentials on the EMG was difficult, and often impossible, to sound 
correctly because of the very low amplitude of many of the peaks. 

Since we digressed essentially from the method recommended by Usov, 
we had to assess its suitability in the modified form. 

Statistical analysis of the distribution of the extreme amplitude values 
of the EMG showed that their distribution is regular and close to normal. The 
histogram of distribution of the extreme amplitude values for 200 readings is 
shown in Fig. 1 and compared with the theoretical normal distribution curve. /125 



The arithmetic mean defines this type of distribution completely. To 
characterize the EMGs we used the arithmetic mean of 30 extreme amplitude 
values (V.V. Usov, 1961). 




Figure 1. Histogram of distribution of extreme amplitude 
values for 200 readings compared with theoretically calcu- 
lated normal distribution curve. Abscissa: extreme values 
of amplitude in mm. Ordinate: frequency. 



/126 



RESULTS 



Altogether 5 delabyrinthized rabbits were studied (operation on the left 
labyrinth in all cases) and 4 intact animals were used as controls. 



tion: 



The experimental rabbits were studied at the following times after opera- 

from the 8th to the 10th month after operation, 

during the 9th month after operation, 

during the 1st week after operation, 

during the 7th month after operation, 

from the 3rd to the 5th month after operation. 

In the course of the investigation of the tome of the sterno-cleido-mastoid 
muscles, 16 tests were performed on the delabyrinthized and 16 on the intact 



No. 


1: 


No. 


2: 


No. 


3: 


No. 


4: 


No. 


5: 



rabbits. Comparative data for the tone of the sterno-cleido- mastoid muscles 
in the delabyrinthized and intact rabbits are given in Fig. 2 and the results of 
their statistical analysis in Table 1. 



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Figure 2. Amplitudes of electromyograms of the sterno- 
cleido-mastoid muscles in jLtV: a) left, b) right; •, in 
intact rabbits; +, in delabyrinthized rabbits. 



As might be expected, there was no difference in electromyographic tone 
of the right and left sterno-cleido-mastoid muscles in the intact rabbits. Like- 
wise there was no difference in the tone of this muscle in the intact and delab- 
yrinthized rabbits on the right (the sound) side. 

The tone of the left sterno-cleido-mastoid muscle was much lower in the 
delabyrinthized rabbits than in the intact (difference 27. 1 ± 15. 5 \i V, probability 
99. 9%). Marked asymmetry of tone of the sterno-cleido-mastoid muscle was 
thus present in the delabyrinthized rabbits: it was greater on the right than 
on the left by 18. 76±13. ji V, with a probability of 99. 9%. 

Hence, as a result of unilateral delabyrinthization, no essential changes 
were found in the tone of the sterno-cleido-mastoid muscle on the sound side; 
however, a very significant decrease in the tone of this muscle was found on 
the side of the operation. 



/128 



TABLE 1. Results of Statistical Analysis of Comparative Data for Tone of 
Sterno-Cleido- Mastoid Muscles in Delabyrinthized and Intact Rabbits 



Details of Values 
Compared 


3 

1 

1 

CD 


Arithmetic mean of differ- 
ence with its mean error 


Value obtained t 

Value of t from tables with 
probability 95% 

Value of t from tables with 
probability 99. 9% 


Qualita- 
tive as- 
sess- 
ment of 
signifi- 
cance of 
differ- 
ence 


Confidence 
intervals 
for 
probability 
99. 9% 


Amplitude of EMG in 
intact rabbits (left) 


16 


0.009 
+1.86 


0.049 


2.13 


4.07 


difference 

not 
significant 




Amplitude of EMG in 
intact rabbits (right) 


16 


Amplitude of EMG in 
delabyrinthized rab- 
bits (left) 


16 


18.76 
+ 3.2 


5.86 


2.13 


4.07 


difference 
significant 


18. 76 juV 
-13/iV, i.e. 
from 5. 8 juV 
to 31. 8 juV 


Amplitude of EMG in 
delabyrinthized rab- 
bits (right) 


16 


Amplitude of EMG in 
intact rabbits (left) 


16 


27.1 
+ 4.2E 


6.4 


2.04 


3.65 


difference 
highly 
significant 


27.1 juV-15.5 
jUV.i. e. ,from 
11. 6 ^V to 
42. 6 juV 


Amplitude of EMG in 
delabyrinthized rab- 
bits (left) 


16 


Amplitude of EMG in 
intact rabbits (right) 


16 
16 


7.6 
+5.6 


1.34 
c 


2.04 


3.65 


difference 

not 
significant 




Amplitude of EMG in 
delabyrinthized rab- 
bits (right) 



NOTE. Amplitude of EMGs given in juV 



/129 



Contraction of the sterno-c lei do- mastoid muscle in the rabbit rotates the 
head to the same side (A. A. Ternet'ev, 1952). However, after unilateral de- 
labyrinthization the tone of the sterno-cleido-mastoid muscle on the side toward 
which the head rotates and inclines is lowered. 



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Figure 3. Amplitudes of electromyograms of long 
spinal muscles in jliV: a) left, b) right; •, in 
intact rabbits; + , in delabyrlnthized rabbits. 



Evidently the inclination and rotation of the head in this case take place on 
account of a redistribution of tone of the more powerful and numerous posterior 
cervical muscles. 



The degree of rotation and inclination of the head in the delabyrlnthized 
animals varied with the time elapsing after operation (rotation of head from 90 
to 15-20°). We do not consider tiiat our material is adequate for establishing a 
relationship between the degree of rotation and inclination of the head and the 
magnitude of the tone of the sterno-cleido-mastoid muscle. 



During investigation of the tone of the long spinal muscles 13 tests were 
carried out on intact rabbits and 9 on delabyrinthized rabbits. The results of 
the tests were given in Fig. 3. 

No statistically significant changes in the tone of these muscles were ob- 
tained after unilateral delabyrinthization. This result may have been due to 
technical errors: when taking the EMG we fixed the rabbit too rigidly in the 
lumbar region, as a result of which the natural distribution of tone of these 
muscles was disturbed. 

The results obtained are in agreement with Mg^nus's conclusions regard- 
ing the unilateral influence of the labyrinths on tone of the neck muscles. 



CONCLUSIONS 

1. The electromyographic tone of the sterno-cleido-mastoid muscles of 
intact rabbits is the same on the right and left sides. 

2. Unilateral division of the 8th nerve causes a marked decrease in tone 
of the sterno-cleido-mastoid muscle on the side of the operation. 

3. The tone of the sterno-cleido-mastoid muscle on the sound side is not 
significantly changed after unilateral delabyrinthization. 

4. The results are evidence in favor of the unilateral influence of the 
labyrinths on tone of the sterno-cleido-mastoid muscle. 



REFERENCES 

I. Ya. Kalinovskaya and Yu. S. Yusevich. Zh. Nevropatol. i Psikhiat. im. 

S. S. Korsakova, Vol. 3, No. 5, p. 668, 1963. 
R. S. Person. "Some problems of interpretation of electromyographic data. " 

Proc, Conf. on Methods of Physiol. Invest, of Man, Moscow, p. 138, 1962. 
A. A. Terent'ev et al. The Rabbit, Moscow, 1952. 

V. V. Usov. Fiziol. Zh. SSSR im. Sechenova, Vol. 47, No. 5, pp. 665-666, 1961. 
Yu. S. Yusevich. Electromyography of the Tone of Himian Skeletal Musculature 

Under Normal and Pathological Conditions, Moscow, 1963. 
L. Bach and H.J. Manoun. Neurophysiol. Vol. 10, p. 331, 1947. 
I. Ewald. Physiologische Untersuchungen Uber das Endorgan den Octavus, 

Wiesbaden, 1892. 

A. Ferraro, B. L. Pacella and S. E. Barrera. J. comp. Neurol. Vol. 73, p. 7, 
1940. 

J. F. Fulton, F.I. Liddell and Rioch. Brain, Vol. 53, p. 327, 1930. 

B. E. Gernandt and C. A. Thulin, Am. J. Physiol. Vol. 172, p. 653, 1953. 
W. H. Kempinsky and A. A. Ward. J. Neurophysiol. Vol. 13, p. 295, 1950. 
W. Krause. Die Antomie des Kaninchen in topographischer und operativer 

RUcksicht. Leipzig, 1868. 
R. Lorente de No. Arch. Neurophysiol. und Psychiat. Vol. 30, 1933. 
R. Magnus. KOrperstellung. J. Springer Verl. , Berlin, 1924. 
L. Molnar. Arch. Psychiat. und Nerveiikrank. Vol. 197, p. 635, 1958. 
A. A. Ward. J. Neurophysiol. Vol. 13, 1950. 

Translated for the National Aeronautics and Space Administration by Scripta 
Technica, Inc., NASw-1694.