Anterior, superior and posterior auricular
muscles were studied electromyographically by
means of wire electrodes. During ear movement
the three muscles acted as a group and the
movement was always directed upwards and
backwards. The highest electrical activities
were observed during natural smiling and
yawning. Mouth opening without the drawing
backwards of the comissura labiorum and the
displacement of galea aponeurotica also produced
electrical activity by the auricular muscles,
with however, less intensity and in only 50% of
the cases studied.
Introduction
Very little has been published on the
cutaneous musculature. As far as the extrinsic
muscles of the ear (anterior auricularis,
superior auricularis and posterior auricularis)
are concerned, we only found the work of Serra
et al. (1986), who studied the posterior
auricularis muscle in lesions of the facial
nerve but did not focus on its kinesiology.
The anatomy textbooks tell us that the
anterior auricularis muscle draws the ear
forward, the superior auricularis muscle draws
it upward and the posterior auricularis muscle
draws it backward. However, most of the authors
considered them in humans as rudimentary muscles
of little or no importance (Testut and Latarjet
1929; Gardner et al. 1960; Rouviere 1970; Orts
Llorca 1970). Lockhart et al. (1965) stated that
the auricular muscles act together, but only to
a limited extension. Chiarugi (1948), Gray
(1973) and Goss (1977) described them as acting
as a group together with the occipitofrontalis
muscle.
Since the specific literature on this
subject is insufficient and the descriptions of
their actions in textbooks conflicting, we have
decided to study the anterior, superior and
posterior auricular muscles in man
electromyographycally.
Material and methods
The anterior, superior and posterior right
auricular muscles (a.m.) of 30 male volunteers,
from 19 to 25 years old, were the subjects of
our EMG study.
The potential of the muscular activity was
recorded with wire electrodes, according to
Sumitsuji et al. (1965). Such electrodes consist
of steel wires (full hard) with a diameter of
0.08 mm and a length of 15 cm which were
introduced manually through the skin into the
muscle being studied. This procedure was
facilitated by the absence of a fascia in the
mimic muscles. The electrode was connected to
the electromyograph by a special spring
connector for fine-wire electrodes (Basmajian et
al. 1966).
The three auricular muscles were analysed
while earring of the following facial movements
or assuming the expressions described:
moving the ear: upward, backward and
forward
smiling naturally
yawning
opening the mouth to maximum extent without
drawing in the comissura labioruin.
closing the eyelids: naturally and
forcefully
opening the eyelids: naturally and
forcefully
making vertical wrinkles on the
forehead.
displacing the galea aponeurotica
posteriorly by attempting to contract the venter
occipitalis
displacing the ga/eu aponeurotica anteriorly
by attempting to contract the venter
frontalis
lowering the eyebrows
blinking the eyes.
Displacement of the ga/eu aponeurorica was
detected by gently placing the observer's
fingertips on this region.
Results
Among 30 volunteers, only 16 could move
their ears when asked, of whom only 6 achieved
it from a rest position and 10 just managed to
move the auricle after lifting the eyebrows. The
ear was always displaced upward and backward; at
the same time in 10 volunteers, the movement was
more upward than backward and in 6, more
backward than upward. In al 16 cases the action
potentials were strong, concomitant and
equivalent in the three muscles regardless of
whether the ear moved in a more backward or more
upward direction.
Action potentials were observed in all 3
auricular muscles during natural smiling and
yawning.
Very tiny displacements of the ear backward
and upward, with slight predominance of the
latter, were observed in 28 volunteers during
natural smiling.
The displacement of the galea aponeurotica
backward was achieved by only 16 volunteers, and
in 13 of these cases a strong simultaneous
electrical potential could be recorded from the
auricular muscles.
It is noteworthy that the volunteers always
tended to raise their eyebrows before trying to
execute movements of the ear or of the galea
aponeurolica.
Discussion
Isolated movements of the ear upward,
forward and backward, as described in anatomy
textbooks, have not been observed. In 16
volunteers, small combined displacements in an
upward and backward direction were observed
concomitantly, and in these cases the three
auricular muscles acted as a group. This agrees
partially with Lockhart et al. (1965) but in
contrast to him we found high action potentials
with some movements in spite of the limited
displacement of the ear.
The synchronised upward and backward
movement of the ear could be explained by the
combined action of the three auricular muscles
(am.). The contractions produce three forces
applied simultaneously to the ear, as can be
seen in Fig. 1. Since F1 (anterior a.m.) and F3
(posterior a.m.) are approximately in the same
plane but act in opposite directions they tend
to cancel each other out if they are exerting
the same force, thus living only the action of
F2 (superior a.m.). The resultant of these
forces would then tend to displace the ear
upward. But if F3 is slightly stronger than F1
the resultant would pull the ear upward and
backward.
Originally we intended to study
electromyographically only the muscular actions
suggested in the literature. Nevertheless,
during the experimental procedures, unforeseen
spontaneous movements with strong action
potential in the three auricular muscles were
observed during natural smiling and
yawning.
Activity of the auricular muscles was also
observed in 50% of the individuals studied when
the galea aponeurotica was displaced forwards.
These results agree with Chiarugi, Gray and
Goss, suggesting an interaction between the
occipital muscle and the extrinsic auricular
muscles.
In conclusion, the results presented
showed that the a.m. are not just rudiments,
since they show marked action potentials in
relation to certain movements of the ear and
face.
