The intrinsic laryngeal muscles of rats have myomyous junctions

1
The intrinsic laryngeal muscles of rats have
myomyous junctions T Yamagata, M Hyodo, A Okada
and J Desaki Dept of Otolaryngology and
Anatomy, Ehime University School of Medicine,
Japan
2
Morphological studies about the intrinsic
laryngeal muscles (ILM) at our department

• Muscle spindle in the ILM
• Innervation pattern of the ILM
• (bilateral innervation of the arytenoid muscle)
• Ultrastructure of the neuromuscular junctions
  (NMJ) of the ILM (denervation regeneration,
  development, aging)
• Ultrastructure of the muscle fiber of the ILM
• (myotendonious junctionMTJ, myomyous
  junctionMMJ)

3
Ultrastructure of the NMJ of the ILMs
My previous study
Acta Otolaryngol 120766-770, 2000., Arch Histol
Cytol 63249-254, 2000.
To observe the NMJ on the muscle fiber by a
scanning electron microscope (SEM), the
connective tissues must be removed.
Desaki reported the method using HCl hydrolysis
to observe the NMJ on the muscle fiber by SEM
(1981). Using this method, we can also
investigate the ultrastructure of the muscle
fiber, such as NMJ and MMJ.
4
NMJ on the muscle fiber
10mm
10mm
Cricothyroid muscle (ILM)
Extensor digitorum longus (hindlimb)
5
MMJ on the muscle fiber
Cricothyroid muscle (CT)
30mm
6
Material method
Wistar rat (13 weeks after birth), n6 Heavy
anesthesia with ketamine and sodium
pentobarbiturate (i.m.) Whole larynx was
excised The CT and PCA muscles were dissected
(CT cricothyroid muscle, PCA posterior
cricoarytenoid muscle)
7
Material method 2
Fixation with 0.1M phosphate buffer 4
glutaraldehyde (2hr) Post-fixation with 2
unbuffered osmium tetroxide (30min) HCl-hydrolysi
s method(8N-HCl, 60oC, 30min) (Desaki
1981) Dehydration, freeze drying and sputter
coating Investigation by SEM
8
MMJ
CT
10mm
9
CT
10
CT
5 mm
11
PCA
10mm
12
Myomyous Junction (MMJ) extra ocular muscles in
rat, sheep and bird (Floyd 1970, Mayr et
al 1975) regenerated muscle fiber in rat
(Bormioli et al 1977) common skeletal muscle in
mouse (Torigoe et al. 1987) (rectus
abdominis, external oblique, gastrocnemius) funct
ion of MMJ integrate the fine and precise
muscular contraction by making motor units
13
Type of MMJ
Extra ocular muscle (Mayr et al.)
End-to-end type
Branch type
14

• Result Discussion
• In the CT, two types of the MMJ were identified
  end-to-end and branch types. And the ends of the
  branch type of the MMJ were divided into two
  groups finger-like tips and tiny round tips.
• end-to-end MMJfinger-like tips
• branch MMJfinger-like tips, branch MMJtiny
  round tips
• In the PCA, all the MMJ observed were branch
  type. And all the end of the branch type of the
  MMJ seemed tiny round tips.
• branch MMJtiny round tips

15

• Result Discussion 2
• The previous comparative study of the CT and PCA
  muscles about the NMJ and MTJ reported that the
  PCA is primitive and that the CT has an
  intermediate nature between the PCA and common
  skeletal muscles.
• We suggested that the PCA has primitive MMJs and
  the CT has both primitive and evolutionary MMJs
  for the phonation.

16

• Next step
• Observation of the MMJs in the thyroarytenoid
  muscle
• Correlation of the MMJs and the muscle fiber types

17
Conclusion 1.We investigated the muscle fibers of
the ILM (CT and PCA) using HCl hydrolysis method
for removal of the connective tissues. 2.The
MMJs, connected between muscle fibers, were
observed in the CT and PCA muscles. This is the
first report about the MMJ of the ILM. 3.The
MMJs consisted of two types end-to-end and
branch types. And the end of the MMJ divided
into two groups finger-like and tiny round tips.
18

• Conclusion-2
• 4.The MMJ of the PCA muscle seems to be a
  primitive style, while the CT muscle has both
  primitive and evolutionary MMJs.
• 5.Taken together, we conclude that the CT muscle
  of the rat gains the evolutionary structure to
  control the pitch of voice on phonation.