The Mediastinum and Autonomic Nervous System
13
March 2008
Mediastinum in right lateral view
Structures
of the mediastinum are not bilaterally symmetrical
·
Esophagus
·
Azygos
·
Right
mainstem bronchus
·
Right
pulmonary artery
·
Right
pulmonary vein
Netter, 2003 pl. 226; Netter, 2006
230
Mediastinum in left lateral view
·
Aorta
- thoracic portion
·
Hemiazygos
·
Left
mainstem bronchus
·
Left
pulmonary artery
·
Left
pulmonary vein
Netter, 2003 pl. 227; Netter, 2006
pl. 231
Superior
Mediastinum - Great Vessels
Superior limit - thoracic outlet; Inferior
limit - sternal angle/T4
·
Brachiocephalic veins
·
Brachiocephalic trunk
·
Left
common carotid
·
Aorta
- arch only
Netter, 2003 pl. 202; Netter, 2006 pl. 206
Trachea
·
Bifuracates at about T4
·
Trachea
primarily superior mediastinum
·
Mainstem
bronchi divide into lobar and segmental bronchi
·
Posterior
mediastinum
Netter, 2003 pl. 198; Netter, 2006
pl. 202
Broncheal
Arteries
Blood
supply to bronchi & the structural tissue of the lungs. Branch directly from aorta
Netter, 2003, pl. 203; Netter, 2006
pl. 207
Veins
of the Mediastinum
·
Aygos
v.& Hemiazygos v.
– Arise from ascending lumbar vv.
– Take in intercostal vv.
– Azygos empties into superior vena cava
– Hemiazygos is variable; may empty into
either azygos or left brachiocephalic
·
Left
& Right Brachiocephalic vv.
– Arise as confluence of subclavian
& jugular vv, bilaterally
–
Join
to make the superior vena cava
·
Submucosal
esophageal venous plexus
·
Branches
of gastric veins
Netter, 2003 pl. 202 & 234; Netter,
2006 pl. 206 & 238
Thoracic
Duct
Begins in abdominal cavity at cysterna chyli.
Passes through diaphragm between the aorta and azygos
vein.
Crosses to left side about T6.
Empties into Left Subclavian vein
Moore & Dalley,
1999, Fig. 1.22
See Netter, 2003 pls. 202, 235
& 258; Netter, 2006 pls. 206, 239 & 266
Typical
Spinal Nerves
·
Spinal
cord
·
Dorsal
root
·
Ventral
root
·
Dorsal
ramus
·
Ventral
ramus
·
Sympathetic
Chain
See Netter, 2003 pl. 250; Netter,
2006 pl. 258
Mixed
Nerves
Functional
Components
Parts
that work to accomplish a particular activity
(fill in chart below)
Soma Viscera
Sensory
Motor
Autonomic
Nervous System
·
Innervates
– smooth muscle (including all blood vessels)
– cardiac muscle
– glands
– arrector pili
muscles
·
Two
neurons
– fibers leaving CNS synapse in autonomic ganglia
– fibers from ganglion innervate the end organ
·
Each
autonomic nerve has two physical parts
·
CNS
to Autonomic ganglia
– preganglionic
·
Ganglia
to end organs
– postganglionic
Two
Divisions
·
Sympathetic
– fight or flight
·
Parasympathetic
– homeostatic processes (rest & digest)
·
Sympathetic
distribution to blood vessels & skin follows spinal nerves
– Synapse in sympathetic trunk
– Postganglionic distributed in peripheral nerves
·
Sympathetic
distribution to viscera by splanchnic nerves
–
Preganglionic until synapsing at preaortic
ganglia
Rosse
& Gaddum-Rosse, 1997, Fig. 7-6
See Netter, 2003 pl. 160; Netter,
2006 pl. 167
Autonomic
Nervous System
·
Distribution
to blood vessels & skin follows spinal nerves
–
Synapse
in sympathetic trunk
–
Postganglionic
in peripheral nerves
·
Distribution
to viscera by splanchnic nerves
–
Preganglionic until synapsing at aortic ganglia
See Netter, 2003 pl. 160; Netter,
2006 pl. 167
The
Sympathetic Trunk or Chain
·
The
sympathetic trunk is a distribution system for sympathetic nerves
·
It
lies parallel to the spinal cord
·
Nerves
arise in the spinal cord and are transferred to the sympathetic trunk via a
white ramus communicans
–
These
branch from spinal nerves T1-L2 as input to the trunk.
·
Two
routes of output from sympathetic trunk
–
Gray
rami communicantes to every
spinal nerve
–
Splanchnic
nerves to abdominal viscera
Spinal
nerves connect with sympathetic chain via communicating rami
(rami communicantes).
A white
ramus communicans brings preganglionic sympathetic fibers from the spinal nerve to
the sympathetic chain. They correspond with the origin of preganglionic
sympathetics from the intermediolateral
horn of the spinal cord (T1 - L3). They
are only associated with spinal nerves T1 - L2 or 3.
A gray ramus communicans takes post ganglionic sympathetic fibers from the sympathetic trunk to
the spinal nerves for peripheral distribution.
A gray ramus comunicans
delivers post ganglionic sympathetic fibers to each
and every spinal nerve.
Splanchnic
nerves carry preganglionic sympathetic fibers to the
abdominal viscera. They exit directly from the trunk (not through the gray rami communicantes). They synapse to become post ganglionic in the abdominal preaortic
sympathetic ganglia.
Autonomic
Nervous System
Each autonomic nerve has two physical parts
·
CNS to Autonomic ganglia
–
preganglionic
·
Ganglia to end organs
–
postganglionic
Two divisions
·
Sympathetic
o
Fight
or flight
·
Parasympathetic
o
Homeostatic processes (rest and digest)
o
Postganglionic in peripheral nerves
·
Distribution to blood vessels & skin
follows spinal nerves
o
Synapse in sympathetic trunk
o
Postganglionic in peripheral nerves
·
Distribution to viscera by splanchnic nerves
o
Preganglionic until synapsing at aortic ganglia
See Netter, 2003 pl. 160; Netter,
2006 pl. 167
Spalanchnic Nerves
·
Greater
·
Lesser
·
Lowest
Rosse
& Gaddum-Rosse, 1997, Fig. 22-17
Netter, 1997; pl. 214, 228, 2003,
pl.222, 236
also see Clemente,
1997; pp. 187, 237
Autonomic
Nerve Plexus
·
Postganglionic
sympathetic fibers from sympathetic trunk,
·
Preganglionic parasympathetic fibers from vagus n.
·
Supply
heart, lungs & esophagus
See Netter, 2003 pl.236;
Netter, 2006 pl. 240
Cardiac
Plexus
Mixing
of sympathetic and parasympathetic nerves innervating the heart & great
vessels.
Derived
from
·
sympathetic
trunk
·
vagus
n.
Is the sympathetic input to the cardiac plexus pre-ganglionic or post ganglionic?
Netter,
2003 pl. 222; Netter , 2006 pl. 226
REFERENCES
Rosse
and Gaddum-Rosse, 1997. Hollinshead's
Textbook of Anatomy. 5th Ed. Lippincott-Raven.
(Note that these figures can also
be found in the 4th edition of this textbook, available in the anatomy lab.)
Clemente,
C.D., 1997. Anatomy: A Regional Atlas of the Human Body. 4th Ed. Williams and
Wilkins. (earlier editions available in the anatomy lab).