Download Intercostal Muscles LO4

Intercostal Muscles LO4
4 List the structures, from superficial to deep, in an intercostal space. Describe their
relationships to each other, to the associated neurovascular bundle and to the pleural cavity.
Review principle RV5 to show how these relationships reflect the typical structure of the body
wall.
Identify, in cadaver specimens, models and diagrams, the intercostal muscles (including the
subcomponents of the internal and innermost layers). Describe their attachments and deduce
their actions individually and apply principle T6 to describe how they act as a group in each
intercostal space.
Apply principles NP3, NP6 & NP7 to describe the structure and functions of a typical intercostal
nerve and its component nerve fibres. Describe the general dermatome pattern of the trunk.
Apply principle NP14 to describe the effect cutting one intercostal nerve would have skin
sensation in the area supplied by that nerve.
Intercostal (IC) Space
Superficial to Deep Structures
Muscle
Innervation
Origin
Insertion
Thoracic
diaphragm
C3-5 phrenic nerves
Xiphoid process,
costal margin,
bodies of L1-L3,
arcuate ligaments
Central tendon
that blends with
the anterior
longitudinal
ligament of the
vertebral column
(C3, C4 and C5 keep the
diaphragm alive)
Position and
Orientation
Horizontal
Spans the length of
the thoracic cavity
Function
General
Chief muscle of
respiration
Muscular dome that
separates the
thoracic and
abdominopelvic
cavities
Expands the thoracic
cavity
Compresses the
abdominal cavity
Inserts onto itself
Separates the thoracic
and abdominal
cavities
External
Intercostals (11)
Intercostal nerves T1-T11 Inferior border or
rib above
Superior border
of rib below
Superficial
Oblique (anterior
inferiorly)
Most active during
inspiration
Elevates ribs
Allows passageway
of inferior vena
cava, aorta and
oesophagus
Active during all
types of forced
respiration to
maintain stability of
intercostal space
Supports intercostal
space
Internal
intercostals (11)
(interchondral &
interosseous)
Intercostal nerves T1-T11 Costal groove of
rib above
Superior margin
or rib below deep
to external
intercostals
Deep
Oblique
(postereoinferiorly)
Most active during
expiration
Depresses ribs
Supports intercostal
space
Active during all
types of forced
respiration to
maintain stability of
intercostal space
Innermost
intercostals
Transverses
thoracis,
Subcostals
Intercostal nerves T1-T11 Costal groove of
rib above
Internal aspect of
superior margin
or rib below
Deep to internal
intercostal
Deepest
Oblique (same
orientation as
internal
intercostals)
Acts with internal
intercostal muscles
Intercostal nerves T1-T11 Inferior margins
of the internal
surface of costal
cartilages 2-6
Inferior and
posterior sternum
Deep surface of the
anterior thoracic
wall
Depresses costal
cartilages
Intercostal nerves T1-T11 Internal surface
of rib above
Internal surface
of rib 2 or 3 ribs
below origin
Maintains rigidity of
thorax
Stabilizes intercostal
Orientated
space
anteriorly inferiorly
Maintains rigidity of
thorax
Deep surface of
May depress the ribs
posterior thoracic
wall
Stabilizes intercostal
space
Fibres parallel to
internal intercostals Maintains rigidity of
the thorax
When asked for origins be general: inferior border of rib above
When asked for insertion for ALL intercostals: superior border of rib below
It is important to note that ALL three layers of the intercostal muscles are active during forced
respiration to maintain the rigidity of the thorax and support the intercostal space.
Third layer is not a
complete layer but
consists of 3
components
Located in anterior
region of rib cage
only
Located in
posterior region of
rib cage only
Cross two ribs at a
time
Intercostal Nerves
Origin:
Ventral rami of T1-T12 spinal nerves
T1-T11 = intercostal nerves
T12 = subcostal nerves
Fibre types:



GSE: Intercostal muscles
GSA: peripheral diaphragm
GVE: sympathetic post ganglionic fibres to innervate blood vessels
Branches of intercostal nerves:
Lateral cutaneous branches
Collateral branches
Muscular branches
Anterior cutaneous branches
They run along the ribs
in the costal groove
Superior to Inferior the run:
Vein: intercostal vein
Artery: intercostal artery
Nerve: intercostal nerve
VAN! 
Dermatome Distribution of the Trunk
Intercostal nerves and vessels run between
the 2nd and 3rd layer of intercostal muscles
Intercostal Nerve Block

One particular area of skin usually receives
innervation from two adjacent nerves, there is
overlap of dermatomes.

Therefore complete loss of sensation usually does
not occur to that area unless two or more
intercostal nerves are anesthetized.