Intercostal Muscles LO4

Transcription

1 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

2 Superficial to Deep Structures

3 Muscle Innervation Origin Insertion Position and Orientation Thoracic C3-5 phrenic nerves Horizontal diaphragm (C3, C4 and C5 keep the diaphragm alive) Xiphoid process, costal margin, bodies of L1-L3, arcuate ligaments Central tendon that blends with the anterior longitudinal ligament of the vertebral column Inserts onto itself Spans the length of the thoracic cavity Function Chief muscle of respiration Expands the thoracic cavity Compresses the abdominal cavity Separates the thoracic and abdominal cavities General Muscular dome that separates the thoracic and abdominopelvic cavities Allows passageway of inferior vena cava, aorta and oesophagus 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 Supports intercostal space Active during all types of forced respiration to maintain stability of 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

4 Innermost intercostals Transverses thoracis, Subcostals Intercostal nerves T1-T11 Costal groove of rib above Intercostal nerves T1-T11 Inferior margins of the internal surface of costal cartilages 2-6 Intercostal nerves T1-T11 Internal surface of rib above Internal aspect of superior margin or rib below Deep to internal intercostal Inferior and posterior sternum Internal surface of rib 2 or 3 ribs below origin Deepest Oblique (same orientation as internal intercostals) Deep surface of the anterior thoracic wall Orientated anteriorly inferiorly Deep surface of posterior thoracic wall Fibres parallel to internal intercostals Acts with internal intercostal muscles Maintains rigidity of thorax Depresses costal cartilages Stabilizes intercostal space Maintains rigidity of thorax May depress the ribs Stabilizes intercostal space Maintains rigidity of the thorax 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 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.

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7 Origin: Intercostal Nerves 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

8 They run along the ribs in the costal groove Superior to Inferior the run: Vein: intercostal vein Artery: intercostal artery Intercostal nerves and vessels run between the 2 nd and 3 rd layer of intercostal muscles Nerve: intercostal nerve VAN! Dermatome Distribution of the Trunk

9 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.