Inspiratory muscles

Question 1

Diaphragm

Answer 1

The diaphragm has 5 layers:

• pleura + fascia endothoracica
• m. phrenicus
• fascia transversa abdominis + peritoneum

Phrenic muscle has its musculary origin(corona muscularis)from different sites,soit has sternal part, costal part and lumbar part, which meet in a central tendineous plate (centrum tendineum), which has an opening for caudal vena cava between thoracic and abdominal cavity (foramen venae cavae)

Cranialmost part of diaphragm’s curve - also seen on X-rays - is called cupula or dome (cupula diaphragmatica) which projects into thoracic cavity.

Lumbal and costal parts are connected by an arch (arcus lumbocostalis), beside there is a triangular region where phrenic muscle is absent (trigonum lumbocostale), that’s why this part is vulnerable to hernias.

Crus dexter and sinister are arising from the 3–4th lumbar vertebrae, and together forming an opening for aorta (hiatus aorticus) (1). As the right crus is thicker, it extends more ventrally and also surrounds oesophagus (hiatus oesophageus)

This is the most important inspiratory muscle, also helps increasing abdominal pressure

Question 2

Mm. intercostales

Answer 2

Two muscle-groups can be distinguished: m. intercostalis externus and internus
o Origin and insertion:
- m. intercostalis externus: muscle fibres run caudoventrally (\)
- from caudal border of one rib to cranial border of the next rib - m. intercostalis internus: muscle fibers run cranioventrally (///)
- from cranial border of one rib to caudal border of the previous rib
o Action:
- m. intercostalis externus: inspiration - m. intercostalis internus: expiration

Question 3

Mm. levatores costarum

Answer 3

Origin: transverse processes of Th1–12 vertebrae o

Insertion: cranial borders of ribs near their angles
(angulus costae); covered by erector spinae muscles

Action: inspiration

Question 4

M. rectus thoracis

Answer 4

Origin: first rib

Insertion: ventral ends of ribs 2–4.

Action: inspiration

Question 5

M. scalenus

Answer 5

It has two parts in dogs: m. scalenus dorsalis and m. scalenus medius

o Origin: m. scalenus dorsalis from C4–6 vertebrae’s transverse processes, m. scalenus medius from C6–7 vertebrae’s transverse processes

o Insertion:
- the dorsal scalenus has two muscular parts, inserting on the cranial border of ribs: the dorsally situated on the first four ribs,
the ventrally situated is longer
and inserts on the first eight-nine ribs
- the middle scalenus inserts on
the cranial border of first rib
(also called: m. scalenus primae costae)

o Action: helps in inspiration,
bilateral contraction: flexes neck ventrally, unilateral contraction: flexes neck laterally

Question 6

M. serratus ventralis

Answer 6

o Origin: cervical part from proc. trans. of C2-7, thoracic part from middle of ribs 1-8.

o Insertion: facies serrata on scapula (medially)

o Action: supports trunk, helps at inspiration,
carries shoulder cranial or caudal with respect to position of forelimb