Muscles of the Thorax Flashcards
Superficial pectoral
extrinsic forelimb muscle
fiber direction: lateral towards proximal humerus
action: to adduct the limb/prevent abduction when non-weight bearing
innervation: ventral branch of spinal nerves C7 and C8
origin: ventral surface of 1st, 2nd, and 3rd sternebrae
insertion: the craniolateral surface of the proximal humerus (the crest of the greater tubercle)
Deep Pectoral
extrinsic forelimb muscle
fiber direction: caudomedial towards xiphoid process
action: if standing pulls trunk cranially and extends the shoulder joint, if NWB adducts limb
innervation: caudal pectoral nerve (C8, T1)
origin: ventral surface of sternum
insertion: lesser tubercle of humerus and greater tubercle of humerus via aponeurosis
latissimus dorsi
extrinsic forelimb muscle
fiber direction: cranioventral towards proximal end of the humerus
action: “digging muscle”
innervation: thoracodorsal nerve (C7, C8, T1)
origin: transverse process of the lumbar vertebrate and the thoracolumbar fascia
insertion: teres major tuberosity of the humerus
cutaneous trunci
most superficial muscle of thoracic body wall
fiber direction: ?
action: makes skin twitch
innervation: lateral thoracic nerve (C8, T1)
no direct bony attachments
trapezius
extrinsic forelimb muscle (has thoracic and cervical parts)
fiber direction: dorsal
action: to elevate and abduct the forelimb
innervation: accessory spinal nerve (cranial nerve XI)
origin: median raphe of the neck and supraspinous ligament
insertion: the spine of the scapula
external abdominal oblique
abdominal muscle covers ventral half of lateral thoracic wall and lateral part of abdominal wall, most superficial abdominal muscle
fiber direction: fibers run caudoventrally
action: aid in urination, defecation, parturition, respiration, and locomotion
costal part arises from last ribs
lumbar part arises from the last ribs and thoracolumbar fascia
rectus abdominus
abdominal muscle extends from pecten of the pubis, as the prepubic tendon, to the sternum
fiber direction: caudal horizontal, distinct transverse tendinous intersections
action: flexes the thoracolumbar part of the vertebral column
rhomboideus
extrinsic forelimb muscle, 3 parts: capitis, cervicis, thoracis
fiber direction:
action: to elevate the forelimb and draw the scapula against the trunk
innervation: ventral branches of cervical and thoracic spinal nerves
origin:
rhomboideus: spinous process of first seven thoracic vertebrae
cervicis: median raphe of the neck
capitis: nuchal crest of the occipital bone
insertion: dorsal border of the scapula
serratus ventralis
extrinsic forelimb muscle (fan shaped)
fiber direction: craniodorsal
action: acts like a “sling” to support the trunk and depress the scapula
innervation: ventral branches of cervical spinal nerves and the long thoracic nerve (C7)
origin: transverse processes of the last five cervical vertebrae and from the lateral aspect of the ventral half of the first seven to eight ribs
insertion: the dorsomedial third of the scapula
scalenus
muscle of the thoracic wall
fiber direction: caudoventral
action: muscle of inspiration
innervation: ?
lies ventral to origin on the cervical and cranial thoracic parts of the serratus ventralis
attachment: first few ribs and the transverse processes of the cervical vertebrae
serratus dorsalis cranialis
muscle of the thoracic wall
lies on dorsal surface of cranial thorax
fiber direction: caudodorsal
action: lifts the ribs for inspiration
innervation:
origin: broad aponeurosis from the thoracolumbar fascia deep to the rhomboideus
insertion: distinct serrations on the craniolateral surfaces of the ribs
serratus dorsalis caudalis
muscle of the thoracic wall
smaller, “muscle leaves” found on dorsal surface of the caudal thorax
fiber direction: cranioventrally
action: drawing the last three ribs caudally in expiration
innervation:
origin: aponeurosis from the thoracolumbar fascia
insertion: caudal borders of the last three ribs
external intercostal
muscle of the thoracic wall
12 external intercostal muscles on each side of thoracic wall
fiber direction: caudoventrally from caudal border of one rib to the cranial border of the rib caudal to it
action: drawing the ribs together during respiration
innervation:
ventral border: near the costochondral junction
internal intercostal muscles
muscle of the thoracic wall
fiber direction: craniodorsal(?) from the cranial border of one rib to the caudal border of the rib cranial to it
action: drawing the ribs together during respiration
innervation:
medial to internal intercostal muscles is pleura, internal intercostals extend the entire distance of the intercostal space
diaphragm
action: respiration
innervation: phrenic nerve
attachments: costal part arises from medial surface of 8th-13th ribs, cranial attachment at xiphoid process, right and left crura attach to bodies of L3 and L4 and along medial surface of costal arch
epaxial
action: extensors of the vertebral column and produce lateral movements of the trunk when contracting on only one side
Innervation: dorsal branches of spinal nerves
iliocostalis: most lateral and ventral system
longissimus: intermediate
transversospinalis: most medial and dorsal system
Extend from dorsal arches of the ribs to the vertebral spinous processes
lie between transverse and spinous processes of adjacent vertebrae
latissimus dorsi
cutaneous trunci
external abdominal oblique
trapezius
deep pectoral
external abdominal obliques
serratus dorsalis caudalis
scalenus
serratus dorsalis cranialis
serratus ventralis
deep pectoral
latissimus dorsi
