Thorax Muscular

Question 1

Surface projection of jugular notch of sternum

Answer 1

Location:
• Manubrium (superior)
• Between medial ends of clavicles

Question 2

Surface projection of xiphoid process

Answer 2

• Sternum (inferior part)

Description:
• Midline shallow depression
• Cartilage until approximately 5th decade of life

Question 3

Surface projection of costal margin

Answer 3

Description:
• Lower margin of thorax
• Formed by ribs 11 and 12 and costal cartilages of ribs 7-10

Comment:
• Provides attachment for diaphragm
• Indicates junction of thorax and abdomen

Question 4

Deltoid m.

Answer 4

Action:
• Anterior part: flexion and medial rotation of arm
• Lateral part: abduction of arm
• Posterior part: extension and lateral rotation of arm

Innervation:
• Axillary nerve

Comment:
• Site for intramuscular injections

Question 5

Pectoralis major m.

Answer 5

Action:
• Adduction of arm
• Medial rotation of arm
• Clavicular head: flexion of arm
• Sternocostal head: extension of arm (from flexed position)

Innervation:
• Lateral pectoral nerve (C5-7)
• Medial pectoral nerve (C8-T1)

Comment:
• Pectoralis major active during forced inspiration

Question 6

Anterior rectus sheath

Answer 6

Location:
• Anterior abdominal wall

Description:
• Anterior fibrous covering of rectus abdominis muscle
• Formed by aponeuroses (flat tendons) of external and internal abdominal oblique muscles

Question 7

External abdominal oblique m.

Answer 7

Action:
• Unilateral: rotation of trunk
• Bilateral: flexion of trunk (sit-ups)
• Compression of anterior abdominal wall and viscera (increases intra-abdominal pressure)

Question 8

Sternocleidomastoid m.

Answer 8

Action:
• Unilateral: rotation of head so face turns to opposite side
• Bilateral: flexion of head

Innervation:
• Accessory nerve (CN XI)

Question 9

External intercostal m. and membrane

Answer 9

Action:
• Muscle of respiration
• Elevation of ribs during inhalation to increase transverse dimensions (anterior-posterior, medial-lateral) of thoracic cavity

Innervation:
• Intercostal nerves (ventral rami of T1-11 spinal nerves)

Comment:
• External intercostal muscle continuous with external intercostal membrane near sternum

Question 10

Pectoralis minor m.

Answer 10

Pectoralis minor m.
Action:
• Stabilizes scapula (holds it against thoracic wall)
• Protraction (abduction) of scapula (assists serratus anterior)
• Lateral rotation of scapula (e.g., depresses the acromion)

Innervation:
• Medial and lateral pectoral nerves

Comment:
• Pectoralis minor active during forced inspiration

Question 11

Rectus abdominis m.

Answer 11

Action:
• Flexion of trunk (sit-ups)
• Compression of anterior abdominal wall

Innervation:
• Ventral rami of T7-12 spinal nerves

Comment:
• Three or four bellies, separated by tendinous intersections
• Encased in fibrous (rectus) sheath
• Important in “straining” (e.g., lifting, defecation, urination, child-birth)
• Functions in respiration (“abdominal breathing”)

Question 12

Serratus anterior m.

Answer 12

Action:
• Protraction (abduction) of scapula
• Medial rotation of scapula (directs glenoid cavity superiorly)
• Stabilizes scapula (holds it against thoracic wall)

Innervation:
• Long thoracic nerve

Comment:
• Serratus anterior is a prime mover in all reaching and pushing movements

Question 13

Internal intercostal m.

Answer 13

Action:
• Muscle of respiration
• Depression of ribs during forced exhalation to decrease transverse dimensions (anterior-posterior, medial-lateral) of thoracic cavity

Innervation:
• Intercostal nerves (ventral rami of T1-11 spinal nerves)

Comment:
• Internal intercostal muscle continuous with internal intercostal membrane near vertebral column