Lab 6 Key Terms
- Appendicular skeleton, meaning any muscle that acts on our arms or leg, on our
shoulder blades, on any part of the pectoral girdle or pelvic girdle that is considered to
be part of the appendicular skeleton.
• Trapezius is a very large fan-shaped muscle. Its action is to elevate and depress the shoulder.
So in actions of shrugging the shoulders, or pushing the shoulders down, the trapezius is
working. It also helps to stabilize the scapula when the arm is doing other movements, such as
raising the arm. It works with other muscle groups to retract and rotate the scapula. So
especially in that shoulder complex, the muscles do work together a lot to perform either a
stabilization role or movement role. So the trapezius is going to perform both a mobility role and
stabilization role.
• Accessory Nerve is the innervation of the trapezius. The trapezius is located alongside our
shoulders and up to our necks. It spans the distance from the back of the skull, down the back
of the neck and alongside the superior aspect of the shoulder girdle.
• Serratus Anterior is going to do a job called protraction of the scapula. So this is going to
work in movements like we’re reaching forward, or an action that involves pushing. So any
forward reaching or pushing motion that we do is completed by the serratus anterior. When the
serratus anterior works together with another muscle called the pectoralis minor, it is also going
to help draw the scapula laterally and forward around the chest wall. The serratus anterior is
located alongside the lateral but superior part of the chest wall. These little muscle fibers, they
look like fingers or daggers that come down. Over top of it you can see in relation to the external
oblique, the serratus anterior is superficial or superior to that muscle.
• Pectoralis Minor is also muscle that is working on the scapula. They are going to move the
shoulder blades in some way. The pectoralis minor, when it’s working with the serratus anterior,
it draws the scapula laterally and forward around the chest wall. This is also one of the
accessory muscles to breathing. So during times of labored breathing, the pectoral minor is
going to help expand the thoracic cavity to allow for more air to come into the lungs.
• Pectoralis Major is the large chest muscle. It acts on the humerus. It is a very superficial
muscle. Its job is to flex, adduct and medially rotate the humerus. It is going to raise the
humerus or raise the arm up. It is going to rotate it in, and it's going to pull the arm closer to the
body in adduction.
, • Medial/Lateral Pectoral Nerve is the innervation for the pectoralis minor and major.
• Latissimus Dorsi is a large muscle alongside our back. The actions are to adduct and
medially rotate the humerus. There is some overlap between the pectoralis major and the
latissimus dorsi. So these muscles often work together. A large role that the latissimus dorsi has
that the pectoralis major does not have is a role in extension of the shoulder, as if you were
pulling down on an object or pulling an oar if you are voting. The latissimus dorsi is also
responsible for the backward swing of the arm. So for example, if you’re bowling, and you bring
the ball back, the latissimus dorsi is working to perform that motion. Its attachment point comes
up onto the humerus.
• Deltoid is the large muscle on the top part or the top aspect of our humerus. It is made up of
three separate components that have anterior fibers, lateral fibers, and posterior fibers. So each
of these components does perform a separate job. The anterior part of the deltoid is going to
flex and medially rotate the shoulder. So it’s going to lift your arm overhead, and it's going to
internally rotate the arm. The lateral aspect of the deltoid is going to abduct to the arm. So it’s
going to take the arm away from the body in abduction. The posterior part of the deltoid is going
to extend and laterally rotate the shoulder. So it will pull the arm back behind the body, or it will
externally or laterally rotate the shoulder.
• Axillary Nerve is the innervation for the deltoid.
• Teres Major is the next muscle that acts on the humerus. It is going to act in shoulder
extension and medial rotation. So it’s going to pull the arm behind the body, or it's going to rotate
the shoulder in. It is a smaller muscle that is located inferior to that deltoid and superior to the
latissimus dorsi.
• Lower Subscapular Nerve is the innervation for the teres major.
The next group of muscles that works on the shoulder or the humerus is a group of muscles
called the rotator cuff. There are four distinct muscles in the rotator cuff. The acronym is SITS.
Together these four muscles work in stabilizing the humeral head inside the glenoid cavity of the
scapula. So when we’re moving our arm overhead, those four muscles will hug the head of the
humerus inside the glenoid cavity so it stays in place.
- Appendicular skeleton, meaning any muscle that acts on our arms or leg, on our
shoulder blades, on any part of the pectoral girdle or pelvic girdle that is considered to
be part of the appendicular skeleton.
• Trapezius is a very large fan-shaped muscle. Its action is to elevate and depress the shoulder.
So in actions of shrugging the shoulders, or pushing the shoulders down, the trapezius is
working. It also helps to stabilize the scapula when the arm is doing other movements, such as
raising the arm. It works with other muscle groups to retract and rotate the scapula. So
especially in that shoulder complex, the muscles do work together a lot to perform either a
stabilization role or movement role. So the trapezius is going to perform both a mobility role and
stabilization role.
• Accessory Nerve is the innervation of the trapezius. The trapezius is located alongside our
shoulders and up to our necks. It spans the distance from the back of the skull, down the back
of the neck and alongside the superior aspect of the shoulder girdle.
• Serratus Anterior is going to do a job called protraction of the scapula. So this is going to
work in movements like we’re reaching forward, or an action that involves pushing. So any
forward reaching or pushing motion that we do is completed by the serratus anterior. When the
serratus anterior works together with another muscle called the pectoralis minor, it is also going
to help draw the scapula laterally and forward around the chest wall. The serratus anterior is
located alongside the lateral but superior part of the chest wall. These little muscle fibers, they
look like fingers or daggers that come down. Over top of it you can see in relation to the external
oblique, the serratus anterior is superficial or superior to that muscle.
• Pectoralis Minor is also muscle that is working on the scapula. They are going to move the
shoulder blades in some way. The pectoralis minor, when it’s working with the serratus anterior,
it draws the scapula laterally and forward around the chest wall. This is also one of the
accessory muscles to breathing. So during times of labored breathing, the pectoral minor is
going to help expand the thoracic cavity to allow for more air to come into the lungs.
• Pectoralis Major is the large chest muscle. It acts on the humerus. It is a very superficial
muscle. Its job is to flex, adduct and medially rotate the humerus. It is going to raise the
humerus or raise the arm up. It is going to rotate it in, and it's going to pull the arm closer to the
body in adduction.
, • Medial/Lateral Pectoral Nerve is the innervation for the pectoralis minor and major.
• Latissimus Dorsi is a large muscle alongside our back. The actions are to adduct and
medially rotate the humerus. There is some overlap between the pectoralis major and the
latissimus dorsi. So these muscles often work together. A large role that the latissimus dorsi has
that the pectoralis major does not have is a role in extension of the shoulder, as if you were
pulling down on an object or pulling an oar if you are voting. The latissimus dorsi is also
responsible for the backward swing of the arm. So for example, if you’re bowling, and you bring
the ball back, the latissimus dorsi is working to perform that motion. Its attachment point comes
up onto the humerus.
• Deltoid is the large muscle on the top part or the top aspect of our humerus. It is made up of
three separate components that have anterior fibers, lateral fibers, and posterior fibers. So each
of these components does perform a separate job. The anterior part of the deltoid is going to
flex and medially rotate the shoulder. So it’s going to lift your arm overhead, and it's going to
internally rotate the arm. The lateral aspect of the deltoid is going to abduct to the arm. So it’s
going to take the arm away from the body in abduction. The posterior part of the deltoid is going
to extend and laterally rotate the shoulder. So it will pull the arm back behind the body, or it will
externally or laterally rotate the shoulder.
• Axillary Nerve is the innervation for the deltoid.
• Teres Major is the next muscle that acts on the humerus. It is going to act in shoulder
extension and medial rotation. So it’s going to pull the arm behind the body, or it's going to rotate
the shoulder in. It is a smaller muscle that is located inferior to that deltoid and superior to the
latissimus dorsi.
• Lower Subscapular Nerve is the innervation for the teres major.
The next group of muscles that works on the shoulder or the humerus is a group of muscles
called the rotator cuff. There are four distinct muscles in the rotator cuff. The acronym is SITS.
Together these four muscles work in stabilizing the humeral head inside the glenoid cavity of the
scapula. So when we’re moving our arm overhead, those four muscles will hug the head of the
humerus inside the glenoid cavity so it stays in place.
