Human Anatomy & Physiology I Lab 8 The skeletal muscles of the head and trunk
Learning Outcomes Learn how a muscle’s name can reflect its characteristics
Assessment: Exercises 8.1
Visually locate and name the muscles of the head.
Assessments: Exercise 8.2
Visually locate and name the muscles of the body.
Assessment: Exercise 8.3
Naming muscles Information
There are a lot of skeletal muscles in the human body, and skeletal muscles often have long and
hard-to-remember names. However, the muscle names often reflect something about their action,
their shape, or their locations. If you know the logic of how a muscle name was derived, it often
makes it easier to remember that muscle’s name and location.
Figures 8-1 and 8-2 show and Table 8-1 lists the anatomical terms for the types of movements
that can occur around joints. Often these terms are incorporated into the names of muscles that
contribute to producing that type of movement at one of the body’s joints.
Sometimes the locations of muscles’s origins or insertions are incorporated into their names.
Muscles are generally attached at two points in the body. One end is pulled by the muscle to create
movement. The end of the muscle that creates movement is called the insertion of the muscle. The
other end of the muscle stays fixed and the part of the muscle that moves is moved towards this fixed
point. The fixed end of a muscle is called the origin of the muscle. Figure 8-3 illustrates muscle
origins and insertions.
Sometimes, the way muscles interact with other muscles are incorporated into their names. Table
8-2 summarizes the anatomical terms associated with these kinds of muscle interactions.
Table 8-3 summarizes many of the ways that a muscle’s characteristics can be incorporated into
its name.
Table 8-1. Anatomical terms describing movement around the body’s joints.
Term Type of movement around the joint
Flexion Decreasing the angle between two bones
Dorsiflexion Decreasing the angle between the foot and shin
Plantar flexion Decreasing the angle between the toes and bottom of the foot (pointing toes)
Extension Increasing the angle between two bones
Abduction Moving a body part away from the midline
Adduction Moving a body part towards the midline
Circumduction Movement in a circular or cone-shaped motion
Rotation Turning movement of a bone about its long axis
Supination Rotation of the forearm or foot so that the palm or sole is moved to face anteriorly
Pronation Rotation of the forearm or foot so that the palm or sole is moved to face posteriorly
Inversion Sole of the foot moved to face medially
Eversion Sole of the foot moved to face laterally
Retraction Movement in the posterior direction.
Protraction Movement in the anterior direction.
Elevation Lifting a body part
Depression Returning a body part to pre-elevated position
Figure 8-1. Types of movements around and about joints, part 1.
Figure 8-2. Types of movements about and around joints, part 2.
Figure 8-3. The biceps brachii muscle of the arm has two origins that are fixed to the scapula bone and one insertion that is attached to and moves the radius bone.
Table 8-2. Anatomical terms describing how muscles interact with other muscles.
Term Type of interaction with other muscles
Agonist Also known as the primer move. A muscle that is primarily responsible for the
movement.
Synergist A muscle that assists the prime mover muscle.
Fixator A muscle that stabilizes the origin of the prime mover (i.e. holds it in place) so that
the prime mover can act more efficiently.
Antagonist A muscle in opposition to the action of a prime mover muscle. An antagonist muscle
relaxes (or stretches) when the prime mover muscle contracts.
Table 8-3. The different ways a muscle’s characteristics can be incorporated into its name
Characteristic Examples Human muscles named this way
Direction of muscle fascicles
relative to muscle midline.
Rectus – parallel
Transverse – perpendicular
Oblique – at a 45° angle
Rectus abdominis
Transversus abdominis
External oblique
Location of or body part
covered by the muscle
Frontal bone
Tibia
Frontalis
Tibialis anterior
Relative size
Maximus - largest
Longus - longest
Brevus – shortest
Major – larger of a pair
Minor – smaller of a pair
Gluteus maximus
Palmaris longus
Peroneus longus
Teres major
Teres minor
Number of origins Biceps – two origins
Triceps – three origins
Biceps brachii
Triceps brachii
Location of origin or insertion
origin at sternum
origin at clavicle
insertion at mastoid process
Sternocleidomastoid
Shape
Deltoid – triangular
Trapezius – trapezoidal
Serratus – saw-tooth edge
Orbicularis - circular
Deltoid
Trapezius
Serratus anterior
Orbicularis oris
Action of muscle
Flexion
Extension
Adduction
Flexor carpi radialis
Extensor digitorum
Adductor longus
Lab exercises 8.1 1. Give the reasons the following muscles were given their names. For muscles with multi-word
names, identify the meaning of or reason for each component of the muscle’s name.
a. Deltoid muscle
b. External oblique muscle
c. Platysma muscle
d. Rectus abdominis muscle
e. Frontal epicranius muscle
f. Zygomaticus major muscle
The muscles of the head Information
Figure 8-4 lists the muscles of the head that you will need to know.
A single platysma muscle is only shown in the lateral view of the head muscles in Figure 8-4.
There are two platysma muscles, one on each side of the neck. Each is a broad sheet of a muscle that
covers most of the anterior neck on that side of the body. The other anterior neck muscles are below
them, and most models have the platysma muscles cut away to show the deeper muscles. The
platysma muscles help pull down the lower jaw (mandible.)
Under the platysma are two sternocleidomastoid muscles. One on each side of the neck.
These muscles have two origins, one on the sternum and the other on the clavicle. They insert on the
mastoid process of the temporal bone. They can flex or extend the head, or can rotate the towards the
shoulders.
The epicranius muscle is also very broad and covers most of the top of the head. The
epicranius muscle includes a middle section which is all aponeurosis. The actual muscle tissue is
only found over the forehead (the portion of the muscle called the epicranius frontalis; sometimes
called the frontal belly of the epicranius) and the back of the head (the portion of the muscle called
the epicranius occipitalis; sometimes called the occipital belly of the epicranius).
The buccinator muscles, one on each side of the face, compress the cheeks when contracted.
The name is from the Latin for trumpet, which requires blowing air out of the cheeks to play, and
also reflects the anatomical adjective for the cheek, buccal.
The two masseter muscles are also on each side of the face. They close the jaw when
contracted. Its name is derived from the same Greek root as mastication, which means to chew.
The zygomaticus major muscles and the zygomaticus minor muscles are found on each
side of the face both have their origins on the zygomatic bone. They both can change the shape of
the mouth by elevating it.
Figure 8-4. The muscles of the head.
Lab exercises 8.2 1. The following are muscles of facial expression. For each, give its location and describe its
action when it contracts.
Muscle Location Action when contracted
Epicranius
frontalis
Epicranius
occipitalis
Orbicularis
oculi
Zygomaticus major
Zygomaticus minor
Buccinator
Orbicularis
oris
Nasalis
2. The following are muscles of mastication. For each, give its location and describe its action
when it contracts.
Muscle Location Action when contracted
Masseter
Temporalis
Platysma
The muscles of the trunk Information
Figures 8-5 and 8-6 shows many of the muscles of the body’s trunk that you need to know, as
well as some of the muscles of the arms and legs you will learn about in the next lab.
The deltoid muscles are the triangular muscles over each shoulder.
Some of the trunk muscles have been given nicknames by gym rats. For instance, the pecs are
the pectoralis major muscles at each breast.
Lats are the latissimus dorsi muscle that covers most of the lower back with its lateral fibers.
The upper back is covered by the large trapezius muscle that is almost diamond-shaped as it
extends from the neck, out to the shoulders, then tapers in midway down the back.
Obliques are the external oblique muscle whose fibers angle down as it covers both sides of
the abdominal region. The external oblique muscle has two sets of fibers, which cover the left and
right abdomen, that are connected by a wide aponeurosis sheet in the center of the abdomen. In most
muscle models that aponeurosis sheet is cut away to reveal the rectus abdominis muscles below it.
What gym rats call the core muscles are three layers of muscle that sit over the abdomen. These
layers are shown in Figure 8-7. The outer layer is the external oblique muscle, with its
aponeurosis covering the medial abdomen. Under the external oblique are the internal obliques on
the sides of the abdomen and the rectus abdominis muscle in-between the internal obliques. The
fibers of the internal obliques run up at an angle, opposite in direction to the fiber angle of the
external obliques. The rectus abdominis muscle is also known as the abs. The deepest layer has the
transverse abdominis muscle, whose fibers run laterally. Its fibers are concentrated at the sides
of the abdomen and, like the external oblique, has an aponeurosis covering the medial abdomen
under the rectus abdominis.
Extending from the back and wrapping around the sides of the rib cage is the serratus anterior
muscle. This muscle’s anterior edges are serrated like the teeth of a saw because this muscle’s
origins are on ribs 1 through 8 and each serration is the attachment point to another rib. This muscle
is shown in Figure 8-8.
Figure 8-5. The major muscles of the body, anterior view. Anatomical right shows superficial
muscles. Anatomical left shows deep muscles.
Figure 8-6. The major muscles of the body, posterior view. Anatomical right shows superficial muscles. Anatomical left shows deep muscles
Figure 8-7. The three layers of muscles in the abdomen.
Figure 8-8. The external muscles of the body, lateral view.
Lab exercises 8.3 1. The following are muscles that move the pectoral girdle. For each, give its location and
describe its action when it contracts.
Muscle Location Action when contracted
Trapezius
Pectoralis
minor
Serratus
anterior
2. The following are muscles that move the arm. For each, give its location and describe its
action when it contracts.
Muscle Location Action when contracted
Pectoralis major
Latissimus dorsi
Deltoid
3. The following are muscles of the abdominal wall. For each, give its location and describe its
action when it contracts.
Muscle Location Action when contracted
Rectus
abdominis
External oblique
Internal oblique
Transversus abdominis
4. Label the indicated facial muscles in Figure 8-9.
Figure 8-9. Facial muscles.
Licenses and attributions. Unless otherwise noted, all figures
Figure 8-1 Source: modified from:
http://cnx.org/resources/619024c8facab9b35a8593fb3b9ef215ccfdf7e0/911_Body_Movements(P
age%201).jpg
Figure 8-2 Source: modified from:
http://cnx.org/resources/8782cf72dca7895dd21c9c591f4411c0aa148ec5/911_Body_Movements(
Page%202).jpg
Figure 8-3 Source: modified from:
https://upload.wikimedia.org/wikipedia/commons/3/36/1120_Muscles_that_Move_the_Forearm
_Humerus_Flex_Sin.png
Figure 8-4 Source: modified from:
https://commons.wikimedia.org/wiki/File:1106_Front_and_Side_Views_of_the_Muscles_of_Fac
ial_Expressions.jpg
Figure 8-5 Source: modified from:
https://cnx.org/resources/8a3b1231f319214a74cffda6b70ff2c166e55a81/1105_Anterior_and_Pos
terior_Views_of_Muscles.jpg
Figure 8-6 Source: modified from:
https://cnx.org/resources/8a3b1231f319214a74cffda6b70ff2c166e55a81/1105_Anterior_and_Pos
terior_Views_of_Muscles.jpg
Figure 8-7 Source: modified from:
https://commons.wikimedia.org/wiki/File:Illu_trunk_muscles.jpg
Figure 8-8 Source: modified from:
https://upload.wikimedia.org/wikipedia/commons/5/50/1112_Muscles_of_the_Abdomen.jpg and
https://commons.wikimedia.org/wiki/File:Serratus_anterior_muscles_lateral.png
Figure 8-9 Source: modified from:
https://en.wikipedia.org/wiki/Facial_muscles#/media/File:Lateral_head_anatomy.jpg