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