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8: The Axial Muscles

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    12528
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    Skeletal muscle is found attached to bones. It consists of long multinucleate fibers. The fibers run the entire length of the muscle they come from and so are usually too long to have their ends visible when viewed under the microscope. The fibers are relatively wide and very long, but unbranched. Fibers are not individual cells, but are formed from the fusion of thousands of precursor cells. This is why they are so long and why individual fibers are multinucleate (a single fiber has many nuclei). The nuclei are usually up against the edge of the fiber. There are striations in skeletal muscle. These are alternating dark and light bands perpendicular to the edge of the fiber that are present all along the fiber.

    Image_183.png

    The muscles of the head and neck

    Figure 8.1 lists the muscles of the head and neck that you will need to know. A single platysma muscle is only shown in the lateral view of the head muscles in Figure 8.1. 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.)

    Image_184.png

    Figure 8.1. The muscles of the head.

    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.

    LAB 8 EXERCISE 8-1

    The following are muscles of facial expression. For each, give its location and describe its action when it contracts. Complete figure 8.1 above by adding in any muscles found in the table below.

    .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

       

    Medial pterygoid

       

    Lateral pterygoid

       

    LICENSES AND ATTRIBUTIONS

    CC LICENSED CONTENT, ORIGINAL

    1. The following are muscles of facial expression. For each, give its location and describe its action when it contracts. Complete figure 8.1 above by adding in any muscles found in the table below.

      Muscle

      Location

      Action when contracted

      Epicranius frontalis

         

      Epicranius occipitalis

         

      Orbicularis oculi

         

      Zygomaticus major

         

      Zygomaticus minor

         

      Buccinator

         

      Orbicularis oris

         

      Platysma

         

      Levator labii sup.

         

      Depressor labii inf.

         

      Levator anguli oris

         

      Depressor anguli oris

         
    2. The following are muscles of mastication. For each, give its location and describe its action when it contracts.

    A&P Labs. Authored by: Ross Whitwam. Provided by: Mississippi University for Women. Located at: http://www.muw.edu. License: CC BY-SA: Attribution-ShareAlike

    CC LICENSED CONTENT, SPECIFIC ATTRIBUTION

    Figure 8-1. The muscles of the head.. Authored by: OpenStax College. Located

    at: https://cnx.org/resources/9b369a7466..._the_Muscles_o f_Facial_Expressions.jpg. License: CC BY-SA: Attribution-ShareAlike

    The muscles of the trunk

    Information

    Figures 8.2 and 8.3 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 8.4. 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 8.5.

    Image_185.png

    Figure 8.2. The major muscles of the body, anterior view. Anatomical right shows superficial muscles. Anatomical left shows deep muscles.

    Image_186.png

    Figure 8.3. The major muscles of the body, posterior view. Anatomical right shows superficial muscles. Anatomical left shows deep muscles.

    Image_187.png

    Figure 8.4. The three layers of muscles in the abdomen.

    Image_188.png

    Figure 8.5. The external muscles of the body, lateral view.

    LAB 8 EXERCISE 8-2

    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

         

      image

    4. Label the indicated facial muscles in Figure 8.6.

      1

      2

      3

      5

      5

      6

      8

      7

      10

      12

      11

      9

      Figure 8.6. Facial muscles.

      LICENSES AND ATTRIBUTIONS

      CC LICENSED CONTENT, ORIGINAL

      • A&P Labs. Authored by: Ross Whitwam. Provided by: Mississippi University for Women. Located at: http://www.muw.edu. License: CC BY-SA: Attribution-ShareAlike

        CC LICENSED CONTENT, SHARED PREVIOUSLY

      • Figure 8-5. The external muscles of the body, lateral view.. Authored by: This image was made out of, or made from, content published in a BodyParts3D/Anatomography web site. . Provided by: BodyParts3D, u00a9 The Database Center for Life Science licensed under CC Attribution-Share Alike 2.1 Japan.. Located

        at: https://commons.wikimedia.org/wiki/F...es_lateral.png. License: CC BY-SA: Attribution- ShareAlike

        CC LICENSED CONTENT, SPECIFIC ATTRIBUTION

      • Figure 8-2. The major muscles of the body, anterior view. Anatomical right shows superficial muscles. Anatomical left shows deep muscles.. Authored by: OpenStax College. Located

        at: https://cnx.org/resources/8a3b1231f3...s_of_Muscles.j pg. License: CC BY-SA: Attribution-ShareAlike

      • Figure 8-3. The major muscles of the body, posterior view. Anatomical right shows superficial muscles. Anatomical left shows deep muscles.. Authored by: OpenStax College. Located

        at: https://cnx.org/resources/8a3b1231f3...s_of_Muscles.j pg. License: CC BY-SA: Attribution-ShareAlike

      • Figure 8-5. The external muscles of the body, lateral view.. Authored by: OpenStax College. Located

        at: https://cnx.org/resources/33fa36d780...he_Abdomen.jpg. License: CC BY-SA: Attribution-ShareAlike

      • Figure 8-6. Facial muscles.. Authored by: Patrick J. Lynch. Located

        at: https://commons.wikimedia.org/wiki/F...ad_anatomy.jpg. License: CC BY-SA: Attribution-ShareAlike

        PUBLIC DOMAIN CONTENT

      • Figure 8-4. The three layers of muscles in the abdomen.. Authored by: Arcadian. Located

        at: https://commons.wikimedia.org/wiki/F...nk_muscles.jpg. License: Public Domain: No Known Copyright

        LAB 8 EXERCISE 8-3

        image

        3

        1

        A

        3 Layers of connective tissue

        Identify the following: epimysium * perimysium * endomysium * muscle fascicle * muscle fiber

        Identify the following: origin * insertion *

        B

        extensor * flexor

        1

         

        2

         

        3

         

        4

        5

        2

           

        4

         

        image

        Note: make some flashcards for studying the

        insertions, origins and actions!

        C

        List the defining visual characteristics of this muscle and draw arrows to features on the photograph that illustrate each characteristic.

        image

        1. Obtain a slide of skeletal muscle tissue from the slide box.

        2. View the slide on an appropriate objective.

        3. Fill out the blanks next to your drawing.

        In the circle below, draw a representative sample of key features you identified, taking care to correctly and clearly draw their true shapes and directions. Draw your structures proportionately to their size in your microscope’s field of view.

        image

        Type of muscle tissue:

        image

        LAB 8 EXERCISE 8-4

        IDENTIFY MUSCLES OF THE HEAD & FACE

        1

        3

        6

        7

        2

        4

        5

        image

        image

        *connective tissue

        insertion, not a muscle

        LAB 8 EXERCISE 8-5

        IDENTIFY THE MUSCLES OF THE TORSO

        1

        4

        5

        2

        6

        7

        3

        8

        LAB 8 EXERCISE 8-6

        IDENTIFY THE MUSCLES OF OR NEAR THE BACK

        1

        4

        5

        6

        2

        7

        3

        8

        MODELS: Head & Neck and Torso

        Name

        Action

        Origin

        Insertion

        Muscles of facial expression

        Frontalis (epicranius)

        Raises eyebrows , wrinkles forehead

        Frontal Bone

        Skin of the brow

        Occipitalis (epicranius)

        Pull scalp posteriorly

        Occipital bone

        Aponeurosis connecting to frontalis

        Orbicularis oris

        Closes mouth

        Maxillae and Mandible

        Lips

        Zygomaticus (major/minor)

        smile 

        Zygomatic Bone

        mouth

        Orbicularis oculi

        Closes eye

        Margin of Orbit

        Eyelid

        Masseter

        Elevates mandible

        Zygomatic Arch

        Mandible

        Temporalis

        Elevates mandible

        Temporal Bone

        Mandible

        Buccinator

        Presses cheek inward

        Maxillae and Mandible

        orbicularis oris

        Muscles of the head, vertebral column and abdominal wall

        Splenius capitis

        extend + laterally flex head

        upper spine

        Temporal & occipital

        Sternocleidomastoid

        Flexes + rotates neck (also elevates ribs)

        Sternum & Clavicle

        Mastoid Process

        Scalenes

        Flexes neck (also elevates ribs)

        Cervical Vertebrae

        1st Two Ribs

        Rectus abdominus

        Flexes vertebral column , compresses abdomen

        Pubis

        Lower Ribs and Xiphoid

        External oblique

        Flexes + rotates vertebral column,

        compresses abdomen

        Lower Ribs

        Linea alba and Ilium

        Internal oblique

        Flexes + rotates vertebral column, compresses abdomen

        Lumbar Vertebrae & Ilium

        Lower Ribs, Linea alba, Sternum

        Transverse abdominus

        Compresses abdomen

        Lower Ribs, Ilium, Lumbar

        Vertebrae

        Linea Alba & Pubis

        Erector spinae group

        Extends vertebral column

        Ilium, Sacrum, Ribs, Vertebrae

        Ribs, Vertebrae, Base of Skull

        Levator scapulae

        Extends neck (also elevates scapula)

        Cervical Vertebrae

        Scapula

        Name

        Action

        Origin

        Insertion

        Thoracic & shoulder muscles

        Pectoralis major

        Flexes, adducts + medially rotates arm at shoulder

        Sternum & Clavicle

        Humerus

        Pectoralis minor

        Elevates ribs (also moves scapula anterior and inferior)

        Ribs

        Scapula

        External intercostals

        Elevates ribs

        Inferior Rib

        Superior rib

        Internal intercostals

        Depresses ribs

        Superior rib

        Inferior Rib

        Diaphragm

        Increases thoracic volume

        Xiphoid Process, Ribs, Lumbar Vertebrae

        Central Tendinous Sheet

        Arm movers

        Serratus anterior

        Moves and fixes scapula anteriorly

        Ribs

        Scapula

        Trapezius

        Elevates, retracts, depresses+ rotates scapula upward (also extends neck)

        Occipital Bone & Thoracic Vertebrae

        Scapula

        Rhomboids (major & minor)

        Elevates + adducts scapula

        Cervical & Thoracic

        Vertebrae

        Scapula

        Latissimus dorsi

        Extends, adducts + medially rotates arm at shoulder

        Thoracic, Lumbar Vertebrae, Ribs

        Humerus

        Deltoid

        Abducts arm at shoulder (also anterior fibers flex + posterior fibers extend arm at shoulder)

        Clavicle & Scapula

        Humerus

        Teres major

        Medially rotate arm

        Scapula

        Humerus

        Rotator cuff (SITS)

        Infraspinatus

        Laterally rotates shoulder

        Scapula

        Humerus

        Supraspinatus

        Abducts shoulder

        Scapula

        Humerus

        Subscapularis

        Medially rotates shoulder

        Scapula

        Humerus

        Teres minor

        Laterally rotates shoulder

        Scapula

        Humerus