After completing this chapter, you should be able to:

13-1 Define key terms.

13-2 Identify the different types of vertebrae in the spinal column.

13-3 Label on a skeletal chart the types of vertebrae and their important features.

13-4 Draw and label on a skeletal chart the muscles of the trunk and spinal column outlined in this chapter.

13-5 Demonstrate all the active and passive movements of the head, neck, and trunk with a partner.

13-6 Palpate on a partner the muscles of the trunk and spinal column emphasized in this chapter.

13-7 Explore the origins and insertions of the muscles emphasized in this chapter.

13-8 Organize and list the muscles that produce the primary movements of the head, neck, and trunk.

13-9 Practice flexibility and strengthening exercises for each muscle group.

CHAPTER SUMMARY

Introduction

• The trunk contains the internal organs, houses the spinal column, and provides attachment for the upper and lower extremities.

Bones

• There are 24 articulating vertebrae in the spinal column, and 5 and 4 fused bones in the sacrum and coccyx, respectively. There are 7 cervical, 12 thoracic, and 5 lumbar vertebrae.
• Parts of the vertebra are the spinous process, transverse process, and body.
• The spine has three normal dynamic curves.
• Abnormal curves either are genetic or can develop for a variety of reasons. The curves include kyphosis, lordosis, and scoliosis.
• There are 12 pairs of ribs, 7 of which are true, attaching to the sternum; 5 pairs are false, and 2 of these pairs are floating ribs. The ribs attach to the vertebrae posteriorly.
• The manubrium of the sternum and the xiphoid process at the end of the sternum provide attachment sites. The clavicle is also an attachment site for the sternocleidomastoid.
• Abdominal muscles attach to pubic and iliac crest bones and to the inguinal ligament.
• The mastoid process and occiput provide attachment for lateral and posterior cervical muscles.

 Joints

• The first joint is the atlantooccipital joint, allowing flexion and extension.
• The atlas and axis form a pivot joint (atlantoaxial joint), allowing rotation.
• The rest of the vertebrae are gliding joints.

Movements of the Trunk and Head

• The head moves forward with flexion, back with extension, and toward the shoulder in lateral flexion; the chin rotates toward the shoulder in rotation.
• The lumbar spine provides movement in flexion, extension, lateral flexion, reduction, and rotation.

Trunk and Spinal Column Muscles

• The sternocleidomastoid is located anteriorly and laterally.
• The splenius muscles connect the thoracic region to the head and upper cervical vertebrae.
• There are additional intrinsic muscles that move the head and neck, including the deep suboccipitals.
• Anteriorly, the rectus abdominis, external oblique, and internal oblique flex the trunk. The transversus abdominis assists in respiration and is the deepest abdominal muscle.
• The erector spinae muscles span the back from the sacrum to the occiput. This large group is divided into three groups of three muscles each, for nine muscles on each side of the spine.
• The quadratus lumborum is situated deep in the posterior lumbar region between the 12th rib and the iliac crest.

Nerves

• The accessory nerve and spinal nerves C2 and C3 innervate the sternocleidomastoid. Spinal nerves innervate the erector spinae and the quadratus lumborum. Intercostal nerves innervate abdominal muscles together with the iliohypogastric and ilioinguinal nerves.

Muscles That Move the Head

• There are many layers of muscles that surround the cervical spine, connect the head to the vertebrae and the vertebrae to the trunk, and provide movement on multiple levels. See table 13.2 on p

Individual Muscles of the Trunk and Spinal Column—Muscles That Move the Head and Neck

• Sternocleidomastoid, named for its attachments, begins at the sternum and clavicle and inserts at the mastoid process. It flexes the head forward, laterally flexes on the same side, and rotates the head to the opposite side.
• Splenius capitis and cervicis are bandage muscles that wrap around the neck. They connect the thoracic spine to the occiput and to the cervical vertebrae. They laterally flex and rotate the head and neck.

Muscles of the Vertebral Column

• Deep muscles of the vertebral column provide a network of muscles that connect the vertebra to vertebra and stability for the spine. See table 13.3 on page 276 for a listing of deep muscles of the vertebral column.

Individual Muscles of the Trunk and Spinal Column—Muscles That Move the Vertebral Column

• Erector spinae comprise nine muscles in three divisions; the group is a spinal extensor on either side of the vertebral column. This elaborate muscle group spans from the sacrum and attaches to ribs and vertebrae on its way to the mastoid process and the occiput. The three major divisions are the iliocostalis, longissimus, and spinalis. Although the erector spinae’s primary action is extension of the whole spinal column, the divisions are involved in lateral flexion of the head and trunk and assist in other movements.
• Quadratus lumborum is a deep lower-back stabilizer. It spans from the 12th rib to the lumbar vertebrae and the iliac crest. It has multiple actions and is prone to soft-tissue injury when bearing the brunt of heavy lifting or incorrect body mechanics.

Muscles of the Thorax

• Muscles of the thorax assist in the process of respiration. See table 13.4 on page 281 for muscles of the thorax.

Individual Muscles of the Abdominal Wall

• Rectus abdominis spans from the ribs and xiphoid process to the pubis. It is a major trunk flexor.
• External oblique is located laterally to the rectus abdominis but connects to it through abdominal fascia. It interdigitates with the serratus anterior and with latissimus dorsi. It laterally flexes the trunk to the same side and will rotate to the opposite side.
• Internal oblique is located anteriorly and lateral to rectus abdominis. It is layered beneath the external oblique. It works with the external oblique to laterally flex to the same side and rotate the trunk.
• Transversus abdominis is the deepest abdominal muscle and is attached to lumbar fascia. It helps with forced expiration.