Cranial and Spinal Muscles

The axial skeleton is manipulated by a complex of large and small muscles. From the point of view of clinical importance, there are several cranial muscles which deserve special mention.

The external muscles of the eye are important, in part, because of their dependence on the intergrity of certain cranial nerves. In general eye movements are under the control of the oculomotor nerve (cranial nerve III). However, convergence of the eyes depends on the trochlear nerve (cranial nerve IV), and abduction is controlled by the abducens nerve (cranial nerve VI). Disorders of eye movement may therefore be important clues to pathology of the cranial nerves or brain stem.The temporalis (figure 1) and masseter muscles are the primary flexors of the temporomandibular joint. Both are innervated by the mandibular branch of the trigeminal nerve (cranial nerve 5). The temporalis is the longer and deeper muscle stretching from the frontal, parietal and temporal bones to the anterior ramus of the mandible. The masseter originates on the zygomatic process and inserts principally on the lateral aspect of the ramus of the mandible. Many other smaller muscles control facial expression. In general, these muscles are controlled by the facial nerve (cranial nerve 7).

Movement of the head on the neck, and neck posture are controlled by several clinically important muscles. The sternocleidomastoid muscle (figure 2) runs from the mastoid process of the temporal bone to the sternum and clavicle. This muscle is frequently injured in hyperextension (whiplash) injuries of the neck. The flexing and rotating activity of the sternocleidomastoid is balanced by the trapezius. The trapezius originates on the lateral clavicle and scapula and inserts on the thoracic spinous processes, nuchal ligament and occiput. Fine movement of the head on the neck is achieved by small segmental muscles and by four suboccipital muscles which link the upper two cervical vertebrae and the occiput. These four muscles are rectus capitis posterior major, rectus capitis posterior minor, obliquus capitis superior and obliquus capitis inferior.

Along the length of the vertebral column are sets of short, intersegmental muscles for fine control, and longer muscles which can achieve larger movements (figure 4). The multifidus and semispinalis muscles link transverse processes to the spinous processes two or more levels above. Multifidus controls local rotation. Long sets of muscles involved in extension and lateral bending include spinalis, longissimus and iliocostalis. The actions of these muscles are balanced by the external intercostal and internal intercostal muscles (figure 5), and by four sheets of muscle which reinforce the abdominal wall (figure 6): rectus abdominis, external oblique, internal oblique and transversus abdominis.

English - Japanese Glossary

external intercostal: 外肋間筋 (gairokkankin); external oblique: 外腹筋 (gaifukukin); internal intercostal: 内肋間筋 (nairokkankin); internal oblique: 内腹筋 (naifukukin); latissimus dorsi: 広背筋 (kouhaikin); levatores costarum brevi: 短肋骨挙筋 (tanrokkotsukyokin); levatores costarum longi: 長肋骨挙筋 (chourokkotsukyokin); longissimus capitis: 頭最長筋 (tousaichoukin); longissimus cervicis: 頚最長筋 (keisaichoukin); longissimus thoracis: 胸最長筋 (kyousaichoukin); iliocostalis cervicis: 頚腸肋筋 (keichourokkin); iliocostalis lumborum: 腰腸肋筋 (youchourokkin); iliocostalis thoracis: 胸腸肋筋 (kyouchourokkin); masseter: 交筋 (koukin); multifidus: 多裂筋 (taretsukin); obliquus capitis inferior: 下頭斜筋 (katoushakin); obliquus capitis superior: 上頭斜筋 (joutoushakin); rectus abdominis: 腹直筋 (fukuchokukin); rectus capitis posterior major: 大後頭直筋 (daigotouchokkin); rectus capitis posterior minor: 小後頭直筋 (shougotouchokkin); semispinalis capitis: 頭半きょく筋 (touhankyokukin); semispinalis cervicis: 頚半きょく筋 (keihankyokukin); semispinalis thoracis: 胸半きょく筋 (kyouhankyokukin); sternocleidomastoid: 胸鎖乳とう筋 (kyousanyuutoukin); temporalis: 側頭筋 (sokutoukin); trapezius: 僧帽筋 (souboukin)

Brian Budgell,
Nov 8, 2014, 5:06 PM