15.9
頭を動かす筋肉
頭を動かす筋肉は、頭部の回転、屈曲、伸展、側屈などの幅広い範囲の動きを促進するために連携しており、動的機能をする複雑な構造を持ったグループの筋である。
両側の胸鎖乳突筋 (SCM)、舌骨上筋および舌骨下筋は、重要な頭部屈筋である。 SCM 筋は胸骨と鎖骨から始まり、側頭骨の乳様突起に着している。 S…
複数の首の筋肉が頭のバランスを取り、大動脈後頭関節での動きを促進するのに役立ちます。
たとえば、両側胸鎖乳突筋(SCM)は、舌骨上筋および舌骨下筋とともに主要な頭屈筋です。
その腹は胸骨と鎖骨から始まり、側頭骨の乳様突起に挿入されます。
SCMが両側に収縮すると、頭を前に曲げるのに役立ちます。対照的に、片側収縮は、同じ側での横方向の屈曲または反対側への頭の回転を促進します。
首の外側の筋肉(前斜角筋、中斜筋、後斜角筋)は、脊柱に沿って斜めに走っています。
それらは頸椎を上部の2つの肋骨に接続し、横方向の屈曲も促進します。
後頸部の筋肉である頭頭脾炎は、脊椎靭帯とC7からT3の棘突起に由来し、後頭骨と側頭骨に挿入されます。
両側に収縮すると、頭の伸展を助けますが、片側収縮は横方向の屈曲と同じ側への回転を助けます。
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Q1: What is the sternocleidomastoid muscle and what movements does it control?
The sternocleidomastoid (SCM) is a major head flexor originating at the sternum and clavicle and inserting into the mastoid process of the temporal bone. Bilateral contraction bends the head forward, while unilateral contraction causes lateral flexion on the same side or head rotation to the opposite side.
Q2: How do the scalene muscles contribute to head and neck movement?
The anterior, middle, and posterior scalenes run diagonally along the vertebral column, connecting cervical vertebrae to the upper two ribs. These lateral neck muscles facilitate lateral flexion and work with other structures to support diverse head movements, stabilization, and coordinated neck function.
Q3: What is the role of the splenius capitis in head movement?
The splenius capitis originates from the nuchal ligament and C7 to T3 spinous processes, inserting onto the occipital and temporal bones. Bilateral contraction aids head extension, whereas unilateral contraction assists lateral flexion and rotation to the same side, enabling diverse directional movements.
Q4: What are the three layers of posterior neck muscles and their functions?
The superficial layer includes the trapezius and splenius muscles, controlling shoulder and head extension. The middle layer contains cervical transversospinalis muscles like semispinalis capitis, extending and rotating the head. The deepest layer includes suboccipital muscles providing fine motor control and proprioception for precise head positioning.
Q5: How do suboccipital muscles differ from other neck muscles in function?
Suboccipital muscles, located just below the occipital bone, are crucial for fine motor control and proprioception—the sense of self-movement and body position. Unlike larger neck muscles that produce major movements, suboccipitals make minor adjustments to head position and coordinate spatial awareness during complex head movements.
Q6: What is the relationship between the suprahyoid and infrahyoid muscles and head movement?
The suprahyoid and infrahyoid muscles are significant head flexors that work alongside the sternocleidomastoid to facilitate forward head bending. These muscles support muscle coordination and action by stabilizing the hyoid bone and enabling smooth, controlled flexion movements of the head.
Q7: How do bilateral versus unilateral muscle contractions produce different head movements?
Bilateral contraction of muscles like the SCM or splenius capitis produces forward extension or head bending. Unilateral contraction of the same muscles causes lateral flexion toward the contracting side or rotation to the opposite side, allowing precise directional control of head position.