Before attempting this chapter - please look at the chapter on joints.
Axial muscles refer to the muscles attached to the head, neck, vertebral column, thorax, abdomen and pelvis.
The head contains the muscles of facial expression and the muscles of mastication (chewing) as well as the muscles that move the eye (see the Nervous System: Special Senses chapter ).
The muscles of facial expression attach to the skin of the face so that when they move the expression of the face changes.
The muscles of mastication are strong muscles which forcibly close the mouth for chewing; they open and close the jaw (mandible) as well as move it forwards and backwards and from side to side.
Muscles of the neck allow us to move our heads as well as to swallow. The neck muscles work together to act on the cervical spine to make us nod our heads up and down and shake our heads from side to side . There are deep intricate muscles which help stabilize the cervical spine as well as the larger external muscles which flex and extend the neck.
Theses muscles allow us to twist and turn, as well as flex and extend the trunk. They are especially important in humans as they allow us to maintain an upright posture.
The muscles on the posterior (back) of the vertebral column extend, laterally flex and rotate the vertebral column as well as rotate and extend the head. These muscle can be grouped into three groups; erector spinae, transversospinalis and the suboccipital muscles.
Erector spinae is the large bulk of muscle that lies in the groove either side of the entire vertebral column. It is divided into 3 main columns, each of which divides further into 3 smaller sections. Erector spinae extends, laterally flexes and rotates the vertebral column.
Transversospinalis are a group of muscles also found either side of the vertebral column and attach to the transverse processes and spinous processes of the spinal cord. Transversospinalis muscles are grouped into 3 main groups; multifidus, semispinalis and rotatores. They extend, laterally flex and rotate the vertebral column.
The suboccipital muscles are a group of 4 small muscles that attach to the top of the cervical spine and the back of the skull (occipital bone). They extend and rotate the head.
This is a triangular space bounded by the superior and inferior oblique muscles and the rectus capitis posterior major. The floor of the triangle contains the posterior arch (back) of the first cervical vertebra (atlas or C1), and just above this the vertebral artery and the emerging first spinal nerve. It is important to understand the anatomy of this region as it is complex and often the site of degenerative disease or trauma.
The muscles on the anterior (front) of the vertebral column flex, laterally flex and rotate the cervical vertebral column as well as flex the head. The main muscles are listed below.
The main muscles of respiration are the diaphragm and the internal and external intercostal muscles. The diaphragm is attached to the lower six ribs and their costal cartilages, as well as the sternum and the sides of the lumbar vertebrae. The intercostal muscles attach to all of the ribs and their costal cartilages. Other muscles of the neck, shoulder, back, abdomen and pelvic floor can also contribute to respiration during forced inspiration/expiration.
The abdominal muscles are important flexors of the the vertebral column and increase the intra-abdominal pressure in a number of processes; coughing, urination, defecation, childbirth, vomiting and respiration.
The front and sides of the abdomen are supported by 3 thin muscles which become aponeurotic sheets along the anterior (front) of the abdomen; transversus abdominis, external oblique and internal oblique.
The tendons of transversus abdominis, internal oblique and external oblique merge together at the front of the abdomen to form a fibrous sheath know as the rectus sheath. Each side of the sheath joins in the mid line to form a strip called the linea alba. The rectus sheath divides around the rectus abdominis muscles and encloses them.
The inguinal ligament is the bottom edge of external oblique. The muscle is aponuerotic at this level and folds over to create a tunnel in which important structures can travel. In the female the round ligaments of the uterus and associated vessels travel through it and in the male the spermatic cord. Underneath the inguinal ligament is a space for the femoral vessels and nerves to pass into the thigh.
The pelvic floor consists of a sheet of muscle that acts like a hammock supporting the pelvic viscera. It extends from the pubis and ischial and pubic rami of the hip bone to the sacrum and coccyx. In the female, the pelvic floor is pierced by three openings, for the vagina, urethra and anus; in the male it is pierced by two openings, for the urethra and anus. The main muscles that contribute to the pelvic diaphragm are the levator ani and coccygeus muscles. Levator ani makes up a large proportion of the pelvic diaphragm and is split into two main parts.