Anatomy of the Thoracic and Abdominal Muscles
Thoracic Muscles
Diaphragm Muscle
The diaphragm is a large, flat, umbrella-shaped or dome-shaped muscle that separates the chest cavity from the abdominal cavity. Its contour is inserted into the lower chest, the costal margin, and the xiphoid sternum. Behind the diaphragm muscle, it is fixed in the first two lumbar vertebral bodies: pillars of the diaphragm (the muscle insertion). The diaphragm muscle, in its central part, has a clover-shaped aponeurosis. This central aponeurosis is called the phrenic center, from which the muscle fibers of the diaphragm muscle radiate. The diaphragm is crossed by three structures: two veins and the esophagus.
- The caudal inferior vena cava is installed in the phrenic nerve in the right rear blade.
- The aorta is in the central part, attached to the vertebral bodies.
- The esophagus is the most important structure that crosses the diaphragm.
Abdominal Muscles
The first abdominal muscle is the diaphragm, which forms the upper wall of the abdomen. It is shaped like a square box.
Anterolateral Wall
The anterolateral wall consists of muscles that crisscross each other and form a kind of strip that closes the abdomen in front and at the sides.
External Oblique Muscle
The most superficial muscle of this wall is the external oblique muscle, which originates in the last seven ribs and the iliac crest and inserts into the lumbar vertebrae. The fibers of the external oblique muscle are directed downward to end in a large aponeurosis that intersects the middle line with the other side.
Internal Oblique Muscle
Inside the external oblique muscle, there is a major oblique muscle that forms a mesh, the internal oblique muscle. It originates from the iliac crest and directs its fibers upward and outward, while others are directed downward and forward. It also ends in a large aponeurosis that intersects the midline to form the linea alba, extending from the sternum to the symphysis pubis.
Transverse Muscle
From inside the oblique muscle, there is the transverse muscle, which has insertions behind the five lumbar vertebrae, in the last ribs, and the iliac crest. Its main feature is that it directs its fibers transversely forward.
These three muscles are also known as the wide muscles of the abdomen. In the wide muscles of the abdomen, there is a broad training of the external oblique called the inguinal ligament. This is a weakness that leaves the spermatic cord of men and is occupied by fluid around the uterus in women. The inguinal canal is carved in the thickness of the muscles through which the inguinal nerves pass. Below and beyond the inguinal nerve, there is a hole through which the femoral vessels pass. When they cross this passage, it is called the femoral ring. These femoral vessels are outside the iliac psoas, which goes in search of the greater trochanter. Inside the hole is the pectineus. Femoral vessels leave the pelvis within the femoral triangle, also known as Scarpa’s triangle. This is also where abdominal hernias occur. There is another weak spot in the abdominal wall where lumbar hernias occur: The lumbar triangle is based on the iliac crest and only the external oblique and transversus muscles are present.
Rectus Abdominis
In the front wall, extending from the sternum to the pubic symphysis, there is another muscle, the rectus abdominis, one on each side. They are characterized by three to five aponeurotic intersections. When it contracts, it pulls the sternum towards the symphysis pubis. The anterior aponeurosis of the wide muscles surrounds the rectus muscles and inserts into the symphysis pubis. All three aponeuroses of the wide muscles pass in front of the rectus muscles. If we look back, we see the shape of an arc: the Arc of Douglas.
Posterior Wall
On the rear wall, leading into the urinary tract, are the psoas and quadratus lumborum, or lumbar spine. On the wall below is the levator ani muscle, which closes the abdominal wall. It is very important for keeping the pelvic organs in place. It extends from the back of the pubis to the ischial spine laterally.
Muscle fibers are fused with the anti-lateral side in front of and behind the rectum.
The levator ani is a muscle that is often injured during childbirth in women or by surgical injury. This can lead to problems with urinary incontinence, which can be improved with muscle training exercises. It is also located around the urethra and vagina.
Head Joints
Virtually all head joints are sutures. The skull bones are pinned together by sutures, with the exception of the temporomandibular joint, the only synovial joint in the skull. Synovial joints allow for mobility. The rest are synarthroses: syndesmosis (bones close together). Sutures sometimes ossify and become synostoses.
Fontanelle
In newborns, the bones of the skull are membranous and have yet to ossify. Between the bones of the cranial vault, there will be no place for the bones to grow, so there are membranes of connective tissue; the fontanelle (present at birth) will gradually close within six months.