Robin has taught college microbiology and environmental science. She has two master's degrees: one in environmental microbiology and the other in public health.
Aponeurosis Versus Tendon
Although the term 'aponeurosis' sounds like the name for a psychological disorder peculiar to apes, it is actually a type connective tissue. Connective tissues support the body and help it move. Aponeuroses are important for human movement and posture and are found all over your body, from the tip of your head to the soles of your feet.
What, exactly, is an aponeurosis? An aponeurosis is a type of connective tissue that provides a point for a muscle to attach to a bone or cartilage. You may be thinking that a tendon also attaches muscle to bone, and you are correct. So, how is an aponeurosis different than a tendon?
- An aponeurosis looks quite different than a tendon. If you placed them next to each other, you would have no trouble telling them apart. An aponeurosis is made of layers of delicate, thin sheaths. Tendons, in contrast, are tough and rope-like. An aponeurosis is made primarily of bundles of collagen fibers (collagen is the primary component of your body's connective tissues) distributed in regular parallel patterns, which makes an aponeurosis resilient.
- Aponeuroses, also called aponeurotica, function differently than tendons. When a muscle moves by flexing or extending, an aponeurosis acts like a spring to bear the extra pressure and tension. A tendon, on the other hand, moves a bone when a muscle contracts. Tendons allow the body to move and be flexible while aponeuroses allow the body to be strong and stable.
- Aponeuroses can act as fascia. Fascia is a fibrous tissue that envelopes muscles or organs, to bind muscles together or to other tissues.
Let's take a closer look at three examples of aponeuroses, starting at the top of your head.
The Epicranial Aponeurosis
Reach up and touch the top of your head. Just below your scalp you'll find the epicranial aponeurosis, the third layer of your scalp. Think of it as a delicate helmet beneath your scalp. Your skin comprises the first layer, and a dense connective tissue comprises the second layer. All three layers move together.
The epicranial aponeurosis provides the insertion point for the occipitofrontalis muscle, a thin, broad muscle that covers the top of your skull. This muscle controls many of your facial expressions. Every time you raise your eyebrows, you can thank your occipitofrontalis muscle and your epicranial aponeurosis!
The Abdominal Aponeurosis
Those 6-pack abdominals that athletes desire would not be possible without the abdominal aponeurosis! The abdominal aponeurosis encloses the long muscles located in the stomach area, from the bottom of the chest to the top of the pubic area. These muscles are called the rectus abdominis muscles. This is one type of aponeurosis that acts as fascia, fibrous tissue that envelopes muscles or organs, and is also called the rectal sheath.
Aponeuroses are thin tissues, and the abdominal aponeurosis is a great example. When you see an athlete with well-defined 6-pack abs, you certainly don't notice the aponeurosis that encloses those ab muscles!
The abdominal aponeurosis also provides the attachment sites for a number of other important abdominal muscles: the external abdominal obliques, the internal abdominal obliques, and the transversus abdominus. The abdominal aponeurosis binds all of these muscles together, which in turn provides stability to the trunk, and helps maintain good posture!
The Plantar Aponeurosis
If you stand up and lift your toes off the ground, you're pulling your plantar aponeurosis, a strong tissue that is found beneath the skin on the bottom plantar side of your foot. It is attached to the heel bone, fans across the bottom surface of your foot, and attaches to the base of each of your five toes.
As you walk, the plantar aponeurosis is engaged when your heel rises and the toes lift off the ground. This type of action is called a windlass mechanism. Sailors are familiar with this term, since a windlass is a type of winch mechanism, where a rope is wound around a drum. The windlass in the foot is the aponeurosis, which is wound around the metatarsals, mid-bones, of the foot.
The plantar aponeurosis also acts as a shock absorber when your foot hits the ground. It stabilizes the arch of your foot and allows the first metatarsal, the bone behind the big toe, to carry the majority of your body weight.
An aponeurosis is a type of connective tissue found throughout the body. Aponeuroses provide an attachment point for muscles to connect to bone, and can also envelope muscles and organs, bind muscles together, and bind muscles to other tissues. They are important for muscle movement and posture. Aponeuroses are thin and sheet-like, while tendons are thick and rope-like.
At the top of your head is the epicranial aponeurosis. It is like a thin helmet beneath the scalp, and provides the attachment sites for the occipitofrontalis muscle, a muscle that controls the eyebrows and facial expressions. The abdominal aponeurosis envelopes the abdominal muscles. It also provides the attachment sites for the external abdominal obliques, the internal abdominal obliques, and the transversus abdominus. The plantar aponeurosis is found on the soles of the feet. This aponeurosis has a windlass mechanism, meaning it winds around the mid-bones of the foot and is engaged during walking, when the heel rises and the toes lift off of the ground. The plantar aponeurosis also stabilizes the arch of the foot and acts as a shock absorber.
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