Science

  • Issue 109 / January -February 2016



    The Fallacy of Vestigial Organs: Outer Ear Muscles

    Arslan Mayda

    The outer ear (auricula) is an oval structure, its wide part facing upwards. When we look at the auricula, we think that it is only composed of skin and cartilage. However there are nine perfectly positioned muscles present in an auricula (Figure 1). In addition, some anatomists accept the m.temparopariatalis muscle, which extends from the skull and attaches to the ear’s skin, as one of the auricula’s muscles. These muscles enable the ear to fulfill many of its significant tasks.


    Some would have you believe that these muscles are useless, or a simple quirk of human development. But in studies, ear muscles were found to contain spindle shaped fibers. There’s a wisdom behind this: spindle shaped muscles are resistant to long term contraction and relaxation. This is because when all the muscles stimulated by the facial nerve contract, the outer ear muscles also work with them. Most people assume that the auricula muscles do not contract and relax. However, when the facial muscles contract and relax, the outer ear muscles do so, too. Thus, spindle shaped muscles that are capable of extensive contraction and relaxation are required for the activities of the external ear. Calcium ions make these muscles so resistant to moving.


    A strong connection

    The auricula connects to the temporal bone at the side of the skull via muscles, ligaments, and skin. It is attached to the skull with five surrounding ligaments and three external auricula muscles.

    The six muscles that bind the crumpled shaped cartilage frame to one another are called inner muscles. The outer muscles, which connect the external ear to the head, are specifically created to form a strong and functional ear. The curvy elastic cartilage section (Figure 2) is tightly connected to the skull via skin and ligaments.

    Many animals also have moving external ears. For instance, a dog moves its ears towards the direction of a sound and pays closer attention. A dog’s ear is perfectly shaped for this task, just as the human outer ear is perfectly shaped with special curves and folds to channel sounds to the eardrum and to generate a balanced vibration in a cone-form structure.



    Muscles protect the outer ear

    The outer ear is a cartilage tissue of 0.5–1 mm thickness. It has a specific folded, curvy shape. When its anatomic structure is observed, three sets of folds follow each other. In addition to collecting sounds, the outer ear also has to detect the direction and location of these sounds. These outer ear muscles have a duty to gather sounds, sense their directions, and yet not become deformed.

    The protection of the cartilage folds is mostly based on the contraction force of the outer muscles of the ear, working together with the inner muscles. In a study, the relationship of m. transversus and m. obliquus, as the inner auricula muscles are called, with the outer ear cartilaginous folds was evaluated. Individuals with post-natal flatness on the first groove of the outer ear were the subjects of this study. The cause of the flatness on the first upper groove (the scapha) was determined to be the lack of the m. transversus and m. obliquus muscles at birth. Hence it is understood that the contraction of all muscles are necessary for the morphology and protection of these folds. Prenatal events such as muscle weakness, abnormal attachment, and muscle deficiency were seen as inhibiting factors for outer ear folds.

    A twelve year old girl had a flat upper ear (stahl ear) without folds. In this ear type, there is no third projection (scapha) on the upper groove. This projection can give a pointy look to the ear (some would describe it as a “Mr. Spock” look). She underwent surgery to eliminate this flat shape. During the operation, an anomaly was noticed at the location of the m.obliquus auruculare muscle. It was discovered that when this muscle fails to attach to its position prenatally, it causes ear deformities. The surgery then made a small incision on the cartilage to move the muscle to its normal location. After three years, an improved look was achieved. 1


    Muscles provide balance

    Three muscles located on the outer ear, named m. auricularis posterior, anterior, and superior balance the pulling force of the inner muscles that cause the outer ear’s folds.

    Usually there are no serious problems in most of the birth related outer ear anomalies (malformations or deformations). Malformations stemming from prenatally ingested drugs or genetic code mistakes occur between the 5th and the 9th week of pregnancy.

    If there are no inner ear muscles present at birth, the outer ear stays saggy, soft, and in a loose position. In cases where the outer ear muscles are deficient at birth or are attached in the wrong places, due to the forward pull of the inner muscles, a specific look known as “flap-ears” appears. With surgery, a tip of a muscle taken from the back of the ear can be positioned towards the front in a corrective autoplasty. The earlier these operations are made, the better the results. 2,10

    Furthermore, due to the pressures applied on the ear from incorrect prenatal postures, the outer ear can also lose its form (deformation anomalies). Apart from surgery, with special applications like casting, these deformations can be fixed within three months. 3


    Veins in the ear muscles

    Our ears turn red and purple in very chilly weather. The reason for the color change is the expansion of blood vessels in order to provide nourishment and warmth to the outer ear. These vessels are located inside the outer ear muscles. Due to the wise, meticulous placement of blood vessels inside these muscles, not only are the blood vessels protected, but nourishment to the outer ear is enabled. In addition, muscles provide warmth to the ear due to their constant activity.


    Cooperation and communication

    The muscles of the outer ear are connected to the center of the cardiovascular and nervous systems; they flex apart from the other muscles and organs of the face. Their operation is united. Their stimulation and reflex responses take place with the same nerve. They feed from the same artery and dump their blood to the same lymphoid and vein system. They are inseparable parts of a single entity. There have been many experiments completed on this subject.

    For instance, during a facial stroke, when the facial muscles are paralyzed, the outer ear muscles are also seen to be paralyzed, as they are stimulated with the same nerve. If the stroke is permanent, single-sided loss of movement, hearing, and flattening of the outer ear curves are observed. 4,12

    In another study, electrodes protruding behind the ears were placed among the projections of the mastoid bones. The reactions upon stimulation are found to be very intense in the ear muscles as compared to the earlobe. 5,9

    In another study with 19 facial stroke (hemi-facial paralyses) patients, the reflex stimulation applied on the eye muscle (orbicularis oris) of the paralyzed side reached behind the back of the outer ear in everybody except for two patients. 6 In opposite situations, stimulation applied on the outer ear’s posterior muscles generated lateral eye movements. 7,11

    The response of the outer auricula muscles to stimuli stems from the reflex center of the primary motor neuron. In patients who suffered a facial stroke after a surgical operation or a trauma, properties of the brain stem reflexes were observed after sound stimuli. Contractions were observed on the outer ear muscles upon application of sound stimuli over the eye. This is believed to happen via transmission of signals from the eye to the spinal cord. 8,11

    We can see that every organ and every tissue in our body is created to serve a purpose. The absence of even the smallest organ or tissue means the termination of a function. Like so many other wisely created pieces, these ear muscles also carry out important roles. They are hardly “vestigial.”


     




    NOTES


    1. Yotsuyanagi T, Nihei Y, Shinmyo Y, Sawada Y. Stahl’s ear caused by an abnormal intrinsic auricular muscle. Plastic and Reconstructive Surgery. 1999 Jan;103(1):171-4. http://www.ncbi.nlm.nih.gov/pubmed/9915179.

    2. Karaaslan O, Sonmez E, Silistreli OK, Can M, Caliskan G, Bedir YK. Splitted posterior auricular muscle flap combined with traditional otoplasty. The Journal of Craniofacial Surgery. 2013 Jul;24(4):1350-2. doi: 10.1097/SCS.0b013e31828b6afc. http://www.ncbi.nlm.nih.gov/pubmed/23851805.

    3. Porter CJ, Tan ST. Congenital auricular anomalies: topographic anatomy, embryology, classification, and treatment strategies. Plastic and Reconstructive Surgery. 2005 May;115(6):1701-12. http://www.ncbi.nlm.nih.gov/pubmed/15861078.

    4. Cho HJ, Kim HY. Interesting sign of Bell’s palsy in an ear wiggler. Neurogical Sciences. 2009 Aug;30(4):345-7. doi: 10.1007/s10072-009-0096-9. Epub 2009 May 30. http://www.ncbi.nlm.nih.gov/pubmed/?term=%22+auriculares+muscles%22.

    5. Matas CG, Neves IF, Carvalho FM, Leite RA. Post-auricular muscle reflex in the Middle Latency Evoked Auditory Response. Brazilian Journal of Otorhinolaryngology. 2009 Jul-Aug;75(4):579-85. http://www.ncbi.nlm.nih.gov/pubmed/19784429.

    6. Kiziltan M, Sahin R, Uzun N, Kiziltan G. Hemifacial spasm and posterior auricular muscle. Electromyography and Clinical Neurophysiology. 2006 Sep;46(5):317-20. http://www.ncbi.nlm.nih.gov/pubmed/17059105.

    7. O’Beirne GA, Patuzzi RB. Basic properties of the sound-evoked post-auricular muscle response (PAMR). Hearing Research. 1999 Dec;138(1-2):115-32. http://www.ncbi.nlm.nih.gov/pubmed/10575120.

    8. Kiziltan ME, Gündüz A, Sahin R. Auditory evoked blink reflex and posterior auricular muscle response: observations in patients with HFS and PFS. Journal of Electromyography and Kinesiology. 2010 Jun;20(3):508-12. doi: 10.1016/j.jelekin.2009.07.009. Epub 2009 Sep 19. http://www.ncbi.nlm.nih.gov/pubmed/19767218.

    9. Bérzin F, Fortinguerra CR. EMG study of the anterior, superior and posterior auricular muscles in man. Annals of Anatomy. 1993 Apr;175(2):195-7. http://www.ncbi.nlm.nih.gov/pubmed/8489041.

    10. Zerin M, Van Allen MI, Smith DW. Intrinsic auricular muscles and auricular form. Pediatrics. 1982 Jan; 69(1):91-3. http://www.ncbi.nlm.nih.gov/pubmed/7054769.

    11. Lovell M, Sutton D, Lindeman RC. Muscle spindles in nonhuman primate extrinsic auricular muscles. The Anatomical Record. 1977 Nov;189(3):519-23. http://www.ncbi.nlm.nih.gov/pubmed/144446.

    12. Iurkianets EA, Matiushkin DP. [Electrical activation of human external auricular muscles (at rest and during perception of acoustic signals)]. Bulletin of Experimental Biology and Medicine. 1973 Mar;75(3):16-9. http://www.ncbi.nlm.nih.gov/pubmed/4804634.


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