Skeletal muscle without antagonist?

Question

Is there any skeletal muscle that does not have an antagonist? Excluding circular muscles such as around eye and mouth. The reason why I am wondering is because in biology normally nothing is ever just like that, there is always an exception. This would be the first biological rule without exception that I came across. I am thinking of humans only for a start but feel free to include any other animal if any have skeletal muscles without antagonists :)

Answer 1

Hello, I realize this question was asked a while ago but hopefully my answer can still be helpful for you!

Besides the exceptions that you noted (orbicularis oculi and orbicularis oris), every muscle group in the human body has an antagonist. However, the key here is muscle "group" not necessarily individual muscles. For example, if we are talking about movement of the ankle in the sagittal plane, there are muscles that plantarflex and muscles that dorsiflex. Due to the mechanical requirements of the body, the muscles that plantarflex are stronger and more powerful than the muscles that dorsiflex. Therefore, there are far more muscles that perform plantarflexion (gastrocnemius, soleus, tibialis posterior, plantaris, fibularis longus, fibularis brevis, flexor hallucis longus, flexor digitorum longus) than muscles that perform dorsiflexion (tibialis anterior, extensor digitorum longus, extensor hallucis longus, fibularis tertius). So, not every individual skeletal muscle has an exact antagonist, but every skeletal muscle group in the body has an antagonist group. Hopefully this helps!