How do cats close their eyes? - briefly
Cats close their eyes by contracting the orbicularis oculi muscle, which is located around the eye socket. This muscle tightens and pulls the eyelids together, effectively closing the eye.
How do cats close their eyes? - in detail
Cats, like many other animals, have a unique mechanism for closing their eyes. This process is governed by several key components of their eye structure and musculature.
Firstly, it's important to understand that cats have a third eyelid, known as the nictitating membrane. This is a thin, translucent membrane that can be voluntarily drawn across the eye for protection or to moisten it. While this third eyelid does not fully close the eye, it plays a significant role in the overall function of eye closure in cats.
The primary mechanism for closing the eyes involves the levator palpebrae superioris muscle. This muscle is responsible for lifting the upper eyelid and keeping the eye open. When a cat wants to close its eyes, this muscle relaxes, allowing the upper eyelid to drop. Simultaneously, another muscle called the orbicularis oculi muscle contracts, pulling the lower eyelid upwards to meet the upper eyelid. This coordinated action of muscle relaxation and contraction results in the complete closure of the eye.
Additionally, cats have a specialized structure within their eyes known as the plica semilunaris. This is a small fold of tissue located at the medial canthus (the inner corner) of the eye. The plica semilunaris contains glands that produce tears, helping to keep the eye moist and protected. When the cat closes its eyes, this structure also plays a role in maintaining the integrity of the eye's protective barrier.
In summary, cats close their eyes through a combination of muscle relaxation and contraction. The levator palpebrae superioris muscle relaxes to drop the upper eyelid, while the orbicularis oculi muscle contracts to raise the lower eyelid. The nictitating membrane and plica semilunaris also contribute to this process by providing additional protection and moisture to the eye. This intricate system ensures that cats can effectively close their eyes for sleep, relaxation, or defense.