Logan Steele
Blinking is a complex action involving the eyelids and eyeball muscles. The main muscles that control blinking are the orbicularis oculi and levator palpebrae superioris muscle. The former closes the eye, while the latter opens it. The orbicularis oculi is a facial muscle that surrounds the orbit of the eyeball and covers the temples and a bit of the cheek. It is divided into three sections: orbital, palpebral, and lacrimal. The orbital section is thicker and responsible for strong eyelid closure. The palpebral section is involved in involuntary blinking and voluntary winking. The levator palpebrae superioris muscle, on the other hand, assists in widening the eyelid aperture.
| Characteristics | Values |
|---|---|
| Main muscles involved in blinking | Orbicularis oculi, levator palpebrae superioris, Müller's muscle, inferior palpebral muscle |
| Muscle responsible for opening the eye | Levator palpebrae superioris |
| Muscle responsible for closing the eye | Orbicularis oculi |
| Number of times humans blink per minute | Up to 20 |
| Average blink speed | 17-28 cm/s |
| Maximum blink speed | 40 cm/s |
| Average blink duration | 100-150 milliseconds |
| Blink duration according to the Harvard Database of Useful Biological Numbers | 100-400 milliseconds |
| Blink duration over 1000 milliseconds defined as | Microsleep |
| Reflex blinking caused by | Loud noise, corneal, conjunctival, or cilial touch, sudden approach of an object, bright light |
| Muscle that acts as a depressor to the lateral tail of the eyebrow | Lateral portion of the orbicularis oculi |
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What You'll Learn
The orbicularis oculi muscle
The eyelid nerve fibers that initiate blinks are largely mechanoreceptors. The orbicularis oculi muscle acts as a depressor to the lateral tail of the eyebrow. It directly contributes to the closure of the eyes and the creation of crow's feet, also known as lateral canthal lines. The contraction of the orbicularis oculi muscle during blinking creates a drainage mechanism for tears, known as the lacrimal pump.
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The levator palpebrae superioris muscle
Blinking is a complex action of eyelid and eyeball muscles. The main muscles that control the opening and closing of the eyelids are the orbicularis oculi and levator palpebrae superioris muscle. The former closes the eye, while the contraction of the latter opens the eye.
The levator palpebrae superioris is a thin, triangular muscle that extends along the roof of the orbit, from the apex of the orbit to the superior eyelid. It originates with a short and narrow tendon from the inferior aspect of the lesser wing of the sphenoid bone, superior and anterior to the common tendinous ring. The muscle belly gradually widens as it courses anteriorly toward the eyelid. The muscle fibres penetrate the upper eyelid, inserting into its parts via two aponeurotic fascicles. Deep fibres attach to the anterior surface of the superior tarsus, while superficial fibres radiate through the eyelid and orbicularis oculi to finally attach to the skin of the superior eyelid.
The levator palpebrae superioris is categorised as a skeletal muscle, not a smooth muscle. It is attached to the check ligament of the superior rectus. All of these connections contribute to the coordinated simultaneous contraction of these two muscles. As the levator palpebrae superioris fans out as a wide aponeurosis, the lateral fibres pass between the orbital and palpebral parts of the lacrimal gland to attach to the orbital tubercle. The medial fibres run adjacent over the reflected tendon of the superior oblique muscle.
The levator palpebrae superioris receives somatic motor innervation from the superior division of the oculomotor nerve (CN III). It is innervated by the oculomotor nerve, which originates from a single caudal subnucleus within the midbrain's oculomotor nucleus. The superior ophthalmic vein empties into the cavernous sinus, while the inferior ophthalmic vein drains into the pterygoid venous plexus. The levator palpebrae superioris receives arterial blood supply from the internal carotid artery, via the ophthalmic artery and its supraorbital branch.
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Voluntary vs involuntary blinking
Blinking is a complex action of eyelid and eyeball muscles. It is a semi-autonomic rapid closing of the eyelid. Blinking is a bodily reflex that the body does automatically to keep the eyes lubricated and healthy. However, it can also be done on command.
Voluntary blinking is when you blink on purpose. For instance, if you want to blink, you can. Voluntary blinking involves the use of all three divisions of the orbicularis oculi muscle. This muscle is responsible for closing the eye.
Involuntary blinking, on the other hand, is a reflexive response to external stimuli such as loud noises, flashes of light, or objects approaching the eye. It is an automatic response that helps protect the eyes from irritants, bright lights, and foreign objects. The blink reflex is controlled by a "blinking center" in the brain, specifically the globus pallidus of the lenticular nucleus. This type of blinking involves the activation of the levator palpebrae superioris muscle, which opens the eye, and the palpebral portion of the orbicularis oculi muscle, which closes the eye.
In summary, voluntary blinking is a conscious action, while involuntary blinking is an automatic response to external stimuli. Both types of blinking involve the coordination of multiple muscles and help protect and lubricate the eyes.
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Reflex blinking
The blink reflex, also known as the corneal reflex or eyelid reflex, is an involuntary blinking of the eyelids that can be caused by practically any peripheral stimulus. However, the two most functionally significant reflexes are:
- Stimulation of the endings of the fifth cranial nerve in the cornea, lid, or conjunctiva, known as the sensory blink or corneal reflex.
- Bright light, known as the optical blink reflex.
The corneal reflex is caused by a loop between the trigeminal sensory nerves and the facial motor nerve innervation of the orbicularis oculi muscles. The reflex is activated when a sensory stimulus contacts the cornea, either through free nerve endings or mechanoreceptors within the epithelium. The corneal reflex also triggers tear production to protect the eyes from foreign substances and irritants.
The blink reflex is a protective eye-closure reflex mediated by brainstem circuits and usually evoked by electrical supraorbital nerve stimulation. It involves the contraction of the orbicularis oculi muscle and relaxation of the levator palpebrae muscle, allowing for the lowering of the upper eyelid. The facial nerve supplies the motor fibres for the orbicularis muscle, while the levator is innervated by the oculomotor nerve.
The blink rate is typically determined by the activity of a "blinking centre" in the globus pallidus of the caudate nucleus, which is a mass of neurons between the base and outer substance of the brain. However, it can also be influenced by external stimuli such as eye movement, fear, anxiety, and mental tasks.
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The role of the Müller's muscle
Blinking is a semi-autonomic rapid closing of the eyelid. It is a complex action of eyelid and eyeball muscles. The main muscles, in the upper eyelid, that control the opening and closing of the eye are the orbicularis oculi and levator palpebrae superioris muscle. The former closes the eye, while the contraction of the latter opens the eye.
The Müllers muscle, or the superior tarsal muscle, is located in the upper eyelid. It is responsible for widening the eyes and is imperative in blinking and other functions such as squinting and winking. The Müllers muscle works in conjunction with the inferior palpebral muscle in the lower eyelid, which pulls down the lower lid when one looks down.
The orbicularis oculi muscle is a facial muscle that surrounds the orbit of the eyeball and covers the temples and a bit of the cheek. It is divided into three sections: orbital, palpebral, and lacrimal. The orbital section is thicker, with fibers taking the shape of a continuous ellipse at the lateral palpebral commissure. When the orbital part of the muscle contracts, it makes the eyes close tightly. Blinks and winks involve the contraction of the palpebral part of the orbicularis oculi.
The Müllers muscle is, therefore, an important component of the complex system of muscles that allow for blinking. Its role in widening the eyes and working in conjunction with the inferior palpebral muscle makes it essential for the blinking process.
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Frequently asked questions
The main muscles involved in blinking are the orbicularis oculi and levator palpebrae superioris muscle. The former closes the eye, while the latter opens it.
Blinking provides moisture to the eye and protects it from irritants. It also helps to remove dust and other elements from the eye, with eyelashes catching most irritants before they reach the eyeball.
The orbicularis oculi muscle is a facial muscle, with its actions translated by the facial nerve root. Its contraction closes the eyelid gently, and it is the muscle of action in an involuntary blink and a voluntary wink.
The levator palpebrae superioris muscle is innervated by the oculomotor nerve. It assists in opening the eyelid and widening the lid aperture.
