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The eyelids contain a thin layer of muscle called the orbicularis oculi, which has three distinct parts: palpebral, lacrimal, and orbital. The palpebral part is responsible for gently closing the eyelids, the lacrimal part is involved in draining tears, and the orbital part is responsible for tightly closing the eyelids. The levator palpebrae superioris and superior tarsal muscles are only present in the upper eyelid and are responsible for opening the eyelid. The eyelids move with the eyes during slow and rapid vertical eye movements, except when blinking, during which the levator is temporarily inhibited and the orbicularis oculi contracts.
| Characteristics | Values |
|---|---|
| Eyelid muscles | Orbicularis oculi, levator palpebrae superioris, superior tarsal, inferior tarsal |
| Orbicularis oculi parts | Palpebral, lacrimal, orbital |
| Orbicularis oculi functions | Controls blinking, winking, tightly shutting the eyelids |
| Levator palpebrae superioris function | Elevates the upper eyelid |
| Superior tarsal function | Elevates the upper eyelid |
| Superior tarsal innervation | Sympathetic nervous system |
| Levator palpebrae superioris innervation | Oculomotor nerve (CN III) |
| Tarsal plates | Superior tarsus (upper eyelid), inferior tarsus (lower eyelid) |
| Tarsal plates composition | Dense connective tissue |
| Tarsal plates function | Form the scaffolding of the eyelid |
| Tarsal plates location | Superior tarsus acts as the attachment site of the levator palpebrae superioris |
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What You'll Learn
- The levator palpebrae superioris and superior tarsal muscles open the eyelid
- The orbicularis oculi muscle has three parts: palpebral, lacrimal, and orbital
- The eyelids move with the eyes during vertical eye movements
- The M-group in the midbrain coordinates vertical eye movements and lid position
- The superior tarsal muscle is innervated by the sympathetic nervous system
The levator palpebrae superioris and superior tarsal muscles open the eyelid
The eyelids are a complex system of muscles, tendons, and ligaments. The levator palpebrae superioris and superior tarsal muscles are responsible for opening the eyelid. These muscles are only present in the upper eyelid.
The levator palpebrae superioris is innervated by the oculomotor nerve (CN III). It originates from the superior part of the common tendinous ring and attaches to the superior and anterior aspect of the sclera. Its main movement is elevation, but it also contributes to adduction and medial rotation of the eyeball.
The superior tarsal muscle, on the other hand, is innervated by the sympathetic nervous system. It originates from the lesser wing of the sphenoid bone, immediately above the optic foramen, and attaches to the superior tarsal plate of the upper eyelid. The superior tarsal muscle is a collection of smooth muscle fibres within the levator palpebrae superioris.
The eyelids move with the eyes during both slow and rapid vertical eye movements, except when blinking. During blinking, the levator palpebrae superioris is temporarily inhibited, and the orbicularis oculi muscle contracts to close the eyelids. The orbicularis oculi muscle is attached to the skin through fibre tissues that form the superficial musculoaponeurotic system. It consists of three distinct parts: palpebral, lacrimal, and orbital. The palpebral part gently closes the eyelids, the lacrimal part is involved in the drainage of tears, and the orbital part tightly closes the eyelids.
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The orbicularis oculi muscle has three parts: palpebral, lacrimal, and orbital
The eyelids move with the eyes during slow and rapid vertical eye movements. The eyelids also move independently of the eyes during blinking. During blinking, the levator muscle is temporarily inhibited and the orbicularis oculi contracts.
The orbicularis oculi is a sphincter-like muscle in the face that closes the eyelids. It is considered the sphincter of the eyelids and is involved in facial expression, ocular protection, and reflexes. The orbicularis oculi muscle has three parts: palpebral, lacrimal, and orbital.
The palpebral part gently closes the eyelids. The palpebral portion of the muscle is thin and pale and arises from the bifurcation of the medial palpebral ligament. It forms a series of concentric curves and is inserted into the lateral palpebral raphe at the outer corner of the eye. The palpebral part contains the preseptal and pretarsal muscles. The pretarsal orbicularis is thought to be responsible for the spontaneous blink. Contraction of the palpebral part results in finer control of the eyelids. These muscle fibres pull the upper eyelids down and raise the lower ones. The palpebral part can also involuntarily close the eyelids as a reflex mechanism.
The lacrimal part is involved in the drainage of tears. It is a small, thin muscle, about 6 mm in breadth and 12 mm in length, situated behind the medial palpebral ligament and lacrimal sac. The lacrimal orbicularis facilitates the tear pump into the lacrimal sac. Contraction of the deep palpebral part pulls the eyelids and lacrimal papillae medially and dilates the lacrimal sac. These actions work together to facilitate tear drainage across the cornea.
The orbital part tightly closes the eyelids. The orbital portion is thicker and of a reddish colour. Its fibres form a complete ellipse without interruption at the lateral palpebral commissure. The upper fibres of this portion blend with the frontalis and corrugator. The orbital and palpebral portions can work independently of each other, as in the furrowing of the brows by contraction of the orbital to reduce glare while keeping the eyes open by virtue of the relaxation of the palpebral. Contraction of the orbital part draws the skin of the forehead and cheek towards the nose. This protective function can partially or completely close the eyelids, limiting exposure to potential damaging factors such as bright light or blowing dust.
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The eyelids move with the eyes during vertical eye movements
The lids are maintained in the open position by the actions of the tarsal and levator muscles, with the latter adjusting lid position during vertical gaze changes. The orbicularis oculi muscle is innervated by the facial nerve, the levator muscle by the oculomotor nerve, and the tarsal muscles by sympathetic pathways to the head. During a blink, the levator is temporarily inhibited, and the orbicularis oculi contracts.
Recent evidence suggests that vertical eye movements and lid position are coordinated through the M-group (supraoculomotor area or supra III) in the midbrain. In upgaze, M-group neurons excite the CCN, causing the levator muscles to contract and the eyelids to open. During downgaze, neurons from the interstitial nucleus of Cajal (inC) inhibit the M-group neurons and the CCN, resulting in levator relaxation and eyelid lowering.
The superior tarsal muscle in the upper lid is innervated by oculosympathetic neurons, while the inferior tarsal muscle in the lower lid is similar and is also innervated by oculosympathetic neurons. The eyelids move with the eyes during both slow and rapid vertical eye movements. The major exception to this occurs during blinking.
The eyes contain six muscles that control which ways they point and contribute to vision. Four of these muscles work together to control vertical eye movements and eye rotation around the mid-orbital axis. To direct the eye upward or downward, two muscles contract synergistically as the two antagonist muscles relax. For example, to elevate the eye while looking straight ahead, the superior rectus and inferior oblique contract together as the inferior rectus and superior oblique relax.
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The M-group in the midbrain coordinates vertical eye movements and lid position
The eyelids move with the eyes during both slow and rapid vertical eye movements, with the exception of blinking. During blinking, the levator is temporarily inhibited, and the orbicularis oculi contracts. The M-group (supraoculomotor area or supra III) in the midbrain coordinates vertical eye movements and lid position.
The midbrain, or mesencephalon, is a complex structure with a range of different neuron clusters, neural pathways, and other structures. The midbrain is involved in several functions, including motor control, particularly eye movements, and the processing of vision and hearing. The substantia nigra, an area of the midbrain affected by Parkinson's disease, is rich in dopamine neurons and part of the basal ganglia, which enable movement and coordination.
The M-group neurons in the midbrain play a crucial role in the coordination of vertical eye movements and eyelid position. During an upgaze, these neurons excite the CCN (central caudal nucleus), leading to the contraction of the levator muscles and the opening of the eyelids. In contrast, during a downgaze, neurons from the interstitial nucleus of Cajal (inC) inhibit the M-group neurons and the CCN, resulting in levator relaxation and eyelid lowering.
The coordination between the M-group neurons and the CCN is essential for maintaining the synchrony between eye movements and eyelid position during vertical gaze shifts. This synchrony ensures that the eyelids move with the eyes, providing a clear field of vision during slow and rapid vertical eye movements. The M-group in the midbrain plays a vital role in maintaining this coordination, demonstrating its importance in eye movement and lid position control.
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The superior tarsal muscle is innervated by the sympathetic nervous system
The superior tarsal muscle, also known as Müller's muscle, is a smooth muscle that helps to raise the upper eyelid. It is a type of skeletal muscle that originates from the undersurface of the levator palpebrae superioris muscle (LPSM) and inserts onto the superior tarsal plate (STP) of the upper eyelid. The superior tarsal muscle is innervated by the sympathetic nervous system.
The superior tarsal muscle receives its innervation from postganglionic sympathetic fibres that originate in the superior cervical ganglion. These fibres travel through the internal carotid plexus, where they communicate with the oculomotor nerve as it passes through the cavernous sinus. The oculomotor nerve is responsible for controlling eye movements and plays a crucial role in eyelid function.
The sympathetic fibres continue to the superior division of the oculomotor nerve and enter the superior tarsal muscle on its inferior aspect. While the exact role of the superior tarsal muscle is not fully understood, it is believed to be an accessory muscle that assists in raising the upper eyelid. This muscle works in conjunction with the LPSM to elevate the eyelid, particularly during states of sympathetic predominance such as excitement, fear, or surprise.
Damage to certain elements of the sympathetic nervous system can lead to inhibition of the superior tarsal muscle, resulting in a drooping eyelid condition known as blepharoptosis or partial ptosis. This condition is often associated with Horner's syndrome, which is characterised by a structural lesion in the cervical sympathetic nervous chain. The superior tarsal muscle is a crucial component of eyelid function and plays a role in maintaining proper eyelid position and visual field.
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Frequently asked questions
The eyelids are moved by the levator palpebrae superioris and superior tarsal muscles, which open the eyelid, and the orbicularis oculi muscle, which closes the eyelids.
The orbicularis oculi muscle has three distinct parts: palpebral, lacrimal, and orbital. The palpebral part gently closes the eyelids, the lacrimal part is involved in the drainage of tears, and the orbital part tightly closes the eyelids.
The levator palpebrae superioris and superior tarsal muscles are responsible for elevating the upper eyelid. They are only present in the upper eyelid.
