eye

Optic Nerve

Optic Nerve The structure indicated is the optic nerve (cranial nerve II). The optic nerve is the second cranial nerve and is responsible for vision. Similar to the first cranial nerve (olfactory nerve), the optic nerve is not a true nerve but is rather an extension of the brain (diencephalon), which means it is technically a part of the central, rather than peripheral nervous system. The primary sensory neurons are the bipolar cells of the retina; these synapse on ganglion cells, the axons of which form the optic nerve which then passes via the optic canal to join with the …

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optic nerve

Inferior Oblique Muscle of the Eye

Inferior Oblique Muscle of the Eye The structure indicated is the inferior oblique muscle of the eye. This muscle is one of six muscles that are involved in the movements of the eye. The muscles which move the eye are referred to as the extraocular muscles, these include: Superior rectus Inferior rectus Lateral rectus Medial rectus Superior oblique Inferior oblique The oculomotor nerve innervates the superior, inferior and medial rectus muscles as well as the inferior oblique muscle. The trochlear nerve innervates the superior oblique muscle The abducent nerve innervates the lateral rectus muscle. When the inferior oblique muscle is …

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inferior oblique

Orbicularis Oculi

Orbicularis Oculi The structure indicated is the orbicularis oculi muscle of the face. The orbicularis oculi muscle is one of the muscles of facial expression belonging to the orbital group. The muscles of facial expression can be organised into functional groups to provide a more structured approach to understanding the muscles. The functional groups include the following: Orbital group Nasal group Oral group Other The orbicularis oculi muscle is the principle muscle of the orbital group of facial muscles and consists itself of two parts: Palpebral part Orbital part There is an additional muscle in the orbital group – the …

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Orbicularis Oculi

Levator Palpebrae Superioris

Levator Palpebrae Superioris The structure indicated is the levator palpebrae superioris muscle. The levator palpebrae superioris muscle is located in the upper eyelid and is responsible for raising the eyelid. Just like the rectus muscles, and oblique muscles of the eyeball, the levator palpebrae superioris muscle is innervated by the oculomotor nerve (cranial nerve III). The eyelids themselves are supported by the tarsus – in the upper eyelid the superior tarsus, and in the lower eyelid, the inferior tarsus. These structures consist of dense connective tissue. Origin: Roof of the orbit on sphenoid bone, above the optic foramen Insertion: Anterior …

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levator palpebrae superioris

Ciliary Body

Ciliary Body The structure indicated is the ciliary body. The eyeball consists of a fibrous outer layer, a vascular layer, and an inner layer. The vascular layer of the eyeball consists of: Choroid Ciliary body Iris The ciliary body is triangular in cross-section and encircles the eyeball. It has two components: Ciliary muscle Ciliary processes The ciliary body has three main functions: Accommodation of the lens Production and resorption of aqueous humor Maintenance of lens zonules

Ciliary Body

Superior Oblique Muscle

Superior Oblique Muscle The structure indicated is the superior oblique muscle. The superior oblique muscle is one of the extra-ocular muscles. The extra-ocular muscles include the medial, lateral, superior and inferior recti muscles, and the superior and inferior oblique muscles. Origin: Annulus of Zinn Insertion: Outer posterior quadrant of the eyeball Innervation: Trochlear nerve Action: Moves the eyeball down and out (depression, abduction, medial rotation). The superior oblique muscle inserts onto the eyeball via a long tendon which loops around a pulley (the trochlea of the superior oblique) on the medial aspect of the orbital roof, just lateral to the …

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Superior Oblique Muscle

Abducent Nerve

Abducent Nerve The structure indicated is the abducent nerve (cranial nerve VI). The abducent nerve (cranial nerve VI), provides general somatic efferent fibres (motor function) to the lateral rectus muscle of the eye. There are three cranial nerves which are responsible for innervating the extrinsic muscles of the eye: Oculomotor nerve (cranial nerve III) Trochlear nerve (cranial nerve VI) Abducent nerve The oculomotor nerve supplies the superior, inferior and medial rectus muscles, as well as the inferior oblique muscle and the levator palpebrae superioris. The trochlear nerve supplies the superior oblique muscle. It originates between the pons and the medulla …

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Abducent nerve

Lateral Rectus Muscle

Lateral Rectus Muscle The structure indicated is the lateral rectus muscle. This muscle is one of six muscles that are involved in the movements of the eye. The muscles which move the eye are referred to as the extraocular muscles, these include: Superior rectus Inferior rectus Lateral rectus Medial rectus Superior oblique Inferior oblique Origin: Lateral part of annulus of Zinn Insertion: Lateral (temporal) aspect of eyeball Action: Abducts the eyeball – moves it away from the midline Innervation: Abducens nerve (Cranial nerve VI) If the abducens nerve is damaged (abducens nerves palsy/sixth nerve palsy), there is failure to abduct …

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Lateral Rectus Muscle