Anatomy of the Orbit and Eye Movement

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Questions and Answers

What is the primary function of the eyelids?

To regulate the amount of light entering the eye

To facilitate venous drainage of the eyeball

To lubricate the eye with tears

To protect the eye from aggressions (correct)

Which of the following veins drains into the cavernous sinus?

Angular vein

Inframbital vein

Superior ophthalmic vein (correct)

Pterygoid plexus

What is the name of the syndrome characterized by palpebral ptosis, miosis, and lack of sweating?

Triángulo de la muerte

Palpebral syndrome

Papilledema

Horner's syndrome (correct)

What is the type of muscle fiber attached to the superior tarsus?

Smooth muscle fibers Signup and view all the answers

What is the primary function of the lacrimal system?

To lubricate the eye with tears Signup and view all the answers

What is the name of the vein that forms from the angular vein of the face and the supraorbital vein?

Superior ophthalmic vein Signup and view all the answers

What is the function of the tarsal glands?

To form the fluid that seals the lids while we sleep Signup and view all the answers

What is the type of nervous system that innervates the smooth muscle fibers attached to the superior tarsus?

Sympathetic nervous system Signup and view all the answers

What is the name of the structure that separates the eyelids from the orbital cavity?

Orbital septum Signup and view all the answers

What is the primary function of the superior and inferior tarsus?

To support the eyelids Signup and view all the answers

What is the function of the sympathetic nervous system in relation to the eye?

Enhances vasomotor activity Signup and view all the answers

Where do tears accumulate before being drained?

Lacrimal caruncle Signup and view all the answers

What is the function of the puncta on the eyelids?

To drain tears Signup and view all the answers

Where does the nasolacrimal duct open?

Inferior nasal meatus Signup and view all the answers

What happens to the tears that flow down from the lacrimal sac?

They enter the nasal cavity Signup and view all the answers

What is the effect of blinking on the lacrimal sac?

It compresses the sac, increasing tear flow Signup and view all the answers

What is the function of the lacrimal canaliculi?

To drain tears into the lacrimal sac Signup and view all the answers

What is the final destination of tears that are drained from the eye?

The oral cavity Signup and view all the answers

What is the gland that is pierced by the tendon of the Levator palpebrae superioris?

Lacrimal gland Signup and view all the answers

What is the path taken by tears after they are drained from the eye?

Lacrimal sac → nasolacrimal duct → nasal cavity → oral cavity Signup and view all the answers

From which part of the brain does the retina derive?

Diencephalon Signup and view all the answers

What is the origin of the lens?

Ectodermal Signup and view all the answers

What is the relationship between the optic vesicle and the lens placode?

The optic vesicle curves around and encloses the lens placode Signup and view all the answers

What happens to the ectodermal cells as they form the lens placode?

They change from polygonal to cuboid Signup and view all the answers

What is the resulting structure formed by the optic vesicle as it curves and becomes concave?

Optic cup Signup and view all the answers

What is the source of layers 2-10 of the retina?

Internal layer of the optic cup Signup and view all the answers

What is the result of trauma to the retina?

Appearance of the intraretinal space Signup and view all the answers

What happens to the choroid fissure during the development of the optic nerve?

It closes and the artery becomes embedded within the optic nerve Signup and view all the answers

What is the function of the hyaloid artery during development?

Provides blood supply to the lens Signup and view all the answers

What forms the retinal layer in the eye?

Inner layer of the stalk Signup and view all the answers

What is the result of the transformation of the optic stalk into the optic nerve?

Growth of the axons of the ganglion cells Signup and view all the answers

What is the space surrounding the optic nerve?

Subarachnoid space Signup and view all the answers

What happens to the distal part of the hyaloid artery in the adult?

It disappears Signup and view all the answers

What would cause an increase in intracranial pressure?

Edema of brain parenchyma Signup and view all the answers

What type of muscle derives from paraxial mesoderm?

Striated muscle Signup and view all the answers

What is the level of origin of the nerves that migrate with the somitomeres?

III, IV and VI CN Signup and view all the answers

Where can the somitomeres be found during the 6th week?

Around the lens placode Signup and view all the answers

How many striate muscles arise from the myotomes of the somitomeres?

7 Signup and view all the answers

What is the point of insertion for all the striate muscles except for the levator palpebrae?

The sclera of the eyeball Signup and view all the answers

What is the name of the ring structure through which the superior oblique muscle tendon passes?

Trochlea Signup and view all the answers

Which muscle has a tendon that pierces the orbital septum and inserts into the skin of the superior eyelid?

Levator palpebrae superioris Signup and view all the answers

What type of muscle fibers attach to the superior tarsus?

Smooth muscle fibers Signup and view all the answers

Which cranial nerve innervates the extrinsic eye muscles?

Trochlear nerve (IV CN) and Abducens nerve (VI CN) Signup and view all the answers

What is the function of the superior tarsal muscles?

To elevate the eyelid Signup and view all the answers

Where do the rectus muscles originate from?

A common tendinous ring Signup and view all the answers

What type of innervation do intrinsic muscles of the eye receive?

Autonomic innervation Signup and view all the answers

What is the function of the constrictor muscle of the pupil?

To decrease pupil diameter Signup and view all the answers

What nerve carries visceral efferents to the intrinsic muscles of the eye?

Oculomotor nerve (III CN) Signup and view all the answers

What is the function of the ciliary muscle?

To accommodate the eye Signup and view all the answers

Which muscle receives sympathetic innervation?

Dilator muscle of the pupil Signup and view all the answers

What is the function of the extrinsic muscles of the eye?

To move the eyeball Signup and view all the answers

Which layer of the eye is continuous with the optic nerve?

Neural layer Signup and view all the answers

What is the name of the thin layer of fat that surrounds the eyeball?

Orbital fat Signup and view all the answers

What is the function of the tarsal plates in the eyelids?

To provide consistency to the eyelids Signup and view all the answers

What is the name of the fascia that surrounds the eyeball?

Tenon's capsule Signup and view all the answers

What is the primary origin of the 7 striate muscles that move the eye?

Somitomeres Signup and view all the answers

Which muscle tendon passes through a ring structure called the trochlea?

Superior oblique muscle Signup and view all the answers

Where do the majority of the striate muscles take insertion in the eyeball?

Laterally, around the ora serrata Signup and view all the answers

Which muscle does not insert into the sclera of the eyeball?

Levator palpebrae muscle Signup and view all the answers

What is the origin of the inferior oblique muscle?

Medial aspect of the orbit Signup and view all the answers

Study Notes

Extrinsic Muscles of the Eye

Extrinsic muscles are striated muscles surrounding the eyeball, responsible for its movement.
Seven key muscles include superior, inferior, medial, and lateral rectus muscles, superior and inferior oblique muscles, and levator palpebrae.
Innervated by cranial nerves III (oculomotor), IV (trochlear), and VI (abducens).

Blood Supply to the Eye

The eye is primarily supplied by branches of the ophthalmic artery, derived from the internal carotid artery.
The central artery of the retina provides essential supply to layers 2-10 of the retina.
Superior and inferior ophthalmic veins drain venous blood from the eye, eventually merging with the cavernous sinus.

Development of the Eyeball

The eyeball originates from the optic vesicle, which forms as an evagination of the diencephalon.
The lens develops from the lens placode, an ectodermal thickening under CNS influence.

Structure of the Eye

The eye is supported by a periosteum lining called periorbita, which thickens anteriorly to form the orbital septum.
Bulbar fascia (Tenon’s capsule) is a thin connective tissue surrounding the eyeball.
Check ligaments (lateral and medial) limit eye movement by attaching to the orbital bones.

Neural Anatomy

Retina is the innermost layer of the eye and part of the central nervous system.
The optic nerve is formed from the optic stalk and is surrounded by the dura mater and arachnoid meninges, transmitting intracranial pressure changes.

Intrinsic Muscles of the Eye

Include ciliary muscle and muscles controlling pupil diameter (constrictor and dilator).
Innervated autonomically; ciliary muscle contraction alters lens curvature, affecting focus.

Actions of Extraocular Muscles

Lateral and medial rectus muscles move the eye horizontally.
Superior and inferior rectus muscles control vertical eye movements.
Oblique muscles provide rotation; superior oblique passes through trochlea.

Clinical Considerations

Intracranial pressure changes can be assessed via the eye’s fundus.
Conditions like papilledema indicate increased pressure due to brain edema, hemorrhage, or tumors.

Eyelids and Lacrimal System

Eyelids are composed of skin, connective tissue, and glands to protect and moisten the eye.
Tear drainage involves puncta connecting to lacrimal sac, leading to the nasolacrimal duct.

Sympathetic Innervation Effects

Horner's syndrome results in ptosis (lid droop) and miosis (constricted pupil) due to disrupted sympathetic tone.

Key Structures in Eye Anatomy

Each extraocular muscle inserts into the sclera, except levator palpebrae, which elevates the eyelid.
Retinal layers include a pigmented epithelium (outer) and sensory layers (inner), essential for vision.

General Functionality

Eye movements are complex, organized by coordinated activation of various muscle groups.
The visual system is sensitive to changes in blood supply and neural health, reflecting the importance of these anatomical structures.### Eye Muscles and Their Functions
Levator Palpebrae Superioris: Unique muscle that elevates the eyelid; not attached to the sclera.
Origin of Rectus Muscles: All four rectus muscles originate from a common tendinous ring, a thickening of the periorbita around the optic canal and superior orbital fissure.
Insertions: Rectus and oblique muscles insert into the sclera. Rectus muscles pull the eyeball backward, while oblique muscles can slightly pull it forward.
Tendon of Levator Palpebrae: Pierces the orbital septum, innervating the skin of the superior eyelid and some fibers attaching to the superior tarsus.
Function: Muscle fibers work collectively to elevate the eyelid. Additional smooth muscle fibers, known as superior tarsal muscles, assist in this process and are controlled by the autonomic nervous system.
Sympathetic Activation: Elevated eyelid indicates readiness, while parasympathetic tone leads to lid closure when tired.

Innervation of Eye Muscles

Cranial Nerve Innervation: Extrinsic eye muscles are innervated by cranial nerves III (Oculomotor), IV (Trochlear), and VI (Abducens).
Abducens Nerve: Travels within the cavernous sinus.

Blood Supply and Structure of Orbit

Orbit Composition: Contains the eyeball, extrinsic eye muscles, lacrimal gland, and a thin layer of protective fat.
Layers of the Eye:
- Innermost Layer: Retina, continuous with the optic nerve; contains axons of the optic nerve.
- Vascular Layer: Includes the choroid (posterior 4/5) and the iris (anterior 1/5).
- Fibrous Layer: Forms the cornea (anteriorly) and sclera (posteriorly), continuous with the meninges surrounding the optic nerve.
Periorbita: Periosteum lining the orbit, thickened to form the orbital septum, connecting to the tarsus for eyelid structure.
Bulbar Fascia (Tenon’s Capsule): Thin connective tissue layer surrounding the eyeball, stopping at the cornea.

Intrinsic Muscles of the Eye

Muscles: Include ciliary muscle, constrictor muscle of the pupil, and dilator muscle of the pupil; these are involuntary and receive autonomic innervation.
Parasympathetic Actions: Contracts the ciliary muscle for accommodation (lens curvature) and constricts the pupil.
Sympathetic Actions: Contracts dilator muscle to increase pupil diameter; no sympathetic innervation to the ciliary muscle is necessary.

Blood Supply to the Eye

Origin: Blood supplied by branches of the ophthalmic artery from the internal carotid artery.
Central Artery of the Retina: Vital for supplying layers 2-10 of the retina; arises where cranial nerves III, IV, and VI emerge.

Development and Muscle Insertion

Somitomeres: Seven striated muscles arise from myotomes of somitomeres.
Insertion Points: Six muscles (superior, inferior, medial, lateral rectus, superior and inferior oblique) insert into the sclera; levator palpebrae elevates the eyelid.
Ora Serrata: Denotes the proximal third of the eye, differentiating the colloid from the ciliary bodies where muscle insertions are predominant.

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Description

Test your knowledge of the orbit's structure and the extrinsic muscles that control eye movement. Learn about the lacrimal gland, fat layer, and nervous system components that support vision.