ANATOMÍA Clase 36 Órganos de los sentidos 1

Anatomy of the Eye

Overview of the Visual Apparatus

• The visual apparatus consists of several elements, including the eye (globo ocular), lacrimal apparatus, eyelids, and orbital cavity that houses these components.

Structure of the Eye

• The eye is a solid spherical organ approximately 95 millimeters in diameter, composed of three concentric tunics. The outermost layer is called the fibrous tunic.

• The fibrous tunic is mostly made up of dense avascular tissue known as sclera, which is perforated by blood vessels but lacks circulation. The anterior sixth features a transparent membrane called the cornea.

Vascular Tunic Details

• The second layer, known as the vascular tunic or uvea, includes an anterior circular partition with a central opening called the iris, which gives color to the eye. The central opening is referred to as the pupil.

• The iris has two types of smooth muscle fibers: circular fibers (constrictor) and radial fibers (dilator). Behind the iris lies the ciliary body, which supports other structures like zonules or suspensory ligaments for the lens.

Lens and Aqueous Humor

• The lens is biconvex and elastic; it changes shape due to contraction or relaxation of ciliary muscles for focusing on near or distant objects. This process involves creating spaces known as anterior and posterior chambers filled with aqueous humor.

• Aqueous humor circulates from posterior to anterior chambers through the pupil and nourishes avascular structures like the cornea while being reabsorbed into venous circulation.

Inner Layer: Retina

• The innermost layer is called retina; it contains neurons essential for visual processing and adheres to choroid via vitreous body—a gelatinous mass that maintains retinal position against choroid layers.

• Key optical media include both chambers filled with aqueous humor, lens, vitreous humor, and cornea—all crucial for light transmission within the eye structure. Additionally, optic nerve originates at papilla level where no receptors exist—creating a blind spot in vision due to absence of photoreceptors there.

Macula and Visual Acuity

• At approximately 3 mm inward from macula lies a region rich in cone cells responsible for high visual acuity; this area is also known as fovea centralis or yellow spot due to its distinct coloration from surrounding tissues.

• Papilla represents convergence point for ganglion cell axons forming optic nerve; it appears whitish with an opening at center where central retinal artery enters supplying nutrients necessary for retinal health but lacks photoreceptors leading to blind spot formation here too.

Eye Anatomy and Function

Orbital Cavity Structure

• The orbital cavity is located outside each nasal fossa, beneath the base of the skull, and above the maxillary bone, resembling a quadrangular pyramid.

• The perspective image shows that the base represents a square while the vertex is at the center, with walls appearing as triangles extending from the base to the vertex.

• The walls consist of bony surfaces with angles separating them; these include openings for communication with various parts of the face.

Walls of the Orbital Cavity

• The superior wall is formed by the frontal bone and lesser wing of sphenoid; its inferior wall includes contributions from both frontal and zygomatic bones.

• The inferior wall also features maxillary bone components, leading to an opening for drainage through a canal.

• The internal wall consists of ascending processes from maxilla, lacrimal bone, and ethmoid bone.

Openings in Orbital Borders

• Notable openings include:

• Superior external border connects to middle cranial fossa.

• Inferior external border has a fissure linking to maxillary sinus.

• Internal borders feature lacrimal duct connections to nasal cavity via two ethmoidal canals (anterior and posterior).

Nerves and Vessels in Orbit

• Key structures include optic canal for optic nerve (CN II), ophthalmic artery, and motor nerves for eye movement (CN III, IV, VI).

• Important nerves passing through are oculomotor (III), trochlear (IV), abducens (VI), along with branches from trigeminal nerve.

Eye Muscles Overview

• Eye muscles are classified into intrinsic (ciliary muscle & iris sphincter) which are involuntary; extrinsic muscles control voluntary movements including four rectus muscles and oblique muscles.

• Rectus muscles insert around an annular tendon called "Zinn's ring," where they converge at their central point before attaching to sclera.

Specific Muscle Functions

• The levator palpebrae superioris elevates eyelid but does not move eyeball; it originates above optic canal on lesser wing of sphenoid.

• Superior oblique muscle changes direction via a pulley-like structure known as "trochlea" before inserting into posterior part of eyeball.

• Inferior oblique muscle arises from maxilla floor; it helps rotate eye outward without head movement.

These notes encapsulate key anatomical details regarding eye structure and function based on provided timestamps.

Muscle Functions and Eye Movement

Overview of Eye Muscle Function

• The exercise involves observing the violet point with the right eye while covering the left eye, directing gaze according to muscle contraction. This helps identify which muscles are engaged during different eye movements.

Specific Muscles and Their Actions

• Looking upwards and inwards utilizes the superior rectus muscle; looking directly inward engages the medial rectus; downward gaze towards the nose activates the inferior rectus; outward gaze employs the superior oblique muscle.

Innervation of Eye Muscles

• The superior rectus and levator palpebrae are innervated by the superior branch of the oculomotor nerve, while other muscles like inferior rectus and medial rectus receive innervation from its inferior branch. The trochlear nerve (IV) innervates only the superior oblique muscle.

Unique Characteristics of Trochlear Nerve

• The trochlear nerve is distinct as it originates from the posterior aspect of the brainstem, unlike other ocular motor nerves that arise anteriorly or laterally. It is often referred to as "pathetic" due to its unique pathway and lack of associations with other structures.

Parasympathetic Innervation in Ocular Function

• The parasympathetic fibers originate from a specific nucleus responsible for photomotor reflexes, traveling alongside cranial nerves to synapse at a ciliary ganglion before reaching intrinsic eye muscles like ciliary and sphincter pupillae muscles. This process facilitates accommodation for near vision (contraction) and pupil constriction (miosis).

Sympathetic Control Over Pupil Size

• Sympathetic innervation does not follow typical pathways but instead travels along blood vessels originating from cervical sympathetic chain ganglia, leading to dilation (mydriasis) through action on dilator pupillae muscles within the iris. This contrasts with parasympathetic functions that restrict light entry into the eye through miosis.