Extraocular Muscles Overview

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary action of the inferior oblique muscle?

Abduction and intorsion

Depression and adduction

Elevation and extorsion (correct)

Adduction and intorsion

Which cranial nerve is responsible for the innervation of the lateral rectus muscle?

Optic nerve

Abducent nerve (correct)

Trochlear nerve

Oculomotor nerve

Which muscle is involved in the action of depression and abduction of the eyeball?

Inferior rectus

Superior oblique (correct)

Lateral rectus

Superior rectus

What muscle assists the lateral rectus in performing abduction?

Inferior oblique Signup and view all the answers

Which of the following combinations of muscles contributes to the action of elevation of the eyeball?

Superior rectus and inferior oblique Signup and view all the answers

Which muscle is responsible for elevation of the eye?

Superior rectus Signup and view all the answers

Which nerves enter the orbit through the superior orbital fissure outside the common tendinous ring?

Lacrimal, Frontal, Trochlear Signup and view all the answers

Which of the following pairs are involved in intorsion of the eye?

Superior rectus and superior oblique Signup and view all the answers

Which autonomic nerve is responsible for constriction of the pupil?

Parasympathetic to the ciliary muscle Signup and view all the answers

Which cranial nerve is primarily responsible for innervating the majority of extraocular muscles?

Oculomotor nerve Signup and view all the answers

Which nerve passes through the optic canal along with the ophthalmic artery?

Optic nerve Signup and view all the answers

What is the function of the inferior oblique muscle?

Elevation and extorsion Signup and view all the answers

Which of the following statements is true regarding the entry of the optic nerve?

It enters through the optic canal. Signup and view all the answers

What is the primary function of the anterior ethmoidal nerve?

Deliver sensory information to the nasal cavity and skin over the nose Signup and view all the answers

Which part of the optic nerve is located within the orbit?

Intraorbital part Signup and view all the answers

What unique characteristic does the optic nerve possess regarding regeneration?

It cannot regenerate after injury due to lack of a neurolemmal sheath Signup and view all the answers

Where does the optic nerve pierce the sclera?

At the posterior pole of the eyeball, medial to the center Signup and view all the answers

What structure does the posterior ethmoidal nerve primarily supply?

Posterior ethmoidal and sphenoidal air sinuses Signup and view all the answers

Which of the following branches of the nasociliary nerve supplies the skin over the upper eyelid?

Infratrochlear nerve Signup and view all the answers

Which of the following statements about the optic nerve is correct?

It represents the axons of the ganglion cell layer of the retina Signup and view all the answers

What is the length of the intraorbital part of the optic nerve?

25 mm Signup and view all the answers

What is the primary function of the cones in the human eye?

Color vision and high visual acuity Signup and view all the answers

What results from a deficiency in vitamin A related to vision?

Lack of rhodopsin leading to night blindness Signup and view all the answers

What type of epithelium is found in the conjunctiva?

Stratified columnar epithelium Signup and view all the answers

Which structure is responsible for draining the aqueous humor in the eye?

Subconjunctival vein Signup and view all the answers

Which type of muscle is present in the eyelid responsible for closing it?

Striated muscle Signup and view all the answers

What type of epithelium replaces the conjunctival epithelium at the corneo-scleral junction?

Stratified squamous epithelium Signup and view all the answers

What is contained within the tarsal plate of the eyelid?

Modified sebaceous glands Signup and view all the answers

What condition results from inflammation of the Zeis or Moll's glands?

Sty Signup and view all the answers

What is the primary effect of dark adaptation in the rods?

It results in a full loading of rhodopsin, taking about 30 minutes. Signup and view all the answers

How does light adaptation affect the rods and cones in bright light?

It decreases the sensitivity of rods and cones to high light levels. Signup and view all the answers

Which structure of the retina is responsible for the highest visual acuity?

Fovea centralis Signup and view all the answers

What happens to photopigments during light adaptation?

They undergo breakdown in both rods and cones. Signup and view all the answers

Where is the macula lutea located in relation to the optic disc?

It is 3 mm from the temporal side. Signup and view all the answers

What is the reason for the blind spot in the retina?

It has no cones or rods. Signup and view all the answers

What is the typical range of increase in retinal sensitivity due to photopigment changes?

Which statement about the fovea centralis is true?

It has a one-to-one ratio of cones to bipolar cells. Signup and view all the answers

Study Notes

Inferior Oblique Muscle

Originates from the orbit floor, lateral to the nasolacrimal groove.
Ascends posterolaterally, inserting into the sclera's lateral part, posterior to the eyeball's coronal equator.
Action: Elevation, abduction, extorsion of the eyeball.

Extraocular Muscle Nerve Supply

Lateral rectus: Abducent nerve (LR6).
Superior oblique: Trochlear nerve (SO4).
Other extraocular muscles (including levator palpebrae superioris): Oculomotor nerve (O3).

Extraocular Muscle Actions

Individual Muscle Actions:
- Medial rectus: Adduction.
- Lateral rectus: Abduction.
- Superior rectus: Elevation, adduction, intorsion.
- Inferior rectus: Depression, adduction, extorsion.
- Superior oblique: Depression, abduction, intorsion.
- Inferior oblique: Elevation, abduction, extorsion.
Compound Actions:
- Adduction: Medial rectus (assisted by superior and inferior recti).
- Abduction: Lateral rectus (assisted by superior and inferior oblique muscles).
- Elevation: Superior rectus + inferior oblique.
- Depression: Inferior rectus + superior oblique.
- Intorsion: Superior rectus + superior oblique.
- Extorsion: Inferior rectus + inferior oblique.

Orbital Nerves

Classified as motor, sensory, or autonomic.
Motor Nerves: Oculomotor, trochlear, and abducent nerves. Supply extraocular muscles.
Sensory Nerves: Ophthalmic nerve (branches: lacrimal, frontal, nasociliary) provide general sensation and vision (optic nerve).
Autonomic Nerves: Sympathetic fibers innervate superior tarsal muscle, dilator pupillae, and blood vessels. Parasympathetic fibers (oculomotor nerve) innervate ciliary muscle and constrictor pupillae. Facial nerve provides parasympathetic innervation to the lacrimal gland.
All nerves enter the orbit via the superior orbital fissure (SOF) except the optic nerve, which enters through the optic canal.

Nasociliary Nerve Branches and Distribution

Communicating branch to the ciliary ganglion (sensory and vasomotor).
Two long ciliary nerves: pierce sclera, supply ciliary body, iris, cornea; carry sympathetic fibers to the dilator pupillae.
Infratrochlear nerve: supplies upper eyelid and skin over nasal bone.
Posterior ethmoidal nerve: supplies posterior ethmoidal and sphenoidal sinuses.
Anterior ethmoidal nerve: continuation of nasociliary nerve; travels through orbital, cranial, and nasal cavities; supplies skin over the nose.

Optic Nerve

Second cranial nerve; responsible for vision.
Develops from the diencephalon.
Enveloped in three meninges (dura, arachnoid, pia) within the orbit. Subdural and subarachnoid spaces extend to the eyeball, explaining papilledema in increased intracranial pressure.
Lacks a neurolemmal sheath; cannot regenerate after injury.
Axons of the ganglion cell layer of the retina.
Pierces sclera 3mm medial to the posterior pole of the eyeball.
Approximately 4 cm long; runs posteromedially to the optic chiasm.

Retina Photoreceptors

Rods (120 million) and cones (6 million) in each retina.
Rods: responsible for vision in dim light, night vision.
Cones: responsible for color vision and high visual acuity. Present in the fovea centralis.

Accessory Structures of the Eye (Ocular Adnexa)

Conjunctiva

Transparent mucous membrane covering sclera (bulbar conjunctiva) and eyelids (palpebral conjunctiva).
Stratified columnar epithelium with goblet cells (except at the corneo-scleral junction).
Functions: Protection and drainage of aqueous humor.

Eyelid

Layers: thin skin (with Zeis and Moll glands), striated muscles (orbicularis oculi and levator palpebrae), tarsal plate (with Meibomian glands), and palpebral conjunctiva.
Inflammation of Zeis or Moll’s glands can lead to a sty.

Dark and Light Adaptation

Dark Adaptation: Increase in retinal sensitivity. Occurs in two stages: rapid, small rise (cone adaptation, 5-10 minutes) and slow, greater rise (rod adaptation, 30 minutes). Retinal sensitivity increases 20-30,000 times.
Light Adaptation: Decrease in retinal sensitivity. Occurs when shifting from dark to bright light. Involves pupil constriction, decreased sensitivity of rods and cones, breakdown of photopigments, and decreased signal intensity in retinal neurons. Takes about 5 minutes.

Retina: Parts of Physiological Importance

Macula lutea: Yellow spot opposite the posterior pole of the eye; 3 mm temporal to optic disc.
Fovea centralis: Central part of macula; contains only cones; highly transparent (no blood vessels); high visual acuity (direct light on cones, 1:1 ratio of cones to bipolar and ganglion cells, highly developed pigmented layer).
Optic disc: Optic nerve exit; lacks rods and cones (blind spot); 3 mm nasal to macula lutea.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the anatomy and functions of the extraocular muscles, including the inferior oblique muscle and its unique actions. Learn about the nerve supply for each muscle and how they work individually and collectively to control eye movement.