Lecture 31- Optic Nerve Part I (Combined)

LLOs: 30.1 - 37.2

A bundle of more than one million retinal ganglion cell (RGC) axons that transmit visual signals from the retina to the brain

Optic Nerve

Segments of the Optic Nerve

Intraocular, prelaminar, laminar, retrolaminar, intraorbital, intracanalicular, and intracranial

Shortest segment of the optic nerve, located within the eye

Intraocular Segment

Part of the optic nerve containing glial tissue that provides support to RGC axons

Prelaminar Region

Sieve-like structure that allows the RGC axons to exit the eye and become myelinated

Lamina Cribrosa

Longest segment of the optic nerve, allowing for eye movement without stretching

Intraorbital Segment

Condition in which the intraorbital segment is stretched taut, causing the eyeball to protrude from the orbit

Proptosis

Point where the optic nerves from both eyes meet and partially cross paths

Optic Chiasm

Protective meningeal layers covering the optic nerve

Dura mater, arachnoid, and pia mater

Blood supply to the optic nerve’s intraocular segment

Posterior ciliary arteries

Area on the retina where there are no photoreceptors, corresponding to the optic nerve head

Physiologic Blind Spot

Measurement for assessing the health of the optic nerve; typically ranges from 0.1 to 0.8

Cup to Disc Ratio

Process by which the optic nerve converts visual signals into neural impulses

Signal Transduction

Ocular reflexes triggered by visual stimulation

Light reflex and accommodative reflex

Biological processes that cycle daily, influenced by changes in light intensity

Circadian Rhythms

Neurons in the retina that collect visual information and transmit it to the brain.

Retinal Ganglion Cells (RGCs)

Process of transporting materials down the axon from the cell body to the terminal

Anterograde Transport

Transport of materials from the axon terminal back to the cell body

Retrograde Transport

Primary excitatory neurotransmitter used by bipolar cells and RGCs in the retina

Glutamate

Supporting cells in the retina that help regulate the retinal environment and remove excess glutamate

Retinal Müller Cells

Area of the optic disc surrounded by the cup and formed by RGC axons

Neuroretinal Rim

Glial cells that provide structural support and maintain the blood-brain barrier in the optic nerve

Astrocytes

A thickened internal limiting membrane over the optic cup

Central Meniscus of Kuhnt

Peripheral retinal barrier composed of retinal Müller cells and ONH astrocytes

ILM of Elschnig

Glial tissue named after Kuhnt that has significance in optic nerve structure.

Intermediary Tissue of Kuhnt

Separates the choroid from the optic nerve

Border Tissue of Jacoby

Scleral collagenous tissue involved in the structure of the optic nerve

Border Tissue of Elschnig

Study of RGCs and their synaptic and action potential activities

Axon Physiology

Arrangement of RGC axons in the optic nerve to facilitate information transmission

Axon Bundles Organization

RGC axons that bypass the fovea to enter the optic disc superiorly and inferiorly

Temporal Macular Fibers

Axonal fibers carrying information from the macula into the temporal half of the optic disc.

Papillomacular Bundle

Crossing of nasal retinal fibers at the optic chiasm during optic nerve organization

Nasal Fibers Decussation

Optic nerve damage can negatively affect the light reflex, triggered by visual stimuli

Light Reflex Impact

Reflex that adjusts the eye's focus for near and distant vision, influenced by optic nerve function.

Accommodative Reflex

Process through which visual information is relayed from the retina to the brain via the optic nerve

Visual Signal Transmission

What are the four segments of the optic nerve?

Intraocular, Prelaminar, Laminar, Retrolaminar, Intraorbital, Intracanalicular, Intracranial.

What characterizes the intraocular segment of the optic nerve?

It is the shortest segment.

What structure is responsible for supporting RGC axons in the prelaminar region of the optic nerve?

Glial tissue.

What is the primary blood supply for the intraocular segment of the optic nerve?

Short posterior ciliary arteries.

What happens in the laminar region of the optic nerve?

RGC axons exit the lamina cribrosa and become myelinated.

What is proptosis in relation to the optic nerve?

It occurs when the intraorbital segment is stretched taut and the eyeball protrudes out of the orbit.

What anatomical feature separates the optic nerve from retinal layers?

Limiting membranes.

Which layer of the meninges is the outermost surrounding the optic nerve?

Dura mater.

What is the function of glial tissues like the Central meniscus of Kuhnt?

They separate the optic nerve from the retinal layers.

What is the average cup to disc (C/D) ratio in a normal optic nerve?

0.3.

What is the physiological blind spot related to the optic nerve?

Site of RGC axon aggregation at the optic disc.

What are the primary functions of the optic nerve?

Signal transduction, ocular reflexes, and circadian rhythms.

How do RGC axons arrange themselves in the optic nerve?

Information from temporal retinal fibers is on the temporal side, macular fibers are central, and nasal fibers are on the nasal side.

What neurotransmitter do retinal ganglion cells (RGCs) primarily use?

Glutamate.

What type of transport do RGCs use for moving neurotransmitter vesicles?

Fast anterograde transport.

What is the role of retinal Muller cells?

They absorb excess glutamate and convert it to glutamine.

What factors influence the optic nerve's role in circadian rhythms?

Changes in light intensity.

What occurs when optic nerve damage affects visual reflexes?

Both light reflex and accommodative reflex can be impaired.

What layer adheres tightly to the optic nerve?

Pia mater.

What does the neuroretinal rim signify in relation to the optic disc?

It is where RGC axons aggregate and turn 90 degrees.

How is blood flow in the optic nerve maintained despite changes in perfusion pressure?

Through continuous non-fenestrated capillaries.

What is the significance of the axonal transport speed in RGCs?

Fast transport is for neurotransmitter vesicles, whereas slow transport carries structural proteins.

What is the physiological definition of 'cup' in the optic disc?

The proportion of cup size to neuroretinal rim size.

What is the defining feature of the papillomacular bundle?

Axonal fibers that carry information from the macula to the temporal half of the optic disc.

What happens to nasal macular fibers as they reach the optic disc?

They travel in the papillomacular bundle to enter the temporal side.

What structural support do astrocyte sheaths provide?

They bundle 1000 axons into each fascicle to pass through the lamina cribrosa.

Describe the significance of the optic chiasm for nasal fibers.

Nasal fibers decussate (cross over) at the optic chiasm.

What can result from dysfunction in RGCs regarding action potentials?

They are the first neurons in the visual pathway to use action potentials exclusively.

What can be observed in the subarachnoid space surrounding the optic nerve?

It contains cerebrospinal fluid (CSF).

How does the structure of RGCs facilitate their functions?

They receive presynaptic input from bipolar and amacrine cells, processing visual signals effectively.

What is the purpose of the retinal blood-brain barrier?

To maintain selective permeability with tight junctions, ensuring stable conditions for neural function.