Recording-2025-03-03T14_07_13.595Z

Nervous System Overview

• The nervous system includes neurons, glial cells, and various functions that will be discussed in lectures.

• Videos are available that detail how neurons operate, their different types, and related concepts.

• These resources are beneficial and should not be overlooked.

Lacrimal Apparatus

• Location: Positioned laterally in the eye's socket, under the corner of the eye.

• Function: Constantly produces fluid unless a condition like dry eyes exists.

• Lacrimal Punctum:

  • A small hole that drains excess lacrimal fluid, functioning like a sink drain.

  • Excess fluid can travel through the nasolacrimal duct into the nasal cavity, causing a runny nose when crying or having watery eyes.

Eye Muscles

• There are six extrinsic muscles that control eye movement:

  • Four primary muscles allow looking up, down, left, or right.

  • Two oblique muscles facilitate additional rolling movements.

  • These muscles are innervated by cranial nerves.

• The levator palpebrae muscle is responsible for moving the upper eyelid.

Eyelids and Conjunctiva

• Eyelids: Protect the eye and aid in eyelid movement.

• Conjunctiva:

  • A membrane that prevents foreign objects from getting behind the eyeball.

  • Attaches to both the eyelid and the eyeball, forming a protective pocket.

Structure of the Eye

• Fibrous Tunic: The outermost layer made of connective tissue.

  • Sclera: The white part of the eye that helps maintain its shape.

  • Cornea: Clear front part of the eye made of connective tissue fibers aligned to allow light passage.

• Vascular Tunic: The middle layer containing blood vessels for nutrient delivery.

  • Choroid Layer: Contains many blood vessels and is darker.

  • Ciliary Body: Connects to the lens and contains smooth muscle that changes lens shape for focusing on near or far objects.

• Lens: Adjusts its shape due to the action of ciliary muscles and suspensory ligaments, altering its focal point.

Iris and Pupil

• Iris: The colored part of the eye containing smooth muscle.

  • Controls the size of the pupil (the hole in the middle) regulating light entry.

• Pupil Response:

  • Constricts in bright light and dilates in low light conditions, protecting photoreceptors.

Neural Tunic (Retina)

• The innermost layer where photoreceptors (rods and cones) reside:

  • Rods: Located on the periphery, provide low-light vision and peripheral view, but are grainy and lack detail.

  • Cones: Provide color vision and detailed images, primarily located in bright light conditions.

• Fovea Centralis: Contains a high concentration of cones for sharp vision, specifically in the center of the retina.

  • The highest acuity area, where detailed images are focused.

• Optic Disc (Blind Spot): The entry point for blood vessels and optic nerve, lacks photoreceptors, leading to a visual blind spot.

  • The brain compensates for this by filling in the "missing" areas based on surrounding information.

Cavities of the Eye

• Posterior Cavity: Filled with vitreous humor, a thick gel-like substance formed during embryonic development. It maintains the round shape of the eye.

• Anterior Cavity: Contains aqueous humor, a watery fluid that is continuously produced and drained through the scleral venous sinus, ensuring proper eye pressure and nourishment.