Human Eye Anatomy and Visual Pathways: Key Concepts and Brain Blood Supply

Aqueous Humor

Clear, watery fluid found in the anterior chamber of the eye.

Choroid

The layer of blood vessels that nourishes the eye and absorbs light due to its high melanocyte content.

Cornea

The transparent tissue covering the front of the eye. It has nerves but no blood vessels.

Iris

A circular band of muscles that controls the size of the pupil. Its pigmentation gives the eye its color.

Lens

A transparent tissue that bends and focuses light as it passes through the eye by changing its shape.

Pupil

The hole in the center of the iris where light passes through. Its diameter is controlled by the iris.

Retina

A layer of tissue on the back of the eye that contains light-responsive cells (photoreceptors) that generate electrical impulses.

Rods

Photoreceptors in the retina that are responsive in low-light conditions.

Cones

Photoreceptors in the retina that are responsive to color and in bright-light conditions.

Sclera

The protective outer coating around the posterior five-sixths of the eyeball.

Vitreous Humor (or Vitreous)

A clear, jelly-like fluid that fills the back portion of the eye, providing constant pressure to maintain the eye's shape.

Pupillary Reflex

The automatic reaction of the iris to adjust the pupil's size continuously in response to changing light conditions.

Optic Disc

The area of the retina where the axons of the ganglion cells bundle together to form the optic nerve. Also known as the blind spot.

Optic Nerve

The pathway that carries nerve impulses from the retina to the brain for visual analysis.

Optic Chiasm

The intersection point of the optic nerves in front of the pituitary gland where some axons switch sides (decussation).

Decussation

The process where axons from the nasal side of each retina cross sides at the optic chiasm.

Optic Tract

The pathway that carries visual information from the optic chiasm to the lateral geniculate nucleus (LGN).

Lateral Geniculate Nucleus (LGN)

The main relay station in the thalamus for the visual pathway, projecting to the primary visual cortex.

Optic Radiation

The projection of nerve fibers from the lateral geniculate nucleus (LGN) to the primary visual cortex.

Ventral Pathway

A major cortical system for visual processing that extends to the temporal lobe; involved in recognizing objects.

Dorsal Pathway

A major cortical system for visual processing that projects to the parietal lobe; essential for locating objects.

Circle of Willis

A ring of arteries at the base of the brain that connects the blood supply from the internal carotid and vertebral arteries, providing a safety mechanism if one artery is blocked.

Internal Carotid Arteries

One of two pairs of arteries that supply blood to the entire brain, branching to form the anterior and middle cerebral arteries.

Vertebral Arteries

One of two pairs of arteries that supply blood to the entire brain, joining at the brainstem to form the basilar artery.

Basilar Artery

A single midline artery formed by the joining of the right and left vertebral arteries.

Thrombosis (in the context of stroke)

The blockage of a blood vessel in the brain or neck caused by a blood clot that formed there.

Embolism (in the context of stroke)

The blockage of a blood vessel in the brain or neck caused by a blood clot that traveled from somewhere else in the body.

Stenosis (in the context of stroke)

The constriction or narrowing of an artery in the head or neck.

Hemorrhagic Stroke

A stroke caused by the bleeding of a blood vessel in the brain.

Glial Cells

Non-neuronal cells in the central and peripheral nervous systems that provide support and protection for neurons.

Astrocyte (Astroglia)

A star-shaped glial cell that provides physical and nutritional support for neurons, transports nutrients, cleans debris, and regulates the extracellular space. (Most important type of glia).

Microglia

Glial cells that act as the primary immune defense of the central nervous system, digesting parts of dead neurons.

Oligodendroglia

Glial cells that provide the insulation (myelin) for neurons in the central nervous system.

Satellite Cells

Glial cells that provide physical support to neurons in the peripheral nervous system.

Schwann Cells

Glial cells that provide the insulation (myelin) for neurons in the peripheral nervous system.

Neurons vs. Glial Cells - Processes

Neurons have two processes (axons and dendrites), while glial cells have only one.

Neurons vs. Glial Cells - Action Potentials

Neurons can generate action potentials, but glial cells cannot. Glial cells do, however, have a resting potential.

Neurons vs. Glial Cells - Synapses

Neurons have synapses that use neurotransmitters, while glial cells do not have chemical synapses.

Oculomotor Nerve (Cranial Nerve III)

The cranial nerve that controls four of the six muscles that move the eyeball.

Trochlear Nerve (Cranial Nerve IV)

The cranial nerve that controls one of the six muscles that move the eyeball.

Abducens Nerve (Cranial Nerve VI)

The cranial nerve that controls one of the six muscles that move the eyeball.

Blind Spot

Another name for the optic disc, the area of the retina that lacks light-sensitive cells.

Ventral Pathway (Location)

The visual processing pathway that extends to the temporal lobe and is involved in recognizing objects.

Dorsal Pathway (Location)

The visual processing pathway that projects to the parietal lobe and is essential for locating objects.