psl 250 lecture 27

triad of near reflex

- 1) accommodation, 2) miosis and 3) convergence

Suppose the suspensory ligaments are loose, which receptor must be activated in the ciliary muscle? Which neurotransmitter is causing this response?

M3. Acetylcholine.

image formation

- light rays are focused on the retinal surface of the eye - image formed is inverted, backwards and a fraction of the actual size

Lens accommodation

- light rays from objects (far) are parallel and (close) divergent - employed to focus objects closer than 20 feet - increase the curvature of the lens

The pupil is not an anatomical structure. How can it be likened to a black hole of the universe?

All light enters the pupil, but none exits it. That is why it appears black.

If the ciliary muscles of the eye are relaxed, which receptor must be activated? What neurotransmitter(s) is binding to the receptor?

B2 receptors. Norepinephrine.

What is convergence?

Convergence is the ability of the eye to focuses light at a focal point. It can also be considered the bending of light rays towards the visual axis.

What are the ways in which the image formed on your retina is different than the object itself?

Inverted (up and down and right to left) and a fraction of the actual size of the object.

lens accommodation

Lens accommodation is the process by which the eye increases its converging power by making the lens more convex.

How would you compare eye motions during convergence for an object more than 20 feet away? Less than 20 feet away?

More than 20 feet away:Ciliary muscles are relaxed, suspensory ligaments are taut and the lens is flattened out. Less than 20 feet away:Ciliary muscles are contracted, suspensory ligaments are loose and the lens is bulged (or very convex).

What is the state of the ciliary body, suspensory ligaments and lens when an object is more than 20 feet away? Less than 20 feet away?

More than 20 feet away:Ciliary muscles are relaxed, suspensory ligaments are taut and the lens is flattened out. Less than 20 feet away:Ciliary muscles are contracted, suspensory ligaments are loose and the lens is bulged (or very convex).

If you were being chased by a bear in the woods, would your eyes undergo miosis or mydriasis? Which part of the ANS is elicited?

Mydriasis. Sympathetic.

Can you list a few drugs that would cause miosis? What receptors are responsible for miosis? Neurotransmitter?

Opiates (such as heroin or morphine) and other central nervous system depressants such as benzodiazepines and barbiturates will give you small pupils while under the influence of the drug. M3. Acetylcholine.

What is miosis? Mydriasis?

Pupillary constriction. Pupillary dilation.

What are the muscles of the iris that control the diameter of the pupil? Which dilate it? Which constrict it?

Pupillary constrictor (sphincter) muscles and pupillary dilator (radial) muscles. Pupillary constrictor (sphincter) muscles. Pupillary dilator (radial) muscles.

can you list a few drugs that would cause mydriasis? What receptors are responsible for mydriasis? Neurotransmitter(s)?

Stimulant drugs like cocaine, amphetamines, methamphetamines and ecstasy will give you big pupils - along with cannabis (marijuana) - and hallucinogenic drugs like LSD and ketamine. alpha 1. Noradrenaline.

When is the triad of near reflex employed?

The triad of near reflex is employed in response to focusing on a near object (closer than 20 ft. from the eye)

If you were to remove a healthy lens from someone's eye. What would the natural conformation be?

bulged in the middle; narrower near the edges (like a magnifying glass)

When viewing an object that is near, the ciliary body is _____________ and the lens is _______________. This is due to the release of norepinephrine from the __________________ nervous system.

contracted; bulged; parasympathetic

Light rays entering the eye from a distant object (>20 feet away) are said to be essentially ___________________________ to each other. While light rays entering the eye from a nearer object (<20 feet away) are still _________________________ from one another.

parallel divergent

When viewing an object that is far away, the ciliary body is _____________ and the lens is _______________. This is due to the release of norepinephrine from the __________________ nervous system.

relaxed; stretched (flattened out); sympathetic

miosis

the neurotransmitter that causes the contraction is acetylcholine occurs when there is contraction of a ring of smooth muscle with fibers arranged in a sphincter (the muscle fibers are laid end to end in a circle) mediated by the parasympathetic nervous system

mydriasis

the neurotransmitter that causes the contraction is norepinephrine occurs when there is contraction of a ring of smooth muscle with fibers arranged radially (like the spokes of a tire) mediated by the sympathetic nervous system

As the eyes converge for the near reflex, the angle between the two visual axes becomes more obtuse (a larger angle). t or f

true

In order for a clear image to be formed, the focal point of all the refraction that happens in the eye must be on the retinal surface, t or f

true

The greater the curvature of a lens (more rounded it is) the greater focal power it has. t or f

true