MCAT Biology : Sensory Organs

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #161 : Biology

Your hand jerks back when you touch a hot stove. Which of the following describes the pathway of nerve impulses responsible for this reflex?

Possible Answers:

Motor neuron → sensory neuron → interneuron

Motor neuron → interneuron → sensory neuron

Interneuron → sensory neuron → motor neuron

Sensory neuron → interneuron → motor neuron

Sensory neuron → motor neuron → interneuron

Correct answer:

Sensory neuron → interneuron → motor neuron

Explanation:

Messages are picked up by sensory neurons in the peripheral nervous system and passed to interneurons in the central nervous system; responses are passed on to motor neurons in the peripheral nervous system

Example Question #87 : Nervous System And Nervous Tissue

When you stare directly at an object, the image focuses on what part of the retina?

Possible Answers:

Fovea centralis

Lens

Pupil

Choroid

Optic disk

Correct answer:

Fovea centralis

Explanation:

The fovea centralis, also known as the focal point, is the point where an image is centered when you stare at objects. This region of the retina has a high number of cone and rod cells, and explains why we can only clearly focus on one object at a time. Only the object lined up with the fovea centralis will remain clear, while peripheral objects appear blurry.

Example Question #88 : Nervous System And Nervous Tissue

Which of the following is true about the cornea?

Possible Answers:

Elasticity of the cornea declines with age

It is avascular

It is largely made of lipids

It is clear with a refractive index of 0.6

Correct answer:

It is avascular

Explanation:

The cornea is avascular and made primarily of collagen, not lipids. When light first reflects off of a focused object, it strikes the eye on the cornea, where its high refractive index (1.4) allows most of the bending of light to occur at the interface between air and cornea. Unlike the lens, the cornea does not change its shape. The lens is tethered by suspensory ligaments, which are further connected to ciliary muscles. When the ciliary muscles contract, they release tension on the suspensory ligaments, thus making the lens more spherical and bringing the focal point closer to the lens. 

Example Question #164 : Biology

Which of the following are responsible for sensing color in the human eye?

Possible Answers:

Pupils

Rods

Retinas

Cones

Correct answer:

Cones

Explanation:

Rods and cones are two photoreceptors located on the back of the retina that are responsible for black, white (dark and light), and color sense. Rods are responsible for light and dark and are extremely sensitive, while cones sense color and are less sensitive.

The pupil and retina are both anatomical structures of the eye. The pupil controls the amount of light to pass through the eye, and the retina converts the electromagnetic signal to a neural stimulus.

Example Question #1 : Sensory Organs

Which of the following explains why there is a blind spot in the eye?

Possible Answers:

This is the location where the lens of the eye is not transparent

This is the location where the retina does not focus light

This is the location where there are no rods

This is the location where there are no cones

This is the location where the optic nerve exits the eye

Correct answer:

This is the location where the optic nerve exits the eye

Explanation:

The optic nerve collects stimuli from the retina and exits through the back of the eye to relay the information to the occipital lobe of the cerebrum. The point at which the optic nerve exits the eye contains no photoreceptors (rods and cones), and is unable to interpret light signals. This leads to a blind spot in the eye at the optic disk.

Example Question #2 : Sensory Organs

Which of the following helps humans see in the dark?

Possible Answers:

Retina

Cones

Optic nerve

Rods

Lens

Correct answer:

Rods

Explanation:

Rods and cones are the primary photoreceptors in our eyes. The rods are responsible for night vision, allowing us to differentiate different grays and blacks, whereas the cones are responsible for sensing color. Rods are concentrated in the periphery of the retina, making them essential for peripheral vision as well.

The retina contains both rods and cones and is responsible for converting electromagnetic stimulation to electrical impulses. These impulses are fired through the optic nerve to the occipital lobe for processing. The lens helps to focus light on the retina.

Example Question #3 : Sensory Organs

Which of the following is responsible for color vision?

Possible Answers:

Rods

Lens

Retina

Optic nerve

Cones

Correct answer:

Cones

Explanation:

Rods and cones are the primary photoreceptors in our eyes. The rods are responsible for night vision, allowing us to differentiate different grays and blacks, whereas the cones are responsible for sensing color. There are three main pigments in cones, each perceiving one type of color: red, green, or blue. Deficiency in one type of cone can result in color blindness.

The retina contains both rods and cones and is responsible for converting electromagnetic stimulation to electrical impulses. These impulses are fired through the optic nerve to the occipital lobe for processing. The lens helps to focus light on the retina.

Example Question #4 : Sensory Organs

Which cell of the retina is utilized most in night vision?

Possible Answers:

Rod cell

Cone cell

Bipolar cell

Ganglion cell

Correct answer:

Rod cell

Explanation:

The two major photoreceptors of the body are cone cells and rod cells. Cone cells are most highly concentrated in the fovea and are best for color vision and visual acuity. In contrast, rod cells are found in higher concentrations away from the fovea (at the periphery of the retina) and used for seeing low levels of light and peripheral vision. Rod cells are therefore the photoreceptors used for night vision.

Ganglion cells and bipolar cells are also cells of the retina. They are used in the transmission of the electrical signals from the photoreceptors to the optic nerve and brain.

Example Question #5 : Sensory Organs

The amount of light that reaches the retina is controlled by the __________, while the focus is determined by stimulation of the __________.

Possible Answers:

iris . . . ciliary muscles

lens . . . iris

ciliary muscles . . . iris

lens . . . ciliary muscles

Correct answer:

iris . . . ciliary muscles

Explanation:

The pigmented part of the eye, called the iris, regulates the amount of light entering the eye. The iris is actually a band of circular muscle capable of regulating the size of the pupil. By dilating or constricting, this ring controls the amount of light that can enter the eye.

The ciliary muscles are responsible for altering the lens shape. When these muscles contract, the lens flattens and the focal length is reduced, allowing focus on objects closer to the eye. While the lens plays an important role in focusing light, it cannot be stimulated directly and relies on action of the ciliary muscles to change its shape.

Example Question #6 : Sensory Organs

Which of the following refers to the optic chiasm?

Possible Answers:

The anterior region of the fetal eye

The blind spot created by the optic nerve leaving the eye

The point of connection between the optic nerve and the cerebrum

The crossing point of the right and left optic nerves

The crossing point of the right and left optic tracts

Correct answer:

The crossing point of the right and left optic nerves

Explanation:

The optic nerves cross over in a location known as the optic chiasm, located posterior to the eyes in the brain. The optic tract refers to the portion of the optic nerve that carries signals prior to the optic chiasm, and thus is not involved in the cross. The result of the optic chiasm is that information from the right eye is transmitted to the left visual cortex, while information from the left eye is transmitted to the right visual cortex.

The blind spot created by the optic nerve exiting the eye is known as the optic disc.

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