MCAT Biology : MCAT Biological Sciences

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #1 : Vision

Which of following is a true statement regarding light and the human eye?

Possible Answers:

Light will pass through the lens before passing through the cornea

The pigments of the iris contain small numbers of photoreceptors

The retina is a small disc located at the focal point at the back of the eye

Light will pass through the aqueous humor before passing through the vitreous humor

Correct answer:

Light will pass through the aqueous humor before passing through the vitreous humor

Explanation:

The first structure that light will encounter as it enters the eye is the cornea, a transparent protein disc designed to refract light toward the eye interior. The aqueous humor is the liquid medium between the cornea and the lens of the eye. Light will pass through the aqueous humor and the pupil before hitting the lens. The lens then focuses the light onto the back of the eye. The vitreous humor is the liquid medium between the lens and the retina at the back of the eye.

The iris is used to control the shape of the pupil, and does not contain photoreceptors. All photoreceptors are located on the retina, which lines the back wall of the eye. A small region known as the fovea centralis houses a large number of cones (photoreceptors) at the back of the eye, but is part of the greater retinal structure.

The only true statement given is that light will pass through the aqueous humor before passing through the vitreous humor.

Example Question #112 : Nervous System And Nervous Tissue

The optic nerve is formed from the axons of all retinal ganglion cells. The optic nerves from each eye join at the optic chiasm and eventually enter either the left or right optic tract. The optic tract projects to three subcortical areas. One is the lateral geniculate nucleus, which is responsible for processing visual information. One is the pretectal area, which produces pupillary reflexes based on information from the retina. Finally, the superior colliculus uses the information from the retina to generate eye movement.

When light is shone upon one eye, it causes constriction of the pupil in both eyes. Constriction of the eye in which the light is shone is the direct response while constriction of the other is known as the consensual response. The pupillary reflexes are mediated through retinal ganglion neurons that project to the pretectal area which lies anterior to the superior colliculus. The cells in the pretectal area project bilaterally to preganglionic parasympathetic neurons in the Edinger-Westphal nucleus. This is also known as the accessory oculomotor nucleus. The preganglionic parasympathetic neurons in the Edinger-Westphal nucleus send axons through the oculomotor nerve to innervate the ciliary ganglion. The ciliary ganglion's postganglionic neuron innervates the smooth muscle of the pupillary sphincter.

The right optic tract can be described as an __________.

Possible Answers:

efferent pathway, containing nerve axons from only one eye

afferent pathway, containing nerve axons from only one eye

afferent pathway, containing nerve axons from both eyes

efferent and afferent pathways, containing nerve axons from both eyes

efferent pathway, containing nerve axons from both ways

Correct answer:

afferent pathway, containing nerve axons from both eyes

Explanation:

Afferent pathway, containing nerve axons from both eyes. Again, this question requires us to draw on our knowledge of the nervous system, and in particular, the eye. One must remember that the information leading towards the brain is found in the afferent nerves. Information leading away from the central nervous system is found in the efferent nerves. Therefore, answer choices, ‘efferent pathway, containing nerve axons from only one eye’, and ‘efferent pathway, containing nerve axons from both ways’ can be eliminated. Now the question becomes whether the optic tract contains information from one eye or two. The answer is two. Information from the nasal hemiretina (medial half of the retina) of the left eye cross the optic chiasm and enters the right optic tract. The right optic tract is also made up of nerve fibers originating from the temporal hemiretina of the right eye. In that way, the right side of the brain processes information from the left side of the visual world.

Example Question #190 : Biology

The optic nerve is formed from the axons of all retinal ganglion cells. The optic nerves from each eye join at the optic chiasm and eventually enter either the left or right optic tract. The optic tract projects to three subcortical areas. One is the lateral geniculate nucleus, which is responsible for processing visual information. One is the pretectal area, which produces pupillary reflexes based on information from the retina. Finally, the superior colliculus uses the information from the retina to generate eye movement.

When light is shone upon one eye, it causes constriction of the pupil in both eyes. Constriction of the eye in which the light is shone is the direct response while constriction of the other is known as the consensual response. The pupillary reflexes are mediated through retinal ganglion neurons that project to the pretectal area which lies anterior to the superior colliculus. The cells in the pretectal area project bilaterally to preganglionic parasympathetic neurons in the Edinger-Westphal nucleus. This is also known as the accessory oculomotor nucleus. The preganglionic parasympathetic neurons in the Edinger-Westphal nucleus send axons through the oculomotor nerve to innervate the ciliary ganglion. The ciliary ganglion's postganglionic neuron innervates the smooth muscle of the pupillary sphincter.

As part of a routine eye exam, the following is noticed: if light is shone directly into the patient's left eye, the patient exhibits a consensual but not a direct response. Which of the following is a likely explanation?

Possible Answers:

The optic nerve of the left eye is damaged, but the efferent limb of the left eye is intact

The optic nerve of the left eye is intact, but the efferent limb of the left eye is damaged

The optic nerve of the right eye is intact, but the efferent limb of the right eye is damaged

The optic nerve of the right eye is damaged, but the efferent limb of the right eye is intact

The optic nerve of the left eye is damaged, and the efferent limb of the left eye is damaged

Correct answer:

The optic nerve of the left eye is intact, but the efferent limb of the left eye is damaged

Explanation:

The question tells us we see a consensual but not a direct response. We can therefore conclude that the optic nerve of the left eye is intact because the optic nerve of the right eye is not involved in the response. The response involves information going down the left optic nerve to the pretectal area. From the pretectal area, neurons project bilaterally to the Edinger-Westphal nucleus. Axons from neurons in the nucleus innervate the ciliary ganglion. We see a consensual response in the right eye. We can therefore conclude that the bilateral projection and the efferent pathway to the right eye arc unharmed, and that there is some problem with the efferent pathway to the left eye. We are not seeing a constriction of the left pupil in response to the light being directly shone into the left eye. Conclusion: The left optic nerve is intact, but the efferent pathway of the left eye is somewhere and somehow damaged.

Example Question #1 : Sympathetic And Parasympathetic Divisions

Sympathetic nervous system reactions are associated with which of the following?

Possible Answers:

Pupil dilation and increased heart rate

Pupil constriction and increased heart rate

Pupil dilation and decreased heart rate

Pupil constriction and decreased heart rate

Correct answer:

Pupil dilation and increased heart rate

Explanation:

The sympathetic nervous system is associated with the "fight or flight" response. Some bodily responses include pupil dilation, increased heart rate, increased perspiration, increased blood flow to muscles, relaxation of the bladder, and decreased digestion.

Example Question #2 : Sympathetic And Parasympathetic Divisions

Which of the following is a parasympathetic nervous system response?

Possible Answers:

Increase digestive activity

Increase heart rate

Increase blood flow to skeletal muscle

Restrict blood flow to excretory system.

All of these are effects of parasympathetic stimulation

Correct answer:

Increase digestive activity

Explanation:

The correct answer is an increase in digestive activity. The parasympathetic nervous system is involved in "rest and digest" functions. This includes a lowering of heart rate, lowering of blood flow to skeletal muscle, and an increase in digestive functions. The incorrect answers are all responses of the sympathetic nervous system.

Example Question #112 : Nervous System And Nervous Tissue

You are watching a scary movie with a friend. You look over and note that they are slightly sweating and their eyelids are elevated more than normal. Which part of the nervous system is responsible for this observed reaction?

Possible Answers:

Central nervous system

Sympathetic nervous system

Parasympathetic nervous system

Peripheral nervous system

Correct answer:

Sympathetic nervous system

Explanation:

Your friend is exhibiting the "fight or flight" response, which is mediated by the sympathetic nervous system. Release of norepinephrine by sympathetic postganglionic neurons causes pupil dilation, increased heart rate, and the release of epinephrine from the adrenal medulla.

In contrast, the parasympathetic nervous system is responsible for the "rest and digest" response, which stimulates the digestive tract and lowers heart rate.

Example Question #1 : Sympathetic And Parasympathetic Divisions

A study finds that subjects have difficulty reading small text when subjected to an electric shock. What phenomenon explains this result?

Possible Answers:

The parasympathetic nervous system has been activated, causing subjects' pupils to dilate

The parasympathetic nervous system has been activated, causing subjects' pupils to constrict

The sympathetic nervous system has been activated, causing subjects' pupils to dilate

The sympathetic nervous system has been activated, causing subjects' visual integration to deteriorate

The sympathetic nervous system has been activated, causing subjects' pupils to constrict

Correct answer:

The sympathetic nervous system has been activated, causing subjects' pupils to dilate

Explanation:

Administration of an electric shock would stimulate the release of epinephrine, which would result in activation of the sympathetic nervous system. The sympathetic nervous system is activated in response to short-term stressors and triggers the "fight or flight" response. One result of this response is dilation of the pupils, causing more light to enter and, in theory, enhancing the ability to visually perceive dangers and threats. Dilation of the pupils, however, also results in difficulty focusing on objects very close to the eye, making it difficult to read during sympathetic stimulation.

Example Question #5 : Sympathetic And Parasympathetic Divisions

Which of the following is a correct description of the sympathetic and parasympathetic nervous systems?

Possible Answers:

The sympathetic and parasympathetic systems derive from both the somatic and autonomic systems.

The sympathetic system is a division of the somatic system, while the parasympathetic system falls under the autonomic system.

The sympathetic system is a division of the autonomic system, while the parasympathetic system falls under the somatic system.

Both the sympathetic and parasympathetic systems are divisions of the autonomic system.

Both the sympathetic and parasympathetic systems are divisions of the somatic system.

Correct answer:

Both the sympathetic and parasympathetic systems are divisions of the autonomic system.

Explanation:

The sympathetic (fight or flight) and the parasympathetic (rest and digest) systems control bodily processes that are involuntary, or autonomic. Somatic refers to voluntary actions, which are not controlled by either the sympathetic or parasympathetic systems.

Example Question #112 : Nervous System And Nervous Tissue

Which of the following pairs describing the sympathetic and parasympathetic nervous systems accurately portray their roles?

Possible Answers:

Sympathetic—vagus nerve, rest and digest

Parasympathetic—epinephrine and norepinephrine, fight or flight

Sympathetic—epinephrine and norepinephrine, rest and digest

Parasympathetic—vagus nerve, fight or flight

Sympathetic—vagus nerve, fight or flight

Parasympathetic—epinephrine and norepinephrine, rest and digest

Sympathetic—epinephrine and norepinephrine, fight or flight

Parasympathetic—vagus nerve, rest and digest

Correct answer:

Sympathetic—epinephrine and norepinephrine, fight or flight

Parasympathetic—vagus nerve, rest and digest

Explanation:

The sympathetic nervous system (fight or flight) releases epinephrine and norepinephrine which activates adrenergic receptors throughout the body, causing bronchodilation, vasodilation to skeletal muscles, and vasodilation to coronary arteries. The parasympathetic nervous system (rest and digest) acts in the opposite manner, slowing the heart rate via the vagus nerve. 

Example Question #1 : Nervous System

The relaxation of bronchial smooth muscle is stimulated by what type of neuron?

Possible Answers:

Parasympathetic motor neurons

Sympathetic postganglionic neurons

Somatic motor neurons

Sympathetic preganglionic neurons

Parasympathetic postganglionic neurons

Correct answer:

Sympathetic postganglionic neurons

Explanation:

Relaxation of bronchial smooth muscle is an involuntary process, which is accomplished by the autonomic system rather than the somatic. It is also a part of the "fight or flight" response, which relates to the sympathetic system. Postganglionic neurons directly stimulate target tissues, while preganglionic neurons stimulate postganglionic neurons.

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