MCAT Biology : Neurons and Action Potential

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #7 : Neurotransmitters

Which of the following are major inhibitory neurotransmitters, causing inhibitory postsynaptic potentials (IPSPs)?

Possible Answers:

GABA and glycine

Synaptobrevin and glutamate

Glycine and acetylcholine

Glycine and epinephrine

Glycine and norepinephrine

Correct answer:

GABA and glycine

Explanation:

GABA and glycine are the two major inhibitory neurotransmitters.

Norepinephrine, epinephrine, glutamate, and acetylcholine cause excitatory responses. Synaptobrevin is a snare protein involved in vesicle docking and fusion; it has no effect on whether or not a neurotransmitter is or is not inhibitory.

Example Question #8 : Neurotransmitters

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 neurotransmitter released by the axons in the Edinger-Westphal neurons is most likely __________.

Possible Answers:

epinephrine

dopamine

norepinephrine

glutamine

acetylcholine

Correct answer:

acetylcholine

Explanation:

Acetylcholine is correct. We are told from the passage that the neurons which make up the Edinger-Westphal nucleus are parasympathetic neurons. Therefore, this question is really testing one's knowledge of the neurotransmitter used by parasympathetic neurons. We cannot be expected to know from the question alone which neurotransmitter these neurons use. However, we are supposed to be aware that neurons that are parasympathetic use the neurotransmitter acetylcholine. 

Example Question #9 : Neurotransmitters

The central nervous system consists of the brain and the spinal cord. In general, tracts allow for the brain to communicate up and down with the spinal cord. The commissures allow for the two hemispheres of the brain to communicate with each other. One of the most important commissures is the corpus callosum. The association fibers allow for the anterior regions of the brain to communicate with the posterior regions. One of the evolved routes from the spinal cord to the brain is via the dorsal column pathway. This route allows for fine touch, vibration, proprioception and 2 points discrimination. This pathway is much faster than the pain route. From the lower limbs, the signal ascends to the brain via a region called the gracile fasciculus. From the upper limbs, the signal ascends via the cuneate fasciculus region in the spinal cord.

 

One of the most common neurotransmitters is acetylcholine.  Which of the following methods will decrease the amount of the neurotransmitters in the synaptic cleft? 

I. Increase the action potential frequency

II. Decrease the calcium concentration surrounding the neuron

III. Inhibit acetylcholine esterase 

Possible Answers:

III only

I only

I and III only

II only

I and II only

Correct answer:

II only

Explanation:

The presynaptic neuron require an action potential in order to open the calcium voltage channel. The opening of this calcium channel will allow the influx of calcium and trigger the release of vesicles with the neurotransmitter inside. The exocytosis of acetylcholine from the presynaptic cleft will then bind to the receptor on the postsynaptic cleft. Inhibiting acetylcholinesterase will prevent the breakdown of the neurotransmitter and allow for it to bind to the receptor longer. Decreasing the surrounding concentration of calcium will inhibit the release of the acetylcholine filled vesicles into the synaptic cleft.

Example Question #10 : Neurotransmitters

The cellular membrane is a very important structure. The lipid bilayer is both hydrophilic and hydrophobic. The hydrophilic layer faces the extracellular fluid and the cytosol of the cell. The hydrophobic portion of the lipid bilayer stays in between the hydrophobic regions like a sandwich. This bilayer separation allows for communication, protection, and homeostasis. 

One of the most utilized signaling transduction pathways is the G protein-coupled receptor pathway. The hydrophobic and hydrophilic properties of the cellular membrane allows for the peptide and other hydrophilic hormones to bind to the receptor on the cellular surface but to not enter the cell. This regulation allows for activation despite the hormone’s short half-life. On the other hand, hydrophobic hormones must have longer half-lives to allow for these ligands to cross the lipid bilayer, travel through the cell’s cytosol and eventually reach the nucleus. 

Cholesterol allows the lipid bilayer to maintain its fluidity despite the fluctuation in the body’s temperature due to events such as increasing metabolism. Cholesterol binds to the hydrophobic tails of the lipid bilayer. When the temperature is low, the cholesterol molecules prevent the hydrophobic tails from compacting and solidifying. When the temperature is high, the hydrophobic tails will be excited and will move excessively. This excess movement will bring instability to the bilayer. Cholesterol will prevent excessive movement.

Which of the following molecules can be found inside of a cell? 

I. Cyclic adenosine monophosphate (cAMP) 

II. Protein kinase A

III. Acetylcholine

Possible Answers:

I and II

I only

II only

I, II, and III

III only

Correct answer:

I and II

Explanation:

Cyclic adenosine monophosphate and protein kinase A are both second messengers in the G protein-coupled receptor pathway. Since they are second messengers, they amplify and transmit the signal inside of the cell. Acetylcholine, however is a hydrophillic neurotransmitter and binds to the receptor located on the surface of the cell, thereby inducing intracellular signaling.  

Example Question #51 : Nervous System And Nervous Tissue

The cellular membrane is a very important structure. The lipid bilayer is both hydrophilic and hydrophobic. The hydrophilic layer faces the extracellular fluid and the cytosol of the cell. The hydrophobic portion of the lipid bilayer stays in between the hydrophobic regions like a sandwich. This bilayer separation allows for communication, protection, and homeostasis. 

One of the most utilized signaling transduction pathways is the G protein-coupled receptor pathway. The hydrophobic and hydrophilic properties of the cellular membrane allows for the peptide and other hydrophilic hormones to bind to the receptor on the cellular surface but to not enter the cell. This regulation allows for activation despite the hormone’s short half-life. On the other hand, hydrophobic hormones must have longer half-lives to allow for these ligands to cross the lipid bilayer, travel through the cell’s cytosol and eventually reach the nucleus. 

Cholesterol allows the lipid bilayer to maintain its fluidity despite the fluctuation in the body’s temperature due to events such as increasing metabolism. Cholesterol binds to the hydrophobic tails of the lipid bilayer. When the temperature is low, the cholesterol molecules prevent the hydrophobic tails from compacting and solidifying. When the temperature is high, the hydrophobic tails will be excited and will move excessively. This excess movement will bring instability to the bilayer. Cholesterol will prevent excessive movement.

Which of the following molecules can be found inside of a cell? 

I. Inositol trisphosphate

II. Protein kinase A

III. Epinephrine 

Possible Answers:

II only

I only

III only

II and III 

I and II 

Correct answer:

I and II 

Explanation:

Inositol trisphosphate (IP3) and protein kinase A are both second messengers in the G protein-coupled receptor pathway. Since they are second messengers, they amplify and transmit the signal inside of the cell. Epinephrine, however is a hydrophilic (impermeable) neurotransmitter and hormone that binds to the receptor located on the surface of the cell. 

Example Question #151 : Mcat Biological Sciences

What side effect may occur after exposure to a chemical that inhibits the release of acetylcholinesterase?

Possible Answers:

Repeated stimulation of postsynaptic neurons

Lack of receptors on the postsynaptic neuron

An inability to stimulate neurons

An inability to release acetylcholine

Correct answer:

Repeated stimulation of postsynaptic neurons

Explanation:

Acetylcholinesterase is the enzyme responsible for breaking down acetylcholine, an excitatory neurotransmitter released into the synaptic cleft. If acetylcholine cannot be broken down by this enzyme, the neurotransmitter will continue to attach to the receptors on the postsynaptic cell. This can result in continuous, uncontrolled stimulation of neurons.

Example Question #53 : Nervous System And Nervous Tissue

What is the normal resting potential of a neuron?

Possible Answers:

Correct answer:

Explanation:

Resting potential is determined by evaluating the relative ion concentrations inside a cell in relation to the ion concentrations outside of the cell. For a resting neuron, the inside of the cell contains large amounts of potassium and the external environment contains large amounts of sodium. However, the resting potential is substantially negative due to the presence of negatively charged DNA and other molecules inside the cell. The normal resting potential of a neuron is .

Example Question #54 : Nervous System And Nervous Tissue

The parietal cells of the stomach are vital for both food digestion and as a defense mechanism against pathogens. When the parietal cells are not functioning properly, diseases such sepsis due to Clostridium difficile and malnutrition may occur. To keep the digestive system healthy, proper nutrition as well as a balanced diet is vital.

The parietal cells of the stomach secrete hydrochloric acid via the hormone gastrin. Gastrin is released when the stomach distends, via the presence of proteins and/or indirectly by the vagus nerve from the parasympathetic nervous system. Hydrochloric acid breaks down certain ingested food as well as activates certain zymogens for further digestion of macromolecules. The high acidity of the stomach due to the release of hydrochloric acid by parietal cells also destroys most pathogens. When the parietal cell is not functioning properly, opportunistic pathogens may create health problems.

Parietal cells also secrete intrinsic factor, a glycoprotein which binds to vitamin B12 to prevent destruction of the vitamin by the hydrochloric acid. Down the gastrointestinal tract, the vitamin is absorbed by the ileum of the small intestine. Vitamin B12 is essential for red blood cell production. A diet low in vitamin B12 may lead to anemia.

Even before the presence of food in the stomach, the parietal cells already began secreting hydrochloric acid during the cephalic phase of digestion. Which of the following best explains how this occur?

Possible Answers:

The distention of the stomach due to the presence of food in the stomach promotes the parietal cells to secrete hydrochloric acid

The activation of the parietal cells by the migrating complex 

The activation of the parietal cells by somatostatin

The activation of the parietal cells by the vagus nerve from seeing the food 

The activation of the parietal cells by the sympathetic nervous system

Correct answer:

The activation of the parietal cells by the vagus nerve from seeing the food 

Explanation:

During the cephalic phase of digestion, seeing the food will activate the cerebral cortex, which will then integrate the visual stimuli and trigger stimulation of the vagus nerve. The vagus nerve will then indirectly stimulate the G cells of the stomach to release gastrin. The release of gastrin will then promote the parietal cells to release hydrochloric acid.  

Example Question #55 : Nervous System And Nervous Tissue

The central nervous system consists of the brain and the spinal cord. In general, tracts allow for the brain to communicate up and down with the spinal cord. The commissures allow for the two hemispheres of the brain to communicate with each other. One of the most important commissures is the corpus callosum. The association fibers allow for the anterior regions of the brain to communicate with the posterior regions. One of the evolved routes from the spinal cord to the brain is via the dorsal column pathway. This route allows for fine touch, vibration, proprioception and 2 points discrimination. This pathway is much faster than the pain route. From the lower limbs, the signal ascends to the brain via a region called the gracile fasciculus. From the upper limbs, the signal ascends via the cuneate fasciculus region in the spinal cord.

If the spinal cord was severed, which of the following functions will still be intact? 

I. Fine touch

II. Pain

III. Knee-jerk reflex

Possible Answers:

III only

I only

II only

None of these

I and II

Correct answer:

III only

Explanation:

According to the passage, both fine touch and pain require the signal to travel up to the brain in order to process the information. A severed spinal cord will interfere with both fine touch and pain. Reflex signals only travel at the level of the stimulus.  

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