MCAT Biology : Systems Biology and Tissue Types
Study concepts, example questions & explanations for MCAT Biology
All MCAT Biology Resources
Example Questions
Example Question #51 : Neurons And Action Potential
What is the normal resting potential of a neuron?
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 #53 : Neurons And Action Potential
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?
The activation of the parietal cells by somatostatin
The activation of the parietal cells by the migrating complex
The activation of the parietal cells by the sympathetic nervous system
The activation of the parietal cells by the vagus nerve from seeing the food
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 vagus nerve from seeing the food
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 #56 : 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
III only
None of these
II only
I only
I and II
III only
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.
Example Question #1 : Glia
Prions are the suspected cause of a wide variety of neurodegenerative diseases in mammals. According to prevailing theory, prions are infectious particles made only of protein and found in high concentrations in the brains of infected animals. All mammals produce normal prion protein, PrPC, a transmembrane protein whose function remains unclear.
Infectious prions, PrPRes, induce conformational changes in the existing PrPC proteins according to the following reaction:
PrPC + PrPRes → PrPRes + PrPRes
The PrPRes is then suspected to accumulate in the nervous tissue of infected patients and cause disease. This model of transmission generates replicated proteins, but does so bypassing the standard model of the central dogma of molecular biology. Transcription and translation apparently do not play a role in this replication process.
This theory is a major departure from previously established biological dogma. A scientist decides to test the protein-only theory of prion propagation. He establishes his experiment as follows:
Homogenized brain matter of infected rabbits is injected into the brains of healthy rabbits, as per the following table:
Rabbit 1 and 2: injected with normal saline on days 1 and 2
The above trials serve as controls.
Rabbit 3 and 4: injected with homogenized brain matter on days 1 and 2
The above trials use unmodified brain matter.
Rabbit 5 and 6: injected with irradiated homogenized brain matter on days 1 and 2
The above trials use brain matter that has been irradiated to destroy nucleic acids in the homogenate.
Rabbit 7 and 8: injected with protein-free centrifuged homogenized brain matter on days 1 and 2
The above trials use brain matter that has been centrifuged to generate a protein-free homogenate and a protein-rich homogenate based on molecular weight.
Rabbit 9 and 10: injected with boiled homogenized brain matter on days 1 and 2
The above trials use brain matter that have been boiled to destroy any bacterial contaminants in the homogenate.
A scientist shows that PrPC in normal nervous cells helps speed nervous transmission. What other structures help speed nervous transmission?
Ependymal cells
Microglia
Astrocytes
All glial cells
Schwann cells
Schwann cells
Schwann cells act as insulators on nervous tissue to help propagate nervous transmission via saltatory conduction. This speeds transmission and makes axonal signal propagation much more rapid.
Example Question #121 : Systems Biology And Tissue Types
The cells that form myelin sheaths around axons outside of the central nervous system are __________.
Schwann cells
oligodendrocytes
ganglia
microglia
dendrites
Schwann cells
It is important to read this question carefully, as it asks for the cells that form myelin sheaths around axons outside of the central nervous system. In essence, it is asking about the peripheral nervous system.
Schwann cells and oligodendrocytes both form myelin sheaths (a white, fatty substance) around axons, which act as electrical insulation and increase the speed of action potential conduction. Schwann cells perform this function for neurons in the peripheral nervous system (outside of the central nervous system), while oligodendrocytes myelinate neurons in the central nervous system.
Example Question #2 : Glia
In humans, nerve impulses are transmitted with the coordinated action of sodium and potassium ion channels. These channels open in a specific sequence, to allow for membrane potential changes to take place in a directional manner along the length of an axon.
Figure 1 depicts a single phospholipid layer of a cell membrane, and three transmembrane channels important to action potential propagation.
Action potential propagation down a membrane, as depicted in the figure, is typically very slow. Which of the following cell types is responsible for speeding nerve propagation by insulating peripheral axons?
Monocytes
Oligodendrocytes
Schwann cells
Ependymal cells
Astrocytes
Schwann cells
Schwann cells insulate peripheral axons with myelin. Oligodendrocytes serve a similar purpose, but do so in the central nervous system, and not the peripheral system.
Example Question #3 : Glia
Where might one find Schwann cells?
Trigeminal nerve
Optic nerve
Broca's area
White matter
Grey matter
Trigeminal nerve
Schwann cells are used to myelinate single axons in the peripheral nervous system. Oligodendrocytes are the counterpart of Schwann cells that exist in the central nervous system, but are capable of myelinating multiple axons at once.
To answer this question, we must select an answer that is part of the peripheral nervous system. Grey matter and white matter only exist in the central nervous system (brain and spinal cord) and can be eliminated. Broca's area is located in the frontal lobe of the cerebrum and will contain oligodendrocytes instead of Schwann cells. The optic nerve and trigeminal nerve are two of the cranial nerves, C2 and CV respectively. The optic nerve is the only cranial nerve to be myelinated by oligodendrocytes. The trigeminal nerve will be myelinated by Schwann cells.
Example Question #61 : Nervous System And Nervous Tissue
Schwann cells are responsible for which of the following?
Myelination of the central nervous system axons
Circulation of cerebrospinal fluid
Myelination of the peripheral nervous system dendrites
Myelination of the peripheral nervous system axons
Myelination of the peripheral nervous system axons
Schwann cells are responsible for producing myelin in the peripheral nervous system. These cells surround the axons with myelin sheaths, which increases the rate of signal transmission on axons.
Oligodendrocytes are responsible for myelinating axons in the central nervous system. Dendrites are not myelinated.
Example Question #1 : Divisions Of The Nervous System
Which of the following is a location in the human body where oligodendrocytes will not be found?
Wernicke's area
Spinal cord
Frontal lobe
Meninges
Pons
Meninges
Oligodendrocytes are cells that insulate axons in the central nervous system. They are capable of producing the myelin sheathes for several surrounding cells and are the counterparts of the Schwann cells, which are located in the peripheral nervous system. The central nervous system includes the brain and spinal cord. Oligodendrocytes are responsible for producing the white matter of the central nervous system. The frontal lobe is a region of the cerebrum and will contain myelin. The spinal cord contains distinct white matter and grey matter regions. Wernicke's area is located in the temporal lobe of the cerebrum, and will contain oligodendrocytes. The pons is located in the hindbrain, or brainstem, and will and will also contain oligodendrocytes.
The meninges are the layers of connective tissue that surround the central nervous system. They are made primarily of collagen and do not contain nerve fibers. Oligodendrocytes will not be found in the meninges.
Example Question #1 : Divisions Of The Nervous System
Which of the following describes the difference between oligodendrocytes and Schwann cells?
Both cell types insulate the axons of cells, but use different insulating materials
Schwann cells can mylinate multiple axons, while oligodendrocytes can only myelinate one axon per cell
Oligodendrocytes myelinate the peripheral nervous system, while Schwann cells myelinate the central nervous system
Oligodendrocytes and Schwann cell myelinate different structures of the neuron
Oligodendrocytes myelinate the central nervous system, while Schwann cells myelinate the peripheral nervous system
Oligodendrocytes myelinate the central nervous system, while Schwann cells myelinate the peripheral nervous system
Both oligodendrocytes and Schwann cells are responsible for myelinating axons in order to increase the transmission rate of signals between neurons. The primary difference is their location. Oligodendrocytes myelinate the central nervous system, while Schwann cells myelinate the peripheral nervous system. Oligodendrocytes are also capable of myelinating multiple axons, while Schwann cells can only myelinate one axon per cell.
Certified Tutor
Certified Tutor
All MCAT Biology Resources
