MCAT Biology : Glia

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #1 : Divisions Of The Nervous System

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?

Possible Answers:

Ependymal cells

Microglia

Schwann cells

All glial cells

Astrocytes

Correct answer:

Schwann cells

Explanation:

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 #1 : Glia

The cells that form myelin sheaths around axons outside of the central nervous system are __________.

Possible Answers:

Schwann cells

microglia

oligodendrocytes

ganglia

dendrites

Correct answer:

Schwann cells

Explanation:

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 #132 : Biology

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.

 

Untitled

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?

Possible Answers:

Schwann cells

Ependymal cells

Astrocytes

Monocytes

Oligodendrocytes

Correct answer:

Schwann cells

Explanation:

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 #4 : Divisions Of The Nervous System

Where might one find Schwann cells?

Possible Answers:

Broca's area

Trigeminal nerve

Optic nerve

Grey matter

White matter

Correct answer:

Trigeminal nerve

Explanation:

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 #63 : Nervous System And Nervous Tissue

Schwann cells are responsible for which of the following?

Possible Answers:

Myelination of the peripheral nervous system dendrites

Circulation of cerebrospinal fluid

Myelination of the peripheral nervous system axons

Myelination of the central nervous system axons

Correct answer:

Myelination of the peripheral nervous system axons

Explanation:

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 #2 : Glia

Which of the following is a location in the human body where oligodendrocytes will not be found?

Possible Answers:

Spinal cord

Wernicke's area

Frontal lobe

Pons

Meninges

Correct answer:

Meninges

Explanation:

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 #3 : Glia

Which of the following describes the difference between oligodendrocytes and Schwann cells?

Possible Answers:

Oligodendrocytes myelinate the peripheral nervous system, while Schwann cells myelinate the central nervous system

Both cell types insulate the axons of cells, but use different insulating materials

Oligodendrocytes and Schwann cell myelinate different structures of the neuron

Oligodendrocytes myelinate the central nervous system, while Schwann cells myelinate the peripheral nervous system

Schwann cells can mylinate multiple axons, while oligodendrocytes can only myelinate one axon per cell

Correct answer:

Oligodendrocytes myelinate the central nervous system, while Schwann cells myelinate the peripheral nervous system

Explanation:

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.

Example Question #8 : Divisions Of The Nervous System

Which of the following structures creates a myelin sheath for axons in the central nervous system?

Possible Answers:

Axon hillock

Nodes of Ranvier

Oligodendrocytes

Schwann cells

Correct answer:

Oligodendrocytes

Explanation:

Oligodendrocytes and Schwann cells both create myelin sheaths for axons, however, oligodendrocytes function in the central nervous system and Schwann cells function in the peripheral nervous system.

Example Question #4 : Glia

Diseases which destroy the myelin sheath of neurons cause __________.

Possible Answers:

cancer

no change

decreased pain perception

a decrease in the speed of nerve conduction

an increase in the speed of nerve conduction

Correct answer:

a decrease in the speed of nerve conduction

Explanation:

Myelin sheathes function in insulating the neuron, and allows for much faster propogation of the action potential due to saltatory conduction. Loss of the myelin sheath would slow conduction of signals down the neural axon.

Pain perception is conducted to free nerve endings known as nociceptors, which are not myelinated.

Example Question #67 : Nervous System And Nervous Tissue

Excessive stimulation of the ulnar nerve results in the sensation known as the "funny bone," and can cause discomfort in the elbow and forearm. What cells are responsible for the myelination of the ulnar nerve?

Possible Answers:

Schwann cells

Astrocytes

Dendritic cells

Oligodendrocytes

Correct answer:

Schwann cells

Explanation:

There are two types of cells responsible for the myelination of axons throughout the nervous system. Oligodendrocytes myelinate the axons of neurons in the central nervous system. Schwann cells myelinate neurons in the peripheral nervous system. This question is referring to a nerve in the elbow, which would be in the peripheral nervous system.

Astrocytes are a type of glial cell primarily found in the blood-brain barrier. Dendritic cells play a role in the adaptive immune response, and are not considered part of the nervous system.

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