MCAT Biology : Other Neural Physiology
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Example Question #51 : Neurons And Action Potential
What side effect may occur after exposure to a chemical that inhibits the release of acetylcholinesterase?
An inability to stimulate neurons
An inability to release acetylcholine
Lack of receptors on the postsynaptic neuron
Repeated stimulation of postsynaptic neurons
Repeated stimulation of postsynaptic neurons
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 #51 : Nervous System And Nervous Tissue
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.
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