Biology: Nervous and Sensory System

How does absolute threshold function as a measure of sensory perception? A. As the minimum stimulus needed to activate sensory receptors at least 50% of the time, this measure of perception varies with age and by person. B. As the maximum stimulus which can be tolerated by sensory receptors before incurring damage, this measure of perception varies with age and by person. C. As the minimum stimulus needed to activate sensory receptors at least 50% of the time, this measure of perception has a well-established profile that differs between men and women. D. As the maximum stimulus which can be tolerated by sensory receptors before incurring damage, this measure of perception has a well-established profile that differs between men and women.

A. As the minimum stimulus needed to activate sensory receptors at least 50% of the time, this measure of perception varies with age and by person. Absolute threshold is the minimum amount of stimulation needed to achieve activation of sensory receptors 50% of the time; this is not a measure of maximum stimulation or capacity. This measure does vary by age and between people, but does not have established values based on the sex of an individual.

How does the auditory cortex in the temporal lobe receive stimulation from the ear? A. Hair cells contacting the tectorial membrane open ion channels to trigger release of neurotransmitter B. Sound waves stimulate baroreceptors to open ion channels in hair cells C. Sound waves flex the tectorial membrane to trigger release of neurotransmitter D. Hair cells directly trigger bipolar auditory neurons via mechanical stimulation

A. Hair cells contacting the tectorial membrane open ion channels to trigger release of neurotransmitter Perception of sound begins with sound waves vibrating the basilar membrane. This causes hair cells (mechanoreceptors) to come in contact with the tectorial membrane, and this contact opens ion channels in the hair cells. The cells depolarize and release neurotransmitter to stimulate the bipolar auditory neurons that run to the auditory cortex in the temporal lobe. Baroreceptors are not involved in this process.

Tetrodotoxin (TTX) is a potent neurotoxin that binds to and inhibits the action of voltage-gated sodium channels in neurons. Poisoning can be rapidly fatal, within 4-6 hours of ingestion. Which of the following is the most likely cause of death from TTX poisoning? A. Respiratory failure B. Increased blood pH due to hypoventilation C. Cardiac arrest D. Dehydration from excessive vomiting

A. Respiratory failure Blocking the action of voltage-gated sodium channels in neurons would prevent the occurrence of action potentials, leading to skeletal muscle paralysis. Because the diaphragm is made of skeletal muscle, it too would become paralyzed, leading to respiratory failure and death. According to the question text, cardiac muscle is not affected, and since heart contraction is not dependent on neural stimulation, TTX would not have a direct effect on the heart ("cardiac arrest" is wrong). Vomiting may occur, but death due to dehydration would take a few days, not a few hours ("dehydration from excessive vomiting" is wrong), and while hypoventilation probably occurs (remember diaphragm contraction depends on neural stimulation), hypoventilation would lead to decreased blood pH, not increased ("increased blood pH due to hypoventilation" is wrong).

The myelin sheath of many axons is produced by the: A. Schwann cells. B. nerve cell body. C. axon hillock. D. nodes of Ranvier.

A. Schwann cells. The myelin sheath is not produced by the neuron it is associated with. Instead, it is produced by a different type of cell, the Schwann cell, that wraps around the axon to create layers of insulating myelin. (Note that this is only the case in the PNS. A different cell, an oligodendrocyte, is responsible for myelination in the CNS.)

A researcher isolates a squid giant axon and places it into an electrolyte bath that mimics its normal conditions. She stimulates the axon and normal action potentials occur. She then introduces a drug into the electrolyte bath that blocks voltage-gated potassium channels, and again attempts to elicit action potentials. Which of the following is most likely to occur? A. The axon will depolarize normally when stimulated but the time to return to rest potential will be exceedingly long. B. The resting potential will become more positive since potassium is unable to exit the cell normally through leak channels. C. Since the voltage-gated channels are blocked, the action potential will not occur. D. Since the cell remains depolarized for a longer period of time, subsequent action potentials will be easier to elicit and the frequency of action potentials will increase.

A. The axon will depolarize normally when stimulated but the time to return to rest potential will be exceedingly long. If a drug is introduced that blocks voltage-gated potassium channels, the most likely occurrence is that the axon will depolarize normally when stimulated but the time to return to rest potential will be exceedingly long. Since the voltage-gated sodium channels are not affected, the cell should still be able to depolarize normally. However, the voltage-gated potassium channels are critical for repolarizing the cell; if these are blocked, the cell will remain in a depolarized state for much, much longer than normal. This would prevent the firing of subsequent action potentials (decrease the action potential frequency) since when depolarized, the cell is in an absolute refractory period, unable to fire additional action potentials. The resting potential of the cell should not be affected since it does not depend on voltage-gated channels (only on the Na+/K+ ATPase and the potassium leak channels).

The cell bodies of a somatic sensory nerve are located in the: A. dorsal root ganglion. B. ventral horn. C. brain. D. spinal cord.

A. dorsal root ganglion. The other answer choices are wrong since the cell bodies of somatic sensory neurons are not located in the CNS. They are located in dorsal root ganglia just behind and along the length of the spinal cord.

In the condition myopia the inverted image formed by the lens falls: A. in front of the retina. B. on the retina. C. behind the retina. D. on the optic nerve.

A. in front of the retina. In myopia, the image is formed in front of the retina, generally due to the shape of the eye being too long.

Damage to which one of the following would be most likely to hinder the detection of high-frequency, but not mid-frequency sound by the ear? A. Malleus, incus, or stapes B. Cochlea C. Auditory nerve D. Outer ear

B. Cochlea Damage to the auditory nerve or to the auditory ossicles (malleus, incus, and stapes) would hinder the detection of all frequencies since the nerve would be unable to send impulses to the brain and the ossicles would be unable to transmit sound waves to the inner ear, and neither of these functions is pitch-specific. Damage to the outer ear would not hinder pitch-specificity at all. The cochlea is a large, curled structure in the inner ear, along which the basilar membrane is stretched. The basilar membrane supports the hair cells of the ear (the sound receptors), and vibrates in sound waves. However, since one end of the basilar membrane is considerably thicker than the other, maximum vibration of a particular area depends of the frequency of the wave stimulating the membrane. Damage to the cochlea is the most likely injury to hinder the detection of particular frequencies.

Which of the following is the correct pathway of light entering the anterior surface of the eye leading to stimulation of the optic nerve? A. Cornea-->pupil-->sclera anterior chamber-->optic disk-->fovea B. Cornea-->anterior chamber-->lens-->retina C. Cornea-->vitreous chamber-->anterior chamber-->choroid D. Choroid-->cornea--> vitreous chamber-->anterior chamber-->retina

B. Cornea-->anterior chamber-->lens-->retina The cornea is the first structure that light must pass through ("choroid cornea vitreous chamber anterior chamber retina" is wrong). The anterior chamber is before the vitreous chamber ("cornea vitreous chamber anterior chamber choroid" is wrong). The sclera is the tough, outer, white covering of the eyeball; light cannot pass through this layer. This is why the cornea exists in the first place—to have a transparent outer layer for light to pass through. In any case, once light has passed through the cornea and the pupil, it can't reach the sclera until it passes through the lens, the vitreous humor, and the retina ("cornea pupil sclera anterior chamber optic disk fovea" is wrong).

Which of the following best characterizes the difference between the soma and axon hillock? A. Axon hillocks are denoted by demyelinated areas between myelin sheets along the axon B. Decreased voltage-gated sodium channel density in the soma C. Decreased myelination surrounding the soma D. Increased ribosomal activity in the axon hillock

B. Decreased voltage-gated sodium channel density in the soma The axon hillock, the area linking the soma to the axon, possesses an increased voltage-gated sodium channel density, allowing it to fire action potentials. In the soma, the decreased density allows for local depolarization which degrades exponentially over the distance of the soma. Neither the soma nor axon hillock are myelinated, and biosynthetic activity takes place in the soma, not the axon hillock. Nodes of Ranvier are the demyelinated areas between myelin sheets along the axon; the hillock is only at the area connecting the axon and soma.

Nerve cells that control thermoregulation are concentrated in which portion of the brain? A. Cerebrum B. Hypothalamus C. Medulla D. Cerebellum

B. Hypothalamus The hypothalamus is a key regulator in many different processes, including food intake, blood pressure, and neuroendocrine control, as well as temperature regulation.

Which of the following would be an appropriate example of difference threshold? A. Creating a list of pros and cons to aid in decision making processes B. Picking up two cantaloupes one after the other to determine which is heavier since each costs the same C. No longer perceiving the sound of a television after being in a room with it for an extended period of time D. Recognizing a family member based on his/her pattern of walking without being able to see his/her face

B. Picking up two cantaloupes one after the other to determine which is heavier since each costs the same Difference threshold is the minimum difference needed between two stimuli to be able to detect that there is in fact a difference at least 50% of the time. The "weighing" of the cantaloupes best describes this, as perceiving a difference in their size would require them to be proportionally distinct in their mass. Adaptation stops us from perceiving a constant sound if exposed to it long enough and top-down processing allows us to make a specific connection or recognition based on prior experience. Decision making strategies are not part of the difference threshold.

When the bladder is full, neurons in the sacral spinal cord notify the brainstem of the need to urinate. Inhibitory signals from the brain prevent urination until the time is judged appropriate; then the inhibition is removed and urination is allowed to proceed under the control of neurons in the sacral spinal cord. Cutting the thoracic spinal cord would most likely cause: A. return of normal bladder function. B. automatic bladder, in which the entire bladder empties when it becomes full, whether the time is appropriate or not. C. stress incontinence, in which urine leaks from the bladder upon physical stress, as in climbing stairs. D. inability to urinate.

B. automatic bladder, in which the entire bladder empties when it becomes full, whether the time is appropriate or not. The brain is required for the inhibition of urination, not the actual urination itself, which is controlled by the sacral neurons. If the brain is removed from the picture by severing the spinal cord between the sacral neurons and the brain (the thoracic region), then urination would simply become automatic. There is no reason to assume stress incontinence, and in any case, severing the spinal cord in the thoracic region would prevent lower body motor function, so climbing stairs would not be possible.

Shapes, patterns, and movement are perceived by the retina and a complex network of pattern-recognition circuits in the brain. Colors, however, are identified: A. by selective filtering of light in the retina. B. by the relative stimulation of cones in the retina, of which there are only three types with regard to color perception. C. by the activation of all cones, which is different for every different wavelength of light. D. by the relative stimulation of rods in the retina, of which there are only three types with regard to color perception.

B. by the relative stimulation of cones in the retina, of which there are only three types with regard to color perception. Cones transduce color for the brain, while rods respond to black and white images. There are only three types of cones, and they are specific for different wavelengths of light. There is no selective filtering of light in the retina.

Which of the following is NOT true of the sympathetic nervous system? A. Epinephrine prolongs and enhances its effects. B. It increase heart rate, dilates bronchial tubes, and increases blood flow to skeletal muscle. C. It increases pupil diameter to enhance near-object vision. D. ACh stimulates the adrenal medulla.

C. It increases pupil diameter to enhance near-object vision. It is NOT true of the sympathetic nervous system that it increases pupil diameter to enhance near-object vision. All of the other answer choices are true. One of the first effects of the sympathetic system is to release ACh onto the adrenal medulla; this triggers the release of epinephrine into the blood to enhance and prolong the overall effects of the system. Among those effects are increased rate and force of cardiac contraction, dilation of bronchial tubes to increase the volume of air that can enter the lungs, and increased blood flow to skeletal muscles to ensure adequate delivery of glucose and oxygen during stress situations. However, while it is true that the sympathetic system increases pupil dilation, this increases distance vision, not near-object vision. Distance vision is an advantage in a stress situation.

How do the photoreceptors of the eye respond to stimulation by light? A. Light opens Na+ channels, the cells become depolarized and the stimulation of the optic nerve stops. B. Light opens Na+ channels, the cells become hyperpolarized and the stimulation of the optic nerve stops. C. Light closes Na+ channels, the cells become hyperpolarized and the optic nerve is stimulated. D. Light closes Na+ channels, the cells become depolarized and the optic nerve is stimulated.

C. Light closes Na+ channels, the cells become hyperpolarized and the optic nerve is stimulated. Stimulation by light causes Na+ channels in the photoreceptors to close. This causes the cells to hyperpolarize and to stop releasing an inhibitory neurotransmitter onto the bipolar cells. Removal of the inhibition causes the bipolar cells to fire action potentials, ultimately transmitted to the optic nerve.

Which description below correctly identifies the role of the myelin sheath in action potential transmission? A. Protein fibers assemble along the axon of neurons, preventing leakage of current across the membrane. B. Glial cells cover the nodes of Ranvier to prevent backflow of current along the axon of neurons. C. Schwann cells insulate the axons of neurons, causing membrane depolarization to jump from node to node. D. Convolutions in the axons of neurons dissipate current through specialized leakage channels.

C. Schwann cells insulate the axons of neurons, causing membrane depolarization to jump from node to node. The myelin sheath insulates the neuronal axon except for small gaps (nodes of Ranvier) through which ions can traverse the membrane, causing the action potential to leap from node to node (saltatory conduction).

On what part of the retina does the image focus on when you stare directly at something? A. Lens B. Pupil C. Optic disk D. Fovea centralis

D. Fovea centralis The image focuses on the fovea centralis when you stare directly at something. The fovea centralis, also known as the focal point, is responsible for extreme visual acuity. When you stare directly at something, the image is focused on the fovea centralis part of the retina to maximize the visual acuity. The lens is not part of the retina, but rather it is in front of the retina. Its role is to focus incoming light beams onto the retina. The pupil is also not part of the retina. Its role is to control the amount of light that enters the eye. While the optic disk is part of the retina, it has no photoreceptors. For this reason, it is also called the blind spot.

Which of the following neurons could directly stimulate the relaxation of bronchial smooth muscle? A. Sympathetic preganglionic neurons B. Parasympathetic postganglionic neurons C. Somatic motor neurons D. Sympathetic postganglionic neurons

D. Sympathetic postganglionic neurons Sympathetic postganglionic neurons could directly stimulate the relaxation of bronchial smooth muscle. Relaxation of bronchial smooth muscle is an involuntary process that is triggered by activation of the sympathetic nervous system. Postganglionic neurons directly stimulate target tissues; preganglionic neurons stimulate postganglionic neurons.

Which of the following processes always result(s) in a negative membrane potential? I. Repolarization II. Depolarization III. Hyperpolarization

I and III only Item I is true: repolarization is defined as a return to resting membrane potential (RMP). Since the RMP is negative (-70 mV), repolarization always results in a negative membrane potential (choice "II and III only" can be eliminated). Item II is false: depolarization is defined as "the movement of membrane potential away from resting potential in the positive (less negative) direction". For example, a change in membrane potential from -70 mV to -60 mV is a depolarization. However, if the change to a less negative potential is enough to cause the voltage-gated sodium channels to open, then membrane potential can spike to positive values. Keep in mind that the question uses the word "always"; sometimes depolarization can lead to a negative potential, and sometimes to a positive potential (choice "I, II, and III" can be eliminated). Item III is true: hyperpolarization is defined as "the movement of membrane potential away from resting potential in the negative direction". Since resting membrane potential is already negative, hyperpolarization will always result in a negative potential (choice "I only" can be eliminated).

Hair cells used to detect motion are found in which of the following structures? I. The organ of Corti II. The skin III. The semicircular canals

I and III only Items I and III are true: Both the organ of Corti and the semicircular canals contain hair cells with small "hairs" that project from the apical surface of the cell into the surrounding fluid. Movement of the fluid around the hair cells detects sound in the organ of Corti and a change in body orientation in the semicircular canals. Item II is incorrect: Hair in the skin is different; it is not made up of "hair cells" but is made up of dead epithelial cells.

Both the sympathetic and parasympathetic divisions of the ANS can affect the cardiovascular system. Which of the following statements regarding sympathetic activation is/are true? I. Activation causes the heart to contract II. Activation relaxes smooth muscle in blood vessels serving skeletal muscle III. Activation relaxes smooth muscle in blood vessels serving skin and digestive organs

II only Activation of the sympathetic division of the ANS leads to the "fight or flight" stress response. Item I is false: The heart is autorhythmic and can generate its own contraction without input from the nervous system. However, activation of the sympathetic division can make the heart contract more frequently (i.e., increase the heart rate). Item II is true: It is helpful to have increased blood flow to skeletal muscles during times of stress to provide adequate oxygen and nutrients to the working muscles. Relaxing the smooth muscle in the blood vessels serving the skeletal muscle would cause dilation of the vessels and increased blood flow. Item III is false: during stress situations, blood is diverted from skin and digestive organs by constricting those vessels (i.e., contracting the smooth muscle).

Which of the following senses relies on chemoreceptors? I. Touch II. Taste III. Olfaction

II, III Item I is false: The sense of touch relies primarily on mechanoreceptors, and somewhat on nociceptors (pain) and thermoreceptors (temperature), but not chemoreceptors. Items II and III are true: Both taste and smell rely on chemoreceptors.