NeuroBiology 31-65 Flashcards
- Which of the following statements about olfactory recep-tors is correct?
A. An olfactory receptor displays rapid adaptation initially
B. The life span of olfactory receptor cells is approxi-
mately 9 months
C. A single olfactory receptor cell typically responds to
only a single odorant
D. The receptor potential occurs when Na* channels are
closed in a manner similar to phototransduction
E. They are cGMP-regulated
A. An olfactory receptor displays rapid adaptation initially
Olfactory receptors (ORs) display rapid adaptation initially and little afterwards. Within the olfactory system, an olfactory stimulus results in the opening of sodium channels, which leads to depolarization and action potentials. These action potentials can increase in frequency to about 20/s. Adenylate cyclase activity catalyzes the formation of cAMP, resulting in opening of many additional channels, which can also increase the rate of discharge in olfactory neurons. Each olfactory neuron is capable of responding to many different odorants, as determined by electrophysiologic studies. The life span of ORs varies from 30 to 120 days in mammalian species. Replacement cells are delivered by mitosis of basal cells. The relatively rapid turnover of ORs makes them par-tially susceptible to damage after radiation therapy and/or chemotherapeutic agents, which target rapidly dividing cells (Kandel, pp. 626-636; Pritchard, pp. 266-267).
- Which of the following sensory systems sends signals directly to both the thalamus and cerebral cortex?
A. Two-point discrimination
B. Taste
C. Olfaction
D. Pain
E. Balance
C. Olfaction
Taste and sensation from the head are carried to
the ventroposterior medial (VPM) nucleus of the thalamus. Sensation and proprioception from the body reach the ventroposterior lateral (VPL) nucleus of the thalamus. The visual system utilizes the lateral geniculate nucleus (LGN) and the auditory system the medial geniculate nucleus (MGN) prior to being relayed to the cortex. Some olfactory information bypasses the thalamus to reach the orbitofrontal cortex, but it should be noted that some projections subserving smell can reach the orbitofrontal cortex via the mediodorsal (MD) thalamic nucleus. The olfactory system, therefore, relies on parallel processing to transmit olfactory inputs to the cortex (Kandel, p. 633).
- Cells most sensitive to radiation therapy
Directions: For each question select one or more than one lettered heading (in parentheses) from Figure 1.33-1.39Q with which it is most closely associated. Each lettered head-ing may be used once, more than once, or not at all.
B,C
Cells are most sen-sitive to radiation during the G2 and M phases of the cell cycle and most resistant in the late S phase. Gl cells have intermediate sensitivity. The precise mechanism(s) accounting for these variations remains unclear, but studies have shown that differences in a cell’s ability to repair DNA damage in different phases after radiation may play an important part. In the Gl phase of the cycle, the nucleus has a diploid amount of DNA (2G), which increases to 4C by the end of the S phase. Only cells in the S phase (DNA synthetic phase) are able to incorporate thymidine analogues (bro-modeoxyuridine) into their nuclear DNA. Nutrient depletion and crowding can result in the movement of cells into the quiescent or nonproliferating phase (GO) of the cell cycle; such cells can eventually re-enter the cell cycle at a later point in time. Mitosis is the most easily identifiable stage of the cell cycle by light microscopy. The genes encoding pl6 (CDKN2A) and pl5 (CDKN2B) map onto chromosome 9p21, a site that is associated with homozygous deletions in high-grade astrocytomas in about two-thirds of gliomas. These proteins act as inhibitors of cyclin-dependent kinases and other pathways during the Gl phase of the cell cycle and help control proliferation at the Gl/S phase of the cell cycle. The TP53 protein assists in several cellular processes, including cell cycle regulation, response of cells to DNA damage (Psr dependent growth arrest following DNA damage occurs in Gl phase of the cell cycle), cell death, cell differentiation, and neovascularization (WHO, pp. 11-14 ; Berger, pp. 204-209) .
- Nutrient depletion or physical crowding are conditions that encourage cells to move into this phase of the cell cycle
For each question select one or more than one lettered heading (in parentheses) from Figure 1.33-1.39Q with which it is most closely associated. Each lettered head-ing may be used once, more than once, or not at all.
E
Cells are most sen-sitive to radiation during the G2 and M phases of the cell cycle and most resistant in the late S phase. Gl cells have intermediate sensitivity. The precise mechanism(s) accounting for these variations remains unclear, but studies have shown that differences in a cell’s ability to repair DNA damage in different phases after radiation may play an important part. In the Gl phase of the cycle, the nucleus has a diploid amount of DNA (2G), which increases to 4C by the end of the S phase. Only cells in the S phase (DNA synthetic phase) are able to incorporate thymidine analogues (bro-modeoxyuridine) into their nuclear DNA. Nutrient depletion and crowding can result in the movement of cells into the quiescent or nonproliferating phase (GO) of the cell cycle; such cells can eventually re-enter the cell cycle at a later point in time. Mitosis is the most easily identifiable stage of the cell cycle by light microscopy. The genes encoding pl6 (CDKN2A) and pl5 (CDKN2B) map onto chromosome 9p21, a site that is associated with homozygous deletions in high-grade astrocytomas in about two-thirds of gliomas. These proteins act as inhibitors of cyclin-dependent kinases and other pathways during the Gl phase of the cell cycle and help control proliferation at the Gl/S phase of the cell cycle. The TP53 protein assists in several cellular processes, including cell cycle regulation, response of cells to DNA damage (Psr dependent growth arrest following DNA damage occurs in Gl phase of the cell cycle), cell death, cell differentiation, and neovascularization (WHO, pp. 11-14 ; Berger, pp. 204-209) .
- Cells can incorporate thymidine analogues into their
nuclear DNA
For each question select one or more than one lettered heading (in parentheses) from Figure 1.33-1.39Q with which it is most closely associated. Each lettered head-ing may be used once, more than once, or not at all.
A
Cells are most sen-sitive to radiation during the G2 and M phases of the cell cycle and most resistant in the late S phase. Gl cells have intermediate sensitivity. The precise mechanism(s) accounting for these variations remains unclear, but studies have shown that differences in a cell’s ability to repair DNA damage in different phases after radiation may play an important part. In the Gl phase of the cycle, the nucleus has a diploid amount of DNA (2G), which increases to 4C by the end of the S phase. Only cells in the S phase (DNA synthetic phase) are able to incorporate thymidine analogues (bro-modeoxyuridine) into their nuclear DNA. Nutrient depletion and crowding can result in the movement of cells into the quiescent or nonproliferating phase (GO) of the cell cycle; such cells can eventually re-enter the cell cycle at a later point in time. Mitosis is the most easily identifiable stage of the cell cycle by light microscopy. The genes encoding pl6 (CDKN2A) and pl5 (CDKN2B) map onto chromosome 9p21, a site that is associated with homozygous deletions in high-grade astrocytomas in about two-thirds of gliomas. These proteins act as inhibitors of cyclin-dependent kinases and other pathways during the Gl phase of the cell cycle and help control proliferation at the Gl/S phase of the cell cycle. The TP53 protein assists in several cellular processes, including cell cycle regulation, response of cells to DNA damage (Psr dependent growth arrest following DNA damage occurs in Gl phase of the cell cycle), cell death, cell differentiation, and neovascularization (WHO, pp. 11-14 ; Berger, pp. 204-209) .
- Cells most resistant to radiation therapy
For each question select one or more than one lettered heading (in parentheses) from Figure 1.33-1.39Qwith which it is most closely associated. Each lettered head-ing may be used once, more than once, or not at all.
A
Cells are most sen-sitive to radiation during the G2 and M phases of the cell cycle and most resistant in the late S phase. Gl cells have intermediate sensitivity. The precise mechanism(s) accounting for these variations remains unclear, but studies have shown that differences in a cell’s ability to repair DNA damage in different phases after radiation may play an important part. In the Gl phase of the cycle, the nucleus has a diploid amount of DNA (2G), which increases to 4C by the end of the S phase. Only cells in the S phase (DNA synthetic phase) are able to incorporate thymidine analogues (bro-modeoxyuridine) into their nuclear DNA. Nutrient depletion and crowding can result in the movement of cells into the quiescent or nonproliferating phase (GO) of the cell cycle; such cells can eventually re-enter the cell cycle at a later point in time. Mitosis is the most easily identifiable stage of the cell cycle by light microscopy. The genes encoding pl6 (CDKN2A) and pl5 (CDKN2B) map onto chromosome 9p21, a site that is associated with homozygous deletions in high-grade astrocytomas in about two-thirds of gliomas. These proteins act as inhibitors of cyclin-dependent kinases and other pathways during the Gl phase of the cell cycle and help control proliferation at the Gl/S phase of the cell cycle. The TP53 protein assists in several cellular processes, including cell cycle regulation, response of cells to DNA damage (Psr dependent growth arrest following DNA damage occurs in Gl phase of the cell cycle), cell death, cell differentiation, and neovascularization (WHO, pp. 11-14 ; Berger, pp. 204-209) .
- P15 and pl6 cause growth arrest in this cell-cycle phase
For each question select one or more than one lettered heading (in parentheses) from Figure 1.33-1.39Q with which it is most closely associated. Each lettered head-ing may be used once, more than once, or not at all.
D
Cells are most sen-sitive to radiation during the G2 and M phases of the cell cycle and most resistant in the late S phase. Gl cells have intermediate sensitivity. The precise mechanism(s) accounting for these variations remains unclear, but studies have shown that differences in a cell’s ability to repair DNA damage in different phases after radiation may play an important part. In the Gl phase of the cycle, the nucleus has a diploid amount of DNA (2G), which increases to 4C by the end of the S phase. Only cells in the S phase (DNA synthetic phase) are able to incorporate thymidine analogues (bro-modeoxyuridine) into their nuclear DNA. Nutrient depletion and crowding can result in the movement of cells into the quiescent or nonproliferating phase (GO) of the cell cycle; such cells can eventually re-enter the cell cycle at a later point in time. Mitosis is the most easily identifiable stage of the cell cycle by light microscopy. The genes encoding pl6 (CDKN2A) and pl5 (CDKN2B) map onto chromosome 9p21, a site that is associated with homozygous deletions in high-grade astrocytomas in about two-thirds of gliomas. These proteins act as inhibitors of cyclin-dependent kinases and other pathways during the Gl phase of the cell cycle and help control proliferation at the Gl/S phase of the cell cycle. The TP53 protein assists in several cellular processes, including cell cycle regulation, response of cells to DNA damage (Psr dependent growth arrest following DNA damage occurs in Gl phase of the cell cycle), cell death, cell differentiation, and neovascularization (WHO, pp. 11-14 ; Berger, pp. 204-209) .
- TP53-dependent growth arrest following DNA damage occurs in this phase
For each question select one or more than one lettered heading (in parentheses) from Figure 1.33-1.39Q with which it is most closely associated. Each lettered head-ing may be used once, more than once, or not at all
D
Cells are most sen-sitive to radiation during the G2 and M phases of the cell cycle and most resistant in the late S phase. Gl cells have intermediate sensitivity. The precise mechanism(s) accounting for these variations remains unclear, but studies have shown that differences in a cell’s ability to repair DNA damage in different phases after radiation may play an important part. In the Gl phase of the cycle, the nucleus has a diploid amount of DNA (2G), which increases to 4C by the end of the S phase. Only cells in the S phase (DNA synthetic phase) are able to incorporate thymidine analogues (bro-modeoxyuridine) into their nuclear DNA. Nutrient depletion and crowding can result in the movement of cells into the quiescent or nonproliferating phase (GO) of the cell cycle; such cells can eventually re-enter the cell cycle at a later point in time. Mitosis is the most easily identifiable stage of the cell cycle by light microscopy. The genes encoding pl6 (CDKN2A) and pl5 (CDKN2B) map onto chromosome 9p21, a site that is associated with homozygous deletions in high-grade astrocytomas in about two-thirds of gliomas. These proteins act as inhibitors of cyclin-dependent kinases and other pathways during the Gl phase of the cell cycle and help control proliferation at the Gl/S phase of the cell cycle. The TP53 protein assists in several cellular processes, including cell cycle regulation, response of cells to DNA damage (Psr dependent growth arrest following DNA damage occurs in Gl phase of the cell cycle), cell death, cell differentiation, and neovascularization (WHO, pp. 11-14 ; Berger, pp. 204-209) .
- Most variable phase of the cell cycle in terms of duration
For each question select one or more than one lettered heading (in parentheses) from Figure 1.33-1.39Q with which it is most closely associated. Each lettered head-ing may be used once, more than once, or not at all
D
Cells are most sen-sitive to radiation during the G2 and M phases of the cell cycle and most resistant in the late S phase. Gl cells have intermediate sensitivity. The precise mechanism(s) accounting for these variations remains unclear, but studies have shown that differences in a cell’s ability to repair DNA damage in different phases after radiation may play an important part. In the Gl phase of the cycle, the nucleus has a diploid amount of DNA (2G), which increases to 4C by the end of the S phase. Only cells in the S phase (DNA synthetic phase) are able to incorporate thymidine analogues (bro-modeoxyuridine) into their nuclear DNA. Nutrient depletion and crowding can result in the movement of cells into the quiescent or nonproliferating phase (GO) of the cell cycle; such cells can eventually re-enter the cell cycle at a later point in time. Mitosis is the most easily identifiable stage of the cell cycle by light microscopy. The genes encoding pl6 (CDKN2A) and pl5 (CDKN2B) map onto chromosome 9p21, a site that is associated with homozygous deletions in high-grade astrocytomas in about two-thirds of gliomas. These proteins act as inhibitors of cyclin-dependent kinases and other pathways during the Gl phase of the cell cycle and help control proliferation at the Gl/S phase of the cell cycle. The TP53 protein assists in several cellular processes, including cell cycle regulation, response of cells to DNA damage (Psr dependent growth arrest following DNA damage occurs in Gl phase of the cell cycle), cell death, cell differentiation, and neovascularization (WHO, pp. 11-14 ; Berger, pp. 204-209) .
- What is the resting membrane potential for nerve cells?
A. -100 mV
B. -90 mV
C. -80 mV
D. -65 mV
E. -40 mV
D. -65 mV
In resting nerve cells the resting membrane potential
is -65 mV. This negative polarity is largely the result of two factors: the selective permeability of the cell membrane to K+ through voltage-gated channels and the Na+, K+pump, which pumps three Na+ions out of the cell for every two K+ions that are pumped inside.
In terms of K permeability, as K+leaks out of the cell
down its concentration gradient, the cell membrane begins to develop a potential difference due to the accumulation of negative charges inside the cell. This eventually slows the continued efflux of K+ions out of the cell as a result of the electrostatic attraction between the inside of the cell and posi-tively charged K+ions outside the cell. Eventually the rate of
K+flow inside and outside the cell reaches a state of equilib-rium (equilibrium potential for K+) due to the balancing of the electrical and chemical forces. This produces a net flow of K+ions that is zero and a net negative potential difference across the cell membrane. This is called the equilibrium
potential for K+ and can be calculated by the Nernst equation.
E = RT/F log(ion)out/(ion)i n= 61 log (150/5.5) = -86 mV
Using standard values of concentration gradients (see dis-cussion question 41, RT/F = 61), the equilibrium potential forK+ is -86 mV, which would also be the resting membrane potential across the cell membrane if K+ were the only ion contributing to the membrane potential. However, rarely
does one ion contribute solely to the membrane potential,which is often a combination of multiple ions diffusing through the membrane. For this reason, the Goldman equa-tion was developed to account for the relationship between membrane potential (V) and relative permeability (P) of each population of ion channels. Given this, the resting membrane potential in neurons (-65 mV) is not identical to E K+ (-86 mV), since the membrane is slightly permeable to other ions as well.
v = 61j PK(K+)„u,+ PNa+(Na+)ol„+Pa(Gl-)in
<sup>8</sup>P<sub>K<sup>+</sup></sub>(K<sup>+</sup>)<sub>jn</sub> + P<sub>X;l<sup>+</sup></sub>(Na<sup>+</sup>)<sub>jn </sub>+ P<sub>a</sub>(Cn<sub>out</sub>
The inequality of charge on either side of the cell mem-brane is also the result of the Na+, K+ pump, which is a large membrane-spanning protein with Na+, K+, and ATP binding sites. If this pump were not present, the gradient across the cell membrane would eventually dissipate. This pump utilizes one ATP molecule to pump 3 Na+ ions out of and 2 K+ ions into the cell. An increase in permeability of Gl” channels usually has little effect on membrane potential, since the resting potential of a typical neuron (-65 mV) and equilib-rium potential for Gl” (-66 mV) are very similar (Kandel,pp. 125-139).
- What is the extracellular concentration of Ca2+
ions in the brain?
A. 0.7 mM/L
B. 2 mM/L,
C. 125 mM/L
D. 150 mM/L
E. None of the above
B. 2 mM/L,
Refer to Table 1.41A. Neurons maintain a high con-centration of K+ ions and organic anions inside the cell, and ions such as Na+ , Gl”, and Ga2+ are more highly concentrated outside of the cell (Kandel, pp. 125-139).
- Columns of neurons in area 3a of the somatic sensory cortex receive input primarily from what type of receptor(s)?
- Rapidly adapting skin receptors
- Slowly and rapidly adapting skin receptors
- Pressure and joint position receptors
- Muscle stretch receptors
A. 1,2, and 3 are correct
B. 1 and 3 are correct
C. 2 and 4 are correct
D. Only 4 is correct
E. All of the above
D
- Which of the following is true of action potentials?
- Action potentials are mediated entirely by changes in K+ voltage-gated channels
- The rate of Na+ influx begins to slow as the membrane potential approaches EK+
- The threshold for initiating action potentials is usually around +15 mV
- The falling phase of the action potential is mediated by delayed activation of K+ conductance
A. 1, 2, and 3 are correct
B. 1 and 3 are correct
C. 2 and 4 are correct
D. Only 4 is correct
E. All of the above
D. Only 4 is correct
The rising phase of an action potential is due to a
stimulus that results in the activation of voltage-gated Na+ channels. The rate of Na+ influx begins to slow as the mem-brane reaches the membrane potential for Na+ (not K+),resulting in a peak amplitude when the Na+ channels become inactivated. The decline in the action potential is then medi-ated by the delayed activation of voltage-gated K+ channels. The efflux of K+ ions is greatest at the peak of the action potential and begins to decline as the membrane potential approaches the equilibrium potential for K+ . The membrane is, however, briefly hyperpolarized, as K+ conductance does not return to resting levels until after the membrane voltage has declined below the normal resting potential. The thresh-old for initiating action potentials may vary but is usually around -50 mV for most mammalian neurons, not +15 mV (Kandel, pp. 150-170; Pritchard, pp. 23-25).
- Cells with concentric receptive fields along the visual
pathway are found in what location(s)?
A. Retina
B. Retina and optic nerve
C. Retina and lateral geniculate nucleus
D. Retina, lateral geniculate nucleus, layer 4 of the visual
cortex
E. Cells in the premotor cortex only
C. Retina and lateral geniculate nucleus
Both ganglion cells in the retina and the lateral
geniculate nucleus are known to have both “on-center” and “off-surround,” or concentric, receptive fields. Cells in the optic nerve and premotor cortex are not known to possess such characteristics. Simple cells in layer IV of the visual cortex do not have circular receptive fields but instead respond to stimuli as lines and bars (rectangles) (Kandel,pp. 517-522, 528-529).
- What is the primary neurotransmitter of the Renshaw cell?
A. Glycine
B. Acetylcholine
C. GABA
D. Serotonin
E. Glutamate
A. Glycine
A special class of inhibitory interneurons called Renshaw cells are found in laminae MI and VIII of the spinal cord. These cells have muscarinic cholinergic receptors that receive oc-motor-neuron cholinergic collateral projections. The Renshaw cell then exerts a negative feedback on the a motor neuron and other homonymous a motor neurons, called recurrent inhibition. The neurotransmitter released by Renshaw cells is glycine. Renshaw cells also make inhibi-tory synaptic connections with la inhibitory interneurons; this arrangement regulates reciprocal inhibition of antago-nistic motor neurons. Renshaw cells receive input from several descending pathways in the spinal cord (Carpenter,pp. 57-79; Kandel, pp. 720-721).