Which of the following brain regions is involved in the regulation of arousal and sleep–wake cycle?
D. The establishment and maintenance of a wakeful state is called arousal. In humans, arousal activity requires at least three brain regions. The most important of these is the ascending reticular activating system (ARAS). ARAS may have a role in setting the level of consciousness. ARAS, via the intralaminar nuclei of the thalamus, project widely throughout the cerebral cortex. A synchronized, rhythmic burst of neuronal activity (20–40 Hz frequency) results from ARAS and thalamic coordination. The degree of synchronization varies directly with the level of wakefulness. During sleep the synchronicity is lost. The third most important region in arousal state is the right frontal lobe. The right frontal lobe is essential for the ‘maintenance’ of attention; this is evident when testing letter-cancellation tasks or trail-making tasks in patients with right frontal lesions.
Reference:
The resting membrane potential of a neurone is estimated to be approximately:
E. Hodgkin and Huxley showed that the inside of a cell, such as a neurone, is negatively charged compared to the outside. This is called the resting membrane potential and its value ranges between −40 mV and −90 mV (average −70 mV), depending on the type of cell. This negative resting membrane potential arises due to the membranes of the resting neurone being more permeable to potassium ions than to any other ions. There are more potassium ions inside the cell than outside it, which is due to a constant outward leak creating a negative potential inside the cell. An action potential is initiated in the axon hillock when the synaptic signals received by the dendrites and soma are sufficient to raise the intracellular potential from −70 mV to the threshold potential of −55 mV. When this potential is reached, the Na+ channels, which are dormant at rest, will open. This Na+ influx causes rapid reversal of the membrane potential from −70 to +40 mV.
Which of the following statements with respect to the neurotransmitter glycine is correct?
D. Glycine is an inhibitory transmitter, predominantly found in the spinal cord; it has relatively insignificant effects in the brain compared to the spinal cord. Glycine acts on a chloride channel that is different from GABAA receptors, called the strychnine-sensitive glycine receptor. On activation, the trans-membrane glycine receptors facilitate entry of chloride ion into the cell, leading to hyperpolarization of the cell. Glycine is synthesized from serine; this conversion is mediated by rate-limiting steps via serine trans-hydroxymethylase and glycerate dehydrogenase. Glycine also serves as an obligatory neurotransmitter adjunct for glutamate activity on the NMDA glutamate receptors (non-strychnine-sensitive glycine site). Some clinical trials have shown a reduction in the negative symptoms of schizophrenia using D-serine or glycine mediated via NMDA receptors, though this has not been widely replicated.
Direct measurement of cerebral glucose metabolism is possible using which of the following methods?
C. Positron emission tomography (PET) is considered as the gold standard of functional neuroimaging modalities. Among other available techniques, only PET can measure cerebral glucose metabolism directly. In addition, a large number of radioligands for receptor characterization are available for PET. Despite these advantages, PET is not widely available due to the expensive nature of the equipment; it requires relatively rapid access to a cyclotron to produce the positron-emitting radionuclides.
A nocturnal surge in the level of growth hormones is observed during which of the following stages of sleep?
C. Most hormones show a diurnal–nocturnal variation in their plasma levels. This is partly related to circadian mechanisms and hypothalamic functions. Level of physical activity and diurnal change in metabolic requirements may also influence the hormonal levels in blood. Growth hormone regulates carbohydrate and lipid metabolism. There is a nocturnal surge of growth hormone seen during slow wave sleep (stage 3 and 4 NREM sleep). Speculative association of growth hormone surge and memory consolidation has not been borne out by experimental results.
Click to expand