Which of the following cells are the only excitatory neurones in the cerebellum?
D. Granule cells are the only excitatory neurones in the cerebellum. The cerebellar cortex is a three-layered structure with the outermost layer containing two types of inhibitory neurones, the stellate cells and basket cells. The middle layer has cell bodies of Purkinje cells (main output) which are GABA-mediated and so are inhibitory in function. The innermost layer contains granule cells, which are excitatory, and Golgi cells, which are inhibitory.
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Which of the following components of cognition is tested by the digit span task?
A. Working memory can be tested using digit span tasks. Using digit repetition forward, a patient’s working memory capacity can be tested. Usually, a list of numbers (in no specific pattern) is read aloud by the examiner and the patient is asked to repeat it immediately in same order (forward span) or reverse order (backward span). Gradually, the length of the numeric string is increased. Consistent error at a particular length is an indication for test termination. The normal forward digit span is 7±2 for most adults. Backward span is more difficult and averages around 5±2.
Ataxia can result from cerebellar lesions or posterior column lesions. Though gait disturbances are predominant in both these conditions, which of the following is seen in sensory ataxia but not cerebellar ataxia?
C. Sensory ataxia is due to posterior column disease, resulting from spinal cord lesions. In this condition, loss of joint position sense and loss of tendon refl exes are seen. In cerebellar ataxia, associated cerebellar signs such as dysarthria or nystagmus may be present. The corrective effects of vision on balance and posture are seen in sensory ataxia. This is elicited by Romberg’s test wherein swaying, which is almost absent when eyes are open and feet together, becomes prominent on eye closure. In cerebellar ataxia, the patient may sway even with eyes open, which worsens on eye closure.
The ability of neurones to change the connection strength with other neurones underlies the electrophysiological process called long-term potentiation (LTP).
Which of the following forms the neurochemical basis of LTP?
C. Long-term potentiation (LTP) is conceptualized as a more or less permanent increase in synaptic efficacy following high-frequency activity across the synapse. Glutamate via NMDA receptor activation influences LTP. This may underlie changes in synaptic plasticity observed in learning- and memory-related processes. LTP is proposed to be the cellular biological correlate of long-term memory.
Which of the following is a major dopaminergic site?
B. Most neurones from the ventral tegmental area of midbrain ascend in the medial forebrain bundle and the nigrostriatal pathway. These neurones are rich in dopamine. The dopamine neurones of the ventral tegmental area (VTA) are thought to play a central role in reward,motivation, and drug addiction. Nucleus basalis of Meynert is a major cholinergic site. Dorsal raphe nucleus is predominantly a serotonergic site. Locus coeruleus contains noradrenergic neurones.
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