Some Questions with their answers on Central Nervous System Physiology by Dr Khaled A Abulfadle

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Q: Tonic neck reflexes

Answer

Tonic neck reflexes

Definition: When the face is turned to the affected side (spastic hemiplegic side in UMNL), the arm and leg on the affected side to which the face is turned extend and abduct

Nature: they are primitive reflexes found in newborn, but, reappears in upper motor neuron lesion

Cause of reappearance in UMNL: the reappearance of the tonic neck reflex in UMNL may be due to:
1-lesion in pyramidal tract which inhibits normally this primitive reflex
2-in UMNL due to internal capsule lesion is accompanied by intact vestibular nucleus which may be responsible for these reflexes

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Q: Explain mechanism of rigidity in case of meningitis

A: Neck stiffness (rigidity) in meningitis occurs because the lining of the spinal cord is connected to the lining of the brain. When this infected and inflamed lining is stretched by looking down, it causes severe pain.

i.e.

In meningitis, if the patient flexes the neck, the spinal canal elongates and the meninges stretch, which is painful if they are inflamed. As a result, the patient will guard against neck flexion and this is what results in nuchal rigidity.

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Question

Define Rheobase and Chronaxie. What is the clinical importance of chronaxie

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Answer

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Question

Define fibrillation and fasciculations. What is their clinical importance?

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Answer

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?Q: What is the skin temperature at which hot and cold pain receptors are stimulated
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A: The average person begins to perceive pain when the skin is heated above 45°C. This is also the temperature at which the tissues begin to
be damaged by heat; indeed, the tissues are eventually destroyed if the temperature remains above this level indefinitely. Below 10°C, cold
pain fibers are stimulated.

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QUESTION

Define, Doctrine of specific nerve energy and law of projection
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ANSWER

=Doctrine of Specific Nerve Energies (Labeled Line): the sensation evoked by stimulation of a receptor or its pathway is sensed as being caused by the receptor's adequate stimulus, no matter what the actual stimulus.
=Law of Projection: sensation is sensed as arising from (projected to) the receptor's receptive field as each part of the body is represented in the sensory cortex.

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Q: spinal cord transaction and hemi-transaction, is it an UMN lesion or LMN lesion
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A: spinal cord transaction and hemi-transaction below level of lesion is UMNL and at level of lesion is LMNL

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Question
Pathophysiology of Parkinsonism

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Answer

Direct pathway in basal ganglia causes inhibition of Globus Pallidus interna which is inhibitory to thalamus and hence motor cortex

Indirect Pathway in basal ganglia stimulates globus Pallidus interna which is inhibitory to thalamus and hence motor cortex

Dopamine inhibits globus Pallidus interna both directly (stimulate direct pathway) and indirectly (inhibit indirect pathway) with resulting stimulation of motor cortex

In parkinsonism, depleted dopamine causes hyperactive globus Pallidus interna with inhibition of thalamus and motor cortex causing hypokinesia and that is why in treatment of parkinsonism you should either compensate for dopamine or even do destruction of globus Pallidus interna

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Q: What is the role of gamma motor neuron in Stretch reflex?
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A:
A gamma motor neuron (γ motor neuron), also called gamma motoneuron, is a type of lower motor neuron that takes part in the process of muscle contraction, and represents about 30% of ( Aγ ) fibers going to the muscle. Like alpha motor neurons, their cell bodies are located in the anterior grey column of the spinal cord. They receive input from the reticular formation of the pons in the brainstem. Their axons are smaller than those of the alpha motor neurons, with a diameter of only 5 μm. Unlike the alpha motor neurons, gamma motor neurons do not directly adjust the lengthening or shortening of muscles. However, their role is important in keeping muscle spindles taut, thereby allowing the continued firing of alpha neurons, leading to muscle contraction. These neurons also play a role in adjusting the sensitivity of muscle spindles.

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Q: Explain how alcohol intake makes the sense of warmness
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A: While alcohol can make the sense of warmness temporarily this is a perception generated by heat sensitive neurons (thermoreceptors) located in the skin that detect a rise in the skin temperature from an increase in blood flow in the vessels close to the skin’s surface. In fact, alcohol actually lowers the core body temperature because the rush of blood to the skin’s surface is a means of body cooling.

So while one may feel warm on the outside, he is getting cold on the inside. Alcohol consumption has also been shown to reduce the perception of cold air temperatures but it is thought that this effect may not come from changes in the dilation of blood vessels but may originate in the brain itself.

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سؤال: هل يوجد بجسم الانسان sensory pool

و sensory unit
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جواب: نعم فى جسم الانسان Sensory unit which is defined as single afferent neuron with all its receptor endings. It is the smallest unit of sensory response.

كما يوجد sensory pool و لكن ليس يسمى بذلك الاسم... بل يسمى Receptive field of multiple sensory units كما بالصور

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Question

What type of sleep releases growth hormone?

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Answer

In adults, the most reproducible pulse of GH secretion occurs shortly after the onset of sleep in association with the first phase of slow-wave sleep (SWS) (stages III and IV).

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