Psychology - Kaplan Question

[shefv]

I am confused about this question.

I am thinking that if the person is still able to show the Babinski Reflex (meaning flex out their toes when the sole of the foot is stroked), that means that their spinal cord is still intact and the sensory command from the stroke and the motor command from the brain and interneurons (reflex arc) is still functioning. So I am thinking that the the LEAST likely cause of still having this reflex in adulthood has to be spinal cord injury.

Corpus collosum being severed made more sense to me because the brain is not able to inhibit this reflex which it should have done in the case of an adult.

Can someone please explain this? Where am I going wrong with this? Thanks!

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[EParker37]

The explanation given is pretty sound actually. Adults do not normally display the babinski reflex, if they do, this is generally an indicator of lesion or spinal trauma. MS would also lead to a positive babinski sign because it affects the myelination of nerve cells, which allows the reflex to bypass the cerebral cortex, which is what normally inhibits the reflex arc.

 

[shefv]

Can someone explain and elaborate on the topic of reflex (reflex arc)?

I know that interneurons play an important role in reflex arc and it allows for a reflex (motor command) to be generated in the spinal cord without waiting for the brain to process the sensory information. This happens in cases of emergencies. I also know the different primitive reflexes.

I am confused about the retention of these reflexes in adults and the biological reason behind them. Can someone explain this topic?

Thanks!

 

[Mantis Toboggin]

Can someone explain and elaborate on the topic of reflex (reflex arc)?

I know that interneurons play an important role in reflex arc and it allows for a reflex (motor command) to be generated in the spinal cord without waiting for the brain to process the sensory information. This happens in cases of emergencies. I also know the different primitive reflexes.

I am confused about the retention of these reflexes in adults and the biological reason behind them. Can someone explain this topic?

Thanks!

There are two types of reflex arcs. The key to remember is that reflex arcs use one sensory (afferent, going towards the spinal cord) and one motor (efferent, going towards the effector muscles), or sometimes have one or more interneurons between these two

1.) polysnaptic- these use interneurons. So think 3 (sensory, interneuron, motor) or more neurons. A typical example is the withdrawal reflex, like when you step on something sharp. The leg affected by the sharp object withdraws while your other leg moves to stop you from falling. Interneurons can also convey info to the brain, but for these purposes consider those not part of the reflex arc

2.) monosynaptic- simple: sensory receptor--> afferent neuron--> efferent neuron. The knee jerk reflex is an example of this.

As for primitive reflexes in adults, just remember that they're usually due to demyelenation. I'm kind of puzzled about this being a symptom of spinal cord disease. My only logical guess is that primitive REFLEXes bypass the brain and just act on similar reflex arcs as those I've mentioned. Of the choices given the corpus callosum definitely makes the least sense. I'm guessing frontal cortex illness would have to do with disease in the somatosensory cortex

Edit: my book didn't say anything about what inhibits these reflexes but apparently the frontal lobe is involved here. This kind of contradicts the idea that the p reflexes bypass the brain, so someone else should explain this

 

[image187]

Just to clarify, a positive Babinski is demonstrated with EXTENSION (up-going; abnormal) of the great toe upon stroking the bottom of the foot, and not FLEXION (down-going; normal). This is an "upper motor neuron" sign, others of which include hyper-reflexia, clonus, spasticity, etc... and this is a result of damage to the "upper motor neuron" (google this). Assuming that the question meant to say "extension" to signify a positive babinski sign, the question is basically asking: Which answer choice is least likely to be associated with this upper motor neuron lesion?

A. Spinal cord injury: causes injury to descending motor fibers --> likely to result in a positive babinski
B. MS: causes CNS demyelination --> may or may not result in demyelination to cause a positive babinski
C. Severed corpus collosum: Dissecting part or all of this structure will not directly affect upper motor neurons.
D. Frontal lobe brain tumor: The motor strip is located in the posterior frontal cortex. A frontal lobe tumor may or may not affect neuron cell bodies in this area, leading to upper motor neuron dysfunction ---> babinski sign.

The only choice NOT associated with an upper motor lesion is choice C. All others may or may not cause a babinski sign. Again, i believe the question is wrong and meant to describe an actual positive babinski