Tutorial 1: Permanent Paralysis

After the second meeting of tutorial 1, my group are still unclear about certain issues. I will list them down here and please contribute your opinions.

1. What is the relationship between increase muscle tone and decrease muscle strength? What are the causes of increased/decrease muscle tone and the causes of increased/decreased muscle strength?

My tutor, Dr.E.Siti Herini, a paediatrics neurologist, said that decreased muscle strength is usually associated with decreased tone. She said that the scenario is kind of contradicting. What did your tutors say about this?

My opinion is that muscle strength will increase if muscle tone increase. The more the impulse delivered to the skeletal muscle, the stronger the muscle will be due to hypertrophy. Decrease muscle tone (or the absence of it) will lead to muscle atrophy. However, I have no idea how spinal injury can lead to increased or decreased muscle tone.

2. What is the reason of increased patellar refelex?

What is the definition of increased patellar reflex? My tutor said that it means the patellar reflex is more easily triggered at places that don't usually lead to the knee jerk. Normally patellar reflex happen when you knock on a certain spot at the quadriceps tendon. Slightly left or slightly right also cannot. But for increased patellar reflex, the area that can trigger the reflex expands. Slightly left, right, up or down also can. It DOES NOT mean that the knee will jerk for a larger angle.

The question is: why the patellar increases? And in what condition will the patellar reflex be absent?

The textbook states that the plexus lumbaris is involved in the motoric control of the lower limb. And patellar reflex is associated with N.Femoralis, which branches from L2,L3 and L4. So some of our peers say that Patellar reflex is a test to measure the functionality of the Lumbar segment 2,3 and 4. In our scenario, the patient can't move his lower limbs but still have patellar reflex? What is the reason behind?

My understanding is that patellar reflex is a monosynaptic reflex that involved a sensory afferent fiber (from spindle fibre) and a motoric efferent (connect to effector). As long as the spinal segments of L2, L3 and L4 are intact, the patellar reflex can occur.

For the voluntary movement of the lower limbs, it involves a signal to be sent from the brain to the L2-L4 before the signal reaches the lower limb muscles. If any injury happen to the descending tract (found in the white column) at Lumbar segment or above lumbar segment, we can move our lower limb anymore. But the patellar reflex is still positive because the grey mater for those lumbar segment are still intact.

3. Which part of spinal cord injury will lead to urinary and fecal incontinence?

The N.errygentes will carry the sensory information from the stretch receptor in the bladder to the centre in the S2-S4 segments. Then the same nerve will carry the motoric impulse to the Internal Urethra sphincter to cause relaxation. For a normal person to voluntarily control micturition, an inhibitory signal need to be sent from the brain to the S2-S4 segments , then through Pudendal Nerve to the External urethral sphincter to cause contraction. If the spinal cord injury happen at the lumbar or sacral region and affect the descending tract, the voluntary control of urination will be loss and lead to urine incontinence or "automatic bladder". I still have a question about this process. If the spinal cord injury happen at the thorac and cervical region, will it lead to urine incontinence? My belief is a yes but my tutor said urine incontinence is usually a result of spinal cord injury at the lower back (lumbar or sacral region).

Defecation process is similar to the micturition process. Stretch receptor at the rectum sent information to the centre at S2 to S4 through N.errygentes. Then this same nerve will cause relaxation of Internal Anal Sphincter. Voluntary control involve Pudendal Nerve that instruct the External Anal Sphinter to contract.

4. What is the definition of Neurogenesis, regeneration, replicate and repair?

The lecture note isn't very clear about the regeneration of the nerve fiber. Under what condition can the nerve regenerate or repair?

My tutor say that certain part of the brain can have "new neurones" especially at the hippocampus part. Extensive reading or learning will lead to thickening of the cornu ammonicus. So, it appears that new neurones are formed.

Do neurones undergo mitosis to produce new neurone? Or neurones can only be differentiated from the stem cells? Some of our peers say that neurones don't have centriol and are unable of performing cell division.

If you have other questions about this tutorial, please put it here and we shall discuss.

Can We Replace Brain Cells?

Until recently, neurons (nerve cells) of the brain were thought to be
irreplaceable; when they died, we thought, they were gone forever. We
believed, indeed, that there was good reason for this. Motor skills and
memories are encoded in intricate neural circuits, and the growth of
new neurons might disrupt those circuits. Now we are not so sure.
A chemical called BrDU (bromodeoxyuridine) can be used to trace
the birth of new cells, because it becomes incorporated into their DNA.
BrDU is too toxic to use ordinarily in human research. However, in cancer
patients, BrDU is sometimes used to monitor the growth of tumors.
Peter Eriksson, at Göteborg University in Sweden, obtained permission
from the families of cancer victims to examine the brain tissue of
BrDU-treated patients who had died. In the hippocampus, a region of
the brain concerned with memory, he and collaborator Fred Gage
found as many as 200 new neurons per cubic millimeter of tissue, and
estimated that up to 1,000 new neurons may be born per day even in
people in their 50s to 70s. These new neurons apparently arise not by
mitosis of mature neurons (which are believed to be incapable of mitosis),
but from a reserve pool of embryonic stem cells. It remains
unknown whether new neurons are produced late in life in other
regions of the brain.

Extracted from: The Unity of Form and Function, Kenneth S. Saladin.

During my skills lab session, I asked the neurologist about the patellar reflex. She gave me a very brief answer, but I believe it was sufficient to trigger further self-study.

She said Patellar reflex will increase if there is something wrong with the Central Nervous System, but will decrease is there is something wrong with the Peripheral Nervous System.

For the questions by wil*i*am such as the muscle tone-muscle strength and patellar reflex, i recommend that explanation is obtained from cindy as she explained during our tutorial session...

Thank you nash for explaining about production of new neurones from stem cells in the hippocampus region.

The other day we asked dr.Soedjono regarding the increased patellar reflex..According to the doc, the condition is due to absence of inhibition from the brain due to the damaged of the ascending and descending tract in the medulla spinalis. I am not sure if this ans william's question..But I've a doubt: do reflexes involve the brain? or it only involves the spinal cord? What I think is, it might involve the brain, just that not the cortex..

I asked the neurologist during the skill lab. He said that injury to the lower motor neurones will cause the absence of the patellar reflex, while injury to the upper motor neurones will cause increased patellar reflex. This is in coherence with what Cindy mentioned. Upper motor neurones damage will result in the loss of the inhibition from the brain, thus the patellar reflex is increased. Lower motor neurones may refer to the injury at the lumbar segments. If pathway is damage, no patellar reflex will be observed.