Lower motor neurons are in the brain stem and spinal cord. They receive signals from the upper motor neurons whose cell bodies are in the motor strip of the cerebral cortex (brain).
Lower motor neurons then send signals to peripheral nerves.
Lower motor neuron findings in ALS include weakness, atrophy, and fasciculations. Upper motor neuron findings include spasticity, hyperreflexia, and slowness.
Pure LMN disease is progressive muscle atrophy (PMA). Pure UMN disease is progressive lateral sclerosis (PLS).
Since ALS is a progressive disease, many people start out LMN-dominant or UMN-dominant and then develop more UMN and LMN features over time.
Most cases of PMA and PLS eventually progress to ALS, but those with these conditions seem to have a longer lifespan than people starting out with mixed UMN/ LMN disease.
karen, thanks for answer. this is a most useful answer i got from anyone, including google.
why do i ask this?
1. neuro diagnose "ishialgia"
2. neuro diagnose (als expert) "according to all noticed results and criteria, it's als" (20 minutes of opservations which included reflexes and emg, forwarded to other rookies who confirmed it after reviewing of all negative results from mri, bloodtests, markers, etcetc, respecting als expert diagnose
3. physiatrist "LMD, according to emng results - emng lower and upper motor neurons compared in 8 last months". as i noticed, no upper neuron inervation found.
4. i've been sent to imunology-rheumatology-pulmology dpt after considering for decades non stop-elevated ALT, AST, newly measured CK (750) and kreatinine (within referent area, but reaching low level).
i talk to neuro (rookie), but he hears only what he wants. i never had any kind of problems upper from waist (weakness etc). "tongues fasciculations suspected, no visible atrophies on tongue, speech is little bit slower, whole left hand atrophy" even i said that i had elbow luxation and it was immobilized for 3 weeks... now,after 4 months it looks more than very good (muscles, power etc..). i have fasciculations all over my body, same as brief reflexes, 3+.
my right side is weaker for 21 years, since i had car accident, and they automatically connect it with spreading ALS. i work for 10 hours a day. sitting, just doing on comp, walking less than 1 km/day. so i have problems with walking for last 4 years which is worse and worse... that is all my problem. only misdiagnose can stop taking me appart from my girl.
It's not like upper motor neurons control the upper part of the body and lower motor neurons control the lower part. Every muscle under voluntary control is controlled by many motor neurons, both upper and lower, in the way that Karen wrote about.
Most EMGs cannot detect upper motor neuron dysfunction. It is an emerging science that more advanced centers use.
So not having problems with the upper body, or not having them as much, does not mean that the ALS diagnosis was in error. The EMG shows problems in multiple regions even before there are symptoms, for the diagnosis to be made.
i have problems with my legs. big problems for at least 2,5 years, started with minor problems year before /3,5 years). no further problems found. i had a problems, even emng was good. maybe wrong muscles opserved (?). right foot dropped, thumb on right foot curled, limp, muscles real atrophy just in legs, some muscle inervation in legs. dizziness i mentioned seems to be - waste of energy trying to concentrate to keep balance. my legs deteriorate on a daily bases for a two years, nothing else. my low motor neuron is affected as emng said for 5 times by now, but it should be visible somewhere&somehow in two years anywhere other then just in legs!
hence, i'm thinking of simple wheelchair, hand powered&controlled untill als spread to hands etc. by the way, it's easier to move arround a house&hospice with it.
last time i visited neuro he said&wrote "left hand atrophy and this is expected, but we couldnt prognose when it will happen". didnt hear what i was saying about luxation. i have appointment in a 3 days, so i'm very interesting what he will say. if he will say anything at all, except write.
Thanks Karen, I am really interested in the correct anatomy here. I've been involved with MND for more than 5 years and looked at lots of images of the structures.
So LMN go from spinal cord to the muscle, yet they are also found from the brain stem to the spinal cord? That's my confusion, I thought the ones going from brain stem to spinal cord were still the UMN?
Yeah that image was no good, try using the manage attachments function to upload an image rather than a link to one if you want to add images any time.
Tillie, I looked this up (thank you — it’s good for me ).
My best understanding of it is that all the upper motor neurons originate in the frontal cortex (motor strip) of the brain. Their cell bodies are in that strip of cortex. These neurons have very long projections (axons), some of those reaching the brain stem, but some going all the way down the spinal cord.
When the axons of these UMNs reach the brainstem or spinal cord, they synapse (connect) with lower motor neurons. These LMNs then exit the brainstem or spinal cord as peripheral nerves and synapse onto the muscles to make them contract.
Tillie, to answer your question, the neurons exiting the brainstem are LMNs. Many of them form cranial nerves and serve muscles of the face and bulbar region.
Karen, I like my diagrams to be really big so I can trace them with my finger and talk myself step by step through it. Usually in private so people don't think I'm simple. Visual learner here.
Re: peripheral vs motor. My understanding is (incomplete) that they (peripheral nerves and the UMN/LMN) are separate yet inter-connected for proprioceptive reasons. The motor cortex takes information from peripheral nerves to help drive balance and assess "place". However, the peripheral nerves are not usually directly affected by motor neuron disease, only the motor control centre's ability to process/use the info gained from sensory/peripheral nerves. But that's also heading into ataxia territory, so my understanding is likely incomplete.