Скачать или смотреть Two-Neuron Chain Explained | UMN vs LMN Lesions, Reflex Arc & Babinski Sign

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Learn the roles of Upper Motor Neurons (UMNs) and Lower Motor Neurons (LMNs), how the reflex arc maintains muscle tone, and the classic signs of UMN vs LMN lesions seen on neuro exam. We’ll also cover the Babinski sign and how to interpret reflex changes at key spinal levels.

1. Explore where UMNs and LMNs are located and how they connect
2. Understand the stretch reflex arc and how it maintains muscle tone
3. Compare the hallmark signs of UMN vs LMN lesions (weakness, atrophy, fasciculations, reflex changes, tone differences)
4. Learn how cranial nerve nuclei serve as LMNs for facial muscles
5. Review the Babinski sign and why it matters in the neuro exam

⏱️Timestamps
0:00 – Intro
0:25 – The Two-Neuron Chain (Upper vs Lower Motor Neurons)
0:49 – Upper Motor Neurons (UMN) in motor cortex & brainstem
1:29 – UMN pathway through brainstem & spinal cord
1:55 – Lower Motor Neurons (LMN) in spinal cord ventral horn
2:25 – LMNs at neuromuscular junction & muscle contraction
2:58 – LMNs in cranial nerve nuclei (facial & cranial motor control)
3:51 – Cranial nerves as LMN pathways
4:23 – LMNs in spinal cord ventral horn
4:55 – The Stretch Reflex Arc explained
5:36 – Patellar reflex example
6:47 – Loss of reflex in LMN damage
7:12 – Role of UMNs in reflex modulation
7:36 – UMN lesion → hyperreflexia
8:04 – Common reflex levels tested (C6, C7, L4, S1)
8:29 – LMN lesions: atrophy, fasciculations, hypotonia, hyporeflexia
10:40 – UMN lesions: weakness, hyperreflexia, hypertonia, Babinski sign
13:00 – Babinski sign explained (normal vs abnormal)
14:12 – Babinski in infants vs adults
14:37 – Key differences between UMN and LMN lesions
15:06 – Summary & wrap-up

This lesson is especially helpful for medical students, or anyone reviewing for anatomy exams.

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