Upper motor neuron lesion is characterised by - - UPPSC 2023

UPPSC 2023

Pathology & Genetics

Easy

Appeared in: UPPSC 2023

Explanation

Upper motor neurons (UMNs) originate in the brain and brainstem, and their pathways descend to control the lower motor neurons (LMNs).
UMNs exert an inhibitory influence on the reflex arcs of the spinal cord.
When a UMN lesion occurs (e.g., from a stroke or spinal cord injury), this inhibitory control is lost.
The loss of inhibition results in exaggerated, overactive spinal reflexes, which manifest as hyperactive deep tendon reflexes (hyperreflexia).
Other key signs of a UMN lesion include increased muscle tone (spasticity) and the presence of pathological reflexes like the Babinski sign.

Option A: Flaccid paralysis, or limpness of the muscles, is a hallmark sign of a lower motor neuron (LMN) lesion.
Option B: Fasciculations are fine, involuntary muscle twitches visible under the skin. They are caused by the spontaneous firing of dying or irritated lower motor neurons.
Option D: Hypotonia is a state of decreased muscle tone, resulting in flaccid, limp muscles. It is a direct consequence of damage to the lower motor neurons.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Characteristics of Upper Motor Neuron (UMN) Lesions as background academic context rather than a clinical decision trigger.
Nurses must be able to differentiate between UMN and LMN signs to perform accurate neurological assessments, report significant changes to the healthcare team, and anticipate patient care needs.
Recognizing UMN signs like hyperreflexia and spasticity alerts the nurse to the need for interventions to manage muscle stiffness, prevent contractures, and ensure patient safety during mobility.
Conversely, identifying LMN signs like flaccidity and hypotonia directs care towards preventing pressure injuries, deep vein thrombosis, and joint subluxation due to lack of muscle support.

How to Approach the Question

First, identify the core of the question, which is to find a characteristic sign of an 'Upper motor neuron lesion'.
Recall the basic functions: Upper Motor Neurons (UMNs) are like the 'managers' in the brain that control the Lower Motor Neurons (LMNs). LMNs are the 'workers' that directly connect to the muscles.
Consider the effect of a UMN lesion: If the 'manager' is damaged, the 'workers' (LMNs) lose their regulation and become overactive and uncontrolled.
This overactivity leads to 'hyper' signs. Scan the options for a 'hyper' term. 'Hyperactive deep tendon reflexes' fits this pattern.
Evaluate the other options: 'Flaccid Paralysis' and 'Hypotonia' are 'hypo' (low/absent) signs, which point to a problem with the 'worker' (LMN) itself. 'Fasciculation' is a sign of LMN irritation.
Conclude that hyperreflexia is the only sign consistent with a loss of higher-level inhibitory control from a UMN lesion.

Concept Tested & Keywords

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