Upper Motor Lesion and Lower Motor Lesion

Question 1

What are upper motor neurons?

Answer 1

Upper motor neurons; originate in the motor cortex of the brain and descend through the brainstem or spinal cord to synapse with lower motor neurons in the brainstem or spinal cord. They are responsible for initiating voluntary muscle movements and exerting inhibitory or faciliatory control over lower motor neurons

Question 2

What are lower motor neurons?

Answer 2

Lower motor neurons; Are located in the anterior horns of the spinal cord or in the brainstem motor nuclei. They directly innervate skeletal muscles, conveying commands from the upper motor neurons to muscles

Question 3

Describe the descending pathway of upper motor neurons

Answer 3

UMNs descend from the cortex through the deep while matter of the cerebrum to form the internal capsule
- These tracts make up the pyramids upon entering the medulla and constitute the lateral and anterior corticospinal tracts .
most of the fibres (70%) in the corticospinal tract cross over to the opposite side of the brain over in medullary pyramidal decussation.
The tract separates into two parts, which have control over different domains of the musculature.
These are axial and appendicular for the anterior and lateral corticospinal tracts, respectively.

Question 4

What is the pathway of lower motor neurons?

Answer 4

These neurons originate in the anterior gray horn of the spinal cord and also the cranial nerve nuclei in the brainstem.
They innervate skeletal muscles directly as part of the final common pathway.

Question 5

What main effects arise from upper motor neuron lesions?

Answer 5

In UML, the corticospinal tract helps in the regulation of lower motor neurons. If we damage UMNs, there is a loss of inhibitory tone of muscles leading to constant contraction of muscles.

Effects of upper motor neuron lesions mainly constitute hypertonia and hyper reflexia with effects occuring in groups of muscles.

Question 6

What main effects arise from lower motor neuron lesions?

Answer 6

In LML, there is damage or loss of neurons thus nothing to tell the muscles to contract hence resulting in hypotonia and flaccid paralysis

Effects of lower motor lesions mainly constitute hypotonia and flaccid paralysis with effects occuring in individual muscles

Question 7

Compare the UMN lesion to the LMN lesion

Question 8

What causes motor neuron lesions?

Answer 8

1. UMNLs
   Can be caused by anything that causes damage to the brain such as stroke, tumours or infection.
   Can also arise from spinal cord or brainstem injury especially to the tracts in the white matter.
   Associated with stroke, multiple sclerosis, B 12 defiecinecy and amyotrophic lateral sclerosis
2. LMLs
   Can be caused by injury to the axons leaving the spinal cord as well as injury to the ventral gray horn
   Associated with Poliomyelitis, cauda equine syndrome