Lower Motor Neurone Flashcards
What is a lower motor neurone?
A somatic motor efferent with a cell body in either laminae IX of spinal cord or cranial nerve motor nucleus
Its axon supplies skeletal muscle directly
What is the function of a motor neurone?
Supplies skeletal muscle to bring about displacement of limbs and set muscle tone
What does an activated motor neurone evoke?
Either a voluntary movement when commanded by UMN or a reflex movement when recruited by spinal motor circuits which do not involve the brain
Define a reflex
An involuntary, unlearned, repeatable, automatic reaction to specific stimulus that does not require the brain
What are the five components of the reflexed Arc?
Receptor or transducer Afferent fibre Integration Centre Effector fibre An effector
What is a stretch reflex?
A wired connection between a LMN and afferents of muscle length sense organs
What are the different types of stretch reflex?
Mono-synaptic
Di-synaptic
Tri-synaptic
Multi synaptic
Why are multisynaptic pathways not usually activated?
Due to inhibition by the reticulospinal tract and UMN’s so you usually just get a mono-synaptic response
Why does an action potential from muscle length receptors get sent to?
Brain via dorsal columns for conscious proprioception
Cerebellum via spinocerebellar tracts for unconscious proprioception
Directly to spinal motorneurones
This leads to contraction
If anything goes wrong with the muscle stretch reflex, where can the defect be?
Stretch receptors or afferents Synapses in the spinal-cord Motor neurone Neuro muscular junction Muscle
How does muscle tone arise?
LMN supply muscles with background electrical impulses which causes minimal contraction of the muscle and gives muscle tone this allows us to maintain body posture
Why do newborns not have muscle tone?
To facilitate birth via the birth canal
What happens to muscle tone in sleep?
Inhibited in deep REM sleep except for in: Respiratory muscles Extraocular muscles Urinary sphincter Anal spinchter
