Spinal Cord: Descending tracts & reflexes Flashcards
The primary motor cortex receives input from which 2 areas which lie anterior to it?
Supplementary motor area
Pre-motor cortex
How many neurons are there in descending motor tracts – what are they?
2 – upper motor neuron, lower motor neuron
What is a motor unit?
A LMN and the muscle fibres it innervates
What are the 2 main types of LMN and what does each innervate?
Alpha motor neurons – innervate motor units of extrafusal fibres
Gamma motor neurons – innervate intrafusal fibres of muscle spindles
Which tract and part of the spinal cord are degenerated in ALS?
Corticospinal tract
Ventral horn of the spinal cord
In ALS, are there UMN or LMN symptoms?
Both (mixed)
Polio affects which type of motor neuron?
LMN
What are the 3 main descending motor spinal tracts?
Lateral corticospinal tract
Ventral corticospinal tract
Lateral vestibulospinal tract
What is the output of the lateral corticospinal tract?
Primary motor cortex
Pre-motor cortex
Supplementary motor area
What is the output of the ventral corticospinal tract?
Primary motor cortex
What is the output of the lateral vestibulospinal tract?
Vestibular nuclei of pons & medulla
What does the lateral corticospinal tract control?
Major voluntary, skilled motor movement
What does the ventral corticospinal tract control?
Minor motor movement
What does the lateral vestibulospinal tract control?
Extensor muscle control (anti-gravity action)
Where do 80-90% of the descending motor fibres decussate?
Which tract do they descend as?
Pyramids of medulla – descend as lateral corticospinal tract
Where do 10-15% of the descending motor fibres decussate? Which tract do they descend as?
Close to termination (at the level of the LMN synapse) – descend ipsilaterally as the ventral corticospinal tract
What is the major motor pathway to the face?
Corticobulbar tract
Would UPM or LMN to the muscles in the head / neck be affected in a brainstem lesion?
LMN / LMN signs
Would UPM or LMN to the muscles of the body be affected in a brainstem lesion?
UMN / UPM signs
Would a brainstem lesion cause ipsilateral or contralateral muscle loss in the face (i.e. if the lesion was on the left side of the brainstem)?
Ipsilateral – LMN loss in left side of face
Would a brainstem lesion cause ipsilateral or contralateral muscle loss in the body (i.e. if the lesion was on the left side of the brainstem)?
Contralateral – UPM loss on right side of body
Which descending motor tract does not decussate?
Lateral vestibulospinal tract
Which condition includes a hemi-section of the spinal cord?
Brown-Sequard Syndrome
What is the name of the reflex that is engaged when you touch something hot?
What muscles does it stimulate and inhibit?
Flexor reflex
Stimulates ipsilateral flexors of limb
Inhibits ipsilateral extensors of limb
