Motor Pathways II Flashcards
Describe the role of the corticobulbar tract in motor control.
The corticobulbar tract controls voluntary movement of skeletal muscles in the head and neck by connecting UMNs in the cortex to LMNs in the brainstem’s cranial nerve nuclei.
Which part of the internal capsule does the corticobulbar tract pass through, and why is this location significant?
The corticobulbar tract passes through the genu of the internal capsule, positioning it close to the corticospinal tract which travels through the posterior limb, which controls voluntary motor movement of the body.
Where does the UMN come from in the corticobulbar tract?
lateral surface of primary motor cotex
What type of fibre is the UMN in the pathway?
supranuclear fibre
What structure travels close to the corticobulbar tract throughout it’s decent into the brainstem?
corticospinal tract
Which cranial nerves are exceptions to the rule of bilateral innervation in the corticobulbar pathway, and how are they unique?
CN VII (facial nerve) and CN XII (hypoglossal nerve) are exceptions.
CN VII’s lower face receives contralateral input only,
CN XII controls the tongue contralaterally, meaning a unilateral UMN lesion will produce distinct patterns of weakness.
What is the only muscle that receives contrallaterally innervation? (in the tongue)
what is it responsible for
genioglossus
protrusion of the tongue
What will a LMN motor neuron in the pathway be?
a cranial nerve
What function will cranial nerve cell bodies innervated by UMN’s have?
a motor function
What are differences between the corticospinal tract and corticobulbar tract?
corticobulbar - cranial nerves
corticospinal - spinal
What will a lesion to most cranial nerves upper motor neurons cause?
e.g CNIII
Lesions typically result in minor weakness (pseudobulbar palsy) in the affected muscles rather than full paralysis.
What clinical symptoms would arise from an upper motor neuron (UMN) lesion affecting the facial nerve (CN VII)?
An UMN lesion affecting CN VII would result in contralateral paralysis of the lower face with sparing of the upper face, due to bilateral innervation of the upper facial muscles.
How would a lower motor neuron (LMN) lesion in CN VII differ in presentation from an UMN lesion?
An LMN lesion in CN VII would cause complete ipsilateral facial paralysis, affecting both upper and lower facial muscles, as there is no alternate bilateral input to compensate.
What is the effect of a UMN (supranuclear) lesion to the hypoglossal nerve?
deviation of tongue, upon protrusion to the opposite (contralateral) side
What is the effect of a LMN (CNXII) lesion?
deviation of tongue, upon protrusion to the same (ipsilateral) side
