7 - Cortical Control of Motor Activity: The Corticobulbar Tract Flashcards
What is the function of cranial nerve? Where are their nuclei located?
Motor and sensory innervation of the head and neck, including special senses. Purely motor, purely sensory, and mixed.
CN nuclei locatin within the brainstem. Motor nuclei more medial and sensory nuclei on the sides.
Nucleus is associated with CNV and what does it innervate? What about CN VII?
CN V - motor nucleus of five; innervatio nof the muscles of mastication
CN VII: facial nucleus; innervation of the muscles of facial expression
Nucleus is associated with CN X and what does it innervate? What about CN XI?
CN X - nucleus ambiguous; muscles of the soft palate, pharynx, and larynx.
CN XI - acessory nucleus; innervates the SCM and trapezius
What nucleus is associated with CN XII? What muscles does it innervate?
Hypoglossal nucleus; intrinsic and extrinsic muscles of hte tongue.
Cranial nerves are _____ ______ _____ becasue they directly innervate muscles of the head and neck.
Lower motor neurons.
What is the corticobulbar (corticonuclear) tract? What is it’s function and what does it project to?
Upper motor neuron that projects to the lower motor neuron in cranial nerve motor nuclei of brainstem.
Controls muscles of the head, face and neck.
What is the route of the corticobulbar tract?
Begins in the precentral gyrus (primary motor cortex), through the corona radiata, and then corticonuclear fibers project through the posterior limb of the internal capsule (closer to the genu than CST fibers) and innervates LMNs of the CN motor nuclei.
Where is the corticobulbar tract located within a midbrain cross-section?
In the center of the crus cerebri next to where the corticospinal tract fibers are located.
In most cases, CN motor nuclei innervation by corticonuclear fibers is __________. What are the exceptions?
Bilateral.
Exceptions are CN VII and CN XII which are contralaterally innervated/
Describe the innervation of the facial nucleus?
Within the pons, the facial nucleus is divided into two parts: one controls the upper part of the face and the other controls the lower part of the face.
The part controlling the upper face recisves bilateral innvervation, while the part controlling the lower part recieves CONTRAlaterall input from the corticobulbar tract.
What happens if you have a unilateral lesion of the corticobulbar tract of the facial nucleus?
You get CONTRAlateral paralysis of the lower quadrant of the face only.
What happens if you have a peripheral lesion of cranial nerve VII? How can this be differentiated from a central CN VII lesion?
Bell’s palsy - this affects the half of the face on the side of the lesion. This differs from a central lesion of CN VII because that results in a contralateral paralysis only on the lower quadrant of the face.
What results from a central (aka upper motor neuron) lesion of the corticobulbar tract affecting the hypoglossal nucleus?
You lose innervation to the contralateral hypoglossal nucleus and those neurons cannot innervate that side of the tongue.
The tongue projects to the side OPPOSITE the lesion.
What happens if you get a peripheral lesion of the hypoglossal nerve?
The tonuge will deviate towards the side of the injury (licking your wounds).
How would you differentiate between an upper motor neuron lesion affecting the hypoglossal nucleus and a peripheral lesion affecting the hypoglossal nerve?
You would have to rely on the patient’s history to determine what type of lesion it is.
What is a pseudobulbar palsy? What are symptoms?
A bilateral lesion of upper motor neurons that make up the corticonuclear tract.
Weakness of muscles involved in chewing, dysphagia, disarthria (difficulty speaking). Loss of emotional control. Hyperreflexia of the soft palate and pharynx.
What are possible causes of pseudobulbar palsy?
Brainstem infarcts, ALS, MS.
What is bulbar palsy? What are symptoms and what can cause this?
A lower motor neuron paralysis affecting the muscles innervated by the CN whose nuclei are in the lower part of the brainstem.
Muscles tend to atrophy and there may be fasciculations.
Can be caused by ALS, cancers, neck trauma, and motor neuron disease.
What is the function of the corticobulbar tract? Which cranial nerve nuclei are contralaterally innervated?
Voluntary movement of the muscles in the head and neck such as smiling or spitting something out.
Facial nerve nucleus and hypoglossal nucleus.
