Flashcards in Lecture 6: Descending Motor Pathways Deck (13):
What is an upper motor neuron?
Starts in CNS and synapses with either cranial nerve nucleus or in the ventral grey horn of the spinal cord.
What is a lower motor neuron?
Axons of LMNs pass from the ventral grey horn of the spinal cord (CNS) and cranial nerve motor nuclei brain stem (CNS) to muscles. From the spinal cord they will run in spinal nerves and from the brain stem they will run in cranial nerves.
What are the consequences of LMN lesions?
- Muscle wasting
- Muscle weakness/reduced power
- Absent tendon reflexes
What are the two types of UMN pathways?
- corticospinal (cortex to spine - spinal nerves) - corticobulbar (cortex to brainstem - cranial nerves)
What are the functions of UMNs?
- Influence LMN activity
- Modify local reflexes
- Superimpose more complex more complex patterns of movement
What happens after damage to the corticospinal tract only?
- flaccid paralysis of opposite limbs
- loss of tendon reflexes
After several days to a week motor function - - recovers but hypertonia
Left with permanent inability to carry out fine movements of hands and feet
Other pathways appear to take over most “corticospinal” functions
Where do descending fibres for the body pass through the internal capsule?
The posterior limb.
Where do descending fibres for the face pass through the internal capsule?
What percentage of UMNs descending contralaterally?
Where do UMNs contact cell bodies of the LMNs?
Contralateral ventral grey horn
What is the corticobulbar pathway?
- Influences LMNs in cranial
nerve motor nuclei
- Fibres originate laterally
within pre-central gyrus
- Innervation of LMNs is largely
bilateral (unlike corticospinal
pathway), with one/two exceptions (facial and hypoglossal).
Describe the innervation of the hypoglossal nerve nucleus.