Week 3 Motor Pathways Flashcards
Where are the lower motor neurons of the neck, trunk, and limbs found? What about for the head?
- in the spinal cord
- neurons that control the proximal muscles are medial in the ventral horn
- neurons that control distal muscles are lateral - Cranial nerve nuclei in the brain stem
Where are the upper motor neurons located?
motor cortex (primary motor cortex and FEF) and subcortical nuclei -neurons of corticospinal and corticobulbar are largely found in pre central gyrus and paracentral lobule
Where do the planning and programming of motor activity occur?
- supplementary motor area (SMA)- located on medial surface of frontal lobe anterior to paracentral lobule
- Premotor area (PMA)- located lateral to the SMA and anterior to the primary motor cortex
Describe the somatotopic arrangement and course of the corticospinal tract.
-Posterior limb of internal capsule: upper limb anterior to those for lower limb
-midbrain: passes through middle 3/5s of crus cerebri. Upper limb fibers more medial to lower limb
-Pons: passes the ventral part of pons, despised among pontine nuclei.
-medulla: axons in upper medulla form pyramid. 75-90% of axons cross at junction of medulla and spinal cord
-spinal cord:
Lateral corticospinal tract: cross over, they follow this tract in the lateral funiculus
anterior: some cross over and some don’t, they follow the ACST in ventral funiculus and end bilaterally
Where are the cranial nerves with somatomotor components located?
CN III: upper midbrain CN IV: lower midbrain CN V: mid pons CN VI: lower pons CN VII: lower pons CN IX and X: upper medulla CN XI: upper 5-6 segments of spinal cord CN XII: upper medulla
Describe the origin and course of the corticobulbar tracts.
-origin: Primary motor cortex close to lateral sulcus (also from PMA, SMA, general sensory cortex, sensory assoc areas)
-corona radiata: mixed with CST
-internal capsule: at genu of posterior limb, anterior to CST
-midbrain: media to CST fibers
-pons and pyramid: mixed with CST and indistinguishable
Axons leave Corticobulbar tract at level of cranial motor nuclei
Corticobular tracts for which cranial nerve nuclei end bilaterally?
CN V: medially at middle 1/3rd of pons
CN IX and X: nucleus ambiguus
CN XI: C2-C5 levels
Corticobular tracts for which cranial nerve nuclei end contralaterally?
CN XII (actually bilateral but contralateral input predominates) -in the upper medulla
Corticobular tracts for which cranial nerve nuclei end bi- and contra laterally? Describe it.
CN 7 facial nerve
- upper group of neurons innervates upper facial muscles
- Bilaterally: LMNs that innervate upper face
- Contralateral: LMNs that innervate lower face
A UMN lesion anywhere along the corticobulbar tract of CN VII will result in what?
- normal upper face due to bilateral sparing (can wrinkle forehead)
- contralateral lower facial paralysis
What will a LMN lesion along the coriticobulbar tract of CNVII cause?
Bell’s palsy
-paralysis of entire half of face ipsilateral to lesion
What do UMN lesions of the corticobulbar tract of CN XII result in?
contralateral tongue weakness
What do LMN lesions of the corticobulbar tract of CN XII result in?
Ipsilateral tongue weakness
What are corticospinal tracts essential for?
- voluntary control of contralateral skeletal muscles of neck, trunk, and limbs.
- voluntary activity in response to sensory
- rapid finely coordinated movements
What are corticobulbar tracts essential for?
-voluntary contractions of the muscles of the head by V, VII, IX, X, XI, XII
