Term
| What are the 2 different courses that Pyramidal tract axons arising from the Cerebral cortex can take to innervate musculature? |
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Definition
Pyramidal tract axons arise from layer V cells in Frontal and Parietal cortex (30% from M1).
SHORT- Can cross over and go lateral, for distal musculature (interneurons and motor-neurons), or stay Ipsilateral and Medial for axial and proximal musculature (only interneurons)
1) At spino-medullary junction, 75-90% cross decussation and proceed in contralateral lateral corticospinal tract.
- They terminate either on interneurons or on alpha and gamma motor-neurons of Distal musculature
2) 10-25% of cells from layer V don't cross at the decussation, and instead proceed as Anterior corticospinal tract.
- They terminate in medial spinal grey mater and innervate interneurons for Axial and Proximal musculature. |
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Term
| What 3 characteristics define Brodman's area 4? |
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Definition
Area 4, or M1 is
1) Thickest region of cortex
2) Sparse, poorly defined layer IV (input)
3) Thick layer V with large pyramidal neurons called "Betz Cells" |
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Term
| What differentiates cells within M1 from cells within S1? What is similar? |
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Definition
1) Columns are not Modality-Specific in M1, but are in S1
- Cells within a column of M1 receive somatsosensory information from skin, muscles and joints of same limb they cause to move
2)
- Both contain distorted representations of different areas of the body.
- Both have columnar organization |
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Term
| How does activity within the Pyramidal tract mediate voluntary movements? |
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Definition
Mono- ad Polysynaptically co-activating alpha- and gamma-motorneurons innervating related (agonist) muscle groups and polysynaptically inhibiting motor units of antagonist muscles (greatest influence on distal musculature).
**Polysynaptically indicates involvement of interneuron** |
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Term
| What the differential clinical outcome of a lesion restricted to the area 4 vs. a lesion to the internal capsule? |
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Definition
Both precede crossing at the pyramidal decussation so we are looking for contralateral paresis. Distal extremities are more effected in both cases
1) Lesions to widespread areas of cortex or to the internal capsule leads to a characteristic UMN phenomenon with a babinski sign and Spastic paralysis (perhaps due to involvement of other, corticobulbar pathways)
2) Lesions restricted to area 4 lead to flaccid paralysis |
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Term
A patient presents with flaccid paralysis of their left side, especially their fingers.
What could be going on? |
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Definition
1) Corticospinal involvement from right side if it is an UMN phenomenon. Since it is flaccid, there is most likely a focal lesion to area 4.
2) Could be a LMN issue, but would look for atrophy and fasciculations as well in this case. |
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Term
| A patient presents with paralysis of the lower left face. What is going on? |
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Definition
UMN lesion on right side (Supra-nuclear Palsy)
Since the upper face is spared, the lesion must be rostral to the Pons, where the facial nerve and nucleus are located (which would effect upper and lower face)
Since the lower face receives only contralateral input from the cortex, the lesion must be on the right side. |
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Term
| How does activity of Pyramidal Tract Neurons modulate motor behavior? |
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Definition
SHORT- Provide "functionally-segregated" (ext vs. flexor with most recruited neurons sharing same function), "task specific" (amount of weight and complexity of action modulates discharge) commands to motor unit
1) Provide motor commands for motor unit (fire preceding contraction)
2) Discharge favors functionally related muscles (either Extensor or Flexor)
3) Amount of discharge is modulated by force required to achieve movement (i.e. if you add antagonistic weight, add discharge)
4) Complex movements involve large populations of neurons with "more or less," functions related to the movement.
5) The finer the movement, the greater the discharge. |
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Term
| What Frontal Motor Association Cortices modulate motor behavior and how? |
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Definition
1) Supplementary motor cortex (area 6)- Planning of action sequences, and execution of complex tasks
- More diffuse receptive fields than M1
- Receives a major input from basal ganglia through VLN of thalamus
2) Premotor Area (area 6, lateral to SMC)- Planning of sensory-guided limb movements (i.e. action sequences driven by visual and tactile stimuli)
- With lesion, see "grasp" reflex from hand touch. |
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Term
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Definition
- Inability to perform skilled voluntary movements in absence of paralysis or severe sensory loss.
- Due to impaired communication between Frontal and Parietal association areas, which is involved in using complex sensory information to produce correct strategies for skills voluntary control. |
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