Descending Pyramidal Motor Pathway

Question 1

Describe the basic structure of the descending pathway

What are the 2 functions of the descending motor pathway

Answer 1

Motor cortex =(UMN)=< o=(LMN)=

Modulate reflexes responses
Voluntary movement

Question 2

What are the 3 fibre types
Name some examples
What do they do

Answer 2

Projection

• join cortex with other areas of the CNS
• corticopetal (afferent)
• corticofugal (efferent)
  
  • CS, CT, CP

Association

• intrahemisphere connections
• short (within grey)
• long (between grey via white)

Commissural

• interhemisphere connections
• corpus callosum
• massa intermedialis

Question 3

What is the function of the CBT

• describe the innervation
• what are the exceptions to this

Answer 3

Motor cranial nerve innervation
-BILATERAL for head and neck

CONTRALATERAL only in

• VII lower face
• XII

Question 4

What is the function of the CST

• what are the 2 branches
• what do they innervate
• where do they decussate and synapse

how are the neurons organized in the SC

Answer 4

Lateral (limbs, trunk)

• medulla decussation
• synapse onto LMN, interneurons

Neurons organized by limb part

• lateral neurons => distal limbs
• medial neurons => proximal limbs

Anterior (neck, axial)

• BILATERAL
• SC decussation
• synapse onto LMN, interneurons

Question 5

Where do the CST, CBT start
What cells make up the UMN of this tract
What NT is released
What is the blood supply

Answer 5

Premotor
Supplementary motor
Primary motor

Betz cells release glutamate

ACA, MCA

Question 6

What structure do the fibres form
What structure do they pass through
-how does this structure relate to the motor homunculus
-describe the blood supply of this structure
-which fibres pass through each section

Which arteries are vulnerable to stroke/aneurysm and why

Answer 6

Corona radiata, pass through int capsule

Post limb (peripheral limbs, CS) MCA + AchA 
Genu (face, CB) MCA
Ant limb (CP) MCA + ACA

Lenticulostriate at right angles to MCA

Question 7

What structure in the midbrain get branches from the tract
-what are their functions

What is the blood supply of this region

Answer 7

Red nucleus - locomotion
Sup coll - head mv from visual stimuli
III, IV - BILATERAL eye mv
Substancia nigra - BG, mv

Basilar
SC
PIC

Question 8

What structures in the pons get branches from the tract
-what are their functions

What is the blood supply of this region

Answer 8

Pontine nucleus
V-VII - BILATERAL except VII lower (contralateral)
Reticular formation

Basilar
SC
AIC

Question 9

What structures in the medullae get branches from the tract

What is the blood supply of this region

Answer 9

IX-XII

Vertebral
Basilar
PIC
AS

Question 10

What is the blood supply of the lateral CST, anterior CST

Answer 10

Lateral CST
-PS

Anterior CST
-AS