Neuronal Pathways: Motor (Efferent - Descending)

Question 0

What is the Direct pathway (pyramidal tracts)?

Answer 0

Descend from the motor cortex regions & do not synapse until reaching the correct spinal cord level.

Question 1

What are the 2 groups descending tracts are divided into?

Answer 1

1. Direct pathways = pyramidal tracts

2. Indirect pathways = extrapyramidal tracts.

Question 2

What is the indirect pathway? (Extrapyramidal)

Answer 2

Descend from sub-cortical motor nuclei (cerebellum, basal ganglia, etc) & are multi-synaptic, complex and often influenced via reflex activity.

Question 3

Motor pathways involve how many neurons? What are there names?

Answer 3

2

Upper motor neuron

Lower motor neuron

Question 4

What are the UMN?

Answer 4

Pyramidal cells of the motor cortex & the neurons of the subcortical motor nuclei (basal ganglia).

Question 5

What are the LMN?

Answer 5

Ventral horn motor neurons which directly innervate the skeletal muscles.

Question 6

What does the Direct (Pyramidal) System regulate?

Answer 6

Fast & fine (skilled) movements.

Question 7

Where does the Direct Pyramidal System originate?

Answer 7

Fibers originate in the pyramidal neurons in the primary motor cortex & related motor cortices.

Question 8

Where do Direct Pyramidal System impulses go?

Answer 8

Descend corticospinal tracts and synapse in the ventral horn (with an Interneuron or directly to a LMN); innervate skeletal muscle.

Question 9

Where do the lateral tracts of the Direct Pyramidal System decussate?

Answer 9

At the medullary pyramids.

Question 10

Corticobulbar tracts are apart of what pathway & innervate what?

Answer 10

Direct Pyramidal System

Innervate cranial nerve nuclei

Question 11

What does the Indirect (Extrapyramidal) System affect?

Answer 11

Modulates pyramidal output, affecting:

• axial muscles that maintain balance
• muscles controlling coarse movements of the proximal limb joint
• control of complex multi-joint movements
• head, neck & eye movement coordination.

Question 12

Where do Indirect (Extrapyramidal) System fibers originate?

Answer 12

In the basal ganglia, substantial nigra, cerebellum, various brain stem vestibular nuclei & some sensory cortex.

Question 13

Where do the Indirect (Extrapyramidal) System tracts go? What do they include?

Answer 13

Tracts descend through the reticular formation (pons & medulla) and include:

• reticulospinal tracts
• vestibulospinal tracts
• rubrospinal tracts
• tectospinal tracts

Question 14

Where does the reticulospinal tract originate? What does it do?

Answer 14

Origin: reticular formation

Maintains balance via posture.

Question 15

Where does the vestibulospinal tract originate? What does it do?

Answer 15

Origin: vestibular nuclei

Maintains balance via posture.

Question 16

Where does the rubrospinal tract originate? What does it do?

Answer 16

Origin: red nucleus

Control of flexor muscles

Question 17

Where does the tectospinal tract originate? What does it do?

Answer 17

Origin: superior colliculi

Mediates head & neck following eye movements