Descending Tracts Of The Spinal Cord

Front 1

Where are somatic motor neurons concentrated?

Back 1

1. Ventral horn

Front 2

What are lower motor neurons?

Back 2

1. Motor neurons that innervate extrafusal muscle fibers

2. Leads to contraction

3. AKA: alpha motor neuron

Front 3

What are the ssx of lower motor neuron dysfunction?

Back 3

1. Muscle weakness or paralysis

2. Hyporeflexia or areflexia

3. Muscle atrophy

4. Fasciculations

Front 4

Where are visceral efferent neurons located in the spinal cord?

Back 4

1. Lateral column

Front 5

In what is the pyramidal motor system involved?

Back 5

1. Volitional, skilled movements to achieve a behavioral goal

2. Determines direction and force of a particular movement

Front 6

What are upper motor neurons?

Back 6

1. Cell bodies in cortex

2. Send long axons to synapse on a lower motor neuron in brainstem or spinal cord

Front 7

What is the location of the primary motor cortex?

Back 7

1. Precentral gyrus

Front 8

Where are upper motor neuron cell bodies located (layer)?

Back 8

1. Expanded layer 5

Front 9

What regions of the body dominate the homunculus?

Back 9

1. Movements of the face and hands

Front 10

Where do axons in the spinal cord gather as they descend?

Back 10

1. Posterior limb of the internal capsule

Front 11

What is the organization of fibers in the internal capsule?

Back 11

1. Neck and upper limb fibers are anterior

2. Fibers to the foot are located posterior

Front 12

Where do descending corticofugal axons come together?

Back 12

1. Middle 3/5 of the crus cerebra of the midbrain

Front 13

What are the medullary pyramids?

Back 13

1. Convergence of fibers on ventral medulla

Front 14

What forms the lateral corticospinal tract? What muscles does it control?

Back 14

1. Corticospinal fibers that cross in the lateral funiculus

2. Terminate on enlargements where they control limb movmenets

Front 15

What forms the ventral corticospinal tract? What muscles does it control?

Back 15

1. Fibers that do not decussate

2. Descent in medial part of ventral funiculus

3. End bilaterally--- control axial and limb girdle muscles

Front 16

What are the ssx of pyramidal motor fiber destruction?

Back 16

1. Loss of volitional movement in affected areas

2. Spasticity

3. Clonus

4. Positive Babinski sign

5. Mild atrophy

Front 17

What is the red nucleus?

Back 17

1. Large nucleus in the tegmenjtum of the midbrain

2. Axons form rubrospinal tract

Front 18

Where do fibers from the rubrospinal tract descend?

Back 18

1. Cross midline

2. Descend through the brainstem and continue into the spinal cord in close proximity to lateral corticospinal tract

Front 19

What is the function of rubrospinal fibers?

Back 19

1. Excitatory to motor neurons in the cervical enlargement

2. Serve upper limb FLEXORS

Front 20

From where doe the red nucleus receive input?

Back 20

1. Motor cortex

2. Cerebellum

Front 21

What tracts of the extrapyramidal system descend in the ventral funiculus from the reticular formation?

Back 21

1. Lateral reticulospinal tract

2. Medial reticulospinal tract

Front 22

With what do reticulospinal tracts synsapse?

Back 22

1. Gamma motor neurons on EXTENSOR muscles of trunk and limbs

2. Modulate overall muscle tone

Front 23

From what does the brainstem reticular formation receive input?

Back 23

1. Cerebral cortex

2. cerebellum

Front 24

What is the function of vestibulospinal tracts?

Back 24

1. Form part of reflex circuits

2. Use vestibular sensory inputs to maintain posture

Front 25

What do the vestibulospinal tracts excite?

Back 25

1. Alpha motor neurons that innervate paravetebral extensors and proximal limb extensors

Front 26

What modulates the output of the vestibular nuclei?

Back 26

1. Cerebellum

Front 27

What pathways participate in reflex turing of the head toward unknown auditory or visual stimulation?

Back 27

1. Medial longitudinal fasciculus

2. Tectospinal tract

Front 28

What does the medial longitudinal fasciculus interconnect?

Back 28

1. Nuclei of oculomotion

Front 29

From where does the tectospinal tract originate?

Back 29

1. Superior colliculus

2. Descends to reflex centers to direct head

Front 30

What modulates the relay of sensory stimuli to higher levels in supra spinal pain modulation?

Back 30

1. Descending axons in the lateral corticospinal tract that arise from somatosensory cortex

2. Synapse on cells of dorsal horn

3. Enkephalinergic neurons inhibit cells whose axons signal pain

Front 31

Where does the pyramidal system originate?

Back 31

1. Motor cortex

Front 32

What is the extrapyramidal system?

Back 32

1. Descending tracts that do NOT originate in the motor cortex

Front 33

Where does the medial reticulospinal tract originate?

Back 33

1. Neuronal somata in the medial vestibular nuclei

2. Descends bilaterally to cervical spinal cord

Front 34

Where does the lateral reticulospinal tract originate?

Back 34

1. Lateral vestibular nuclei

2. Descends ipsilaterally to all levels of spinal cord