Pathways

Question 1

What are the major divisions of the motor pathways?

Answer 1

Pyramidal
Extrapyramidal
Hypothalamospinal
Raphe-spinal

Question 2

What are the pyramidal pathways?

Answer 2

Corticospinals:

• lateral (90%) -decussate at pyramids
• anterior (10%) -decussate at level of action

Corticobulbars: cranial nerves

Question 3

What are the extrapyramidal pathways?

Answer 3

Medial:
-Rubrospinal -red nucleus

Lateral:

• Tectospinal -tectum (sup. and inf. colliculi)
• Vestibulospinal -vestibular nuclei
• Reticulospinal -reticular formation

Question 4

Hypothalamospinal pathway

Answer 4

hypothalamus -> preganglionics in lateral gray hord of spinal cord

Question 5

Raphe-spinal pathway

Answer 5

inhibitory, suppress pain

raphe nuclei

Question 6

What is the path of the corticospinal tract from Cortex to spine?

Answer 6

motor/premotor cortex -> internal capsule

• > cerebral peduncles -> basal pons
• > pyramids -> medulla
• > ventral gray horn of spinal cord

Question 7

Describe the lateral corticospinal tracts

Answer 7

• decussate in pyramids
• in lateral white columns
• precise, agile, skilled function of limbs

Question 8

Describe the anterior corticospinal tracts

Answer 8

• decussate in anterior commissure at the level of their LMN

* trunk (posture) and proximal limb movements

Question 9

Describe the corticobulbar pathways

Answer 9

• cranial nerves

* follow corticospinal tracts to brainstem -> terminate in/near motor nuclei of their CN

Question 10

Which CNs have bilateral or contralateral innervation?

Answer 10

all except for VII (lower face) are bilateral

Question 11

What is the mnemonic device for sensory vs motor CNs?

Answer 11

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Question 12

Describe the rubrospinal pathway

Answer 12

• red nucleus (reticular formation) -> lateral part of anterior gray horn
• goal directed movements, flexor muscles
• decussate in midbrain

Question 13

Describe the tectospinal pathway

Answer 13

• tectum (superior colliculus of midbrain) -> anterior gray horn (anterior columns)
• cross in midbrain
• coordinate head and eye: move head to/away from visual stimulus

Question 14

Describe the reticulospinal pathway

Answer 14

• medial reticular formation -> anterior gray horn (anterior columns)
• do NOT decussate
• medial (pontine) inhibitory
• lateral (medullary) tracts -extitatory
• basic posture and balance

Question 15

Describe the vestibulospinal pathway

Answer 15

• vestibular nuclei -> anterior gray horn
• the rest is like reticulospinal:
-do NOT decussate
-medial vs lateral tracts
-posture and balance

Question 16

Describe the spinothalamic tract

Answer 16

• pain, temp.
• 1st order neurons terminate in dorsal horn
• 2nd order neurons decussate within 1 segment by ventral commissure
• 3rd order neurons in ventral posterior nucleus of thalamus
• to somatosensory cortex

Question 17

Describe the gracilis and cuneatus (dorsal columns) pathways

Answer 17

• proprioception, discrimative touch from ipsilateral side of body
• 1st order neuron ascends to nucleus gracilis or cuneatus
• 2nd order neuron decussates in medulla
• terminate in ventral posterior nucleus of thalamus on 3rd order
• project to somatosensory cortex

Question 18

Describe the spinocerebellar tracts

Answer 18

• muscle spindles, golgi tendon organs, tectile receptors
• posture and coordination
• only above L3
• NO decussation

Question 19

Describe the anterior spinocerebellar tract

Answer 19

• muscle spindles, golgi tendon organs, tectile receptors
• posture and coordination
• decussate at level of insertion
• decussate a 2nd time right before cerebellum

Question 20

What are the differences between posterior and anterior spinocerebellar tracts?

Answer 20

Posterior:
• no decussation
• only above L3

Anterior:
• decussate x2

Question 21

What are the effects of an UMN lesion?

Answer 21

• spasticity (paralysis/paresis, hyper-reflexia, hypertonia)
• interruption of motor INPUT
• LMN stretch reflex intact
• lost inhibition of gamma motor neurone -> increases sensitivity of spindles to stretch -> hypertonia and hyper-reflexia
• no profound atrophy

Question 22

What are the effects of a LMN lesion?

Answer 22

• damage to either: ventral grey horn or axons
• lost alpha and gamma innervation to muscles and spindles
• lost deep tendon reflex
• flaccid muscle
• patchy atrophy
• fasciculation (visible twitches due to motor unit contraction)

Question 23

What are some causes of brown-sequard syndrome?

Answer 23

• penetrating trauma (gunshot, knife)
• blunt trauma (vertebral fracture, intervertebral disc herniation)
• space occupying lesion
• multiple sclerosis
• spondylosis
• ischaemic
• inflammatory -infections

Question 24

What are the consequences of a hemisection of the spinal cord (brown-sequard syndrome)?

Answer 24

At lesion level:
• ipsilateral lost all sensation
• ipsilateral flaccid (ventral gray horn: LMN lesion)

Below lesion level:
• ipsilateral spastic (lateral corticospinal tract UMN lesion)
• ipsilateral lost touch, proprioception (gracile & cuneate)
• contralateral lost pain and temp. (spinothalamic tract)
-Incontinence

Question 25

What is the special risk of high cervical lesions?

Answer 25

phrenic nerve -> respiratory paralysis

Question 26

What tracts are located in the internal capsule?

Answer 26

Anterior limb: corticopontine and thalamocortical

Genu: corticobulbar

Posterior limb: corticospinal, thalamocortical