What are the major divisions of the motor pathways?
Pyramidal
Extrapyramidal
Hypothalamospinal
Raphe-spinal
What are the pyramidal pathways?
Corticospinals:
- lateral (90%) -decussate at pyramids
- anterior (10%) -decussate at level of action
Corticobulbars: cranial nerves
What are the extrapyramidal pathways?
Medial:
-Rubrospinal -red nucleus
Lateral:
- Tectospinal -tectum (sup. and inf. colliculi)
- Vestibulospinal -vestibular nuclei
- Reticulospinal -reticular formation
Hypothalamospinal pathway
hypothalamus -> preganglionics in lateral gray hord of spinal cord
Raphe-spinal pathway
inhibitory, suppress pain
raphe nuclei
What is the path of the corticospinal tract from Cortex to spine?
motor/premotor cortex -> internal capsule
- > cerebral peduncles -> basal pons
- > pyramids -> medulla
- > ventral gray horn of spinal cord
Describe the lateral corticospinal tracts
- decussate in pyramids
- in lateral white columns
- precise, agile, skilled function of limbs
Describe the anterior corticospinal tracts
- decussate in anterior commissure at the level of their LMN
* trunk (posture) and proximal limb movements
Describe the corticobulbar pathways
- cranial nerves
* follow corticospinal tracts to brainstem -> terminate in/near motor nuclei of their CN
Which CNs have bilateral or contralateral innervation?
all except for VII (lower face) are bilateral
What is the mnemonic device for sensory vs motor CNs?
Some Say Marry Money; But My Brother Says Big Boobs Matter More
Describe the rubrospinal pathway
- red nucleus (reticular formation) -> lateral part of anterior gray horn
- goal directed movements, flexor muscles
- decussate in midbrain
Describe the tectospinal pathway
- tectum (superior colliculus of midbrain) -> anterior gray horn (anterior columns)
- cross in midbrain
- coordinate head and eye: move head to/away from visual stimulus
Describe the reticulospinal pathway
- medial reticular formation -> anterior gray horn (anterior columns)
- do NOT decussate
- medial (pontine) inhibitory
- lateral (medullary) tracts -extitatory
- basic posture and balance
Describe the vestibulospinal pathway
• vestibular nuclei -> anterior gray horn • the rest is like reticulospinal: -do NOT decussate -medial vs lateral tracts -posture and balance
Describe the spinothalamic tract
- 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
Describe the gracilis and cuneatus (dorsal columns) pathways
- 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
Describe the spinocerebellar tracts
- muscle spindles, golgi tendon organs, tectile receptors
- posture and coordination
- only above L3
- NO decussation
Describe the anterior spinocerebellar tract
- muscle spindles, golgi tendon organs, tectile receptors
- posture and coordination
- decussate at level of insertion
- decussate a 2nd time right before cerebellum
What are the differences between posterior and anterior spinocerebellar tracts?
Posterior:
• no decussation
• only above L3
Anterior:
• decussate x2
What are the effects of an UMN lesion?
- 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
What are the effects of a LMN lesion?
- 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)
What are some causes of brown-sequard syndrome?
- penetrating trauma (gunshot, knife)
- blunt trauma (vertebral fracture, intervertebral disc herniation)
- space occupying lesion
- multiple sclerosis
- spondylosis
- ischaemic
- inflammatory -infections
What are the consequences of a hemisection of the spinal cord (brown-sequard syndrome)?
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
