Descending Motor System Flashcards
Paresis
partial weakness
Plegia
no voluntary movement
Paralysis
no voluntary movement
Palsy
weakness or no movement
Hemi
one side of the body
Para
both legs
Mono
one limb
Di
both sides of the body are equally affected
Quadri/Tetra
all four limbs affected
What is an upper motor neuron (UMN)?
Neurons with cell bodies in the motor cortex or brainstem whose axons descend in white motor tracts in the CNS to govern activity of lower motor neuron cell bodies
What is a lower motor neuron (LMN)?
Neurons with cell bodies in the spinal cord or brainstem with axons that project to muscles in the periphery
True or False
LMN are entirely contained in the PNS
False
Cell bodies of LMN are found in the CNS (spinal cord and brainstem)
What is an alpha motor neuron?
LMN with a large cell body and target in the skeletal muscle
Gamma motor neuron
LMN with a smaller axon diameter and target in muscles spindles to help control stretch reflex
Beta motor neurons
LMN that are fewer in number and innervate both muscles within and outside of the muscle spindle
Motor output is influenced by…
Basal ganglia
Cerebellum
True or False
Motor output pathways are organized based on their location in the spinal cord
True
UMNs are divided in medial motor systems or lateral motor systems
Describe the lateral motor system
- Descends in the lateral column of the spinal cord
- Synapse on lateral ventral horn with LMN or interneuron
- Controls distal limb muscles
- Consists of lateral corticospinal tract and rubrospinal tract
Describe the medial motor system
- Descends in the anteromedial columns of the spinal cord
- Synapse on medial ventral horn with LMN or interneurons
- Control proximal axial muscles
- Consists of anterior corticospinal tract, vestibulospinal tracts, reticulospinal tract, and tectospinal tract
What tracts are in the lateral motor system?
Lateral Corticospinal tract
Rubrospinal tract
What tracts are in the medial motor system?
Anterior Corticospinal tract
Vestibulospinal tract (medial, lateral)
Reticulospinal tract
Tectospinal tract
Describe pyramidal tracts
- Originate in cortex
- Terminate in brainstem or spinal cord
- Control volitional movement
- Corticobulbar and Corticospinal tracts
Describe extrapyramidal tracts
- Originate in brainstem
- Modulated by other inputs (cerebellum and basal ganglia)
- Terminate in spinal cord
- Involuntary and automatic control of muscle tone, balance, posture, and modulation of other motor plans
- Rubrospinal, Vestibulospinal, Reticulospinal, Tectospinal tracts
True or False
Only damage to pyramidal tracts will present with UMN signs
True
They are volitional pathways
Describe the Lateral Corticospinal Tract
Origin: primary motor cortex
Decussation: pyramidal decussation/cervicomedullary junction
Level of Termination: lateral ventral horn, cervical and lumbar enlargements of cord
Function: volitional movement of contralateral distal extremities
What structures does the lateral corticospinal tract travel through?
Corona radiata > internal capsule > cerebral peduncle > pyramids > decussation of pyramids > lateral column
What is the somatotopic organization of the cortex?
Legs are medial and arms are lateral
What is the somatotopic organization of all levels aside from the cortex?
Legs are lateral and arms are medial
What are key aspects of the Corticobulbar tract?
- Fibers project from cortex to brainstem
- Travel with corticospinal tract
- Some fibers terminate bilaterally on local circuit neurons, others provide direct input to contralateral LMN at CNN level (CN 5, CN 7, CN 12)
Describe the Rubrospinal Tract
Origin: red nucleus
Decussation: ventral tegmental decussation
Level of Termination: lateral ventral horn and intermediate zone, cervical cord
Function: movement of contralateral upper limb
What tract is suggested to innervate flexor muscles?
Rubrospinal tract
Flexor (decorticate) posturing will occur in upper extremities with a lesion to….
Corticospinal tract above the red nucleus
Extensor (decerebrate) posturing will occur in upper extremities with a lesion to…
Rubrospinal tract below the red nucleus
Describe the Anterior Corticospinal Tract
Origin: primary motor cortex
Decussation: some remain ipsilateral , some cross in ventral white commissure of cord
Level of Termination: cervical and upper thoracic
Function: bilateral axial and girdle muscles
Describe Medial Vestibulospinal Tract
Origin: medial and inferior vestibular nuclei
Decussation: descends bilaterally
Level of Termination: cervical and thoracic cord
Function: positioning of head and neck
Describe the Lateral Vestibulospinal Tract
Origin: lateral vestibular nucleus
Decussation: does not cross
Level of Termination: entire cord
Function: balance
Which Vestibulospinal tract is being described?
- input from semicircular canals
- bilateral
- neck and proximal shoulder muscles
- activates extensors
- align head with body
Medial Vestibulospinal Tract
Which Vestibulospinal tract is being described?
- input from otoliths
- ipsilateral
- proximal limbs and trunk muscles
- activates extensors and inhibits flexors
- postural alignment and balance
Lateral Vestibulospinal Tract
What do both the medial and lateral Vestibulospinal tracts do?
- Involuntarily activate extensors
- Use compensatory feedback to respond to postural instability detected by vestibular system
Describe the Reticulospinal Tract
Origin: pontine and medullary reticular formation
Decussation: does not cross
Level of Termination: entire cord
Function: automatic posture and gait-related movements
Describe the Tectospinal Tract
Origin: superior colliculus
Decussation: dorsal tegmental decussation
Level of Termination: cervical cord
Function: coordination of head and eye movement
