5.1.2 Central Motor Systems I Flashcards
Describe the Spindle load compensation mechanism.
What is the importance of Laminas VIII and IX? How are they arranged from medial to lateral?
- motor neuron groups in medial and lateral portions of the ventral gray
- Medial: LMNs for axial and proximal musculature
- Lateral: LMNs for distal muscles of arm/leg
What are the results of a transection of the spinal cord?
Paraplegia: loss of voluntary movement below level of lesions
- Results from interruption of descending pathways from motor centers in brain stem and higher centers
Loss of conscious sensation from below level of lesions
Initial loss of reflexes due to spinal shock
- Loss of excitation to alpha and gamma motor neurons
- Limbs flaccid, reflexes absent
- Partial recovery over time
What are the characteristics of the Tectospinal tract?
- Originates from superior colliculus in the midbrain
- Travels in the ventral column, primarily crossed and terminates on interneurons and motoneurons in cervical spinal cord
- Plays role in reflexive control of neck muscles in response to visual stimuli
- More developed in other animals
Transection above the level of the red nucleus will result in?
-Decorticate posturing and intact tonic neck reflexes
What are the 4 tracts in the ventral column of the white matter of the spinal cord? What do they control?
Vestibulospinal tract, Ventral reticulospinal tract, ventral corticospinal tract, and tectospinal tract
-Adjustment of proximal muscles and posture
What is the origin of the Reticulospinal tract?
Originates from reticular formation of medulla and pons
What are the characteristics of the Rubrospinal tract?
- Originates in red nucleus
- -Receives input from the contralateral deep cerebellar nuclei and motor cortex bilaterally
- Travels in lateral column to terminate on interneurons in spinal cord
-Largely crossed
-Controls distal limb muscles
- -Stimulates flexors
- -Inhibits extensors
Lesion in the Rubrospinal tract will lead to?
Little or no deficit
Compare Decerebrate and Decorticate postures.
Lesions in the Reticulospinal tract will lead to?
Severe impairment of axial/proximal muscles, loss of righting reflexes
What is the motor component of the corticospinal system?
Motor: motor cortex (precentral gyrus) ⇒ ventral gray of the spinal cord
-Acts on alpha and gamma motorneurons
What are the characteristics of the vestibulospinal tract?
Originates from vestibular nuclei
Primarily lateral vestibular nucleus (Dieters’ nucleus)
Terminates mainly on interneurons and motorneurons in anterior horn, mainly on ispilateral side
Plays role in facilitating anti-gravity muscles in order to maintain an erect posture
Somatic motor activity depends on and what does it integrate?
depends on pattern and rate of discharge of spinal motor neurons and homologous neurons in the motor nuclei of cranial nerves
Integrates activity of multiple inputs to regulate posture of body and make coordinated movements possible
What are the characteristics of UMN lesions?
reduced strength, hyperactive (spastic) reflexes, hypertonic (spastic, claspknife) tone, withdrawal spasms, abnormal reflexes
Lesion in the lateral corticospinal tract will lead to?
-Loss of fine motor control
What is the role of the corticobulbar tract?
face region of sensorimotor cortex ⇒ cranial nerve nuclei thru posterior limb of IC and middle portion of crus cerebri
Compare the Ventral vs Lateral Reticulospinal Tract.
Ventral - Fibers from pontine reticular formation and travel in ventral column
Lateral - Fibers from medullary reticular formaiton and travel in lateral column
What is the importance of coactivation of Gamma Motorneurons with alpha MNs?
- Coactivation increases spindle afferent activity which in turn further excites alpha motoneurons, assisting with the movement
- Coactivation also makes spindle system sensitive to changes in length resulting from external load perturbations
-Changes compensate for changes in external load
What is the sensory component of the Corticospinal System what are the characteristics?
primary somatosensory cortex (postcentral gyrus) ⇒ dorsal column nuclei
- Excite or inhibit dorsal horn and dorsal column neurons
- Modulates activity in the ascending systems and may allow screening out of routine stimulation of skin (aka adaptation)
- May also enable heightened sensation of interesting stimuli
What are the characteristics of LMN lesions?
reduced strength, muscle atrophy, hypoactive reflexes, hypotonic (flaccid), fasciculations but not abnormal reflexes
Both ventral and lateral reticulospinal tracts do what?
- Both tracts act primarily on extensors to modulate spinal reflex activity
- Pontine: stimulates
- Medullary: inhibits
Transection above the level of the lateral vestibular nucleus will result in?
-Decerebrate rigidity due to removal of central inhibition
Transection above the level of the pontine reticular formation will result in?
-Decerebrate rigidity
Lesions in the Vestibulospinal tract will lead to?
Severe impairment of axial/proximal muscles, loss of righting reflexes
What is included in the pyramidal tracts (3)?
corticobulbar
lateral corticospinal
ventral cortical spinal
What are the excitatory and inhibitory roles of the descending fibers of the spinal cord?
Excitation:
- -Descending fibers make direct, excitatory monosynaptic connections with both alpha and gamma motorneurons
- -Descending fibers can synapse with interneurons to excite spinal reflex pathways
Inhibition:
- -Descending fibers can synapse with interneurons to inhibit spinal reflex pathways
What are the 3 tracts in the lateral column of the white matter of the spinal cord? What do they control?
lateral corticospinal tract, rubrospinal tract, and lateral reticulospinal tract
-Skilled voluntary movements
Fill in this chart for corticospinal (pyramidal) and extrapyramidal syndromes
