Motor Systems II Flashcards
Motor tract origin
Corticospinal tract
Corticobulbar tract- to brainstem, movement of face
Primary motor cortex
Area 4
Immediately Anterior to central sulcus
Primary motor cortex lesion
Paralysis
Paresis of specific muscle groups
Some recovery of function may occur due to cortical plasticity
Damage depends on part of human homunculus involved
Stroke brain regions
Always involve multiple cortical areas
Stroke involving occlusion of MCA
Affect almost all of one side of frontal lobe
Severe motor disability in all parts of contralateral body except for lower limb (supplied by ACA)
Infraction of proximal M1 segment of MCA
Affect blood supply of basal ganglia via lenticulostriate arteries
Affects blood supply to motor cortex
More disabling than stroke that affects motor cortex (M3) alone
The more proximal an infarction…
The more problems arise
Premotor and Supplementary motor cortex Damage
Areas 6 and 8
Motor Apraxia –> normal reflexes + no muscle weakness, but difficulty performing complex motor tasks
Impair motor response to visual or other sensory cues
Damage to 1 side –> minimal as contralateral side can take over
Posterior parietal cortex
Areas 7 and 19
Damage can lead to sensory apraxia –> difficulty performing complex motor tasks when triggered by sensory input
More a difficulty in linking a sensory input to the motor system
Damage to Broca’s area
Motor aphasia
Difficulty generating speech motor outputs
Difficulty linking word strings into complex sentences
–> can’t construct meaningful word sequences
Damage to Frontal Eye Fields
Oculomotor Apraxia (OMA)
Difficulty moving eyes horizontally + moving them quickly to follow moving object
Patient have to turn head to compensate
Interferes with motor programmes controlling voluntary eye movements
Can appear to have perception problems, but acc just have difficulty with eye movement motor programmes
Sensory apraxia
Damage to connections from posterior parietal lobe to premotor cortex
40% of Corticobulbospinal tract axons arise from..
Anterior parietal lobe (somatosensory cortex), which lies immediately posterior to central sulcus
- -> axons command down to spinal cord that modulate sensory input
- -> modulate reflexes
Dorsolateral prefrontal cortex
Areas 9 and 10
Planning of movement
Evaluate future actions
Problem solving and judgement
Dorsolateral prefrontal cortex lesions
Apathy
Personality changes
Lack of ability to plan or to sequence actions or tasks
Left hemisphere damage- poor working memory for verbal information
Right hemisphere damage- poor working memory for spatial information
Wisconsin Card Sorting test
Test for frontal lobe function
Orbitofrontal cortex
Area 11
Control (inhibition) of motor responses with limbic system
Responses to hunger, thirst, sexual drive
Orbitofrontal cortex damage
Pseudopsycopathic behaviour- impulsiveness, puerility, jocular attitude, sexual disinhibition, complete lack of concern for others
Motor thalamus
VL + VA thalamic nuclei
Only route for motor commands from basal ganglia + cerebellum to be fed into corticospinal tract
Basal ganglia + cerebellum project to motor thalamus –> motor cortex
Corticobulbospinal tract
Passes through internal capsule on way to brainstem
Vulnerable to stroke in this area
Corticobulbar tract- terminates on which cranial nerve nuclei
V + VII for cortical control of muscles of head
Oculomotor nuclei (III, IV + VI) for control of eye movements
Cells on pontine nuclei
Reticular formation
Red nucleus
Red nucleus
Large round nucleus in midbrain next to oculomotor nuclei
Corticospinal tract
Decussates in medullary spinal junction- to opposite side
Forms lateral corticospinal tract and small medial corticospinal tract
Motor decussation
Upper spinal cord C1-5
If brain injured above spinal cord/medulla junction, motor deficit on other side
If spinal cord injured, motor deficit on same side
CST effects
Monosynaptic connections- motor neurones of thumbs + digits
Motor actions initiated in other muscles by CST are mediated by actions of CST on spinal interneurones
CST damage
Loss of control of hands and fingers
Extrapyramidal system
Originate from groups of cell bodies in brainstem
Lateral vestibulospinal tract (2c)
Reticulospinal tract (2b)
Lateral vestibulospinal tract (2c)
Origin- vestibular nuclei in upper medulla/lower pons
Nucleus projects ipsilaterally to antigravity muscles
Tonically active during upright posture
Controls posture + balance
Reticulospinal tract (2b)
Arises in reticular formation of pons + medulla
Projects bilaterally down spinal cord
Responsible for autonomic control (drives preganglionic symp. neurones)
Drive to respiration (phrenic)
General arousal of spinal cord
Rubrospinal tract (2a)
Vestigial in humans
Origin- red nucleus in brainstem
Red nucleus receives main input from cerebellum
Carries cellular commands to spinal cord
Plays role in control of movement velocity
Plays role in transmitting motor commands from cerebellum to musculature
Red nucleus
Large nucleus in midbrain
Gives rise to rubrospinal tract + large ascending projection to motor thalamus
Activation- excitation of flexor muscles, inhibition of extensor muscles
Rubrospinal tract lesion
Slowness in movement
Minor extrapyramidal tracts
Tectospinal tract
Medial vestibulospinal tract
Tectospinal tract
Coordinates voluntary head and eye movements
Activates reflex movements of head in response to visual + auditory stimuli
Originates in superior colliculus
Receives afferents from retina
Terminates in laminae VI, VII and VIII
Medial vestibulospinal tract
Continuation of medial longitudinal fasciculus
Reflex co-ordination of head + neck muscles
Extraocular eye muscles- maintain objects in view despite movement
UMN act on
Most on interneurones
Only ones to directly act on LMNs are those driving muscles of thumb + fingers
Spasticity
Abnormally increased muscle tone
Increased tendon reflexes
UMN lesion
Clonus
Series of jerky contractions of a particular muscle following sudden stretching of muscle
Hyperreflexia
Abnormally brisk tendon reflex in 1 or more muscles
Decorticate posturing
Damage to corticospinal tract in midbrain
- -> Arms adducted and flexed
- -> Wrists + fingers flexed on chest
- -> legs internally rotated + stiffly extended
- -> Plantar flexion of feet
Decerebrate posturing
Severe injury to brain at level of brainstem, including damage to corticospinal + Rubrospinal tract
- -> arms abducted and extended
- -> Wrists pronate and fingers flexed
- -> legs externally rotated + stiffly extended
- -> plantar flexion of feet
Decerebrate posture MOA
Excessive activity (disinhibition) in extrapyramidal system
Damage to red nucleus
Only in unconscious
Decorticate posture MOA
Damage to CST
More favoured than decerebrate
Unconscious usually
Unilateral or bilateral
Hemiplegic dystonia
Persistent flexion of arms + extension of legs
Spinal shock- acute effects
Paralysis or paresis + reduced reflex responses in all muscles below region of injury
Spinal shock- chronic effects
Eventually wears off- days, weeks, months depending on severity
Exaggerated + hyperactive reflex
Clonus
Babinski sign
