7. Motor Systems II Flashcards
cortical areas:
general functions
- fine motor control
- volitional/voluntary movement
brain stem: general functions
- face and head muscles
- automatic control
- posture and balance
spinal cord:
general functions
- trunk and extremity muscles
- reflex movements
- repetitive movements
list the tracts from the:
cerebral cortex
- corticoSPINAL (lateral & anterior)
- corticoBULBAR
- corticoRETICULAR
list the tracts from the:
brainstem
- RETICULOspinal, medial/lateral
- VESTIBULOspinal, medial and lateral
corticoSPINAL tract:
actions
- volitional control
- trunk and extremities
- fractionating finger movements (moving each one separately)
- precision grip
corticoBULBAR tract:
actions
- volitional control
- muscles of mastication
- facial expression
- tongue
- vocal cords
corticoRETICULAR tract:
actions
- volitional movement
- cortical drive to neurons of reticulospinal tracts
- reaching
- power grip
RETICULOspinal tract:
actions
- postural control of proximal limb and trunk muscles
VESTIBULOspinal tract:
actions
- lateral - postural control
- medial - part of the system to coordinate head and eye movements
how are the descending motor systems
(involv. in movement of trunk/extremities) divided?
which are included in each?
- medial (anterior funiciulus and ventromedial portions of lateral funiculus)
- VESTIBULOspinal - from brainstem
- RETICULOspinal - from brainstem
- CORTICOspinal - from cerebral cortex
- lateral (in lateral funiculus)
- *mostlylateral corticospinal tract
origins contributing to the corticoSPINAL tract
- postcentral gyrus
- primary motor cortex
- premotor cortex
- supplementary motor cortex
postcentral gyrus of corticoSPINAL tract:
function
- efference copy
- informing sensory structures of motor plan to optimize use of proprioceptive feedback related to planned movement
primary motor cortex of corticoSPINAL tract:
function
- volutary movement
- fractionating finger movements
- control of distal limb muscles assoc. w/ volitional movements
- precision grip
premotor cortex of corticoSPINAL tract:
function
- voluntary movement
- reaching and power grip/grasping
- control of proximal limb muscles involved in volitional movements
supplementary motor cortex of corticoSPINAL tract:
function
- mental rehearsal of skilled movements
- volitional movement
somatotopy in primary motor cortex:
describe
- typically, the area of the body corresponds to a point on the primary somatosensory cortex (postcentral gyrus)
- The areas which are finely controlled (e.g., the digits) have larger portions of the somatosensory cortex whereas areas which are coarsely controlled (e.g., the trunk) have smaller portions
- *viscera do not have sensory locations on postcentral gyrus
medial descending motor pathways;
list and major function
- medially descending pathways
- anterior corticoSPINAL tract
- RETICULOspinal
- VESTIBULOspinal
- major fxn: control of axial and girdle muscles relating to posture and balance
VESTIBULOspinal tract:
info pathway
- receive information through the vestibulocochlear nerve about changes in the orientation of the head.
- The nuclei relay motor commands through the vestibulospinal tract
- part of medial pathway
MEDIAL reticulospinal tract:
origin
pons
LATERAL reticulospinal tract:
origin
medulla
reticulospinal tracts (medial & lateral):
functions
- automatic responses to postural changes to maintain posture/balance (works w/ vestibulospinal tracts)
- controlled by cerebral cortex via corticoreticular tract
- (corticoreticulo-reticulospinal system provides postural control required by volitional movement activities)
- walking
CC: upper motor neuron lesions
(mechanism/where damaged)
- lesions to descending motor neurons
- 2 types
- lesions to brain: involve corticospinal tract, and closely assoc. corticobulbar and corticoreticular tracts
- lesions to spinal cord: damages all of the descending motor tracts on either one side or both sides
which tracts are damaged when there is a lesion in the brain to the descending motor systems?
- corticoSPINAL tract, and the closely assoc.
- corticoBULBAR
- corticoRETICULAR
CC: upper motor neuron lesion
symptoms
Damage to corticospinal tract –>
- weakness, esp in distal musculature of the extremities
- unable to fractionate finger movements
- poor manual dexterity
- (an enduring deficit)
- alteration in stretch reflexes & muscle tone
- dec in stretch reflexes/muscle tone –> develops into
- exaggeration of stretch reflexes and muscle tone (hyperreflexia and hypertonia) (spasticity)
- spasticity –> difficulty w/ gait
- abnormal plantar reflex (Babinski)
CC: Babinski reflex
- In infants:
- NORMAL: due to delayed development of corticospinal tract, extension/dorsiflexion of large toe & fanning of other toes (extensor plantar response)
- In adults
- NORMAL: flexor plantar response; toes curl inward
- ABNORMAL: Babinski sign - extension/dorsiflexion of large toe & fanning of other toes
CC: hemiplegic (spastic) gait
- abnormal gait w/ damage to corticospinal tract
- unilateral weakness and spasticity with the upper extremity held in flexion and the lower extremity in extension. The foot is in extension so the leg is “too long” therefore, the patient will have to circumduct or swing the leg around to step forward.
comparison of upper and lower motor neuron syndromes:
muscle bulk
- upper motor: slight atrophy due to disuse
- lower motor: pronounced atrophy
comparison of upper and lower motor neuron syndromes:
status of voluntary movements
- upper motor: deficient-paralysis or paresis, esp of skilled movement
- lower motor: deficient- paralysis, final common pathway is interrupted
comparison of upper and lower motor neuron syndromes:
distribution of abnormalities
- upper: *never individual muscles – groups of muscles supplied by motor nuclei below level of lesion
- lower: segmental - limited to muscles inn. by damaged alpha motor neurons or their axons
lower motor neuron or nuclear infranuclear lesion:
CNS vs. PNS
These are lesions that involve the lower motor neurons:
- in the CNS, these lesions could damage cell bodies of the lower motor neurons (e.g. in ventral horn of spinal cord), or the axons of the lower motor neurons while they are sill in the CNS
- lower motor neuron lesions in the PNS just involve the axons of lower motor neurons, NOT their cell bodies
which of the following are signs on an UPPER MOTOR NEURON LESION?
- weakness
- atrophy
- fasciculations
- reflexes
- tone
- weakness
- reflexes
- tone
(w/ acute upper motor lesions, reflexes and tone may be decreased)
there may be SOME mild atrophy due to disuse
which of the following are signs on an LOWER MOTOR NEURON LESION?
- weakness
- atrophy
- fasciculations
- reflexes
- tone
- weakness
- atrophy
- fasiculations
another name for pyramidal tract
corticospinal tract
which tract(s) are considered extrapyramidal?
- corticoBULBAR
- corticoRETICULAR
- VESTIBULOspinal
- RETICULOspinal
difference between lesions in upper motor neurons (descending motor systems) and lower motor neurons
- upper motor neurons: destroys neurons & axons in cortex/brainstem that projects down to spinal cord to innervate lower motor neurons
- lower motor neurons: damage to neurons that project out of CNS to innervate muscle
CC: what is the long term consequence of upper motor neuron lesion?
- hyperreflexia and hypertonia
- (exaggeration of stretch reflexes and muscle tone)
- the combinaiton of the 2 is considered “spasticity” –> causes difficulty w/ gait
which type of motor neuron lesion is identified by:
significant musclular atrophy
*lower motor neurons;
upper motor neurons only have mild muscle atrophy over a long period of time due to disuse
which type of motor neuron lesion is identified by:
fasiculations
lower motor neuron lesion
