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4 components of motor systems.
- descending projection pathways
- -motor neurons & interneurons
- -basal ganglia
- (during movements of the leg and the trunk by regulating skeletal muscles
what does hte motor systems of CNS regulate?
2nd component of the motor system is for what?
- for muscles of hte limbs and trunk
- -motor neurons and interneurons
where is the motor neurons and interneurons located in?
ventral horn and hte internal zone fo the spinal cord
Whats a parallel that exists for the muscles of the head?
cranial nerve motor nuclei and reticular formation in the brainstem
whats the 1st function of hte brainsteam?
to serve as the spinal cord for the head
whats the 3rd and 4th components of the motor system?
basal ganglia and cerebellum
where do the basal ganglia and cerebellum project?
does not project directly to motor neurons, but synapse on descending pathways and an important influence
Example of primary visual cortex? and what order in where?
seeing a cup; higher order in post parietal lobe (for id object)
example of prefrontal association areas?
- "get the idea"
- for maturation and cognition
examples of the premotor areas?
"plan of action"
example of cerebellum and basal ganglia
feedback control and movement intention
organization and function of descending pathways
1. motor control pathways
- 2. regulate somatic sensory processing: somatic sensory relay nuclei (brainstem) and dorsal horn neurons (spinal cord)
- eg. pain suppression triggering of motor reflexes damage -> spasticity
- 3. regulate ANS
- cortex, amygdala, hypothalamas, brainstem --> preganglionic autonomic nerves of brainsteam and sc
whats the 7 major descending motor control pathways from cerebral cortex/brainstem nuclei
- lateral corticospinal tract
- -ventral corticospinal tract
- corticobulbar tract (cranial n. motor nuclei)
- rubrospinal tract
- reticulospinal tract
- -vestibulospinal tract
- -tectospinal tract
which motor control pathways came from?
- from FRONTAL CORTEX
- lateral corticospinal tract,
- ventral corticospinal tract
- corticobulbar tract
- FROM BRAINSTEM NUCLEI:
- rubrospinal tract
- reticulospinal tract
- vestibulospinal tract
- tectospinal tract
what is interneuron connections?
sometimes an intermediary before motor neurons
what are 2 interneuron connections?
- segmental interneurons
- propiospinal neurons
what's segmental interneurons?
short branches within single spinal cord segment
what are Propiospinal neurons?
- projects for multiple spinal segments before synapsing onto motor n.
- long projections coordinating movements of upper and lower limbs; may transmit control signals lower, for some paths ending in cervical areas
- from lateral descending paths...
- lateral: limbs
- Medial: axial
What tract starts in the primary motor cortex?
lateral corticospinal tract
lateral corticospinal tract. where does it start and go?
start in primary motor cortex, decussation zone and lateral motor nuclei of cervical and lumbrosacral cord
why is the lateral corticospinal tract segmented?
red nucleus (magnocellular) to midbrain decussation to lateral intermediate zone and ventral horn
What does hte rubrospinal tract do?
- provides additional (residual) motor control
- -connection with the cerebellum
Medial (Ventral Corticospinal tract - pathways
Ipsilateral ventral column to bilateral projections to medial grey matter
What does the medial corticospinal tract control?
- Axial and girdle muscles
- -controls espeically for head, should, and upper trunk muscles
What ar ethe lateral descending pathways?
Rubrospinal tract and the lateral corticospinal tract
Reticulospinal tract pathways
- terminate in cervical cord
- but...secondary projections to propiospinal neurons may influence lower aixal muscles
- Pontine to ventral column
- Medullary reticular formation to the lateral column (ventrolateral)
What controls do the reticulospinal tract have?
autonomoic movements: posture and repetitve movements
Tectospinal tract pathways
- superior collulus (deep)
- -coordinate head and eye movements
vestibulospinal tracts pathways and controls?
- lateral vestibular n. to lateral vestibulospinal tract (to all spinal limbs)
- -medial n. - med tracts for control of head position (cervical only)
- -maintains balance
Motor regions of the cerebral cortex (front lobe)
Higher-order cortical regions
- planning movement
- -integration of info from diverse cortex
- a. bg à VA (thal) à
- supplementary motor area (bimanual
- coordination) ß
- prefrontal cortex
- cerebellum à
- VL (thal) à premotor cortex à reticulospinal tracts (control of girdle muscles).
- c. Cingulate motor areas (part of limbic system) –
- rhythmical movements (e.g., pedaling a bike).
- - may
- be important in triggering movements initiated by emotions and drives.
where does the descending projections go through?
- through Internal capsule and corticospinal fibers
- -posterior limb of the IC contains corticospinal tract
- -somatotropic: organization is maintained
pathways within Midbrain
- corticospinal tract courses in base of midbrain (basis pedunculi)
- -somatotopic organization is retained here
- -origin of tectospinal tract (superior colliculus) and rubrospinal tract (red nucleus) - these tracts cross close to their origins in midbrain
pathways within pons
descending cortical fibres are no longer on ventral surface --> dive deeper within the pons (and also branch up into fasciculi) among pointe and pontocerebellar fibres
medullary decussation & function
- nuclei of dorsal pons and medulla: start of vestibulospinal and reticulospinal tracts
- functions: reticular formation has mutliple projections, which makes this system highly integrative (ex. between motor and sensory)
- -analogous to intermediate zone of spinal cord
pathways thru medulla and decussation of corticospinal tract
- fibres from cortex collect on ventral surface, forming pyramids
- -decussations occurs in medulla -specifically of lateral corticospinal tract axons
spinal cord, inputs?
- motor pathways synapse on motor neurons of ventral horn and interneurons (segmental, propiospinal) of intermediate zone
- -generalized organization of grey and white matter
- -ventral horn: Rexed's laminae (VIII, IX)
- Intermediate zone: (Laminae VII)
motor terminations at various levels of spinal cord
- medially descending and terminating pathways ->girdle and axial muscles
- - cross-overs and bilateral connectivities: coordinates contaction during postural adjustments
lateral descending/terminating paths
- distal limb muscles
- terminations only evident in cervial and lumbrosacral segments (sensory limbs)
- medial input=continuous
- lateral input = interrupted
lesions of the descending cortical pathways
- lesions of posterior limb of internal capsule, ventral brainstem
- on 1 side produce a sequential series of symptoms (focus primarily on limb muscles)
- 1. flaccid paralysis (immed)
- 2. spasticity (a few weeks later)
Flaccid paralysis (immed)
-> decrease strength + muscle tone due to corticospinal interruption
spasticity (a few weeks later) ->
increase muscle tone + exaggerated reflexe (Babinski sign) due to reticulospinal and sensory input damage (decrease feedback)