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where is the motor cortex located?
posterior 1/3 of the frontral lobe, anterior to the central sulcus
what are the 3 subareas of the motor cortex?
- primary cortex
- premotor area
- supplementary motor area
each has its own topographical representation of mm groups and specific motor functions
what does the primary motor cortex contain? (what muscle groups are represented)
- face and mouth region
- arm and hand (in the midportions)
- trunk (near apex of brain)
- leg and foot (in the area that dips into the longitudinal fissure)
more than 1/2 of the the entire primary motor cortex is concerned with controlling what muscles?
hand and speech muscles
where in the motor cortex is the premotor area located?
anterior ot the lateral portions of hte primary motor cortex
what is the topographical orgainzation of the premotor area?
- roughly the same as the primary motor cortex:
- (primary mortor arrangement: face and mouth region, arm and hand (in the midportions), trunk (near apex of brain), leg and foot (in the area that dips into the longitudinal fissure))
what results from most signals generated in the premotor area (along with integrated info from other areas)?
cause patterns of movment that involve groups of muscles performing a specific task (exp: position the shoulders and arms so the hands are properly oriented to perform a task)
information from what other brain centers are integrated into signals from the premotor area?
basal ganglia, thalamus, and primary motor cortex
where in the motor cortex is the supplementary motor area?
just superior to the premotor area
what is the function of the supplementary motor area?
functions along with premotor area to provide fixation movements of the diff body segements, positional movements of the head and eyes which are necessary for fine motor control generated in premotor area and primary motor cortex
it assists the other motor areas w/ complicated movements
motor signals are transmitted DIRECTLY from the motor cortex to the spinal through what system/pathway?
pyramidal system/pyramidal pathway/corticospinal tract
motor signals are transmitted INDIRECTLY through pathways from where to the spinal through what system/pathway?
from basal ganglia, cerebellum, and brainstem nuclei using extrapyramidal system/extrapyramidal pathway ("subcortical motor pathways")
what are the different extrapyramidal pathways?
- these are small pathways which receive info from the cortex but generate their own output to the SC
- they DO NOT cross to the opp side of the SC
- 1. reticulospinalis tract
- 2. rubrospinalis tract
- 3. tektospinalis tract
- 4. vestibulospinalis tract
how many fibers from the sensoric pathways finish in the pre-central gyrus?
approx 40% of dorsal column fibers
where does the info in the corticospinal tract/pyramidal pathway original?
- 30% from primary motor cortex
- 30% from premotor and supplmentary areas
- 40% from somatic sensory areas
what is the path of information travel in the cortiospinal tract/pyramidal pathway?
- leaves cortex
- passes down btwn caudate nucleus and putamen through brainstem (medulla)
- at medulla, majority CROSS to opp side and descend in lateral corticospinal tract
- those that do not cross travel down the ventral corticospinal tract
what is the most important motor pathway we have?
the corticospinal tract/ pyramidal pathway
corticospinal tract fibers cross where?
- at the medulla
- but some stay on the same side
- "crossing of the pyramids"
fibers of the corticospinal tract that cross travel where in the spinal cord?
lateral corticospinal tract
fibers of the corticospinal tract that do not cross travel where in the spinal cord?
ventral corticospinal tract
what is the internal capsule?
- passageway through basal ganglia that is the most narrow part of communication btwn SC and higher brain areas
- common place for stroke (middle cerebral artery?)
what is the orientation of the fibers in the corticospinal tract/pyramidal pathway?
- opposite from that of the dorsal column fibers
- distal body parts are represented laterally
- proximal body parts are represented medially
where do the fibers from the corticospinal and extrapyramidal pathways terminate?
- most terminate on interneurons in the intermediate area of the spinal corde gray matter
- some terminate directly on anterior motor neurons
what fibers from the corticospinal and extrapyramidal pathways terminate directly on anterior motor neurons?
- fibers controlling the hands and fingers
- creates a direct route from brain to quickly activate muscle contractions
what happens if the primary motor cortex is removed?
- varying degrees of paralysis
- loss of voluntary control of discrete movements of distal limbs (esp hands and fingers)
- if caudate nucleus and adjacent premotor and supplementary motor areas are not damaged then gross postural and limb fixation movements can still occur
what parts of the brain are usually damaged in a stroke?
the motor cortex and corticospinal pathway
what happens if the primary motor cortex alone is damaged?
hypotonia bc this is the part of the brain that stimulates natural muscle tone (has a continuous excitatory effect on motor neurons of the spinal cord)
what happens if the primary cortex and adjacent cortical areas (esp basal ganglia) are injured?
spasms occur on the opposite side bc of damage to signals sent in extrapyramidal pathways that normally inhibit the vestibular and reticular brain stem nuclei
what happens when the brain stem nuclei lose the normal inhibition from the extrapyramidal pathway?
- they become spontaneously active and cause excessive spastic tone
- (normally accompanies a stroke)
what parts of the brain make up the brain stem?
medulla, pons, and mesencephalon
what is the brain stem's roll?
- to control body movements
- (reticular and vestibular nuclei are main components of this control)
what are the divisions of the reticular nuclei?
- pontine and medullary nuclei
- (are antagonistics)
what type of signals do the pontine nuclei of the brain stem recticular nuclei transmit?
they have a high spontaneous excitability that is enhanced by signals from vestibular nuclei
what type of signals do the medullary nuclei of the brain stem recticular nuclei transmit?
- no spontaneous activity
- transmit inhibitory signals to antigravity muscles after being activated by signals from pyramidal/extrapyramidal pathways
what happens in way of paralysis and spasticity if there is a complete SC cut?
- paralysis at the level of the cut
- spasticity below that gradually develops once spinal shock wears off (immediately after injury, will experience flacid paralysis below the cut - regain natural excitability a few hrs to a few weeks after)
spinal cord motor functions are mainly localized in what part of the cord?
what are the different spinal cord neurons that are responsible for motor functions?
- anterior motor neurons (alfa and gamma)
what is the role of alpha neurons in the SC?
- (anterior motor neurons)
- transmit signals into skeletal muscles at the MU
what is the role of gamma neurons in the SC?
- (anterior motor neurons)
- innervate intrafusal fibers in muscle spindles to create muscle tone
what is the role of interneurons in the SC?
responsible for motor neuron interconnections (Renshaw cell inhibitory cells)
what is the main function of the spinal cord?
control of involuntary motor movements (reflexes)
types of reflexes controlled by the SC?
- myotactic reflex
- golgi tendon reflex
- flexor reflex
- crossed extensor reflex
what is the flexor reflex?
- a reaction on almost any type of cutaneous stimuli
- elicited most powerfully by pain
- aka withdrawal reflex
- based on reciprocal inhibition
what is the crossed extensor reflex?
- activates flexors of one limb and extensors of another
- can push entire body away from painful stimulus
- based on reciprocal innervation
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