L39 Corticospinal and Corticobulbar Fibers Flashcards
what cortex does motor planning?
prefrontal and limbic cortex
what cortex does production of motor programs?
premotor cortex (BA 6)
what cortex executes motor activity?
primary motor cortex (BA 4)
what do the premotor cortex pyramidal layer 5 cells that project via? what does it do?
corticospinal tract
excite motor neurons
what does the medial aspect of the premotor cortex contain?
the supplemental motor area
what do the layer 5 pyramidal cells of the primary motor cortex make excitatory synapses to?
LMN’s in the spinal cord both directly and indirectly via interneurons
what has a distinct somatotropic map?
primary motor cortex
where does the motor cortex receive input from?
- primary somatosensory (BA 3,1,2)
- post. parietal areas (BA 5,7) = integrates sensory info for motor planning
- basal ganglia (via thalamus and premotor area)
- cerebellum (via thalamus)
- visual center
- auditory center
- limbic and prefrontal areas
where does the premotor cortex receive input from?
- post. parietal area
- basal ganglia (via thalamus)
- cerebellum (via thalamus)
what does simple finger movement activate?
- motor cortex
- somatosensory
what does complex finger movements activate?
- premotor cortex
- supplemental motor cortex
what does rehearsed finger movements activate?
-supplemental cortex (programmed from rehearsal)
what is the predominant role of the lateral corticospinal tract?
voluntary contraction of distal flexor muscles of the limbs - reaching and walking
sensory input from the lateral corticospinal tract is constantly processed by the ____ and modified by the ___ and ____
cortex
BG
cerebellum
where does the corticospinal tract start?
pyramidal cells layer 5 of preCG
where does the corticospinal tract end?
contralateral anterior horn (gray matter) of the spinal cord where the UMN synapse on alpha-gamma LMNs
what is the route of the corticospinal tract?
- corona radiata
- internal capsule
- crus cerebri
- basilar pons
- pyramid (medulla)
- pyramidal decussation (causal medulla)
- (lateral) corticospinal tracts in spinal cord
- alpha/gamma LMNs
what do LMN lesions result in?
- paralysis/paresis
- areflexia/hyporeflexia
- atrophy/wasting
- faciculations due to denervation which show on EMG as fibrillations
what side, in relation to the damage, do LMN symptoms occur?
ipsilateral (same)
what are examples of LMN syndromes?
- ALS (Lou Gehrig’s disease)
- peripheral nerve damage (traumatic)
what do UMN lesions result in?
initially - flaccifity and arefleia due to spinal shock
after weeks - spinal cord circuits regain function and motor sx/sx emerge to include
-spastic paralysis (increase muscle tone)
-postitive babinski reflex
-hyperreflexia
in UMN lesions, above the lesion which side is affected?
contralateral to side of lesion
in UMN lesions, below the lesion, which side is affected?
ipsilateral to side of lesion
what are the symptoms of paraplegia?
- flaccid paralysis below lesion (spinal shock) then spasticity
- increase deep tendon reflex and clonus
- +Babinski reflex
- urine retention,
- painless bladder distension + overflow
- decrease flexor spasms
- loss of all somatosensory below
the lateral corticospinal and corticobulbar tracts are the most important motor pathways that arise in the primary motor cortex and overlap with what?
- precentral gyrus (lateral)
- anterior paracentral lobule (medial)
how do the thalamus permit regulation of the motor cortex?
by BG and cerebellum
*BG and cerebellum does not control LMN, they talk to motor centers, so they can INDIRECTLY regulate LMN
what is the medial premotor (supplementary) area involved in?
planned sequences
what is the lateral premotor areas involved in?
sensory-guided movements
axons forming these two are the same - if you damage one, you will get degenerations of the other.
crus cerebri
pyramids
the continuous axons from crus cerebri to pyramid are not visible on the ventral surface of the pons, given the presence of _____ which form the middle
cerebellar peduncles.
superficial transverse pontine fibers
which part of the internal capsule do the corticospinal and corticobulbar fibers run?
posterior limb of internal capsule
A minority of corticospinal fibers (typically arising from parietal areas) will
terminate in the _____ presumably to regulate sensory inputs.
dorsal spinal gray matter
The upper motor neurons
commonly release glutamate onto
AMPA receptors, either directly or
indirectly activating ______
alpha / gamma LMN
when does paraplegia occur?
after spinal cord injury
