Motor Systems Flashcards
(38 cards)
what is general flow of motor systems?
frontal lobes (motivation) —> premotor cortex (motor plan) –> primary motor cortex (action)
Frontal lobes
provide “motivation” or “ideation of motor plan”
- input comes from sensory stimuli in the parietal motor area as well as emotions/memory from the limbic system
premotor cortex? BA?
- motor plan
- provides “blueprint” or “module” for movement
- premotor cortex (lateral BA6)
- supplementary cortex (medial BA6 & BA8)
what are the two UMN system?
- primary motor cortex
- brainstem nuclei
- have action of LMN in spinal cord and cranial motor nuclei
- all systems converge on LMNs to produce movement, its the final common pathway.
alpha-LMNs
synapse on and innervate SKELETAL MUSCLE
- “final common pathway”
- always excitatory and release NT => contraction
- target is ipsilateral to soma
- very large
- found in spinal cord ventral rami and cranial n. motor nuclei
- have baseline activity, changed by excitatory and inhibitory synapses, to adjust firing rate
what is a motor unit
1 LMN and all of the m. fibers that it innervates
- 10 fibers/neuron = fine control, extraocular mm.
- 1000 fibers/neuron = gross postural control mm.
how do we regulate the strength of muscle contraction?
- recruitment- “size principle” = # motor units firing = more strength
(smallest motor units are recruited first) - AP frequency- increased AP frequency results in increased strength
general UMN characteristics
- locations: cerebral cx and brainstem nuclei
- UMN = axon from brain that influences a LMN, mostly indirectly through interneurons
- interneurons can be excitatory or inhibitory
- never synapse directly on muscle
- 8 different UMN pathways (2 from primary motor cx)
Lateral motor systems
influence distal limb mm.
- precise, fractionated mvmts
medial motor systems
axial/proximal limb mm.
- affects postural mvmts.
flexors/extensors? distal vs. proximal muscles? - orientation in spinal cord?
flexors are posterior in gray matter, extensors are more anterior
proximal musculature is more medial, distal limb musculature for fine mvmts are more lateral
important features of lateral corticospinal tract
LCST:
- largest motor tract of humans
- contralateral projection
- some UMNs synapse directly on LMNs
- necessary for critical and complex fractionated mvmts of hands
- think “volition”, voluntary
anatomy of LCST?
comes from more than just BA4
- 1/3 from primary motor cortex
- 2/3 from frontal lobes and somatosensory cortex (“posterior parietal motor area” links motor activity, especially of hands to sensory input)
where is premotor cx of LCST located?
in lateral BA6 and 8
- active in motor planning at the start of voluntary unit (involved in blueprint and timing)
where is supplmenetary motor cx of LCST?
medial BA6
- involved in motor planning and interconnected with contralteral side = bimanual mvmt
- active right before movement takes place
- will instruct proper UMN to carry out movement
Corticobulbar tract
similar to corticospinal but it terminates in brainstem
- influences:
- cranial nerve motor nuclei (LMNs) of facial expression/chewing
* influences nuclei bilaterally - UMN nuclei: gives voluntary control of proximal limb voluntary muscles
- vestibular nuclei
- reticular nuclei
- red nucleus
LMN damage?
- hypo- to areflexia
- hypo- to atonia
- paralysis/paresis (varying)
- flaccidity (limp)
- RAPID/SEVERE ATROPHY (due to loss of trophic relationship with motor neuron- “neurogenic atrophy”)
- EMG changes: see spontaneous activity in mm.
paralysis vs paresis
paralysis = complete loss of mvmt paresis = partial loss of movement
UMN damage?
hyperreflexia
- increased stretch reflex –> hypertonia
- appearance of pathological reflexes
- paresis/paralysis (spastic, esp. in antigravity mm.)
- disuse atrophy
- Few EMG changes
how are reflexes increased with UMN damage?
- loss of normal inhibitory background
- results in sprouting of local affarents (to increase input)
- also results in increased expression of receptors on surface of LMNs and interneurons (denervation hypersensitivity)
-plegia
literally means “stroke” = paralysis from stroke
paralysis
complete loss of voluntary mvmt
paresis
partial loss of voluntary mvmt
hemi, para, quadra
hemi = half
para = pair of limbs
quadra (or tetra) = four limbs
