Pt13 Central Control Of Movement Flashcards
What are the 2 forms movement can be divided into?
- Flexor muscles
-learned, voluntary, conscious, skilled
-discrete contraction of few muscle groups
-distal to spinal cord - Extensor muscles
-postural, antigravity, subconscious, involuntary
-long term contraction of lg group of muscles
-located closer to spinal cord (proximal & axial)
How are the 2 types of movements controlled?
by the nervous system
-FLEXORS: lateral system (lateral funiculus) of lower & upper motor neurons
>UMN tracts inhibitory to extensors, facilitatory to flexor
>corticospinal
>rubrospinal
>medullary reticulospinal
-EXTENSORS: medial system (ventral funiculus) of neurons & tracts
>UMN tract inhibitory to flexors, facilitatory to extensors
>pontine reticulospinal
>vestibulospinal
What is the organization of the CNS structures that control movement?
- Simple movement/movement patterns
-caudal regions of CNS - Complex/skilled patterns
-rostral regions of CNS
What is voluntary movement directed by?
-primary motor cortex
-initiated by CC
>cerebellum
>basal nuclei
>spinal cord
>brainstem
Describe the higher level VS lower level motor system hierarchy.
- Higher order: action, sequence of actions, coordination of activity of limbs
>CC, cerebellum, basal nuclei - Lower order: force & velocity of muscles, changes in posture
>LMN, brain stem, spinal cord
Describe the spinal cords role in movement control.
-contain alpha LMN innervating skeletal muscle
-interneurons & complex neural circuits = spinal reflexes
-low level commands = generate forces on muscle groups
>LMN can recruit more motor units or increase freq of AP to control amount of force on muscle
># of muscle fibers innervated by LMN decreases as need for fine control of muscle increases
How is posture maintained by the motor system?
- Tonic excitatory bias to motor circuits that excite extensor muscles (antigravity)
stretch reflex = contracts extensor muscles whenever stretched by postural changes - Modulate stretch reflex circuits
Describe the gamma loop.
CNS modulates stretch reflex & muscle tone by modulating the gamma loop
-higher motor center via reticulospinal tract activates gamma motor neuron innervating the muscle spindle
-causes increase in firing of sensory fibers
-excitation of alpha motor neuron innervating the extensor muscle = contraction
Describe the relationship between postural support & the stretch reflex.
-the quads, hock extensor muscles, & hepaxial & hypaxial muscles stretched by gravity = reflex stimulated contraction & posture support
Describe what walking depends on.
-know initial starting position & force applied to limb
-proprioceptive info by golgi tendon & muscle spindles (also imp for spinal reflexes - motor control)
-walking = extension & flexion via spinal cord reflexes
>stretch reflex -> (muscle spindle) contracts muscle being stretched
>inverse stretch reflex -> (golgi tendon) relaxes muscle being tensioned
>withdrawal/flexor reflex -> (proprioceptive & nonproprioceptive receptors) flexion of limb being stimulated
modulated by cortex
Describe the crossed-extensor reflex.
-0.2-0.5s after stimulus = withdrawal reflex in one limb & opposite limb extends
-works in coordination with withdrawal reflex to avoid loss of balance when limb is flexed
-balance & body posture maintains anytime limb is flexed
-physiological when walking but pathological during neuro exam = UMN lesion
Describe the positive supportive reaction.
-pressure in footpad causes limb to extend against pressure applied to foot
-complex circuit in interneurons
-keeps animal from falling to that side
Describe why muscle tone is important.
-maintains posture
-support for joints to stabilize their position
-muscle resistance to being stretched
-regulated by local spine reflexes (muscle spindle/golgi tendon) & by higher levels of brain (gamma loop)
-muscle tone examined in neuro exam via the extensor tone
-apply pressure to palmer/plantar surface of pelvic/thoracic limbs
-animals should flex when pressure is applied
>extensor tone increase (rigid/hypertonic) = UMN lesion - inhibition from UMN is lost
>tone is decreased (flaccid/hypotonic) = LMN lesion = direct control from LMN is lost
Describe what the reflex circuitry within the spinal cord is based on.
-stepping & oscillation between extension/flexion & weight bearing/non weight bearing = based on reflex circuitry within cord
Describe the neuronal networks of the CNS.
-produce oscillatory outputs
-control rhythmical motor activity
-dependent on groups of spinal interneurons
>locomotion, scratching, chewing, barking
>’central pattern generators’
>excitatory/inhibitory neurons
*CPG’s of locomotion & scratching = neuronal circuit in spinal cord intumescence (spinal cord reflexes)
*control centers that initiate & terminate the rhythmical activity = brainstem
Where does sensory input for the reflexes come from?
-muscle spindle
-golgi tendon
-joints
-tactile receptors
>integration of input in spinal cord causes inhibition/excitation of LMNs
—in same/opposite limb or limbs of other girdle
activity of muscles of trunk, neck & tail = interlinked
Describe proprioceptive input.
-proprioceptive input to forebrain = conscious awareness of posture & movement
-coordination of motor activity
-activates reflexes & sends sensory info to cerebellum
Describe the LMN & UMN of the muscle activity in the body.
-LMN = stimulated/inhibited by both reflex connections & input from UMN
-UMN = initiate, modify, terminate muscle activity
*extrapyramidal tract [brainstem] = (quadruped) gait & movement
*pyramidal tract [corticospinal] = voluntary skilled movement
What are the 2 major descending motor system pathways from brain to spinal cord?
- Brainstem UMN pathway ‘extrapyramidal’
-4 diff tracts - Corticospinal ‘pyramidal’
-motor cortex & cord
What is the major role of the medial pathways?
-maintain body subconsciously in an upright position against the pull of gravity
-control of axial & proximal extensor muscles
>bilateral control
>prevent from falling to ground
Describe the vestibulospinal (medial).
- Vestibulospinal
-regulate antigravity muscle tone
-sensory info from vestibular system (acceleration of head)
-body position
-disturbances of balance
Describe reticulospinal tract. (Medial)
-antigravity muscle tone
-speed & rhythm of walking
-consciousness
-pain perception, respiration, circulatory
Describe the tectospinal tract. (Medial)
-reflex orientation of head toward environmental stimuli (rapid reflex movement of eyes)
-axons project at the upper cervical regions of spinal cord (muscles that move the head)
-process visual, auditory, somatosensory info about position of stimuli
coordinate head & eyes so gaze is fixed on stimulus
Describe the main function of the lateral brainstem pathway.
-controls distal limb muscles associated with movement
-rubrospinal tract
>unilateral control of muscles (flexors with skilled movements)
>input from higher levels of motor system + cerebellum (synchronizes muscle by fine tuning movement initiated by the corticospinal tract)
>motor cortices influence indirectly the spinal LMNs
