NSCS 730
description
Transcript of NSCS 730
621 - Subconscious motor
NSCS 730
Subconscious Motor Control
Dr. Mark Kindy503 - STB; 792-0559; [email protected]
621 - Voluntary motor
Descending regulation of motor activity
• Simplest control is by reflex connections
• Voluntary motor control is by direct cortical pathways
• Subconscious motor control is carried out by several pathways with connections in brainstem
• All descending pathways use reflex interneurons
• All descending activity converges on -motor neuron pools
Reflexconnections
Voluntary motor
Subconscious motor
621 - Subconscious motor
Descending systems to regulate posture & tone• Pathways arising in
brainstem influence muscle tone and posture– operate at subconscious
level
• Pathways: (more medial projections than corticospinal)– Reticulospinal– Vestibulospinal– Cerebellum influences
tone & posture indirectly through these other systems
621 - Subconscious motor
Upper vs Lower Motor neuron lesions• All motor neuron lesions include
paralysis• Lower motor neuron lesions: injury to
segmental () motor neurons– Dysfunction may involve single muscle– Muscle atrophy, wasting– Tone and reflexes absent, flaccidity– Fasciculation of muscle cells
• Upper motor neuron lesions: injury to higher order neurons or descending tracts– Usually all muscles of a part of the
homunculus– Spasticity: especially in extensors
(antigravity muscles)– Lack atrophy & fasciculation
• Spasticity: increased tone and stretch reflexes– Resistance to passive movement– Clasp-knife, clonus– Babinski’s sign
Upper
Lower
2/9/09 621 - Subconscious motor
2/9/09 621 - Subconscious motor
621 - Subconscious motor
Reticular formation of brainstem affects tone• Reticulospinal
tracts (from brainstem reticular formation) important for regulating tone
• Strong influence on -motor neurons
• Two systems have opposite effects which are normally in balance• Medial reticular formation inhibits extensors
– Receives strong excitation from motor cortex
• lateral reticular formation facilitates extensors• Lesions of corticospinal tracts leaves reticular influences unbalanced
– Extensor fascilitation, spasticity
2/9/09 621 - Subconscious motor
621 - Subconscious motor
Spasticity - hypertonia, hyperreflexia• Spasticity
– Results from abnormally high -motor input
• Resistance to passive movement, increased tone– Especially for extensors– Velocity dependent: rapid
stretch - more resistance– Hyperactive stretch reflexes– Clasp-knife , clonus • Altered plantar reflex:
• Normal adult – toes ventroflex
• After upper MN injury – toes dorsiflex and fan– Babinski’s sign
621 - Subconscious motor
Vestibular system• Vestibular portions of
inner ear:• 3 semicircular canals
– Respond to angular acceleration
• Utricle & Saccule– Respond to linear
acceleration & gravity
• Membrane-lined fluid filled cavities in temporal bone
• Receptors are hair cells– Depolarize when stereocilia are bent– Specializations allow head movement to stimulate them
621 - Subconscious motor
Semicircular canals• Respond to angular acceleration
• 3 on each side– Filled with fluid– Perpendicular to each other– Pairs of canals in same plane
621 - Subconscious motor
Semicircular canals• Mechanism of stimulation:
• Hair cells located in ampulla - Gelatinous Cupula covers stereocilia
• During rotation of head in the plane of a canal:– Fluid moves around canal– Tilts the cupula; Stereocilia
bent– Afferents excited on one
side & inhibited on the other
621 - Subconscious motor
Vestibular system• Vestibular portions of
inner ear:• 3 semicircular canals
– Respond to angular acceleration
• Utricle & Saccule– Respond to linear
acceleration & gravity
• Membrane-lined fluid filled cavities in temporal bone
• Receptors are hair cells– Depolarize when stereocilia are bent– Specializations allow head movement to stimulate them
621 - Subconscious motor
Utricle and Saccule• Respond to linear
acceleration & gravity• One of each on each side
– Utricle - macular surface horizontal
– Saccule - macular surface vertical
• Mechanism of stimulation:– hair cells in macular surface– Stereocilia covered by
gelatinous matrix– Otoliths embedded in gelatin
• Otoliths more dense than water
– Linear acceleration or gravity forces otoliths to move gelatin and bend stereocilia– Utrical signals horizontal forces– Saccule signals vertical forces
621 - Subconscious motor
Vestibular system• Vestibular portions of
inner ear:• 3 semicircular canals
– Respond to angular acceleration
• Utricle & Saccule– Respond to linear
acceleration & gravity
• Membrane-lined fluid filled cavities in temporal bone
• Receptors are hair cells– Depolarize when stereocilia are bent– Specializations allow head movement to stimulate them
621 - Subconscious motor
Central vestibular connections
• Afferent fibers relay through 4 vestibular nuclei
• 2 vestibulospinal tracts• Lateral:
– receives much input from utricle and saccule
– Changes muscle tone in response to gravity
• Medial:– receives much input from
semicircular canals– Causes movement of head and
shoulders to coordinate head and eye movements
• Other vestibular pathways ascend to oculomotor nuclei- CN-III, IV, VI
• Cause eye movement in response to head rotation: Nystagmus
• Strong input to cerebellum
621 - Subconscious motor
Vestibulo-occular control• Subject seated on stool and rotated to left• Initial response (hard to visualize)
– Slow tracking eye movements to right– Fast eye movements back to left
• Nystagmus: alternate slow and fast eye movement
• Response to stopping turning (post-rotatory)– Head stops but fluid continues moving left– Eyes track slowly left, quick movement to right
• Nystagmus normal for head rotation and repetitive moving object (optokinetic)– Nystagmus without movement = sign of lesion
Post-rotatory nystagmus
621 - Subconscious motor
Cerebellum
• attached to brainstem
• Elaborate cortex & deep nuclei
Compares sensory inputs with motor programs to correct and fine-tune movements
Deep nuclei
Cortex
621 - Subconscious motor
Cerebellar Input / Output• Sensory inputs:
– Somatic - tactile, proprioceptors– Vestibular– Visual, auditory
• Motor input:– From motor and premotor cortex– Signals about the intended
movement
• All inputs converge on cerebellar cortex
• Complex cortical processing• All output is from purkinje cell
axons to deep nuclei • Deep nuclei compare cerebellar inputs with cortical output pattern, and relay error signals back to cerebral motor centers
621 - Subconscious motor
Cerebellar Outputs• No direct
connections to -motor neurons
• Output from cerebellum returns to motor areas of cortex to fine-tune motor programs
Red nucleus
thalamus
621 - Subconscious motor
Function of cerebellum• Compares sensory
inputs with motor programs to correct and fine-tune movements
• Signs of Cerebellar damage:– Ataxia, unsteady gait
and stance– Intention tremor– Dysmetria– Asynergy– Reduced muscle tone
621 - Subconscious motor
Basal ganglia• Large nuclei of
forebrain below cerebral cortex
• Striatum– Caudate nucleus– putamen
• Globus pallidus• Substantia nigra
(dopamine cells)
• Receive wide cortical inputs
• Send output up to premotor areas to help organize stereotypic motor sequences
621 - Subconscious motor
Basal ganglia diseases• Dysfunctions:• Excess movements
– Resting tremor – Choreoform– Athetoid– ballistic
• Bradykinesia– Absent or difficult initiation
• Rigidity– Leadpipe or cogwheel
• Examples:• Parkinson’s disease
– Loss of dopamine-containing cells of substantia nigra
– Resting tremor, leadpipe rigidity, bradykinesis
• Huntington’s disease– X-linked genetic– Degeneration of gaba-ergic &
cholinergic cells of striatum– Choreoform movements– Mental deterioration
Cerebral palsy• About 10 percent of children with cerebral palsy have athetoid
cerebral palsy. Athetoid cerebral palsy is caused by damage to the cerebellum or basal ganglia. These areas of the brain are responsible for processing the signals that enable smooth, coordinated movements as well as maintaining body posture. Damage to these areas may cause a child to develop involuntary, purposeless movements, especially in the face, arms, and trunk. These involuntary movements often interfere with speaking, feeding, reaching, grasping, and other skills requiring coordinated movements. For example, involuntary grimacing and tongue thrusting may lead to swallowing problems, drooling and slurred speech. The movements often increase during periods of emotional stress and disappear during sleep. In addition, children with athetoid cerebral palsy often have low muscle tone and have problems maintaining posture for sitting and walking.
2/9/09 621 - Subconscious motor