Transcript No Slide Title

NSCS 730
Subconscious Motor Control
Dr. Mark Kindy
503 - STB; 792-0559; [email protected]
621 - Subconscious motor
Descending regulation of motor activity
• All descending activity converges on a-motor neuron pools
• 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
Subconscious motor
Voluntary motor
Reflex
connections
621 - Voluntary 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 (a) motor neurons
–
–
–
–
Dysfunction may involve single muscle
Muscle atrophy, wasting
Tone and reflexes absent, flaccidity
Fasciculation of muscle cells
Upper
Lower
• Upper motor neuron lesions: injury to
higher order neurons or descending
tracts
• Spasticity: increased tone and
– Usually all muscles of a part of the
stretch reflexes
homunculus
– Spasticity: especially in extensors
(antigravity muscles)
– Lack atrophy & fasciculation
621 - Subconscious motor
– Resistance to passive
movement
– Clasp-knife, clonus
– Babinski’s sign
2/9/09
621 - Subconscious motor
2/9/09
621 - Subconscious motor
Reticular formation of brainstem affects tone
• Reticulospinal
tracts (from
brainstem reticular
formation)
important for
regulating tone
• Strong influence
on g-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
621 - Subconscious motor
2/9/09
621 - Subconscious motor
Spasticity - hypertonia, hyperreflexia
• Spasticity
– Results from abnormally high
g-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:
• Other vestibular pathways ascend to
oculomotor nuclei- CN-III, IV, VI
• Cause eye movement in response to
head rotation: Nystagmus
• Strong input to cerebellum
– 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
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
621 - Subconscious motor
Post-rotatory nystagmus
Cerebellum
• attached to brainstem
• Elaborate cortex &
deep nuclei
Deep nuclei
Cortex
Compares sensory inputs with motor programs to correct and
fine-tune movements
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
• Deep nuclei compare cerebellar
axons to deep nuclei
inputs with cortical output
pattern, and relay error signals
back to cerebral motor centers
621 - Subconscious motor
Cerebellar Outputs
• No direct
connections to amotor neurons
• Output from
cerebellum returns
to motor areas of
cortex to fine-tune
motor programs
thalamus
Red nucleus
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
–
–
–
–
• Examples:
• Parkinson’s disease
Resting tremor
Choreoform
Athetoid
ballistic
– Loss of dopamine-containing
cells of substantia nigra
– Resting tremor, leadpipe
rigidity, bradykinesis
• Huntington’s disease
• Bradykinesia
– Absent or difficult initiation
• Rigidity
– Leadpipe or cogwheel
– X-linked genetic
– Degeneration of gaba-ergic &
cholinergic cells of striatum
– Choreoform movements
– Mental deterioration
621 - Subconscious motor
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