Motor Flashcards
Simple reflexes with brief muscle activation
Ex: eyeblink, hiccup, finger twitch
Movements
Complex sequential movements
Ex: honking your car horn, writing your name, playing lead guitar
Acts (action patterns)
A set of muscle commands established before the action occurs
Motor plan (motor program)
- most of the brain’s activity
- preparing to move, moving, correcting ongoing movement
Motoric
The only reason we need a brain at all is
To move
The whole point of our brain is to
Guide movement
- open-loop control
- ballistic movements
Two control mechanisms optimize accuracy and speed
- maximizes speed
- no guiding external feedback
Open-loop control
- rapid
- completed no matter what sensory feedback is received
Ballistic movements
- closed-loop control
- ramp movements
Two control mechanisms optimize accuracy and speed
- maximizes accuracy
- information from what is being controlled flows back to the controlling device
Closed-loop control
- smooth movements
- slower, sustained motions guided by feedback
Ramp movements
-skeletal system and muscles
-spinal cord
-brain stem
-primary motor cortex
-nonprimary motor cortex
-cerebellum and basal ganglia
Hierarchy of motor control systems
Power movement
Skeletal system and muscles
Control skeletal muscles
Spinal cord
Integrates motor commands
Brainstem
Initiates commands for action
Primary motor cortex
Initiates cortical processing
Nonprimary motor cortex
Tweak these systems
Cerebellum and basal ganglia
-planning
-initiating
-directing voluntary movements
-descending systems (upper motor neurons)
Motor cortex
-basic movements
-posture control
-descending systems (upper motor neurons)
Brainstem centers
-reflex coordination
-spinal and brainstem circuits
Local circuit neurons
-lower motor neurons
-spinal cord and brainstem circuits
Motor neuron pools
Gating proper initiation of movement
Basal ganglia
Sensory motor coordination
Cerebellum
Muscles that contract when others extended are
Antagonists
Muscles that act together are
Synergists
Flexor and extensor muscles are balanced
At rest
-alternation of flexor-extensor contraction
-normally present, but if poorly regulated it is debilitating
Tremor
Biceps and triceps are
Antagonists
-a muscle is composed of
-each contain two kinds of regularly arranged, overlapping filaments
Muscle fibers
Thick filaments
Myosin
Thin filaments
Actin
Shortens the fiber length
Contraction
Voluntary
Striated muscles
-fast twitch muscle fibers
-slow twitch muscle fibers
Two types of fibers
-contract slowly but resist fatigue
-first to be recruited
-use fat for fuel
Slow twitch fibers
-contract rapidly but fatigue easily
-last to be recruited
-use glucose
Fast twitch fibers
Send their axons to innervate muscles
Motorneurons
Travel down the motorneuron, which branches into many terminals near its target
Action potentials
-motor neuron terminal and muscle fiber meet
-acetylcholine is released
Neuromuscular junction
One motorneuron’s axon and all its target fibers
Motor unit
Muscles that make fine, precise movements have only a few
Muscle fibers per axon
1/13
Innervation ratio
Is guided by sensory feedback
Action of muscles
Information about body movements and position
Ex: how tiger knows when to start his downswing
Proprioception
-muscle spindles
-gogli tendon organs
two kinds of muscle proprioceptive receptors
responsive to muscle stretch
muscle spindles
respond to muscle contraction, less to stretch
togli tendon organs
Are like the lad who is too little to play football, so he serves as team statistician
Muscle spindles
If a muscle is stretched, ______ ______ also stretches
muscle spindle
Afferent nerve impulses tell ______ ______ of the stretch
spinal cord
Muscle contracts to maintain ‘_____’ length
present
Stimulation of ______ _____ _______ inhibits motorneurons, thereby relaxing extreme tension to prevent damage
Golgi tendon organs
- Muscle is stretched
- Excitation of muscle spindle afferents
- Excitation of motoneurons
- Agonist muscle stimulated to oppose stretch
- Antagonist muscle is inhibited
Stretch Reflex Circuit
Muscle is stretched
Stretch reflex circuit #1
Excitation of muscle spindle afferents
Stretch reflex circuit #2
Excitation of motoneurons
Stretch reflex circuit #3
Agonist muscle stimulated to oppose stretch
Stretch reflex circuit #4
Antagonist muscle is inhibited
Stretch reflex circuit #5
Touching back of the hand resets the muscle spindles, for a few secs
Arm wrestling hack
Impaired control of the stretch reflex
Spasticity
-normally keeps a tight rein (inhibition) on reflex behavior
-reflexes don’t interfere with voluntary movements
Motor cortex
When normal cortex input is cut off, spinal cord becomes
hyperreflexic
normal reflexes are exaggerated as in
clonus
Muscles of the body
Pyramidal
Muscles of head and neck
Extrapyramidal
- direct control
- Primary motor cortex
- non primary motor cortex
- spinal cord
Pyramidal
- indirect control
- basal ganglia
- thalamus
- cerebellum
Extrapyramidal
A two-neuron chain
Pyramidal system pathway
Upper Motor neuron
neuron #1
lower motor neuron
neuron #2
The cross over of the primary motor cortex and the pyramid in the medulla
Upper motor neuron
From spinal cord to muscle
Lower motor neuron
changes as a result of learning
primary motor cortex
early music training results in expansion of
motor cortex
plans movement
nonprimary motor cortex
- M1
- Primary motor cortex
Motor cortex
-SMA
-encodes sequences of movements during skill acquisition
Supplementary motor area
neurons fire just before performing an activity
Premotor cortex
guides movement through inhibition
Cerebellum
contains Purkinje cells which only send inhibitory messages
Cerebellum cortex
modulate movement
cerebellum and basal ganglia
are more involved in early phase of a movement than SMA and cerebellum
Primary motor cortex and basal ganglia
need postural adjustment
voluntary movements
- predicts postural consequences of planned (pyramidal) movement
- acts to prevent loss of balance
Extrapyramidal system
neutral circuit that generates rhythmic behaviors
central pattern behavior
rhythmic activities, such as walking, are generated in the
spinal cord
a very long journey
input to output
- power
- largely a pyramidal function
strength
- posture
- largely an extrapyramidal function
tone
causes weakness
pyramidal damage
impairs movement control
extrapyramidal damage
primary disorder of muscle
myopathy
progressive degeneration of muscle
muscular dystrophy
- a protein needed for normal muscle function
- produced by X chromosome
Dystrophin
- an autoimmune disorder
- patient develops antibodies to their own acetylcholine (ACh) receptors
- weakness develops over the day and resolves with sleep
Myasthenia gravis
Tension (acetylcholine agonist) test
Myasthenia gravis diagnosis
- destroys spinal motoneurons and sometimes cranial motoneurons
- no treatment
- spinal cord with loss of motoneurons
Poliovirus (polio)
- Lou Gehrig disease
- degeneration of motoneurons and consequent loss of their target muscles
Amyotrophic lateral sclerosis (ALS)
- result in paralysis
- reflexes, sensation, and strength below level of the injury are lost
spinal cord injuries
- inability to sequence movements
- no muscle paralysis exists
Apraxia
motor planning disorder
Sequencing
- new acts are ramped (feedback-controlled)
-slow, variable
Frontal and parietal cortex
- well-learned acts are ballistic
- fast, consistent
Cortex and basal ganglia
- tremor
- bradykinesia
- shuffling gait
- postural instability
Parkinson’s disease
a basal ganglia protein
a-synuclein
- a defective gene for a-synuclein
-an inherited cause of - environmental exposures also contribute
Parkinson’s disease
degeneration of dopamine cells in _________ ______, which project to basal ganglia
substantia nigra
- a precursor to dopamine
- use as a drug improves the symptoms
L-dopa
dancing hands and feet
chorea
- progressive destruction of the caudate nucleus and putamen
- cerebral cortex also is impaired
Huntington chorea
- impairs motor control
-Purkinje cells die
cerebellar damage (ataxia)
childhood tumors of
cerebellar vermis (ataxia)
alcoholism causes
gait ataxia (ataxia)
inherited degeneration of
cerebellum (ataxia)
- abnormal sustained posture
- basal ganglia dysfunction
dystonia (severe)
tics and obsessive-compulsive disorder
Tourette syndrome
basal ganglia and cortex disorder
Tourette syndrome
- boys more than girls
- usually end by adulthood
- affect face and shoulders more than hands and legs
- coprolalia (swearing) is rare in children
clinical features of Tourette syndrome
- motor cortex damage, such as stroke, causes motor impairment
- weakness (paresis) of voluntary movements
Hemiparetic gait
