EXAM 2: Motor System 1 Flashcards
feedforward
the anticipatory use of sensory information to prepare for movement
feedback
the use of sensory information during or after movement to make corrections either to ongoing movement or to future movements
Automatic movements require continuous integration of:
- visual
- somatosensory
- vestibular info
- motor processing
In the absence of vision, reaching depends on this to locate objects
- somatosensation
- proprioception
What disrupts positioning of limbs in individuals with complete deafferentation?
Loss of somatosensation
What does neural activity begin with?
with a decision made in the anterior part of the frontal lobe
follow the path of neural activity
- frontal lobe
- motor planning areas activated
- control circuits activated (in UMN tracts)
- UMN tracts deliver signals to interneurons and LMNs
- LMNs transmit signals to skeletal muscles
What are control circuits?
consist of cerebellum and basal ganglia
What do control circuits do?
- regulate activity in UMN tracts
- activation results in excitation or inhibition of motor neurons
UMN tracts deliver signals to
- interneurons
- LMNs
classification of UMN tracts
- postural/gross movement tracts
- fine movement tracts
- nonspecific UMNs
postural/gross movement tracts control:
automatic skeletal muscle activity
fine movement tracts control:
fractionated movements of limbs and face
nonspecific UMNs control:
all motor neurons
What do LMNs do?
- transmit signals directly to skeletal muscles
- elicit contraction of muscle fibers that move the upper limbs and fingers
How is voluntary movement controlled?
top down
- brain
- spinal cord
- muscle
properties of skeletal muscle
- excitable
- contractile
- extensile
- elastic
t-tubules
- transverse tubules
- projections of muscle cell membranes that extend into the muscle
sarcoplasmic reticulum
series of storage sacs for Ca2+ ions
myofibrils
individual muscle fibers
sarcomeres
arrangement of proteins in a myofibril
two protein types in sarcomeres
- structural
- contractile
structural proteins of sarcomeres
- Z line
- M line
- titin
M line
anchors fibers in center of sarcomere
titin
- connects Z line with m line
- maintains position of myosin relative to actin
- prevents sarcomere from being pulled apart
contractile proteins of sarcomeres
- myosin
- actin
- tropomyosin
- troponin
contraction
- Produced when active slides relative to myosin
- Repeated attachment, swiveling, and detachment of myosin heads produce contraction of the muscle
What do muscles behave like?
springs
______ springs generate more resistance to stretch than the same spring when it is _______
- stretched
- shortened
What determines total resistance to muscle stretch?
- active contraction
- titin
- weak actin-myosin bonds
muscle tone
resistance to stretch in a resting muscle
How is muscle tone assessed?
assessed clinically using PROM
When tone is normal, resistance to passive stretch is
minimal
Normal resting muscle tone provided by
- titin
- weak actin-myosin bonds
weak actin-myosin bonds
- attached, but myosin heads don’t swivel
- no muscle contraction, but there is resistance
What happens to actin-myosin bonds if muscle is immobile for a prolonged period?
- bonds continually form
- broken by stretching the muscle
stretch velocity and actin-myosin bonds
The faster the stretch, the greater the resistance
What happens when healthy innervated muscle is continuously immobilized in a shortened position for a prolonged period?
sarcomeres disappear from the ends of myofibrils
Why do sarcomeres get lost when immobilized in a shortened position?
Loss of sarcomeres is a structural adaptation to the shortened position so the muscle generates optimal force at the new resting length
What happens when a structurally shortened muscle is stretched?
it quickly reaches the limits of its elasticity and is resistant to stretching
What happens if a muscle is immobilized in a lengthened position?
the muscle adds new sarcomeres
cocontraction
simultaneous contraction of antagonist muscles
What does cocontraction do?
- stabilizes joints
- UE: enables precise movements
- LE: allows individual to stand on an unstable surface
