What kind of changes often use feed-forward strategy?
Postural responses
What kind of muscle fibers are commonly involved in posture?
Slow motor units
How long does calcium stay in the cell for in slow twitch fibers compared to fast and FFR fibers?
Much longer due to slow type L-type channels and calcium pumps take a while to reduce [Ca2+]
What does wave summation do to contraction?
Progressively increases tension until tetanus based on firing rate
What is muscle feedback control important for?
Allows real-time responsiveness to local changes such as adaptation of muscle recruitment and tension.
Facilitated coordination about joints
Instantaneous but is slower than initial action.
What controls skeletal muscle contraction?
Large alpha-motor neurons
What are the three levels of hierarchy in reflex circuitry?
Control of individual muscles
Control of muscles around a joint
Coordination of muscles at several joints
What sensory receptors are involved in motor response reflexes?
Muscle receptors such as muscle spindles and GTOs
Cutaneous receptors
Where are GTOs located in muscles?
Encapsulated ‘tension-gated’ receptors in myotendinous junction.
How do GTOs react to increases in tension?
Firing rate increases due to opening of cation channels on mechanical receptors.
What does it mean if a response is ‘stereotyped’?
They appear on different parts of the body in slightly different ways
How do GTOs transmit their signals very rapidly?
They use large, fast type 1b fibers
GTOs signal tension throughout the entire physiological range. What do GTOs do at very high strain?
They instigate a specific drop reflex
What are the types of muscle spindles?
Primary ending: Encircles central portion of each intrafusal fiber
Secondary ending: Innervate the receptor region on sides
What are the types of fibers that muscle spindles use to transmit primary ending signals very rapidly?
Type 1a fivers
Why are their 2 types of nerve endings transmitting signals from spindles?
Primary ending are for dynamic movements requiring immediate response
Secondary endings are for static responses
What are nuclear bag fibers?
Dynamic spindles that look like nuclear bags. (Dominant fibers) Very strong response and stops quickly
What are nuclear chain fibers?
Chain looking static spindles which provide a slowly adapting response
What happens to nuclear bags when shortened?
They become more hyperpolarized
What spindles excite primary nerve endings?
Both bag fibers and chain fibers but bag fibers are dominant
What spindles excite secondary nerve endings?
Only nuclear chain fibers
What happens to action potentials from primary and secondary endings during stretch?
Both endings start to depolarize more rapidly when stretched
Primary endings hyperpolarize when muscle is shortening whereas secondary spindles start to fire less rapidly due to repressing effect of the primary fibers.
What motor neurons control the tone of the muscle spindles?
gamma motor neurons which is not as fast as the alpha motor neurons that innervate the muscles.
What does more gamma stimulation mean? What does less gamma stimulation mean?
Hyper reflexivity and vice versa for less gamma stimulation.
How is nuclear bag and nuclear chain response separated as required?
Both act on different gamma motorneurons
How is reflex strength modulated?
Input from higher centers in the brain modify sensitivity of response
Inhibitory interneurons receive excitatory and inhibitory inputs that can alter motorneuron response
yMNs regulate sensitivity of stretch reflex
Static vs dynamic responses are modulated via yMN excitation of nuclear chain or nuclear bag fibers.
How is sensitivity of the stretch reflex modulated by yMNs?
They either tighten or relax the fibers within the spindle.
Messages to do this come from the reticular nuclei in the pons and the medulla which inhibit/excite antigravity muscles and control reflex gain controlled by gamma motorneurons. (Hypo/hyper-reflexia)
Where are visual cues responded to?
Tectospinal nuclei (superior colliculi) receive visual input and this influences head/neck muscles via the tectospinal tract
Where are vestibular responses responded to?
Vestibular nuclei which receive vestibular input and in turn activate vestibulospinal tract and pontine reticular nuclei.
Which parts of the brain do visual inputs go to?
Tectosponal tract (superior colliculi contain tectosponal nuclei)
Which parts of the brain do vestibular inputs go to?
Cerebellum, vestibulospinal tract, and pontine reticular nuclei
Where do non auditory and visual inputs go to in the brain?
They go to reticular nuclei in both the pons and the medulla.
What effect do pontine reticular formation neurons have on reflexes?
Activates motorneurons (hyperreflexia)
What effect do medullary reticular formation neurons have on reflexes?
Inhibits motorneurons (Hyporeflexia)
What happens if there are lesions above the vestibular nuclei in the brain?
Hyperreflexia (It cuts out negative signals which calm the muscle tone down)
What happens to a conscious motor idea before it is acted on?
It must go through basal ganglia / lateral cerebellum and then the premotor and then motor cortex before action can take place
What parts of the brain are involved in the strategy stage of motor control?
Strategy: Prefrontal cortex and posterior parietal cortex as well as basal ganglia
What parts of the brain are involved in the tactics stage of motor control?
Pre-motor cortex and Supplementary motor area
Cerebellum
What parts of the brain are involved in the execution stage of motor control?
Primary motor cortex
Brain stem
Spinal cord
What do the premotor cortical areas do?
Provide motor image and generate complex patterns of movement across bilateral body areas as well as postural stabilization during conscious movements. Feeds learned patterns into primary motor cortex and corticospinal tract.
What do the basal ganglia do?
They are important for posture and planning as well as coordination of motor actions.
They plan and control complex patterns/relative intensities/direction/sequence/complicated motor goals.
What does the cerebellum do?
Controls equilibrium
Coordination of motor action based on sensory information and timing/rapid, smooth progression/control intensity/interplay between agonist and antagonist muscle groups