Muscle Control - Physiology Flashcards
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.
