Muscle Control - Physiology

Question 1

What kind of changes often use feed-forward strategy?

Answer 1

Postural responses

Question 2

What kind of muscle fibers are commonly involved in posture?

Answer 2

Slow motor units

Question 3

How long does calcium stay in the cell for in slow twitch fibers compared to fast and FFR fibers?

Answer 3

Much longer due to slow type L-type channels and calcium pumps take a while to reduce [Ca2+]

Question 4

What does wave summation do to contraction?

Answer 4

Progressively increases tension until tetanus based on firing rate

Question 5

What is muscle feedback control important for?

Answer 5

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.

Question 6

What controls skeletal muscle contraction?

Answer 6

Large alpha-motor neurons

Question 7

What are the three levels of hierarchy in reflex circuitry?

Answer 7

Control of individual muscles

Control of muscles around a joint

Coordination of muscles at several joints

Question 8

What sensory receptors are involved in motor response reflexes?

Answer 8

Muscle receptors such as muscle spindles and GTOs

Cutaneous receptors

Question 9

Where are GTOs located in muscles?

Answer 9

Encapsulated ‘tension-gated’ receptors in myotendinous junction.

Question 10

How do GTOs react to increases in tension?

Answer 10

Firing rate increases due to opening of cation channels on mechanical receptors.

Question 11

What does it mean if a response is ‘stereotyped’?

Answer 11

They appear on different parts of the body in slightly different ways

Question 12

How do GTOs transmit their signals very rapidly?

Answer 12

They use large, fast type 1b fibers

Question 13

GTOs signal tension throughout the entire physiological range. What do GTOs do at very high strain?

Answer 13

They instigate a specific drop reflex

Question 14

What are the types of muscle spindles?

Answer 14

Primary ending: Encircles central portion of each intrafusal fiber

Secondary ending: Innervate the receptor region on sides

Question 15

What are the types of fibers that muscle spindles use to transmit primary ending signals very rapidly?

Answer 15

Type 1a fivers

Question 16

Why are their 2 types of nerve endings transmitting signals from spindles?

Answer 16

Primary ending are for dynamic movements requiring immediate response

Secondary endings are for static responses

Question 17

What are nuclear bag fibers?

Answer 17

Dynamic spindles that look like nuclear bags. (Dominant fibers) Very strong response and stops quickly

Question 18

What are nuclear chain fibers?

Answer 18

Chain looking static spindles which provide a slowly adapting response

Question 19

What happens to nuclear bags when shortened?

Answer 19

They become more hyperpolarized

Question 20

What spindles excite primary nerve endings?

Answer 20

Both bag fibers and chain fibers but bag fibers are dominant

Question 21

What spindles excite secondary nerve endings?

Answer 21

Only nuclear chain fibers

Question 22

What happens to action potentials from primary and secondary endings during stretch?

Answer 22

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.

Question 23

What motor neurons control the tone of the muscle spindles?

Answer 23

gamma motor neurons which is not as fast as the alpha motor neurons that innervate the muscles.

Question 24

What does more gamma stimulation mean? What does less gamma stimulation mean?

Answer 24

Hyper reflexivity and vice versa for less gamma stimulation.

Question 25

How is nuclear bag and nuclear chain response separated as required?

Answer 25

Both act on different gamma motorneurons

Question 26

How is reflex strength modulated?

Answer 26

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.

Question 27

How is sensitivity of the stretch reflex modulated by yMNs?

Answer 27

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)

Question 28

Where are visual cues responded to?

Answer 28

Tectospinal nuclei (superior colliculi) receive visual input and this influences head/neck muscles via the tectospinal tract

Question 29

Where are vestibular responses responded to?

Answer 29

Vestibular nuclei which receive vestibular input and in turn activate vestibulospinal tract and pontine reticular nuclei.

Question 30

Which parts of the brain do visual inputs go to?

Answer 30

Tectosponal tract (superior colliculi contain tectosponal nuclei)

Question 31

Which parts of the brain do vestibular inputs go to?

Answer 31

Cerebellum, vestibulospinal tract, and pontine reticular nuclei

Question 32

Where do non auditory and visual inputs go to in the brain?

Answer 32

They go to reticular nuclei in both the pons and the medulla.

Question 33

What effect do pontine reticular formation neurons have on reflexes?

Answer 33

Activates motorneurons (hyperreflexia)

Question 34

What effect do medullary reticular formation neurons have on reflexes?

Answer 34

Inhibits motorneurons (Hyporeflexia)

Question 35

What happens if there are lesions above the vestibular nuclei in the brain?

Answer 35

Hyperreflexia (It cuts out negative signals which calm the muscle tone down)

Question 36

What happens to a conscious motor idea before it is acted on?

Answer 36

It must go through basal ganglia / lateral cerebellum and then the premotor and then motor cortex before action can take place

Question 37

What parts of the brain are involved in the strategy stage of motor control?

Answer 37

Strategy: Prefrontal cortex and posterior parietal cortex as well as basal ganglia

Question 38

What parts of the brain are involved in the tactics stage of motor control?

Answer 38

Pre-motor cortex and Supplementary motor area

Cerebellum

Question 39

What parts of the brain are involved in the execution stage of motor control?

Answer 39

Primary motor cortex

Brain stem

Spinal cord

Question 40

What do the premotor cortical areas do?

Answer 40

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.

Question 41

What do the basal ganglia do?

Answer 41

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.

Question 42

What does the cerebellum do?

Answer 42

Controls equilibrium

Coordination of motor action based on sensory information and timing/rapid, smooth progression/control intensity/interplay between agonist and antagonist muscle groups