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Flashcards in Lecture 8 Deck (27)

What is muscle covered by?

-sheath of connective tissue that penetrates from surface into the muscle and envelops each fiber and divides muscle into columns or bundles
-etension of this tissue= tendons


What do antagonistic muscles do?

-move a body part in two opposing directions


What do flexors do?

-bend a limb


What do extensors do?

-straighten a limb


Why are muscle fibres grouped into whole muscles?

-twitch is too weak to be useful
-muscles can act cooperatively, stronger than a twitch


What is twitch summation?

-when APs close together then the muscle twitches combine= increase in strength


What happens in tetanus?

-lot of APs close together, doesn't have time to relax (the muscle fibre)
-normal process
-there is a disease as well but that's uncontrolled tetanus


More muscle fibres contracted results in=

= greater tension


What's a motor unit?

-motor neurons and all the muscle fibres it supplies


What's motor unit recruitment?

-muscle divided into more muscle units, more units activated= more strength, more tension
-size of the motor units also affects the tension


What is asynchronous recruitment of motor units?

-during prolonged contraction brain switches which units it's using and moves it around so they don't get as tired, only possible when the strain isn't too big, then all are used!


Do larger motor units have more relative strength?



What does whole muscle tension depend on?

-number of muscle fibres contracting
-the tension on each fibre


What does a single AP do in a muscle fibre?

- all or none twitch


What does repetitive stimulation of a muscle fibre achieve?

-contractions with longer duration and greater tension


Why is twitch summation possible?

-as the muscle twitch last far longer than an AP and is not over by the time another AP is initiated


Describe the length-tension relationship.

-every fiber can be stretched only so much
-so tension depends on how stretched it is at the onset of contraction
-best result at optimal length (when thick and thin filaments have optimal overlap)= most actin binding sites available for the cross bridge


Why is less tension developed at larger than optimal length of a fiber?

-fewer actin sites
-if too far= no actin sites and no further contraction can occur


Why is less tension developed at smaller than optimal length of a fiber?

-thin filaments from the opposite sides of the sarcomere overlap
-thick filaments forced against the Z lines, further shortening impeded


Is optimal length equal to relaxed length?



What's an isotonic contraction?

-muscle tension constant but muscle length changes and muscle does work (moves something)
-picking something up (during the process)


What's an isometric contraction?

-muscle doesn't shorten, doesn't do work and tension remains the same
-maintaining posture
-holding something


Describe load-velocity relationship.

-can pick up light object quickly, heavy= slower
- with increased load the velocity decreases


What is movement controlled by? -the whole pathway

-premotor and supplementary motor areas
-primary motor cortex
-brain stem nuclei (reticular formation and vestibular nuclei)
-motor neurons
-muscle fibres

-then reported back
-sensory consequences of movement
-peripheral receptors
-afferent neuron terminals
-brain stem
-primary motor cortex...


What are the two regions that influence movement directly?

-primary motor cortex
-brain stem
-all the rest indirect


What are muscle spindles?

-proprioreceptors = tell where muscles are in space
-collection of intrafusal fibers (spindle)
-has non-contractile central portion
-contractile bits (myofibrils) only at the ends
-each has own afferent and efferent nerve supply
-detect changes in muscle length
-key role in stretch reflex


Stretch reflex?

example= knee jerk
-tapping a tendon passively stretches the muscle activating the spindles= detect length change
-stretch reflex= contraction of the extensor muscle= knee jerk