Lecture 8

Question 1

What is muscle covered by?

Answer 1

• 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

Question 2

What do antagonistic muscles do?

Answer 2

-move a body part in two opposing directions

Question 3

What do flexors do?

Answer 3

-bend a limb

Question 4

What do extensors do?

Answer 4

-straighten a limb

Question 5

Why are muscle fibres grouped into whole muscles?

Answer 5

• twitch is too weak to be useful

- muscles can act cooperatively, stronger than a twitch

Question 6

What is twitch summation?

Answer 6

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

Question 7

What happens in tetanus?

Answer 7

• 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

Question 8

More muscle fibres contracted results in=

Answer 8

= greater tension

Question 9

What’s a motor unit?

Answer 9

-motor neurons and all the muscle fibres it supplies

Question 10

What’s motor unit recruitment?

Answer 10

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

Question 11

What is asynchronous recruitment of motor units?

Answer 11

-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!

Question 12

Do larger motor units have more relative strength?

Answer 12

-yes

Question 13

What does whole muscle tension depend on?

Answer 13

• number of muscle fibres contracting

- the tension on each fibre

Question 14

What does a single AP do in a muscle fibre?

Answer 14

• all or none twitch

Question 15

What does repetitive stimulation of a muscle fibre achieve?

Answer 15

-contractions with longer duration and greater tension

Question 16

Why is twitch summation possible?

Answer 16

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

Question 17

Describe the length-tension relationship.

Answer 17

• 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

Question 18

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

Answer 18

• fewer actin sites

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

Question 19

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

Answer 19

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

Question 20

Is optimal length equal to relaxed length?

Answer 20

-approximately

Question 21

What’s an isotonic contraction?

Answer 21

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

Question 22

What’s an isometric contraction?

Answer 22

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

Question 23

Describe load-velocity relationship.

Answer 23

• can pick up light object quickly, heavy= slower

- with increased load the velocity decreases

Question 24

What is movement controlled by? -the whole pathway

Answer 24

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

• then reported back
• sensory consequences of movement
• peripheral receptors
• afferent neuron terminals
• brain stem
• thalamus
• primary motor cortex…

Question 25

What are the two regions that influence movement directly?

Answer 25

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

Question 26

What are muscle spindles?

Answer 26

• 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

Question 27

Stretch reflex?

Answer 27

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