Muscle & muscle function 3

Question 1

• Skeletal muscle contractions are under voluntary control
• Stimulation originates in motor cortex
  What happens?

Answer 1

• α-motor neurons, releasing acetylcholine (main neurotransmitter for muscle), stimulate muscle contraction (nicotinic receptor)

Motor neuron = one large neuron originating from the CNS to muscle fibers.

Question 2

 1 motor neuron can innervate more than 1 muscle fiber
 X = 1 motor neuron and all the muscle fibers it innervates
 = Basic unit of contraction in a muscle, smallest you can get

Answer 2

X Motor unit

Question 3

Which motor neuron innervates the highest number of muscle fibers?

Answer 3

In the leg

Question 4

Site differences hand/leg?

Answer 4

Hand: 3-5 fibers/neuron, leg: 100-2000 fibers/neuron

Question 5

1 motor unit only contains fibers of the same type: true/false

Answer 5

true

Question 6

What type of motor unit is activated during very high intensity?

A) Slow type (1)
B) Fast, fatigue resistant (2a)
C) Fast, fatigable (type 2x)
D) All of the above

Answer 6

D)

Question 7

Resistance training increases muscle strength by:
A) Increasing the physiological cross-sectional area of the muscle
B) Increasing the relative effort distance (joint axis + connection tendon distance)
C) Improving motor neuron functioning
D) 1 + 2
E) 1 + 3
F) 1 + 2 + 3

Answer 7

A) Increasing the physiological cross-sectional area of the muscle
B) Increasing the relative effort distance (joint axis + connection tendon distance)
C) Improving motor neuron functioning
D) 1 + 2
–> 1 + 3
F) 1 + 2 + 3

Question 8

Force of muscle action dependent on:

Answer 8

• Number of muscle fibers contracting (recruitment)
• Frequency of fiber contraction (statis)

Question 9

electrical changes with training?

Answer 9

• Training improves force and speed
• Associated with stronger and faster muscular electrical activity
• Also associated with an increasing firing frequency of motor units

Question 10

Exercise increases the capillarization of muscle tissue.
>40% increase in the number of capillaries/muscle.
Angiogenesis (formation new blood vessels), regulated by:

Answer 10

 Important role for vascular endothelial growth factor (VEGF)
Larger supply of oxygen for aerobic ATP production

Question 11

How can oxidative phosphorylation be measured by high resolution respirometry?

Answer 11

Oxidative phosphorylation = primary oxygen consumptive process. Can be measured by oxygen consumption of the cell:
* Measures disappearance oxygen from medium

Question 12

The higher the muscle statis, the higher the X capacity of your muscle cells

Answer 12

oxidative capacity

Question 13

Post-exercise recovery of phosphocreatine is depending in…

Answer 13

depending on oxidative metabolic pathways → reflects mitochondrial oxidative functioning
 The higher your mito capacity, the faster resynthesis of PCr
 Mono-exponential curve: rate constant reflect mitochondrial functioning

Question 14

P-MRS can be used for
NIRS can be used for

Answer 14

1 PCr measurement (very expensive)
2 measuring oxygen consumption of the muscle

Question 15

Immediately after exercise, muscle O2 consumption remains transiently elevated to restore PCr levels. Higher mito capacity will result in a ..
Faster/slower recovery of muscle O2 consumption and faster/slower recovery of PCr

Answer 15

Faster, faster

Question 16

Q: Increased mito density and capacity is likely to be associated with..

A) Glycolytic enzymes
B) Enzymes involved in beta oxidation
C) Enzymes of the citric acid (krebs) cycle
D) Enzymes in oxidative phosphorylation

Answer 16

B), C), D)
* All 3 processes take place in mito’s, all 3 need to be increased to increase mito capacity

Question 17

Three suggested mechanisms that link exercise to adaptations in mitochondrial biogenesis and function:

Answer 17

• Increased [Ca2+] in cytosol/mitochondria
• Increased ATP turnover → increased activity of AMP-activated protein kinase (AMPK)
• Increased activity of mitogen-activated protein kinase p38γ

Question 18

MAPK p38γ activation increases muscle contraction. It is activated by..

Answer 18

 Increased production of reactive oxygen species (ROS)?
 Increased [Ca2+] in cytosol/mitochondria?

Question 19

• p38γ MAPK essential for adaptation to exercise training. True/false

Answer 19

true

Question 20

PGC-1alfa seems to be central switch in X as well as X to exercise

Answer 20

adaptation of mitochondria
angiogenesis

Question 21

PGC-1alfa is a transcriptional co-activator (cannot bind to DNA itself). It is activated by..

Answer 21

AMPK (exercise). Learn the scheme on page 46

Question 22

What is NRF?

Answer 22

compound that needs to react together with PGC-1a (Nuclear respiratory factor-1)

Question 23

How is NRF-1 expression increased?

Answer 23

• Exercise increases NRF-1 expression
• Effect stronger in untrained subjects

Question 24

What does NRF-1 also stimulate?

Answer 24

mito transcription factor A (TFAM)

Question 25

TFAM is essentially involved in…

Answer 25

mito biogenesis

Question 26

Learn scheme on page 48

Answer 26

ok