26 October 2009

This Week in Physiology:Wednesday Quiz: 1 Question based

on Today’s LectureLab: Muscle Physiology #1

Lectures: Ch. 9 Muscle Physiology

Increasing tension in a whole muscle

• Frequency of stimulation of motor neuron• Activate larger motor units• Recruitment: activate more motor units

• These factors influence actual tension– Fiber length (length-tension) relationship– Fiber diameter– Level of fatigue (state of activity)

Muscle Metabolism• Fiber types

– Speed of myosin ATPase– Metabolic sources of ATP– Timing of fatigue

• Muscles in action– Causes of Fatigue– Training and fiber type– Creatine supplements

Migratory fowl?

Fig. 09.24b

Comparison of contraction time (measured?): extraocular muscle (IR, internal rectus), gastrocnemius (G), and soleus (S)

Classes of Myofibers based on Twitch Duration

The muscle fibers express different myosins:

• Fast twitch = rapid hydrolysis of ATP means crossbridges cycle faster

• Slow twitch = slower hydrolysis, isozyme catalyzes the reaction slower

3 Sources of ATP in muscle

Classes of Myofibers based on Metabolism and Enzyme profiles

• Oxidative: at peak activity rely on full aerobic cellular respiration– many mitochondria, enzymes for oxidative

phosphorylation, numerous capillaries, lots of myoglobin (red)

• Glycolytic: at peak activity rely on glycolysis– few mitochondria, many glycolytic enzymes, large

store of glycogen, fewer capillaries, little myoglobin (white)

Type I

Type IIA

Type IIB

What are the causes of fatigue?

Depends on the type of activity…

Causes of fatigue• High intensity, short duration exercise

– Conduction failure in t-tubules– Lactic acid accumulation– Accumulation of ADP and inorganic phosphate

• Low intensity, long duration exercise– As above, and– Depletion of muscle glycogen– Low plasma glucose (hypoglycemia)– Dehydration

• Control pathways: “willpower”– Common in couch potatoes

Response to training

• Resistance trainingType II change enzyme profilesType II add more actin and myosinType II increase CS area (hypertrophy)

• Endurance training– Type I increases vascularity– Type I increase number of mitochondria

Fig. 09.24bRead section of King et al., 1999 that deals with analysis of muscle biopsy material in subjects taking Andro or placebo.

Fig. 09.26Relationship between recruitment and fiber type

Creatine phosphate, then oxidative phosphorylation (OP) from glycogen, then OP from blood glucose, then blood fatty acids. If intense, switch to glycolysis… then take a breather… oxygen debt

Sources of fuel with moderate exercise

                                                                                  

A 1998 Review on the Use of Creatine as aNutritional Supplement

Fig. 09.03

What accounts for the slow dynamics?

How are actin and myosin anchored?

Figure 9.34Sources of calcium?

Slow!!!

Benefit?

Comparison:

How does tension diminish?

Thank God for latch state!Crucial for long-term tension of sphincters.