26 October 2009 This Week in Physiology: Wednesday Quiz: 1 Question based on Today’s Lecture Lab: 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 b

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 training Type II change enzyme profiles Type II add more actin and myosin Type II increase CS area (hypertrophy) Endurance training – Type I increases vascularity – Type I increase number of mitochondria

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

Fig Relationship 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 a Nutritional Supplement

Fig

What accounts for the slow dynamics?

How are actin and myosin anchored?

Figure 9.34 Sources of calcium? Slow!!! Benefit?

Comparison: How does tension diminish? Thank God for latch state! Crucial for long-term tension of sphincters.