26 October 2010 This Week in Physiology: Lab: Frog Muscle Physiology Lectures: Wednesday: Ch. 9 Muscle Physiology Friday Finish Muscle, then Ch. 10 Control of Movement Abstracts due Friday Test on Monday Coverage to be posted to Website Starts with Nervous System Ends with Muscle Physiology

1QQ # 22 for 8:30 am 1. What events occur during the latent period before a muscle develops tension? 2. Once a muscle is stretched greater than 120% of its optimal length, what happens? 3. As a muscle contracts, a) A bands get narrower b) I bands get narrower c) H bands get narrower d) Z lines move closer together e) M lines move closer together

1QQ # 22 for 9:30 am 1. What term applies to the type of muscle contraction where the tension developed is less than the load on the muscle? 2. What are the three roles of ATP in skeletal myofibers? 3. What causes a muscle contraction to end?

Fig. 09.13 S 1 Motor unit = a single somatic motor neuron and all the muscle fibers in innervates 09.13.jpg

S 2 Size Principle

Increasing tension in a whole muscle Frequency of stimulation of motor neuron Activate larger motor units Recruitment: activate more motor units These factors also influence actual tension Fiber length (length-tension) relationship Fiber diameter Level of fatigue (state of activity)

Muscle Metabolism Fiber types Speed of myosin ATPase (fixed for a cell) Slow isozyme = slow twitch = Type I Fast isozyme = fast twitch = Type II Metabolic sources of ATP Oxidative phosphorylation Glycolytic Timing of fatigue Oxidative = fatigue resistant Glycolytic = fatigue quickly (but recover quickly)

Classes of Myofibers based on Twitch Duration Each muscle fiber express only one of two different myosins isozymes: Fast twitch = rapid hydrolysis of ATP means crossbridges cycle faster Slow twitch = slower hydrolysis, isozyme catalyzes the reaction slower Isozymes not modified by athletic training! Contraction velocity also affected by load!

S 5 Lifting a load and contraction velocity

S 7 Comparison of contraction time (measured?): extraocular muscle (IR, internal rectus), gastrocnemius (G), and soleus (S) Whole muscles consist of many motor units. Each motor unit has myofibers of only one type (I, IIA or IIB)

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)

Fig. 09.03 S 9 Type I Type II A Type II B 09.03.jpg

3 Sources of ATP in muscle Powerstroking & Disconnecting crossbridges 09.22.jpg 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

Use of Creatine as a Nutritional Supplement                                                                                    A 1998 Review on the Use of Creatine as a Nutritional Supplement

Type I Type IIA Type IIB S 12 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

Fig. 09.26 S 14 Relationship between recruitment and fiber type 09.26.jpg

S 15

Fig. 09.24b S 16 Read section of King et al., 1999 that deals with analysis of muscle biopsy material in subjects taking Andro or placebo while resistance training. What changes were expected? What changes were observed? 09.24b.jpg