Duration of Muscle Contraction - Physiology and Anatomy - Quiz | Exercises Physiology

V. Factors Affecting the Force, Velocity, and Duration of Muscle Contraction

A. Factors affecting the force of contraction

1. Number of muscle fibers stimulated

2. Relative size of the muscle

3. Degree of muscle stretch

B. Factors affecting the velocity and duration of contraction

1. Muscle fiber type

a. Slow-twitch or Type I fibers, slow-oxidative fibers

b. Fast-twitch or Type II fibers, fast-glycolytic fibers

c. Type IIA fibers, fast oxidative

VI. Effects of Exercise

A. Improved ability to obtain ATP from oxidative phosphorylation

B. Increase size and number of mitochondria

C. Less lactic acid produce per given amount of time

D. Increased myoglobin content

E. Increased intramuscular triglyceride content

F. Increased lipoprotein lipase (enzyme needed to utilize lipids from blood)

G. Lower rate of glycogen depletion during exercise

H. Improved efficiency in extracting oxygen from blood

I. Decrease number of type II (fast glycolytic fibers); increased number of type IIA (fast oxidative)

VII. Smooth Muscle

A. Physiology

1. Ca+2 and calmodulin activate myosin light chain kinase (MLCK)

2. MLCK transfers a phosphate group from ATP to myosin heads

3. Cross-bridge formation occurs with phosphorylation of myosin heads

4. Detachment of myosin heads requires myosin phosphatase (removes Pi from myosin heads)

B. Types of smooth muscle

1. Visceral, or unitary smooth muscle

a. More common – muscle of digestive, reproductive, and urinary tracts

b. Numerous gap junctions allow action potentials to pass from one fiber to another

c. Muscle fibers function as a

unit

(like the 3 Musketeers – “All for one and one for all”!

d. Is often autorhythmic (digestive); some contracts only when stimulated (urinary)

2. Multiunit

a. Occurs as sheets (blood vessels), as small bundles (arrector pili, iris)

b. Fewer gap junctions; cells or groups of cells act as

independent

units

c. Contracts only when stimulated by hormones or nerves

C. Electrical properties of smooth muscle

1. Slow waves of depolarization

2. Action potentials superimposed on a slow wave of depolarization

3. Spontaneously generated action potentials

a. Characteristic of muscle in the uterus, ureter, and digestive system

D. Functional properties of smooth muscle

1. Some smooth muscle exhibits autorhythmic contractions

2. Smooth muscle tends to contract in response to being stretched; a slow increase in length

produces less of a response than a more rapid increase in length

E. Regulation of smooth muscle

1. Most important neurotransmitters are ACh and norepinephrine

2. Hormones (epinephrine, oxytocin)

3. Locally-produced substances (carbon dioxide, prostaglandins, histamine)

Docsity.com

Partial preview of the text

Download Duration of Muscle Contraction - Physiology and Anatomy - Quiz and more Exercises Physiology in PDF only on Docsity!

V. Factors Affecting the Force, Velocity, and Duration of Muscle Contraction A. Factors affecting the force of contraction

Number of muscle fibers stimulated
Relative size of the muscle
Degree of muscle stretch B. Factors affecting the velocity and duration of contraction
Muscle fiber type a. Slow-twitch or Type I fibers, slow-oxidative fibers b. Fast-twitch or Type II fibers, fast-glycolytic fibers c. Type IIA fibers, fast oxidative VI. Effects of Exercise A. Improved ability to obtain ATP from oxidative phosphorylation B. Increase size and number of mitochondria C. Less lactic acid produce per given amount of time D. Increased myoglobin content E. Increased intramuscular triglyceride content F. Increased lipoprotein lipase (enzyme needed to utilize lipids from blood) G. Lower rate of glycogen depletion during exercise H. Improved efficiency in extracting oxygen from blood I. Decrease number of type II (fast glycolytic fibers); increased number of type IIA (fast oxidative) VII. Smooth Muscle A. Physiology
Ca+2^ and calmodulin activate myosin light chain kinase (MLCK)
MLCK transfers a phosphate group from ATP to myosin heads
Cross-bridge formation occurs with phosphorylation of myosin heads
Detachment of myosin heads requires myosin phosphatase (removes Pi from myosin heads) B. Types of smooth muscle
Visceral, or unitary smooth muscle a. More common – muscle of digestive, reproductive, and urinary tracts b. Numerous gap junctions allow action potentials to pass from one fiber to another c. Muscle fibers function as a unit (like the 3 Musketeers – “All for one and one for all”! d. Is often autorhythmic (digestive); some contracts only when stimulated (urinary)
Multiunit a. Occurs as sheets (blood vessels), as small bundles (arrector pili, iris) b. Fewer gap junctions; cells or groups of cells act as independent units c. Contracts only when stimulated by hormones or nerves C. Electrical properties of smooth muscle
Slow waves of depolarization
Action potentials superimposed on a slow wave of depolarization
Spontaneously generated action potentials a. Characteristic of muscle in the uterus, ureter, and digestive system D. Functional properties of smooth muscle
Some smooth muscle exhibits autorhythmic contractions
Smooth muscle tends to contract in response to being stretched; a slow increase in length produces less of a response than a more rapid increase in length E. Regulation of smooth muscle
Most important neurotransmitters are ACh and norepinephrine
Hormones (epinephrine, oxytocin)
Locally-produced substances (carbon dioxide, prostaglandins, histamine)

Docsity.com

g. Conformation change in DHP receptors opens calcium release channels (Ryanodine receptors) that allows calcium diffusion into the sarcoplasm from sarcoplasmic reticulum h. Binding of Ca++^ to torponin (Tn-C site) i. Exposure of myosin binding sites by movement of tropomysin j. Powerstroke process (see above) k. Uptake of Ca++^ and relaxation of muscle III. Physiology of Skeletal Muscles A. The muscle twitch

Latent period
Period of contraction
Period of relaxation B. Stimulus frequency and muscle contraction
Action potential which causes contraction is completed long before the contraction phase is completed.
Contractile mechanism of muscle exhibits no refractory period; i.e., relaxation of muscle is not required before a second action potential can stimulate a second contraction.
Therefore, as frequency of action potentials increase, the frequency of contraction increases. a. Summation

Tension produced by a muscle increases as the frequency of contraction increases b. Incomplete tetanus c. Complete tetanus d. Treppe – the staircase effect C. Stimulus strength and muscle contraction

Subthreshold stimulus produces no action potential and thus no contraction
Threshold stimulus produces an action potential and a contraction
Motor units – respond as a single unit

All fibers of a MN contract to produce a constant force in response to threshold stimulus

Whole muscle responses

More complex than those of individual muscle fibers or motor units
Respond to stimuli in graded fashion – strength of contraction can range from weak to strong
Multiple motor unit summation (recruitment) – force of contraction increases as more and more motor units are recruited
Asynchronous activation of motor units – alternate response of motor units to produce smooth, sustained contractions D. Length-Tension Relationship of Muscle Contraction E. Force-Velocity

Shows the inverse relationship between “load” and the velocity of muscle shortening F. Type of muscle contractions
Isotonic contractions
Isometric contractions
Eccentric contractions IV. Energy Sources for Muscle Contraction A. Maximal Oxygen Uptake (VO2 max) B. Lactate threshold C. Energy pathways in muscle contraction
Direct phosphorylation of ADP by creatine phosphate
Anaerobic glycolysis and lactic acid formation
Aerobic respiration

Duration of Muscle Contraction - Physiology and Anatomy - Quiz, Exercises of Physiology

Related documents

Partial preview of the text

Download Duration of Muscle Contraction - Physiology and Anatomy - Quiz and more Exercises Physiology in PDF only on Docsity!

Docsity.com

Docsity.com