muscle physio pt.2

Treppe: The Staircase Effect

When a muscle is first used, it will show a gradual

increase in force with a maximal stimulus until it is 'warmed up"

Muscle Tone

slightly contracted state of muscle that is maintained by reflexes

originating in the spinal cord. Maintains posture and readiness for active contraction

muscle tension -

force generated by a muscle

load

force resisting movement of a muscle.

Muscle tension must be greater than load to move it

isometric contraction

muscle doesn’t change length (trying to lift a box that is too

heavy)

isotonic contraction -

muscle moves the load (doing bicep curls with weights)

Force of Contraction

determined by several factors

1. number of motor units activated

2. size of muscle

a. size increased by increasing the SIZE of individual muscle cells (not increasing

cell #)

Series-Elastic Elements

connective tissue that attach muscle to bone. affects muscle by transferring force to load produced by out muscles. tendons dont have as much blood supply as muscles or as many cells so takes a longer time to regenerate

Degree of Muscle Stretch (Actin-Myosin Overlap)

dictates the amount of overlap between actin and myosin. optimal stretch - muscle produces max force at their resting length , at this length, their is an actin myosin overlap allowing max # of crossing.

Effect of the Load on a Muscle

maller the load, faster the contraction

b. larger load: slower contraction/less duration

Red Slow-Twitch Fibers (small, red)

low twitch; slow acting myosin ATPases

ii lots of myoglobin (red) to store oxygen

iii. many mitochondria, active enzymes

iv. use fat as primary fuel source

v. very aerobic, long duration contraction . SPECIALIZED IN ENDURANCE WITHOUT FATIGUING

White Fast-Twitch Fibers (large, pale)

ast twitch; fast acting myosin ATPases

ii. few mitochondria, primarily anaerobic

iii. glycogen stores used for anaerobic resp.

iv. lactic acid produced, fatigues quickly

V. rapid, intense, short duration contraction….. SPECIALIZED IN STRENGTH, POWER BUT FATIGUE QUICKLY

Intermediate Fast-Twitch Fibers (medium, pink)

fast twitch; fast acting myosin ATPases

ii. aerobic with myoglobin present

iii. somewhat resistant to fatigue

aerobic exercise -

that requiring steady oxygen

a. capillaries, myoglobin, mitochondria increase

b. better endurance and strength

resistance exercise

short duration, high load

a. actin, myosin, myofibers (in size) all increase

b. hypertrophy - increase in muscle size

b. glycogen stores and connective tissue increase

Disuse Atrophy

lack of use can result in loss of size (atrophy) and strength of a muscle

denervation

lack of nervous stimulation can also cause severe atrophy

whats the immediate reserve when we need ATP for muscle contraction

ADP - Creatine Phosphate (Immediate Reserve)

how does the ADP - Creatine Phosphate (Immediate Reserve) work?

Creatine-phosphate + ADP → Creatine + ATP

How long does the body use the ADP - Creatine Phosphate (Immediate Reserve) system for?

used for first 3 - 5 seconds of activity while respiration processes are warming up

if we still need more ATP what system do we use next

anaerobic respiration

anaerobic respiration pathway

glycolyis (6 C) glucose → pyruvic acid (INSUFFICIENT oxygen)

pyruvic acid → lactic acid

characteristics of anaerobic respiration

used for short-term, intense activity (10 - 15 sec)

** used when oxygen demand CANNOT be met by resp/circ

** yields only 2 ATP per glucose

** lactic acid is reconverted to pyruvic acid when oxygen becomes available

** pyruvic acid then broken down all the way to C02 to release 34 more ATP

Aerobic Respiration (Sufficient Oxygen Supply) pathway

glucose → pyruvic acid (SUFFICIENT oxygen)

pyruvic acid → H20 + C02

characteristics of aerobic respiraiton

used for more prolonged, steady activity (walking)

** used when oxygen demand CAN be met by resp/circ

** yields 36-38 ATP per glucose (18-19 X anaerobic!!!)

** glycolysis occurs in the sarcoplasm

oxidative reactions

using pyruvic acid to make more ATP, occurs in the mitochondria

Electron Transport Chain

Most ATP is produced at this stage

Occurs on inner mitochondrial membraneOccurs on inner mitochondrial membrane

Electrons from NADH and FADHNADH and FADH22 are transferred toare transferred to

electron acceptors, which produces aelectron acceptors, which produces a proton gradient

Proton gradient

used to drive synthesis of ATP.

Chemiosmosis

ATP synthase allows H++ to flow acrossto flow across

inner mitochondrial membrane down concentrationinner mitochondrial membrane down concentration

gradient, which produces ATP.gradient, which produces ATP.

The electron transport chain ONLY works when OXYGEN is available at the end works when

OXYGEN is available at the end

of the chain to accept the electrons and Hof the chain to accept the electrons and H++ toto

form water.

muscle fatigue

inability of a muscle to contract on a physiological basis

a. when there is less ATP than the muscle requires

b. lactic acid buildup decreases pH, affects enzymes

c. salt loss (Na+, K+, Ca++); ionic imbalance

d. ATP required to drive Na+-K+ ATPase Pump

contractures

continuous contracted state of the muscle ("heads" are not released)

oxygen debt

oxygen must be "paid back" in order to restore muscle to original rested

state:

a. restore reserves of ATP and Creatine Phosphate

b. lactic acid converted back to pyruvic acid

c. restore reserves of glucose and glycogen

d. restore oxygen reserves (stored in myoglobin)

e. athletic conditioning increases the efficiency of oxygen use, thereby reducing oxygen

debt

heat production -

muscle contraction produces heat which can be dangerous (extreme body

temperature) or can be useful (generate heat by shivering)