Lecture 6 Flashcards by Jesse Sachs

Two types of muscle contraction

Isometric (increase in tension, muscle doesn’t shorten, flexing)
Isotonic (muscle contracts, muscle shortens, join moves)

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Isometric contraction does what?

Maintains posture

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Two types of isotonic contraction

Concentric (muscle shortens)
Eccentric (muscle contracts as it lengthens)

Concentric bicep curl, eccentric letting the weight back down slowly. You do both every time you walk.

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A lower motor neuron and all the muscle fibers it supplies is called

Motor Unit
(Spinal cord to muscle)

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What determines how many motor units you use

The demand on muscles

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Three phases of a muscle twitch are

Latent period (2 msec), stimulation is taking place
Period of contraction (15 msec), cross bridges form, muscle shortens
Relaxation (25 msec), ca2+ is reobsorbed into the SR, tension goes to zero

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A single stimulus that results in a single contractile response

muscle twitch

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Frequently delivered stimuli increases contractile force

Wave summation

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More rapidly delivered stimuli results in

Incomplete (unfused) tetanus

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If stimuli are given rapidly enough:

Complete (fused) tetanus

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The stimulus at which first observable muscle contraction occurs

Thredshold stimulus

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Using multiple motor unit summation to control force of contraction

Recruitment

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Turn on muscle fibers selectively for smooth movement

From smallest to largest muscle fibers for economy

Asynchronous recruitment

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Simultaneous use of all muscle fibers

Synchronous recruitment

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The constant, slightly contracted state of all muscles which does not produce active movements

Muscle Tone

Like an idling engine

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Tone of muscle above normal

Hypertonic (muscle spasm)

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Tone of muscle going up

Hypertonic (muscle spasm)

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Tone of muscle below normal

Hypotonic (flaccid)

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Only source used directly for contractile activity

ATP

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ATP stores regenerated by these three mechanisms

1- Creatine phosphate (CP)
2- Anaerobic glycolysis
3- Aerobic respiration

ATP hydrolized (used up) in 5 seconds

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Direct phosphorylation

CP + ADP = Creatine + ATP

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Nitrogenous organic acid made in liver

Creatine Phosphate

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Creatine breakdown product

Creatinine

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How many seconds of ATP does the body store

5 seconds

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how many seconds of CP does the body store

15 seconds

Pyruvic acid converted into lactic acid

Anaerobic glycolysis

Duration of anaerobic glycolysis

30-40 (maybe 60) seconds | When you start breathing, lactic adcid turns back into pyruvic acid

95% of ATP supplied this way for resting skeletal muscles

Aerobic glycolysis

Aerobic Pathway produces how many ATP

32!

Duration of Aerobic glycolysis

Hours

ATP production fails to keep pace with ATP use

Muscle fatigue

Issues from muscle fatigue

ion imbalances lactic acid accumulation contractures dt deficit of ATP

Hemoglobin brings oxygen to

Myoglobin

Extra amount of O2 needed for muscle restoration

Oxygen debt (afterburn), lactic acid conversion back to pyruvic, etc.

% of energy released in muscle activity that goes into work

40%

% of energy released in muscle activity that is given off as heat

60%

Force of muscle contraction based on:

Motor unit and therefore number of muscle fibers (cells) contracting

Two types of muscle fibers

Slow and fast twitch

Muscle fibers that use aerobic pathways

oxidative fibers

Muscle fibers that use anaerobic pathways

Glycolytic fibers

So, three types of muscle fibers

1- slow oxidative fibers 2- fast oxidative fibers 3- fast glycoliytic fibers

contract slowly, have slow acting myosin ATPases, and are fatigue resistant

slow oxidative fibers

contract quickly, have fast myosin ATPases, and have moderate resistance to fatigue

fast oxidative (intermediate) fibers

contract quickly, have fast myosin ATPases, and are easily fatigued

fast (power burst) glycolytic

Where is smooth muscle found in the body?

visceral organs, stomach, bladder, respiratory passages

Smooth muscle is under what kind of control

Autonomic control

Smooth muscle straited or not striated?

NOT

Two layers of smooth muscle

Longitudinal and circular

Smooth muscle innervated by

autonomic fibers with varicosities with large, diffuse junctions - these facilitate slow activity

Structures of smooth muscle cells

1- gap junctions that provide electrical synapses 2- dense bodies that allow physical attachment of cells to each other and to cytoplasma membrane

sarcomere-like structures in smooth muscle

most viscera of the body, including the gut, bile ducts, ureters, uterus, and many blood vessels is made of what kind of smooth muscles?

Unitary, or visceral smooth muscle

ciliary muscle of the eye, the iris muscle of the eye, and the piloerector muscles that cause erection of the hairs

multiunit smooth muscle

Force capability of smooth relative to skeletal muscle

up to 50% more

smooth muscle contractions are initiated by

Hormones Autonomic motor nerve impulses Stretch

a regulatory protein in smooth muscle similar to troponin, ca2+ binds to this

calmodulin

Ca2+ calmodulin complex activates

enzyme myosin light chain kinase

What do kinase enzymes do

phosphorelate

toxin that prevents the releaseof ACh at the neuromuscular junction, leading to a potentially fatal muscular and respiratory paralysis

botulism

ACh receptors at the neuromuscular junctions attacked by autoantibodies. MBS

Myasthenia Gravis

within a few hours, the skeletal muscle fibers have run out of ATP and the SR becomes unable to pump Ca2+ out of the sarcoplasm

rigor mortis