Lecture 6 Flashcards
Two types of muscle contraction
Isometric (increase in tension, muscle doesn’t shorten, flexing)
Isotonic (muscle contracts, muscle shortens, join moves)
Isometric contraction does what?
Maintains posture
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.
A lower motor neuron and all the muscle fibers it supplies is called
Motor Unit
(Spinal cord to muscle)
What determines how many motor units you use
The demand on muscles
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
A single stimulus that results in a single contractile response
muscle twitch
Frequently delivered stimuli increases contractile force
Wave summation
More rapidly delivered stimuli results in
Incomplete (unfused) tetanus
If stimuli are given rapidly enough:
Complete (fused) tetanus
The stimulus at which first observable muscle contraction occurs
Thredshold stimulus
Using multiple motor unit summation to control force of contraction
Recruitment
Turn on muscle fibers selectively for smooth movement
From smallest to largest muscle fibers for economy
Asynchronous recruitment
Simultaneous use of all muscle fibers
Synchronous recruitment
The constant, slightly contracted state of all muscles which does not produce active movements
Muscle Tone
Like an idling engine
Tone of muscle above normal
Hypertonic (muscle spasm)
Tone of muscle going up
Hypertonic (muscle spasm)
Tone of muscle below normal
Hypotonic (flaccid)
Only source used directly for contractile activity
ATP
ATP stores regenerated by these three mechanisms
1- Creatine phosphate (CP)
2- Anaerobic glycolysis
3- Aerobic respiration
ATP hydrolized (used up) in 5 seconds
Direct phosphorylation
CP + ADP = Creatine + ATP
Nitrogenous organic acid made in liver
Creatine Phosphate
Creatine breakdown product
Creatinine
How many seconds of ATP does the body store
5 seconds
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
