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Physiology-Muscles
Exam 3
18
Physiology
Undergraduate 3
12/01/2013

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Term
3 functions of muscles
Definition
locomotion
movement of food
intracellular transport
Term
motor molecules
Definition
1. myosin
2. dynein
3. kenesin

drive motion in living organisms, all three kinds are capable of chemomechanical transduction (transformation of chemical energy to mechanical energy)
Term
myosin
Definition
kind of motor molecule
creates motion in vertebrate striated muscles by interacting with actin
Term
dynein
Definition
kind of motor molecule
in cilia and flagella
causes sliding motion via beating of fibers of cilia and flagella
Term
kinesin
Definition
kind of motor molecule
creates movement via ATP binding/unbinding; kinesin "walks" across cytoskeleton
Term
Muscle structure of striated muscles
Definition
muscle fibers: long, multinucleated cells
microbrils: in muscle fibers, made of sarcomeres
sarcomeres: contractile units where motion is generated
Term
sarcomere structure
Definition
contractile unit where motion is generated

z-disk: two z-disks determine edges of sarcomere; they move in space
A band: large dark area; stays constant length during muscle contractions
I band: large light area; gets shorter during muscle contractions
H zone: smaller, lighter area in middle of A band; gets shorter during muscle contractions
**darkness/lightness is caused by overlapping of filaments

thick filaments: myosin (myofilaments have two thick filaments that coil around each other and cluster at end where there are myosin light chains)
thin filaments: actin (acts like a string of beads with tropomyosin and troponin wrapped around it)
**are all anchored on z-disk in a scaffold-like structure
Term
sliding-filament theory
Definition
-tension in apparatus is caused by compression of filaments (shorten/lengthen sarcomere)
-the longer the sarcomere, the greater the potential to create tension
Term
How does sliding of filaments in muscle happen?
Definition
1. Actin and myosin bind in a weak bond
2. ATP breaks actin from Myosin
3. Myosin becomes Myosin-ATP, which phosphyorylates to become Myosin-ADP-Pi (changes shape)
4. Myosin-ADP-Pi reaches out and grabs Actin as it changes shape
5. Actin replaces the Pi
6. Actin and Myosin separate and restart cycle

"crossbridge cycling"
Term
regulation of muscle contraction
Definition
-troponin: 3 protein complex
troponin C (binds Ca++), troponin I, troponin T
**in absense of Ca++, troponin blocks binding sites of myosin to actin
**in presence of Ca++, troponin T/I/C affinity is strengthened, and they lift off of binding sites to allow myosin to bind to actin

Ca++ exposes binding sites via cross-bridge cycling
Term
How does an action potential result in Ca++ release in a muscle contraction/relaxation?
Definition
1. Neural input initiates depolarization
2. AP is conducted into muscle via t-tubules
3. Dihydropine receptors open ryanodine receptors
4. Ca++ floods out of sarcoplasmic reticulum until channels close
5. Ca++ binds to troponin, freeing myosin binding sites
6. unlinked myosin heads bind to actin
7. ATP releases and repeats the cycle
8. Ca++ pumps in sarcoplasmic reticulum lowers Ca++ level, binding sites on acting are obstructed
Term
Muscle fiber types
Definition
1. Tonic fibers; slow, continuous contraction, no twitches
no action potentials
efficiently generate isometric tension
often in postural muscles (constant use)
house stretch receptors

2. Slow-twitch fibers (Type I): contract slowly, fatigue slowly
generate all-or-none APs

3. Fast-twitch oxidative fibers (Type IIA): contract quickly, activate quickly, fatigue slowly
have many mitochondria, specialized for rapid repetition

4. Fast-twitch glycolitic fibers (Type IIB): contract quickly, fatigue quickly
have rapid Ca++ kinetics, have few mitochondria and are not able to sustain activity
Term
types of muscle contraction
Definition
isometric contraction: having tension without change in length

isotonic contraction: change in length without constant tension
Term
Why do we have different kinds of muscle fibers?
Definition
Trade off between speed and energetic cost
mechanical properties and energetic properties depend on V and Vmax

different Vmax profiles have different efficiency profiles
Term
Muscle adaptions
Definition
-change amount of thick and thin filament overlap
-change relative shortening velocity (V and Vmax)
-change time and duration of active state
Term
energy storage in muscle systems
Definition
store energy over time, can release it extremely quickly; some movements happen too quickly for muscles to function, so stored energy actually creates the motion
Term
Movement in sound production
Definition
sound can be made by rapid contractions (rapid vibrations)
don't want summation to occur, so there would be a decrease in refractory period (via increased reuptake of Ca++)
sonic muscle adaption happens by having very high Ca++ levels so you can distinguish each AP
Term
Vertebrate muscle
Definition
-motor neuron: each muscle fiber has only one motor neuron that can stimulate it
each motor neuron can activate multiple fibers
-motor unit: multiple fibers
-motor pool: units coming into a muscle

strength of a contraction is regulated by
-activation of different numbers of motor units
-frequency of activation

tension is correlated with percent of motor pool and strength of activation of motor units

fine control: smaller motor units (more of them, more dense)
course control: larger motor units (more spread out)
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