Post on 14-Apr-2018
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MUSCLECONTRACTION
DODY TARUNA,dr, M.KesDEPT. OF PHYSIOLOGY
HANG TUAH MEDICAL FACULTY
SURABAYA
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Muscle Types
Cardiac heart
Smooth internal organs
Skeletal
"voluntary"Attach to bone
Move appendages
Support body
Antagonistic pairs
Flexors
Extensors
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Muscle Types
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Describe the structural and physiological
differences between cardiac muscle and
skeletal muscle;
Describe the structural and physiological
differences between smooth muscle and
skeletal muscle; and
Relate the unique properties of smooth
muscle to its locations and functions.
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About 40% body mass
Muscle fibers cells
Fascicle
bundleMotor unit
Muscle
sheath
Attach to tendons (which attach to bone)
Skeletal Muscle Anatomy
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Skeletal Muscle Anatomy
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Multiple nuclei
Sarcolemma
T-tubules
Sarcoplasmic reticulum
Sarcoplasm
Mitochondria Glycogen & ions
Myofibrils
Muscle Fiber Structure
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Muscle Fiber Structure
Figure 12-3b: ANATOMY SUMMARY: Skeletal Muscle
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Actin "thin fibers"
Tropomysin
Troponin
Myosin "thick fibers"
Tinin
elastic anchorNebulin non-elastic
Myofibrils: Site of Contraction
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Myofibrils: Site of Contraction
Figure 12-3c-f: ANATOMY SUMMARY: Skeletal Muscle
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Sarcomere length
Problem
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Muscular
Contraction
The sliding filamentmodel Movement of the
actin filament overthe myosin filament
Formation of cross-bridges betweenactin and myosinfilaments
Reduction in thedistance between Z-discs of thesarcomere Actin
Myosin
Actinin (z-disc)
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MUSCLE CONTRACTION
The process of muscle contraction and
relaxation can be viewed as occurring in
four major phases:
(1)excitation.
(2)excitation-contraction coupling.
(3)contraction.(4)relaxation.
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MUSCLE CONTRACTION
1.Excitation
Excitation is the process in which actionpotentials in the nerve fiber lead to action
potentials in the muscle fiber.
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EXCITATION
1.1.A nerve signal the synaptic knob
stimulates voltage-gated calcium channels
OPEN Calcium ions enter the synaptic knob.
1.2.Calcium ions stimulate exocytosis of thesynaptic vesicles release acetylcholine (ACh)
into the synaptic cleft.
One action potential causes exocytosis of about
60 synaptic vesicles, and each vesicle releases
about 10,000 molecules of ACh.
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EXCITATION
1.3.ACh diffuses across the synaptic cleft
binds to receptor proteins (LIGAND GATEDion channels) on the sarcolemma.
1.4.ACh (the ligand) binds to receptor rec.change shape open an ion channel
through the middle of the rec. proteinNadiffuse quickly into the cell and K diffuseoutward the sarcolemma reversespolarityits voltage quickly jumps fromRMP(resting membrane potential) of -90 mVto a peak of +75mV as Na enters, and thenfalls back to a level mV as Na close to theRMP as K diffuses out called the end-platepotential (EPP).
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EXCITATION
1.5.Areas of sarcolemma next to the end
plate have voltage-gated ion channels
open in response to the EPP. Some of the
voltage-gated channels are and admit it tothe cell, while specific for Na others are
specific for K and allow it to leave.
These ion movements create an actionpotential.The muscle fiber is now excited
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MUSCLE CONTRACTION
2.Excitation-Contraction Coupling
Link the action potentials on thesarcolemma activation of the
myofilaments, Preparing them to
contract
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Excitation-Contraction Coupling
2.1.A wave of action potentials spreads from
the end plate in all directions, like ripples
on a pond. When this wave of excitation
reaches the T tubules, it continues downthem into the sarcoplasm.
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Excitation-Contraction Coupling
2.2.Action potentials open voltage-regulated
ion gates in the T tubules. These are
physically linked to calcium channels in
the terminal cisternae of the sarcoplasmicreticulum (SR), so gates in the SR open as
well and calcium ions diffuse out of the
SR, down their concentration gradient andinto the cytosol.
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Excitation-Contraction Coupling
2.3.The calcium ions bind to the troponin of
the thin filaments.
2.4.The troponin-tropomyosin complex
changes shape and shifts to a new
position. This exposes the active sites on
the actin filaments and makes them
available for binding to myosin heads.
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MUSCLE CONTRACTION
3. Contraction
In 1954, two researchers at theMassachusetts Institute of Technology, Jean
Hanson and Hugh Huxley, found evidence fora model now called the sliding filamenttheory.
This theory holds that the thin filaments slide
over the thick ones and pull the Z discsbehind them, causing the cell as a whole toshorten
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CONTRACTION
3.1.The myosin head must have an ATPmolecule bound to it to initiate thecontraction process. Myosin ATPase, anenzyme in the head, hydrolyzes this ATP.The energy released by this processactivates the head, which cocks into anextended, high-energy position. The headtemporarily keeps the ADP and phosphate
group bound to it.3.2.The cocked myosin binds to an activesite on the thin filament.
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CONTRACTION
3.3.Myosin releases the ADP andphosphate and flexes into a bent, low-energy position, tugging the thin
filament along with it. This is called thepower stroke. The head remains boundto actin until it binds a new ATP.
3.4.Upon binding more ATP, myosinreleases the actin. It is now prepared torepeat the whole Process.
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CONTRACTION
A fiber, however, may shorten by as much
as 40% of its resting length, so obviously
the cycle of power and recovery must be
repeated many times by each myosinhead. Each head carries out about five
strokes per second, and each stroke
consumes one molecule of ATP.
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MUSCLE CONTRACTION
4.Relaxation
When its work is done, a muscle fiberrelaxes and returns to its resting length.
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Relaxation
4.1.Nerve signals stop arriving at the neuromuscularjunction, so the synaptic knob stops releasing ACh.
4.2.As ACh dissociates (separates) from its receptor,acetylcholinesterase breaks it down into fragments that
cannot stimulate the muscle. The synaptic knobreabsorbs these fragments for recycling. All of thishappens continually while the muscle is beingstimulated, too; but when nerve signals stop, no new
ACh is released to replace that which is broken down.
Therefore, stimulation of the muscle fiber by AChceases.
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Relaxation4.3.Active transport pumps in the
sarcoplasmic reticulum (SR) pumpCa from the cytosol back into thecisternae. Ca binds toCalsequestrinstored until fiber
stimulated again. ATP is needed formuscle relaxation as well as for musclecontraction
4.4.As calcium ions dissociate fromtroponin, they are pumped into the SRand are not Replaced.
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Relaxation
4.5.Tropomyosin moves back into the
position where it blocks the active sites of
the actin filament. Myosin can no longer
bind to actin, and the muscle fiber ceasesto produce or maintain tension.
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Relaxation
A muscle returns to its resting length with the aid
of two forces:
(1)like a recoiling rubber band, the series-elastic
components stretch it; and(2)since muscles often occur in antagonistic pairs,
the contraction of an antagonist lengthens the
relaxed muscle. Contraction of the triceps
brachii, for example, extends the elbow and
lengthens the biceps brachii.
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Energy for Contraction: ATP &
Phosphocreatine
Aerobic Respiration Oxygen
Glucose
Fatty acids
30-32 ATPs
Anaerobic Respiration Fast but
2 ATP/glucose
PhosphocreatineATPs
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Energy for Contraction: ATP &
Phosphocreatine
Figure : Phosphocreatine
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Central "Feeling"
Lactic acid
Peripheral Glycogen depletion
Ca2+ interference
High Pi
levels
ECF high K+
ACh depletion
Muscle Fatigue: Causes not well known
Figure : Locations and possible causes of muscle fatigue
Fiber Contraction Speed: Fast
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Rate 2-3 times faster
SR uptake of Ca2+
ATP splitting
Anaerobic/Fatigue easily
Power lifting
Fast/delicate
Sprint
Fiber Contraction Speed: Fast
Twitch
Fiber Contraction Speed: Fast
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Fiber Contraction Speed: Fast
Twitch
Figure : Fast-twitch glycolytic and slow-twitch muscle fibers
Fiber Contraction Speed: Oxidative
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Oxidative Fast Twitch Intermediate speed
Anaerobic & aerobic
Slow Twitch: Aerobic, less fatigue More mitochondria
More capillaries
Myoglobin
Endurance activities
Postural muscles
Fiber Contraction Speed: Oxidative
Fast & Slow
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Coordinating the Fibers: Force of Contraction
Figure : Length-tension relationships in contracting skeletal muscle
Excitation and Twitch
LengthTension: more crossbridges: more
tension
M t U it Fib I t d
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Motor Unit: Fibers Innervated
from 1 neuron"All or none"Fine touch
1:1 nerve to fiber
Finger tips
Big muscles
1: 2000
Leg muscles
PLAYAnimation: Muscular System:
Contraction of Motor Units
Figure 12-18: Motor units
Recruitment of Fibers: Produce
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Weak stimulus
Lowest threshold fibers
Slow twitch typically
Moderate: adds Fast
OxidativeHigh stimulus: all fibers
Asynchronous:
Units take turns
Prevents fatigue
Recruitment of Fibers: Produce
Graduated Force
Figure 12-18: Motor units
Mechanics of Body Movement:
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Tendons: muscle to bone
Ligaments: bone to boneMuscles: contraction force
Isotonic: movement
Isometric: no movement
Mechanics of Body Movement:
Joints
Mechanics of Body Movement:
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Mechanics of Body Movement:
Joints
Figure 12-19: Isotonic and isometric contractions
Coordinating the Fibers: Summation to
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Coordinating the Fibers: Summation to
Tetanus
Figure : Summation of contractions
Hi t h i l St i i f Fib
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Histochemical Staining of Fiber
Type
Type IIa
TypeIIb
Type I
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Preferential recruitment of
fibres by exercise type
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Higher % of
type 1 fibers
elevates
VO2max
True of both
athletes and
non-athletes
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Muscle: origin near body, insertion distal
Levers: bones, Fulcrum: joints
Physics of Joint Movement:
Figure : The arm is a lever and fulcrum system
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Establishes smooth
voluntary muscle
contractions and tone
Alpha/gamma co-
activation
Gamma activation leads
alpha activation in
voluntary movement
The Gamma system
Vestibular Apparatus and
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Vestibular Apparatus and
Equilibrium
Located in the innerear
Responsible formaintaining generalequilibrium andbalance
Sensitive tochanges in linearand angularacceleration
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Motor Control Functions of the Brain
Brain stem
Cerebrum
Cerebral cortex
Organization of complex movement
Storage of learned experiencesReception of sensory information
Motor cortex M1 (Area 4 and 6)
Most concerned with voluntary
movement
Cerebellum
Monitoring complex movement
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Smooth Muscles: Contrasted to
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Homeostatic role
Control fluid
Sphincters
Tonic contractions
Support tubes
Move products
Slow contractions
Little fatigue
Low O2 use
Smooth Muscles: Contrasted to
Skeletal Muscle
Figure : Duration of muscle contraction in
three types of muscle
Smooth Muscles: Contrasted to
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Smooth Muscles: Contrasted to
Skeletal Muscle
Figure : Types of smooth muscle
S th M l Ch t i ti
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Stimulation
Electrically coupled
Hormones
Paracrines
Various receptors
Single Unit
Multiple unit
Single tapered cells
Longer actin & myosin
Smooth Muscles: Characteristics
S th M l Ch t i ti
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Smooth Muscles: Characteristics
Figure : Anatomy of smooth muscle
Smooth Muscle Contraction:
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Smooth Muscle Contraction:
Mechanism
Figure : Smooth muscle contraction
Smooth Muscle Relaxation:
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Smooth Muscle Relaxation:
Mechanism
Figure : Relaxation in smooth muscle
Cardiac Muscle: Contrasted to
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Cardiac Muscle: Contrasted to
SkeletalShort branched fibers
Single nucleus
Intercalated discs
Gap junctions
Stimulation
Pacemaker
Autonomic
Hormonal
Cardiac Muscle: Contrasted to
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Cardiac Muscle: Contrasted to
Skeletal
Figure : ANATOMY SUMMARY: The Heart
Summary: Comparison of Three
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Su a y Co pa so o ee
Muscle Types
Table : Comparison of Three Muscle Types
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