Physiology31 Lecture
Chapter 12 – Muscle Physiology
I. Overview
A. Muscle Tissues
B. Skeletal Muscle
C. Mechanics of Body Movement
D. Smooth Muscle
E. Cardiac Muscle
II. Muscle Tissues include skeletal, cardiac, and smooth muscle
A. ____________ muscle – striated, multinucleate cells. Functions:
1. ___________ Movement via skeletal muscles attached to bones
2. Contract in response to _________ motor neuron stimulation
3. Joint stabilization via muscle _______ - a constant, low level of force generated keeps tension on tendons that cross joints
4. _______ generation - helps to maintain a constant body temp.
B. __________ muscle – striated, uninucleate cells separated by intercalated discs.
Functions:
1. Involuntary, composes heart ___________
2. Cells contract _____________ in synchronized rhythm
3. Regulatable by the _______
C. __________ muscle - nonstriated, uninucleate cells. Functions:
1. Found in the walls of body tubes (e.g.: ____, respiratory, urogenital tracts, and blood
vessels)
2. Involuntary, regulatable by the _____
2. Promotes wavelike ____________ contractions in the GI tract
3. Responsible for vasodilation and vasoconstriction of blood _________
III. Skeletal Muscles
A. Three sheets of ___________ tissue hold skeletal muscle together:
1. ____mysium - surrounds the entire muscle
2. _____mysium - surrounds the muscle cell bundles (fascicles) within the epimysium
3. ______mysium - surrounds the individual muscle fibers (cells) within the fascicles
4. All three CT sheets strengthen and insulate muscle, and join to form the _________ that
attaches the muscle to the bone
B. Skeletal Muscles are composed of muscle ___________ (cells). Muscle structures from
large to small include:
whole muscle → fascicle groups → muscle fibers → myofibrils → myofilaments
C. Skeletal Muscle Fibers are _______ cells that consist of
1. Many myo___________ composed of
a. Myo________ of actin (thin) and myosin (thick) protein fibers
b. ____________ - contractile units of muscle, between Z lines.
1) ___ bands - are light bands of actin
2) ___ bands - are dark bands of myosin and actin
3) ___ zone - central part of A band with ________, no actin
2
4) ___ line - center of H zone with rods that hold myosins together
5) ___ discs - protein discs where _______ filaments attach; distance between Z lines
shortens during contraction.
2. Each cell is multi__________, with peripheral nuclei.
3. Cells have many _____________
4. Sarco________ is the cytoplasm within the
5. Sarco________ (plasma membrane) surrounds each muscle cell.
6. Transverse (T) __________ - invaginations of the sarcolemma through the muscle cell;
carries electrical impulse into the cell
7. Sarcoplasmic reticulum (____) - smooth E. R. that surrounds each myofibril within the
sarcolemma; contains ____ ions necessary for muscle contraction.
8. Terminal ______________ - sac-like portions of the SR on both sides of the T-tubules.
D. Three types of ____________ (protein microfilaments) compose a myofibril
1. Thick filaments - “golf club” like _______ proteins composed of
a. 2 intertwined polypeptides forming the shaftlike ______ and
b. A double globular protein _______ projecting from the tail at an angle.
c. A thick filament is a _________ of 200-500 myosin “golf clubs” with their heads
spiraling outward from the bundle
2. ______ filaments – include actin, tropomyosin, and troponin proteins.
a. __________ proteins are composed of
1) ________ (F) actin – 2 intertwined strands of protein “beads” called
2) __________ (G) actin, each of which has an active (myosin __________) site that
can bind a myosin head
b. Tropo________ is a fibrous protein that blocks actin’s myosin binding sites when the
muscle cell is relaxed
c. ___________ is a small calcium-binding protein attached to the tropomyosin molecule
at regular intervals
3. __________ filaments – elastic proteins that connect the thick filament to the Z disc and
keep the thick and thin filaments aligned, to resist muscle overstretching
E. Muscle contraction and relaxation occurs in 4 major ________: excitation, excitationcontraction coupling, contraction, and relaxation
1. ____________ – the process by which the electrical nerve impulse is transmitted to the
muscle cell
a. A nerve impulse stimulates the uptake of ___ ions into the axon terminal
b. Ca2+ ions stimulate the exocytosis of synaptic _________ with ACh into the synaptic
cleft
c. _____ diffuses across the cleft and binds to ACh receptors in the sarcolemma motor
end plate
d. An electrical impulse is initiated in the muscle motor ________
2. Excitation-contraction ____________ – events that link the electrical impulse on the
sarcolemma to the activation of the myofilaments, preparing them to contract
a. The electrical impulse ripples across the motor end plate, then down into the
sarcoplasm via the ___-tubules
3
b. The impulse causes the sarcoplasmic reticulum __________ to release ____ ions into
the cytosol
c. Ca2+ ions bind to the ___________ of the thin filaments, causing a shape change that
removes tropo_______ from the myosin binding sites of actin
3. ____________ – how the muscle fiber develops tension and may contract. In the sliding
filament theory of muscle contraction, thin filaments slide over thick filaments:
a. ______ bound to myosin heads is hydrolyzed to ADP + Pi, “cocking” the heads into an
extended, high ________ position
b. Energized _______ heads bind to exposed myosin-binding sites on ________, forming
cross-bridges
c. ________ stroke - myosin heads release the ADP + Pi and ____ into a bent, low
energy position, pulling the thin filaments toward the center of the ____________
d. __________ stroke – ____ binds to myosin heads, which causes the myosin to detach
from the actin
4. __________ – muscle fiber relaxes and returns to its resting length
a. Nerve ___________ cease, and ACh is no longer released by the axon terminal
b. _____ separates from motor end plate receptors, and is broken down by ______, which
ends muscle stimulation
c. ___ ions separate from troponin and are actively transported from the sarcoplasm back
into the SR terminal __________
d. Tropomyosin returns to its position blocking myosin-binding sites on _______
F. Skeletal muscle contraction requires _____
1. ATP Sources – two main pathways of ATP __________ are anaerobic fermentation and
aerobic respiration
a. ____________ fermentation occurs when a cell metabolizes glucose the absence of
oxygen; lactic acid and 2 ATP are generated
1) Advantage – allows the cell to produce ATP without ______
2) Disadvantage – produces ________ ______, a toxic product, and depletes
___________ reserves in muscle and liver rapidly
b. __________ respiration occurs mostly in the mitochondria in the presence of oxygen;
glucose is broken down and its energy is used to regenerate about 36 ATP molecules.
Waste products are CO2 and H2O.
1) Advantage – produces more ____ and less toxic by-products
2) Disadvantage – requires continuous __________ supply
c. Immediate Energy for short (6-60 sec), intense exercise is provided by two
_________ systems
1) __________ - transfers Pi groups from one ADP to another, forming ATP (and
AMP)
2) Creatine _____ obtains Pi from ______creatine and donates it to ADP, forming
ATP (and creatin)
d. Short-term Energy – after the immediate energy is exhausted, for the next minute or
so, _______ from the blood and glycogen stored in muscles is used to produce ATP
(anaerobically)
e. Long-term Energy – in the third minute, the respiratory and cardiovascular systems
“catch up” and deliver _________ to the muscles for aerobic respiration
4
f. ______ acids are broken down to acetyl CoA via beta-oxidation and used in cell
respiration during moderate exercise
2. Oxygen _____ is the difference between the resting rate of oxygen consumption and the
elevated rate following strenuous exercise
1. At rest or _________ activity, the respiratory and circulatory systems can supply the
muscles with enough oxygen for ______ respiration
2. With ________ exercise, there is not enough oxygen for aerobic respiration, so the
muscle uses _________ respiration for energy
3. Extra __________ consumed after strenous exercise is used to
a. Replenish the body’s oxygen reserves in _____________ and hemoglobin
b. Oxidize _______ acid to _______ acid, then to glucose in the liver, where it is
stored as ________
G. Muscle _________ – progressive weakness and loss of muscle contractility with
strenuous exercise. Some causes include:
1. ___________ and phosphocreatin reserves in muscles and liver become depleted
2. Accumulating ________ acid causes muscle acidosis, inhibiting __________ involved
in contraction, ATP synthesis, etc.
4. ____ may be used faster than it can be synthesized in the motor neuron
H. Types of Skeletal Muscle ________
1. Red _____-twitch fibers (oxidative)
a. Look red due to abundant _________, the oxygen storing protein in muscle
b. Have many capillaries and a large number of _____________ for aerobic
respiration
c. Fibers contract _______ and are resistant to fatigue as long as oxygen is present
d. Found in the lower ______ muscles that contract continuously to maintain posture
2. White fast-twitch fibers (__________)
a. Look pale due to less myo________
b. Are about twice the _________ of red fibers
c. Contain more myo___________ and generate more power
d. Have fewer _____________ & capillaries but many glycogen containing
glycosomes
e. _______________ respiration is their main energy source
f. Common in upper ___ muscles that lift heavy objects briefly
3. Fast-twitch ________ fibers
a. Have diameters, power, and fatigue resistance __________ red & white fibers
b. Contract quickly like ________ fibers
c. Like ____ fibers, are oxygen dependent, have much myoglobin and many
capillaries
d. Abundant in lower ______ muscles for standing and walking
5
4.
Muscles contain a _________ of the 3 muscle types, so they can do different things at
different times
5. The proportion of red to white fibers one has is believed to be _____________
determined
I. _____ ______ - a motor neuron and all the muscle cells it stimulates
1. Muscles that require _______ motor control, such as eye muscles, finger muscles, etc.,
have ___ muscle fibers per neuron (e.g., 25/1)
2. Muscles involved in __________, such as in the back, legs, etc., have ______ muscle
fibers per neuron (e.g., 1,000/1)
J. The __________ of a muscle twitch is determined by the length of individual sarcomeres
1. Each __________ will contract with optimum force if it is an optimum _______ before
contraction begins
2. ___________ exercises before strenuous activity help sarcomeres to be at optimal length,
and prevent muscle tears
K. Muscle __________ involves a threshold, latent period, and twitch
1. __________ is the minimum voltage required to produce a muscle contraction; lower
voltages do not cause muscle contraction
2. A ________ is one cycle of muscle contraction and relaxation
3. The minute time between the stimulus and the twitch is the _____ period (about 2
millisec)
4. For a few millisec after contraction, the muscle cannot contract again, no matter how
much stimulus is received, this is the __________ period
L. Contraction _________ of twitches is achieved by two methods
1. ___________ (multiple motor unit summation)– as more strength is needed, more
neurons “fire,” activating more motor units
2. High ____________ stimulation
a. Less than 10 stimuli/sec allows muscle to fully recover between stimuli, generates
_______ muscle tension
b. 10-20 stimuli/sec causes each twitch to develop more tension than the twitch before it
(the staircase phenomenon = ______)
c. 20-40 stimuli/sec allows twitchs to “piggyback” on each other, generating higher
tension (___________ summation), produces sustained partial contraction called
incomplete tetanus
d. At 40-50 stimuli/sec, the muscle does not relax between stimuli, so twitches blend into
a smooth, prolonged contraction called complete __________ (not the same as
lockjaw tetanus)
IV. Mechanics of Body Movement
A. Isometric & Isotonic ____________
1. Iso________ contraction involves muscle ________ without a change in muscle length;
no external muscle movement occurs
6
2. Iso________ contraction is a change in muscle _______ without a change in muscle
tension; muscle tension overcomes external resistance and moves
3. Isometric and isotonic are ______ involved in normal muscle contraction
B. Muscle disorder
1. Duchenne’s Muscular __________
a. __________ as a sex-linked recessive disease, thus affects more males than females
b. Skeletal muscle degenerates due to lack of __________ protein, and is gradually
replaced by adipose and fibrous tissue.
V. Smooth Muscle
A. ________ muscle cells are small, single, spindle shaped, and unstriated, with a single
nucleus
1. Thick and thin filaments form spiral bundles (myofibrils) within the cell, but no visible
striations and no ________
2. Tropomyosin is present, but not troponin, instead another Ca2+ binding protein called
_________ is present
3. No Z-disks are present, thin filaments are attached to the cytoskeleton via protein
______ bodies on the inner sarcolemma
4. Sarcoplasmic reticulum is sparse and there are no __-tubules
5. Ca2+ to activate muscle contraction comes from ____________ fluid through Ca2+
channels in the sarcolemma
6. Not all smooth muscle is innervated, when nerves are present, they are
_____________, not somatic motor fibers
B. Two types of ______ muscle are multiunit and single-unit smooth muscle
1. ______unit SM is found in large arteries, _______, and intrinsic eye muscles
a. Though __________, innervation is similar to skeletal muscle
b. Terminal branches of a nerve fiber synapse with individual muscle cells to form a
motor _____
c. Each motor unit contracts _________
2. ________-unit (visceral) SM is found in most blood vessels, as well as the
____________ and urogenital tracts
a. Usually forms an inner circular and outer longitudinal layer in walls of hollow
__________
b. Muscle cells are joined by _____ junctions that allow ions to flow freely from cell
to cell, thus many cells contract as a unit
C. Stimulation of Smooth Muscle
1. SM can contract without ________ stimuli
2. Some SM contracts in response to _________, CO2, low pH, O2 deficiency, and
________
3. Single-unit SM in the GI tract has ______________ cells that set off wavelike
contractions through the muscle layer (peristalsis)
4. SM is innervated by _____________ motor nerve fibers that can trigger or modify its
contractions
7
5. SM cells don’t have motor end plates, they have _________ junctions
a. Their _________ sites are scattered across their surface
b. One nerve fiber with beadlike ____________ passes along many muscle cells and
stimulates all of them at once
D. Contraction & Relaxation of Smooth Muscle
1. SM contraction is __________ to skeletal muscle in that:
a. Actin and ________ interact by a sliding filament mechanism
b. A rise in ____ level triggers contraction
c. _____ energizes the sliding process
2. SM contraction ________ from skeletal muscle in that:
a. Ca2+ diffuses mainly through the cell __________ to initiate contraction
b. Ca2+ interacts with components of the myosin filament, namely __________ and a
kinase enzyme to activate myosin
3. Sequence of SM contraction and relaxation ________
a. ____ binds calmodulin
b. __________ is activated
c. Calmodulin activates the ________ enzyme
d. The kinase transfers a phosphate from ____ to myosin
e. Myosin interacts with _______ (power & recovery strokes)
f. ___________ occurs when
1) Intracellular ____ is ‘pumped” out of the muscle cells by active transport and
2) Myosin is dephosphorylated by myosin ___________
4. SM contraction is _________ than skeletal muscle, but more sustained and resistant to
fatigue
a. Small blood vessels and visceral organs maintain a degree of sustained contraction
(_______) without fatiguing due to:
1) ____ efficient contraction
2) Lower ______ requirements than skeletal muscle
3) ______ contraction time (30x longer than skeletal mus.)
b. Because SM has low _______ requirements, it has
1) Few __________
2) Mostly ___________ ATP pathways
5. _________ of SM Contraction is similar to skeletal mus. in that:
a. Neuro_________ are released in response to a nerve impulse
b. Neurotransmitters bind to _________ in the SM sarcolemma
c. ____ is released into the sarcoplasm and triggers contraction
6. SM regulation is ___________ to skeletal mus. in that:
a. Not all neural signals to SM result in ___________
b. Not all activation is due to neural signals, some SM can contract in response to
__________ & mechanical stimuli
c. SM autonomic motor neurons release two types of neuron___________:
1) Acetylcholine (___)
2) Nor____________ (NE)
8
d. Both neurotransmitters may be either excitatory or inhibitory, because there are
excitatory and inhibitory __________ in SM membranes. Examples:
1) ACh _________ smooth muscles in bronchioles
2) Norepinephrine _________ smooth muscle in bronchioles
3) Norepinephrine _________ smooth muscle in blood vessels
7. Some __________ stimuli affect SM Ca2+ levels, causing the muscle cells to contract
or relax
a. _________, such as gastrin from stomach and small intestine, cause SM
contraction
b. Lack of _________ or excess CO2 relaxes SM (e.g., in lung bronchioles)
c. Low blood ___ relaxes SM
VI. Cardiac Muscle
A. Cardiac muscle tissue is found in the heart wall (myo_________)
B. The cells are involuntary, striated, single ____nucleate cells, not voluntary multinucleate
cells like skeletal muscle cells
C. A cardiac muscle _______ is a long row of joined cardiac muscle cells
D. Cardiac muscle contracts via the ________ filament mechanism, similar to skeletal
muscle
E. Cardiac cells branch and join together at complex junctions, called ____________ discs,
which are composed of
1. ____________ that hold the cells together
2. _____ junctions that allow ions to pass from cell to cell to synchronize muscle
contractions
F. Cardiac muscle can be stimulated by the ____ and hormones; but it can also contract
rhythmically without innervation (autorhythmic)
G. We will discuss cardiac muscle further during the cardiovascular unit.