Muscles & Muscle Tissue
Muscles & Muscle Tissue
A. Functions
1. provide energy for movement
2. maintain posture
3. thermogenesis
4. maintain hollow organ volume
Muscles & Muscle Tissue
B. characteristics
1. excitability
2. contractility
3. extensibility
4. elasticity
Muscles & Muscle Tissue
C. Three types
1. Skeletal
A) long, cylindrical cells, multinucleated, non-branching, and
voluntary
B) striated – caused by special
arrangement of myofilaments
C) stimulus from nervous system
Muscles & Muscle Tissue
2. Cardiac
A) only in heart
B) striated, mononucleated, branching,
and involuntary
C) intercalated discs – gap junctions
between cells; distinguishing
characteristic
D) stimulus is intrinsic
Muscles & Muscle Tissue
3. Smooth
A) found lining the digestive, respiratory
& reproductive tracts; also surrounding
blood vessels
B) mononucleated, no striations
(distinguishing characteristic), and
involuntary
C) stimulus from nervous system, some
hormones or on its own (stretch)
Muscles & Muscle Tissue
D. Structure of Skeletal Muscle
1. Whole muscle – bundle of fascicles
A) epimysium – CT layer
surrounding whole muscle
2. Fascicle – bundle of muscle fibers
(cells)
A) perimysium – CT layer
surrounding and tying together
fascicles
Muscles & Muscle Tissue
3. Muscle fiber – bundle of myofibrils
A) endomysium – CT layer surrounding
and tying together muscle fibers
B) sarcolemma
C) sarcoplasm
D) transverse-tubules (T-tubules) –
inward projections of the
sarcolemma; unite with the
sarcoplasmic reticulum
Muscles & Muscle Tissue
4. Myofibrils – composed of 2 types of
myofilaments
A) thin – composed of 3 protein fibers
1) actin – contractile protein;
contains myosin binding sites
2) troponin – regulatory protein
Muscles & Muscle Tissue
3) tropomyosin – regulatory protein;
combines with troponin to form the
troponin-tropomyosin complex
a) when the muscle is relaxed, the
troponin-tropomyosin complex blocks
the myosin binding sites on the actin
Muscles & Muscle Tissue
B) thick – composed of 1 protein fiber
1) myosin – contractile protein; golfclub shaped
a) head – will bind to the myosin
binding sites on the actin during
contraction
b) tail – intertwined to hold the
myosin fibers together
Muscles & Muscle Tissue
5. Sarcomere – specialized arrangement of
myofilaments
A) functional unit of muscle
Muscles & Muscle Tissue
6. Sarcoplasmic reticulum (SR) – fluid
filled tubes surrounding each myofibril
A) storage site of calcium (Ca++)
B) adjacent terminal cisternae unite
with the T-tubules to form the triad
Muscles & Muscle Tissue
1) the terminal cisternae are enlarged
portions of the SR surrounding each Ttubule
2) allow an impulse to be transmitted
from the T-tubules to the SR
Muscles & Muscle Tissue
E. Skeletal Muscle Contraction
1. Involves a motor unit
A) a single muscle may have many
motor units
2. Three steps
A) Nerve-Muscle Communication
1) Occurs at the neuromuscular
junction
a) motor-end plate
b) synaptic cleft
Muscles & Muscle Tissue
2) Process:
a) an impulse travels down the motor
neuron
b) ACh is released from the neuron
into the synaptic cleft
c) ACh binds to receptors on the
motor-end plate causing chemicalgated Na+ channels to open
Muscles & Muscle Tissue
d) Na+ moves into the muscle fiber
causing depolarization of the motor-end
plate
e) depolarization of the motor-end plate
causes an opening of voltage-gated Na+
channels in the sarcolemma
f) this causes an action potential to be
transmitted along the length of the
sarcolemma
Muscles & Muscle Tissue
B) Excitation-Contraction Coupling
1) involves T-tubules and sarcoplasmic
reticulum (SR)
2) process:
a) AP travels down the sarcolemma,
also travels down the T-tubules
b) AP is then transferred to the SR
at its intersection with the T-tubule
Muscles & Muscle Tissue
c) the AP causes an opening of Ca++
release channels in the SR
d) Ca++ floods the sarcoplasm
surrounding the thin & thick filaments
e) Ca++ binds to troponin causing a
shifting of the troponin-tropomyosin
complex exposing the myosin binding
sites on the actin
Muscles & Muscle Tissue
C) Sliding Filament Mechanism
1) involves the thin and thick filaments
2) process:
a) ATP is split by ATPase on the myosin
head resulting in an “energized”
myosin head
i) this occurs at the end of the
previous contraction
ii) ADP & P stay attached to the
myosin head
Muscles & Muscle Tissue
b) the energized myosin head binds to
the exposed binding site on the actin
c) using the energy from ATP, the myosin
head swivels inward pulling the thin
filament towards the center of the
sarcomere = power stroke
i) the ADP & P are released
Muscles & Muscle Tissue
d) ATP binds to the myosin head causing
it to break away from the binding site
e) the ATP is split by ATPase, reenergizing the myosin head
f) the process repeats and will continue
as long as ATP and Ca++ are present
Muscle Contraction
Ca+2
ADP + P
Ca+2
ADP + P
Ca+2
1 Exposed binding sites on actin allow the muscle
contraction cycle to occur
ADP + P
Contraction
cycle
ADP + P
5 ATP splits, which
provides power to
“cock” the myosin
cross-bridge
ATP
ADP + P
ADP + P
2 Cross-bridge
binds actin to
myosin
ATP
ADP
ATP
P
ATP
4 New ATP binds to myosin, causing linkage to
release
ADP
P
ADP + P
3 Cross-bridge pulls actin filament (power stroke),
ADP and P released from myosin
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Muscles & Muscle Tissue
F. Relaxation – 2 mechanisms
1. Acetylcholinesterase
A) breaks down ACh in the synaptic
cleft
2. Ca++ active transport pumps
A) found in the walls of the
sarcoplasmic reticulum
B) pump Ca++ back into SR
Muscles & Muscle Tissue
G. Muscle Metabolism
1. Muscle stores enough ATP for about
4-6 sec of work
2. Three processes provide muscle
cells with more ATP
Muscles & Muscle Tissue
A) phosphagen system
1) creatine kinase transfers a
phosphate group from creatine
phosphate (CP) to an ADP molecule
creating 1 ATP for each CP
2) allows for about 10-15 seconds of
energy for maximum activity
Muscles & Muscle Tissue
B) fermentation (anaerobic) – no oxygen
needed; occurs in cytoplasm
1) incomplete oxidation of glucose
2) produces 2 pyruvic acid & 2 ATP
from 1 glucose molecule
3) pyruvic acid is converted to lactic
acid
4) allows for about 30-40 seconds of
max activity
Muscles & Muscle Tissue
C) cellular (aerobic) respiration – requires
oxygen; occurs in mitochondria
1) complete oxidation of glucose
2) produces 6 CO2, 6 H2O, & 32 ATP
from one glucose molecule
3) can also use fatty acids & amino
acids
4) amount of energy produced depends
on fitness of individual
Muscles & Muscle Tissue
H. Muscle fatigue
1. Can be caused by a number of factors
A) inadequate O2
B) glucose/glycogen depletion
C) ACh depletion
D) lactic acid accumulation
2. Oxygen debt – the amount of O2
necessary to restore the muscle to
normal state
Muscles & Muscle Tissue
I. Muscle Contractions
1. Muscle twitch – response of the motor
unit to a single impulse
A) latent period
B) contractile period
C) relaxation period
2. Graded muscle responses
A) the way muscles normally function
B) creates smooth contractions of
varying strength
Muscles & Muscle Tissue
C) 2 primary graded responses
1) wave summation – increases the
strength of contraction by increasing the
frequency of the stimulus
a) tetanus
2) multiple motor unit summation
(recruitment) – increases the strength
of contraction by activating more motor
units
Muscles & Muscle Tissue
D) treppe
1) stronger contractions resulting from
no increase in stimulation
2) possibly due to increased Ca++
availability and temperature
3) basis behind “warming up” before
exercise
Muscles & Muscle Tissue
E) muscle tone
1) slight contraction seen in “resting”
muscles
2) keeps muscles firm, healthy, and
ready to respond
F) types of contractions
1) isometric contraction
a) muscle does not change in length
b) tension increases
Muscles & Muscle Tissue
2) isotonic contraction
a) muscle length changes
b) tension remains constant
c) 2 types
1) concentric
a) muscle shortens as it contracts
2) eccentric
a) muscle lengthens as it contracts
Muscles & Muscle Tissue
J. Muscle Fiber Types
1. Slow (Red) Oxidative Fibers
A) rely on aerobic metabolism
1) more myoglobin
2) more capillaries
3) more mitochondria
B) long, slow contractions
C) fatigue resistant
Muscles & Muscle Tissue
2. Fast (White) Glycolytic Fibers
A) rely on anaerobic metabolism
1) less myoglobin
2) fewer capillaries
3) fewer mitochondria
B) rapid, powerful contractions
C) fatigue easily
Muscles & Muscle Tissue
3. Fast (Pink) Oxidative Fibers
A) similar to red fibers except:
1) faster contractions
2) can use anaerobic metabolism
3) fatigues more easily than red
fibers but not as easily as white
fibers
Muscles & Muscle Tissue
K. Benefits of Exercise
1. increases in fiber size and strength
2. increased muscle tone
3. increase in blood supply, therefore
increased RBCs
4. increased cardiovascular & respiratory
function
5. lowers BP
Muscles & Muscle Tissue
L. Smooth Muscle Contraction
1. Same principle as skeletal muscle
but a slower and longer sustained
contraction
2. Differences include:
A) no T-tubules or sarcomeres
B) Ca++ from SR & ECF
C) no troponin-tropomyosin complex
Muscles & Muscle Tissue
1) calmodulin instead of troponin
2) myosin light chain kinase instead of
ATPase
D) contracts in response to
norepinephrine as well as ACh
E) contracts in response to certain
hormones (ex. oxytocin)
F) contracts in response to stretch
Muscles & Muscle Tissue
M. Cardiac Muscle Contraction
1. Again, same contractile principle as
skeletal except:
A) contracts continuously
B) contracts as a unit
C) stimulus is intrinsic, but also neural
and hormonal control
D) Ca++ from SR & ECF
E) cannot undergo tetanus
Muscles & Muscle Tissue
N. Muscular Disorders
1. Myasthenia gravis – characterized by
drooping upper eyelids, difficulty
swallowing & talking, and generalized
muscle weakness
A) results from loss of ACh receptors
2. Rigor mortis – muscle stiffness
following death
A) results from lack of ATP to break the
myosin cross-bridges
Muscles & Muscle Tissue
3. Atrophy – loss of muscle mass
A) results from immobilization or loss of
neural stimulation
B) occurs to a small extent from non-use
of healthy muscles
4. Muscular dystrophy – a group of inherited
muscle destroying diseases
A) muscles enlarge due to fat and CT
deposits while muscles fibers atrophy