Muscular System Part 1 Muscular Tissue

Honors Anatomy & Physiology
 3 types:
1. Skeletal
striated & voluntary
2. Cardiac
striated & involuntary
3. Smooth
Smooth & involuntary
 most attached to bone
 striations:
 see light & dark bands under microscope
 found only in walls of heart chambers
 heart has a pacemaker that initiates each
 called autorhymicity
 controlled by hormones & neurotransmitters
 in walls of hollow organs
 attached to hair follicles
 some autorhythmic (wall of intestines)
 regulated by ANS motor neuron& hormones
 1. producing body movements
 moving whole body or parts of body
 2. stabilizing body position
 skeletal muscles stabilize joints & halp
maintain body positions
 postural muscles hold sustained contractions
(holding head up all day)
 3. storing & moving substances w/in body
 storing: accompanied by sustained
contractions of ringlike bands of smooth
muscle called sphincters (hold material in
 contraction/relaxation of smooth & cardiac
muscle moves material thru bld vessels 
heart  bld vessels
 4. generating heat
 process called thermogenesis
 most of heat generated by muscle
contraction maintains normal body temp of
 shivering: involuntary contraction of skeletal
muscle increases heat production
 1. electrical excitability
 ability to respond to certain stimuli by
producing electrical signals called action
 2 main types stimuli:
1. autorhythmic electrical signals
2. chemical stimuli (neurotransmitters)
released by neurons
 2. contractility
 ability of muscle fibers to contract forcefully
when stimulated by an action potential
 muscle fiber shortens & pulls on whatever it
is attached to
 if force > resistance of object, movement occurs
 3. extensibility
 ability of muscle tissue to stretch w/out
being damaged
 smooth muscle fibers are stretched every
time your stomach or bladder is really full
 4. elasticity
 ability of muscle tissue to return to original
length & shape after contraction or extension
 fascia: sheet or broad band of fibrous CT
that supports & surrounds muscles or other
 2 layers: superficial & deep
 2. 3 layers of CT extend from deep fascia 
deeper into muscle tissue
epimysium: outermost layer, encircles
entire muscle
2. perimysium: surrounds groups of 10 – 100
muscle fibers = a fascicle
3. endomysium: surrounds individual muscle
 3. tendon: extension of epimysium,
perimysium, & endomysium beyond muscle
that attaches the skeletal muscle to another
structure (bone or another muscle)
 hypertrophy: enlargement of existing
muscle fibers
 ex: muscle growth in newborn
 hyperplasia: increase in # of muscle fibers
 ex: growth hormone causes increase in #s
from childhood  adult
 fibrosis: replacement of muscle by fibrous
scar tissue
 satellite cells: stem cells in muscle tissue;
limited capacity
 sarcolemma: plasma membrane
 sarcoplasm: cytoplasm
 myofibril: contractile organelles; thread-like
structures; each extends length of muscle
 T tubules: (transverse) invaginations of
sarcolemma into sarcoplasma; increasing
surface area
 filled with interstitial fluid
 ensures action potentials excites all parts of
muscle fiber
 sarcoplasmic reticulum: (SR) endoplasmic
reticulum that encircles individual
 dilated end sacs called terminal cistern
 T tubule + 2 terminal cisterns = triad
 in relaxed muscle fiber SR stores Ca++
 release of Ca++ triggers contraction
 3 kinds proteins in myofibrils:
contractile proteins
myosin make up thick filaments, golf-club
shape (myosin head)
 actin  thin filaments
2. regulatory proteins
tropomyosin & troponin: both in thin
3. structural proteins
~12 different ones function in alignment,
stability, elasticity, & extensibility of myofibrils
1. ATP hydrolysis
ATP attached to myosin head
2. attachment of myosin head to actin to
form cross bridges
3. power stroke
cross bridges rotate  center  slides thin
filament past thick filament
4. detachment of myosin from actin
ATP binds to myosin head & cross bridges
 somatic motor neurons innervate muscle
fibers to contract
 synapse: functional junction between 2
neurons or between a neuron & an effector
(muscle or gland); may be electrical or
 1st side of synapse: end of axon of motor
neuron called synaptic end bulb
 then synaptic cleft (the space)
 lastly, motor end plate: part of sarcolemma
that has receptors for neurotransmitter
acetylcholine (ACh)
 1. release of ACh
 2. activation of ACh receptors
 3. production of muscle action potential
 4. termination of ACh activity
 ACh stored in vesicles in synaptic end bulb
 action potential travels down axon 
reaches synaptic end bulb  induces
exocytosis of neurotransmitter from
synaptic vesicles
 ACh diffuses across synaptic cleft toward
motor end plate
 2 molecules of ACh bind to ACh receptors
embedded in sarcolemma  opens ion
channel  allows Na+ diffuse across
 inflow Na+ makes inside of muscle fiber
more + charged
 this change in membrane potential triggers
a muscle action potential  propagates
along sarcolemma  T tubules
 this causes SR to release Ca++  sarcoplasm
 contraction
 effect of ACh binding short because ACh is
rapidly broken down by enzyme
acetylcholinesterase (AChE)
 @ midpoint of muscle fiber:
 muscle action potential propagate  both
ends of fiber
 allows simultaneous activation & so
contraction of all parts of muscle fiber
 South American plant derivative
 causes paralysis by binding to & blocking
ACh receptors on motor end plates
 curare-like drugs used in general anesthesia
to relax skeletal muscles
 disease caused by Clostridium botulinum 
toxin that blocks exocytosis of synaptic
vesicles so no ACh released so no muscle
 toxin one of most lethal chemicals known
 causes death by paralyzing skeletal muscles:
breathing stops when diaphragm &
intercostal muscles stop contracting
 “equal tension”
 force of contraction developed by muscle
remains almost constant while muscle
changes its length
 used for body movements & for moving
 2 types:
1. concentric isotonic contraction
2. eccentric isotonic contraction
 when tension generated is enough to
overcome resistance of object being moved
…muscle shortens & pulls on another
structure (tendon) ….producing movement
that reduces angle at a joint
 tension exerted by the muscle resists
movement of the load (whatever was lifted
up) slowing the lengthening process
 tension generated by the muscle is < tension
needed to overcome resistance of the object
 muscle does not change its length
 same arrangement actin/myosin: striations
 muscle fibers branched
 *intercalated discs: unique to cardiac muscle
 autorhymicity alone: 75 bpm
 remains contracted 10-15 x’s longer than
skeletal muscle after 1 action potential
 due to prolonged delivery of Ca++ (SR +
interstitial fluid
 larger & more #s of mitochondria
 +thick & thin filaments but no T tubules &
less SR so no striations
 from mesoderm
 starts ~4 wks
 cardiac muscle
forms tubes 
bends & folds to
form heart
 spasm: sudden involuntary contraction of a
single muscle is a large group of muscles
 tic: an involuntary twitching by muscles
that are normally under voluntary control
 tremor: rhythmic, involuntary, purposeless
contraction that produces a quivering or
shaking movement
 fasiculation: involuntary, brief twitch that is
visible under the skin; occurring irregularly
& not ass’c with movement
 seen in MS or ALS
 fibrillation: spontaneous contraction of
single muscle fiber that is not visible under
skin but can be recorded by EMG
 signals destruction of motor neurons
 muscle strain: tearing of muscle due to
forceful impact + bleeding +pain
 most often affect quadraceps femoris
 tx‘d RICE (rest, ice, compression ie a wrap,

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