Muscular System Part 1 Muscular Tissue
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Transcript 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
contraction
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
organ)
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
37°C
shivering: involuntary contraction of skeletal
muscle increases heat production
1. electrical excitability
ability to respond to certain stimuli by
producing electrical signals called action
potentials
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
organs
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
fibers
1.
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
fiber
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
myofibrils
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:
1.
contractile proteins
myosin make up thick filaments, golf-club
shape (myosin head)
actin thin filaments
2. regulatory proteins
tropomyosin & troponin: both in thin
filaments
3. structural proteins
~12 different ones function in alignment,
stability, elasticity, & extensibility of myofibrils
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/fre
e/0072437316/120104/bio_b.swf::Sarcomere%20Shortening
http://www.wiley.com/college/pratt/0471393878/student/anim
ations/actin_myosin/actin_myosin.swf
http://brookscole.cengage.com/chemistry_
d/templates/student_resources/shared_reso
urces/animations/muscles/muscles.html
http://bcs.whfreeman.com/thelifewire/content
/chp47/4702001.html
http://www.sumanasinc.com/webcontent/ani
mations/content/muscle.html
https://highered.mcgrawhill.com/sites/0072495855/student_view0/cha
pter10/animation__breakdown_of_atp_and_cr
ossbridge_movement_during_muscle_contraction
.html
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
released
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
chemical
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
membrane
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
contraction
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
objects
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
http://www.youtube.com/watch?v=jKygojJg
FQE
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
(electromyograph)
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,
elevation)