Download CH 11 shortened for test three muscles A and P 2016

CH 11
muscle tissue
types of muscles
microscopic anatomy of muscles
how muscles work
three kinds of muscles
skeletal – voluntary
smooth – involuntary
cardiac - involuntary
muscles are/have
excitability – generate electrical changes
conductivity – wave of excitability
contractility – shortens
extensibility – can stretch without breaking
elasticity – move back to zero point
- a muscle is a complex structure
- it has an origin and an insertion
- a muscle consists of many fascicles
- a fascicle consists of many muscle fibers
- a muscle fiber consists of many long & thin myofibrils
- the functional unit of a myofibril is a sarcomere
- a myofibril has many sarcomeres
- a sarcomere consists of many thick and thin myofilaments
- a sarcomere is able to contract and return to normal length
-many myofilaments and associated organelles form a myofibril
-each myofibril is surrounded by a sarcoplasmic reticulum
-T tubules penetrate deep into the endomysium covered myofibril
a group of myofibrils surrounded by a sarcolemma = muscle fiber
-groups of muscle fibers surrounded by perimysium form fascicles
-numerous fascicles surrounded by epimysium form a muscle
a muscle fiber has a very developed SR
so a muscle contains many thousands of SR
sliding filament theory
thick filaments – myosin heads (light and heavy) in an inactive
form each attached to a long twisted tail with a flexible
portion and a longer portion linked to other longer tails,
heads are able to hydrolyze ATP and release the energy
needed to allow the myosin head to change position and
link to troponin on thin filament
thin filaments
- two intertwined strands of globular actin
- two strands of tropomyosin which cover
the active sites on the globular actin
- calcium binds to troponin on tropomyosin
causing exposure of active sites
on globular actin
the whole process
nerve impulse – causes calcium to enter synaptic knob
- ACh is released – Ach binds to sarcolemma receptor
– causes Na/Ca channels to open – sarcolemma reverses polarity
– creates action potential – reaches T tubules = Ca released
– Ca enters muscle fiber – binds to troponin on thin filament
– thin fiber changes shape – active actin sites now exposed
– myosin ATPase an enzyme on myosin splits ATP
- energy allows myosin head to bind to actin & bend into
a high energy position = power stroke
- power stroke – myosin releases ADP + P
- bends into a low energy position,
- picks up ATP, & releases actin= recovery stroke
–energy from ATP used to attach to actin
– same happens over and over by thousands of myosin heads
all acting at the same time & in a coordinated fashion= Z
line come closer= contraction
-nerve impulse stops - AChE breaks Ach-Ca reabsorbed by
sarcoplasmic reticulum - active sites covered - no more
contraction
- plasma membrane of muscle fiber = sarcolemma
- cytoplasm of muscle fiber = sarcoplasm
- the protein cords which make up the sarcomeres = myofibrils
- muscle fibers are rich in glycogen & myoglobin
- some myoblasts remain as = satellite cells (stem cells)
- smooth endoplasmic reticulum is called the sarcoplasmic reticulum
- sarcoplasmic reticulum has channels called terminal cisternae which
cover the myofibrils from side to side
- the sarcolemma sends a tube called transverse (T) tubules
associated with two terminal cisternae which travel with the
terminal cisternae from side to side
- the SR is a reservoir for Ca needed for sarcomere contraction
smooth muscle
no striations, 1 nucleus, no T tubules,
no Z discs, no sarcomeres, no myofibrils,
scant sarcoplasmic reticulum
small groups of myocytes for fine control
autonomic (not always innervated) NE sym & Ach parasym
synaptic vesicles have multiple varicosities
no motor end plate
receptors spread over muscle surface
slow response long to fatigue
very energy efficient
mitosis, hyperplasia, move things, hold things
contraction and relaxation
NE or ACh binds to receptors and open Ca channels
Ca binds to calmodulin on myosin
activates myosin light chain kinase
adds phosphate to regulatory protein and activates ATPase
myosin performs repetitive power stroke and recovery stroke
thick pull thin in & attached cytoskeleton and dense bodies
cause muscle cell to shorten and twist
removal of Ca is slow so contractions long
latch mechanism hold cell contracted without more energy
cardiac muscle
heart – regular rhythm – non stop – resists fatigue
cells contract in unison – contract long enough to pump blood
striated – short and thick cardiocytes – gap junctions
intercalated discs (tight junctions) – small SR – large T tubules
pacemaker – ANS stim= ↑or ↓ of contr. and/or strength
mostly aerobic, myoglobin↑, glycogen↑, large mito,
nerve muscle relationship
some muscles contract spontaneously but most
muscle fibers contract as a response to a nerve stimulation
the nerves which stimulate a muscle are called
somatic motor fibers whose cell bodies are in
the brainstem and spinal cord
a neuron has a few to many
terminal branches which
end on individual
muscle fibers
all of the muscle fibers innervated
by the terminal branches of a neuron
are called a
motor unit
small(fine control) = 3 - 10 large(coarse) = average 200
100 neurons innervate 1000 muscle fibers
1 neuron innervate 1000 muscle fibers
different groups of fibers within a muscle
are innervated by different motor units
this allows for continued contraction
as one group of fibers fatigue
others continue to function
words we need to remember and understand
somatic motor fibers
neuromuscular junction
synaptic cleft
acetylcholine (ACh)
acetylcholinesterase(AChE)
motor unit
motor end plate
Schwann cell
ACh receptors
synapse
synaptic knob
synaptic vesicle
junctional folds
nerves and muscle cells are described
as electrically excitable
this is based on
the difference in concentrations
between the intercellular fluid ions
compared to the extracellular fluid ions
the inside of the cell has more negative ions
than the outside of the cell
this difference in polarity is referred to
as a resting membrane potential
the inside of the muscle cell compared
to the fluid outside of the cell
is -90 mV (milli volts)
stimulation of a nerve or muscle causes
- channels open in the plasma membrane
- Na rushes in from high to low concentration
- the positive Na ions depolarize the cell (goes from – to +)
- Na channels close and K channels open
- K leave the cell and repolarizes and hyperpolarizes the cell
- this cycle of de and re polarization is an action potential
- so much K enters the cell that the RMP drops to more than
-90 mV and the cell becomes refractory (cannot initiate
another action potential until RMP returns to -90mV)
muscle relaxation
as the local potential becomes an action potential
there is no more need for calcium at the initial site
but there is still a need for calcium
until the nerve stops firing
at this point the calcium channels close
calcium is reabsorbed by the sarcoplasmic reticulum
and large amounts of calcium are stored in the
SR bound to a protein calsequestrin
and stored in the SR without Ca precipitation
length strength relationship
too contracted = weak response to stimulation
too stretched = weak response to stimulation
optimum length = strong response to stimulation
at optimum length the
body maintains partial contraction
known as muscle tone
not all stimuli result in an action potential
or muscle contraction
too much or too little stretch = less than maximum contraction
fatigued muscle = less than maximum
cold muscle = less than maximum
too little hydration = less than maximum
long stimuli intervals = less than maximum
intensity vs frequency
a weak stimulus activates a twitch with weak or no contraction
stronger stimulus activates more fibers = weak or no contraction
stronger stimulus activates more fibers = weak or small contraction
strong stimulus activates more fibers = small to strong contraction
stronger stimulus activates more fibers = strong contraction
as the stimulus increases more motor units are recruited and more
muscle fibers are stimulated resulting in stronger contractions
known as MMU multiple motor unit summation
low frequency stimulation = muscle relaxes completely before
next stimulus
higher frequency stimulation = before one twitch comes to rest
the next stimulus adds to the previous twitch
– strength can build quickly to more than a single twitch
very high frequency = no relaxation, twitches fuse to tetanus
isometric and isotonic
scientists describe 4 different types of contractions
isometric - isotonic - concentric - eccentric
isometric = contraction without a change in length
isotonic = contraction with a change in length but
no change in tension
concentric = muscles shorten as it maintains tension
eccentric = muscle lengthens as it maintains tension
where do muscles get the energy
to do the work that they all do?
ATP
aerobic and anaerobic
with oxygen or without oxygen
resting = aerobic respiration using fatty acids
during exercise = anaerobic, short term, & long term
- if still active = homeostasis catches up & oxygen becomes
available & aerobic respiration takes over (long term energy)
- the body accommodates over 3 to 4 minutes & energy
production levels of at a steady state
– 90% of energy is aerobic for exercise of more than 10 min
– up to 30 minutes energy is from glucose & fatty acids
and then only fatty acids after glucose stores depleted
fatigue
K concentration
ADP/P accumulation
lactic acid accumulation
fuel depletion ** - glucose and glycogen depletion
electrolyte loss ** - too much sweat, too little intake
central fatigue ** - NH3 accumulation inhibits CNS signals
XS post exercise oxygen consumption (oxygen debt)
oxygen is required for
synthesize ATP
ATP needed to regenerate creatinine phosphate
regeneration of myglobin
liver need oxygen to destroy lactic acid
raised body temperature increases need for oxygen
slow and fast twitch muscles
slow = small motor units, long duration of twitch, excitable,
weak strength, aerobic, fatigue resistance, many organelles,
many BV, slow ATP hydrolysis, slow oxidative, red color
fast = large motor units, short duration of twitch, less excitable,
strong contraction, anaerobic, easy fatigue, fewer organelles,
white color, rapid ATP hydrolysis, fast glycolytic, few BV,
extensive sarcoplasmic reticulum, much glycogen, high CP,
most muscles have both types in various amounts
type of muscles you have may determine choice of activity
muscle strength depends on
size = thickness
fascicles = arrangement/orientation of fibers
motor units = larger generate more strength
multiple summation = involve more motor units
temporal summation = increased frequency increases strength
stretch = optimum stretch results in optimum strength
fatigue = more rest produces more strength
resistance exercise = contraction against a load, results in more
and thicker myofibrils, does not increase endurance
endurance exercise = improves resistance against fatigue,
more organelles, better use of oxygen, more BV,
increases skeletal strength, does not increase strength
to increase both strength and endurance
requires cross training