Muscular System Flashcards
What are the six functions of the muscular system?
- body movement
- maintenance of posture
- protection and support (ex. abdominal wall)
- movement of materials (blood, air, food)
- heat production (shivering)
- communication (verbal and non-verbal)
What is the function of muscle tissue?
contract to generate movement
What are three types of muscle tissue?
smooth, cardiac, and skeletal
What is the name of muscle cells?
myocytes
Smooth muscle tissue characteristics
- tapered (pointy ends)
- non-striated
- uni-nucleated
Smooth muscle tissue location
organ walls
Smooth muscle tissue: voluntary or involuntary?
involuntary
Cardiac muscle tissue characteristics
- has branches
- striated
- 1-4 nuclei
Cardiac muscle tissue location
heart
Cardiac muscle tissue: voluntary or involuntary?
involuntary
Skeletal muscle tissue characteristics
- long
- striated
- multi-nucleated
Skeletal muscle tissue location
skeleton
Skeletal muscle tissue: voluntary or involuntary?
voluntary
What is another name for skeletal muscle tissue?
muscle fibers
What is a muscle fiber?
a cell
Skeletal muscle tissue is responsible for what?
shivering
Thousands of myocytes =
muscle fibers
Skeletal muscle composition?
- thousands of myocytes
- blood vessels
- nerves (sensory + motor)
What are the three layers of connective tissue surrounding skeletal muscle?
- epimysium
- perimysium
- endomysium
Epimysium
around each muscle
Perimysium
around each fascicle
Endomysium
around each muscle fiber
Fascicle
a bundle of skeletal muscle fibers surrounded by perimysium, a type of connective tissue
What does fascicle mean?
bundle
What happens when the epimysium, perimysium, and endomysium, merge together?
forms tendons
What are the seven characteristics used to name skeletal muscle?
- action
- body region
- attachment
- orientation of muscle fibers
- shape
- size
- # of muscle heads
Skeletal muscle is what?
an organ
What is another word for muscle heads?
cephal
What are the actions of skeletal muscle?
- adductor/abductor
- flexor/extensor
Body region: Cervicis
neck
Body region: Oris
mouth
Body region: Brachial
arm
Body region: Carpi
wrist
Body region: Femoris
thigh
Body region: Profundus
forearm/antebrachial
Body region: Superior
towards the head
Skeletal muscle naming: attachment
intercostal
What does intercostal mean?
between the ribs
What are the three orientations of skeletal muscle?
- rectus
- oblique
- orbicularis
Rectus
straight
Oblique
diagonal/slanting
Orbicularis
circular
Where can orbicularis skeletal muscle be found?
the mouth and eyes
What are the shapes of skeletal muscle?
- deltoid
- quadratus
- trapezius
- teres
Deltoid
triangle
Quadratus
square
Trapezius
trapezoid
Teres
rounded
What are the sizes of skeletal muscle?
- longus/brevis
- major/minor
- latissimus
-minimus/maximus/medius
Longus
long
Brevis
short
Major
largest
Minor
smallest
Medius
medium
What does “fund-“ mean?
foundation/al or base
What does “rect-“ mean?
straight
Orientation
which way something is going
What does “orbi-“ mean?
circle
What does “brev-“ mean
brief
Latissimus
broadest
Muscles only what?
pull
What is the rule of thumb for minimus, maximus, and medius?
if you have one then all three exist
What are the possible number of cephals or muscle heads of the skeletal muscle?
- bicep
- tricep
-quadricep
Bicep
2
Tricep
3
Quadricep
4
How are muscle fibers (skeletal muscle cells) formed?
embryonic myoblasts fuse together to form muscle fibers
Satellite cell function
muscle repair/regeneration
What type of tissue uses “myo-“ and “sarco-“?
muscles
Sarcolemma
muscle cell’s plasma/cell membrane
Sarcoplasm
muscle cell’s cytoplasm
Sarcoplasmic reticulum (SR)
muscle cell’s endoplasmic reticulum
Myofibril
contractile organelle
Sarcolemma composition
lipid bilayer + imbedded proteins and carbs
The sarcolemma is what?
semi-permamble
Resting membrane potential
the difference in charges across the membrane when at rest
What are the charges of the sarcolemma?
+ on the outside and - on the inside
What is the resting potential for myocytes?
90 mV
What does mV mean?
millivolt
What are the reasons for the difference in charges of the sarcolemma?
-Na-K ion pump
- K+ leak channel (H to L)
What do Na-k ion pumps do to the sarcolemma?
- move more + outside
- creates a concentration gradient of ions
What does K+ leak channels do to the sarcolemma?
addxs “+” outside
What is the rule of Na-K ion pumps?
three sodium out, two potassium in
What are the invaginations created by the sarcolemma called?
t-tubules
T-tubules function
deliver the signal into the interior
The sarcoplasmic reticulum forms what?
terminal cisternae on both sides of t-tubules
Terminal cisternae function
store Ca2+ (signaling ion)
About 80% of sarcoplasm is taken up by what?
hundreds of myofibrils
Myofibrils are made up of what?
thin and thick filaments
Sacromeres
filaments organized into repreating units
Filaments are organized into sarcomeres for what function?
contraction
Sarcomeres stretch from what to what?
z disc to z disc
Thick filament
a bundle of the contractile protein myosin
What are the two parts of a thick filament?
the actin binding site and the ATP binding site
What is the function of the actin binding site in thick filaments?
attachment
What is the function of the ATP binding site in thick filaments?
energy
What are the three characteristics of thin filaments?
- actin contractile protein with myosin binding sites
- tropomyosin
- troponin
Tropomyosin
a regulatory protein (cover actin)
Troponin
a regulatory protein (with Ca2+ binding sites)
Regulation of skeletal muscle contraction is done by what?
- motor neurons
- motor unit
- neuromuscular junction (synapse)
What initiates skeletal muscle contraction?
motor neurons
Motor unit
each motor neuron and the multiple fibers it controls
Neuromuscular junction
location where a motor neuron innervates a skeletal muscle cell/fiber
Synaptic knob
houses the synaptic vesicles and neurotransmitter acetylcholine (ACh)
Synaptic cleft
fluid filled space separating the synaptic knob from the motor end plate
Motor end plate
heavily folded sarcolemma with ACh receptors (receiving end for ACh)
What are the three steps of the physiology of skeletal muscle contraction?
- Excitation
- Excitation- Contraction coupling
- Cross bridge cycling
Where does excitation occur?
at the neuromuscular junction
What is the first step of excitation?
a nerve signal delivered by a motor neuron triggers the entry of Ca2+ into the synaptic knob through the gated Ca2+ channels
What is the second step of excitation?
There (the synaptic knob) Ca2+ binds to the synaptic vesicle and triggers them to bind with the plasma membrane. ACh is then released into the synaptic cleft
What mechanism is used to release or diffuse ACh into the synaptic cleft?
exocytosis
What is the third step of excitation?
ACh diffuses across the cleft and binds to the ACh receptor at the motor end plate
What are the three phases of contraction coupling (where/when these are taking place)?
- Motor end plate
- Edge of the motor plate
- When action potential reaches the t-tubules
Motor end plate phase
ACh bonds to the ACh receptor causing:
- chemically gated channel opens
- fast diffusion of Na+ in the cell
- inside becomes more “+”
What is the ACh receptor in the motor end phase?
chemically gated ion channel
What is the motor end plate phase called?
end plate potential (EPP)
Edge of the motor plate phase
altered membrane potential (EPP)
- voltage gated Na channel opens
-fats diffusion of Na+ in the cell
- action potential
- muscle impulse
Action potential
local reversal of charges
Muscular impulse
wave of voltage gated Na+ channels opening along the sarcolemma and into the t-tubules
When action potential reaches t-tubules phase?
opening of voltage gated Ca2+ channels in the terminal cisternae of the SPR
- Ca2+ diffuses into the sarcoplasm and reaches sarcomere
What are sarcomeres?
contractile units
What are the three kinds of channels involved in the physiology of skeletal muscle contraction?
- chemically gated ion channels
- voltage gated Na channels
- voltage gated Ca2+ channels
What triggers cross-bridge cycling?
Ca2+ comes in binds to troponin, shifts tropomyosin thus opening myosin binding sites.
Where does crossbridge cycling take place?
in the sarcomeres
What are the four steps of cross-bridge cyclying?
- “attach”
- “pull”
- “release”
- “reset”
Attach =
Cross-bridge formation
Pull =
Power stroke
Release =
Release of myosin head
Reset =
Reset myosin head
Cross-bridge formation
myosin heads bind to the myosin binding sites forming a crossbridge
Power Stroke
The myosin head swivels toward the center of the sarcomere, pulling the thin filaments.
What is released during the power stroke?
ADP and Pi (phosphate)
Release of myosin head
ATP binds to the myosin head, which causes the release of the myosin head from actin
Reset of myosin head
ATP is split into ADP and Pi (phosphate) providing the energy to reset the myosin head
What is used to “cock” the myosin head while at rest?
energy/ATP
Stimulation above the threshold results in what?
a muscle generates force
What is muscle tension?
when a muscle generates force
What is a twitch?
a muscles response to a single stimulation
Latent (lag) period
a short delay from the time when the action potential reaches the muscle until tension can be observed in the muscle
What are the three phases or periods of a twitch?
a latent period, contraction phase, and a relaxation phase
Muscle tone
resting tension
Why is muscle tension never at zero?
muscle tone
What four factors influence performance of a muscle?
- stimulus intensity
- stimulus frequency
- effect of sustained exercise
- effect of aging
Intensity =
how strong
What happen when the intensity is increased?
- the number of motor units recruited increases
- the muscle tension increases
Max contraction
when all the motor units are recruited, the maximum possible tension is achieved
Graded response
a muscle ability to produce varying levels of force based on our needs
Frequency =
how often
Frequency: <10 per second
a twitch each time
Frequency: <10-20 per second
build up of Ca2+ resulting in treppe
Treppe
The muscle tension increases in a graded manner that to some looks like a set of stairs (step wise)
Frequency: 30-40 per second
wave summation and incomplete tetany occur
Wave summation
occurs when stimulations are delivered to a muscle fiber faster than it is able to completely relax.
Frequency: > 50 per second
fused contraction and complete tetany occur
Incomplete tetany
quivering at max contraction
What happens if 50 twitches per second continues beyond complete tetany?
the muscle fatigues
Fused contraction/complete tetany
when there is no relaxation of the muscle fibers between stimuli and it occurs during a high rate of stimulation; strongest single-unit twitch in contraction.
What are the two outcomes of sustained exercise?
Hypertrophy or hyperplasia
Hypertrpohy
an increase in fiber size as the result of increase in the amount of mitochondria, myofibrils, and glycogen reserve
Hyperplasia
increase in the number of fibers (cells)
Hyperplasia is what?
limited
Hypertrophy and hyperplasia result in what?
increased muscle tension
Lack of muscle activity results in what?
atrophy
Atrophy
decrease in fiber size and power
Prolonged inactivity results in what?
fibrosis
Fibrosis
muscle tissue converts to connective tissue
Effects of aging
- sarcopenia
- injury recovery
- fibrosis
Sarcopenia
- decrease in fiber number/diameter
- decrease in blood circulation
- decrease in power of skeletal muscles
Injury recovery with aging
decrease in the number of satellite cells
Fibrosis causes what?
decrease in flexiblity
What does a decrease in flexibilty cause?
restriction of movement and circulation
