muscles Flashcards
how does skeletal muscle look like?
striated (has banding pattern) also known as sacromeres
voluntary - we control the skeletal muscle
-no hormones that effect it
what is smooth muscle?
-non striated
-involuntary
what is cardiac muscle ?
striated
involuntary
what is the contraction rates what is the fastest and slowest ?
fastest happens in skeletal muscle
cardiac muscle is a little slower but 1 second for contraction and relaxation
smooth muscle is very slow
what are the levels of organizations of muscles?
1.muscle group
2. muscle fascicles
-bundles
3.muscle fibers
-cells
4.myofibrils
- myofilaments (actin, myosin)
what is the connective tissue organization?
Endomysium
-muscle fibers
perimysium
-muscle fascicles
epimysium
-muscle group
effects of muscle fascicle arrangement?
fascicles form patterns with respect to the tendons
- parallel
-fusiform
-circular
-triangular
-pennate - angles in more muscle fibers, but it is slightly smaller than if it was parallel
lever system: bone-muscle relationships
load- resistance (opposes movement)
ex. try to move load in the arm, but the weight of my arm muscle and tissue is known as a load.
effort: applied force: what muscle has to create to move that force
- this is muscle contraction, applied force where muscles attaches to bone
lever: a rigid bar that moved
: these are bones
fulcrum : a fixed point: joints
what are the types of levers?
first class:
-not common
- example is nodding head forwards and back
second class:
-uncommon
-load is between the fulcrum and the effort
eg. standing on you tip-toes
third class:
is the most common
- always at a mechanical disadvantage, harder to move but once starts moving its a big force
what are the structures of skeletal muscle?
sarcomere
- series of repeaters, form Z-line to Z-line
-repeater units
myofibrils:
-thin filaments
-many actin/myosin filaments
- surrounded by sarcoplasmic reticulum
light region
I band
darker region
A band
no overlap and only thick filament
H zone
what are the muscle proteins for contractile?
myosin
actin
what are the muscle proteins for regulatory?
troponin
tropomyosin
what are the muscle proteins for
structural?
-titin
-nebulin
-myomesin
-dystrophin
what is titin and nebulin?
titan stabilizes myosin
-rebound and spring action
nebulin aligns actin
what is myomesin and dystrophin?
myonesin: part of the m-line
dystrophin:
-attaches myofilaments to sarcolemma (membrane) and fascia
- helps transmit tension and shortening to muscle group
Myomesin:
Located in the M-line of the sarcomere, the structural unit of muscle.
Helps stabilize thick filaments (myosin) and maintain the organization of the sarcomere.
Dystrophin:
Connects myofilaments to the sarcolemma (muscle cell membrane) and the surrounding fascia.
Transmits tension generated by muscle contraction across the cell membrane, helping the muscle as a whole to contract and move effectively.
what does our muscle look like at rest?
tropomyosin covers the actin binding sites
- no cross-bridges
- no shortening
what does our muscle look like when there is an activation of actin ?
ca2+ binds troponin
-shifts tropomyosin
-reveals actin binding sites
-cross-bridges are now possible
what is excitation- contraction coupling?
Excitation-contraction coupling explains how a muscle contraction is initiated:
Neuromuscular Junction:
The connection between a motor neuron and a muscle fiber.
The axon terminal releases a chemical messenger called acetylcholine (ACh).
Steps in the Process:
ACh -acetyl-colyn is released from the neuron and binds to receptors on the muscle end-plate.
This triggers an action potential (electrical signal) in the muscle fiber.
The action potential travels along the muscle membrane and leads to the release of calcium ions (Ca²⁺) from the sarcoplasmic reticulum.
Calcium binds to troponin, allowing actin and myosin to interact, leading to muscle contraction.
step 1: Action poteintial arrives at the end -plate
step 2: acetylcholine is released from the axon end
-binds to receptors at the muscle endplate
-EPP: end-plate potential
step 3: EPP travels to the side of the end-plate, becomes a muscle action potential
step4: AP moves down the T-tubules to the inner core of muscle- close to sarcoplasmic reticulum
step 5: voltage change in T-tubules triggers the release of Ca2+ from the SR
step 6: calcium binds to troponin
shifts the tropomyosin
cross bridges and shortening are now possible
where is ca2+ stored ?
sarcoplasmic reticulum
what is the cross-bridge cycle? step 1
step 1:
the energized myosin binds to actin
what is step two of the cross-bridge cycle?
step 2:
the power stroke
- myosin head pivots
-increases the overlap of actin and myosin
- this is where we use the energy from the ADP and pi
- sarcomere shortening
what is step 3 of the cross- bridge cycle
myosin binds ATP
-myosin head can release from actin
what is step 4 of the cross bridge cycle?
- atp hydrolyzes into ADP + Pi
- this allows myosin to re-pivot
- myosin is now re-energized and ready to attach to another actin molecule
do we change the myosin or just the overlap?
overlap
with contraction what happens to the sacromere and the different parts?
sacromere decreases in seize
I band decreases
H zone decreases
A band stays the same
Overlap zones increase in size
how does relaxation take place in muscles?
calcium pumps remove Ca back into SR
- needs ATP
-tropomyosin slides over actin sites
-no crossbridges
-actin and myosin go back to resting length
what are isotonic contractions?
creating a force and moving a load
concentric- shortening
eccentric- muscle lengthening
what is isometric contractions?
create force without moving a load
what is the difference between isotonic and isometric contractions?
Isotonic Contraction:
- visible shortening
The muscle changes length while maintaining a constant tension.
Example: Lifting a weight (the muscle shortens) or lowering it back down (the muscle lengthens).
The load is moved, and the muscle visibly shortens or lengthens.
Isometric Contraction:
-no visible shortening
The muscle does not change length, but tension increases.
Example: Pushing against a wall or holding a heavy object in place.
The muscle is contracting, but there is no movement of the load.
In short:
Isotonic: Muscle moves the load.
Isometric: Muscle holds the load without moving.
whats happening in the latent period?
The latent period is the short time between when a muscle is stimulated and when it actually starts to contract.
During this period, excitation-contraction coupling occurs, where the signal travels to the muscle and calcium is released.
There’s also a build-up of tension in the muscle, but no visible movement yet.
As the load (weight) increases, the latent period gets longer because the muscle takes more time to develop enough force to move the load.
In simple terms, it’s the delay between the signal to contract and the actual beginning of muscle movement.
more action potential what happens to contraction?
you can hold the contraction for longer stable time
-held until the action potential is gone or reached fatigue
what is tetanus?
Tetanus in muscle contraction occurs when action potentials (nerve signals) are sent to the muscle very quickly:
High Frequency of Signals:
The signals come so fast that the muscle doesn’t have time to relax between contractions.
Result:
This creates a sustained and continuous contraction.
There are two types:
Incomplete Tetanus: Some small relaxation occurs between contractions.
Complete Tetanus: The muscle stays fully contracted with no relaxation.
In simple terms, tetanus means holding a muscle contraction steady by sending rapid signals.
what is motor unit summation?
Motor unit summation is when more motor units (a motor neuron and the muscle fibers it controls) are activated together to produce a stronger muscle contraction.
More motor units = more force.
It helps increase muscle strength by recruiting additional muscle fibers.
In simple terms, it’s about using more muscle fibers at once to make a contraction stronger.
if you have a increased heavy load what do your muscles need?
more tension needed
longer latent period
decreased contraction distance
- decreased contraction velocity
-slower cross-bridge recycling
what are some things that determine muscle force?
-Muscle Fiber Diameter:
Larger muscle fibers have more actin and myosin filaments, allowing for more cross-bridges to form.
More cross-bridges mean a stronger contraction, so thicker muscle fibers can generate greater force.
Muscle Fiber Length (Length-Tension Relationship):
There is an optimal (skeletal) length where the muscle fiber can generate the most force. This happens when the actin and myosin filaments overlap just right, allowing for the maximum number of cross-bridges to form.
If the muscle is too stretched or too shortened, fewer cross-bridges can form, leading to less force.
Too short: Filaments overlap too much, and cross-bridges can’t form effectively.
(cardiac)
Too long: Filaments barely overlap, limiting cross-bridge formation.
what are the energy sources in muscle?
atp
creatine phosphate
glycogen
what are the muscle fibre types?
slow oxidative (type I)
- highest endurance,
-dark
-most blood flow
fast oxidative (IIa)
- light pink
- intermediate
Fast glycolytic (IIb)
(anaerobic)
- based on how fast they can recycle
- do not need lots of blood flow so they are white
what is slow oxidative fibers? (type I)
- slow cross bridge cycling
-uses oxidative metabolism for energy - myoglobin (stores oxygen), mitochondria, high blood flow to deliver glucose and oxygen
- very red
- low intensity
-high endurance
eg. core muscles
what is fast twitch fiberes (type II)?
fast oxidative fibers (II a)
- faster cross-bridge cycling
- higher intensity
-lower endurance
fast glycolytics (IIb)
-100 m sprint
- use glycolysis for energy
-anaerobic
- highest intensity but lowest endurance
-“emergency fibers”
-white fibers
muscle fatigue is due to what?
increased lactic acid
decreased ATP
increased wastes
Ca2+ changes
muscle cells do not divide so this means what?
they are in G0 so fibers get bigger but dont increase in #
what are the short term effects of excercise?
increased blood supply
increased temp
increased lactic acid and wastes
what are the effects of long term exercise?
-more maintained blood flow to muscles
- larger muscle fiber diameter
- more mitochondria
- conversion of fast glycolytic fibers to fast oxidative fibers
-more actin/myosin
what is the affects of steroid effects?
similar to testosterone
- increases # of actin and myosin myofilaments
- if too large, can overload the tendon
-cardiac hypertrophy
what is the stretch receptor reflex?
protective mechanisms
prevents over-stretch of the muscle
-triggers a reflex contraction
what is the golgi tendon organ reflex?
protective mechanisms
prevents over-contraction (and stretch of tendon)
- triggers a reflex relaxation
eg. muscle failure with high load
what is a strain?
overstretching injury of muscle
-damage to actin and myosin
-muscle stiffness
treatment
rest
anti-inflammatories
smooth muscles ?
walls of hollow organs and tubes
-gut, blood vessel’s
- no striations
-filaments do not form myofibrils
- cells usually arranged in sheets
- spindle shaped cells
-single nucleus
what are the three filaments in smooth muscles?
thick myosin filaments:
-longer than in skeletal muscle
thin actin filaments:
tropomyosin but no troponin
intermediate filaments:
- not part of contraction
-cytoskeletal - supports cell shape
how is smooth muscle different from skeletal muscle?
when smooth muscles contract, it squeezes from all directions making the cell shorter and fatter
- the contraction is controlled by activating myosin, not actin
explain the process of activation of myosin in smooth muscle…
or contraction
different from skeletal muscle.
n smooth muscle, calcium (Ca²⁺) triggers contraction by:
Calcium enters the cell and binds to calmodulin.
This activates myosin kinase, which adds a phosphate to myosin (phosphorylation).
Phosphorylated myosin can then bind to actin, allowing the muscle to contract.
- but in smooth our actin is already turned on
in skeletal myosin was always activated because it already had phosphate on there and we just had to turn on actin
how is relaxation different in smooth muscles?
skeletal: calcium pumps and bring calcium back into sarcoplasmic reticulum
smooth: we use another enzyme called a phosphatase, takes off a phosphate from myosin sliding back to normal
what are the two types of smooth muscles?
multiunit smooth muscle
- lots of cells but work independently
-single cell contracting
single unit smooth muscle
- where you have lots of cells connected by gap junctions and behave as a single unit
what is a multiunit smooth muscle?
- neurogenic - triggered by nerve only
- discrete units function independently
-each must be stimulated
-large blood vessles
-iris of eye
-base of hair follicle goose bump
-large airways to lungs
what is a single-unit smooth muscle?
- also called visceral smooth muscle
- gut, urogenital tract
-self-excitable
doesnt require nervous stimulation - fibres contract as single unit
-contraction slow
what is a cardiac muscle?
striated
- shorter
-involuntary
- have regions called intercalated discs
- lots of gap junctions
- run by autonomic nervous system
contraction in cardiac muscle?
Action potential starts:
An electrical signal (action potential) is generated, usually by the pacemaker cells in the sinoatrial (SA) node.
Calcium channels open:
The action potential travels through the muscle cell membrane, causing calcium ions (Ca²⁺) to enter the cell from outside.
Calcium-induced calcium release:
The incoming calcium triggers the release of more calcium from the sarcoplasmic reticulum (a storage site inside the cell).
Calcium binds to troponin:
The released calcium binds to troponin, causing a change in shape that moves tropomyosin away from actin’s binding sites.
Cross-bridge formation:
Myosin heads attach to actin (forming cross-bridges) and pull, leading to muscle contraction.
Relaxation:
Calcium is pumped back into the sarcoplasmic reticulum and out of the cell.
The muscle relaxes as cross-bridges detach.
In simple terms: Electrical signal → Calcium entry → Cross-bridge formation → Contraction → Calcium removal → Relaxation.
compare the speed of contraction in skeletal, smooth, and cardiac?
skeletal: fast- slow
smooth single unit: very slow
smooth multiunit: very slow
cardiac muscle: slow
compare the spot of activating calcium in skeletal, smooth, and cardiac?
ST - SKELETAL
SMOOTH: SR AND EXTRACELLULAR
CARDIAC : SR AND EXTRACELLULAR
Explain what happens to muscle tissue throughout life
with increased age:
-connective tissue increases in muscles
- number of muscle fibers decreases
loss of muscle mass with aging
-decrease in muscular strength is 50% by age 80
sarcopenia- muscle wasting
