Chapter 10 Flashcards
what 3 layers of CT surround the muscle?
- Epimysium
- Perimysium
- Endomysium
Epimysium
dense layer of collagen fibers that covers the entire muscle
perimysium
covers bundle of muscle fibers called fascicles
fascicles
collagen + elastic fibers, blood vessels and nerves
Endomysium
surrounds muscles fibers
-contains elastic fibers, capillaries and nerves
Tendon
where endomysium, perimysium and epimysium come together
names for muscles cells
- muscle cell
- myofiber
- muscle fiber
myofibril
-organelle that contains myofilaments
myofilaments
- consists of 2 things
- responsible for
- thick (myosin) and think (actin) filaments
- muscle contraction
sarcolemma
plasma membrane surrounding the cytoplasm
Sarcoplasmic reticulum
- what is it similar to
- what does it contain
Similar to smooth ER
-contains large amount of Ca++ ions
terminal cisternae
SR tubules fuse and form an expanded chamber
Triad
2 terminal cisternae and 1 T-tubule
T-tubule
- definition
- what do they form
narrow tubes continuous with sarcolemma
-form passage ways through the muscle cells
Sarcomere
- definition
- function
- functional unit of the myofilament
- gives the appearance of striations under microscope
4 components of the sarcomere
- thick filaments (myosin)
- Thin filaments (actin)
- Proteins that stabilize these filaments
- Proteins that regulate interactions between filaments
in between the I band
Z line that connects thin filaments
in between the A band
H zone that contains think but no thin
Thin filament
-composed of 4 things
- Troponin
- Tropomyosin
- Actin
- Active site
Active site of thin filament
- location
- binds to
- what is it covered by when resting
- on actin molecules
- myosin
- tropomyosin
Thick filament
-contains
-head and tail
Sliding filament theory
Thin filaments slide toward center of each sarcomere along side of each thick filament
During contraction what happens to the length of:
- A band
- I band
- H zone
- Zone of overlap
- Sarcomere
- remains constant
- shortens
- shortens
- increases
- Shortens
4 principles governing the contraction of skeletal muscle cells
- When muscle cells contract they pull on the attached tendon
- Contraction occurs only when skeletal muscle fibers are activated by neurons at a neuromuscular junction
- Tension produced is dependent on the number of motor neurons stimulated
motor neurons
neuron and muscle fibers it stimulates
How does the size of the motor unit relate to movement controlled
Size of the motor unit relates to how well the movement is controlled
small motor units
- 1 neuron stimulates
- allows for
1 neuron stimulates 4-6 muscle fibers
-fine control
Large motor units
-1 neuron stimulates
1000-2000 muscle fibers
Physiology of muscle contraction
-2 things
- Control by nervous system: the events of the neuromuscular junction
- Excitation contraction coupling
Events of the neuromuscular junction
-5 steps
- Electrical signal travels down the terminal branch of the motor neuron
- This causes Ca++ to enter the axon terminal
- Vesicles in axon terminal are going to move to plasma membrane, fuse and discharge contents into synaptic cleft
- Ach diffuses across synaptic cleft and binds to a receptor on the muscle cell sarcolemma
- This initiates an electrical signal along sarcolemma of muscle cell (the muscle is now excited)
electrical signal=
action potential
what are neurotransmitters made up of
acetylcholine
Excitation contraction coupling
- definition
- 7 steps (continuation)
- link between generation of an action potential in the sarcolemma and start of muscle contraction
6. electrical impulse conducted into a T-tubule
7. impulse is going to reach the sarcoplasmic reticulum (at the triad)
8. Sarcoplasmic reticulum releases Ca++ into the sarcoplasm
9. Ca++ diffuses to myofibril and binds to troponin on thin filament
10. When Ca++ binds to troponin, troponin changes its shape (causes tropomyosin to change position)
11. This exposes the active site on actin
12. Myosin head binds to the active site on actin
contraction cycle
-3 steps
- Cross bridge attachment
- Cross bridge rotation (pivoting)
- cross bridge detachment
Cross bridge attachment
- -what happens
- allows for
- myosin head acts as am ATPase to hydrolyze ATP to ADP + P
- binding of myosin head to active site on actin
Cross bridge rotation
powerstroke occurs as ADP + P and is released from myosin head
Cross bridge detachment
- what binds
- what does binding do
- ATP binds myosin head
- disrupts linkage between myosin head and active site on actin
All or none principle
After stimulation by a nerve, an individual muscle cell either contracts to its fullest or not at all (does not apply to the entire muscle)
Principle of graded strength
strength of the contraction can range from weak to strong
Single stimulus
Twitch
twitch
- response of a muscle cell to a single stimulus
1. latent phase
2. contraction phase
3. Relaxation phase
latent phase of a twitch
begins at stimulation - action potential spreads down sarcolemma and SR releases Ca++
-Ca++ will bind to troponin as soon as its released from SR
contraction phase of a twitch
tension rises to peak (crossbridges are forming)
relaxation phase of a twitch
Ca++ levels are falling and active sites are covered
Summation
- definition
- produces
- 2 types
Adding individual twitches together
- graded contractions
1. multiple motor unit summation
2. Temporal (wave) summation
multiple motor unit summation
- increased force of contraction caused by an increase in stimulus strength
- sub-threshold, threshold, sub-maximal, maximal stimulus
threshold
minimum stimulus needed to produce a contraction
maximal stimulus
Maximum stimulus without any additional force of contraction
tension produced by skeletal muscle is determined by:
-2 things
- stimulated muscle fibers
2. total number of stimulated muscle fibers
temporal (wave) summation
increased force of contraction caused by an increase in the frequency of stimulation
tetanus
stimulation of a muscle at even higher frequency produces “fusion” of summation twitches
Frequency of temporal summation
- definition
- what happens to the strength
next stimulus arrives before relaxation phase has ended
-strength of stimulus remains the same
why does increase in the frequency of stimulation increase the force of contraction (temporal summation)?
- muscle cell has not had a chance to fully relax before the next stimulus arrive
- muscle is still partially contracted and Ca++ stores are still available from last contraction
Treppe
- definition
- why?
If a muscle is stimulated a 2nd time immediately after the relaxation phase has ended the force of contraction will be greater than the 1st stimulus
-increased Ca++ availability (in sarcoplasm) and heat increases activity of muscle enzyme
Muscle tone
- definition
- why does it occur
- example
- constant tension produced by muscles for extended periods of time
- because some motor units are active even when whole muscle is not contracting
- muscles that keep the back and legs straight, the head upright and the abdomen flat
Isotonic contraction
muscle develops tension, overcomes resistance and object is moved
Isometric contraction
Muscle develops tension, cannot overcome resistance and object is not moved
Muscle fatigue
- lack of O2
- depletion of ATP
- accumulation of lactic acid
- ionic imbalances
Fast fibers
- definition
- common?
- color
- capillary supply
- mito
Rapid movements for short periods of time
- most muscle fibers in humans
- white
- scarce
- few
Slow fibers
- definition
- type of muscle
- color
- capillary supply
- mito
- high endurance and contracts for an extended period of time
- postural muscle
- red
- dense
- many
Oxygen debt (excess post - exercise O2 consumption)
- definition
- 3 examples
- what does rapid breathing do
- Amount of O2 needed to restore homeostasis in the muscle tissue
- ATP stores must be replenished
- Lactic acid that builds up during exercise must be converted to glycogen
- Creatine needs to be converted back to creatine phosphate
- ATP stores must be replenished
- helps to replenish O2
The role of creatine phosphate
- energy sources
- what is it used for
- formula
- ATP + creatine phosphate
- used to produce ATP in muscle cells
- ADP+ creatine phosphate -> creatine + ATP
Muscle hypertrophy
Muscle cell enlargement in response to repeated stimulation
Muscle Atrophy
Muscle cells reduce in sixe in response to a lack of stimulation
Delayed onset muscle soreness
-3 proposed mechanisms
- small tears in muscle tissue (damaged sarcolemma) (permits the loss of enzymes and chemicals that stimulate pain receptors
- muscle spasm in affected muscles may cause pain
- tears in connective tissue and tendons of affected muscles
