MUSCLE PHISIOLOGY Flashcards
What are the three types of muscle?
Skeletal muscle, Cardiac Muscle, and Smooth muscle.
What are the characteristics of Skeletal Muscle?
Multi-nuclei, striated, long, stretches the entire length of muscle
What is the function of skeletal muscle?
Skeletal movement. Maintain body posture and position. protect internal organs (abdominal & Pelvic). Generate heat via friction.
What are the three connective tissue layers ?
Outer layer- epimysium
middle layer- perimysium
Inner layer- endomysium-
What is the connective tissue layer organization?
A bundle of myofibril= muscle fiber
bundle of muscle fiber=fasicicle
What does the endomysium surround?
The muscle fiber which is made up of myofibrils
What does the epimysium surround?
Entire muscle
What does the perimysium surround?
The fascicles which is made up of fibrils
What are T- tubules?
Invaginations (tunnel) that penetrate deep into the cell
What role does the sarcoplasmic reticulum play in muscle contraction?
The SR stores calcium
What makes up a triad
1 T-tubule and 2 cisterna (enlarged regions of the SR that are close to T-tubules)
What is a sarcomere?
The contractile units of skeletal and cardiac muscle. The distance between two z-disc = sarcomere
What are the 5 components of the sarcomere?
A band
I Band
H zone
Z line
M line
Describe the A band
The zone of overlap. Contains thin and thick filaments. Ranges from the inner edge of each I Band
Describe the I band
Only contains thin filaments and z disc
Describe the Z line
dissects each I band. Contains titin, nebulin, desmin, and actin which anchor thin filaments
Describe the M line
The center of the sarcomere. The place thin and think filaments do not overlap
Describe the H zone
Contains only thick filaments
How does the sarcomere change during muscle contraction?
It shortens. Actin and myosin do not change length, they slide past one another. Thick filaments remain stationary, thin filaments move toward the center m line. H zone and I band narrow. A band remains the same
Describe the thick filaments
made of myosin composed of intertwining protein chains that form a long stiff tail, an elastic hinge region and two heads.
Describe the role of light chain and heavy chain heads in contraction
The heavy chain binds ATP necessary for muscle contraction. The light chain is a regulatory subunit.
Describe the thin filaments
Mainly made of actin which is a globular protein (G actin) arranged as a chain of repeating units, forming two strands of an alpha helix.
Each G actin has a myosin binding site
tropomyosin wraps around actin filaments covering the myosin binding sites
What is troponin and what is its role?
It is made of 3 subunits
TN-T- attached to tropomysoin
TN-I- inhibits myosin binding site on actin
TN-C- has ca2+ binding sites ( 4 ca2+ for each TN-C)
5 steps of muscle contraction (tropomyosin vs troponin)
1) ca2+ levels increase in the cytosol
2) ca2+ binds to troponin
3) Troponin -Ca2+ complex pulls tropomyosin away from actin binding sites
4) myosin strongly binds to actin to complete power stroke
5) actin filaments moves with the myosin head
How does the stimulation of muscle cells lead to contraction?
- Excitation: the action potential generation at the neuromuscular
junction - Coupling occurs when the action potential propagates to the triads
resulting in the release of calcium from the sarcoplasmic reticulum - Contraction occurs when calcium binds to the myofibrils and the
muscle fiber shortens (powerstroke occurs) - Relaxation occurs when calcium is released from the myofibrils and
returned to the SR
What is Excitation-contraction coupling?
the process in which an
action potential causes calcium concentration to increase in the
cytosol, leading to contraction of the muscle
What is a neuromuscular junction
area of junction between motor neuron and muscle cell, There is not physical connection between the two.
what the the synaptic cleft?
The small space between the motor neuron and muscle cell
neuromuscular junctions steps
1.Action potentials are propagated down the somatic motor neuron
2. The presynaptic terminal becomes depolarized and voltage-gated calcium channels
open, increasing calcium permeability
3. Calcium ions entering the presynaptic terminals stimulate the fusion of ACh-containing
vesicles with plasma membrane
4. (a) ACh is released into the synaptic cleft and diffuses to the postsynaptic membrane
4. (b) The motor-end plate contains nicotinic receptors that bind ACh
5. The nicotinic receptors open allowing Na and K ions flux across the motor end plate
causing depolarization and the development of an end plate potential (EPP)
6. The EPP spreads across the muscle fiber, resulting in depolarization and the firing of an
action potential in skeletal muscle which spreads along the t-tubules
7. The EPP is terminated when ACh is degraded by Acetylcholinesterase (AChE) in the
synaptic cleft
Sequence of Events at the Neuromuscular
junction for Skeletal Muscle Contraction4.
Do skeletal muscle require extracellular calcium?
no
What is excitation ?
the generation of the action
potential at the neuromuscular junction
What is DHP?
a voltage gated calcium channel (Dihydropyridine receptor) located on t-tubule membrane that measure the action potential/depolarization of t-tubule membrane
What is a ryanodine receptor?
A calcium release channel located on the membrane of the SR that releases Ca2+ from the SR into the cytoplasma when DHP (L type Ca2+ channel voltage sensor) senses and depolarization of T-tubules and causes a conformational change in ryanodine.
What are the sequence of events in a power stroke?
1.At rest, myosin heads are bound
to adenosine diphosphate and
are said to be in a “cocked”
position in relation to the thin
filament
2.Ca2+ binding to the troponin—tropomyosin complex induces a
conformational change in the thin filament that allows for myosin heads to cross-bridge with thin filament actin
3.Myosin heads rotate,
move the attached
actin, and shorten the
muscle fiber, causing
the power stroke.
4.At the end of the
power stroke myosin
releases ADP, exposing
the ATP-binding site in
the myosin HC
5.The release of ADP stabilizes the myosin-actin
interaction
6.in the continuous presence of
ATP and Ca 2+ , ATP binds to a now
exposed site on the myosin HC.
7.ATP binding destabilizes the
myosin-actin interaction; myosin
releases actin and returns to the
“cocked” position.
What is the function of ATP in muscle contraction?
To relax the cell by releasing myosin from actin.
When does relaxation occur?
when calcium is released from the
myofibrils and returned to the SR
relaxations steps
- Sarcoplasmic recticulum Ca2+-ATPase pumps Ca2+ back into SR
- Decrease in free cytosolic ca2+ to unbind from troponin
- tropomyosin re-covers binding site, when myosin heads release elastic elements pull filaments back into their relaxed position
What are the two types of contraction?
Isometric and isotonic
what is isotonic contraction?
the entire muscle shortens. ex. curl a weight
what is isometric contraction?
force that occurs before muscle can shorten, theres no movement. Ex. army straight before you do a curl
what is a muscle twitch?
muscle contraction in response of a single event of stimulation, muscle completely relaxes between each twitch
what is the optimal resting length of a sarcomere?
2.0-2.3um
What is length tension?
What is total force?
what is wave summation?
What is tetanus?
What are the 3 sources of energy for muscle contraction?
What are the three types of skeletal fiber?
What are the characteristics of the cardiac muscle ?
what is the optimal resting length of the cardiac muscle? why
1.8um because it can only increase contractile force up to the optimal length so it needs space to be able to increase
Where does the cardiac muscle get Ca2+ from for contraction? Why?
The extracellular fluid becasue the SR of the cardiac muscle is less developed.
What is the refractory period for cardiac muscle ?
heart must fully relax before next contraction, Refractory period is 90% of the length of the action potential
