Physiology Flashcards
Skeletal muscle
- description
- type of control
- when does it contract
- somatic effector
- striated
- generally voluntary control
- normally does not contract w/o nervous stimulation
Major diff between connectivity of skeletal m compared to cardiac m
lacks anatomical and functional connections between individual muscle fibers
Describe a muscle cell
- aka muscle fiber
- arranged end to end
- grouped into parallel bundles
- derived from myodermal myoblasts (remain in tissue to replace cells)
Satellite cells
- describe
- small, little cytoplasm
- can give rise to more satellite cells OR differentiate to muscle fiber
Proliferation of satellite cells influenced by what
- IGF-1 (insulin like growth factor)
- proliferations to provide growth and repair
Three layers of skeletal muscle tissue
- epimysium
- Perimysium
- Endomysium
Epimysium
- external sheath
- septa carry vessels and nerves inward
Perimysium
- thin
- wraps bundles of muscle fibers to form fascicles (the functional unit)
- penetrated by vessels and nerves
Endomysium
- very thin
- surrounds each muscle fiber
Define:
- sarcolemma
- sarcoplasm
- sarcoplasmic reticulum
- plasma membrane
- cytoplasm
- like endoplasmic reticulum
What is contained in the sarcoplasm
myoglobin which holds O2
Describe the sarcoplasmic reticulum
- elaborate
- surrounds myofibrils
- contains Ca2+ pumps
Terminal cisterna
- part of the sarcoplasmic reticulum
- sac-like junctions of SR
- release calcium
T-tubule
- folds of sarcolemma (increases surface area)
- encircle myofibrils near A-I junctions
- depolarization wave runs through t-tubules deep into cell
What is the “triad”
- aka sarcotubular system
- 2 terminal cistern (sarcoplasmic reticulum) and 1 T-tubule (sarcolemma)
- links calcium release and depolarization
define myofibril
- filament bundle
A band and I band
A band
- anisotropic
- thick filaments, myosin
I band
- isotropic
- thin filaments, actin
Z band
- region of I band w/o A band overlap
- appears to bisect I band
- where actin attach, allows shortening of fiber
- edge of sarcomere
Sarcomere
- functional unit of myofibril
- Z band to Z band
Thick filament
- fiber type
- which band
- describe
- myosin
- A bands
- rod like tail
- two globular heads
- head contains ATP binding site and actin binding site
M Line
- in the H zone
- reversal of polarity of cross bridges
- she didn’t seem to care much about this…
Thin filament
- fiber type
- which bands
- actin, tropomyosin, and troponin
- I bands
Actin
- describe
- composed of G actin subunits
- 2 strands coil to form actin helix
tropomyosin
- describe
long filaments that spiral around actin
Troponin
- describe
- three types
- located at intervals along tropomyosin
- TnI: binds actin
- TnT: binds tropomyosin
- TnC: binds calcium
Name four additional structural proteins
- Actinin
- Titin
- Creatine kinase
- Myoglobin
Actinin
- binds actin to Z lines
Titin
- connects Z lines to myosin
- provides structure, stretch, and resistance
- can coil and stretch
Creatine Kinase
- at M line
- phosphorylation of ATP from phosphocreatine (holds phosphate so can turn ADP into ATP when needed)
- provides contractile E source
myoglobin
- holds on O2
- higher affinity for O2 than hemoglobin
- O2 will transfer from hemoglobin to myoglobin dt Bohr effect
Bohr affect - three factors that affect O2 dissociation
will dissociate when:
- heat
- low pH
- increased DPG
*and opposite
Very basic overview of muscle excitation
- somatic motor nerve is depolarized
- releases Ach
- Ach binds to nicotinic receptor on motor end plate of resting cell (muscle)
What is the resting potential of a muscle cell?
What is depolarized membrane potential?
-90 mV
30 mV
Muscle cell excitation steps
- Ach triggers opening of voltage gated Na+ channels
- sodium influx
- local depolarization in all directions along sarcolemma and into T tubules
- voltage gated calcium channels on SR open, calcium not sarcoplasm
- contraction of muscle
action potential of muscle cells
- how long does it last
- can it be partial?
- 1-2 milliseconds
- no, is all or none, once action potential is initiated, full contraction of stimulated cell occurs
What happens to calcium after it is released into the sarcoplasm?
- ATP dependent calcium pumps return calcium to sarcoplasmic reticulum
- another reason muscle contraction is ATP expensive
Repolarization
- returns sarcolemma to resting state
- Na+ gates close
- K+ gates open, K+ efflux
What is the name for the period of time during repolarization
refractory period - cannot depolarize
When/what returns
- electrical resting state
- ionic resting state
- electrical: during repolarization
- ionic: via Na/K pump
what is the resting blockade?
Myosin binding site on actin is blocked by tropomyosin
What happens when calcium binds troponin
- binds to TnC
- conformational change in tropomyosin
- myosin binding site on actin exposed
Describe steps after myosin binding site of actin is exposed
- myosin head binds myosin binding site on actin (cross bridge attachment)
- powerstroke
- repeat until calcium concentration decreases
Powerstroke steps
- release of ADP = myosin head pivots (release of energy)
- draws actin toward
center of sarcomere - head binds ATP, releases actin
- ATP hydrolysis cocks head to attachment position
About how many power strokes per head
5
What is a motor unit
- motor neuron and all the muscle fibers it supplies
- one motor nerve has 100s of axons branching to many axonal terminals
- when nerve fires, all fibers served are stimulated
What does it mean that the fibers served by a motor neuron are not clustered?
stimulation of a single motor unit causes weak contraction of the entire muscle
About how many fibers per motor unit?
average is 150 fibers/motor unit
Muscle twitch
- single action potential causes brief contraction followed by relaxation
- there is a small latent period between action potential and start of contraction
- duration of twitch varies with muscle type
- can trace on myogram
Slow twitch fibers
- myoglobin
- cell description
- myosin ATPase
- contraction
- primary E source
- metabolism type
- length of contraction
- abundant myoglobin = red
- thin cells
- slow acting myosin ATPase (allows for globular head to move, allows contraction)
- slow contraction
- fat is primary E source
- aerobic metabolism
- can contract for long periods
fast twitch fibers
- myoglobin
- cell description
- myosin ATPase
- contraction
- primary E source
- metabolism type
- length of contraction
- less myoglobin = white
- large cells
- fast acting myosin ATPase
- quick, powerful contraction
- abundant glycogen reserve
- glucose is primary fuel
- anaerobic pathway, lactic acid production
- quickly fatigued
What does graded muscle responses mean?
variations in degree of contraction. Depends on
- rate at which firing (increased rapidity of stimulus to create contraction)
- recruiting increased number of motor units
*muscle contractions are smooth and prolonged, not a muscle twitch
Wave summation
- subsequent impulses create a stronger contraction that appears to build on prior contractions
- when second contraction is stimulated before muscle has completely relaxed
- creates smooth, continuous muscle contraction
Tetany
- no muscle relaxation
- wave summation results in continue contraction
- nerve stimulus is in rapid succession
- fatigue of m eventually occurs (run out of O2, ATP, etc.)
Treppe
- staircase effect in contraction, subsequent contractions are greater strength despite same stimulus
- activity produces heat = enzymes more efficient
- increases avail of calcium for contraction
- why warm up before exercise
How is force of contraction increased?
increased number of motor units stimulated
Delicate touch vs. strong grip
- delicate: few motor units
- Grip: many motor units
*still all or none!!
Muscle tone
- relaxed m exhibits certain amt of contraction (tone)
- involuntary
- d/t spinal reflexes in response to stretch receptors in muscle/tendon
- provides joint stability, maintains posture, readiness for stimulation
Describe muscle tension
- force exerted by a contracting muscle
Describe load
- weight or reciprocal force exerted by objection on muscle
- thing muscle is trying to move
- influences velocity and duration of muscle work
Describe movement
tension overcomes load
- greater the load, longer the latent period, slower the contraction and shorter duration of contraction
Isotonic contraction
- tension exceeds load
- muscle shortens
- load is moved
- movement of body
Isometric contraction
- tension equals load
- muscle does not shorten
- load is not moved
- posture and balance
what type of contraction (isotonic vs. isometric) are most movements?
combo of both :)
Describe length-tension relationship
- ideal stretch that produces maximal force of contraction (resting length)
- related to sarcomere length and overlap of myofibrils
- skeletal m are attached to bones at optimum length, slightly stretched to voice max movement
What is required for all muscle contractile events
ATP
- crossbridge stroke and detachment
- calcium pump, returns calcium to SR
How does muscle get ATP?
little stored in muscle, most must be generated
List two sources of energy for muscle
- Glucose
2. Fatty Acids
Glucose energy source for muscles (2)
- via circulation
- glycogenolysis (from glycogen stored in m tissue)
Fatty acid energy source for muscles
- TG in muscle cells and circulation
- lipolysis from adipose, release FA to circulation, 2 carbon bodies enter Krebs cycle as acetylene-coA
*muscle loves fat as an E source
Anerobic respiration for muscle metabolism
- glucose into glycolysis
- pyruvate is oxidized to relish NADH
- ATP and lactic acid are produced
- lactate converted to pyruvate once O2 is available
Creatine phosphate
- liver produces creatine from arg, gly, meth
- creatine kinase phosphorylates creatine into phosphocreatine which is stored in muscle cells
- CK-MB acts at junction of myosin head/actin to provide phosphate to generate ATP from ADP for contraction
- can be regenerated
what is creatinine
- breakdown product of creatine phosphate
- marker for renal function :)
List the energy sources from shortest to longest duration
- ATP
- creatine phosphate (4 sec)
- anaerobic glycolysis (2-3 min)
- aerobic glycolysis (1-2 hours)
- fatty acid oxidation (many hours)
