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22 Cards in this Set

  • Front
  • Back
3 Types of Muscle
1) skeletal - striated, voluntary control
2) cardiac - striated, involuntary control
3) smooth - unstriated, involuntary control
Organization of Skeletal Muscle
1) muscle
2) muscle fiber
3) myofibrils
4) sarcomere
a. thick filaments - myosin (myosin ATPase site, actin binding site)
b. thin filaments - actin, tropomyosin, troponin (Ca2+ binding site)
3 Types of Skeletal Muscle
1) Type I - Slow Oxidative :
a. slow contraction
b. ATP source: oxidative phosphorylation
c. have many mito, rich blood supply, abundance of myoglobin

2) Type IIa - fast oxidative
a. quick contraction
b. ATP source - oxidative phosphorylation
c. many mito, rich blood supply, abundance of myoglobin

3) Type IIb - Fast Glycolytic
a. quick contraction
b. ATP source - glycolysis
c. few mito, ltd blood supply, abundace of glycogen, small amt of myoglobin
Contraction of Skeletal Muscle via:
myosin-actin cross bridge
Consequences of Cross Bridge
1) sarcomere, H zone, I band shortens
2) A band, individual actin molecules, and myosin fibers maintain a constant length
Activation of Muscle Contraction :
Exciation-Contraction Coupling
1) AP at the axon hillock
2) AP propagates down the length of the axon and invades the pre-synaptic terminal
3) voltage gated Ca2+ channels open near the active zone, activating the Ca2+ sensors on docked synaptic vesicles
4) vesicle exocytose and release neurotransmitter into the synaptic cleft
5) transmitter binds to ligand gated channels on the post-synaptic membrane
6) a graded potential in the muscle
7) if the stimulus is strong enough, an AP is generated
8) AP propagates down T-tubules, spreading into the depths of the muscle
9) Ca2+ from the lateral sacs are released into the sarcoplasmic reticulum
10) Ca2+ binds to the troponin-tropomyosin complex of the sarcomeres, revealing actin subunit for binding
12) binding of ATP to ATP site on myosin causes ATP hydrolysis, coking back the head of myosin
13) cocked myosin head binds to actin & power stroke occur, releasing ADP
14) 2nd ATP binding to myosin head, releases the actin/myosin binding
15) After AP ceases, Ca2+ is reuptake and relaxation of the muscle occurs
Define motor unit.
def. a motor neuron and all the muscle fibers it inervates
Define motor unit recruitment.
def. the process of increasing the number of motor unit that participates in muscle contraction; stronger contraction requires more, delicate contraction requires less
Factors contributing to muscles tension
1) frequency of stimulation
2) the length of the fiber at the onset of contraction
3) the extent of fatigue
4) the thickness of the fiber
Source of ATP for Muscle metabolism
1) creatine phosphate -
a. primary source
b. generated via creatine kinase
c. during rest, excess ATP generated by glycolysis and oxid. phosph. is stored as creatine phosphate

2) oxidative phosphorylation
a. requires oxygen, aerobic, therefore has abundance of myoglobin that facilitates the transport of oxygen from the blood
b. fueled by glucose or fatty acids from glycogen or fat reserves

3) glycolysis:
a. anaerobic
b. utilize glucose to generate 2 net ATP and 2 pyruvate that is converted into lactic acid & removed by the bloodstream
Purpose of ATP Metabolism in Muscle
1) power stroke apparatues
2) active transport of Ca2+ into the SR
Cause of Fatigues
1) cell muscle unable to synthesize sufficient quantities of ATP to maintain contractile activity
2) muscle accumulate too much latic acid fro glycolysis
3) neuromuscular fatigue when Ach stores are depleted and NM synaptic transmission can't keep its pace
Define recovery
def. a period following a period of intense exercise the oxygen demands of skeletal muscle remain high so that metabolism can replenish the stores of muscle glcogen and creatine phosphate
Where are smooth muscle located?
- located ni the walls of hollow organs and tubes such as blood vessels and the intestine
Physiology of Smooth Muscle
- small, unstriated
- spindle shape, single nucleus, arranged in sheets
- long, thick myosin filaments
- thin actin filaments that contain tropomyosin, but lack troponin
- contain IF's for structural support
- lack the distinct sarcomeres as in skeletal muscle, but contain dense bodies that act as anchors
- lack T-tubule organization of the PM
- poorly developed SR
- 10-15 thin filaments for each thick filament, oriented diagonally
- contraction of the filament lattice cause cellular shortening and expansion
- contractile apparatus is made of thin filaments that slid relative to stationary thick filaments in response to ta rise in cytosolic Ca2+
Activation of smooth muscle contraction
- synaptic transmission from autonomic neuronal fibers : multi-unit smooth muscle
- self excitation : aka single-unit smooth muscle causing functional syncytium via gap junction and exhibit pacemaker and slow wave activity
Define pacemake potential
def. gradual depolarization until threshold is reached
Define slow-wave potential
def. alternating depolarizaing and hyperpolarizing swings in membrane potentials
Features of Innervation of Smooth Muscle from Autonomic Postganglionic Nerve Terminals
1) no motor unit recuitment as all cells ar connected by gap junction
2) given smooth muscle cell can be influenced by different nerve fibers
3) neural input does not directly initiate contraction but can modify the rate and stregth of contraction
Excitation-contraction coupling in Smooth Muscle
1) self-excitation or neuronal excitation leads to Ca2+ entry from the EC space thru voltage-gated Ca2+ channels
2) Ca2+ entry triggers internal release of more Ca2+ from the SR
3) Ca2+- calmodulin binding
4) Ca2+-calmodulin complex activates myosin kinase which phosphorylates myosin
5) phosphorylated myosin binds to actin to form the activated cross bridge
6) removal of Ca++ leads to dephosphorylation of myosin and the dissociation of myosin from actin
7) gap-junctions enable excitation of one cell to propagate rapidly to all the coupled cells in a network
8) contraction strength is graded in proportion to the cytosolic Ca++ concentration
Where are Cardiac Muscle Located?
- found only in the heart
Characteristics of Cardiac Muscle
1) cardiac muscle is striated
2) the thin filaments contain tropomyosin and troponin
3) contains an abundance of mitochondria and myoglobin
4) possess T-tubules and sarcoplasmic reticulum
5) EXTRACELLULAR Ca++ enters the cytosol from voltage-gated Ca++ channels in the plasma membrane and triggers the further internal release of Ca++
6) displays pacemaker activity initiating its own action potentials
7) connected by gap-junctions
8) innervated by autonomic neuronal fibers
9) action potentials are longer in duration than both smooth and skeletal muscle