Muscle Tissue II: Lecture 16 Flashcards
action potential
quick, local, temporary change in membrane potential generated by opening and closing of gated Na+ and K+ channels in plasma membrane in response to stimulus
resting membrane potential
muscle
-85 mV
- resting phase
gated channels are closed Na+ and K+ gradients maintained by sodium/potassium pumps and potassium leak channels
- depolarization phase
Na+ channels open in response to a depolarizing stimulus
Na+ enters the cell down its gradient and further depolarizes the membrane
- repolarization phase
Na+ channels close, K+ channels open, K+ exits down its gradient and repolarizes the membrane
innervation
motor neurons stimulate skeletal muscle to contract; all skeletal muscle fibers are innervated
synapse
muscle
connection between a single motor neuron and many muscle fibers
neuromuscular junction (NMJ)
synapse that transmits signals (nerve impulse/action potential) from neuron to sarcolemma of muscle fiber
components of NMJ
axon terminal, neurotransmitters, synaptic cleft
axon terminal
contains synaptic vesicles filled with neurotransmitter acetylcholine (ACh)
neurotransmitters
chemicals trigger changes in a target tissue; allow for cell to cell communication
synaptic cleft
space between axon terminal and muscle fiber; filled with collagen fibers and gel that anchors neuron in place
motor end plate
specialized region of muscle fiber plasma membrane; folded surface has many ligand-gated Na+ channels
ACh is ligand that opens gates, allowing Na+ to diffuse into muscle cell
phases of muscle contraction
excitation, excitation contraction coupling, prep for contraction, contraction, relaxation
excitation phase
ACh triggers an end-plate potential in the motor end-plate
excitation/contraction coupling phase
resulting action potential in the sarcoplasma travels down the t-tubules and triggers Ca+ ions to release from the SR to the cytosol
preparation for contraction
calcium binds to troponin which moves the tropomyosin away from the active site of actin
contraction phase
actin and myosin bind, ATP detaches actin and myosin; cycle repeats leading to muscle contraction
muscle relaxation
neurons stop releasing ACh, contraction of calcium returns to normal ranges, resting stage; active sites of actin are blocked and fiber relaxes
energy sources
immediate sources, anaerobic glucose catabolism, aerobic glucose catabolism
immediate sources
creatine phosphate (CP) -10s
anaerobic glucose catabolism
glycolysis -1m
aerobic glucose catabolism
Krebs cycle
