muscle tissue 2
DESCRIPTION
Muscle physiology, mechanism of muscle contraction.TRANSCRIPT
Muscle Tissue 2
Nerve impulse (action potential)Motor units
Neuromuscular junctionsPhysiology of Muscle contraction (sliding filament theory)
Nerve impulseNecessary for muscle contractionAlso known as action potential
Momentary change in electrical potential due to rapid changes in ion concentration
Motor neuronNeuron with cell body located in the brain or spinal cordEnds at neuromuscular junction / synaptic end bulb
Motor unitThe functional unit of a skeletal muscle Consists of a motor neuron and the muscle fibers it stimulatesmuscles with large ratio motor units (1 neuron: many muscle fibers) provide powerful contractions but cannot provide delicate control muscles with small ratio motor units (1 neuron: few muscle fibers) provide delicate control for very precise movements
Resting potentialIon pumps actively maintain concentration gradients[Na + ] much higher outside cell[K + ] much higher inside cell3 Na + transported out for every 2 K + transported inResults in net – 70 mV charge inside nerve cell; cell is polarized
Action potentialNerve impulseNa + channels open, Na + rush in to nerve axonInternal cell environment no longer polarizedK + channels open; K + rush out of nerveRepolarizes cellProcess travels down length of cell axon
Neuromuscular junctionMeeting point at which motor neuron meets muscle fiber
SynapseRegion of communication between two neurons or a neuron and a target cell
NeurotransmitterChemical that crosses synaptic cleft (gap) allowing for communication between two cells
Acetylcholine (ACh) is the neurotransmitter released from synaptic end bulb of motor neurons
Nerve impulse initiates contractionNerve impulse arrives at NMJ
Acetylcholine (Ach) released via exocytosis across synaptic cleft
ACh stimulates Na + / K+ ion channels to open, muscle cell depolarizes
Depolarization of sarcolemma causes Ca2+ release
Ca2+ allows myosin / actin crossbridge and ultimately, sarcomere shortening
Key players of muscle contractionMyosin
~300 molecules comprise each thick filamentImagine two golf club twisted together
ActinThin filament molecules extending from anchoring points in the Z disc
TitinExtends from Z disc to M lineOne of largest molecules known to exist; molar mass = 3million grams
Key players of muscle contractionTropomyosin
Part of thin filament; blocks sites where actin / myosin bind
TroponinHolds tropomyosin in position. When Ca2+ is present, troponin changes shape (conformational change)Linked to tropomyosin, actin/mysoin binding site is uncovered when Ca2+ is present in sarcoplasm.
MyomesinForms M line of sarcomere
Sarcomere regionsZ line (disc)
Lateral terminus of sarcomere; separate adjacent sarcomeres
A bandRegion where thick filaments present; darker appearancesome overlap of thin filament in relaxed sarcomeremore overlap of thin filament in contracted sarcomere
Sarcomere regionsI band
Region where thin filaments (no thick filaments) are presentLighter in appearanceNarrowed in contracted sarcomere
H zoneCenter of A band, thick filaments onlyDisappears during sarcomere contraction
M lineCentral to sarcomere, myomesin proteins anchor myosin and titin proteins