Motor Unit
A motor neuron and all of the muscle fibers it innervates
Motor Neurons
Skeletal muscle fibers are inntervated (stimulated) by
Neuromuscular junction
motor neuron and muscle fiber intersect
Motor end plate
Region of the sarcolemma of a muscle fiber that includes acetylcholine receptors which bind ACh released by synaptic end bulbs of somatic neurons
End plate potential (EPP)
the graded depolarization in the skeletal muscle fiber that is elicited in response to one action potential from the motor neuron
Sarcolemma
Cell membrane of a muscle cell
Excitation Contraction coupling
Includes all the events associated with muscle contraction from action potential through the cross bridge cycle
Muscle Twitch
one contractile response to a single action potential
Latent period
the cellular events involved in excitation-contraction coupling occur. the time between stimulation and the onset of contraction; cross bridges cycle and when muscle tension exceeds the load, muscle shortening occrs
Contraction phase
skeletal muscle twitch phase; the time between the end of the latent period and the peak muscle tension
Relaxation phase
diastole
Tendons
Skeletal muscles are connected to the bones by
Fibers
Skeletal muscles are composed of hundreds to thousands of individual cells
Aceytlycholine
an action potential in a motor neuron triggers the release in which neurotransmitter
Force transducer
-used to measure isometric contraction
Electrical stimulation
Sending a weak electric current into the muscle to activate it
Single Action Potential
Single action potential and a single contractile event in the muscle fiber it innervates
Calcium
stored in sarcoplasmic reticulum
Threshold Voltage
minimal stimulus needed to cause depolarization of the muscle plasma membrane (sarcolemma)
Motor unit recruitment
an increase in the number of active muscle fibers to increase the force developed in a muscle
Active tension or (force)
determined by the amount of myosin bound to actin; in a skeletal muscle fiber results from activation of cross bridge cycling via increased intercellular calcium levels
Maximal Voltage
all the muscle fibers contained in the muscle are depolarized and they develop active force (that is that they are were successfully recruited)
During a single twitch of a skeletal muscle
maximal force is never achieved
Wave summation
when muscle fibers are repetitively stimulated twitches can overlap each other and result in a stronger muscle contraction than a stand alone twitch; muscle fibers are stimulated again before fibers have relaxed; achieved by increasing the muscle frequenc
Stimulus Intensity
increase in the force of a stimulus (e.g. increased voltage)
Stimulus Frequency
Rate of stimulating voltage delivery to the muscle
Unfused Tetanus
Stimuli continues to apply more frequently it will eventually reach a plateau; muscle tension increases and decreases; reached at about 80 sec (int he lab)
Fused (complete) Tetanus
when the greater frequency is applied the peaks and valleys of each twitch become indistinguishable
Maximal tetanic tension
stimulus frequency reaches a value beyond which no further increases in force are generated by the muscle
Tetanus
sustained muscle tension due to very frequent stimuli;
Fatigue
the failure of a muscle fiber to produce tension b/c of previous contractile activity;
decline in a skeletal muscles ability to maintain a constant level of force or tension after prolonged repetitive stimulation
Isometric Force
the skeletal muscle is generating force but stays at a fixed length
Passive Force
the force that results from muscles being stretched; largely caused by the protein titin
Isotonic Contraction
the force generated is greater than the weight of the attached load; increases with heavier loads; length of the muscle changes
Load
when a muscle attempts to move an object that is equal in weight to the force generated by the muscle
Shortening Velocity
speed of the contraction, heavier loads, slower muscle twitch; decreases with heavier loads
Load Velocity relationship
the heavier the load, the slower the velocity