Exercise 2: Lab activity 1-7

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