Lab Exam 3

resting membrane potential

-70mV

motor unit

A motor neuron and all of the muscle fibers it innervates

voltage gated potassium channels

Allow K+ to flow out of the cell, moving the potential back towards the negative equilibrium potential of potassium.

amplitude

For a wave or vibration, the maximum displacement on either side of the equilibrium (midpoint) position.

how increasing the stimulus voltage affects muscle contraction.

Increasing the stimulus voltage on isolated skeletal muscle increases the amount of active force produced by the muscle

how muscle fiber length affects the contraction force of a motor unit

Isotonic contractions generate force by changing the length of the muscle and can be concentric contractions or eccentric contractions. A concentric contraction causes muscles to shorten, thereby generating force. Eccentric contractions cause muscles to elongate in response to a greater opposing force.

recruitment

Motor unit recruitment is a measure of how many motor neurons are activated in a particular muscle, and therefore is a measure of how many muscle fibers of that muscle are activated. The higher the recruitment the stronger the muscle contraction will be.

isometric contraction

Muscle contracts but there is no movement, muscle stays the same length

how skeletal muscles increase the force of contraction

Muscles exist in this state to optimize the force produced during contraction, which is modulated by the interlaced myofilaments of the sarcomere. When a sarcomere contracts, myosin heads attach to actin to form cross-bridges. Then, the thin filaments slide over the thick filaments as the heads pull the actin.

how recruitment of motor units occurs during isometric contraction.

Starting with the smallest motor units, progressively larger units are recruited with increasing strength of muscle contraction. The result is an orderly addition of sequentially larger and stronger motor units resulting in a smooth increase in muscle strength.

the minimal voltage required to stimulate a motor unit

The minimal voltage that induces an action potential is called the threshold stimulus

how stimulation frequency affects the contraction force of a motor unit

With increasing stimulation frequency, summation of force can be observed, resulting in a steep rise in the FFR (Fig. ... Studies often quantify differences in the FFR by reporting the frequency needed to produce a set percentage of maximum force (e.g., the frequency required to produce 50% of maximum force).

electromyography

a diagnostic test that measures the electrical activity within muscle fibers in response to nerve stimulation

action potential

a neural impulse; a brief electrical charge that travels down an axon

where graded potentials trigger the generation of action potentials.

dendrites

myograph

instrument used to record muscular contractions

voltage gated sodium channels

membrane proteins that open sodium channels in response to a sufficient voltage change, and initiate and transmit the action potential as Na+ enters through the channel

eccentric isotonic contractions

muscle generates force as it lengthens

concentric

muscle shortens

isotonic contraction

muscle shortens because muscle tension exceeds load

graded potential

shift in electrical charge in a tiny area of the neuron (temporary);

twitch contraction

the brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron

muscle tone

the state of balanced muscle tension that makes normal posture, coordination, and movement possible

refractory period

the time following an action potential during which a new action potential cannot be initiated

wave summation

this occurs when a second stimulus is received before the muscle fiber has relaxed, creating a second contraction that is stronger than the first