Skeletal Muscle: Electromyography Lab Flashcards
Skeletal muscle is ensheathed in a tough connective tissue called___________
epimysium
fascicles
bundles of muscle fibers
Each muscle is made up of many ________ that are ensheathed in a connect _______ _________.
fascicles, tissue perimysium
what does connect tissue perimysium do?
allow for passage for vasculature and nerves
what does each fascicle consist of?
many muscle fibers that are ensheathed by connective tissue endomysium.
what does connective tissue at each level help with?
To distribute force, resist tensile force and maintain shape of muscle
Each skeletal muscle fiber is a __________ _________ surrounded by ___________ which contains __________ and many myofibrils.
multi nucleated syncytium, sarcolemma, sarcoplasm
multi nucleated syncytium
fusion of multiple cells
sarcolemma
plasma membrane
sarcoplasm
cytoplasm
myofibril
chain of sarcomeres
What is the function unit of contraction?
sarcomere
why are skeletal muscle fibers considered striated?
because of the striped appearance of sarcomeres under the microscope
what causes the striped appearance under the microscope when looking at a muscle fiber?
the highly organized alternating pattern of A bands and I bands
what are A bands and I bands produced by?
actin and myosin myofilaments
Z-line (disc)
sarcomere boundary
A-band
region of myosin with some actin overlap
I-band
region of only actin
H-zone
region of only myosin
Skeletal muscle is under _________ control and is innervated by _______ _______.
voluntary, motor neurons
neuromuscular junction
chemical synapse between motor neuron and a muscle fiber
what does Acetylcholine released from the motor neuron do?
it diffuses across the synaptic cleft and binds to nicotinic acetylcholine receptors
After acetylcholine binds to nicotinic acetylcholine receptors, what happens next?
This binding brings out end-plate potentials which triggers action potentials in the muscle fiber
what does action potentials in the muscle fibers cause?
causes the release of Ca2+ from the sarcoplasmic reticulum (storage site) which allows myosin to bind with actin
forming a cross-bridge.
list the steps of action potentials in muscle fibers
- release of Ca2+ from the sarcoplasmic reticulum which allows myosin to bind with actin forming a cross-bridge.
- Myosin then pulls actin towards the center of the sarcomere.
- The sliding of actin over myosin causes each sarcomere to shorten
- This occurs simultaneously in all the sarcomeres of a muscle fiber and generates a muscle contraction.
sliding filament theory of contraction
The sliding of actin over myosin to generate force
During contraction, the sliding of actin over the myosin causing the I band, H zone, and ultimately the entire sarcomere to?
shorten, whereas the A band remain the same length.
T/F: Although the axon of the motor neuron branches multiple times (as collateral branches) to innervate multiple muscle fibers, each muscle fiber in a muscle is innervated by one, and only one, motor neuron.
TRUE
Motor unit
A motor neuron and all the muscle fibers it innervates
The number of muscle fibers controlled by a single motor neuron can vary from?
5 to more than 500
what is an example of a motor neuron that uses 5 muscles fibers?
fine motor control of muscles of the fingers
what is an example of a motor neuron that uses 500 muscles fibers?
gross control of the quadriceps
T/F: Groups of motor units work together to coordinate
the contraction of a single muscle.
true
motor pool
All the motor units of a specific muscle.
The degree of contraction (and the force generated) is mediated by the central nervous system via 2 mechanisms, what are they?
- Multiple motor unit summation (= recruitment)
- Temporal summation (= wave summation)
Multiple motor unit summation (= recruitment)
increasing the contractile force of a muscle by increasing the number of motor units within a muscle.
Temporal summation (= wave summation)
increasing the contractile force of a muscle by increasing action potential frequency of individual motor units
The strength of a muscle contraction is proportional to?
The load placed on the muscle.
When an increase in strength is required to perform a task, the force of muscle contraction can be increased by?
- increasing the number of motor units being activated
- increasing the stimulation of those active motor units
T/F: During rest, muscle is in a constant state of slight tension (tonus) that serves to maintain the muscle is a state of readiness.
True
tonus
state of slight tension
what is tonus produced by?
produced by alternate periodic activation of a small number of motor units via innervation of CNS motor neurons
T/F: The propagation of action potentials by motor neurons and muscle fibers during contraction generates voltage differences (mV) in the overlying skin that can be
detected through surface electromyography.
TRUE
what can electromyography be used for?
used to examine the electrical activity of muscle during varying degrees of contraction
What is the subsequent recording of an electromyography known as?
electromyogram (EMG)
