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Action potential

Electrical current conducted along the membrane of a nerve or muscle cell

Excitation-contraction coupling

The series of events linking the electrical signal to muscle contraction

Neuromuscular junction

Region where the motor neuron comes into close contact with the muscle cell

Synaptic cleft

Extracellular space between the neuron terminal and the muscle cell membrane (sarcolemma)

Synaptic vesicles

Small membranous sacs containing a neurotransmitter


Neurotransmitter released at the neuromuscular junction


Loss of negative charge inside the cell

Refractory period

The period during repolarizaton when the cell is insensitive to further stimulation

All-or-none response

An action potential, once initiated, ultimately results in full contraction of the muscle cell

Acetyl cholinesterase

An enzyme located on the sarcolemma in the neuromuscular junction which degrades acetylcholine

Motor unit

lower motor neuron that comes from the spinal cord and muscle fibers it stimulates. They can be small or large.


The smallest functional unit of muscle tissue.

Muscle Fiber

One single muscle tissue cell. Has its own components that make a cell.


Bundle of muscle fibers. Several thousands in a muscle

Sliding Filament Theory

Thin filaments slide over thick filaments


the protein that is pulled toward the center of the sarcomere by the myosin during contraction


Energy in the form of what is needed to contract or release a muscle

Thick filament

contains myosin heads that stick out in six different directions to pull thin filaments.

Thin filament

Contains Actin, Tropomyosin, Troponin

Neuromuscular junction

the point at which the motor neuron and muscle connect

Central nervous system

All skeletal muscles are connected with a motor neuron from where?

excitation-contraction coupling

molecular events of a muscle contraction

Step 1a - active site exposure

impulse from CNS, ACh released, diffuses across cleft, stimulates fiber/cell

Step 1b

impulse travels across sarcolemma in all directions, into SR via T-tubules

Step 1c This movement exposes the binding site actin

Ca+2 diffuses out of sarcoplasmic reticulum, binds to troponin, alters its shape and position of tropomyosin

Step 2 Cross bridge attachment

myosin binds to actin binding sites

Step 3 "ratchetting"

"power stroke" myosin cross brindge bends, pulling thin filaments toward center of sarcomere + contraction/muscle fibers shorten

Step 4 Cross-bridge detachment

ATP binds myosin, which breaks the linkage to actin

Step 5a Myosin reactivation

ATPase (enzyme in myosin) breaks down ATP, energy is released (catabolism), myosin uses energy to straighten its cross-bridge

Step 5b

Myosin cross-bridge can now combine with another binding site further down the actin filament and pull again

muscle relaxation

No more ACh = no stiumlation to sarcolemma = SR pumps Ca+2 back inside = no Ca+2 meansactin binding sites are covered

Sarcoplasmic reticulum

storage of Ca+2


breaking the linkage between actin & myosin requires what?


reposition/re-energize the myosin head (cross bridge) requires what?


Pumping Ca+2 back into the sarcoplasmic reticulum requires what?

Rigor mortis

Ca+2 floods ICF from sarcoplasmic reticulum AND extracellular fluid, actin & myosin are binding but no ATP to break the myosin/actin bond

Creatine Phosphate

a quick way to get more ATP, used to convert ADP to ATP. provide ATP before aerobic metabolism only last 15 sec

Aerobic respiration

Yields high amounts of ATP during resting to moderate activity

Tropomyosin & troponin

proteins attached to actin that help control the myosin-actin interactions involved in muscle contraction

converted into lactic acid

What happens to pyruvic acid when there is a lack of oxygen in the muscle?


causes parlysis of the muscle "botox"

functons of skeletal muscle

maintains posture and moves the body

somatic nervous system

controls muscular system

Frontal lobe

What lobe initiates voluntary movement?


cell membrane


polypeptide strands that wrap around the actin to help stabilize it


protein which has active sites for the myosin heads.

Elastic filament

composed of the protein titin. Extends from the z disk to the thin filament and runs with it to attach to the m line

Z discs

anchor the thin filaments.


smooth ER that surround each myofibril. Mitochondria and glycogen granules produce energy during contraction

thin filament

positioned on either side of the sarcomere and are pulled toward the center of the sarcomere during contraction

Transverse tubules

increase surface area


stimulates the release of Ca2+ when it moves across

Small motor units

give fine motor control. 1:10

Large motor units

give gross movements. 1:500


excitation contraction coupling AP-T tubules CA++ release---binding---troponin


myosin heads in crossbridge cycle


CA++ transported back to the SR

warm up effect

Single cell- can experience treppe effect where subsequent twitches can generate more force


run out of synaptic vesicles ACH lactic acid build up.

Recruitment of motor unit

Whole muscle you have many motor units with different thresholds. Recruit more motor units for stronger whole muscle contraction.


high frequency of stimulus---fused twitches---sustained contraction

Crossbridge cycle

myosin heads of thick filaments bind and pull the thin filaments

Crossbridge step 1

1. Energized thick filament (give ATP and phosphorus.) Myosin heads in a cocked back position.

Crossbridge step 2 stimulus

2. Stimulus- causes binding sites on actin to be uncovered. Myosin heads bind to actin binding site.

Crossbridge step 3 powerstroke

"ratchetting" of myosin heads---thin filaments are pulled torward the center of the sarcomere. During the powerstroke the ADP & phosphorus leave the myosin head.

Crossbridge step 4

4. Myosin head detaches from the actin thin filament . This occurs when ATP binds to the myosin head.

Crossbridge step 5

5. ATP is hydrolyzed to ADP and inorganic phosphate to energize the myosin head and cock it back again.

Isotonic contraction

"same-length" muscle generates the same force through whole muscle during contraction.

Energy for contraction

ATP- not stored . It is made as it is needed by burning fuel.

ATP supply

1. aerobic- less efficient without 02 (can do for hours) by using glycolysis, Krebs, ETC

ATP supply

2. anaerobic with out oxygen. High intensity, few min, less efficient

Intero sensory receptor

detect muscle stretch and contraction (shortening) Protects from overstretching


larger diameter, pailer color (less 02 carrier mypglobin,) faster contracting, less mitochondria, more anaerobic metabolism, can generate more power. Power lifting fatigues fast.

Slow twitch

darker= myoglobin that carries the 02 to mitochondria for aerobic metabolism. High endurance but fairly low power.

Stretch- thin elements of the muscle


Stretch- thin elements of the muscle

endomysium CT around the fiber

Stretch- thin elements of the muscle

perimysium- around fasicles

Stretch- thin elements of the muscle

epimysium around the whole muscle

Stretch- thin elements of the muscle



proteins inside the myofibril

when does crossbridge formation occur?

When myosin heads bind to actin molecules located on the thin filaments.

The series-elastic component of a muscle must

bind muscle fibers together at the neuromuscular junction,

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