Motor Units Flashcards
(32 cards)
In what order do parts of the neuron receive signals from other cells?
- Dendrites
- Body
- Axon
- Axon terminals
What is the point of connection between muscle cells and terminal branches called?
Neuromuscular junction (NMJ)
What is the purpose of the myelin sheath coating the axon?
- Prevents signals from moving backwards up the axon
- Speed up signal transmission
What neurotransmitter is released by the neuron into the neuromuscular junction?
Acetylcholine (ACh)
What is the term for the outer membrane of a muscle cell?
Sarcolemma
What does acetylcholine do when it’s released and reaches the sarcolemma?
It depolarizes it
What is the depolarization of the sarcolemma called?
An action potential
Where does an action potential travel into in the muscle cell?
Into the transverse (T) tubules
What happens when an action potential enters the T-tubules?
It reaches the sarcoplasmic reticulum and causes calcium to be released into the cell
What does calcium do when it’s released by the sarcoplasmic reticulum into the cell?
It binds troponin on actin filaments
What does troponin do when calcium binds to it?
It pushes tropomyosin out of the way
What does tropomysosin move to reveal on the actin filament?
The active sites
What binds to active sites?
Myosin heads
What happens when the myosin heads attach to the actin active sites?
A cross bridge connection is formed and ATPase is activated, which causes a release of energy and a resulting muscle tension
What is the difference between concentric and eccentric contractions on the cellular level?
Concentric contractions move with a ratcheting motion, whereas eccentric have a pull and catch motion
What is the unit between two Z disks called?
A sarcomere
What happens when the Z disks of a sarcomere get close enough to butt against each other?
The muscle has reached full contraction and cannot pull more (e.g. when a person’s muscles lock out at the top of a bench press)
What is a nerve and the muscle fibers it innervates called?
A motor unit
How many muscle fibers can one neuron innervate?
Several hundred up to a thousand
What are the characteristics of Type 1 or slow twitch muscle fibers? (4)
- More aerobic and more O2
- Lighter color
- Longer lasting
- Less fibers/smaller motor unit
What are the characteristics of Type II or fast twitch muscle fibers?
- Anaerobic and less O2
- Darker color (from red blood cells)
- Bigger, stronger
- More fibers/larger motor units
What 4 things contribute to hypertrophy on a cellular level?
- More protein structure (actin, myosin, and sarcomeres)
- Increase in carbohydrate/glycogen stores in muscles
- More fluid sarcoplasm
- More H+, pyruvate, and lactate stimulate muscles to be bigger to fit more byproducts
What 4 things contribute to strength increases on the cellular level?
- Increase in muscle size
- Increase in surface area of the axon terminal (more ACh = more motor units fired)
- Synchronization of motor units
- Increase in the theshold of the Golgi tendon organ
What is the Golgi tendon organ?
A sensory receptors that detects when an intensity is too strong and relaxes the muscles to prevent injury
