Ch 11: The motor unit Flashcards
Wonder on can stimulate how many muscle cells?
Multiple
Without nerve stimulation, what happens to skeletal muscle contraction?
No contraction, hypertrophy of muscle
A whole muscle is innervated by how many motor units?
Large muscle has two or more dispersed throughout muscle
How many Muscle fibers contained in an average motor unit?
200
Small motor units are Weaker but good for:
Fine degree of control
Large motor units are good for:
Strength and powerful contractions
Neuromuscular junction
Interaction between motor neuron and skeletal muscle at the synapse between axon terminal and sarcolemma
What neurotransmitter is released into the neuromuscular junction?
Acetyl choline
Which receptors On the sarcolemma Accept acetylcholine?
Cholinergic receptors
What happens after acetyl choline binds to cholinergic receptors on the sarcolemma?
Cholinergic receptors cause excitation in local potential and sarcolemma and an action potential fires which stimulates the Myofilaments to make a contraction
Enzyme that stops muscle contraction
Acetylcholinesterase (AChE)
Motor end plate
We are axon terminal is in direct contact with a sarcolemma
Electrochemical gradient causes what because why?
Depolarization due to changes in the electrochemical gradient based on membrane potential on inside versus outside of cell.
Stimulation = Opening of channels that allow ions to move down there electrochemical concentration gradient from high to low
Resting membrane potential of a muscle cell
-90mV
Phases of stimulation of a skeletal muscle
- Excitation
- Excitation – contraction coupling
- Contraction
4. Relaxation
What happens during the excitation phase of muscle stimulation?
- Action potential arives. Ca^2+ channels open.
- ACh released into synapse
- ACh binds to Cholinergic receptors on satcolemma
- Ligand gated channels open; starts depolarization.
- Open VG ion channels;
-threshold: -55mV
-VG Na+ channel open (Na+ enter)
-rapid depolarization
- +35 mV closes VG Na+ and opens
VGK+ (K+ leave)
- repolarization
- hyperpolarization
 phase 2 of muscle stimulation: excitation – contraction coupling
- Movement of action potentials down T tubules
- Release of calcium from SR at terminal cisterns
- Activation of myofilaments
 Interaction between two tubules and Sarco plasmic reticulum in excitation – contraction coupling 
- DPH is protein voltage sensor that helps (acts as key to open)
- Ryanodine Receptor to open and cause Ca^2+ to flood into cytosol and bind to troponin to get tropomyosin off actin’s active sites
3rd phase of muscle stimulation in skeletal muscles
Contraction: Sliding filament theory.
Actin gets pulled by myosin heads closer to M line so sarcomeres shorten. Pi then ADP released from myosin head to cock. ATP attaches and head moves back
Stage four of muscle stimulation in a skeletal muscle
Relaxation:
-Nerve stimulation ends
-ACh Breaks down by AChE
-Calsequestrin gathers Ca^2+ And reabsorbs back into SR
What happens to muscle contractions in skeletal muscle without calcium and ATP?
Nothing! No contraction
What does nerve gas inhibit and what effect does it have?
Blocks neuromuscular transmission by inhibiting acetylcholinesterase.
Causes skeletal muscle paralysis and death from asphyxiation

What does botulism toxin block and what are the effects?
Blocks the release of acetylcholine from Axon terminals, so no muscle stimulation.
Can cause paralysis
Medical application of botulinum toxin
Helps lazy Eye
Stops excessive sweat glands
Treats migraines
Treats wrinkles
