Ch 11: The motor unit

Question 1

Wonder on can stimulate how many muscle cells?

Answer 1

Multiple

Question 2

Without nerve stimulation, what happens to skeletal muscle contraction?

Answer 2

No contraction, hypertrophy of muscle

Question 3

A whole muscle is innervated by how many motor units?

Answer 3

Large muscle has two or more dispersed throughout muscle

Question 4

How many Muscle fibers contained in an average motor unit?

Answer 4

200

Question 5

Small motor units are Weaker but good for:

Answer 5

Fine degree of control

Question 6

Large motor units are good for:

Answer 6

Strength and powerful contractions

Question 7

Neuromuscular junction

Answer 7

Interaction between motor neuron and skeletal muscle at the synapse between axon terminal and sarcolemma

Question 8

What neurotransmitter is released into the neuromuscular junction?

Answer 8

Acetyl choline

Question 9

Which receptors On the sarcolemma Accept acetylcholine?

Answer 9

Cholinergic receptors

Question 10

What happens after acetyl choline binds to cholinergic receptors on the sarcolemma?

Answer 10

Cholinergic receptors cause excitation in local potential and sarcolemma and an action potential fires which stimulates the Myofilaments to make a contraction

Question 11

Enzyme that stops muscle contraction

Answer 11

Acetylcholinesterase (AChE)

Question 12

Motor end plate

Answer 12

We are axon terminal is in direct contact with a sarcolemma

Question 13

Electrochemical gradient causes what because why?

Answer 13

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

Question 14

Resting membrane potential of a muscle cell

Answer 14

-90mV

Question 15

Phases of stimulation of a skeletal muscle

Answer 15

1. Excitation
2. Excitation – contraction coupling
3. Contraction
   4. Relaxation

Question 16

What happens during the excitation phase of muscle stimulation?

Answer 16

1. Action potential arives. Ca^2+ channels open.
2. ACh released into synapse
3. ACh binds to Cholinergic receptors on satcolemma
4. Ligand gated channels open; starts depolarization.
5. 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

Question 17

 phase 2 of muscle stimulation: excitation – contraction coupling

Answer 17

1. Movement of action potentials down T tubules
2. Release of calcium from SR at terminal cisterns
3. Activation of myofilaments

Question 18

 Interaction between two tubules and Sarco plasmic reticulum in excitation – contraction coupling 

Answer 18

1. DPH is protein voltage sensor that helps (acts as key to open)
2. Ryanodine Receptor to open and cause Ca^2+ to flood into cytosol and bind to troponin to get tropomyosin off actin’s active sites

Question 19

3rd phase of muscle stimulation in skeletal muscles

Answer 19

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

Question 20

Stage four of muscle stimulation in a skeletal muscle

Answer 20

Relaxation:
-Nerve stimulation ends
-ACh Breaks down by AChE
-Calsequestrin gathers Ca^2+ And reabsorbs back into SR

Question 21

What happens to muscle contractions in skeletal muscle without calcium and ATP?

Answer 21

Nothing! No contraction

Question 22

What does nerve gas inhibit and what effect does it have?

Answer 22

Blocks neuromuscular transmission by inhibiting acetylcholinesterase.
Causes skeletal muscle paralysis and death from asphyxiation


Question 23

What does botulism toxin block and what are the effects?

Answer 23

Blocks the release of acetylcholine from Axon terminals, so no muscle stimulation.
Can cause paralysis

Question 24

Medical application of botulinum toxin

Answer 24

Helps lazy Eye
Stops excessive sweat glands
Treats migraines
Treats wrinkles