Functional Neuro-muscular Units

Question 1

What is the functional organization of muscle?

Answer 1

1. Skeletal muscle (surrounded by epimysium) contains muscle fascicles
2. Muscle fascicles (surrounded by permysium) contains muscle fibers
3. Muscle fiber (surrounded by endomysium) contains myofibrils
4. Myofibril (surrounded by sarcoplasmic reticulum) consists of sarcomeres
5. Sarcomeres contain thick & thin filaments

Question 2

What is a neuromuscular junction? What are its 5 components?

Answer 2

Site where axon & muscle fiber communicate.

1. motor neuron
2. motor end plate
3. synaptic cleft
4. synaptic vesicles
5. neurotransmitters

Question 3

How does muscle contraction take place at a neuromuscular junction?

Answer 3

Motor nerve impulses cause release of acetylcholine (ACh) from synaptic vesicles which bind to receptors on the motor end plate and generate muscle contraction

Question 4

How does muscle relaxation take place at a neuromuscular junction?

Answer 4

Acetylcholinesterase breaks down ACh, motor neuron impulses stop, Ca moves back into sarcoplasmic reticulum, Myosin & actin binding prevented

Question 5

What is a motor unit?

Answer 5

1. Single motor neuron & all the muscle fibers it controls
2. Functional connection btwn the nervous system & the muscular system
3. when motor unit fires, all the muscle fibers contract together
4. 1 muscle fiber may act w/several motor units depending upon demand

Question 6

True/False. 1 neuron may innervate several muscle fibers; 1 muscle fiber may be innervated by several motor neurons

Answer 6

TRUE!

This creates both large/small motor units for strength/fine control respectively

Question 7

What is a twitch?

Answer 7

single brief stimulus to a muscle that produces a quick cycle of contraction & relaxation lasting less than 1/10 second (1 = not enough to do work), 3 phases - latent/contraction/relaxation, occurs w/ low frequency stimuli, each phase produces identical twitch response

Question 8

What is treppe?

Answer 8

relaxation = complete before next stimulus occurs, each contraction is a little stronger than previous, gradually increased contraction intensity during sequential stimulation, occurs w/moderate freq. stimulation (10-20 /sec), each contraction is stronger than the previous until after a few where they equal out

Question 9

What is wave summation?

Answer 9

if second stimulus is applied before relaxation is complete, 2nd contraction = greater

Question 10

What is tetanus?

Answer 10

higher frequency of stimulation, muscle relaxation btwn contractions is reduced

Question 11

What is incomplete tetanus?

Answer 11

produces peak tension during rapidly alternating cycles of contraction & partial relaxation

Question 12

What is complete tetanus?

Answer 12

sustained maximal contraction at peak tension, typical of normal muscle contraction