Muscle Mechanics Video

What are the three types of muscles in the human body?

• smooth muscle

• skeletal muscle

• cardiac muscle

_____ is the most abundant tissue in the body.

Skeletal muscle

There are approximately ____ skeletal muscles in the body, ____ of which are prime movers.

430; 80

The functions of skeletal muscle include:

• facilitate movement

• protect the structures that are under them

• give our bodies structure

There is constant _____ activity of our muscles.

static and dynamic

Different structural appearance of muscles correlate to their…

different functions and roles

Organization of skeletal muscle from inner —> out

• muscle

• fascicle

• muscle fiber (cell)

• myofibril

• sarcomere

What is muscle composed of?

muscle cells, blood vessels, and nerves

Muscle is covered by ______.

epimysium (a type of connective tissue)

What is the fascicle composed of?

bundles of muscle cells

The fascicle is surrounded by the _____.

perimysium

What are muscle fibers surrounded by?

endomysium

What is a myofibril?

a complex organelle

Sarcomere

the basic contractile unit of muscle

Filaments

protein strands important during muscle contraction

The structure of muscle correlate to its ____.

function and ability

What is a triad made up of?

a T-tubule and two terminal cisternae (of the sarcoplasmic reticulum)

The sarcoplasmic reticulum is critically important to delivering calcium to…

the muscle fibers during contraction.

The primary excitatory neurotransmitter in the musculoskeletal system is ___.

acetylcholine

Titant molecule

• the span of connection between the actin and myosin filaments in a sarcomere

• think of it as the superglue that holds the thick and thin filaments together

Sliding Filament Theory

explains muscle contraction as the actin (thin) filaments sliding past myosin (thick) filaments, shortening the sarcomere

Sliding Filament Theory Steps

1. An action potential triggers the release of calcium

2. calcium binds to troponin

3. Tropomyosin moves off the binding sites on actin so myosin can bind

4. myosin heads pull the actin filaments inward

5. ATP binds to myosin, causing detachment

6. ATP —> ADP + P to allow the myosin heads to reset for another cycle

What occurs during the resting phase of the sliding filament theory?

• little to no calcium is in the myofibril

• no tension occurs

• there are few cross bridges

What occurs during the excitation-contraction phase of the sliding filament theory?

• the sarcomere is stimulated by calcium release

• calcium binds to troponin

• this causes tropomyosin to move off the active sites in actin

• myosin binds to actin and cross bridges form

What occurs during the contraction phase of the sliding filament theory?

• ATP binds to myosin

• ATP —> ADP + P

What occurs during the recharge phase of the sliding filament theory?

• ATP is restored

• calcium is replenished

• Myosin ATPase is ready

What occurs during the relaxation phase of the sliding filament theory?

• motor nerve stimulation stops

• calcium refills in the sarcoplasmic reticulum

• no cross bridges form

A single stimulus leads to a ____.

muscle twitch

There are three parts of a muscle twitch. What are they?

1. latent period

2. contraction period

3. relaxation period

What is going on in parts a-d of this picture?

a. Single twitch: a normal action potential occurs

b. Wave summation: a second action potential is generated near the end of the first, leading to increased force and time of contraction

c. Unfused tetanus: more consecutive action potentials are generated, leading to more force and increased time of contraction

d. Fused tetanus: a smooth even contraction occurs due to rapid generation of multiple action potentials, leading to a plateau force that eventually declines

_____ is the normal muscle function.

Fused tetanus

What are the takeaways from the length-tension relationship?

• max tension occurs at 100% sarcomere length, meaning that the optimal position for muscle to generate force is from resting length or just beyond

• At 75% sarcomere length: the cross bridges are formed and the muscle is in too short of a position to generate optimal force

• At 170% sarcomere length: no cross bridges are formed and the muscle is too long to generate forces

____ length maximizes the ability of muscle to contract when stimulated.

Resting

Max tension is generated at muscle ____

resting length

Beyond resting length, ____ components rise and ____ components fall.

passive; active

Active Tension

allows for the greatest number of cross bridges to form and greatest potential of active force