SKELETAL MUSCLE NOTES

Terms

• epi = upon

• peri = around

• endo = within or inner

• mys = muscle

• sarco = flesh

• lemma = husk

• fasci = bundle

Structure of skeletal muscle fiber

A sarcomere

Twizzler analogy

Many packages of Twizzlers =

Fascicle

Twizzler analogy 2

1 package of

Twizzlers =

Muscle fiber

The packaging =

Sarcolemma

Twizzler analogy 3

1 bundle of twizzlers =

myofibril

Twizzler analogy 4

1 Twizzler strand =

Filament

Terms associated with skeletal muscles

• Tendon- Attaches muscle to bone

• Ligament- Attaches bone to bone

• Origin- The location where the muscle is attached to the relatively immovable end of the bone

Insertion- end of the muscle that is attached to the movable bone

• Prime mover- the muscle that provides most of the movement

• Synergist- muscle that assists the prime mover

• Antagonist- the muscle that opposes the action of the prime mover

Muscle Contraction

Neuromuscular Junction

Neuromuscular junction animation

• animation

Sliding Filament theory

• Boat = Myosin (thick filament)

• Oar = Myosin side arm

• Water = Actin (thin filament)

• Life ring = Calcium

Resting1. ATP is bound to myosin side arm.

2. ATP cleaves into ADP + P (high energy)

Step 1 Action potential1. A nerve action potential releases acetylcholine

into the synaptic cleft opening the Na+ channels.

2. Action potential spreads across sarcolemma releasing Ca into sarcoplasma

Step 2 Myosin-actin binding1. Ca binds to troponin2. A shape change in troponin moves

tropomyocin out of the way of actin binding site3. Actin and myosin bind using energy from

cleaved ATP.

Step 3 Power Stroke1. Side arm pivots so myosin and actin slide by

each other shortening the sarcomere.

2. ADP and P released (low energy)

Step 4 ATP binding and actin-myosin release

1. A different ATP molecule binds to active site.

2. Actin released

Step 5 ATP cleavage

1. Return to high energy state

2. Cycle will repeat if Ca still available.

A few thoughts• The boat (myosin) does not move far in one

cycle, a muscle contraction requires many cycles

• What happens if ATP is not available?• Muscle stays contracted- cramps• Why does rigor mortis occur?• ATP is not available to control Ca release

so contractions are continuous 6-8 hours after death. Body relaxes 16-24 hours as enzymes break down contractile structures

Sarcomere summary

Final animation

• animation 2

• Watch “Distonia: movie

Muscles of the Head

Anterior torso muscles

Posterior torso muscles

Anterior shoulder and arm

Anterior forearm

Anterior thigh

Lateral thigh

Posterior thigh