Do Now 1. Draw a picture of a sarcomere 2. Label actin, myosin, Z-line, H-zone, I band, A band 3. What is the difference between actin and myosin? 4. List the hierarchy of muscle structures starting with the whole muscle down to myofilaments.

Explain how muscles contract Describe the sliding filament model Today…. Explain how muscles contract Describe the sliding filament model Compare and contrast origins, insertions, agonists, and antagonists

For the purposes of this class… You will need to know 8 steps to muscle contraction p.348-349 in your textbook is your best friend

Step 1- p.341 Motor neuron receives an impulse

Motor Unit or Neuromuscular Junction 1.  Neuron         2.  Sarcolemma   (or motor end plate)        3.  Vesicle      4.  Synapse        5.  Mitochondria

Step 2 – p.341 Motor neuron releases the neurotransmitter acetylcholine into the gap between the neuron and the muscle

Step 3 – p.342 The acetylcholine attaches to receptors on the muscle fiber membrane

Step 4 – p.342 The muscle responds by releasing calcium ions into the myofibrils

Step 5 – p.345 The calcium ions attach to the Actin and unlock the binding site

Step 6 – p.345 The cross-bridges from the myosin attach to the binding sites

Step 7 – p.345 The cross-bridges fire and pull the actin which shortens the sarcomere

Step 8 – p.345 All of the shortening sarcomeres lead to shortening (contracting) of the muscle

What is rigor mortis? A few hours after a person or animal dies, the joints of the body stiffen and become locked in place. This stiffening is called rigor mortis. Depending on temperature and other conditions, rigor mortis lasts approximately 24-72 hours. The phenomenon is caused by the skeletal muscles partially contracting. The muscles are unable to relax, so the joints become fixed in place.

What is tetanus? Tetanus causes cholinosterase to not break down the acetylcholine in the synapse.  This results in a person's muscles contracting and not relaxing. A tetanus shot must be administered shortly after exposure to the  bacteria. Once you develop tetanus, there is no cure.

Sliding Filament Model Create a model of muscle contraction The model must show all stages of actin- myosin binding Think beyond a poster – possible ideas could include a series of photographs, short video, 3D models You may work by yourself or with a partner

How Skeletal Muscle Moves

Muscles ♥ Bones Muscles and Bones work together to create MOVEMENT!

Origin vs. Insertion Origin = the immovable end of the muscle Insertion= the movable end of the muscle Typically, the origin lies proximal to the insertion

Contract that muscle! When a muscle contracts, it shortens & thus pulls the insertion closer to the origin

Extension vs. Flexion Extension = increases the angle of joint Flexion = decreases angle of joint

*The same muscle can do both! Think about one of the quad muscles (rectus femoris) EXTENSION at the knee joint FLEXION at the hip joint

With your groups… List three examples of flexion List three examples of extension

Agonists, synergists, antagonists Agonist = main muscle Synergists = assist & stabilize the agonist Antagonists = capable of doing opposite movement

Example: Bicep curl Agonist = Synergists = Antagonists= Biceps! Pectorals, deltoids, laterals, trapezius Antagonists= triceps