Muscle Cell Function

Muscle Cell Function Vertebrate Anatomy – Ch. 9

Muscle cell structure

 Long, cylindrical cell  Produced by union of many ______cells; Leads to huge cells - Up to 12 inches long; 10x larger in diameter than avg. cell  Many ______in each fiber; Again, indicates fusion of many cells

- Arranged just below the plasma membrane - Nuclei pushed to periphery to make more room for unified contracting fibers  Plasma membrane – called ______ Cytoplasm – called ______ Muscle cells contain Lots of stored ______- a sugar storage molecule that can provide lots of ______ Muscle cells also contain lots of ______which is an ______- binding protein. Lots of oxygen is needed for energy production. This molecule is a lot like ______which carries oxygen in the ______.

Muscle fiber - close up

Each muscle fiber contains a large number of rod-like ______that run in parallel fashion and extend the entire length of the cell.

Myofibrils are densely packed within the muscle fiber.

Myofibrils appear ______. These bands are also called ______- Hence, the term striated muscle is used to describe skeletal muscle.

Banding is due to two types of smaller fibers

______filaments - made of ______

______filaments – made of ______

Thick filament structure

Myosin is long filaments that have small "knobs" hanging off called myosin ______.

Myosin heads can ______and “stick to” ______at certain locations on the actin fiber

Thin filament structure

Actin - ______strings of ______

Actin molecules possess ______sites. These are locations where

______heads can bind to the actin molecules These myosin head binding sites remain ______when the muscle is NOT contracting

Troponin and Tropomyosin

Troponin and Troposmyosin are molecules associated with the ______filaments

Troponin Troponin molecules are actually ______binding sites also located on actin filaments

Tropomyosin “rope” molecule that covers and hides ______binding sites

The Sarcomere

The ______is the unit of muscle contraction

______– anchor points for actin filaments

Sarcomere – extends from from ______to ______

Interaction of Thick and Thin filaments – muscle contraction

1. Myosin head bound to ______.

At this point, myosin head is in a ______energy state

Energy from ATP cannot be released until ATP is broken into ______and ______

2. Myosin head hydrolyzes (breaks down) ATP to ADP and Pi.

Release of energy causes myosin head to change its shape. It moves to its ______energy position.

3. Myosin head binds to ______forming a ______

This occurs as long as the myosin ______sites on the actin filaments have been

______. Remember these were hiddin by the ______molecule

4. Once the myosin head binds to actin, it releases ADP and Pi Once ADP and Pi are released, myosin head returns to Low Energy State

REMEMBER: The myosin head is still hooked to the ______molecule! THIS ______THE THIN FILAMENT

5. A new ______binds to the ______. This causes a shape change in the myosin head that releases the myosin head from the actin molecule But that’s not all….

Remember Tropomyosin, Troponin and Calcium ….. Where do these chemicals fit it in? They help to

______of the muscle contraction – that is, they help determine WHEN the

muscle will contract. This is based on a signal sent from your BRAIN (usually).

Control of muscle contraction:

Tropomyosin covers ______binding sites on actin filaments

Troponin – these molecules are ______binding sites

Here's how it works:

1. Calcium binds to ______.

2. When bound by calcium, Troponin molecules ______– this causes

______molecules to move, too.

When tropomyosin molecules move, the ______binding sites are revealed.

This allows the myosin head to bind to the actin filament, forming a crossbridge.

BUT…where does this calcium come from and WHY?

Calcium is stored in the ______(fancy ER)

A ______is responsible for releasing calcium from SR into

______(cytoplasm).

1. Nerve impulse travels across from neuron (nerve cell) across a synapse to the

______(muscle cell membrane).

2. The nerve impulse follows the sarcolemma until it "falls down the manhole" – that is,

until it falls down the ______. These are tubes of cell

membrane that carry the impulse down into the cell.

3. Impulse travels to the ______

4. When nerve impulse reaches SR, ______is released

This ensures that muscle contraction occurs, ONLY when the nerve impulse has told it to do so.