ANS205: Exam 2 Muscle Cards

Do skeletal muscles have sarcomeres?

Yes

What does it mean to have sarcomeres; i.e what does it look like?

Striations

What two muscular subunits make up sarcomeres?

Actin and myosin

What complex rests on top of the binding site of myosin heads?

Tropomyosin

What is attached to the tropomyosin?

Troponin

What is troponin sensitive to?

Calcium

At what event does skeletal muscle excitation at the neuromuscular junction end and skeletal muscle excitation within the cell begin?

This occurs when sodium enters the muscle cell, generating an action potential.

In the muscle cell during skeletal muscle contraction. where does sodium diffuse down into?

T-Tubule

What is the structure that links the T-Tubule to the Sarcoplasmic Reticulum?

DHP Receptor

What is the DHP sensitive to? What happens when this sensitivity is activated?

DHP is voltage sensitive, so when an action potential is generated, the plate attached to the DHP Receptor is lifted up, opening the calcium ion channels located on the SR

What populates the inside of the SR?

Calcium Ions

What happens when the calcium channels open up on the SR?

Calcium ions can enter the cytoplasm

When is the tropomyosin/troponin complex hindered?

When tropomyosin is still attached to actin, blocking myosin from binding to actin

What causes the tropomyosin/troponin complex to be un-hindering?

The flooding of calcium from the Sarcoplasmic Reticulum; One of these calcium ions will bind to troponin - a calcium sensitive protein - causing a conformational change which will lift the tropomyosin from the actin-myosin binding site.

What is on the myosin heads that is very important?

ATPase!!!

What happens in the myosin head before the binding of actin and myosin?

The myosin head uses its ATPase to break ATP into ADP and P, storing the energy generated from the breaking

What are the two reasons that actin was able to bind myosin?

1. Hindrance was removed

2. Energy stored due to the cleaving of ATP

What anatomical part of the myosin head mainly contributes to the movement of actin strands?

The hinge attached to the myosin head

Where does the actin strand move closer to?

The M Line

So actin strands are moving by the _________/_________ of myosin heads, which is facilitated by the cleavage of _______.

Binding/Unbinding, ATP

What two regions of the sarcomere get reduced; which region can entirely disappear?

The H Zone and I Band; the H Zone can disappear during contraction

What are the two molecules that make up the acetylcholine transmitter?

Acetic Acid and Choline

What bond is used to connect Acetic Acid and Choline?

Ester Bonds

What enzyme bound to the muscle cell membrane is used to break down acetylcholine?

Acetylcholine Esterase

What happens to the separated acetate and choline model when they are broken up?

Choline is packaged and absorbed pack into a vesicle, and returns back into the motor neuron. Acetate diffuses away from the synapse.

If acetylcholine is no longer bound to the receptor on the muscle fiber, will sodium still enter/depolarize the cell?

NO

Although sodium can no longer get in the cell after the acetylcholine is cleaved, what is STILL BOUND in the muscle fiber?

Calcium is still bound to Troponin

What do we want to happen to the calcium that is still bound to troponin during skeletal muscle relaxation?

We want the calcium to diffuse back into the SR.

What issue arises when trying to diffuse Ca2+ back into the SR?

We have to move Ca2+ from a low region of concentration (ICF) into a higher region of concentration (SR).

How do we solve the issue of pumping calcium against a concentration gradient back into the SR?

We rely on the use of a calcium ATPase which is in the membrane of the SR. This enzyme cleaves ATP, allowing for calcium to move back into the SR.

What does the movement of Calcium back into the SR cause?

• Calcium levels in the ICF decrease

• Calcium bumps off of Troponin

• Tropomyosin covers up the myosin head binding site on the actin strand ; hindering again

• Sarcomere relaxes

  • H Zone and I Band Re-lengthen

What cell membrane structure is located in smooth muscles, that is not present in skeletal muscles?

Caveoli

What is structure/region in the smooth muscle where actin can be found?

Dense bodies

What can be found between the dense bodies connecting them?

Myosin

What are the two locations of calcium ion channels in smooth muscle?

• Caveoli

• Sarcoplasmic Reticulum

Can you find troponin in smooth muscles?

No

What is the calcium-sensitive protein found in smooth muscle?

Calmodulin

Is there tropomyosin in smooth muscle?

No

Is there sarcomeres in smooth muscle?

No

What cell adhesion molecule can be found between individual smooth muscles?

Gap junctions

What travels through the gap junctions of the smooth muscles during depolarization?

Sodium ions

In smooth muscles, does every cell need a neuromuscular junction?

NO

What are the two kind of chains that Myosin has?

Light and Heavy

What myosin chain gets phosphorylated?

Light chain

What are the two ways in which smooth muscles are classified?

Location and their communication with neighboring cells

Where can smooth muscles be found?

In hollow regions… ex GI, reproductive, vascular, ocular, urinary, and respiratory

What are the types of cells that communicate with neighboring cells?

Single-Unit and Multiunit

Between Single-Unit and Multi-Unit, which is more abundant?

Single-Unit

How do single-unit cells contract; indiviudally or together in unison?

Together in unison

Between single-unit cells and multiunit cells, which have their own nervation?

Multiunit

What are the two anatomical regions on animals you can find multiunit cells in?

• Hackles (spinous processess of the thoracic vertebrae)

• Ciliary body

What is the name of the autonomic nervous system neuron that is used in neuromuscular junctions?

Varicosity

In smooth muscles, what protein helps keep the actin and myosin in place?

Cytoskeleton Proteins

How many ways can we excite the smooth muscle?

FOUR WAYS

What are the four ways in which a smooth muscle cell can get excited?

1. Autonomic neurotransmitter and hormones

2. Mechanical stretch

3. Slow electrical activity

4. Paracrine Signals

What are the two sources of calcium for smooth muscle cells?

ECF and the SR

What causes the calcium ion channel on the caveoli to open?

Depolarization/ The voltage generated from the sodium ions entering the smooth muscle cell

What causes the calcium channels on the SR to open?

The influx of calcium ions from the ECF into the smooth muscle

Once Ca2+ floods the sarcoplasm of smooth muscle cells, what happens to it, and by what molecule?

Calmodulin binds the Ca2+ molecules

What complex is activated by the Calcium-Calmodulin complex? How does it activate it?

Myosin Light Chain Kinase (MLCK), By Binding the Calmodulin-Ca2+ complex to MLCK

What does MLCK do?

MLCK cleaves an ATP molecule into ADP and P, and extracts that P and uses it to phosphorylate the MLC (Myosin Light Chain)

What does the MLC Phosphorylation activate?

The ATPase in the myosin head

What does the ATPase in the myosin head do; what does it cause?

The ATPase in the myosin head cleaves ATP, and utilizes the energy stored from the broken bond to power the movement of actin closer to each other

What molecule is important in smooth muscles for halting the movement of actin/dense bodies?

Myosin Light Chain Phosphorylase

What does MLCP do?

MLCP dephosphorylates the phosphorylated mysoin head

What does the dephosphorylation of the myosin head cause

It causes the ATPase activity in the head to be dampened, thus causing actin and myosin to return to their original states.

For smooth muscle relaxation to occur, what has to happen to calcium? How does this happen?

Calcium must return to where it came from : ECF and SR. This is done through utilizing cell membrane and SR Ca2+ ATPase pumps to move Ca2+ against its concentration gradient.

In smooth muscle cells, what happens when Ca2+ levels drop in the sarcoplasm?

Calmodulin unbinds the calcium

For the cell to truly relax, what must happen after Ca2+ returns to its original state? How did this happen?

The cell repolarizes/ This is done through potassium leaking back into the ECF, followed by the Na/K ATPase Pump

What four anatomical structures are characteristic of cardiac muscle cells?

• Sarcomeres

• Intercalated Discs

• Branching

• Syncytium

Are there gap junctions in cardiac muscle… if so, where?

Yes, and they are located in the intercalated discs

What CAM in the cardiac muscle aids in keeping the branching together?

Desmosomes

How is cardiac muscle similar to skeletal muscle?

It is striated and has sarcomeric strucutre.

How is cardiac muscle different from skeletal muscle?

Muscle fibers are shorter, they contain a single nucleus, and they branch

How is Cardiac Muscle similar to smooth muscle?

• Electrically linked together

• Two sources of Calcium

• Under autonomic and hormone control

How is cardiac muscle unlike smooth muscle?

There are gap junctions in the intercalated disks and then there are desmosomes present

What are the top two chambers of the heart called?

Atria

What are the bottom two chambers of the heart called?

Ventricles