Muscles

Question 1

What are the four major tissue types?

Answer 1

The four major tissue types are:

• Muscle
• Nervous
• Connective
• Epithelial

Question 2

What are tendons?

Answer 2

Tendons are connective tissue that connect muscle to bone

Question 3

What are ligaments?

Answer 3

Ligaments are connective tissue that connect bone to bone

Question 4

What are the three types of muscle?

Answer 4

The three types of muscle are:

• Smooth
• Skeletal
• Cardiac

Question 5

What germ layer are muscles derived from?

Answer 5

Muscles are derived from the mesoderm

Question 6

What is cardiac muscle and its characteristics?

Answer 6

Cardiac muscle is the muscle tissue of the heart

• Has intercalated discs between cells. This is a membranous boundary between adjacent cells
• Usually has a single nucleus
• Striated
• Involuntary muscle
• Full of Gap junctions between cells that connect the cytoplasm of heart cells to one another. This allows for rapid transmission of ions across the heart to coordinate the pumping of it. We often refer to these gap junctions as being electrically coupled.
• 40% of the cytoplasmic volume contains mitochondria, compared to 2% in skeletal muscle. It’s a huge amount.

Question 7

What is atrial natriuretic factor?

Answer 7

Cardiac muscle cells contain granules that contain atrial natriuretic factor.
- It’s a hormone that acts on the kidneys to help lower blood pressure by allowing sodium and water loss.

Question 8

What is cardiac hypertrophy?

Answer 8

Cardiac hypertrophy occurs in athletes and is caused by certain pathologies as well.
- Cardiac cells increase in size

Question 9

How does the body repair heart damage?

Answer 9

The body doesn’t regenerate lost cells due to heart damage. Instead it replaces the dead heart cells with fibrous connective tissues. Thus the need for heart transplants

Question 10

What is smooth muscle and its characteristics?

Answer 10

Smooth muscle is the muscle of our involuntary contractions, found in walls of blood vessels, GI tract, urinary tract, reproductive tract, urinary bladder, and internal organs such as stomach and intestines

• No striations
• Involuntary
• has a single nucleus
• Regulated by: Hormones, autonomic nervous system, local physiological conditions
• Regeneration of cells can occur, thus they can undergo mitosis (unlike cardiac muscle cells)
• Actin and myosin are not regularly arranged along the cell length, the myosin is scattered in the cytosol, and the actin is attached to structures called dense bodies. (Thus no striations are noted)
• Ca++ complex with a calcium-binding protein called calmodulin which is involved in the contraction of smooth muscle. (this is sufficient for the DAT)

Question 11

What is Calmodulin?

Answer 11

Calmodulin is a calcium-binding protein.

- It binds with Ca++ to facilitate the contraction of smooth muscle.

Question 12

What is skeletal muscle and its characteristics?

Answer 12

Skeletal muscle is:

• Striated
• Voluntary
• Multi-nucleated

Question 13

How do skeletal muscle cells regenerate?

Answer 13

Like cardiac muscle, the nuclei do not undergo mitosis. However, limited regeneration can occur

• Muscle building satellite cells might be able to fuse with preexisting muscle cells to increase the muscle mass
• Satellite cells reside on the external surface of skeletal muscle cells and are not part of cardiac muscle.

Question 14

What is the epimysium?

Answer 14

The epimysium is dense connective tissue that surrounds the entire muscle

Question 15

What are the three types of skeletal muscle fibers?

Answer 15

The three types of muscle fibers are:

• Red: Many mitochondria, rich in myoglobin, rich in oxidative enzymes, and rich in blood supply
• White: Few mitochondria, poor in myoglobin, poor in oxidative enzymes, poor in blood supply
• Intermediate: mixture of the two.

Most muscles have all three, but the percentages vary. Think dark vs white meat on chicken

Question 16

What are myofibrils?

Answer 16

Myofibrils are long cylindrical structures that make up a large portion of skeletal muscle.

• Myofibrils are composed of thin and thick filaments
• Thin filaments are Actin
• Thick filaments are Myosin

Question 17

What kind of arrangement of bands is seen in myofibrils?

Answer 17

We see a filament arrangement pattern of light and dark bands

NB: Favorite DAT question

Question 18

What is the sarcomere?

Answer 18

The sarcomere is the structural and functional unit of the myofibril.

Question 19

What is the sarcomere separated into?

Answer 19

The sarcomere is separated into:

• A Band: The dark band where myosin overlaps with actin and where it doesn’t.
• I Band: The light band of thin actin filaments where it doesn’t overlap with myosin.
• H Zone: Center of the A band, where myosin doesn’t overlap with actin. It’s the lighter middle part of the sarcomere.
• Z Line: Actin and α-Actinin combined to form a line that separates each individual sarcomere.

Question 20

What is Titin?

Answer 20

Titin is a protein that helps position the thick myosin filaments, thus stabilizing the sarcomere.

Question 21

What is Nebulin?

Answer 21

Nebulin is a protein that helps stabilize the thin filaments of actin, thus helping stabilize the sarcomere as a whole.

Question 22

What is α-Actinin?

Answer 22

α-Actinin is a protein that helps stabilize the thin filaments of actin, thus helping stabilize the sarcomere.

Question 23

What happens to the parts of the sarcomere when the muscle contracts?

Answer 23

When a muscle contracts:

• I bands shorten
• H-zone shortens
• A-bands do not change
• Z- Lines come closer together.

The Actin and Myosin contract together and pull on one another to shorten the sarcomere.

NB: This is almost always a DAT question in one shape or another

Question 24

What of the structure of Actin?

Answer 24

Actin is a thin filament that is composed of additional proteins:

• Tropomyosin: A regulatory protein
• Troponin complex: More proteins

Question 25

Describe the steps of muscle contraction

Answer 25

- The presynaptic nerve releases acetylcholine. Acetylcholine binds to the muscle fiber receptor and depolarization occurs. In other words, an impulse occurs and goes to the interior of the fiber via Transverse-tubules (T-Tubules) which is conveyed to the sarcoplasmic reticulum. - The sarcoplaplsmic reticulum releases Ca++ through voltage-gated Ca++ release channels and enter the cytosol to bind to troponin. - When Ca++ binds to troponin, a conformational change occurs that pulls the tropomyosin out of the way of the myosin binding sites on actin. - Myosin has an ADP and a phosphate group attached to it, left over from the last muscle contraction. Myosin releases the phosphate group and this puts Myosin in a state to bind to actin. - Myosin binds to Actin and then loses the ADP group initiating the cocking of the myosin head. - ATP then binds to Myosin causing it to release its bond to actin. - ATP is then hydrolysed into ADP and a phosphate group. This reaction gives the Myosin the energy to cock its head for another push. - The Phosphate group is released initiating binding once more and the process repeats until the motor neuron stops firing or the cell runs out of ATP. - When the Motor neuron stops firing, the sarcolemma and the T-tubles repolarize and the Ca++ is pumped back into the Sarcoplasmic reticulum.

Question 26

What is Rigor Mortis?

Answer 26

Rigor Mortis occurs about 2-6 hours after death. - The lack of ATP prevents the dissociation of the Myosin from the Actin filaments, and we see a static muscle contraction. - After a few days, the body starts to decompose and the body relaxes again.

Question 27

What is putrescine?

Answer 27

Putrescine is a compound that is produced as a body decomposes

Question 28

What is cadaverine?

Answer 28

Cadaverine is a compound that is produced as a body decomposes.

Question 29

What is a power stroke?

Answer 29

A power stroke is when the myosin heads stroke together to pull the actin toward the middle to contract the H Zone

Question 30

What is creatine phosphate?

Answer 30

Creatine Phosphate is a molecule that can donate a phosphate to ADP to create ATP. - A cell has about 5x more creatine phosphate than ATP

Question 31

What is the order of use of energy in the muscle cell?

Answer 31

Glycogen is broken down first and then fatty acids can be broken down into acetyl CoA for the TCA cycle and ETC.

Question 32

What is the sarcolemma?

Answer 32

The sarcolemma is the membrane that surrounds a muscle cell.

Question 33

What are T-Tubules?

Answer 33

T-Tubules (Transverse Tubules) extend inward and pass all the way through the fiber. - Each of these tubules opens to the outside of the muscle fiber and contains the extracellular fluid. - T-Tubules carry depolarization from the sarcolemma to the sarcoplasmic reticulum, leading to the release of Ca++ ions into the cytoplasm

Question 34

What is a triad in a muscle fiber?

Answer 34

A triad is a T-tubule associated with a sarcoplasmic reticulum cisternae on either side. - When the T-Tubule becomes depolarized, it passes that depolarization to the cisternae and Ca++ is released from the sarcoplasmic reticulum. - When the membranes repolarize, Ca++ is pumped back into the sarcoplasmic reticulum.

Question 35

What is recruitment?

Answer 35

recruitment is when many motor units are activated in unison by their motor neurons. The more recruitment occurs, the stronger the contraction.

Question 36

What is a muscle twitch?

Answer 36

A muscle twitch is the tension increasing, peaking, and declining in response to an electrical impulse.

Question 37

What is a summation in regard to muscle contractions?

Answer 37

Multiple muscle twitches are additive. If a new muscle twitch occurs before the old one ends, there is a summation and the contraction is longer.

Question 38

What is a tetanus?

Answer 38

Tetanus (tetanic contraction) is a summation of a lot of muscle twitches that result in a long sustained contraction. - This occurs until the stimulus is removed or the muscle gets fatigued.

Question 39

What are the forms a tetanic contraction can take?

Answer 39

A tetanic contraction can take the form of: - Isotonic: muscle tension is constant, muscle shortens as it contracts - Isometric: Muscle generates tension, muscle does not change length.

Question 40

What are the two types of isotonic contractions?

Answer 40

The two types of isotonic contractions are: - eccentric contractions: Muscle tension is constant, but the muscle lengthens - concentric contractions: Muscle tension is constant, but the muscle shortens.

Question 41

What is a tonus?

Answer 41

Tonus (Muscle tone) is a slight sustained contraction that occurs in skeletal muscles. - Tonus is maintained throughout our life - Consists of short cycles of contraction and relaxation of the motor units, that always cycle as to not fatigue our muscles. - The body resists the passive stretch of muscle. Think falling asleep in class, and your head suddenly twitching upright. - Tonus helps us maintain balance and posture.

Question 42

What is the Golgo Tendon Organ?

Answer 42

The Golgi Tendon Organ (GTO) is a group of mechanoreceptors found at the junctions of muscles and tendons. - They monitor the force of muscle contractions - They help regulate the amount of force needed for a given task, allowing variability of force for a given task. - Think ratcheting a bolt and then suddenly finding resistance and increasing the torque on the ratchet in response to the resistance.

Question 43

What are the types of skeletal systems?

Answer 43

They types of skeletal systems include: - hydrostatic - exoskeletons - endoskeletons

Question 44

Describe a hydrostatic skeletal system

Answer 44

A hydrostatic skeletal system consists of: - muscles and fluids - Muscles are used to generate a force that changes the shape of a fluid filled spaces. - Seen in annelids, nematodes, (round worms), cnidarians such as hydra and jelly fish, and platyhelminthes (flat worms).

Question 45

Describe an exoskeleton

Answer 45

An Exoskeleton: - Is made up of calcium carbonate CaCO3 - Encloses organisms such as mollusks - Arthropods have an exoskeleton composed of chitin, a nitrogen sugar containing polysaccharide.

Question 46

Describe an endoskeleton

Answer 46

An endoskeleton: - composed of hard structures like bone, CaCO3, and cartilage found within soft tissues. - Echinoderms have ossicles beneath their skin. These provide rigidity and protection. Sea Urchins, starfish, Sea cucumbers contain these ossicles and they are made up of Ca or Mg carbonates. - Chordates like us have an endoskeleton made up of cartilage and bone.

Question 47

How do worms move?

Answer 47

Worms move by muscles. They have small bristles called setae that help anchor the worm as it contracts its segments and moves through locomotion.