A&p Chapter 9 Study Guide Answers

Front 1

Actin

Back 1

Thin filaments made of contracting contractile proteins that extend across the I band and partially into the A band.

Front 2

Myosin

Back 2

Thick filaments (of contractile proteins) that extend the entire length of the A band

Front 3

Muscle Fiber

Back 3

A muscle cell

Front 4

Sarcolemma

Back 4

The plasma membrane of a muscle cell

Front 5

Insertion Vs. Origin

Back 5

(Insertion) is the side of the muscle attached to the moveable bone. This moves towards the immovable or less movable bone (the origin)

Front 6

Sarcoplasm

Back 6

The muscle cell cytoplasm

Front 7

Aponeurosis

Back 7

A flat sheet of tendon that connects a muscle and the part it moves.

Front 8

Glycosomes

Back 8

Granules of stored glycogen that provide glucose (energy) during periods of muscle cell activity

Front 9

Myoglobin

Back 9

Oxygen – binding red pigment in the muscle

Front 10

Myofibrils

Back 10

Rod-like bundle of contractile filaments (Myofilaments or Actin & Myosin) found in the muscle fibers (cells)
•The arrangement of myofibrils within a fiber is such that a perfectly aligned repeating series of dark A bands (dark ) and light I bands (light) is evident

Front 11

Sarcoplasmic Reticulum

Back 11

An elaborate Smooth Endoplasmic Reticulum

Front 12

T tubules

Back 12

(T=transverse) they help to increase surface area, conduct impulses deep into the muscle fibers, stimulate release of calcium from the terminal cisternae and form part of the Triad. They are found at the junction of the A band and I band where the sarcolemma of the muscle cell protrudes deep into the cells interior

Front 13

Terminal Cisternae

Back 13

They are end sacs of the Sarcoplasmic Reticulum that form cross channels at A& I band junctions. They always occur in pairs and act as storage closets for calcium. They contain large numbers of mitochondria and glycogen which helps produce energy for contractions while calcium gives the final “go” signal.

Front 14

Triads

Back 14

Successive groupings of three membrane structures (terminal cisternae, T tubules, termainal cisternae)

Front 15

What are the 3 types of muscle? Describe, in words, what each muscle type looks like, the function of each and where you would find each type in the human body.

Back 15

Skeletal muscle – Long muscle cells, Striated, Voluntary, and multinucleate. Used for mobility and found covering the bony skeleton.
Cardiac Muscles – Striated, generally uninucleate, striated with intercalated discs. Used for contraction of the heart and propulsion of blood. Found in the heart.
Smooth Muscle – Spindle shaped cells, uninucleate, nonstriated, and involuntary. Used for propulsion of fluids and other substances through the body. Found in the digestive tract.

Front 16

Skeletal Muscle: How is it organized?

Back 16

Whole skeletal muscleFasciclesMuscle Fiber (cell)MyofibrilMyofilaments (actin and myosin)

Front 17

How is skeletal muscle attached to bone? Where does the epimysium fit into this attachment process?

Back 17

Muscles are attached to bones in two places - origin (immovable bone) and Insertion (moveable bone).
It can also have two different types of attachments - Direct and Indirect.
Direct attachment is where the epimysium (outer layer of muscle) and periosteum (outer layer of bone) or perichondrium (outer layer of cartilage) are fused together.
Indirect attachment is where the connective tissue wrapping extends into a tendon or aponerosis (flat sheet of tendon) attaches to the bone or outer layer of other muscles.

Front 18

What is myoglobin? Why is it important for sk. muscle to have such a supply?

Back 18

Myoglobin is the red pigment that carries oxygen in the muscle cells. Very similar to hemoglobin in the blood
Since skeletal muscles help us with movement and exercise oxygen would be extremely important to those muscles. The movement that is considered aerobic would require an oxygen supply.

Front 19

How do myofibrils differ from sarcomeres?

Back 19

They are both contractile units, but Myofibrils house Sarcomeres. The A band is the darkest band that gives us the appearance of striations when sitting next to the I band.

Front 20

How does the structure of myosin and actin differ? How do they associate with each other?

Back 20

Myosin has a rod like tail and two globular heads (double headed golf club).
Actin is made like a double strand beaded necklace made up of F actin and G actin. F actin are the fibrous protein that make up the strands while G actin are globular units that make up the beads.
These two myofilaments need to slip over each other to carry out a contraction, so myosin will use binding sites on the actin to travel across with the help of ATP taken in to a receptor site on Myosin.

Front 21

Describe the role of calcium in generating a muscle contraction. Be sure to include the role of troponin and tropomyosin.

Back 21

The release of calcium from the terminal cisternae is what separates the muscle contraction from the action potential. The action potential triggers the release then the calcium binds with troponin and causes tropomyosin to move out of the way. When this happens the myosin binds with the G actin and contraction takes place.

Front 22

What does calcium have to do with sending a neuronal impulse to the muscle fiber?

Back 22

When the action potential comes down the axon it triggers a voltage channel that allows Ca++ to enter the axon terminal. This triggers vesicles to release ACh into the synaptic cleft and bind to ACh receptor sites on the sarcolemma. This transfers the action potential to the muscle fiber.

Front 23

What is meant by the refractory period? Why is it so important?
Why is the refractory period so crucial for cardiac tissue!

Back 23

The refractory period takes place during repolarization of a cell. It is the period of time when another action potential will most likely not take place. This period keeps us from muscles spasms or seizing.
In cardiac tissue this would be important because there wouldn’t be enough blood pumping due to the speed.

Front 24

What is isometric contraction? What is isotonic contraction? There are 2 types of isotonic contraction. What are they and how do they differ?

Back 24

Isometric contraction means muscle length changes and moves the load. The two types of Isometric contractions are concentric (shortening the muscle to work) and eccentric (lengthening the muscle to work).
Isotonic is where the muscle can be working just as hard, but neither shortening or lengthening

Front 25

What is a motor unit? How does a motor unit differ in our eyes versus in our gastrocnemius? With regards to the motor unit, what is recruitment?

Back 25

A motor unit is a motor neuron and all of the muscle fibers it supplies (they are not clustered, so they have the ability to cause a weak contraction through the entire muscle with one motor unit). These can be large or small meaning the amount of muscle fibers they control. It also depends on how precise the movement needs to be. In our eye they would be small while in our gastrocnemius they would be large and less precise.
Recruitment is when on motor unit activates more and more motor units to create a contractio

Front 26

What is a muscle twitch and what are the phases of a muscle twitch? Now that you are experts in muscle contraction, discuss the role of calcium in a muscle twitch.

Back 26

A muscle twitch is the response of a single motor unit (motor neuron and muscle fibers) to a single action potential. This has three phases latent period (follows stimulation and excitation-contraction coupling is happening), the period of contraction (cross bridges are active and contraction is taking place), and the period of relaxation (initiated by the Ca++ reentering the SR).
Calcium plays a role in all of these steps, because it is necessary to carry out excitation-contraction coupling, it allows the cross bridges to continue to be active, and it must be removed for relaxation to take place.

Front 27

How is a muscle twitch different from a full muscle contraction?

Back 27

The difference between twitch and contraction is that a muscle twitch affects muscle fibers and contractions affect the entire muscle. Also when it comes to voluntary muscles a twitch can still be involuntary.

Front 28

With wave summation, why is it that the muscle can’t relax fully before going through another contraction? With this one, think about the location of calcium in the muscle fiber. It doesn’t have time to get pumped back to someplace. What is that place?

Back 28

The combination of responses from a motor unit that has had two or more stimuli applied to it in quick succession. A motor unit of a muscle responds to a single stimulus with a simple twitch response. When a second stimulus is applied to the motor unit before the response to the first is completely lost, the two responses combine to produce a greater muscle tension than that produced by a single response. If stimulation continues, the combination of the individual responses may result in tetanus.
The quick succession of stimuli doesn’t allow for the Ca++ to be pumped back into the terminal cisternae of the sarcoplasmic reticulum, so it stays bound to traponin and keeps tropomyosin out of the way. This allows cross bridges to stay active and contraction to become stronger.

Front 29

What is happening to the relaxation step in incomplete tetanus? You aren’t getting that full relaxation. Why? What is happening with complete tetanus? What happens to the relaxation step here?

Back 29

In incomplete tetanus the muscle is stimulated at an increasingly faster rate ad relaxation is becoming shorter and shorter. This is because the concentration of calcium is becoming higher and wave summation is getting closer together. Described as sustained but quivering.
In complete tetanus the stimulus is becoming stronger and more frequent until relaxation completely disappears and you have a sustained contraction.
Can’t continue forever…fatigue will take place and no contraction will be possible.

Front 30

Describe the importance of threshold. What happens to a muscle if it reaches threshold? What happens if threshold is not reached?

Back 30

It is the stimulus needed to see the first observable contraction. It begins an action potential. The minute a muscle reaches threshold it is the point of no return…a contraction will take place. If threshold isn’t reached then there is no observable contraction, but it may reduce the amount of stimuli needed to achieve threshold the next time.

Front 31

How is skeletal muscle organized? Why is it organized in such a fashion?

Back 31

Whole skeletal muscleàFasciclesàMuscle Fiber (cell)àMyofibrilàMyofilaments (actin and myosin)
It’s organized this way because it allows for specific compartmentalization for the muscle to contract. Just imagine what might occur if muscle wasn’t so ordered! This is more of a thinking question for you.

Front 32

Explain excitation-contraction coupling. Again, this should be a concise answer and an easy one to explain!

Back 32

An axon releases a message to the axon terminal which connects with a muscle fiber. This message signals the release of calcium that triggers a muscle contraction. You need excitation to get a contraction.

Front 33

What do neurons have to do with muscle contraction? What is the role of a
neuromuscular junction?

Back 33

Neurons are needed to change membrane potential and begin an action potential. They send all of the original stimulus.
NMJ - Neurons release Ach which binds to receptors on the sarcolemma. This opens ion channels which changes the voltage and opens voltage channels. This leads to depolarization which triggers an action potential that travels across the sarcolemma and into T tubules telling the terminal cisternae to release Ca++. We then see the muscle contraction take place.

Front 34

Excitability, or irritability

Back 34

the ability to receive and respond to stimuli

Front 35

Contractility

Back 35

the ability to shorten forcibly

Front 36

Extensibility

Back 36

the ability to be stretched or extended (fun fact: it's more important to stretch your muscles after you exercise)

Front 37

Elasticity

Back 37

the ability to recoil and resume the original resting length

Front 38

Elasticity

Back 38

fine sheath of connective tissue composed of reticular fibers surrounding each muscle fiber

Front 39

Perimysium

Back 39

fibrous connective tissue that surrounds groups of muscle fibers called fascicles

Front 40

Epimysium

Back 40

an overcoat of dense regular connective tissue that surrounds the entire muscle

Front 41

What is the nerve and blood supply for muscles? How does the blood supply work?

Back 41

•Each muscle is served by one nerve, an artery, and one or more veins

•Each skeletal muscle fiber is supplied with a nerve ending that controls contraction

•Contracting fibers require continuous delivery of oxygen and nutrients via arteries (in)

•Wastes must be removed via veins (out)

Front 42

Why do skeletal muscle fibers have multiple nuclei?

Back 42

Because they don’t readily divide

Front 43

What type of cells are muscle fibers? What organelles are found in skeletal muscle fibers?

Back 43

•Each cell is a syncytium (lots of nuclei but not divided into separate cells) produced by fusion of embryonic cells

•Fibers contain the usual organelles, myofibrils, sarcoplasmic reticulum, and T tubules

Front 44

What are sarcomeres?

Back 44

• The smallest contractile unit of a muscle

• The region of a myofibril between two successive Z discs
• Composed of myofilaments made up of contractile proteins

• Myofilaments are of two types – Myosin and Actin

Front 45

What are Z-discs

Back 45

• The smallest contractile unit of a muscle

• The region of a myofibril between two successive Z discs

• Composed of myofilaments made up of contractile proteins

• Myofilaments are of two types – Myosin and Actin

Front 46

Describe the banding pattern of a sarcomere in detail

Back 46

Myosin:
thick filaments that extend the entire length of an A band
Actin:
thin filaments that extend across the I band and partway into the A band
Z-disc
coin-shaped sheet of proteins (connectins) that anchors the thin filaments and connects myofibrils to one another

Actin filaments do not overlap thick filaments in the lighter H zone

M lines appear darker due to the presence of the protein desmin

Front 47

What makes up myosin tails? What makes up myosin heads?

Back 47

Tails: two interwoven, heavy polypeptide chains
Heads
two smaller, light polypeptide chains called cross bridges
binding sites for actin of thin filaments
binding sites for ATP
ATPase enzymes (breaks down ATP) (down and back burns up one molecule of ATP)

Front 48

Describe the Triad relationship

Back 48

T tubules and SR provide tightly linked signals for muscle contraction

T tubule proteins act as voltage sensors

SR foot proteins are receptors that regulate Ca2+ release from the SR cisternae

Front 49

What causes muscle shortening?

Back 49

Axonal endings, which have small membranous sacs (synaptic vesicles) that contain the neurotransmitter acetylcholine (ACh)
The motor end plate(directly across from axonal ending) (invaginations to increase surface area for more receptors [acetylcholine receptors] to receive ACh) of a muscle, which is a specific part of the sarcolemma that contains ACh receptors and helps form the neuromuscular junction
Though exceedingly close, axonal ends and muscle fibers are always separated by a space called the synaptic cleft (same as synaptic gap)

Front 50

What destroys Acetylcholine? Why?

Back 50

ACh bound to ACh receptors is quickly destroyed by the enzyme acetylcholinesterase (stops the signal)

This destruction prevents continued muscle fiber contraction in the absence of additional stimuli (this prevents us from muscle spasm)

Front 51

What is an action potential?

Back 51

A transient depolarization event that includes polarity reversal of a sarcolemma and the propagation of an action potential along the membrane

Front 52

What is the role of acetylcholine in an action potential?

Back 52

ACh binds its receptors at the motor end plate

Binding opens chemically (ligand) gated channels

Na+ diffuses in and K+ diffuse out and the interior of the sarcolemma becomes less negative

This event is called depolarization (upward deflection of resting membrane potential from -70mV to +30mV))

Front 53

What are the electrical conditions of a polarized sarcolemma?

Back 53

The outside face is positive, while the inside face is negative

This difference in charge is the resting membrane potential

The predominant extracellular ion is Na+

The predominant intracellular ion is K+

The sarcolemma is relatively impermeable to both ions

Front 54

What is Rigor Mortis?

Back 54

Stiffening of the body beginning 3 to 4 hours after death

Deteriorating SR releases Ca2+

Ca2+ activates myosin-actin cross-bridging and muscle contracts, but can not relax

Muscle relaxation requires ATP and ATP production is no longer produced after death

Fibers remain contracted until myofilaments decay

Front 55

What is Muscular Dystrophy?

Back 55

group of inherited muscle-destroying diseases where muscles enlarge due to fat and connective tissue deposits, but muscle fibers atrophy

Front 56

What is Duchenne Muscular Dystrophy?

Back 56

Inherited, sex-linked disease carried by females and expressed in males (1/3500)

Diagnosed between the ages of 2-10

Victims become clumsy and fall frequently as their muscles fail

Progresses from the extremities upward, and victims die of respiratory failure in their 20s

Caused by a lack of the cytoplasmic protein dystrophin (holds the myofibrils together to create a nice organized structure) Without it they crumble

There is no cure, but myoblast transfer therapy shows promise

Front 57

What is salutatory conduction?

Back 57

Current passes through a myelinated axon only at the nodes of Ranvier

Voltage-gated Na+ channels are concentrated at these nodes

Action potentials are triggered only at the nodes and jump from one node to the next

Much faster than conduction along unmyelinated axons