Physiology Exam 1: Muscle Contraction Questions

Front 1

What does Muscle consist of?

Back 1

Hundred to thousands of muscle cells, connective tissue wrappings, blood vessels, and nerve fibers.

Front 2

What is Muscle covered by externally?

Back 2

Epimysium

Front 3

What do Fascicles consist of?

Back 3

Discrete bundle of muscle cells, segregated from the rest of the muscle by a connective tissue sheath

Front 4

What is a Fascicle covered by externally?

Back 4

Perimysium

Front 5

What is a muscle fiber?

Back 5

An elongated multinucleate cell with a banded (striated) appearance

Front 6

What is a Muscle Fiber covered by externally?

Back 6

Endomysium

Front 7

List all the components of the Actin (thin) filament of Skeletal muscle

Back 7

Tropomyosin, Troponin, G-Actin, F-Actin

Front 8

During contraction, what do the Ca2+ ions bind to?

Back 8

Troponin

Front 9

During contraction, what causes the exposure of the active sites on the actin myofilaments?

Back 9

Ca2+ ions binding to Troponin

Front 10

During contraction, what gets released during the creation of a cross-bridge?

Back 10

A phosphate

Front 11

During contraction, the head of the myosin myofilament moves the head of the myosin molecule. Where does the myosin get this energy from? What gets released in this process?

Back 11

The energy is stored in the myosin head.
ADP is released from the myosin head

Front 12

What causes the release of actin from myosin to terminate muscle contraction?

Back 12

An ATP molecule binding to the myosin head

Front 13

Before muscle contraction, where is Calcium found?

Back 13

Intrinsic Calcium: Stored in the triad of the SR.
Extrinsic Calcium: Function as the releasing factors for the Intrinsic Calcium

Front 14

What is Interdigitation triggered and controlled by, in muscle contraction?

Back 14

The entrance of Ca2+ ion into a protein called Troponin located on the actin filament

Front 15

When Ca2+ exits the muscle fiber, what happens to the filaments?

Back 15

The bridges uncouple which relaxes the filaments, and result in lengthening

Front 16

In muscle contraction, what is the reason for the increased permeability of the Sarcoplasmic Reticulum to Ca2+ ions?

Back 16

The depolarization of the T tubule causes voltage-gated Ca2+ ion channels to open, which results in the increased permeability

Front 17

Before Ca2+ gets released into the muscle, what is G-Actin bound to?

Back 17

G-Actin is initially bound to Troponin.

Front 18

What needs to move in order for G-Actin to be available for the Myosin to bind?

Back 18

When Ca2+ attaches to Troponin (causing a conformational change), the G-Actin gets released from the Troponin which causes the Tropomyosin to move, exposing the G-Actin active sites.

Front 19

The function of Tropomyosin is generally seen as?

Back 19

Blocker (G-Actin - Myosin)

Front 20

What happens to the Ca2+ after it is no longer needed for muscle contraction?

Back 20

It gets reabsorbed into the SR after the action potential ends

Front 21

What deactivates the blocking action of Tropomyosin, and what reactivates it?

Back 21

Deactivation: When Ca2+ attaches to Troponin (causing a conformational change), the G-Actin gets released from the Troponin which causes the Tropomyosin to move, exposing the G-Actin active sites.

Reactivation: Removal of Ca2+ by re-uptake into the SR restores the Tropomyosin blockage

Front 22

What kind of muscle is composed of almost exclusively Smooth Muscle?
What is the one exception?

Back 22

Visceral Muscle

Exception: The heart - cardiac muscle

Front 23

Small, spindle-shaped cells, each with one centrally located Nucleus, is characteristic of what type of muscle?

Back 23

Smooth Muscle

Front 24

Compare and Contrast: Smooth muscle width and length vs. Skeletal muscle width and length?

Back 24

Skeletal Muscle fibers are 20x wider and 1000x's longer than Smooth Muscle fibers

Front 25

Describe the Sarcoplasmic Reticulum and T-Tubules of Smooth Muscle fibers?

Back 25

Poorly developed SR
Absent T-Tubules

Front 26

Skeletal muscle Thick:Thin filaments =

Smooth muscle Thick:Thin filaments =

Back 26

Skeletal muscle Thick:Thin filaments = 1:2

Smooth muscle Thick:Thin filaments = 1:16

Front 27

What does Smooth muscle filaments lack, when compared to Skeletal Muscle filaments?

Back 27

There are no:
T-Tubules
Troponin
Sarcomeres
Highly structured neuromuscular junctions

Front 28

How does Smooth muscle compensate for the absence of Sarcomeres?

Back 28

Thick and Thin filaments are collected into bundles that correspond to myofibrils

Front 29

In Smooth muscle fibers, what attaches to dark staining bodies and are OCCASIONALLY anchored to the sarcolemma?

Back 29

Non-contractile intermediate filaments

Front 30

In Smooth muscle, what are considered the counterparts of Z lines in Skeletal muscle, also serving as an attachment point for the Thin filaments?

Back 30

Dense Bodies

Front 31

What are Dense bodies?

Back 31

Serve as attachment point for thin filaments in Smooth Muscle.
Counterparts of Z lines in Skeletal Muscle.

Front 32

In Smooth Muscle, what forms the strong, cable-like intracellular cytoskeleton that harnesses the pull generated by the sliding of the myofilaments during contraction?

Back 32

Intermediate filament-Dense body network

Front 33

In most cases, how many smooth muscle sheets are present and how are they oriented?

Back 33

At least two smooth muscle sheets are present and oriented at right angles to each other.

Front 34

Describe the two typical smooth muscle sheets.

Back 34

Longitudinal Layer: Runs with the long axis of the organ
Circular Layer: Runs around the circumference of the organ

Front 35

The cyclic contraction and relaxation of the opposing Longitudinal and Circular layers of the Smooth muscle sheets allowing the lumen of the organ to alternately constrict and dilate so that substances are mixed and squeezed along the internal pathway, is termed what?

Back 35

Peristalsis

Front 36

What are three organs that benefit from the Smooth Muscle's Peristalsis ?

Back 36

Rectum
Urinary Bladder
Uterus

Front 37

Where is the function of mixing by peristalsis beneficial?

Back 37

In the Small intestine = Segmentation
In the Stomach = Churning

Front 38

How does Smooth muscle compensate for the lack of highly structured neuromuscular junctions, that is seen in Skeletal muscle?

Back 38

Variscosities = Bulbous endings in which the innervating nerve fibers approach the Smooth Muscle

Front 39

What structure is responsible for releasing a neurotransmitter into a wide synaptic cleft in the general area of the Smooth Muscle cells (Diffuse junction)?

Back 39

Variscosities

Front 40

What mechanism powers the cycling process during muscle contraction?

Back 40

Release of energy by ATP hydrolysis (ATPase)

Front 41

Which type of muscle exhibits this type of contraction:

Adjacent cells exhibit slow, synchronized contractions, where the whole sheet responds to a stimulus in unison.

Back 41

Smooth Muscle Cells

Front 42

Which type of muscle exhibits this type of contraction:

Cells are electrically isolated from each other, with each stimulated to contract by its own neuromuscular junction.

Back 42

Skeletal Muscle Cells

Front 43

What characteristic of Smooth muscle cells allows transmission of action potentials from cell to cell?

Back 43

Presence of Gap Junctions

Front 44

Which type of muscle's membranes are "self-excitatory"?

Back 44

Smooth Muscle (Pacemaker cells)

Front 45

What characteristic of some smooth muscle fibers sets the contractile pace for the entire sheet of smooth muscle?

Back 45

Pacemaker cells, once excited, act as "drummers".

Front 46

Can all Smooth muscle Pacemaker cells depolarize spontaneously? What must be absent to allow for spontaneous depolarization?

Back 46

No, only some can.
Must be in the absence of external stimuli

Front 47

Can BOTH the rate and intensity of smooth muscle contraction be modified? How?

Back 47

Yes, BOTH can be modified by Neural and Chemical stimuli.

Front 48

In both Skeletal and Smooth muscle, what is the final trigger for contraction?

Back 48

IntrAcellular rise in Calcium ion level.

Front 49

In both Skeletal and Smooth muscle, how is the sliding process energized?

Back 49

By ATP

Front 50

Is the Sliding Filament mechanism seen in BOTH Skeletal and Smooth muscle?

Back 50

Yes

Front 51

In both Skeletal and Smooth muscle, what causes depolarization?

Back 51

Skeletal: Neural Stimulation
Smooth: Neural and Chemical (non-nervous) Stimulation

Front 52

Where does Calcium bind in Skeletal vs. Smooth muscle?

Back 52

Skeletal: Calcium binds to Thin filaments (Troponin)

Smooth: Calcium binds to Thick filaments

Front 53

What percent is Myosin ATP-ase activity in Smooth muscle compared to Skeletal muscle?

Back 53

1/10th compared to Skeletal muscle, even at optimal conditions

Front 54

What two characteristics of Smooth muscle result in a much slower contraction and a greater economy of energy usage?

Back 54

1/10th the use of Myosin ATP-ase (compared to skeletal muscle).

Lower numbers of Myosin filaments.

Front 55

How long does it take for Smooth muscle to begin to contract after being excited?

Back 55

50-100ms

Front 56

How long does Smooth muscle remain contracted for?

Compared to Skeletal muscle, how much longer is this?

Back 56

1-3 seconds

30x longer than a single skeletal muscle contraction

Front 57

How much less of the energy cost can Smooth Muscle maintain the same tension of contraction as a Skeletal Muscle?

Back 57

Less than 1% of the energy cost

Front 58

Why is it extremely important for Smooth muscle to have the ability to maintain tension for a prolonged period while using relatively small amounts of ATP?

Back 58

Overall body Homeostasis is dependent on this.

Front 59

What organs/vessels are routinely called on to maintain a moderate degree of contraction (WITHOUT FATIGUING) day in and day out?

What is the term for this tonic contraction of Smooth muscle?

Back 59

Small Arterioles
Other Visceral organs

The term for tonic contraction of smooth muscle is called: Smooth Muscle Tone.

Front 60

Can Smooth muscle generate adequate ATP to support its contractile activity, even in the absence of oxygen?
Why or why not?

Back 60

Yes.
Because the energy requirements of smooth muscle are low, most ATP synthesis can occur via anaerobic pathways.

Front 61

Are the events leading to the activation of smooth muscle by a neural stimulus the same as of skeletal muscle?

Back 61

Yes, identical

Front 62

What is the difference when a Smooth muscle is innervated by a neurotransmitter as opposed to Skeletal muscle?

Back 62

When skeletal muscle is innervated by a somatic nerve ending, it always releases ACh, which ALWAYS excites the skeletal muscle.

A smooth muscle can be innervated by a nerve fiber and be stimulated or inhibited.

Front 63

What is "coupling" referring to in muscle contraction?

Back 63

The binding of neurotransmitter molecules to membrane receptors COUPLED to the release of calcium ions into the sarcoplasm.

Front 64

What do all Somatic nerve endings release?

Back 64

Acetylcholine

Front 65

What does the effect of a given neurotransmitter on a given type of smooth muscle depend on?

Back 65

The type of receptor molecules (stimulatory or inhibitory) on the smooth muscle sarcolemma.

Front 66

What is the effect of ACh binding to ACh receptors on smooth muscle cells in the bronchioles?

What is the effect of Norepinephrine binding to Norepinephrine receptors on the same smooth muscle cell?

Back 66

ACh = Excitatory: Strong contraction in the Bronchioles

Nor = Inhibitory: Dilating the air passages

Front 67

What is the effect of Norepinephrine binding to smooth muscle in the walls of most blood cells?

Back 67

Excitatory, constriction of the vessels

Front 68

What is the alternate mechanism for Smooth muscle cells who receive no Neural stimulation at all?

Back 68

Spontaneous depolarization or respond to chemical stimuli.

Front 69

Can the same smooth muscle respond to both neural and chemical stimuli?

Back 69

Yes

Front 70

What are the 4 chemical factors that can promote smooth muscle contraction or relaxation without an action potential (enhancing Ca2+ ion entry)?

Back 70

1. The presence of certain hormones
2. Lack of Oxygen
3. Excess CO2
4. Low pH

Front 71

What is most responsible for maintaining Smooth Muscle tone, and can cause changes in smooth muscle activity according to local tissue needs?

Back 71

The direct response of Smooth muscle to CHEMICAL stimuli.

Front 72

Give an example to show how the direct response of smooth muscle to chemical stimuli is most responsible for changes in its activity according to local tissue needs.

Back 72

The presence of the hormone Gastrin in the stomach increases contractile activity of the smooth muscle so that it can more efficiently churn foodstuffs.

Front 73

How do Skeletal or Cardiac muscle respond to stretch?
How about Smooth muscle?

Back 73

Vigorous contractions for Skeletal and Cardiac muscle.

Smooth muscle also responds by contracting, which automatically moves substances along an internal tract.

Front 74

What is the mechanism called when a Smooth muscle contracts and the tension returns to its original level, allowing a hollow organ to become filled or expand slowly to accommodate an increased internal volume without promoting expulsive contractions?

Back 74

Stress-Relaxation Response

Front 75

The ability for hollow organs to be able to store their contents temporarily is due to what characteristic of smooth muscle?

Back 75

Stress-Relaxation Response

Front 76

The time needed for digestion and absorption of nutrients is available due to what characteristic of smooth muscle?

Back 76

Stress-Relaxation Response

Front 77

What allows for urine storage until excretion is appropriate?

Back 77

Stress-Relaxation Response

Front 78

What is the region spanning the length of the Myosin (thick) filaments?

Back 78

A-Band

Front 79

What is the region spanning the area between the free ends of the Actin (thin) filaments?

Back 79

H-Zone

Front 80

What is the region of the center of the sarcomere?

Back 80

M-Line

Front 81

The region between two Z-disks is called?

Back 81

The Sarcomere

Front 82

What is one end of the Actin myofilament attached to?

Back 82

Z-Disk