skeletal/cardiac/smooth muscle

Question 1

skeletal and cardiac muscle cells are sometimes called striated muscles. true or false?

Answer 1

true

Question 2

structure of skeletal muscle cell:

Answer 2

long, thin, cylindrical and contains many nuclei; ranging from a few millimeters to 10cm or more.

Question 3

individual muscle fibers are embedded in connective tissue called the:

Answer 3

endomysium

Question 4

Groups of muscle fibers are bound together by connective tissue called the:

Answer 4

perimysium

Question 5

cardiac muscle consists of individual cells lined together by junctions called:

Answer 5

intercalated discs

Question 6

How is cardiac muscle cell different from skeletal muscle cell?

Answer 6

cardiac muscle is made up of many individual cells linked together by an intercalated disc and electrically coupled via gap junctions. they have generally single nucleus.

Question 7

The process by which a muscle action potential triggers a contraction is known as:

Answer 7

excitation-contraction coupling

Question 8

which one, troponin or tropomyosin is lifted first as a result of incoming action potential?

Answer 8

troponin

Question 9

When ATP levels fall to zero after death, the cross-bridges between the actin and myosin do not dissociate. The muscles lose their plasticity and become stiff, a state known as:

Answer 9

rigor mortis

Question 10

The response of a muscle to a single stimulus is called:

Answer 10

muscle twitch

Question 11

describe slow twitch muscle fibers

Answer 11

they are the type 1 muscles. they are able to contract at about 15 mm/s and relax relatively slowly. the type 1 fibers are thin and rich in both mitochondria and the oxygen-binding protein myoglobin. This gives them the reddish appearance. They rely on mainly oxidative metabolism of fats for their energy supply and, as they have a copious blood supply, they are very resistant to fatigue. They are activated by their motor neurons at a continuous, steady rate, which enables them to maintain a steady muscle tone so enabling them to perform maintenance of posture.

Question 12

describe fast twitch muscle fibers

Answer 12

Fast muscles have a predominance type 2 muscle fiber. They shorten rapidly and relax relatively quickly. type 2A fiber are fast oxidative glycolytic fibers which have a high myosin ATPase activity compared to the slow fibers, they are relatively thin, have a good blood supply and are rich in both mitochondria and myoglobin. they are relatively resistant to fatigue and rely on oxidative metabolism and utilize either glucose or fats as their source of energy.
Type 2B muscle fibers are fast glycolytic fibers with a large diameter. they have a high myosin ATPase activity contain large quantities of glycogen and have high concentrations of glycolytic enzymes. This enables type 2B fibers to develop great tension rapidly. They have few blood supply, few mitochondria and little myoglobin, they are easily fatigued. They are therefore well adapted to provide short periods of high tension development during anaerobic exercise. Their lack of mitochondria and myoglobin gives them pale appearance.

Question 13

What is isometric force?

Answer 13

if a muscle contracts against a load which prevents shortening

Question 14

what is isotonic force?

Answer 14

if a muscle shortens against a constant load

Question 15

How do we determine the work of a muscle?

Answer 15

By the distance it is able to move a given load and the power of a muscle is the rate at which it performs work.
power= forceXvelocity

Question 16

Describe the force-velocity relationship

Answer 16

The maximum force is developed during an isometric contraction but maximum speed of shortening occurs in a unloaded muscle. Maximum power is developed when the muscle shortens at about one-third of maximum velocity. When a muscle shortens isometrically, it does no external work as the load is not moved through a distance. Consequently, no power is developed (its x axis is 0) Equally, if the muscle contracts while it is not acting on an external load, no work is done and no power is developed. In between these two extremes, the muscle performs useful work and develops power.

Question 17

what kind of nerve fibers innervate skeletal muscles

Answer 17

myelinated nerve fibers

Question 18

What sets the heart rate (HR)?

Answer 18

the pacemaker cells at the SA node

Question 19

In disease states, myocytes in other parts of the heart can slow pacemaker activity which causes irregular beating of the heart known as:

Answer 19

arrhythmia

Question 20

How does the cardiac myocytes maintain the long duration of action potential?

Answer 20

cardiac action potentials are between 150-300 ms in duration. This has important consequences for the contractile response for cardiac muscle. Cardiac myocytes may either have rapidly activating action potentials for atrial fibers and ventricular fibers or slowly activating action potentials for the myocytes of the SA node.

Question 21

What is the action potential like in the Purkinje fibers?

Answer 21

The AP in purkinje fibers form the conducting system of the ventricles and have similar appearance to those of ventricular fibers while those of the AV node have an appearance similar to those of SA node.

Question 22

the resting membrane potential of atrial and venticular myocytes in determined mainly by the:

Answer 22

permeability to potassium ions of the membrane

Question 23

What is the most negative voltage of the membrane potential of cells in the SA node after an AP?

Answer 23

-60 mV

Question 24

The slow depolarization that precedes the action potential is known as the:

Answer 24

pacemaker potential; and the rate at which it falls towards threshold is an important factor in setting the heart rate.

Question 25

How do nerves and hormones alter the HR?

Answer 25

• they may hyperpolarize the membrane of the SA node cells e.g. inhibition following brief stimulation of the vagus nerve.
• they may change the slope of the pacemaker potential e.g. during stimulation of the cardiac sympathetic nerves
• they may both hyperpolarize the membrane and change the slope of the pacemaker potential

Question 26

activation of action potential in different types of cells:

Answer 26

upstroke of the AP is due to a rapid increase in the permeability of the membrane to sodium ions similar to that seen in nerve axons and skeletal muscle fibers. The initial rapid phase of repolarization is due to inactivation of these sodium channels and to the transient opening of potassium channels. The long phase, plateau phase, of depolarization is due to slowly activating calcium channels, which increase the permeability of the membrane o calcium ions. As these calcium channels progressively inactivate, the membrane repolarizes and assumes a value close to the potassium equilibrium potential.

Question 27

The upstroke of the AP in SA node cells is caused by a large increase in the permeability of the membrane to what ions?

Answer 27

calcium. not sodium ions as is the case for the myocytes of the atria and ventricles

Question 28

Cardiac muscles cannot be tetanized. Why?

Answer 28

A second AP cannot occur until the first has ended and since the mechanical response of the cardiac muscle largely coincides with the AP. The heart needs to relax fully between beats in order to allow time for filling.

Question 29

Explain the CICR or calcium induced calcium release.

Answer 29

calcium activates the contractile machinery of cardiac muscle. If the heart is placed in a solution lacking calcium, it will stop beating. In the cardiac muscle, the rise in calcium ions within in myocyte during the plateau phase of the AP is mainly derived from the calcium store within the sarcoplasmic reticulum. The AP causes L type voltage gated calcium channels to open and the resulting calcium influx activates calcium release channels to open and the resulting calcium influx activates calcium release channels. Once these channels are open, much of the ions are rapidly released.

Question 30

which pump takes up calcium ions back into the sarcoplasmic reticulum?

Answer 30

the Ca2+ -ATPase metabolic pump

Question 31

What happens when there is a great load of venous return?

Answer 31

the ventricular muscle will stretch to a greater degree as more blood comes in and the muscles will have to contract at a greater force. This is the Starling law of the heart. This ensures that the heart will pump out all the blood it receives.

Question 32

what happens during exercise when the heart beats faster?

Answer 32

mediated by the sympathetic nerves that innervate the SA node and the ventricles, and by circulating adrenaline (epinephrine) secreted by the adrenal medulla.

Question 33

Change in rate of heart beat is called:

Answer 33

chronotropic effect

Question 34

change in force of contraction is called:

Answer 34

inotropic effect

Question 35

The positive inotropic effect is…?

Answer 35

occurs without any change in the length of the cardiac muscle fibers. The increase in contractility is caused by an increase in calcium influx following activation of the Beta-adrenergic receptors and the subsequent generation of cyclic AMP.

Question 36

What does cyclic AMP do?

Answer 36

activates protein kinase A

Question 37

What does protein kinase A do?

Answer 37

phosphorylates the calcium channels of the plasma membrane. The phosphorylated channels remain open for longer following depolarization and this, in turn leads to an increased calcium influx that results in an increase in the force of contraction.

Question 38

what does the smooth muscle form?

Answer 38

muscle of the internal organs such as the gut, blood vessels bladder and uterus. It forms a heterogeneous group with a range of physiological properties. They perform different properties: during pregnancy they can contract very forcefully but normally they are quiescent.

Question 39

what are the gap junctions in smooth muscle?

Answer 39

two types of junctional contact:

points of close cotact for mechanical coupling and the gap junction for electrical signalling between cells.

Question 40

what do the gap junctions do?

Answer 40

provide eletrical continuity between cells and thus provide a pathway for the passage of electrical signals between cells.

Question 41

describe a single cell of the smooth muscle

Answer 41

Each cell has a single nucleus, is about 2-5 micrometers in diameter at its widest point and is 50-200 micrometers in length. In some tissues such as the alveoli of the mammary gland and the blood vessels, they are lined by a single layer known as myoepithelium. No cross striations under microscope but they still contain actin and myosin. In comparison to skeletal cells, smooth muscles have more actin filaments than myosin filaments.

Question 42

The smooth muscle has an additional intermediate filament. What does it do?

Answer 42

Assist in transmitting the force generated to the neighboring smooth muscle cells and connective tissue.

Question 43

Are there Z lines in the smooth muscle?

Answer 43

No

Question 44

They have dense bodies instead of Z lines. what do these dense bodies do?

Answer 44

they are distributed throughout the cytoplasm and which serve as attachments for both the thin and intermediate filaments.

Question 45

Thin (actin) filaments and intermediate filaments are anchored to the plasma membrane (sarcolemma) at what part?

Answer 45

the dense patches as well as at the junctional complexes between neighboring cells.

Question 46

Is ATP splitting much faster in smooth muscles than skeletal muscle?

Answer 46

no; much slower

Question 47

In smooth muscle of the vas deferens and the gut, the AP depends on mainly the influx of what ions?

Answer 47

calcium ions

Question 48

In smooth muscle of the bladder and ureters depends on an influx of what ions?

Answer 48

sodium, just like in skeletal muscles

Question 49

What is the difference between the plateau phase of smooth muscle and cardiac muscle?

Answer 49

The plateau phase can be prolonged in duration but similar in appearance.

Question 50

Contraction initiation is not by troponin like in the skeletal muscles. How are they excited?

Answer 50

By the myosin light chain kinase in conjunction with calmodulin (calcium binding protein)

Question 51

What does the myosin light chain kinase do?

Answer 51

This enzyme phosphorylates sites on myosin cross-bridges, so inducing
interaction of cross-bridges with actin, and contraction

Question 52

How does the smooth muscle relax?

Answer 52

relaxation occurs after removal of

calcium and is due to dephosphorylation of myosin by a phosphatase.

Question 53

The rhythmic activity of muscles in gastrointestinal tract is controlled, primarily, by “myogenic” (i.e. non neuronal) pacemaker activity. How does this work?

Answer 53

which induces consecutive depolarizations (of 4-10 s duration) and repolarizations that induce series of (relatively short-lasting) action potentials when the depolarizations are sufficiently strong.

Question 54

Examples of certain neurotransmitters and hormones that enhance the activity of the pacemaker depolarization.

Answer 54

acetylcholine and pentagastrin

Question 55

Examples of certain neurotransmitters that slows the depolarization of the pacemaker:

Answer 55

noradrenaline and neurotensin

Question 56

What are the rhythmic contractions in smooth muscles called?

Answer 56

slow waves

Question 57

under which activities does modification of contractile activity occur>?

Answer 57

neuronal input and via hormonal action

Question 58

In muscles of the blood vessels, contraction can occur without much membrane depolarization. This is because:

Answer 58

catecholamine receptors of the cell membrane, when occupied with noradrenaline, cause formation of
second messenger IP3; this, after combining with sites on the S.R., opens calcium channels of
S.R.

Question 59

What is the tone of the smooth muscle?

Answer 59

The steady level of contraction in the smooth muscle of the hollow organs

Question 60

Smooth muscle tone depends on both intrinsic and extrinsic factors. What are these factors

Answer 60

Extrinsic factors include activity of the autonomic nerves and circulating hormones, while intrinsic factors include the slow rate of cross bridge cycling, the response of stretch, local metabolites, locally secreted chemical agents (e.g. nitrous oxide in the blood vessels) and temperature.