Muscle Physiology

Question 1

Types of muscle

Answer 1

Striated and smooth. Cardiac and skeletal are types of striated muscle.

Question 2

Skeletal muscle properties

Answer 2

multinucleated, muscle fibers may be centimeters long and 50 micrometers in diameter, have myofibrils that give striated appearance.

Question 3

Describe regions of striated cell (parts of a myofibrils, bands)

Answer 3

The A band in the region of thick filaments. The Z disk is a line where the thin filaments attach. The H zone is composed of ONLY thick filaments. Thick filaments attach to the M-line. The I-band is composed of only thin filaments (and the Z-line).

Question 4

True or False: Thin filaments shorten during contraction of the muscle.

Answer 4

False. Neither thick or thin filaments shorten. The sarcomere shortens because the filaments slide past each other. However, the H zone and I band do shorten.

Question 5

Thick filaments are composed of ___.

Answer 5

Myosin

Question 6

Components of thin filaments

Answer 6

actin, tropomyosin, and troponin

Question 7

Describe the process of muscle contraction

Answer 7

ATP causes the globular head of myosin to pivot where it connects to the fibrous tail. Actin combines with the myosin and the stored energy in the myosin is released. When this happens, the globular head pivots back to its normal position. Tropomyosin blocks the binding site on actin when the muscle is resting. When calcium binds to troponin, it moves tropomyosin so that the site opens up.

Question 8

Flow of calcium in a muscle

Answer 8

Calcium is stored in the sarcoplasmic reticulum. ATP-dependent calcium pumps pump calcium into the sarcoplasmic reticulum. Calcium is released via Calcium-dependent channels (the positive feedback ensures that a large quantity of calcium is released at once). Where transverse tubules meet the sarcoplasmic reticulum, voltage activated calcium channels in the plasma membrane (T tubule) are linked to calcium-induced calcium-release channels in the sarcoplasmic reticulum.

Question 9

True or false: The sarcoplasmic reticulum is continuous with the plasma membrane of the muscle fiber.

Answer 9

False.

Question 10

What is the main difference between cardiac muscle and skeletal muscle (besides the branching)?

Answer 10

Gap junctions are present in cardiac cells (at the intercalated disks)

Question 11

How hormone receptors in smooth muscle work

Answer 11

External hormonal signals are detected by specific receptor molecules in the membrane. This causes hydrolysis of phosphatidyl inositol bisphosphate (a component of membrane phospholipids) into IP3 (inositol triphosphate). IP3 binds to the calcium release channel in the sarcoplasmic reticulum membrane to release calcium.

Question 12

True or false: Tropomyosin is present in smooth muscle.

Answer 12

True

Question 13

True or false: Troponin is present in smooth muscle.

Answer 13

False

Question 14

In smooth muscle, contraction is caused by _____, which is catalyzed by ____. Contraction is reverse by ____.

Answer 14

The phosphorylation and dephosphorylation of myosin (similar to striated cells still),
myosin light chain kinase,
myosin light chain phosphatase

Question 15

Myosin light chain kinase is regulated by ____.

Answer 15

Calmodulin (a calcium binding protein)

Question 16

Twitch

Answer 16

The brief contractile response of a muscle to a single maximal volley of impulses in the nerve supplying it. It outlasts the duration of the action potential. (10-100 ms)

Question 17

Tetanus

Answer 17

At sufficiently high stimulus frequencies, twitches fuse to generate a steady level of force (which is tetanus)

Question 18

The motor unit types

Answer 18

Slow, Fast fatigue-resistant, fast fatigable

Question 19

Slow fibers

Answer 19

contract slowly and have a small peak force, highly resistant to fatigue during prolonged activation

Small somas and dendritic trees, small-diameter axons, low conduction velocities. Relatively long after-hyperpolarizations

Question 20

Fast fatigable fibers

Answer 20

Can produce large twitch forces rapidly but fatigue quickly. Large somas, dendritic trees, and axons and high conduction velocities. Action potentials followed by short after-hyperpolarizations

Question 21

Ways to increase force of contraction

Answer 21

Recruit more motor units, increasing the rate of firing of individual units

Question 22

Order of recruitment of motor units

Answer 22

Slow, fast fatigue-resistant, fast fatigable. This ordering is known as the size principle

Question 23

Normal firing rate of a neuron

Answer 23

8-25 Hz

Question 24

Malignant hyperthermia and it’s affect on muscles

Answer 24

It causes uncontrolled muscle contraction from hereditary defect of ryanodine receptors (which causes calcium to build up in the skeletal muscle)
It is treated with dantrolene sodium, which works on the ryanodine receptor to prevent calcium release.
It is a genetic disease that is (autosomal?) dominant.

Question 25

What is myotonic dystrophy?

Answer 25

It is a form of muscular dystrophy. It is an autosomal dominant mutation resulting in decreased chloride channels in muscle and delayed repolarization. It is treated with quinine or newer anti-arrhytmia drugs. (Treats the myotonia only)