skeletal muscle structure and function

Question 1

__ muscle is multi-nucleated

Answer 1

skeletal

Question 2

___ muscle has intercalated discs

Answer 2

cardiac

Question 3

Name the general features of skeletal muscle

Answer 3

Voluntary control, striated, triads with t tubules, long multinucleated cells

Question 4

4. Describe the organization of muscle from deep to superficial

Answer 4

-Muscle fibrils are bundled together and surrounded by endomysium to form a muscle fiber

-Muscle fibers are bundled together and surrounded by the perimysium to form a fascicle

-Fascicles are bundled together and surrounded by the epimysium to form a muscle structure

Question 5

Name the major components of a sarcomere

Answer 5

z discs, A band, I band, H zone, M line

Question 6

what is found in the I band?

Answer 6

thin filaments

Question 7

what is found in the A band?

Answer 7

thick and thin filaments

Question 8

what is found in the H zone?

Answer 8

thick filaments

Question 9

what is the M line?

Answer 9

myomesin that stabilizes thick filaments

Question 10

what is the function of desmin?

Answer 10

ties the sarcomere to the sarcolemma via z discs

Question 11

what is the function of titin

Answer 11

stabilizes thick filaments by connecting z disc to M line

Question 12

what connects thin filaments to the z disc?

Answer 12

alpha actinin

Question 13

what is the function of tropomyosin?

Answer 13

regulates muscle contraction by covering the actin-myosin binding site

Question 14

Describe the functions of the 3 tropnin types

Answer 14

TnT: attaches to tropomyosin
TnC: binds calcium
Tnl: regulates myosin-actin interaction

Question 15

Describe the process of a muscle contraction in a sarcomere

Answer 15

-Calcium binds to TnC and actin binding site is exposed

-Myosin binds actin and ATP

-Hydrolysis of ATP occurs and the head cranks. This causes the sctin filaments to slide toward the center

-The ADP and Pi are released and a new ATP binds, releasing the myosin head and allowing the muscles to release from their contracted position

Question 16

The ATP binding site is located on ___

Answer 16

the myosin head

Question 17

Describe the molecular processes involved during excitation-contraction coupling
by which an action potential of a ventral motor neuron in the spinal cord leads to
contraction of a skeletal muscle

Answer 17

-Action potential causes a release of Ach at the synaptic cleft, which then binds to receptors at the motor end plate of the sarcolemma.

-The generated depolarization spreads along the t tubule

-Calcium ions release from terminal cisternae and into the sarcoplasm

-Calcium binds TnC and actin binding site is exposed

-Cross-cycling occurs

Question 18

each muscle fiber is innervated by ___ neuron(s)

Answer 18

one

Question 19

What is an innervation ratio? What is the significance of this?

Answer 19

The number of muscle fibers innervated by a single neuron; lower rations allow for finer movements, while larger ratios allow for bulkier, forceful movement

Question 20

What are the components of a motor end plate?

Answer 20

Synaptic vesicles, synaptic cleft, and postsynaptic membrane

Question 21

Describe DHPR and RYR receptors

Answer 21

DHPR are receptors in the membrane of t tubules. ATP spreading down the T tubules causes a conformational change in DHPR, which causes a mechanical opening of the RYR receptors in the cytoplasm. This allows calcium out of the sarcoplasmic reticulum.

Question 22

what is calsequestrin?

Answer 22

a calcium binding protein in the terminal cisternae that stores calcium. this causes relaxation of muscle

Question 23

what is Sarcalumenin

Answer 23

a calcium binding protein that aids SERCA by sequestering the calcium near the pump

Question 24

describe SERCA

Answer 24

ATPase in the sarcoplasmic reticulum that pumps calcium into the terminal cisternae to sequester calcium

Question 25

Describe the features of slow and fast twitch muscles.

Answer 25

Slow motor units: resisting gravity, sustained movement, posture
Fast oxidative motor unit: sustained locomotion
Fast glycolytic motor unit: burst power

Question 26

Describe the two modes of growth for skeletal muscle

Answer 26

Hypertrophy: seen in strength training; increase in size of cells

Hyperplasia: seen in endurance training; increase in number of cells