Lecture 7

Question 1

skeletal muscle characteristics

Answer 1

voluntary movement, transverse striations, nuclei on side, myofibrils regularly arranged -> ring pattern

Question 2

cardiac muscle characteristics

Answer 2

involuntary, can’t contract continuously (relaxation is needed), initiate their own contraction, transverse striation, intercalated disks, nuclei in middle

Question 3

smooth muscle characteristics

Answer 3

not consciously controllable -> visceral musculature

Question 4

how do we call the muscle cell, the cell membrane, the cytoplasm and the endoplasmic reticulum ?

Answer 4

muscle fiber, sarcolemma, sarcoplasm, sarcoplasmic reticulum

Question 5

describe the composition of a skeletal muscle

Answer 5

connective tissue, blood vessels, nerves, muscle fascicles composed of muscle fibers (cells)

Question 6

describe the composition of a muscle fiber

Answer 6

multiple nuclei, sarcoplasm, sarcolemma and T-tubules -> linked to the sarcoplasmic reticulum.

In the sarcoplasm : myofibrils, mitochondria, glycogen granules

Question 7

what is the role of sarcoplasmic reticulum ?

Answer 7

storage of Ca2+

Question 8

composition of myofibrils (and roles)

Answer 8

1) actin (thin)
2) troponin : ca2+ bindind site
3) tropomyosin : shifts to expose myosin binding site on actin
4) myosin (thick)
5) titin : keeps myosin parallel, prevents overstretching
6) nebulin : keeps actin parallel

Z disks at the border of sarcomere

Question 9

structure of actin filament

Answer 9

spherical actin molucules (G-actin) aggregate into two bead string-like chains, helically coiled around eachother

Question 10

structure of myosin filament

Answer 10

schaft and head (all heads on the extremities).
On the head : actin binding site, ATPase with different rates

Question 11

role of T-tubules ?

Answer 11

bring the action potentials into interior of muscle fiber

Question 12

contraction cycle

Answer 12

1) Ca2+ concentration increases (due to AP) which releases P from ADP+P
2) myosin head binds to actin
3) ADP is released and myosin head pulls actin inwards
4) ATP binds to head and head detaches
5) ATP is hydrolyzed into ADP+P

Question 13

what is the motor end plate ?

Answer 13

region of muscle membrane that contains high concentrations of ACh receptors

Question 14

What is the only neurotransmitter at neuromuscular junctions ? name of the receptor ?

Answer 14

acetyl choline (ACh)
Nicotinic receptor (causes Na+ influx)

Question 15

property of the AP of motoneurons ?

Answer 15

always generate a subthreshold excitatory postsynaptic potential at the neuromuscular endplate (travels into T-tubules)

Question 16

what converts AP into Ca2+ release ? what happens with Ca2+ in the end ?

Answer 16

DHP receptor opens RyR release channels in sarcoplasmic reticulum (SR).

Sarcoplasmic Ca2+-ATPase pumps Ca2+ back into SR. Even during relaxation, we consume ATP !

Question 17

What are the 3 skeletal muscle fiber types and what do they look like ?

Answer 17

1) Red muscle fiber (type I) : slow twitch -> endurance. Red because more mitochondria. The muscle has more type I fibers than IIs.

2) Type IIa intermediate

3) White muscle : type IIx, fast twitch : maximum force (less mitochondria because anaerobic processes).

Question 18

Force and fatiguability of the three fiber types

Answer 18

Force : type IIx > type IIa > type I

Fatiguability : type IIx > type IIa > type I (never fatigues)

Question 19

tyo types of muscular contractions

Answer 19

1) isotonic : muscle shortens -> moves the load

2) isometric : muscle does not shorten -> not enough force to move load

Question 20

two types of smooth muscle

Answer 20

1) single unit smooth muscle cells (small intestine) : cells are connected by gap junctions -> contract as single unit

2) multi-unit smooth muscle cells (eye) : not electronically linked -> each one must be stimulated independently