Muscle Summary

Question 1

Location

Answer 1

Skeletal – mostly attached to skeleton but also to other muscles
Smooth – walls of hollow organs, blood vessels
Cardiac- heart

Question 2

Function: Develop force and shorten for…

Answer 2

Skeletal – movement, posture, heat production
Smooth – varies with structure involved
Cardiac – pumps blood out of heart

Question 3

Initiation of contraction

Answer 3

Skeletal – exclusively neural (neuromuscular transmission)
Smooth – myogenic (pacemaker), neural, hormonal, local mediators
Cardiac- myogenic (pacemaker)

Question 4

Role of innervation

Answer 4

Skeletal – initiate contraction
Smooth – can initiate / modify contraction
Cardiac – modify conduction/contraction

Question 5

Innervation and level of control

Answer 5

Skeletal – somatic nerves, conscious / subconscious regulation
Smooth – autonomic nerves / involuntary
Cardiac – autonomic nerves / involuntary

Question 6

Muscle cells electrically coupled (gap junctions) (Unitary)

Answer 6

Skeletal – NO
Smooth – Varies (unitary versus Multiunit)
Cardiac – YES (within each chamber)

Question 7

Mechanism of contraction

Answer 7

Skeletal – sliding-filament mechanism
Smooth – sliding filament mechanism
Cardiac - sliding filament mechanism

Question 8

Presence of thick (myosin) and thin (actin) filaments

Answer 8

Skeletal – YES
Smooth – YES
Cardiac – YES

Question 9

Presence of troponin / tropomyosin

Answer 9

Skeletal – YES

Smooth – tropomyosin only Cardiac- YES

Question 10

Presence of T-tubules

Answer 10

Skeletal – YES
Smooth – NO
Cardiac – YES

Question 11

Crossbridges cycling turned “on” by calcium

Answer 11

Skeletal – YES (thin filament control)
Smooth – YES (thick filament control)
Cardiac- YES (thin filament control)

Question 12

Source of cytosolic calcium

Answer 12

Skeletal – sarcoplasmic reticulum (SR)
Smooth – Extracellular fluid + SR
Cardiac – Extracellular fluid + SR

Question 13

Nature of “calcium sensor” for contraction

Answer 13

Skeletal – Troponin
Smooth – Calmodulin
Cardiac- Troponin

Question 14

Activation of cross-bridge cycling

Answer 14

Skeletal – Ca2+ binding to troponin / removal of interaction block between myosin and actin
Smooth – Ca2+ binding to calmodulin / Activation of myosin light chain kinase and phosphorylation of myosin light chain
Cardiac – Ca2+ binding to troponin / removal of interaction block between myosin and actin

Question 15

Termination of contraction

Answer 15

Skeletal – Breakdown of Acetylcholine / re-uptake of Ca in SR
Smooth – Decrease sarcoplasmic Ca / Myosin light chain phosphatase
Cardiac- Repolarization / Decrease sarcoplasmic Ca

Question 16

Metabolism

Answer 16

Skeletal – oxidative / glycolytic Smooth – dominantly glycolytic
Cardiac – Dominantly oxidative

Question 17

Regulation of Force

Answer 17

Skeletal – Frequency of stimulation and motor unit summation
Smooth – Balance of Myosin light chain kinase and phosphatase activity
Cardiac- Regulation of calcium entry

Question 18

Contraction speed / Energy usage

Answer 18

Skeletal – FAST / 20% BMR (rest)
Smooth – SLOW / 1-2% BMR (economical)
Cardiac – INTERMEDIATE / 10% BMR

Question 19

Primary function of all muscles

Answer 19

generate force or movement in response to a physiological stimulus

Question 20

generate force or movement in response to a physiological stimulus

Answer 20

• depends on the conversion of chemical energy (ATP)