Transcript Muscular System GR Answers

Muscular
System G.R.
Answers
Chapter 12
1.
Arrange these skeletal system components in order,
from outermost to innermost: sarcolemma, connective tissue
sheath, myofilaments, myofibrils

Connective Tissue
– Sarcolemma
 Myofibrils
–Myofilaments
2. Why are the ends of the A band the
darkest region off the sarcomere when
viewed under a light microscope?
 That
is the region where
there is overlap between
the thick and thin
filaments.
3. What are the characteristics of the
three types of muscles in the human
body? Where is each type found?

Skeletal: Striated, multi-nucleated,
voluntary movements
– Attached to skeleton

Cardiac: Striated, branched,
intercalated disks, uni-nucleated,
involuntary
– Walls of heart

Smooth: non-striated, stacked, uninucleated, involuntary
– Walls of internal organs
4. What are the microscopic levels of
structure in a skeletal muscle?



Thick Filaments: myosin chains
Thin Filaments: actin
Sarcomere: contractile unit (Z-disk - Zdisk)
– I-Band: thin filaments only
– H-zone: thick filaments only
– A-band: entire length of thick filaments
– Z-Disk: attachment site for thin
filaments
– M-Line: attachment site for thick
filaments
5. How does contraction of a
skeletal muscle come about?

Initiated by Motor Neuron synapsing at
neuromuscular junction.
– ACh is released and binds to receptor of
sarcolemma
– Action potential travels down sarcolemma and Ttubules
– DHP receptors (voltage-sensitive) trigger
Calcium release from S.R.
– Ca2+ binds to troponin, opening up binding site
for myosin head, leading to Power Stroke:
 ATP hydrolyzed, Myosin head attaches to
actin, ADP and Pi released power stroke
occurs pulling the actin filaments.
6. What is the role of ATP in
muscle contraction?



ATP is the energy source for the power
stroke.
When ATP is hydrolyzed it produces
potential energy that powers the
movement of the myosin head.
ATP binding to myosin causes the
myosin head to return to resting position
7. Compare and contrast the different
ways our muscle cells produce ATP.


1. Creatine Phosphate
– Anaerobic
– Creatine phosphate broken down to produce
ATP
– Short-term high intensity exercise (5 secs)
2. Fermentation
– Glucose broken down to Lactate
anaerobically
– 2 ATP produced per glucose
– Glycogen is broken down to produce the
glucose
– Fast-acting

3. Cellular Respiration
– Aerobic
– Oxygen delivered to Mitochondria via
myoglobin
– Glucose comes from either stored
glycogen, glucose from blood, and/or
fatty acids from fat digestion.
– 32 ATP produced per glucose!!
– Slower acting
8. How are slow-twitch and fast-twitch
designed to perform their respective
roles?

Fast Twitch:
– Motor units with many fibers
– Anaerobic = explosions of energy, but
fatigue easily
– Strength
– Pump Ca2+ into S.R. more quickly =
faster twitches

Slow-Twitch
– Large amounts of myoglobin (an
oxygen-transport protein to the
mitochondria)
– Large amounts of mitochondria
– Aerobic respiration
– High resistance to fatigue
– Used for posture and endurance sports
9. Describe the sliding filament model of muscle
contraction within a sarcomere. Begin with nerve
impulses and end with the relaxation of the muscle.




Refer back to earlier question of Calcium
exiting S.R. and binding to troponin, which
moves tropomyosin and allows myosin to
bind to actin.
ATP is hydrolyzed, myosin head binds to
actin
Power Stroke: Myosin head pulls actin
towards the M-Line; ADP and Pi are released
ATP binding causes myosin head to return to
resting rate.