Chapter 11.5 - Muscular System Flashcards
Where is smooth muscle found
walls of our organs, airways, blood vessels
Smooth muscle is not:
striated
smooth muscle contracts and relaxes:
involuntarily
What gives muscles a striated appearance?
sarcomeres
cardiac muscle contracts and relaxes:
involuntarily
cardiac muscle has __ nucleus/nuclei per cell
1 nucleus
Which muscles are striated?
skeletal and cardiac
Which muscle contains intercalated discs?
cardiac cells
Intercalated discs contain:
desmosome and gap junction
Gap junction allows for:
cells can pass ions quickly allowing heart to depolarize and contract in unison
skeletal muscle cells are:
long, multinucleated, striated
Smallest to largest unit of skeletal muscle
myofibril –> muscle fiber –> fascicles –> muscle
protective sheath encasing the muscle fiber:
sarcolemma
Cytoplasm of muscle fiber
sarcoplasm
Epimysium
The most superficial sheath. Covers the muscle itself
Perimysium
Covers the muscle fascicles
Endomysium
the deepest sheath, covers muscle fibers
Myofibril contain many repeating units called:
sarcomeres
Functional unit of muscle fibers
sarcomeres - shorten to faciliatte muscle contraction
Neuromuscular junction
space between the presynaptic motor neuron and postsynaptic muscle fiber
When a motor neuron sends an action potential, it releases ___ into the ___ ___
acetylcholine; neuromuscular junction
Steps to transfer action potential to muscle
- acetylcholine released at neuromuscular junction, binds to voltage gated Na+ channels
- graded potential created (small depolarization)
- opens more Na+ channels
- creates action potential in muscle
T-tubules
invaginations in the sarcolemma - allow the action potential initiated on the muscle fiber to spread throughout the cell very quickly, ensuring a coordinated contraction
Muscles contract across:
a joint
Muscles __ the bone they ___ upon closer to the bone they ____ from
pull; insert; originate
Muscle contraction is always:
a pull motion
The sarcolemma is:
muscle fiber’s cell membrane
sarcomeres contain:
array of long filament proteins (myofilaments)
Examples of myofilaments
thin actin filaments, thick myosin filaments
neuromuscular junction
space between the presynaptic motor neuron and postsynaptic muscle fiber
Which NT is released by a motor neuron?
Acetylcholine
What does acetyl choline do once it is released by motor neuron?
creates graded potential - facilitates the opening of ligand gated sodium channels on the muscle fiber
Invaginations in the sarcolemma
T-tubules
Sarcoplasmic reticulum
specialized ER that stores calcium ions in muscle fibers
What causes voltage gated Ca2+ channels to open?
Depolarization traveling across T-tubules
When Ca2+ is released, it travels from ___ to ___
sarcoplasmic reticulum; sarcoplasm
actin’s binding site for myosin is covered by:
tropomyosin
Tropomyosin is held in place by
troponin
How does tropomyosin move away from myosin binding site?
Ca2+ in sarcoplasm binds to troponin
Troponin has _ binding sites:
3; A, C, T
troponin A site
binds actin
troponin C site
binds Ca2+
troponin T site
binds tropomyosin
How does myosin form cross bridge?
hydrolyzes ATP to extract energy, enters high energy state to bind to actin forming cross bridge
What happens when myosin releases ADP and Pi?
power stroke
rigor mortis
happens in dead animals, no ATP being produced –> myosin released from actin –> maintains contraction
Z line
periphery (ends) of each sarcomere
M line
midpoint of each sarcomere
I bands
areas where only actin is present (including where Z line is)
A bands
areas where myosin and actin overlap
H zone
where only myosin is present
Which band does not shorten during muscle contraction?
A band
Small motor units
few muscle fibers, innervated by single motor neuron
Precision movements are created by:
small muscles containing many motor units
large motor units have:
many muscle fibers, innervated by one motor neuron
How are powerful movements created? (how many motor units)
large muscles with few motor units
What is a twitch contraction?
brief contraction a muscle fiber experiences as the result of a single action potential stimulating an entire motor unit
All-or-none principle of muscle contraction
Either the depolarization is above threshold in which all fibers twitch, or it is below threshold and none twitch
Phases of twitch
latent; contraction; relaxation
Muscle fiber types
- slow oxidative fibers
- fast oxidative-glycolytic fibers
- fast glycolytic fibers
___ fibers have the slowest acting myosin ATPase
Type I
Type I fibers = ___
slow oxidative fibers
Type II-a fibers:
Fast oxidative-glycolytic fibers
type II-b fibers
Fast glycolytic fibers
Describe slow oxidative fibers
- small diameter (weak contractions)
- dark red
- aerobic respiration
- efficient
- resistant to fatigue
Describe fast oxidative glycolytic fibers
- intermediate diameter
- dark red
- an/aerobic respiration
- reasonably efficient but susceptible to fatigue
Describe fast glycolytic fibers
- white
- anaerobic respiration
- strongest contractions
- somewhat inefficient, fatigues quickly
True or false: since twitch will always be the same size, overall force of contraction remains the same
false - contraction varies due to wave summation/ motor unit summation
wave summation
refers to the process of depolarizing muscle fibers in a motor unit again during their relaxation period
Tetanus
process where the muscle fibers of a motor unit are being maximally stimulated by a motor neuron and tension can no longer increase
Tetanus usually happens when:
sending action potentials down a motor neuron with such a high frequency that we don’t experience any relaxation
Motor unit summation affects force of contraction because:
action potentials are traveling to different motor units at different times
Muscle tone (tonus)
due to weak and involuntary twitches of small groups of motor units within a muscle, due to a continuous output of action potentials from the brain and spinal cord
True or false: continuous muscle tonus causes fatigue
False - we never feel fatigued by our tonus because different motor units of a muscle are being stimulated at different times
Which muscle has no inherent muscle tone?
cardiac muscle tone
Hypotonicity
muscles lose tone and thus feel flaccid. occurs as the result of damage to PNS/reduced electrolytes
hypertonicity
when muscles gain tone and thus feel spastic and rigid; occurs as the result of damage to the central nervous system.
