Muscle Physiology Flashcards
1
Q
The human body has 3 types of muscle tissue
A
skeletal muscle
cardiac muscle
smooth muscle
2
Q
Elongated cells
•Multiple peripheral nuclei
•Visible striations
•Voluntary
A
skeletal muscle
3
Q
- Branching cells
- Single central nucleus
- Visible striations
- Involuntary
A
Cardiac muscle
4
Q
- Spindle shaped cells
- Single central nucleus
- No visible striations
- Involuntary
A
Smooth muscle
5
Q
bundles of muscle cells
A
Fascicles
6
Q
individual cells
A
muscle fibers
7
Q
arrangement of myofilaments consisting of thick and thin filaments
A
Myofibrils
8
Q
two types of myofilament
A
myosin and actin
9
Q
Muscle fibers
A
muscle cells
10
Q
Sarcolemma
A
cell membrane; also called T-tubule
11
Q
Sarcoplasm
A
cytoplasm
12
Q
Sarcosomes
A
mitochondria
13
Q
Sarcoplasmic reticulum
A
smooth endoplasmic reticulum
14
Q
consists of longitudinal tubules, which release Ca 2+ and terminal cistern, enlarged regions at the end
of the tubules that concentrate and sequester Ca 2+.
A
Sarcoplasmic reticulum
15
Q
pass down into the muscle cell and go around the myofibrils, conduct impulses from the surface of the cell (sarcolemma) to SR.
A
Transverse tubules (T tubules)
16
Q
One T tubule and its two flanking cisternae are called
A
a triad
17
Q
Thin filaments are mainly composed of ______. Thick filaments are mainly composed from _____
A
actin
myosin
18
Q
______ ______ from crossbridges between thick and thin filaments. Each cross-bridge has two sites crucial for muscle contraction: _____ binding site and _____ binding site.
A
Myosin heads
ATP
actin
19
Q
the arrangement of thick and thin filaments forms light and dark alternating bands called ______ along the myofibril.
A
striations
20
Q
A bands are ______
I bands are ______
A
dark
light
21
Q
functional unit of skeletal muscle (Z line to Z line)
A
Sarcomere
22
Q
the proper alignment of filaments within a sacromere is ensured by two proteins:
A
titin (the largest known protein) and nebulin.
23
Q
force created by contracting muscle
A
Muscle tension
24
Q
weight that opposes contraction
A
Load
25
creation of tension in muscle, active process requires energy input from ATP.
contraction
26
release of tension
relaxation
27
summary of muscle contraction
```
events at NMJ
excitation-contraction coupling
Ca signal
contraction-relaxation
muscle twitch or sliding filament theory
```
28
During muscle contraction, each sarcomere _____ as the thin filaments _____ ______ between the thick filaments so that Z lines are pulled closer together.
shortens
| slide inward
29
how does calcium signals initiate contraction
```
Ca level increase in cytosol
Ca binds to troponin
troponin-tropomyosin complex separate
myosin binding site exposed
power stroke
actin filaments move
```
30
what is the molecular basis of contraction
- atp bind to myosin (affinity for actin decrease)
- myosin hydrolysis atp, rotates head & binds to new actin
- Ca signal/power stroke
- myosin releases ADP
31
troponin contains 3 subunits which bind to
Ca
actin
tropomyosin
32
molecules that help align actin
nebulin
33
provides elasticity and stabilizes myosin
Titin
34
actin molecules bind to form _______
helix
35
state where there's a lack of ATP; ATP has been exhausted
rigor mortis state
36
The Action Potential (AP) of a skeletal muscle fiber begins at the_________, where the terminal of a motor neuron contacts and forms a synapse with the muscle fiber.
Neuromuscular Junction (NMJ)
37
what are the steps that occur after action potential is reach which leads to the release of calcium in the cytosol
- AP causes release of Ach into synaptic cleft
- Ach binds to nicotenic receptors
- receptor activation causes opening of channels (Na, K influx/efflux)
- threshold is reached
- AP is then propagated along muscle fiber and -enters t-tubule (invagination)
- allows for electrical transmission inside cell and SR
- DHP receptor changes confirmation when AP reached
- causes ryanodine to open releasing Ca to cytosol
38
how is contraction terminated
SR pumps Ca back to lumen via Ca ATPase decreasing cytosolic Ca
this causes troponin to release Ca and tropomyosin block binding site
contraction ends and muscle fibers relax
39
single contraction-relaxation cycle in a skeletal muscle fiber
Muscle twitch
40
toxic effects of batrachotoxin (BTX)
caused by sustained, irreversible opening of voltage-gated sodium channels of nerve and muscle.
41
non-depolarizing blocker
```
acts as competitive antagonist to nicotinic receptors occupying site of Ach.
Prevents depolarization (channels don't open)
```
42
depolarization
acts on the nicotinic receptor inducing irreversible opening of the channels.
Depolarizes membrane to where muscle fibers become non-responsive to stimulation
43
antibodies affect neurotransmission in 3 ways
- complement
- antigenic modulation (cross linking of receptors increase nicotinic receptor degradation, decreasing # of receptors)
- Ach receptor blocker
44
what are the two phases of the depolarizing blocker
phase 1: depolarizing phase (twitches)
| phase 2: desensitizing phase (full neuromuscular block)
45
succinylcholine
depolarizing blocker; relax skeletal muscles during surgery. It does not relieve pain or produce sedation.
46
interferes with muscle contraction by binding the RyR1 receptor channel and inhibiting Ca2+ release from SR.
Dantrolene
47
Used to treat muscle spasm, associated with spinal cord injuries, stroke, multiple sclerosis or cerebral palsy
Dantrolene
48
dantrolene contains a special application in treatment of _______ ______
malignant hyperthermia
49
a neurologic syndrome caused by a toxic proteolytic enzyme produced by the bacterium Clostridium botulinum - spore-forming, obligate anaerobe found most commonly in soil.
Botulism
50
can result from ingestion of contaminated
| food, colonization of the gastrointestinal tract in an infant, or wound infection
Botulism
51
major steps in botulinum toxin action
- enters lumen of digestive tract
- absored and enters blood stream
- reaches target cell at motor neuron terminal
- gets internalized
- light chain/heavy chain dissociate
- light chain acts as protease and degrades snare complex
- Ach release inhibited
52
important for synaptotagmin exocytosis; cannot occur when degraded by light chains of botulin toxin (neurotransmission inhibited)
snare complex
53
blocking acetylcholine release at the NMJ, botulinum toxins cause ______ ______. The mortality of botulism is usually secondary to paralysis of the respiratory muscles.
flaccid paralysis
54
small doses of this drug is effective in the treatment of conditions characterized by muscle hyperactivity: cervical dystonia, blepharospasm, strabismus, urinary incontinence. Also used to prevent headaches in adults with chronic migraine, treat the symptoms of severe underarm sweating and reduce the facial wrinkles.
botulinum toxin A (Botox)
55
tetrootoxin
batrachotoxin
local anesthetics
these inhibit:
Action potential
56
botulinus toxin inhibits
ACH release
57
curare alkaloids inhibit
depolarization (permeability of Na, K)
58
succinylcholine inhibits
depolarization (permeability of Na, K)
59
tetrodoxin also inhibits
muscle ation potential
60
dantrolene inhitbits
muscle contraction
61
extraocular muscle weakness (ptosis or diplopia) and later develop limb and bulbar muscle weakness. Worsening of weakness after prolonged and sustained muscle contraction (fatigability).
Reduces efficiency of neuromuscular transmission
Myasthenia gravis
62
inhibitor of acetylcholinesterase
neostigmine
63
contains wide synaptic folds. Leads to muscle weakness and fatigue
neostigmine
64
Myasthenia gravis treatment
acetylcholinesterase inhibitor neostigmine
65
what causes Myasthenia gravis
presence of antibodies which target the nicotinic receptors
66
a reversible condition on which a muscle is no longer able to generate or sustain the expected power output
fatigue
67
two types of fatuge
central fatigue
| peripheral fatigue
68
fatigue resistant, smaller in diameter, and darker color
slow-twitch
69
easily fatigued, pale in color and larger diameter (sprinter)
fast-twitch
70
single twitches
muscle relaxes completely between stimuli
71
summation
stimuli closer together of not allow the muscle to relax fully
72
when AP continues to stimulate the muscle fiber at high frequency, relation between contractions diminishes until the muscle fiber achieves state of maximal contraction
tetanus
73
basic unit of contraction in a skeletal muscle is
motor unit
74
Although motor neuron innervates multiple muscle fibers, each muscle fiber is innervated by _____ motor neuron.
one
75
muscles used for fine motor actions, such as the muscles that move the eyes, a motor unit contains only ~____________
3-5 muscle fibers.
76
In muscles used for gross motor actions such as standing or walking, each motor unit may contain _________ of muscle fibers.
hundreds or thousands
77
All muscle fibers in a single motor unit are of the same fiber type:
fast-twitch motor units and slow-twitch motor units.
78
Muscle can vary contraction force and duration by changing: (2)
1) the types of motor units that are active
| 2) the number of motor units that are responding at any one time.
79
Sequential activation of motor units to perform a designated task is called
motor unit recruitment
80
Asynchronous recruitment of motor units help avoid ________.
fatigue
81
sustained painful contraction of skeletal muscles
-caused by hyperexcitability of the motor neuron: as it fires repeatedly, muscle fibers of its motor unit go into state of painful sustained contraction.
Muscle cramp (“charley horse”)
82
Muscle cramp (“charley horse”) can be relieved by
forcibly stretching
83
Muscular Dystrophies
- cause progressive weakness of skeletal muscle
| - Associated with genetic defects that involve proteins expressed exclusively in muscle
84
what are the events that occur in Duchenne muscle dystrophy
- deletion/duplication of gene encoding dystrophin
- causes frameshift
- mRNA syn. diminishes for dystrophin
- low levels of dystrophin affect structural integrity of muscle cell
- contraction stres muscle
- cell dies
- fatal muscular weakness
85
what causes duchenne muscle dystrophy
deletion or duplication of gene encoding dystrophin- causes frame shifts; located on x-chromosome
86
Death associated with Duchenne is generally due to _________ insufficiency
respiratory
87
extensively used to treat many chronic inflammatory disorders (systemic lupus, sarcoidosis, rheumatoid arthritis, bronchial asthma, etc.)
Glucocorticoids
88
antagonist for transcription factor NF-KB activated by inflammation
glucocorticoid
89
increase levels of glucocorticoid lead to
atrophy
90
Weakness of the diaphragm may develop in asthmatics on prolonged use of _______ therapy
glucocorticoid
91
insulin-like growth factor is inhibited by
glucocorticoid
92
inhibits protein degradation, stimulates protein synthesis and does not diff into muscle cells
growth-like factor 1
93
stimulated by glucocorticoid, inhibits protein synthesis, stimulates protein degradation reducing muscle mass
myostatin
94
a class of drugs used to lower cholesterol levels.
Statins (or HMG-CoA reductase inhibitors)
95
the used of this drug my lead to adverse effects which include myalgia, exercise intolerance, fatigability, and potentially fatal rhabdomyolysis. (myotoxicity)
statin
96
When tang statin periodic blood work is done to check _______ levels, which indicate muscle breakdown
creatine kinase
97
are anabolic hormones that promote protein synthesis - anabolic steroids.
Androgens
98
adverse effects of this drug include liver tumors, infertility, and aggression
androgens
99
addictiveness to steroids resuts in
mood swings, fatigue, restlessness, depression
