Chapter 9- Muscle and Muscle Tissue Flashcards
1
Q
Movement
A
Voluntary or involuntary
2
Q
Body posture and position
A
muscles work to hold us up against gravity
3
Q
joint stability
A
muscles and tendons reinforce joints
4
Q
Maintaining body temperature
A
muscle contraction produces heat
5
Q
Muscle characteristics
A
Excitability- Membrane potential changes in response to stimulus
Contractility- Muscle cells shorten
Extensibility- Muscles cells can lengthen/stretch
Elasticity- Healthy muscle cells return to their original shape
6
Q
Types of muscle tissue
A
Skeletal
Smooth
cardiac
7
Q
Skeletal Muscle Tissue
A
Voluntary
Striated
skeletal
adaptable
most force
multinucleate
8
Q
Smooth muscle tissue
A
involuntary
no striations
moves fluids and substances through body
all hollow organs
uninucleate
9
Q
Cardiac muscle tissue
A
involuntary
moves blood through body
striated
uninucleate
pacemaker cells set rate of contraction
10
Q
innervation of skeletal muscle tissue
A
Each muscle receives 1 motor nerve
nerve ending controls activity
motor neuron stimulates muscle fibers to contract
neurotransmitter released- acetylcholine
11
Q
Vascularization of skeletal muscle tissue
A
Each muscle receieve 1 artery and 1 or more veisn to bring in nutrients and remove waste
12
Q
connective tissue sheaths of skeletal muscle tissue
A
supports muscle, holds it tg
3 layers:
endomysium- innermost (surrounds individual muscle fibers)
perimysium- middle layer (discrete bundles of muscle fibers grouped together - form fascicles
epimysium- outermost later (surrounds entire muscle and draws boundaries between different skeletal muscles together
13
Q
Skeletal muscle types of attachments
A
- direct- epimuysium of muscle fuses directly to bone or catilage
- indirect- involves tensions - bands of dense fibrous connective tissue that connects a muscle to a bone (tendon more common bc thicker)
14
Q
skeletal muscle points of attachment
A
- origin- where hte muscle attaches to a less movable bone (proximal)
- insertion- where the muscle attaches to a movable bone (distal)
15
Q
Skeletal muscle cells
A
myocytes, muscle fibers
largest and longest in the body
16
Q
Sarcolemma
A
plasma membrane of muscle fibers
17
Q
Sarcoplasm
A
cytoplasm of fluid muscle fibers
contain high numbers of
1. glycosomes- organelles that store glycogen (polysaccharide that is converted to glucose for ATP production)
2. myoglobin- red pigment organelle that stores oxygen (for ATP production)
18
Q
Myofilaments
A
protein filaments in muscle tissue
1. thick filament - myosin
thin filament - actin
they interact during muscle contraction
19
Q
Myosin filaments
A
4 light chains
2 heavy chains
Myosin head found at end of each heavy chain
20
Q
2 regulatory proteins associated with actin filaments
A
- tropomyosin- arranged along length of thin filament that blocks myosin binding sites on actin
- troponin- globular protein associated with tropomyosin (binds tropomyosin to position it on the actin filament)
21
Q
Myofibrils
A
rod-like organelles of muscle cells
made up of bands of myofilaments
creates striations
22
Q
Myofibril bands
A
A band- region of myofibril where actin and myosin filaments overlap (h xone at the center of A has only filaments)
I band- region of myofibriil with only actin filaments (z disc at center holds the actin filaments in place)
23
Q
Sarcomere
A
A and I bands create thi
24
Q
Other intracellular structures that regulate muscle contraction
A
T-tubules- extensionso fht esarcolemma that wrap around deeper muofibrils that increase surface area of muscle fiber sarcolemma (changes in membrane potential can reach myofibils not in direct contact with sarcolemma
Sarcoplasmic reticulum- smooth endoplasmic reticulum of muscle
Highly branched, wraps around myofibrils
Form terminal cisterns around T-tubules
(stores and releases intracellular ca2 for muscle relaxation and contraction
25
The Neuromuscular Junction
site of synapse between a somatic motor neuron and a muscle fiber
neurotransmitter released- Acetylcholine- affects voluntary movements
26
junctional folds
formed by folded Sarcolemma at synaptic cleft
increase surface
27
For stimulation of muscle fiber to occur, to following steps must take place:
1) Events at the neuromuscular junction
(ACh is released & binds to chemically-gated ion channels on the sarcolemma)
2. Generation of the action potential across the sarcolemma
ACh binds to and opens ion channels on sarcolemma to create end plate potential (EPP)
EPP is a graded potential specific to muscle tissue
EPP depolarizes sarcolemma
If strong enough → action potential generated on sarcolemma
3. Occurs when action potential spreads from sarcolemma to T-tubules
When action potential arrives at T-tubules → voltage-gated proteins in T-tubules change shape
Channels will open
When T-tubule proteins change shape → Ca2+ channels in terminal cistern forced open
Result: Ca2+ released from sarcoplasmic reticulum & flows into cytosol of muscle fiber
4. Cross Bridge Formation & Muscle Contraction
Temporary attachment between actin and myosin
Once Ca2+ enters cytosol → interaction between actin and myosin filaments can begin
Cross bridge: the attachment of myosin to actin
28
The Process of Cross Bridge Formation:
A) Ca2+ binds troponintroponin changes shape
B) Change in troponin shape causes tropomyosin to roll to the side
C) When tropomyosin is movedmyosin binding site on actin is exposed
Myosin head will bind to actin binding site with use of ATP
D) Myosin head splits ATP into ADP + Pi
This allows myosin head to bind to actin
E) ADP + Pi is released from myosin head, causing the myosin head to bend
Effect: myosin head “pulls” actin filament
This is called the power stroke
F) Myosin head binds to another ATP → myosin head detaches from actin binding site
G) The myosin head binds to a different actin binding site
Steps D-G repeat until muscle contraction ends or ATP/Ca2+ run short
Repeated formation/breaking of cross bridges between myosin and actin results in myosin “walking” along actin filament
29
Ending cross-bridge formation & muscle contraction
Motor impulses no longer sent to muscle fiber
Action potential to muscle fiber ends
Ca2+ is returned to sarcoplasmic reticulum
When Ca2+ levels in sarcoplasm drop, it can no longer bind to troponin
Troponin returns to original shape
Result: Tropomyosin movescovers actin binding sites
30
Sliding Filament Model of Contraction:
During contraction, actin filaments “slide” over myosin filaments --> the sarcomere shortens and generates tension in the muscle
31
Motor Units
a single motor neuron and all the muscle fibers it innervates
32
Motor Unit Rules
Rule 1: when the motor neuron fires - all fibers it innervates will contract
Rule 2: number of muscle fibers a single motor neuron innervates influences movement
33
Rule 1: when the motor neuron fires - all fibers it innervates will contract
Fibers innervated by a single motor neuron are spread out over the entire muscle - not clumped together!
34
Rule 2: number of muscle fibers a single motor neuron innervates influences movement
Motor neuron innervating few fibers (coarse control - not as precise)
Walking
VS.
Motor neuron innervating many fibers (fine control - very precise)
Writing
35
Muscle Twitch
response of a muscle to a single stimulus
Measured with a twitch myogram
36
3 phases of a myogram:
1) Latent period: first few milliseconds following stimulation
Excitation-contraction coupling occurs, but no tension observable in muscle
2) Period of contraction
Active cross-bridge formation with increasing tension
3) Period of relaxation
Cross bridge formation declines, muscle tension declines to resting value
37
Graded Muscle Contractions
sustained muscle contraction that is modified by the nervous system to produce varying amounts of force
How hard/soft a muscle contracts to ensure twitching doesn’t happen as frequently
38
Muscle contrations can be graded in 2 ways
1) Temporal summation → increasing the frequency of stimulation of a muscle
2) Motor Unit summation → increasing the strength of stimulation of a muscle
39
Temporal Summation
Increasing the firing rate of a motor neuron can generate more force at the muscle
increase the force produced by the muscle fiber and it will become stronger and stronger
40
Fire stimuli in rapid succession in. temproal summation means...
the second twitch hits the muscle before the first twitch has ended and muscle tension increases
Increase in membrane potential = the muscle contraction occurs
2nd action potential - The more calcium released, the more myocin
Third action potential prior to depolarization from the second, another surge of calcium, more force generated by the muscle fiber and will completely depolarize with force
41
Temporal summation can lead to 2 forms of tetanus:
unfused tetanus
fused tetanus
42
Unfused (incomplete) tetanus:
rate of stimulation creates a sustained & quivering muscle contraction
Little ability of the muscle fiber to contract
43
Fused (complete) tetanus
rate of stimulation creates smooth, sustained muscle contraction
No relaxation occurs
Action potentials are back to back
Most force you can produce by the muscle - no quivering quality so it is sustained
44
Motor unit summation
recruitment of additional motor units in a muscle to generate more force during contraction
45
Size principal of motor unit summation
Motor units with smallest muscle fibers recruited first
Motor units with largest muscle fibers recruited last → create most force
46
Muscle tone
Relaxed muscles are always slightly contracted → creates muscle tone
47
Loss of muscle tone leads to...
loss of responsiveness
Muscle will not respond to stimuli
Ex: stroke victims
48
Isotonic contraction
muscle tension develops to overcome the load, muscle shortening occurs
Moving a load
49
Two subtypes of isotonic contraction
1) Concentric contraction: muscle shortens and does work
Ex: upward motion of a bicep curl
2) Eccentric contraction: muscle generates force as it lengthens
Ex: downward motion of a bicep curl
Provides stability to the movement of the load
50
Eccentric contraction
Provides stability to the movement of the load
Sliding of the filaments in the opposite direction of the concentric
Allows you to slowly lower a dumbbell instead of just dropping it
50% stronger at an equal weight load as opposed to concentric
Allows for muscle building
51
Isometric Contraction
tension develops in a muscle, but the length of the muscle does not change
Occurs when the load is not moved
Cross bridge formation still occurs, bu the actin filaments do not slide
Ex: most muscles responsible for body posture, plank position, wall sits, etc.
Muscles in neck
52
Energy Needs for Contraction
ATP in the form of glycogen
for 4 seconds regernerated really fast
53
3 Pathways used to regenerate ATP:
1) Direct phosphorylation
2) Anaerobic pathways
3) Aerobic pathways
54
Direct phosphorylation
Creates ATP from ADP + Pi using creatine phosphate (CP) - t
Catalyzed by creatine kinase
1 ATP produced per CP molecule
Does not require oxygen
Supplies ~15 seconds worth of ATP
55
Anaerobic Pathways
Glycolysis and Lactic Acid Formation
Glucose (from glycogen in muscle cell) broken down to form 2 ATP & pyruvic acid
If oxygen is present, pyretic acid will be used int he next step
In absence of O2 → pyruvic acid converted to lactic acid
Lactic acid not used by muscle → diffuses into blood
Liver and kidneys take care of it
Does not require oxygen
Fast method to create ATP
Can rely on anaerobic pathway/glycolysis
Drawbacks:
A lot of glucose used for low ATP yield (2 ATP)
Lactic acid build-up results in DOMS
Delayed onset muscle soreness
Stored glycogen, creatine phosphate, & glycolysis provide ~1 minute of ATP
Some muscle movement don’t need to be long
56
Aerobic Pathway
Cellular Respiration
Creates 95% of ATP used by muscle during rest and light to moderate long-term exercise
Requires pyruvic acid produced in anaerobic pathway
Walking, jogging, etc.
Requires oxygen and takes place in the mitochondria
Produces ~30 ATP, H20, and COs
ATP is the slowest of the processes
Drawbacks:
Slow process
Requires constant O2 and glucose
57
Muscle Fatigue
Muscle is physiologically incapable of contracting
58
Why is muscle fatigue necessary and important? What happens to muscle fibers if ATP is completely depleted?
Cant do anything else to survive - prevents it from running out of ATP; if it runs out of ATP, you die
59
High intensity exercise
muscles will tire out quickly; rate fast, but it doesn’t stay fatigued for very long
weightlifting
60
Low intensity exercise
muscles will tire out slowly; rate slow, takes longer for muscle cells to recover from fatigue
long distance running; you don’t run a marathon every day
61
Force- (Muscle Contraction)
Force of contraction is determined by the number of cross bridges formed between myosin and actin filaments
62
Force is influenced by four factors
1) Frequency of stimulation → temporal summation
2) Number of muscle fibers recruited → motor unit summation
3) Size of muscle fiber
4?
63
Size of muscle fiber
Hypertrophy
increase size of muscle fibers in muscle to increase force generated
64
Rate of hypertrophy
dependent on genetics, sex, nutrition, etc.
Testosterone- muscle promoting hormone
Estrogen- doesn’t create muscle
65
Fiber type influences velocity & duration of muscle contraction
1) Speed of contraction
Dependent on:
A) How fast ATP is splithow fast cross bridges can form & break
B) Electrical activity of motor neuronsfast neurons = fast contraction
Very heavy myelinated so the motor neuron will be able to send the message even faster
2) Load and recruitment
Small loads allow faster contraction
Lesser weight = faster contraction
Faster to life 10 lbs as opposed to 100 lbs
More motor unit recruitment = faster contraction
3) Pathway of ATP production
Oxidative fibersuse aerobic pathways
Slower pathway
Glycolytic fibersuse anaerobic pathways
Low ATP yield
Faster
66
Most organs have 2 layers of smooth muscle tissue that never contract simultaneously in the same area:
1. longitudinal layer
2. circular layer
67
Longitudinal layer
muscle fibers run the length of the organ
More superficial
What happens to the organ when this layer contracts? Short and wide
68
Circular layer
muscle fibers run the circumference of the organ
Deep to longitudinal layer
What happens to the organ when this layer contracts? Will be long and thin
69
Differences from skeletal muscle fibers:
(smooth muscle)
1) Smooth muscle fibers are short, spindle-shaped
2) Covered only by endomysium
Only connective tissue sheet covering the muscle cells
3) No neuromuscular junctions → innervation forms varicosities
Autonomic fibers have bulb-like swellings scattered over smooth muscle tissue surface
One individual fiber that spans across
Importance: creates diffuse junctions
Wide synaptic clefts that release neurotransmitter to multiple muscle fibers
Release and scatter over smooth muscle cells
4) Smooth muscle fibers have no T-tubules & less sarcoplasmic reticulum
Sarcoplasmic reticulum releases only a small amount of Ca2+
Caveolae: invaginations of sarcolemma of muscle fiber
Have Ca2+ ion channels
Where does most Ca2+ come from? Outside of the cell (extracellular fluid)
5) Muscle fibers have gap junctions
Cause neighboring cells to depolarize
Depolarization spreads from cell to cell
Allows smooth muscle cells to pass info about smooth muscle cells quickly between each other
6) No striations or sarcomeres
There are still thick and thin filaments, but:
Fewer thick filaments overall
Myosin heads found along entire length of thick filament
7) No troponin
Calmodulin → protein that acts as Ca2+ binding site
8) Thick and thin filaments arranged diagonally
Filaments spiral down axis of muscle fiber
Effect: when a muscle fiber contracts - it twists
Cell twists around because of the diagonal arrangement
70
Types of smooth muscleq
unitary
multi-unit smooth muscle
71
Unitary Smooth Muscle
Everything described so far are characteristics of unitary smooth muscle
Much more commonfound in hollow organs
Smooth muscle is involuntary
72
Multi-Unit Smooth Muscle
Have no gap junctions or spontaneous depolarization
Muscle fibers are structurally independent
Forms motor units
Have graded contractions with recruitment
73
Regulation of Contraction
neural regulation
hormones and local chemcial factors
74
neural regulation
Neurotransmitter can excite or inhibit smooth muscle tissue
Response is dependent on receptor molecules on sarcolemma
Done by hormones and local chemical factors to tell it when the muscle should contract and relax
75
Hormones & Local Chemical Factors
Some smooth muscle has no innervation → respond only to local chemicals
Others spontaneously depolarize
Act by enhancing or inhibiting Ca2+ entry into sarcoplasm
76
Unique Features of Smooth Muscle
1) Response to stretch
Smooth muscle responds to stretch by contracting
Importance: increases ability to push substances through organ
Stress-relaxation response: if an organ is filled slowlyit will not contract strongly
2) Length and tension changes
Smooth muscle can stretch more & can generate more tension while stretched
Can still contract when stretched 150% its length
Stomach- overstretching when you eat a lot, if the stomachs response to that was a really hards contraction, you would push a ton of food into the small intestine and runs the risk f physically ripping open the walls and it would take you a really long time to digest and aborb any of the food
Important- length and tension changes
Skeletal muscle tissue can something 60%
