Chapter 10: Muscular Tissue Flashcards
1
Q
Three types of muscular tissue
A
- skeletal
- cardiac
- smooth (visceral)
2
Q
Functions of muscular tissue
A
- producing body movements
- stabilizing body positions
- storing and mobilizing substance within the body
- generating heat ex; “shivering”
3
Q
Properties of muscular tissue
A
- electrical excitability (when its “on” muscle shorter, when its “off” it relaxes and lengthens
- contractility (when you contract biceps; triceps relax and vice versa)
- extensibility
- elasticity
4
Q
How are muscles formed?
A
fusion of myoblasts into skeletal muscle
5
Q
Muscle cell nucleus and length
A
- muscles cells are very long and therefore are multinucleated.
6
Q
Myofibrils
A
- protein filaments that run parallel along the length of the muscle cell
7
Q
Muscle connects to
A
bones by tendons
8
Q
Muscle fascicle
A
muscle cells are arranged in bundles called muscle fascicle
9
Q
Endomysium
A
layer of connective tissue that wraps around the sarcolemma (membrane that surrounds muscle cells)
10
Q
Perimysium
A
surrounds each muscle fascicle
11
Q
Epymysium
A
a whole muscle is surrounded by epimysium
12
Q
The more muscle cells a person has…
A
the more strength the person has (myofibrils in specific)
13
Q
Function of T-tubules
A
they fold inward to allow membrane proteins to get close to the sarcoplasmic reticulum
14
Q
Glycogen granules in muscle cells
A
- muscle cells carry their own energy all the time
15
Q
Myoglobin
A
protein found only in muscle cells and caries oxygen
16
Q
Dystrophin
A
- accessory protein
- functions to anchor the length of the cells
17
Q
Muscular hypertrophy
A
- enlargement of EXISTING muscle fibers
- due to increased production of myofibrils, mitochondria, sarcoplasmic reticulum, and other organelles
18
Q
Muscular atrophy
A
decrease in size of muscle fibers due to loss of myofibrils
- occurs as a result of aging or disuse
19
Q
What causes striations in muscle cells
A
- there are regions in skeletal fibers where it looks darker and lighter through microscope because i band has only thin filaments whereas A band has thick filaments
20
Q
Z discs
A
Narrow, plate-shaped regions of dense material that separate one sarcomere from the next
21
Q
A band
A
dark, muddle part of sarcomere that extends entire length of thick filaments and includes those parts of thin filaments that overlap thick filaments
22
Q
I (i) band
A
lighter, less dense area of sarcomere that contains remainder of thin filaments but no thick filaments.
- a Z disc passes through the center of each i band
23
Q
H band
A
narrow region in center of each A band that contains thick filaments but no thin filaments
24
Q
M line
A
region in center of H band that contains proteins that hold thick filaments together at the center of the sarcomere
25
As a sarcomere shortens...
the zone of overlap increases and i band disappears
26
Thick filaments
myosin
27
Thin filaments
actin
- connected to Z discs and myosin
28
Contraction simple explained
myosin pulls actin filaments therefore, pulling z discs causing sarcomere and entire myofibril to shorten (contract)
29
What are contractile proteins
myosin and actin
30
Myosin descrption
contractile protein that makes up thick filament; molecule consists of a tail and two myosin heads, which bind to myosin-binding sites on actin molecules of thin filament during muscle contraction
31
Actin description
Contractile protein that is the main component of thin filament; each actin molecule has a myosin-binding site where myosin head of thick filament binds during muscle contraction
32
Regulatory proteins in myofibrils
- Tropomyosin
- Troponin
33
Tropomyosin description
regulatory protein that is a component of thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin
34
Troponin description
Regulatory protein that is a component of thin filament; when calcium ions (Ca+) bind to troponin, it changes shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin
35
Structural proteins of myfibrils
- Titin
- a (alpha) actinin
- Myomesin
- Nebulin
- Dystrophin
36
Titin (structural protein)
structural protein that connects Z discs to M line of sarcomere, thereby helping to stabilize thick filament position; can stretch and then spring back unharmed, and thus accounts for much of the elasticity and extensibility of myofibrils
(holds sarcomere structure)
37
a Actinin (alpha)
Structural protein of Z discs that attaches to actin molecules of thin filaments and to titin molecules
38
Dystrophin
- links edge of sarcomere to sarcolemma
- muscular dystrophy lacks dystrophin
39
The contraction cycle; step 0
- before you contract a sarcomere you must release calcium to each myofibril
40
The contraction cycle; step 1
- myosin head hydrolyzes ATP and becomes energized and oriented
- myosin head winds back (changes orientation) using ATP hydrolysis
41
The contraction cycle; step 2
- myosin head binds to actin, forming a cross bridge (connection between myosin + actin)
- phosphate leaves and myosin head goes back and pulls actin back with it
42
The contraction cycle: step 3
- myosin head pivots, pulling the thin filament past the thick filament toward center of the sarcomere (power stroke)
- ADP leaves
43
The contraction cycle; step 4
- as myosin head binds ATP, the cross bridge detaches from actin
and the cycle repeats
44
When the contraction cycle repeats the myosin grabs..
a new position making the sarcomere shorter until it can't contract anymore
45
ATP hydrolysis?
when ATP turns into ADP
46
What happens when there is no ATP you cannot release the cross bridge
the muscle stays contracted (occurs when a person dies)
- after 24 hours the body starts to relax because the proteins get broken down.
47
Rigor mortis (what happens)
state of rigidity in muscles that occurs after 3-4 hours after death
- calcium leaks out of sarcoplasmic reticulum
- myosin heads to bind to actin forming cross-bridge
- cross bridge can't detach since ATP synthesis has ceased
48
When does rigor mortis disappear
disappears after 24 hours as proteolytic enzymes digest the cross-bridge
49
Length-tension relationship
- the force of a muscle contraction depends on the length of the sarcomeres in a muscle prior to contraction
50
What does neuromuscular junction or neuromuscular synapse produce
produces a muscle action potential
51
Steps of NMJ or NMS
1. voltage-gated calcium channels in a neurons synaptic end bulb open
2. Ach binds to Ach receptor
3. Muscle depolarization and calcium releases from the sarcoplasmic reticulum
4. Ach gets broken down by acetylcholinesterase
52
Step 1 in NMJ or NMS
1: voltage-gated calcium channels in a neuron's synaptic end bulb open
- resulting in calcium influx
- this causes exocytosis of the neurotransmitter acetylcholine (Ach) into synaptic cleft
53
What does acetylcholine do
turns on muscle cells
54
Step 2 in NMJ or NMS
Ach binds to Ach receptor on the motor endplate, which causes an influx of NA+ into muscle (action potential)
- sodium rushes from outside of muscle cell into the cell. Eventually you reach action potential
55
Step 3 in NMJ or NMS
The muscle is now depolarized and it results in Ca to be released from the sarcoplasmic reticulum
56
Step 4 in NMJ or NMS
Ach gets broken down by acetylcholinesterase
- should be able to turn off the cell and not be contracted all the time
57
What does acetylcholinesterase do
breaks down Ach and it prevents prolonged muscle contraction
58
Motor neuron to skeletal muscle cell ratio
1 motor neuron can connect to several skeletal muscle cells
59
Only contraction uses..
ATP not relaxing because relaxing is passive
60
3 ways that muscles produce ATP
- Creatine phosphate (least)
- Anaerobic glycolysis (middle)
- Aerobic respiration (most)
61
Creatine phosphate explained
- happens during periods of rest
- Creatine kinase catalyzes the transfer of a phosphate group from creatine phosphate to ADP to rapidly yield ATP
- myosin is always hydrolyzing ATP
62
Anaerobic glycolysis explained
- when creatine phosphate stores are depleted, glucose is converted into pyruvic acid to generate ATP
- glycolysis produces 2 ATP by pushing pyruvate away from mitochondria through the lactate dehydrogenase reaction
63
Aerobic respiration explained
- under aerobic conditions, pyruvic acid can enter the mitochondria and undergo a series of oxygen-requiring reactions to generate large amounts of ATP
- 4 molecules of ATP are produced per glucose
64
Central fatigue
- occurs due to changes in the central nervous system (brain) and generally results in cessation of exercise
- protective mechanism to prevent the overuse of muscles
65
Muscle fatigue
- inability to maintain force of contraction after prolonged activity
66
Reason for onset of muscle fatigue
- inadequate release of Ca+ from the sarcoplasmic reticulum
- depletion of creatine phosphate, oxygen and nutrients
- build up of lactic acid and ADP
- insufficient release of acetylcholine at the neuromuscular junction
67
Why do you continue to breathe heavily for a period of time after stopping exercise
to allow your body to recover
68
The extra oxygen when breathing heavily after exercise goes toward
- replenishing creatine phosphate stores
- converting lactate into pyruvic acid (pyruvic acid is used for ATP production via aerobic respiration)
- reloading O2 onto myoglobin
69
Other reasons the body needs extra oxygen after exercise
- increased rate of chemical reactions that is accompanied by elevated body temperature
- increased consumption of oxygen from the heart and respiratory muscle tissues
- tissue repair processes are occurring at an increased pace.
70
The strength of a muscle contraction depends on
how many motor units are activated
71
What does a motor unit consist of
consists of a somatic motor neuron and the muscle fiber it innervates
- activating only few motor units will generally result in a weak contraction, activating many will generally result in a strong muscle contraction
72
Wave summation
occurs when a second action potential triggers muscle contractions before the first contraction has finished and the skeletal muscle fiber has relaxed
- the second stimulus occurs after the refractory period but before the skeletal muscle has relaxed
73
Unfused tetanus
when the muscle fibers do not completely relax before the next stimulus because they are being stimulated at a fast rate
74
Fused tetanus
no relaxation period between muscle contractions
75
Motor unit recruitment
- weakest are recruited first, followed by stronger motor units
- motor units contract alternately to sustain contractions for longer periods of time (they do not all relax at the same time)
76
Muscle tone; even when at rest, a skeletal muscle exhibits
a small amount of taughtness or tension, called muscle tone
77
What is muscle tone established by
neurons in the brain and spinal cord that excite the muscle's motor neurons
78
What happens when a motor neuron thats serving skeletal muscle gets damaged or cut
the muscle becomes flaccid
79
Isotonic contractions
tension is constant while muscle length changes
- concentric: muscle length shortens
- eccentric: muscle length lengthens
80
Isometric contractions
- does not change length of the muscle
- tension generated is not enough to exceed the resistance so the muscle length does not change
(generates just enough to keep balance of objects)
81
Intercalated discs function in cardiac muscle
- contain desmosomes that hold the cardiac muscle fibers together
- contain gap junctions that allow muscle action potentials to spread from one cardiac muscle fiber to another
82
Cardiac muscle cells have more...
mitochondria and their contractions last 10-15 times longer than skeletal muscle contractions
83
What type of ATP does cardiac muscle use
uses aerobic respiration
84
Somatic motor neurons connect to
skeletal muscle to provide voluntary movements
85
Autonomic motor neurons connect to
smooth muscle and allows involuntary movements
86
Smooth muscle contractions
start more slowly and last longer than skeletal and cardiac muscle contractions
87
Smooth muscle can shorten and stretch to a greater extent than
skeletal and cardiac muscle
