Ch. 9 - Muscles Flashcards
1
Q
General functions of muscles
A
- maintain posture and body positions (contract to stabilize joints)
- muscle contraction pulls on tendons and thus moves bones
- contraction utilizes energy and some is converted into heat (to maintain body temperature)
- voluntary control (skeletal)
- supports and protects visceral organs
2
Q
Basic properties of muscles
A
- excitability - able to respond to stimulation (receive/respond to chemical or electrical stimuli)
- contractility - able to shorten and exert tension
- extensibility - contract when stretched
- elasticity - returns to original shape when stretched, excited, or contracted in any way
3
Q
Composition of muscles (brief overview)
A
- Connective tissue with arteries, veins, nerves, and lymphatics (muscles are organs)
- contractile cells
4
Q
Muscle types (3 of them)
A
Skeletal, Cardiac, Smooth
5
Q
Skeletal Muscle (brief overview facts)
A
- attaches to bone
- striated with light or dark bands
- voluntary
- long, thin and multinucleated fibers (muscles cells can have 100 or more nuclei)
- DO NOT BRANCH
- arranged in packages to cover bones
- contract rapidly but tire easily
- may exert great force
6
Q
Cardiac Muscle (brief overview facts)
A
- striated
- involuntary
- uninucleate
- involuntary
- autorhythmic
- network of fibers with intercalated discs
- found only in heart
- DO BRANCH
7
Q
Smooth Muscle (brief overview facts)
A
- attached to hair follicles (arrector pilli muscle is smooth)
- in walls of hollow organs and blood vessels
- non-striated
- involuntary
- slow sustained contractions
- spindle shape
- DO NOT BRANCH
8
Q
Skeletal Muscle Organization
A
- skeletal muscle made up of fascicle (fascicles are up of 10-100 muscle cells *fibers)
- fascicle made up of muscle fibers
- muscle fibers made up of myofibrils
- myofibrils made up of sarcomeres
9
Q
CT layers of Skeletal Muscle
A
deep fascia, epimysium, perimysium, endomysium
10
Q
Epimysium
A
surrounds the entire muscle and the perimysium and is made up of many fascicles
- connects muscle to deep fascia
- dense irregular CT that contains large arteries, veins, and nerves
11
Q
Deep fascia
A
a layer of thickened connective tissue that covers the entire muscle and is located over the epimysium
12
Q
Perimysium
A
surrounds muscle fascicle
- areolar CT
- branches of arteries, veins, and nerves that supply the fascicle
13
Q
Endomysium
A
surrounds muscle fibers
- areolar CT
- contains capillaries that supply muscle fibers
14
Q
Tendons and contraction
A
When a muscle fiber (cell) contracts it pulls on the myofibrils which pull on the tendon to move the specified target bone
-muscle comes to dense regular CT (tendons) at ends of muscles *tendons are whitish ends of muscles
15
Q
Aponeuroses
A
thin, flat, broad sheaths (made of collagen) that resemble tendons but have more give and aren’t as tough as tendons
*connect muscle to muscle or other structures
16
Q
Muscle fiber
A
single muscle cell, extends entire length of muscle
17
Q
Basic structures of a muscle fiber
A
sarcoplasma, sarcolemma, multinucleated, sarcoplasmic reticulum, transverse tubule, triad, myosatellite cells
18
Q
sarcoplasma
A
cytoplasm of muscle fiber (contains mitochondria, glycogen to store glucose, myoglobin to store O2)
*obviously would contain myofibrils as well
19
Q
sarcolemma
A
plasma membrane of muscle fiber, it is excitable
*located inside the endomysium
20
Q
sarcoplasmic reticulum (terminal cisternae)
A
smooth ER, regulates/stores intracellular Ca (no ribosomes attached)
21
Q
transverse (T) tubules
A
infoldings of sarcolemma that conduct impulses from the surface of the cell (SARCOLEMMA) down into the cell
22
Q
triad
A
pair of terminal cisternae and T-tubule
*occur in zone of overlap
23
Q
myosatellite cells
A
dormant myoblasts involved in muscle repair
muscle damage:
1. minor- repair damage
2. major- build new fibers
24
Q
Fiber Development
A
Myoblasts:
- stem cells
- embryonic cells that fuse to form muscle fibers (muscle building cells)
- myoblasts cells fuse together and each contribute their nucleus to create a muscle fiber
- myoblasts that do not fuse become myosatellite cells to help with repair if needed
25
Myofibrils
- contractile organelles
- extend length of muscle fiber
- surrounded by sarcoplasmic reticulum and T-tubules
- functional units of myofibrils are sarcomeres (composed of myofilaments)
26
Myofilaments (2 types)
actin- thin red filament
| myosin- thick purple filament
27
Thick filament (myosin)
- thick filament of twisted protein strands with globular heads (cross-bridge)
- about 50 myosin molecules per one thick filament
- each has elongated tail and free globular head
- heads referred to as "cross-bridges" because they connect to thin filaments during contraction process
* M-line runs down the middle of the myosin band connecting all the myosin filaments in the center
28
Thin filament (actin)
twisted strand of F-actin
-F-actin is made of 300-400 globular G-actin molecules
-nebulin= thin protein strand that holds F-actin together
2 regulatory proteins:
1. tropomyosin- rod-shaped protein (twisted strands) that block the active site on actin when muscle is relaxed
2. troponin- binds tropomyosin and helps position it on actin (keeps tropomyosin in place)
29
Sarcomere (general and Z-line info)
repeating unit of myofilaments
- defined by adjacent Z-lines (Z-line marks end of a specific sarcomere)
- Z-lines are where actin filaments of adjacent sarcomeres attach
30
Sarcomere bands
have striated appearance
1. A-band = myosin overlapping actin (entire myosin band end to end)
* myosin filaments attached to Z-line by titin protein
2. I-band = contains only thin filaments (actin on both sides of Z-line) *between 2 A-bands
3. H-zone= area in center of myosin band that only contains thick filaments (small area in center where myosin and actin DO NOT overlap)
4. zone of overlap= where thin filaments pass through thick filaments
31
Sarcomere lines
1. Z-line = anchors thin filaments together (ends of sarcomere)
- made of protein called actinin
- this is where thin filaments branch to the adjacent sarcomere
2. M-line = stabilizes thick filaments
32
Stabilizing proteins of sarcomere
1. titin - runs through core of myosin filaments and is attached to the Z-line
- highly elastic (can stretch and retract)
- helps maintain normal alignment of thick and thin filaments
2. nebulin = thin protein strand that holds F-actin together
3. actinin = protein that makes up the Z-line (necessary for the attachment of actin myofilaments to the Z-line)
33
Sliding filament theory for muscle contraction
1. Ca+2 ions are released into the zone of overlap by the sarcoplasmic reticulum
2. Ca+2 ions bind to the troponin heads, causing the troponin to change shape, thus causing tropomyosin to roll away from the active sites on the G-action molecules, exposing the binding sites for the myosin filament heads.
3. ATP attaches to myosin head, and ATP is hydrolyzed into ADP and inorganic phosphate. ADP and phosphate bind to actin active site, and phosphate is released to make the bond stronger.
4. ADP is then released from the myosin head, causing the head to pivot, therefore sliding the actin filament closer to the center line.
5. ATP then binds to the myosin head, causing it to detach from the actin filament, and it can return to its hi-energy position where ATP is hydrolyzed into ADP and phosphate while the myosin head is at rest.
* myosin bands don't change length but overlap of thick and thin filaments just increases
34
effects of muscle contraction
1. zone of overlap enlarges
2. A band is constant
3. I and H bands shorten
4. Z-lines come closer together
5. M line is constant
35
Nerve stimulus to muscle (parts that make up the process)
motor unit, neuromuscular junction, synaptic terminal, motor end plate, synaptic cleft, neurotransmitter
36
motor unit (nerve impulse)
one neuron plus all muscle fibers that are stimulated by that neuron (one neuron could stimulate 3 muscle fibers or hundreds)
37
neuromuscular junction
site of chemical communication between axon of nerve and muscle fiber
38
neurotransmitter
chemical released by nerve upon arrival of impulse (acetylcholine in skeletal muscles)
*ACh maintains contraction stimulator
39
Events of muscle contraction (neuromuscular junction)
1. an action potential is sent through a neuron, down the axon into its synapses. voltage gated ion channels on the nerve synapse release calcium into the synapse and calcium causes the exocytosis of acetylcholine vesicles, causing acetylcholine molecules to be released from the presynaptic membrane into the synaptic cleft.
2. acetylcholine binds to ligand-gated cation receptors on the sarcolemma, and this causes the receptor channels to open, which in turn causes an influx of sodium ions into the muscle fiber and an outflux of potassium ions into the synaptic cleft. This flow of sodium and potassium ions across the sarcolemma depolarizes the sarcolemma and eventually reaches threshold to send an action potential down the T-tubules
3. Once threshold of the sarcolemma is reached during depolarization, the action potential moves down the T-tubules and stimulates voltage gated channels of the sarcoplasmic reticulum inside the muscle fiber. The voltage gated channels release calcium ions into the sarcoplasm, and calcium ions bind to troponin and change its shape so tropomyosin moves and exposes the active sites on the G-actin molecules. Now myosin heads can bind to the actin filaments and muscle contraction occurs.
40
Events of muscle relaxation
1. acetylcholine no longer binds to the ligand-gated receptors on the postsynaptic membrane (sarcolemma), and acetylcholine-esterase breaks acetylcholine down into acetic acid and choline.
2. These two molecules are recycled back into the presynaptic membrane and form acetylcholine once again, and are stored in vesicles in the neuron synapse, waiting for another action potential to stimulate the acetylcholine.
3. Calcium ions are actively transported back into the sarcolemma and tropomyosin covers the active sites of the G-actin molecules, preventing myosin head binding. muscle contraction ceases, and sarcomeres go back to resting length.
41
Threshold stimulus
minimum stimulus needed for a motor unit to conduct muscle contraction
42
Sources of energy for contraction
ATP is an immediate source of energy
3 ways to regenerate energy:
1. creatine phosphate- storage form for excess energy in a cell (pool of creatine phosphate in muscle fiber is about 10 times larger than ATP)
-actively donates a phosphate to ADP to make ATP (does not require oxygen so its anaerobic) *quick energy but doesn't last long
2. anaerobic glycolysis and lactic acid formation *quick energy but doesn't last long
3. aerobic respiration *takes longer but produces more energy for a longer period of time
43
all-or-none law
a muscle fiber responds completely or not at all once threshold is reached (no partial contractions in motor units)
44
graded response
individual muscle fibers contract completely but the response of a muscle as a whole is graded (sometimes not the entire muscle is contracted, maybe contraction is concentrated in a specific area of a muscle)
* Muscle tension is affected by:
1. frequency of stimulation
2. number of motor units involved in stimulation
45
muscle twitch
fraction of a second response of a muscle to a single stimulus
- a single momentary contraction
- the response to a single stimulus *as the rate of stimulation increases, muscle tension increases*
46
Muscle Tone
even when a muscle is at rest, some motor units are always active. their contractions do not produce enough tension to cause movement, but the muscle is tensed. (neck muscles and back muscles to maintain posture)
-motor units randomly contract while others rest (different parts of muscle contract)
function:
-maintain body position (posture) and hold things in place
-stabilize joints by keeping constant tension on tendons while some motor units (muscle fibers) can relax
47
Hypertrophy
synthesis of more myofibrils due to demand (constant exhaustive stimulation increases number of organelles/proteins in the muscle fiber) *no new cells, cells just get bigger
can increase:
-mitochondria
-glycolytic enzyme reserves
-myofibrils
-filaments within myofibrils
(exercise leads to bigger muscles in this way^^^)
48
Atrophy
```
loss of myofibrils from disuse
-lack of constant motor neuron stimulation reduces number of organelles/proteins
due to:
-age
-hormones
-lack of use
-nerve damage
*atrophy is reversible if muscle fiber is not dead (can increase myofibrils again*
```
49
Origin (muscle attachments)
attachment site that does not move (usually more proximal area of muscle)
50
Insertion (muscle attachments)
attachment site that moves (insertion pulled toward origin usually)
51
Fascicle Arrangements (4 types)
parallel, convergent, pennate, circular
52
Parallel fascicle arrangement
-fascicles parallel to long axis
-unidirectional force
-stronger than convergent but less strong than pennate
types:
1. fusiform parallel- round in the middle then get thinner near ends as they run into CT tendons at the ends of the muscle (ex. biceps brachii)
2. strap-linear = flat muscles (muscles of the neck and abdomen)
53
Convergent fascicle arrangement
fan-shaped muscles
- multi-directional force
- versatility
- if entire muscle contracts, fibers do not pull as hard as a parallel muscle
- this fascicle arrangement generates the least amount of force per bundle compared to parallel bundle (forces of convergent cancel each other out during certain movements)
- the muscle fibers are spread over a broad area, but all the fibers come together at a common tendon (attachment site)
* ex. pectoralis muscles*
54
Pennate fascicle arrangement
-fascicles oblique (slanted) to long axis
-tendon passes through muscle *in multipennate*
-exert greatest force
types:
1. unipennate = fibers found on one side of a tendon *ex. extensor digitorum muscle*
2. bipennate = fibers arranged on either side of tendon (run oblique to tendon) *ex. rectus femoris muscle*
3. multipennate = tendon branches within a muscle
-fascicles run parallel to tendons
-each fascicle section has its own tendon running through it
*ex. deltoid muscle*
55
Circular fascicle arrangement
concentric fascicles around an opening
- circular muscles guard entrances/exits of internal pathways like the digestive/urinary tracts.
- and the mouth
56
monoaxial (uniaxial) movement
-permits angular or rotational motion around ONE axis
rotational= pivot joints like the atlantoaxial joint
angular= knee joint or interphalangeal joints
57
biaxial movement
movement that occurs along 2 axes
| angular= flexion/extension or abduction/adduction
58
multiaxial movement
```
movement on all axes
angular=same as biaxial
rotation
circumduction
ex. BALL AND SOCKET JOINTS
```
59
agonist
prime mover
| -main muscle responsible for action
60
antagonist
opposes agonist movement
- opposite action that opposes agonist's primary action
ex. triceps oppose biceps *stabilizes the primary action*
61
synergist
assists/modifies movement of agonist
- may provide additional pull near the insertion
- may stabilize the point of origin
62
fixator
stabilizes
| ex. deltoid stabilizes shoulder joint in order to isolate bicep in bicep curl
63
Lever systems
```
can modify movements
can change:
-magnitude
-speed
-direction
-distance of limb movement
```
64
Components of lever systems
lever (L) - skeletal element
applied force (AF) - occurs at the insertion point
fulcrum (F) - joint
resistance (R) - body part/object moved
65
first class levers
the applied force (AF) and the resistance are on opposite sides of the fulcrum (F). fulcrum is in the middle.
-this lever can change the amount of force transmitted to the resistance and alter the direction and speed of movement
ex. atlanto-occipital joint :
R=skull
F=atlanto-occipital joint
AF= neck muscles
**see-saw motion**
66
second class levers
the resistance lies between the AF and the fulcrum (AF opposite of F to move R)
-this arrangement magnifies force at the expense of distance and speed, the direction of movement remains unchanged.
**wheel-barrow**
ex. plantar flexion :
R= weight of body
F= metatarsal-phalangeal joint
AF= calf muscle
67
third class levers
**most common lever**
the AF is between the resistance and the fulcrum
-this arrangement increases speed and distance moved but requires a larger applied force
Ex: elbow flexion
R = weight distal to joint (weight of forearm and hand)
F = elbow joint
AF = biceps brachii
68
Muscle force is affected by:
1. diameter of muscle
2. fascicle arrangement
3. number of motor units activated
4. muscle biochemistry
69
Fast muscle fibers
fast acting/high energy requirement
- anaerobic
- large diameter (has a lot of myofibrils)
- densely packed myofibrils
- large glycogen reserves
- few mitochondria (because they're anaerobic)
- rapid, powerful contractions but BRIEF
- white, paler fibers (WHITE MEAT)
70
Slow muscle fibers
slower, sustained contractions
- more myoglobin (to hold O2)
- aerobic (more mitochondria)
- smaller diameter (less myofibrils)
- takes longer to contract
- continue to contract (won't fatigue as quickly)
- darker color (DARK MEAT)
71
Intermediate fibers
attributes of both fibers
- similar to fast but greater resistance to fatigue
- more mitochondria than fast fibers
72
Smooth Muscle characteristics
-smallest type of muscle cell
-one central nucleus
-contractile proteins not aligned (actin and myosin not aligned in sarcomeres, therefore smooth muscle is NOT STRIATED)
-extracellular matrix = collagen/elastic fibers
-contract slowly
-resistant to fatigue
stimulated by: nervous system, hormones, and stretching
73
single unit smooth muscle (most common)
- many gap junctions (each cell connected to neighbor cell) *if one cell is stimulated they all are*
- fibers contract simultaneously (behave line one unit)
ex. digestive tract, respiratory tract, urinary tract
- exhibit rhythm
74
multi-unit smooth muscle
no or very few gap junctions *muscle cells aren't connected
- occurs as separate cells (don't act as a unit)
- cells only contract when stimulated (a cell needs to be directly stimulated to contract
ex. walls of large BV's, uterus, iris of eye
