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Human Histology > Unit 4: Muscle > Flashcards

Unit 4: Muscle Flashcards

(75 cards)

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1
Q

What are the types of muscle tissue?

A

Skeletal
Cardiac
Smooth

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2
Q

What is the function of skeletal muscle?

A

moves the skeleton by pulling on tendons attached to bones

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3
Q

What is the function of cardiac muscle?

A

pumps blood through heart chambers and blood vessels

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4
Q

What is the function of smooth muscle?

A

regulates movement of “contents” through hollow organs and blood vessels

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5
Q

What are the key properties of muscles?

A

Excitability
Contractility
Extensibility
Elasticity

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6
Q

What is the excitability property of muscle?

A

Ability to respond to stimuli such as chemical, electrical or mechanical

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7
Q

What is the contractility property of muscle?

A

Ability to develop tension in response to stimulus.
Enables movement of the structures to which muscles are attached.
Contractility due to interaction of myofilaments (thick and thin filaments composed of myosin and actin)

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8
Q

What is the extensibility property of muscle?

A

Ability to stretch

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9
Q

What is the elasticity property of muscle?

A

Ability to return to normal resting length

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10
Q

What does a skeletal muscle consist of?

A

Contractile tissue composed of muscle cells (aka muscle fibers or myocytes)
Series of collagen-based connective tissue coverings (the “mysiums”)

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11
Q

What do the Series of collagen-based connective tissue coverings (the “mysiums”) of skeletal muscle do?

A

Binds muscle fibers together
Help links skeletal muscle to bone (usually), skin, or fascia
Help transduces force to attached structure(s)
Conveys blood vessels and nerves

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12
Q

What is the control of contraction & relaxation in skeletal muscle? How is it innervated?

A

Voluntary
Innervation by motor neurons provide contraction signa

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13
Q

How is skeletal muscle developed?

A

During embryological development, multiple mesodermal stem cells (myoblasts) fuse to form a single skeletal muscle cell
Each skeletal muscle cell (aka muscle fiber or myocyte) is a syncytium (multinucleated cell)

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14
Q

Can muscle fibers divide?

A

Once fusion occurs, muscle fibers cannot divide

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15
Q

How do muscle cells enlarge?

A

Muscles enlarge by cell hypertrophy, not hyperplasia

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16
Q

How does regeneration occur in skeletal muscle?

A

Some myoblasts (satellite cells) remain in muscle
Regenerative capacity is robust, but can be overwhelmed

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17
Q

What happens with myoblasts (satellite cells) that remain in skeletal muscle?

A

Satellite cells = stem/progenitor cell-like cells
Can divide and fuse to generate new muscle fibers
Activated when needed for healing/repair

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18
Q

What happens when the regenerative capacity of skeletal muscle is overwhelmed?

A

After severe muscle trauma or due to disease (e.g. muscular dystrophy)
Fibrosis (replacement of muscle with fibrous tissue) occurs when repair process fails and/or is overwhelmed

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19
Q

What is the shape of skeletal muscle?

A

Long cylindrical cells (look polygonal in cross section); length varies by location (few mm to >500 mm).

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20
Q

What do the nuclei look like in skeletal muscle?

A

Multinucleated, with nuclei pushed to periphery, just beneath plasma membrane (sarcolemma)

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21
Q

What does the cytoplasm look like in skeletal muscle?

A

Cytoplasm (sarcoplasm) filled with myofibrils, bundles of longitudinal arrays of myofilaments

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22
Q

How do the thick and think filaments appear in skeletal muscle?

A

Overlapping arrangement of thick and thin filaments in myofibrils gives striated appearance

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23
Q

What are striations?

A

alternating pattern of light and dark bands visible by light microscopy

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24
Q

What are found between myofibrils in skeletal muscle?

A

Mitochondria and glycogen deposits found between myofibrils
• Generate ATP for muscle contraction

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25
What is the appearance of skeletal muscle fibers in longitudinal sections?
Portions of elongated, cylindrical cells Portions of multiple fibers seen in parallel Slivers of endomysium in “spaces” between fibers Striations perpendicular to long axis of fiber are visible Slender, elongated nuclei at periphery of each fiber
26
What is the appearance of skeletal muscle fibers in cross sections?
Fibers often look polygonal rather than cylindrical Myocyte nuclei, when visible, are at periphery Each muscle fiber surrounded by endomysium May see small vessels, fibroblast nuclei in endomysium
27
What are the layers of connective tissue that surround skeletal muscle?
Endomysium Perimysium Epimysium
28
What is endomysium?
delicate layer of reticular fibers that immediately surrounds individual muscle fibers. It carries small diameter blood vessels and fine neuronal branches
29
What is perimysium?
thicker CT layer that surrounds a group of fibers to for a bundle or fascicle. Fascicles are functional units of muscle fibers. Larger blood vessels and nerves travel here
30
What is epimysium?
sheath of dense CT that surrounds a collection of fascicles that constitutes the muscle (deep investing fascia). Major vascular and nerve supply of the muscle penetrates the epimysium. Continuous with tendon attaching to bone
31
What are the functional units of muscle?
Multiple muscle fibers grouped to form a bundle or fascicle Each fascicle surrounded by thicker layer of connective tissue (perimysium) Larger branches of blood vessels and nerves are found in perimysium Each fascicle functions as a unit; muscle fiber in each fascicle work together Multiple fascicles are grouped together to form a muscle Each muscle encased in a sheath of dense connective tissue called the epimysium
32
What is the myotendinous junction?
Site of attachment of a muscle fiber and the contiguous connective tissue of the tendon
33
How are the myotendinous junctions attached?
Muscle fibers send numerous cytoplasmic projections into connective tissue of tendon - Interdigitations increase surface area of contact and enhance adhesion Collagen fibrils of tendon linked to basal lamina of muscle fiber by multi-adhesive matrix proteins
34
What do nerves, arteries, veins, and lymphatics do in skeletal muscle?
Run together in a neurovascular bundle through the connective tissue coverings of a skeletal muscle
35
What vasculature surrounds each muscle fiber?
Capillary beds surround each muscle fiber • provides oxygen and nutrients • carries away CO2 and waste
36
What do nerves of skeletal muscles contain?
axons of somatic motor neurons Cell bodies of these neurons are in brain or spinal cord
37
How do axons travel to skeletal muscle?
travel in neurovascular bundle to skeletal muscle and branch to innervate each fiber to control contraction
38
How do axons control skeletal muscle movement?
Axons of motor neurons branch to innervate varying numbers of muscle fibers - Few branches to innervate small number muscle fibers (fine movement) - Many branches to innervate hundreds/thousands of muscle fibers (gross movement)
39
What does motor innervation do for skeletal muscle homeostasis?
Motor innervation of muscles maintains muscle function Motor neuron damage causes denervation atrophy -Decreased muscle fiber diameter and myofilament expression
40
What is the structure of myofibrils in the sarcoplasm?
Long bundles of myofilaments (thick & thin filaments) Extend the entire length of the fiber Occupy the bulk of space in the sarcoplasm
41
What are myofibrils?
arrays of a repeating unit called a sarcomere sarcomere contains thick and thin filaments organized in specific overlapping pattern
42
What are the types of skeletal muscle fibers?
Red fibers Intermediate fibers White fibers
43
What are red fibers? What is the rate of contractile speed and fatigue?
Slow twitch Slowest speed of contraction, but fatigue resistant Found in limb muscles, erector spinae muscle
44
What are intermediate fibers? What is the rate of contractile speed and fatigue?
fast oxidative-glycolytic fibers Fast speed of contraction and relatively fatigue resistant Major muscles of the legs
45
What are white fibers? What is the rate of contractile speed and fatigue?
Fast glycolytic/twitch Fastest speed of contraction, but fatigue quickly Found in muscles generating “explosive” force or controlling movement of eye & digits
46
What is the A band?
Dark bands that contains thick filaments and overlapping portion of thin filaments
47
What is the I band?
Light bands that contain the remaining portion of thin filaments
48
What is the Z line/disc?
Protein dense region separating one sarcomere from next. Contains proteins that anchors thin filaments
49
What is the H zone/band?
Central, lighter portion of A band containing only thick filaments (no thin segments) No myosin head, contains M line
50
What is the M line?
Protein dense region at center of H zone. Contains proteins that anchor thick filaments
51
What are aligned in myofibrils and muscle fibers?
Adjacent sarcomeres in myofibrils are aligned (“in register”) so A bands, I bands, etc. are all aligned in the myofibril Myofibrils in sarcoplasm of a single muscle fiber also aligned so they are in register within the muscle fiber
52
What is myosin?
hexamer composed of 2 heavy chains & 4 light chains Molecular motor protein Major component of thick filaments
53
How does myosin form thick filaments?
Tails of myosin heavy chains associate laterally in antiparallel fashion to form thick filament
54
What is the arrangement of thick filament with myosin?
Form thick filament with “bipolar” arrangement -Central bare zone -Myosin heads radiate around ends
55
What does the myosin head do?
Contains actin binding site and ATP binding site/ATPase activity ATP hydrolysis/release of Pi + ADP causes movement of myosin head (molecular motor) to power muscle contraction
56
What is actin?
Major component of thin filaments Filament formed from globular actin Contain binding site for myosin head
57
What are regulatory proteins of the sarcomere?
Associate with actin on thin filament Tropomyosin Troponin
58
What does tropomyosin do?
covers myosin binding sites on actin
59
What is Troponin and what does it do?
Heterotrimer Troponin T binds to tropomyosin Troponin I binds to actin Troponin C (TnC) binds to calcium ions - Ca2+ binding to TnC causes conformational change, this moves tropomyosin & makes myosin binding site on actin accessible
60
What happens to the filaments when skeletal muscle contracts?
thin filaments slide over the thick filaments
61
How do thin filaments slide over the thick filaments when skeletal muscle contracts?
Result of sequential interaction between myosin head and actin Myosin head pivots and bends, pulling actin along with it Thick filaments do not move, thin filaments slide toward the M line
62
What drives thin filaments to slide over the thick filaments when skeletal muscle contracts?
Driven by Ca2+- and ATP-dependent interaction between myosin and actin
63
What is the appearance of skeletal muscle contraction?
Z discs (line) move closer together (sarcomere length reduced) I bands narrow H zone (band) narrows/disappears A band remains the same length because thick filaments do not move Thick/thin filaments do not change in length
64
How are sarcomeres oriented?
parallel to long axis of the skeletal muscle cell Thus...contraction of muscle fibers in a muscle occurs in a single direction
65
What is the structure of the sarcoplasmic reticulum?
Special type of sER Composed of a system of membranous sacs and anastomosing channels encircling each myofibril Arranged as a series of adjacent networks or segments Dilated sacs at ends of each network are called terminal cisternae
66
What is the function of the sarcoplasmic reticulum?
Stores high concentration of stored Ca2+ in the terminal cisternae Calsequestrin: Ca2+ binding protein in SR Ca2+ released from the SR binds TnC, allows actin-myosin interaction, sliding filament mechanism
67
What are the mitochondria and glycogen deposits in the sarcoplasmic reticulum?
Between the myofibrils, adjacent to to SR Function: Provide ATP for muscle contraction
68
What is the structure of transerve tubules (T-tubules)
Invaginations of sarcolemma into the cell Form network of channels lined by specialized plasma membrane that wrap around each myofibril Lumen of T-tubules is continuous with extracellular space/contains extracellular fluid WhereT-Tubule wraps around myofibril, it associates with terminal cisternae of two sarcomeres (triad)
69
What is the function of transverse tubules (T-tubules)?
Allow action potential from surface of muscle fiber to travel rapidly to interior of cell Permits simultaneous contraction of all sarcomeres in the cell Action potential in T-tubule membrane signals to adjacent SR in triad, resulting in Ca2+ release that allows contraction
70
What is the structure of the neuromuscular junction?
axon forms a dilation called the axon terminus (aka synaptic end bulb, synaptic bouton, synaptic knob) that houses synaptic vesicles containing Acetylcholine (Ach)
71
Where do axon terminals lie for muscle fibers?
In the depression of the sarcolemma of the muscle fiber Sarcolemmaunderlyingaxonterminusisdeeplyfolded Folds contain Ach Receptors (AchR)
72
What is the function of the neuromuscular junction?
Signaling at NMJ initiates cascade of events leading to skeletal muscle contraction
73
How does an action potential cause muscle contraction in muscle cells?
Action potential reaches axon terminus Ach released and binds AchR on sarcolemma Ach binding to AchR leads to influx of Na+ Ultimately leads to muscle cell action potential/membrane
74
How many axon termini and what is the size of neuromuscular junctions?
NMJ are small but diffuse structures that contain multiple axon termini Size may correlate with muscle fiber diameter
75
How do neuromuscular junction motor units discharge?
It is a graded response to contraction signal Not all discharge at once

Human Histology (6 decks)

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