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SMS Week 3 > Muscle Tissue > Flashcards

Flashcards in Muscle Tissue Deck (36):
1

skeletal muscle

Striated (voluntary)
T-tubule system
Well-developed sarcoplasmic reticulum
Multinucleated
Nuclei at cell periphery

Cell shape:
-Cylindrical (10 m –100 m in diameter)
-Great variations in length (1 mm -- 4 cm)
-Bulky muscles: larger cells
-Delicate muscles: smaller cells
Nuclei
-Several hundred/cell
-Flattened, oval, and elongated
-Located at cell periphery, beneath sarcolemma

Origins:
Loose mesenchyme -> myoblasts
Myoblasts fuse -> multinucleate myotubes
Myofilaments appear
-Irregular at first
-Gradually become aligned into myofibrils

2

smooth muscle

General features
-No striations
-No T-tubules
-Involuntary


Sympathetic: synaptic vesicles contain norepinephrine

Parasympathetic: synaptic vesicles contain acetylcholine

Iris (eye): every muscle fiber is innervated

Other areas: only small percentage of muscle cells innervated


Cells retain mitotic capability
Example: pregnant uterus
Can be formed from pre-existing pericytes

3

cardiac muscle

Striated (involuntary)
T-tubule system
Sarcoplasmic reticulum less well developed than in skeletal muscle
Single nucleus/cell; centrally located
Intercalated disks are diagnostic features of cardiac muscle tissue
numerous mitochondria
No fusion of myoblasts

One cell/nucleus
Centrally located
oval and fairly large

Myofibrils
-Branch and blend with adjacent myofibrils
~Thus less distinct than in skeletal muscle
-Sarcomeres, A-bands, I-bands, Z-disks, etc. are all present
Sarcoplasm most apparent at poles of nucleus

Atrial granules
-Unique to atrial cardiac muscle cells
-Contain atrial natriuretic peptide
-Lowers blood pressure by decreasing renal tubules ability to resorb (conserve) sodium and water

4

myofiber

muscle cells

5

myofibril

Tiny cylindrical rods within sarcoplasm

Responsible for appearance of cross-striations
Due to registry of adjacent myofibrils to one another

composed of actin and myosin filaments

6

myofilament

actin and myosin filaments

7

sarcolemma

plasma membrane

Numerous invaginations along cell surface
Form the T-tubules
Lumen of T-tubule continuous with extracellular space
T-tubules wind between myofibrils
Typically seen at A-I junction between the two ‘collars’ of the sarcoplasmic reticulum

8

sarcoplasm

cytoplasm

Between myofibrils
Beneath sarcolemma
Around nuclei
Mitochondria: near nuclei, beneath sarcolemma, between myofibrils
Sarcoplasmic reticulum

9

sarcoplasmic reticulum

smooth er

Network of cisterns and/or membranous tubules running between and around myofibrils
Tends to form ‘collars’ at A-I junctions
‘Collars’ connected by longitudinal components
Two ‘collars’ at each A-I junction
‘Collars’ separated from each other by T-tubules
Binds and releases Ca ++ (membranes contain voltage-gated Ca ++-release channels)

10

fascicle

a

11

actin

Thin
Extend from Z-disks to edge of H-band

G-actin (globular actin)
-Globular monomer
-Polymerizes to form F-actin

F-actin (fibrous actin)
-Composed of G-actin monomers
-Two helically-wound strands of polymerized G-actin

12

myosin

Thick
Extend from one side of A-band to other side of A-band
Thin cross-bridges extend from each myosin filament towards neighboring actin filaments

13

tropomyosin

Fibrous; arranged head to tail in a linear series

Helically wound along grooves of F-actin helix

Ca++
-Binds to TnC
-Binding to TnC induces a conformational shift in tropomyosin, exposing previously blocked active sites on the actin filament

14

actinin

Component of the Z-disk
Holds actin filaments in register by binding them in parallel array

15

troponin

Troponin complex (3 subunits)

TnT: binds entire troponin complex to tropomyosin

TnC: great affinity for Ca++

TnI: binds to actin, preventing actin-myosin interactions

16

T-tubule

Lumen of T-tubule continuous with extracellular space
T-tubules wind between myofibrils
Typically seen at A-I junction between the two ‘collars’ of the sarcoplasmic reticulum

17

triad

T-tubule + 2 lateral cisternae of sarcoplasmic reticulum
Membranes of T-tubules appear to be closely ‘coupled’ to membranes of sarcoplasmic reticulum
Facilitates transmission of electrical impulse from sarcolemma to interior depths of cell
Two ‘triads’/sarcomere (at the A-I junctions)

18

diad

T-tubule + a terminal portion of adjacent sarcoplasmic reticulum

19

nebulin

Long, non-elastic protein

Two molecules of nebulin wrap around each thin filament

Help anchor thin filament to Z-disk

20

titin

Helps position myosin filaments precisely within the sarcomere
Extends from each half of a myosin filament to the Z-disk

21

caveolae

smooth muscle
Pinocytotic-like invaginations of sarcolemma
Probably play the role of the T-tubules found in skeletal and cardiac muscle
May work in concert with sarcoplasmic reticulum to modulate Ca++ availability

22

dense bodies

smooth muscle
Two locations
-Inner aspects of sarcolemma
-Throughout cytoplasm
Comparable to Z-disks of skeletal & cardiac muscle
-Contain -actinin
-Serve as anchor sites for actin-myosin interactions as well as intermediate filaments (vimentin; desmin)

23

Z-disk

Region where attachment of ends of actin filaments in adjacent sarcomeres occurs
Appears filamentous and electron dense
Contains -actinin

24

sarcomere

linear unit

25

intercalated disk

Dark cross-bands; frequently appear step-like

Occur where a Z-disk should be observed

Mark spots of cell-cell attachments (i.e, at ends of cells)

26

Be able to describe and explain the predictable filament pattern that you would observe in cross sections through the I-band, A-band, H-band.

M-line
At center of H-band
Contains myomesin, C-protein, and other proteins
interconnect the thick myosin filaments to maintain their specific lattice arrangement

27

Be able to explain the changing banding patterns that you would see as a muscle (skeletal or cardiac) contracts.

a

28

Be able to explain the function(s) of the sarcoplasmic reticulum serves in muscle tissue

a

29

epimysium

Outermost sheath of c.t.; surrounds entire muscle

30

perimysium

Connective tissue sheath around groups of muscle fibers (fasicles)
Continuous with tendon fibers

31

endomysium

Sheath of fine c.t. around individual muscle fibers
Fine reticular fibers and ground substance

32

Be able to describe what Purkinje fibers are and do.

Composed of modified cardiac muscle cells called Purkinje fibers (cells)
Myofibrils reduced in number
Contain more sarcoplasm
Nuclei more rounded
Large diameter
Lack T-tubules
More glycogen

33

neuromuscular spindles

Small specialized muscle fibers in a c.t. capsule
-Small fibers = intrafusal fibers
Two zones
-Central (equatorial) region of intrafusal fibers
~Nuclei chain fibers
~Nuclear bag fibers
-Polar regions are long and tapered

Capsules
-Internal capsule immediately surrounds intrafusal fibers; encloses inner axial space
-External capsule surrounds internal capsule and creates periaxial space between inner and outer capsules

Innervation
Sensory
-Large fibers form annulospiral or primary endings around nuclear bag & nuclear chain regions
-Smaller diameter afferents form flower spray or secondary endings on intrafusal fibers on polar segments
Motor
-Efferent fibers form motor end plates on either side of mid-region of intrafusal fibers

Act like miniature strain gauges

34

Golgi tendon organs

Structure
-Spindle-shaped bodies comprised of collagen and enclosed by a thin capsule
-Afferent (sensory) fibers penetrate between the collagen fibers
-Sensitive to stretching forces on tendons


35

motor end plates

Myelin sheath lost as nerve fiber approaches surface of muscle cell
Axon branches near surface of muscle cell
-Branches occupy recesses in cell surface
-Recesses called synaptic troughs or primary synaptic clefts
Sub-neural apparatus
Synaptic vesicles

Sub-neural apparatus
-Secondary synaptic clefts formed by folds in sarcolemma
-Acetylcholinesterase located at surface of sarcolemma
Synaptic vesicles
-In axon terminals
-Contain acetylcholine

36

Contractile mechanisms

Ca++ + calmodulin form a complex
Ca++ probably stored in caveolae
Complex activates myosin light chain kinase
Myosin light chain kinase
phosphorylates one of the two light chains associated with the myosin molecule head

Phosphorylation of light chain
Exposes an ‘actin-binding’ site on the myosin molecule
Enables myosin molecule to ‘straighten out’ and form small bipolar filaments
Slow process
Smooth muscle contraction takes longer and is more prolonged than skeletal or cardiac muscle contraction