Skeletal and Smooth Muscle

Question 1

Muscle Tissue

Answer 1

Specialized for movement

Sliding Filaments (actin/myosin)

• 3 types
  
  • skeletal
  • smooth → found in blood vessels, GI Tract
  • cardiac → heart only

Question 2

Define: Orientation

Answer 2

organization of fibers (tissues) (structures with longitudinal and lateral axes) relative to organ with longitudinal and lateral axes

Question 3

Define: Sectioning

Answer 3

How structure with longitudinal and lateral axes was cut

Question 4

Types of Sectioning

Answer 4

Longitudinal → cut length wise

oblique → angle cut

circular → through

Question 5

Sectioning vs. Orientation: Smooth Muscle

Answer 5

Cells longer than they are wide

Left → longitudinal section

Right → transverse section

IC → oriented circularly

OL → oriented longitudinally

Question 6

How was the tissue cut?

Answer 6

Longitudinal

Question 7

Movement of muscles

Answer 7

sliding filaments of actin and myosin

Question 8

Arrangement of fibers: Skeletal/Cardiac

Answer 8

Lined up to form striations

Question 9

Arrangement of fibers: Smooth

Answer 9

No regular arrangement → no striations

Question 10

Globular Actin

Answer 10

polymerizes to filamentous actin

Question 11

Actin Filaments

Answer 11

thin cytoskeletal structures known as microfilaments

Question 12

Bundles of Actin Filaments

Answer 12

• form large stress fibers
  
  • visible on light microscopy
  • important in cells that resist shear stress

Question 13

Actin-binding proteins (ABP)

Answer 13

Regulate microfilament function (e.g. junctions)

Include motor protein myosin

Question 14

Define: Myosin

Answer 14

motor protein with actin and ATP binding sites

Question 15

Myosin Filament Orientation

Answer 15

Striated

Smooth

Question 16

Sliding Filaments

Answer 16

• Ca²⁺ binds to troponin
  
  • moves it out of the way (shifts)
• ATP binds to myosin
  
  • detaches it from actin
• ATP cleaved to ADP
  
  • draws myosin head up and back
• Myosin head drops down
• Myosin attaches to actin
  
  • pulls actin filaments
• ADP Detaches
• ATP binds again

Energy Dependent Process

Question 17

How filaments generate force

Answer 17

actin and myosin must be connected to membrane for whole cell to contract

Question 18

Skeletal Muscle Structure

Answer 18

• Muscle fiber is a syncytium (multicellular/multinuclear)
• Bundles of filaments (fibrils) in the sarcoplasm (cytoplasm)
• Mitochondria between
• SR (Ca storgae) net to T tubules (activate Ca release in cells)
• Z line: a-actinin → helps anchor to sarcolemma
• I band: actin and motor proteins
• A band: I band plus myosin
• H band: C protein

Question 19

Syncytium Formation

Answer 19

• Embryonic myoblasts due to form myotube
  
  • plasma membrane (sarcolemma)
  • surround by basal lamina and satellite cells
• Finger-like sarcolemma processes
  
  • T-tubules
  • extend into sarcoplasm
  • connect with SR
• Sarcoplasm filled with myofibrils
  
  • surrounded by mitochondria
  • composed of thick (myosin) and thin (actin) myofilaments

Question 20

Skeletal Muscle Syncytium Histology

Answer 20

Question 21

Skeletal Muscle: Myofibril Structure

Answer 21

Question 22

Sarcomere

Answer 22

Z-line to Z-line

Question 23

Skeletal Muscle Histology

Answer 23

Question 24

Skeletal Muscle Organization

Answer 24

Myofilaments → myofibril → single muscle fiber/cell → fascicle → muscle

Question 25

Skeletal Muscle: Endomysium

Answer 25

envelopes each muscle cell

Question 26

Skeletal Muscle: Perimysium

Answer 26

surrounds each fascicle

Question 27

Skeletal Muscle: Epimysium

Answer 27

surrounds the entire muscle formed by groups of fascicles

Question 28

Neuromuscular Junction

Answer 28

Question 29

Skeletal Muscle: Initiation of Contraction

Answer 29

ACh initiates depolarization → Ca²⁺ channels open and release Ca²⁺ → Ca²⁺ binds troponin C → initiates contraction → Ca²⁺-dependent ATPase mediates return of Ca²⁺ to SR

Question 30

Skeletal Muscle Histology: Orientation/Sectioning

Answer 30

Question 31

Muscle Spindle

Answer 31

propioceptive mechanoreceptor contributes to reflex

Question 32

Muscle Spindle Histology

Answer 32

Question 33

Smooth Muscle Cells

Answer 33

Question 34

Fusiform Nucleus

Answer 34

Thick in the middle. thin on the ends

Question 35

Smooth Muscle Histology

Answer 35

Question 36

Smooth Muscle: Initiation of Contraction

Answer 36

* Ca²⁺ from outside the cell * Responsive to nerve, hormone, or stretch stimulation * Phosphorylation of Myosin II light chain initiates movement * by MLCK * MLCK activated by calmodulin * Calmodulin only active when Ca²⁺ bound

Question 37

Smooth Muscle: Structural Changes

Answer 37

Question 38

Smooth Muscle Cell Histology: Contracted

Answer 38

Question 39

Skeletal v. Smooth Muscle

Answer 39