Histology - Muscle Tissue

Front 1

Muscle cells are derived from?

Back 1

Mesenchyme, formed by mesenchymal cells, derived from mesoderm, middle layer of embryo

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Muscle Fiber

Back 2

Myofiber = Muscle Cell

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Sarcoplasm

Back 3

Cytoplasm of muscle fiber

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Sarcolemma

Back 4

Plasma membrane of muscle fiber

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Sarcoplasmic Reticulum

Back 5

Smooth ER of muscle fiber

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Basal Lamina

Back 6

Sheetlike extracellular material produced by and located between cells (muscle, adipose, epithelial, schwann) and the subajacent CT

Front 7

Basal Lamina - Function

Back 7

Barrier that limits or regulates exchanges between connective tissue and other tissues
In muscle tissue - binds muscle cells into a single functional mass, allows "transmission" of contractile forces

Front 8

Skeletal Muscle Tissue - surface coverings

Back 8

Epimysium
Perimysium
Endomysium

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Epimysium

Back 9

Dense irregular CT, surrounds entire skeletal muscle

Front 10

Perimysium

Back 10

Loose CT, surrounds bundles of skeletal muscle fibers called fascicles

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Endomysium

Back 11

Loose CT composed of basal lamina and reticular fibers, collectively forming a basement membrane, which surrounds individual skeletal muscle fibers

Front 12

Skeletal Muscle Tissue Contains

Back 12

Blood vessels, lymph vessels, nerves

Front 13

Skeletal Muscle Architecture

Back 13

Myofilaments -> Myofibrils -> Muscle Fibers -> Muscle Fasciculi (Parallel Bundles) -> Muscle

Front 14

Microscopic Structure of (Extrafusal) Skeletal Muscle Fibers

Back 14

Cylindrical (tapered ends), unbranched, 1-30cm long, 10-100um in diameter
Capable of Hypertrophy but not Hyperplasia

Front 15

Myofibrils

Back 15

Each muscle fiber contains dozens to hundreds of myofibrils, oriented parallel to long axis of muscle fiber
Composed of sarcomeres arranged in series

Front 16

Sarcomere

Back 16

Contractile unit of striated muscle fibers.
From Z line to Z line
Shorten with contraction
2.5um long

Front 17

Z-Line

Back 17

Dark line bisecting I band
Contains cytoskeletal proteins that anchor thin filaments and "tie" adjacent sarcomeres together
Alpha Actin

Front 18

I Band

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Light region bisected by Z line
Thin filaments that do not overlap thick filaments
Shorten with contraction

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A Band

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Dark central region
Primarily thick filaments + overlapping thin filaments

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H Band

Back 20

Center of A band
Only thick filaments
Shorten wiht contraction

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M Line

Back 21

Bisects H band
Region where adjacent thick filaments are connected

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Thick Filaments

Back 22

Myosin
Rodlick tail region and globular (double) head region
Each "Head" region contains ATP binding site, w/ATPase activity, and an actin binding site
Rodlike portions overlap and globular head regions direct towards either end of sarcomere

Front 23

Thin Filaments

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2 Twisted chains of actin w/tropomyosin and its attached troponin positioned in groove between actin chains.

Front 24

Troponin

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Contains calcium binding site when bound to Ca++ causes change in configuration of thin filament to allow interaction with thick filament

Front 25

Sarcolemma - Transverse T-Tubules - Structure

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Invaginations of the sarcolemma that lie perpendicular to long axis of muscle fibers encircling myofibrils at regular intervals

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Sarcolemma - Transverse T-Tubules - Function

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Conduct electrical impulses from surface to interior of muscle fiber

Front 27

Organelles - Sarcoplasmic Reticulum - Structure

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System of tubules that runs in long axis of muscle fibers and surrounds individual myofibrils.
Dilated terminal segments adjacent to sides of T-Tubules called Terminal Cisterns

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Organelles - Sarcoplasmic Reticulum - Function

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Calcium storage and mobilization
Triad - T-Tubule + 2 terminal cisternae (either side)

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Nucleus - Muscle Cell

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Numerous, Peripherally Located

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Motor Unit

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Single motor neuron and all of hte muscle fibers that it innervates. All muscle fibers in a motor unit are of the same type.
Most muscles are composed of both fiber types.

Front 31

Mutability

Back 31

Muscle fibers are capable of altering "type" in response to hormones, neural input, and/or load or activity pattern placed upon the muscle

Front 32

Mechanism of Contraction - Excitation Contraction Coupling

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AP in Alpha Motor Neuron
ACh release @ NMJ
ACh binds to muscle receptor
Sarcolemma depolarizes
AP conducted via T-Tubules
Signal SR to release Ca++
Ca++ binds to troponin
Actin-Myosin interaction (ATP)
Ca++ re-uptake

Front 33

Sliding Filament Theory

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Thin filaments slide relative to thick filaments causing shortening of the sarcomere.

Front 34

Neuromuscular Junction

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One NMJ per muscle fiber. Consist of: Alpha Motor Neuron, Synaptic Cleft, Skeletal Muscle Fiber

Front 35

Alpha Motor Neuron

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Travels through perimysium towards the muscle fiber, giving rise to several terminal twigs. At site of innervation it loses its myelin sheath and forms a dilated terminal bud.

Front 36

Synaptic Cleft

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Space btw neuron and muscle, in which lies the basal lamina which contains the enzyme 'cholinesterase' which breaks down ACh.

Front 37

Skeletal Muscle Fiber

Back 37

Region of sarcolemma has clefts and ridges called junctional folds which contain ACh receptors

Front 38

Proprioceptors: Muscle Spindle - Structure

Back 38

Specialized skeletal muscle fibers (intrafusal) encapsulated by a fibrous connective tissue.
Middle is surrounded by sensory nerve fibers

Front 39

Proprioceptors: Muscle Spindle - Function

Back 39

Detect changes in muscle length and relay info to spinal cord
Spindles -> Stretch

Front 40

Proprioceptors: Muscle Spindle - Distribution

Back 40

Throughout skeletal muscle
Connected in parallel w/extrafusal muscle fibers

Front 41

Proprioceptors: Golgi Tendon Organs - Struture

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Composed of a network of sensory nerve fibers intertwined w/bundles of collagen fibers of a tendon and encapsulated by fibrous connective tissue

Front 42

Proprioceptors: Golgi Tendon Organs - Function

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Detect changes in muscle tension and relay info to spinal cord
Tendon -> Tension

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Proprioceptors: Golgi Tendon Organs - Distribution

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At musculotendinous junction
Connected in series w/extrafusal muscle fibers

Front 44

Satellite Cells

Back 44

Muscle stem cells that persist after skeletal muscle differentiation
When activiated, can proliferate and fuse to form muscle fibers
(regenerate muscle cell if satellite cell and blood supply are both present)

Front 45

Satellite Cells - Structure

Back 45

Mono-nucleated spindle shaped
Lie within basal lamina surrounding each mature muscle fiber

Front 46

Skeletal Muscle: Aging - Structural Changes

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Decrease in # of muscle fibers and muscle fiber size
Motor unit: remodeling, decrease in total number, increase in size of remaining, increase in proportion of type I motor units

Front 47

Skeletal Muscle: Aging - Functional Changes

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Loss of muscle mass (sarcopenia) and consequent decrease in strength

Front 48

Cardiac: Surface Coverings - Endomysium

Back 48

Loose CT composed of basal lamina and reticular fibers (Basal Membrane), surrounds individual muscle fibers
Mechanically transmit forces generated by contracting muscle cells

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Cardiac: Surface Coverings - Contain

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Blood vessels
Lymph vessels
Nerves

Front 50

Muscle Architecture

Back 50

Myofilaments -> Myofibrils -> Muscle Fibers -> Muscle Fasciculi (Interwoven Bundles) -> Heart

Front 51

Microscopic Structure of Cardiac Muscle Fibers

Back 51

Cylindrical, branced, 85 to 100um long, 15um diameter
Cross striations not as prominent as skeletal muscle
Capable of hypertrophy, not hyperplasia

Front 52

Cardiac: Cytoplasm (Sarcoplasm) contents

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Myofibrils
T-Tubules
SR
Mitochondria
Intercalated Discs
Nucleus

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Cardiac: Myofibrils

Back 53

Structure and function same as skeletal muscle

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Cardiac: T-Tubules and SR

Back 54

Not as organized as skeletal muscle fibers

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Cardiac: Mitochondria

Back 55

Numerous (many more than skeletal muscle)

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Cardiac: Intercalated Discs - Structure

Back 56

Contain three types of junctions, including gap

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Cardiac: Intercalated Discs - Function

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Anchor myofilaments
Bind ends of cardiac muscle fibers together
Provide ionic continuity btw cardiac muscle fibers

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Cardiac: Nucleus

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One or two centrally located

Front 59

3 Hallmarks to differentiate Cardiac from Skeletal

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Branched fibers
Intercalated Discs
Centrally located nucleus (1 or 2)

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Innervation of Cardiac Muscle (2 types)

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Myogenic - spontaneous, intrinsic rhythmic activity of cardiac muscle fibers
ANS - via rhythmic impulse-generating and conducting structures (SA, AV, AV Bundle, Purkinje) - modifies contractile activity

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Cardiac: Regulation of Contraction

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Calcium and ionic coupling by gap junctions

Front 62

Smooth Muscle: Surface Coverings

Back 62

Individual fibers surrounded by basal lamina and reticular fibers (basement membrane)
Fibers bound together by a network of loose CT
Contain: blood & lymph vessels, nerves

Front 63

Smooth Muscle: Architecture

Back 63

The tapered end of one smooth muscle fiber lies adjacent to large midpoint of neighboring smooth muscle fibers
(large region of one next to thin of other)
Muscle fiber -> Muscle fasciculi (irregular branching) -> Smooth muscle -> Sheet or multiunit

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Microscopic Structure of Smooth Muscle

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Fusiform, unbranced, 20 to 500um in size
No cross striations (no myofibrils)
Capable of hypertrophy and hyperplasia

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Smooth Muscle: Cytoplasm (Sarcoplasm) - Contents

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No myofibrils or T-Tubules
Rudimentary SR
Thick and Thin myofilaments in criss/cross pattern throughout
Contain Dense Bodies

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Smooth Muscle: Dense Bodies - Structure

Back 66

Composed of protein a-actinin (alpha)

Front 67

Smooth Muscle: Dense Bodies - Function

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Transmit contractile force to adjacent smooth muscle cells and surrounding connective tissue

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Smooth Muscle: Nucleus

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Single centrally located

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Smooth Muscle: Innervation

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Enteric Nervous System
ANS

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Smooth Muscle: Enteric Nervous System

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Motor and sensory neurons in two interconnected plexuses in walls of GI tract.
Control coordinated contraction and relaxation of intestinal smooth muscle and regulate gastric secretion and blood flow.

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Smooth Muscle: ANS (visceral and multiunit)

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Visceral Smooth Muscle (Hollow Organs): Poor innervation, specialized for slow prolonged contraction.
Multiunit Smooth Muscle (Iris): Rich innervation, specialized for precise graded contractions

Front 72

Smooth Muscle: Regulation

Back 72

Calcium and ionic coupling via gap junctions