Muscle Cell Histology

Question 1

what are the 3 places where skeletal muscle is not attached to bone? (visceral striated muscle)

Answer 1

tongue, esophagus and diaphragm

Question 2

what are nearly all muscle pathologies associated with?

Answer 2

ECM fibrosis

Question 3

what is contained in the epimysium

Answer 3

surrounds a muscle Dense connective tissue containing fibroblasts, collagen and elastic fibers Merges with dense collagen of tendons, aponeuroses, and superficial fascia Contains blood vessels, nerves, and lymphatic vessels

Question 4

what is contained in the perimysium

Answer 4

surrounds a fascicle dense, connective tissue Functions to bundles myofibers into fascicles Conduits for nerves, arteries, arterioles, veins, and houses muscle spindles

Question 5

what is contained in the endomysium

Answer 5

surrounds a single muscle fiber ( a fiber is a muscle cell) Delicate connective tissue composed of collagen, elastic fibers, reticulin fibers, as well as extracellular matrix proteins, e.g., laminin-2, Contains capillaries which are permeable and often closed at rest: 1.7 capillaries adjacent to each individual fiber 0.7 capillaries per fiber when looking at a cross-sectional area Contains terminal axons that synapse on myofibers at neuromuscular junctions

Question 6

define a costamere

Answer 6

help bridge the contractile apparatus to the extracellular matrix. TRANSMIT FORCE TO ENDOMYSIUM “rib-like” complexes of proteins connecting z-lines to sarcolemma

Question 7

Dystroglycan/Sarcoglycan complex

Answer 7

help bridge the contractile apparatus to the extracellular matrix. TRANSMIT FORCE TO ENDOMYSIUM Sarcolemmal complex transmitting internal forces to ECM Dystrophin is t connects complex to subcortical actin cytoskeletal

Question 8

What are Myotendinous Junctions

Answer 8

Function: Highly folded membrane increases surface area and converts tensile stress to sheer stress Last sarcomere lacks a z-line Actin filaments extend from the A-band and attach to the sarcolemma Collagen fibrils extend between the projections of the membrane (arrows)

Question 9

Identify the type of muscle shown here

Answer 9

The whole thing is the epimysium, the

perimyseum are the bundles

The endomysium are inside of the fasicles

Question 10

ID this structure

Answer 10

Question 11

How do you differentiate the nervous tissue from the tendon and the skeletal muscle

Answer 11

The nerve has the flat perineurym, the tendon is in the skeletal muscle and also has microfilaments

Question 12

what is the function of the pacinian corpusle

Answer 12

detect vibration

Question 13

How does proprioception occur

Answer 13

provide afferent signals to the CNS that tells us where our body is postioned based on how tensed the intrafusal muscle fibers are

the intrafusal fibers have afferent and efferent information

intrafusal fibers send sensory information via large myelinated fibers from the central zone to dorsal root to spinal cord; anterior horn cells neurons (gamma fibers) innervate the distal zones and regulate contraction of the distal regions

Question 14

what are infusal fibers and how dothey relay

Answer 14

A muscle spindle is encapsulated by modified perimysium, with concentric layers of flattened cells, containing interstitial fluid and a few thin muscle fibers filled with nuclei and called intrafusal fibers. Several sensory nerve axons penetrate each muscle spindle and wrap around individual intrafusal fibers. Changes in length (distension) of the surrounding (extrafusal) muscle fibers caused by body movements are detected by the muscle spindles and the sensory nerves relay this information to the spinal cord.

Different types of sensory and intrafusal fibers mediate reflexes of varying complexity to help maintain posture and to regulate the activity of opposing muscle groups involved in motor activities such as walking.

Question 15

What is the signifince of the T tubule

Answer 15

allows to spead the wave of depolarization down into the layers of cytoplasm within the muscle cell

Question 16

define the triad

Answer 16

the T tubule with the 2 cisterns of SR on each side

Question 17

where does the triad reside

Answer 17

A-I junction

Question 18

ID these structure

Answer 18

Question 19

function of the M

function of Z-disk

function of A band

function of I band

a actin

Answer 19

M: bisects the sarcomere and organize myosin filaments

Z-disk: Organizes actin filaments and Defines the boundaries of sarcomeres

A band: where mysosin filaments reside, defines the legnth the only one that wont change

I band: Regions lacking myosin, Stretches across two sarcomeres

Question 20

signifiance of tropomysin and nebulin and titian

Answer 20

The proteins are often mutated in disorders

nebulin: determines the length
tropomysoin: caps it and stabilizes it at that length
titain: prevents over stretching, extends from Z disk to the M line

Question 21

what makes up the striated appearance

Answer 21

alternating A and I bands

Question 22

what are the 3 kinds of troponin

Answer 22

Calcium released from sarcoplasmic reticulum binds Troponin C–> Conformational change of Troponin-Tropomyosin complex –>Myosin head binding sites exposed

T- binds to tropomyosin

I- inhibit the binding of actin to myosin

C- binds to Ca and only in skeletal muscle

Question 23

what is the Sliding-filament Model

Answer 23

• During contraction, the thin and thick myofilaments do not change length
• Instead, as muscle shortens the thick and thin filaments slide past each other
• Consequently the length of the H zone and I band shortens
• The A band, which is determined by the length of the myosin myofilaments, stays the same length

Question 24

marker of muscle cell death

Answer 24

creatine kinase

Question 25

How would type 1 and 2 fibers differ in Myofibrillar ATPase (and eosin) and NADH-Tetrozolium Reductase staining?

Answer 25

type 1 would have more NADH-Tetrozolium Reductase because they have more mitochondria type 2 would have more ATPase (and eosin) because they would have more fast myosin and bind ATP at a higher ability

Question 26

differentiate skeletal fibers 1 and 2

Answer 26

1- Many mitochondria slow twitch high lipid high in myoglobin rich in oxidative enzymes •Function in tonic contraction 2- A and B subtypes few mitochondria fast twist low lipid low myoglobin more glycolysis •Function in rapid phasic contractions

Question 27

What determines the fiber type

Answer 27

The fiber type is determined by the by the rate at which the innervating neuron fires; for a motor unit, one axon is innervating multiple fibers...all myofibers of the same unit are of the same type, NEURON IS THE MASTER CONTROLLER

Question 28

can you change fiber type

Answer 28

Yes but only under pathological conditions. Training does not change the fiber type.

Question 29

what is a sign of chronic deinervation

Question 30

where is the connective tissue of uscle located?

Answer 30

in the endomysium

Question 31

how does exercise enlarge skeletal muscle

Answer 31

The variation in diameter of muscle fibers depends on factors such as the specific muscle, age, gender, nutritional status, and physical training of the individual. Exercise enlarges the skeletal musculature by stimulating formation of new **myofibril**s and **growth in the diameter of individual muscle fibers**. This process, characterized by increased cell volume, is called hypertrophy

Question 32

name these components

Answer 32

muscle spindle shows the capsule (C), lightly myelinated axons (MA) of a sensory nerve, and the intrafusal muscle fibers (MF). These thin fibers differ from the ordinary skeletal muscle fibers in having very few myofibrils. Their many nuclei can either be closely aligned (nuclear chain fibers) or piled in a central dilation (nuclear bag fibers). Muscle satellite cells (SC) are also present within the external lamina of the intrafusal fibers.

Question 33

What is this characteristic of

Answer 33

fiber grouping is a pathological condition that occurs which chronic denervation. The devervation leads to angular shaped atrophied cells, which the other axon resprouts to innervate these muscle cells. This results in diminished mixing of muscle types

Question 34

what is this characteristic of

Answer 34

fiber disarray in the central region of cells seen with NADH-tetrozoliumreductase (TR) staining ## Footnote Central region lacks mitochondria/sarcoplasmic reticulum (SR) **Intermediate region has a high proportion of mitochondria and SR** Peripheral region is normal in mitochondria content and myofibril architecture

Question 35

what is autophagocytosis

Answer 35

important in ischemic conditions Foci of cytoplasmic degeneration within cells are engulfed by primary lysosomes to form cytolysosomes

Question 36

what is the timeline of muscle and nerve injury after ischemia

Answer 36

decreased ox phosphorylation loss of ATP and pump maintence decrease in aerobic functions, decrease in NA pump detachment of ribosomes the loss of the pumps lead to increased Ca influx and K efflux --\> necrosis and cell swelling Loss of aerobic functions leads to an increase in lactic acid and decreased pH and decreased glycogen --\> clumbing of nuclear chomatin the loss of chromosomes --\> decrease in protein synthesis

Question 37

explain the process of segmental necrosis in muscle degeneration

Answer 37

Because the fibers are so long, t**he myofiberfragments into segments** and o**nly the severely damaged segments undergo necrosis** the affected segment undergoes cell swelling and Ca dsyregulation **reinnervation is possible** if the myofiber external lamina and endomysialtubule is intact

Question 38

what is the mechanism for cell swelling in reversible injury and how can this lead to necrosis

Answer 38

ATP depleted cells can no longer drive Na+/K+ATPase Na+ and water enters the cell leading to cell swelling and dilation of the rER **ØIn the liver we called this ‘ballooning degeneration’** **ØIn compartment syndrome, cellular swelling significantly contributes to increasing compartment pressure**

Question 39

how do ischemic myofibers appear under the microscope

Answer 39

ATP depletion leads to abrogation of ribogenesisand degradation of ribosomes; hence ischemic myofibers appear eosinophilic

Question 40

what is the mechanism for the Ca dysregulation in skeletal muscle injury

Answer 40

loss of Ca homeostasis is what marks irrersible point of muscle injury this is caused by loss of ATP stores inabling the cell from pumping Ca out activation of ca leads to activation of caspaces (cyt C), proteases, endoases and ATPases which ultimately lead to decreased ATP, nuclear and membrane damage and ultimately necrosis

Question 41

why is CK a good marker for muscle damage

Answer 41

Creatine phosphate provides a reservoir of easily accessible phosphate to transfer to ADP to regenerate ATP. The enzyme that carries out this reaction, creatine phosphokinase, is often used as a marker for **muscle damage because as the cell is damaged it spills out of cell**

Question 42

Discuss the differences underlying whether scar formation/fibrosis or would healing will predominate after injury? If fibrosis predominates what impact will that have on healing from scar formation

Answer 42

if the **ECM is intact** and the damage is contained to the cell then would healing can occur. This is due to the **scaffold** that the ECM provides for proliferating and migrating cells, establish polarity of cells, blood vessel formation If it is not then scar formation will predominate. If fibrosis occurs then contracture of the wound due to the transdifferentiation of **myofibroblasts which express SMC a** and can bind to mysosin to form SM Myofibroblasts form focal adhesions that bind to the extracellular matrix via fibronectin and is reinforced by **type I collagen,** which has high tensile strength

Question 43

function of sarcoglycans

Answer 43

connecting the muscle fibre cytoskeleton to the extracellular matrix, preventing damage to the muscle fibre sarcolemma through shearing forces.

Question 44

What would these IHC targets indicate? * Dystrophin: * LaminA/C: * Sarcoglycans: * Merosin(Laminin2 subunit): * Tropomyosin: * Desmin:

Answer 44

* Dystrophin: Duchenneand Becker muscuslardystrophy * LaminA/C: Limb Girdle muscular dystrophy 1B * Sarcoglycans: Limb Girdle muscular dystrophy 2C-2F * Merosin(Laminin2 subunit): congenital muscular dystrophy * Tropomyosin: Nemilinemyopathy * Desmin: desminstorage myopathy

Question 46

what does histochem staining such as MyofibrillarATPase and NADH-tetrazolium reductase indicate

Answer 46

remember difference between IHC and hictochem * MyofibrillarATPase: reflects myosin heavy chain activity at high and low pH * NADH-tetrazolium reductase: reflects mitochondrial activity