Mod 7 Skeletal and Smooth Muscle Histology

Objective: 1. Identify and describe the cellular characteristics and the mechanism of contraction in the 3 muscle types. 2. Identify muscle microanatomy in microscopic images. 3. Describe the organization of contractile proteins in a sarcomere and the sliding filament theory. 4. Compare and contrast between the 3 types of muscles

What are the 4 types of tissue?

epithelial, connective, muscle, nerve

What are the 3 types of muscle tissues?

skeletal, cardiac, smooth

Each microfilament strand is assembled from bead-like subunits, called?

G-actin (G = globular)

What type of muscle is the tongue?

skeletal

What is the G-acting polymerized into?

F-actin (F = fibrous)

What is an F-actin?

two strands wrap around each other to form the microfilament

Is skeletal muscle voluntary or involuntary?

voluntary

What is the function of skeletal muscle?

locomotion/movement

Is cardiac muscle voluntary or involuntary?

involuntary

Is smooth muscle voluntary or involuntary?

involuntary

Where are smooth muscles?

tube like hollow organs (artery, GI tract, reproductive tract)

Why does the GI tract and fallopian tubes have partial contractions?

conduct peristalsis (smooth muscle push contents out)

What are microfilaments made up of?

actin

Are these all the same (microfilament = actin filament = F-actin)

yes

What does F-actin interact with to move on contractions?

myosin filaments

What do myosin and actin form?

the contractile ring

How do all kinds of muscle contractions occur?

sliding of actin filaments over myosin filaments

What does muscle have a lot of?

smooth ER

What do muscle cells not have?

any ribosomes on their surface

What is the function of smooth ER?

storage and release of calcium in skeletal and cardiac muscle

What does calcium do in the muscle?

activate contractile mechanisms

What is the smooth ER called in muscle?

sarcoplasmic reticulum

What is the cytoplasm of a muscle called?

sarcoplasm

What is the plasma membrane of a muscle called?

sarcolemma

What is skeletal muscle that makes it show very evident striations?

multinuclei

What is the contraction like for skeletal muscle?

quick and strong

Which muscles has cells that are branched?

cardiac

What does it mean for cardiac cells to have branches?

one cell will have nucleus that is often surrounded by glycogen inclusion bodies

How does cardiac muscle use glycogen?

for energy

What does the connections between the cardiac muscle cells look like?

small bands

What are the small bands in cardiac muscle called?

intercalated discs

What are smooth muscles contractions like?

not very strong involuntary contrations

What is the shape of smooth muscle cells?

fusiform (football/spindle) and lack striations

How are smooth muscle cells arranged?

staggered

how is skeletal muscle cells arranged?

rows

Where does skeletal muscle come from?

embryonic mesenchymal cells

What do muscle fibers look like?

long multinucleated

What are the skeletal cells that differentiate (specialize) called?

myoblasts

What is the process of the contractile proteins, actin and myosin forming?

embryonic mesenchymal cells → myoblasts → multinucleated tube-like structure → striated skeletal muscle fiber → forms contractile proteins myosin and actin

What makes skeletal muscle?

myoblast

What are the myoblasts that stay dormient (reserves) called?

satellite cells

Where can you find satellite cells?

attached to muscle fiber on the outside of the sarcolemma

What is the function of satellite cells?

muscle repair after damage by undergoing cell division and making new fibers when needed

What is the outer most layer (a dense connective tissue) that the muscle is covered in called?

epimysium

Where is epimysium?

under deep fascia

What does epimysium do?

connect bone to muscle

What is the epimysium layer made of?

fascicles

What is a fascicle covered by?

perimysium

What is perimysium

thin dense connective tissue

Which is thinner, epimysium or perimysium?

perimysium

What is inside the fascicles?

numerous skeletal muscle fibers/skeletal muscle cells

What is each skeletal muscle fiber covered in?

endomysium

What are both mysium laters containing?

collagen 1 and 3 and fibroblasts

What supplies the epimysium?

large nerves, blood, and lymph vessels

What supplies the endomysium?

small blood vessels and nerve

What supplies the perimysium?

nerves, blood vessels, and lymph vessels

What is the order of layers from outside in?

Epimysium

Skeletal muscle

Perimysium

Fascicle

Endomysium

Muscle fiber/ cell

When shown a skeletal muscle transverse section, what should you see?

perimysium, endomysium, and epimysium

What is the “P” in this picture

perimysium

What is the En in the picture?

endomysium

How many muscle cells - muscle fibers?

3

What do the light nucleus mean?

leptochromatic = highly active

What has become clear in this image?

striations (I and A bands)

What do you find when you cut through a muscle cell?

myofibrils

What is the I band consist of?

actin

What does the A band consist of?

mostly myosin (plus actin)

What is the middle lighter zone in the A band called?

H zone

What is the H zone divided by?

M line

Draw out the structure of myofibril

explain the closer look at the lighter striation.

light bands are I bands and divided in the middle by a darker line called Z disc

What are the two other proteins actin is always associated with?

tropomyosin and troponin

What is actin made of?

G-actin

What does G-actin form once polymerized

F-actin

What does every G-actin monomer have?

myosin binding site

What is the myosin binding site of the action monomer covered by

tropomyosin (when muscle is not activated)

What is the role of tropomyosin?

cover and expose binding site

What makes up the thin filament?

F-actin + tropomyosin + troponin

What does troponin bind to?

tropomyosin

How many subunits does troponin have?

3 (TnT, TnI, TnC)

What are the subunits of troponin?

TnT, TnC, and TnI

What does TnT do

bind to tropomyosin

What does TnC do

bind to Ca+

What does TnI do

mediates the interaction between actin and myosin

What is another name for myosin?

thick filament

What is myosin made of?

two tails and two globular heads

Where do the myosin heads face?

outward

What does it mean to say myosin is a motor protein?

uses ATP to do its function

What binding sites does myosin have?

actin binding site and ATP binding site

Sarcomere

z to z disc

What is thick filament called?

myosin filament

What is thin filament called?

actin filament

Where are the actin chains attached?

at Z disc

Where do the myosin bundles span?

entire A band

What forms the I band?

the part where actin doesn’t overlap myosin

What forms the H zone?

the part where myosin doesn’t overlap actin

sacromere in TEM images

muscle breakdown

How many subunits do tropinin have and what are they?

3 (TnT, TnI, TnC)

What is this process called: A series of binding and unbinding events of the myosin heads to the F-actin causes the sliding of Myosin bundles over the actin fibers, causing contraction of the sarcomere. It looks like the myosin heads are walking over the actin fibers.

sliding filament theory. 

What is the t-tubule and terminal cisterna together called?

triad