Microanatomy Muscle/Bone/Cartilage

Block 6

other names for muscle cells

myocytes, myofibers

what shape are muscle cells

spindle shaped

what is the embryological origin for muscle cells

mesoderm

T/F: muscle cells are specialized cells capable of contraction to produce movement

true

sarcoplasm

cytoplasm of muscle cells

what two substances can be found in the sarcoplasm

glycogen, myoglobin

sarcolemma

plasma membrane of muscle cell

sarcoplasmic reticulum

highly specialized smooth endoplasmic reticulum of a muscle cell

T/F: sarcoplasmic reticulum regulates sodium flow

false

regulates calcium flow

which types of muscle tissue are cross striated

skeletal muscle, cardiac muscle

how does the structure and length of cardiac muscle compare to skeletal muscle

cardiac muscle is shorter in length but has a branching structure

which type of muscle do the following measurements most align with:

A) diameter 10-100 um, length 40mm-50cm

B) diameter 15 um, length 100um

C) diameter 6-8 um, length 20-40um

A - skeletal muscle

B - cardiac muscle

c- smooth muscle

the length of smooth muscle, normally 20-40 um long, can reach up to 1mm in length in what organ

uterus

what is the shape of smooth muscle cells

fusiform, spindle-shaped

skeletal muscle accounts for what % of body weight

50%

what 2 muscles are considered some of the strongest muscles of the body

tongue muscle

masseter muscle

T/F: skeletal myocytes are uninucleate

false

multinucleate, contain multiple peripherally-located nuclei

where in the cell might you see skeletal myocyte nuclei

peripherally-located

when cut in longitudinal section, what distinguishing feature can you observe in myocytes

striations

which muscle cell types are voluntary and which are involuntary

voluntary: skeletal

involuntary: smooth, cardiac

most skeletal muscles insert on what structures of the body

bones of the skeleton

voluntary sphincters in what regions of the body are made of skeletal muscle

GI tract, urinary systems, and muscles in the esophagus and tongue

is skeletal muscle contraction fast or slow

fast

what are myotubes

multinucleated tubes formed when mesenchymal cells / myoblasts align and fuse during skeletal muscle development

what step of skeletal muscle development accounts for the peripheral location of skeletal muscle cell nuclei

when myotubes differentiate into functional myofilaments, the nuclei are displaced against the plasma membrane

what are the cells that do not differentiate and remain mesenchymal stem cells

satellite cells

satellite cells have function in what process

muscle repair

Epimysium

dense irregular connective tissue surrounding muscles

Fascicles

small bundles of muscle cells

Perimysium

surrounds fascicles

Are myofibrils visible with light microscopy

no

Endomysium

Reticular fibers surrounding individual myocytes

Myofibers

cylindrical multinucleated cells

Myofibrils

contractile elements of myofibers/myocytes, composed of repeating myofilament sections (actin and myosin), which creates light and dark bands

What are the contractile proteins of myofilaments

actin, myosin

What are the regulatory proteins of myofilaments

tropomyosin

What 2 bands are responsible for striated appearance of skeletal muscle

A bands (dark) and I bands (light)

What bisects each I band

z-line

(Protein disc)

Where do actin filaments anchor

z-line

What are the functional units of myocytes

sarcomeres

T/F: Z lines of sarcomeres draw closer together at full contraction

true

In which band do thick and thin filaments overlap

A band

In which band is there only thin actin filaments

I band

During contraction, which bands shorten

I band, because actin filaments slide over myosin filaments and shorten the I band

T/F: muscle cells mediate motion by converting chemical energy into mechanical energy

true

Chemical energy = ATP

What oroteins hold acting and myosin in position in the myofibril

desmin, tropomyosin, troponin

I bands are longer or shorter when skeletal muscle is stretched

longer

in the sliding filament model, each sarcomere shortens, the I band shortens, and thin filaments slide past thick filaments. Does the myofilament length stay the same or shorten?

myofilament length stays the same

what are myofibrils made of

myosin and actin myofilaments

what structure stores and releases calcium in a myocyte

sarcoplasmic reticulum

what are terminal cisterna

the expanded ends of sarcoplasmic reticulum

what are transverse T-tubules

deep tubular finger-like invaginations of the sarcolemma of skeletal muscle, which creates an anastomosing network of tubules

are T tubules present in skeletal muscle? cardiac muscle? smooth muscle?

skeletal and cardiac muscle

not present in smooth muscle

the invaginations of the T-tubules allow what to occur regarding the muscle contraction process

depolarization of membrane to quickly penetrate to cell interior to allow calcium release from sarcoplasmic reticulum

cardiac cells have how many nuclei and where in the cell are they located

uninucleate, one central nucleus

T/F: cardiomyocytes do not have cross striations

false

intercalated discs in cardiac cells include what two structures

gap junctions

desmosomes

do myocardiocytes have sarcoplasmic reticulum

yes

cardiac myocytes have mitochondria up to __% the cell volume

20%

what brown pigment can be found in cardiac muscle cells

lipofuscin

function of intercalated discs

attach cardiac muscle cells to each other, providing strength and giving them the ability to act as a synctium

why is the heart muscle not a true synctium

a true syncytium would have multinucleate cells, like skeletal muscle cells

which element of intercalated discs is the transverse element and which is the longitudinal element

transverse - desmosome

longitudinal - gap junction

desmosomes in intercalated discs function

anchor, strong attachment

gap junctions in intercalated discs function

communication between cells, passage of ions, propagate electric impulses

what are the 2 types of cardiomyocytes

contractile

conductile (purkinje fibers)

T/F: purkinje fibers are modified cardiac muscle cells that form cardiac nodes and fibers involved in impulse conduction

true

number of nuclei in purkinje fibers

1 or 2

myofibrils in purkinje fibers are sparse or dense and where in the cell are they

sparse

restricted to periphery of cell

T/F: purkinje fibers are arranged in groups, and the cells are bigger and stain paler than contractile cardiomyocytes

true

number of nuclei in smooth muscle cells and the location of the nuclei in the cell

one centrally located nucleus

T/F: smooth muscle has striations

false

smooth muscle cells do not have myofibrils. Actin and myosin myofilaments are present, but not organized into striation pattern

in smooth muscle cell, what structures act as anchors for myofilaments

cytoplasmic dense bodies

T/F: smooth muscle cells do not contain desmosomes or gap junctions

false

they do have desmosomes and gap junctions

T/F: smooth muscle cells do not have T-tubules and the sarcoplasmic reticulum is poorly developed

true

shape of smooth muscle cells

spindle shaped (fusiform)

what surrounds a smooth muscle cell

basal lamina and reticular fibers

T/F: smooth muscle cells have parasympathetic and sympathetic innervation

true

where is single (unitary) smooth muscle found

in visceral organs

in single smooth muscle, cells contract independently or as a syncytium

as a syncytium

T/F: single smooth muscle has sparse nerve innervation but cells communicate via gap junctions

true

where is multi-unit smooth muscle found

in the iris of the eye

T/F: multi-unit smooth muscle contraction is precise

true

how is multi-unit smooth muscle innervated

independent innervation of each myocyte so contract individually (no gap junctions)

name four functions of smooth muscle cells

1. peristalsis - wave-like contractions

2. vascular dynamics - contraction alters blood flow and regulates blood pressure

3. propulsion

4. secretion

in what organs does smooth muscle function for propulsion

urinary bladder, uterus

example of a body sytsem where smooth muscle functions in peristalsis

GI tract

what are the 2 layers of tunica muscularis in the wall of luminal organs

inner circular layer

outer longitudinal layer

shape of the nucleus in dense bodies

oval-shaped

smooth muscle cells can shorten by up to __% during contraction

80%

in a contracted state, how does the nucleus of smooth muscle appear

corkscrew appearance

what embryological origin for myoepithelial cells

ectodermal origin

location of myoepithelial cells

salivary glands, mammary glands, lacrimal glands

T/F: myoepithelial cells are similar to smooth muscle and contain actin/myosin

true

what shape are myoepithelial cells

basket-like

what do myoepithelial cells enclose

clusters of glandular cells

what embryological origin do myofibroblasts come from

mesoderm

myofibroblasts function

wound contraction

where are satellite cells located

between basal lamina and sarcolemma

do satellite cells retain mitotic potential

yes

therefore can accomplish some regeneration / repair