cardiac muscle and smooth muscle

what’s the functional component of a myofibril?

sarcomere

what do intercalated disk contain? what’s their function?

desmosomes

gap junctions

acts as z lines - anchor site for actin in the last sarcomere of the cell

desmosomes function

found in intercalated disks

permit two adjacent cells to attach and creating long strings of cardiac muscles

gap junctions function

found in intercalated disks

allows cells to communicate

endomysium has two functions in cardiac muscle 

• CT covers individual cell

• supports capillaries between cardiac cells

what does it mean by the sarcoplasmic reticular being “leaky” ?

Ca 2+ ions constantly leaking out, initiating contractions over and over

how is the internal rhythm of the heart modulated?

by autonomic (sympathetic & parasympathetic) external input to the cardiac conduction system (SA, AV nodes, Purkinje fibers)

what is part of the cardiac conduction system?

SA, AV nodes and Purkinje fibers

why is the contraction of the heart rhythmic?

DUE TO LEAKY SACOPLASMIC RETICULUM

can you identify;

• cardiac muscle cells 

• nucleus 

• intercalated disks 

• striations showing evidence of myofibrils and sarcomeres 

can you identify the structures

white arrows - pointing at intercalated disks

capillaries found on the upper right side - red blood cells flowing by

nucleus - circle in the middle

dotted lined - cardiac muscle cell

• notice it forming two branches - skeletal muscle WOULD NOT do this

identify structure green arrows are pointing

lipofuscin

what are lipofuscin?

turnover of cellular material in lysosomes

accumulates with aging as cardiac muscle cells and most skeletal muscle cells do not undergo mitosis

what are you looking at?

cardiac muscle cell transverse section 

notice the blood vessel found embedded in endomysium 

nucleus of cell found in the middle — opposite of skeletal muscle 

what type of shape does smooth muscle cell have?

fusiform shape

how does the nucleus of the smooth muscle cell look?

elongated in the center of the cell

how are adjacent cells in smooth muscle connected to each other?

gap junctions

multiunit

each smooth muscle cell is innervated directly by a nerve

unitary

only a few smooth muscle cells are innervated, transmit depolarizing signal to adjacent cells via gap junctions

do smooth muscle cells have sarcomeres?

no, but rather as a lattice that crosses through the cell

still contain actin and myosin*, DO NOT CONTAIN MYOFIBRIL

dense bodies

of a smooth muscle cell

protein complexes where contractile units are anchored at the cell wall and where they meet inside the cell

what type of contraction does a smooth cell have?

slow prolonged contraction

contraction shortens the cells in more than one direction

name the indicated structure

smooth muscle cell

notice its fusiform shape and elongated nuclei

what type of connective tissue are smooth muscle cells surrounded by?

reticular fibers 

very THIN CT

what’s required to visualized the CT that surrounds smooth muscle cells?

extra stain; Masson trichrome stain

-reticular fibers (CT) is so thin that is not able to be visualized by regular H&E stain