Smooth and Cardiac Muscle Flashcards
What type of muscle has intercalated discs?
cardiac muscle
what type of muscle has no striations?
smooth muscle
cardiac muscle appearance
-elongated branching cells, joined by intercalated discs
-single central nucleus typical, some cell binucleate
-striated fibers
cardiac muscle contractility
-involuntary muscle, spontaneously contractile, autonomic modulation
-sliding filament mechanism of contraction
cardiac muscle organization
-prominent endo-, peri, and epimysium
-arrangement of contractile proteins into sarcomeres
smooth muscle organization
-endo-, peri-, and epimysium
-bound together into highly irregular, branching fascicles, specialized for prolonged contraction with low force
-no sarcomeres
smooth muscle appearance
-small cells, fusiform shape
-single central nucleus
-surrounding network of collagen
-no striations
-nucleus spiral shaped when contracted
smooth muscle contractility
-involuntary
-inherent contractility- rhythmic, wave-like contractions independent of neurological stimulation; can respond to local changes & hormones
-cells shorten and broaden on contraction
smooth muscle Z-disc equivalent
dense bodies- provide attachment site for actin
dense bodies
-in smooth muscle
-lacks troponin to control myosin binding
-uses calmodulin instead
calmodulin
binds Ca & activates myosin cross-bridging in smooth muscle
caveolae
structure of smooth muscle cell membrane that allows for calcium diffusion
smooth muscle contraction mechanism
-thin filaments of actin associated with tropomyosin
-myosin (thick filaments) only bind to actin if one chain is phosphorylated
-on membrane excitation, free Ca ions released into cytoplasm & bind to calmodulin
-calmodulin activates an enzyme that phosphorylates myosin allowing it to bind to actin
-energy efficient (uses little ATP)
smooth muscle innervation
-influenced by autonomics (along with hormones and local metabolites)
-most smooth muscle has dual sympathetic & parasympathetic innervation
in the gut, sympathetic stimulation of smooth muscle is:
inhibitory
in the gut, parasympathetic stimulation of smooth muscle is:
stimulatory
smooth muscle single unit
-tonic smooth Mm
-fibers contract as a unit
smooth muscle multi-unit
-phasic smooth Mm
-individual muscle fibers contract independently
diad
-present in cardiac muscle
-composed of one T-tubule & one cisterna of ER
-located @ Z-disc
intercalated discs
-fuses two cardiac Mm cells together
-unique to cardiac muscle
-allows synchronous contractions
-want heart to function as single cell
intercalated discs made of:
desmosomes, fascia adherens & gap junctions
cardiac muscle contraction mechanism
similar to skeletal muscle
-depolarization of sarcoplasm travels through T-tubules down to sarcoplasmic reticulum (takes longer in cardiac Mm)
-calcium channels (located in walls of T-tubules & sarcoplasmic reticulum) open & release Ca ions into sarcoplasm
-Ca allows myosin & actin to form cross-bridges & slide past each other
-excitation & contraction passed on to neighboring cells via intercalated discs
can cardiac muscle proliferate?
yes
components of conducting system of the heart
-SA node
-AV node
-Bundle of His
-Purkinje fibers
cardiac conduction system
-all structures consist of highly modified myocytes that coordinate conduction
-joined by extensive gap junctions
-larger than surrounding myocytes –> conduct impulses faster
cardiac conduction system staining
paler staining than surrounding myocytes due to higher glycogen content
