Lecture 12: Muscle Types Flashcards
Smooth muscle features
Involuntary, unitary or multiunit. Can be an individual cell too.
Unitary vs multiunit smooth muscle
Aka myogenic/visceral (uni) vs neurogenic/vascular (multi). Unitary smooth muscle responds and acts as one, while multiunit is closer to a 1:1 ratio of axons to cells.
Individual cell smooth muscle
Myofibroblasts: MSC-derived, roles in wound healing
Myoepithelial cells: epithelium-derived, surround glands and help squeeze out secretions
Cardiac muscle features
-Striated
-Sarcoplasmic cone where filaments bend around central nucleus
-Gap junctions and fascia adherens intercalated discs connecting cardiomyocytes
-Some cardiac conducting cells with fewer myofilaments
Skeletal muscle features
-Parallel and perpendicular arrangements
-Striated
-Adjacent myofibrils bind to cell membrane via intermediate filaments
-Fibrils anchored to costameres via dystrophin
Parallel arrangement of skeletal muscle
1 fascicle has several myofibers
1 myofiber has many myofibrils
1 myofibril consists of many repeating sarcomeres
1 sarcomere is made of thick/thin myofilaments
Perpendicular arrangement of skeletal muscle
Z-lines made of α-actinin, binding actin via nebulin
M-lines made of myomesin + C-protein; binds titin + myosin
3 types of skeletal muscle
- Oxidative slow twitch Type 1 (red)
- Glycolytic fast twitch Type IIb (white)
- Mixed Type IIa
Sarcolemma
Skeletal muscle cell membrane
Myofiber
Basic unit of skeletal muscle; formed from syncytium of several myocytes
Myocyte
Developmental pre-fusion muscle cell
Myosatellite cell
Muscle SCs contained within the external membrane
CT investments of skeletal muscle
External membrane separating sk. muscle fibers from CT
Ext. memb. connects to endomysium around 1 fiber
Perimysium surrounds 1 fascicle
Epimysium surrounds entire muscle vs surrounding tissue
Skeletal muscle neurological features
-Junctional folds to increase AChR numbers at NMJ
-Muscle spindles in parallel
-Golgi tendon organs in series
Muscle spindle
Muscle stretch sensor, composed of bag + chain fibers. Has γ motor neurons to alter sensitivity. Sensory nerve fibers start @ bag+chain surface
Golgi tendon organ
Muscle tension sensor (in series), located between muscle fibers/tendon. Primarily assoc. w/ reflexive muscle responses
Caveolae
Endocytic vesicles that shuttle Ca++ to be sequestered in the SR; key protein caveolin
Cardiac SR dyad
1 transverse tubule + 1 terminal cistern
Skeletal muscle SR triad
2 terminal cisternae + 1 t-tubule
Dense bodies
Aka dense plaques. Anchoring points for sm. muscle actin. Dense bodies bind cytoskeletal intermediate filaments; desmin (visceral muscle) and vimentin (vascular muscle)
Caveolin
Targets caveolae to cholesterol-rich regions of cell memb. (lipid rafts) and forms lattice to pull in the bleb of membrane.
Pericytes
SCs for vascular smooth muscle, can wrap individual capillaries and may regulate vascular permeability + BBB
Myocardial endocrine cells
Mostly found in atria; contain granules of Atrial Natriuretic Protein which decreases body fluid, lowering BP.
Features of cardiac conducting cell
Usually larger with more gap junctions, more glycogen, and fewer myofibrils
White muscle PAS stain
White muscle contains lots of glycoproteins and so is stained red by PAS
Skeletal muscle development path
MSC -> myoblasts -> 1° myotubes -> 2° myotubes in ext. memb. of 1° -> separation into additional fibers. Some myoblasts persist as quiescent myosatellite cells.
Skeletal muscle tendon anchoring
Anchoring region is folded with the tendon to maximize interactions parallel to the direction of force
