Lecture 12: Muscle Types

Question 1

Smooth muscle features

Answer 1

Involuntary, unitary or multiunit. Can be an individual cell too.

Question 2

Unitary vs multiunit smooth muscle

Answer 2

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.

Question 3

Individual cell smooth muscle

Answer 3

Myofibroblasts: MSC-derived, roles in wound healing
Myoepithelial cells: epithelium-derived, surround glands and help squeeze out secretions

Question 4

Cardiac muscle features

Answer 4

-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

Question 5

Skeletal muscle features

Answer 5

-Parallel and perpendicular arrangements
-Striated
-Adjacent myofibrils bind to cell membrane via intermediate filaments
-Fibrils anchored to costameres via dystrophin

Question 6

Parallel arrangement of skeletal muscle

Answer 6

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

Question 7

Perpendicular arrangement of skeletal muscle

Answer 7

Z-lines made of α-actinin, binding actin via nebulin
M-lines made of myomesin + C-protein; binds titin + myosin

Question 8

3 types of skeletal muscle

Answer 8

1. Oxidative slow twitch Type 1 (red)
2. Glycolytic fast twitch Type IIb (white)
3. Mixed Type IIa

Question 9

Sarcolemma

Answer 9

Skeletal muscle cell membrane

Question 10

Myofiber

Answer 10

Basic unit of skeletal muscle; formed from syncytium of several myocytes

Question 11

Myocyte

Answer 11

Developmental pre-fusion muscle cell

Question 12

Myosatellite cell

Answer 12

Muscle SCs contained within the external membrane

Question 13

CT investments of skeletal muscle

Answer 13

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

Question 14

Skeletal muscle neurological features

Answer 14

-Junctional folds to increase AChR numbers at NMJ
-Muscle spindles in parallel
-Golgi tendon organs in series

Question 15

Muscle spindle

Answer 15

Muscle stretch sensor, composed of bag + chain fibers. Has γ motor neurons to alter sensitivity. Sensory nerve fibers start @ bag+chain surface

Question 16

Golgi tendon organ

Answer 16

Muscle tension sensor (in series), located between muscle fibers/tendon. Primarily assoc. w/ reflexive muscle responses

Question 17

Caveolae

Answer 17

Endocytic vesicles that shuttle Ca++ to be sequestered in the SR; key protein caveolin

Question 18

Cardiac SR dyad

Answer 18

1 transverse tubule + 1 terminal cistern

Question 19

Skeletal muscle SR triad

Answer 19

2 terminal cisternae + 1 t-tubule

Question 20

Dense bodies

Answer 20

Aka dense plaques. Anchoring points for sm. muscle actin. Dense bodies bind cytoskeletal intermediate filaments; desmin (visceral muscle) and vimentin (vascular muscle)

Question 21

Caveolin

Answer 21

Targets caveolae to cholesterol-rich regions of cell memb. (lipid rafts) and forms lattice to pull in the bleb of membrane.

Question 22

Pericytes

Answer 22

SCs for vascular smooth muscle, can wrap individual capillaries and may regulate vascular permeability + BBB

Question 23

Myocardial endocrine cells

Answer 23

Mostly found in atria; contain granules of Atrial Natriuretic Protein which decreases body fluid, lowering BP.

Question 24

Features of cardiac conducting cell

Answer 24

Usually larger with more gap junctions, more glycogen, and fewer myofibrils

Question 25

White muscle PAS stain

Answer 25

White muscle contains lots of glycoproteins and so is stained red by PAS

Question 26

Skeletal muscle development path

Answer 26

MSC -> myoblasts -> 1° myotubes -> 2° myotubes in ext. memb. of 1° -> separation into additional fibers. Some myoblasts persist as quiescent myosatellite cells.

Question 27

Skeletal muscle tendon anchoring

Answer 27

Anchoring region is folded with the tendon to maximize interactions parallel to the direction of force