Intro to Muscle Physio Flashcards Preview

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Flashcards in Intro to Muscle Physio Deck (15)
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1

Skeletal Muscle

Striated
Multinucleated
Voluntary
Not self-stimulating (motor units stimulate)
Fast Contracting
Not rhythmic
Highest energy requirement
Fatigues Easily

2

Cardiac Muscle

Only in heart
Mononucleated
Striated
Involuntary
Branching of cells and intercalated discs
Self-stimulating
Rhythmic Contractions
Doesn't Fatigue

3

Smooth Muscle

Mononucleated
Involuntary
Not Striated
Self-stimulating
Lowest energy requirement
Rhythmic Contractions
Doesn't Fatigue

4

Motor Unit

Made up of: alpha motor neuron and the muscle cells it innervates
Each individual muscle fiber is only connected to/controlled by ONE alpha motor neuron.
Recruit nearby motor units for a larger contraction
Fire in ALL OR NONE fashion

5

Sarcomere

Basic unit of striated muscle fibers
Z line --> Z line
Contains 2 protein filaments, Thick (myosin) and Thin (actin)

6

A-Band

The length of thick (myosin) fibers
Myosin and actin
DOES NOT SHRINK DURING CONTRACTION

7

I-Band

Sits between A-bands (only actin fibers and Z-disc)
Shortens during contraction

8

H-Zone

Space between adjacent actin filaments (myosin only)
Part of A band that doesn't have overlap of filaments
Shortens during contraction

9

Titins

Elastic filaments that anchor myosin to Z-line (look like little springs)

10

Excitation-Contraction Coupling

Converting an electrical stimulus (Action potential) to a mechanical response (contraction) at NMJ

11

Steps of Excitation-Contraction Coupling

1. Motor neuron action potential reaches synapse
2. Ca+ enters synapse via voltage-gated channels
3. Acetylcholine released from synapse to bind to muscle surface receptors
4. Na+ enters muscle cell
5. Local current between depolarized end and adjacent muscle plasma membrane
6. Muscle fiber action potential initiation
7. Porpogated AP in muscle plasma membrane
8. AP to the T tubules
9. AP triggers Ca+ release from Sarcoplasmic Reticulum
10. Ca bind to troponin which clears actin binding sites (moves tropomyosin)
11. Myosin (active state) binds to actin
12. Power stroke- myosin pulls actin filaments towards center of sarcomere
13. ATP binds to myosin, myosin releases actin and is back into active "cocked" state

12

Muscle contraction cycle can continue as long as:

1. Muscle is activated
2. ATP is available
3. Physical limit of sarcomere shortening has not been reached

13

Cardiac Muscle Details

Ca+ sources from SR (like skeletal) AND L-type calcium channels (extracellular fluid)
Desmosomes along intercalated disks to allow for mechanical stress of heart beat
Gap junctions allow for electrical conduction via pacemaker cells
AEROBIC RESPIRATION why heart is sensitive to hypoxia (stops in absence of O2)
Large mitochondria
High myoglobin content (store O2)

14

Smooth Muscle Cells

Spindle-shaped without sarcomeres
Actin attach obliquely to cell wall and dense bodies in cytoplasm.
Contract towards center
Ca+ from SR, Extracellular Fluid, AND mitochondria
LACKS TROPONIN

15

Relaxation of Smooth Muscle

DOES NOT always happen when Ca+ levels decrease
1. Dephosphorylation of myosin via light chain phosphatase
2. dissociation of Ca+ calmodulin complexes