Muscle

Question 1

NMJ
motor endplate:
motor unit:

Answer 1

endplate: where NT communicates with muscle and binds to a receptor

motor unit: a neuron can branch and cause contraction of multiple muscle fibers when it fires

Question 2

EPPs VS EPSP

Answer 2

EPP: NT released over a large surface to many receptors –> contraction, no summation required

Question 3

Mechanics of muscle contraction
Tension:
Load:

Answer 3

Tension: force exerted on object by contr. muscle - holding (water skiing)
Load: force exerted on muscle by object

Question 4

Mechanics of muscle contraction
Isometric contraction:
Isotonic contraction:

Answer 4

Isometric: muscle develops tension, but does not shorten
iso= same metric=length

Isotonic: muscle change length, load remains, (curl)
Concentric: shortening
Eccentric: lengthening negative - maintain tension, consequence of external force

Question 5

Isometric

Answer 5

A: Force on hand by weight = Force of muscle(holding), agonist(biceps) tense but no shortening
B: fist: contract biceps and triceps

Question 6

Isotonic

Answer 6

Force of muscle is more than the weight (lifting) - contraction of muscle + shortening (agonist), antagonist (triceps is relaxed)

Question 7

Twitch

Answer 7

response of muscle to AP
Isometric: latent period -> time for chemical work
and contraction: building up tension

Isotonic: longer latent period: tension has to exceed weight = ISOMETRIC after that it is an ISOTONIC CONTRACTION with shortening

Question 8

what is the L0 in ISOMETRIC contraction

Answer 8

optimal muscle length for maximum force, most myosion heads attached to thin filaments + most possible space to slide

Question 9

ATP source in muscle

Answer 9

Myosin ATPase - contraction provides ADP +P
Creatin adds P to ADP + P

Glycolysis
Oxid. Phosphorylation: needs mitochondria, O2, fatty acids, amino acids, is slower

Question 10

Muscle fatigue

Answer 10

after repetitive stimulation followed by fatigue, Rest overcomes fatigue but fatigue reoccurs sooner

Question 11

Tetanus

Answer 11

repetitive stimulation (without relaxing) leads to maintain contraction - most of our movements (standing up, holding something) - fused tetanus

Question 12

Types of muscle fibers
by velocity of shortening

Answer 12

fast/type II: high rate of ATP splitting
slow/type I: low rate

Question 13

Types of muscle fibers
by ATP pathway

Answer 13

oxidative/red (lot of myoglobin, O2, lot of blood supply) 36-38ATP

glycolytic (white): few mitochondria, more glycogen, and glycolysis, fast energy but not much (2ATP p Glucose)

Question 14

Factors determining muscle tension

Answer 14

Tension created by each fiber:
AP frequency
fiber length (length-tension relation), fiber diameter (glycolytic most)
fatigue

-) number of active fibers:
number of fiber/ motor units (branching, neuron controls multiple fibers)
number of active motor units

Question 15

Skeletal muscle

Answer 15

Striated (from sarcomer),
Somatic nervous system (ACh - nicotinic receptor)
very long, multiple nuclei, unable to divide, tropomyosin + troponin

Question 16

Smooth muscle- sourrond viscera (visceral)

Answer 16

in blood vessel, GI tract and resp system
autonomic: sympathetic (NE-alpha beta rec + parasymp n. system (ACh - musac. receptor)
single nucleus
divide
tropomyosin and no troponin

Question 17

Smooth muscle contraction !!!

Answer 17

Ca binds to Calmodulin -> calmodulin activates myosin light chain kinase -> takes on P from ATP and phosphorylates myosin light chain, which can now cross-bridge with actin filament

myosin light chain phosphate removes P from myosin light chain (is always active-constitutive!!)

Question 18

smooth muscle tone

Answer 18

maintain a low level of basal cross-bridge activity, through certain amount of Ca

Question 19

how are smooth muscles controlled
inhibitory or excitatory

Answer 19

autonomous nerve system (Symp, parasymp)
can be inhibitory or excitatory

Question 20

what are varicosities in smooth muscle- mostly on autonomous nerves

Answer 20

they also release NT, stimulated by depolar. -> Ca comes in and cause vesicles to fuse with membrane and release of NT

just like on the postsynaptic cleft,

Question 21

how are cardiac muscles able to work (pump) as a structural unit and functional unit

Answer 21

structural: through desmosomes - tight together

functional: gap junctions, if one part is excited, the “neighbor” will too

Question 22

Source for Ca in cardiac muscle (also for smooth muscle)

Answer 22

Depolar. -> opening of L type(long-lasting) Ca channel in T-tubules -> Ca walks into cytosol first and then activates ryanodine receptor

Ca binds on Ca receptor (ryanodine) external of SR, causing to open up Ca channel out of SR into the cytosol –> causing contraction

most of Ca from SR

Question 23

Unique features for cardiac muscles

Answer 23

actin-linked muscle (not ready) = tropomyosin covers actin

amount of Ca is not enough to activate all actins

long lasting depolar. caused by L receptors (Ca comes in) -» no summation of AP, no tetanus for heart muscles, so that it can relax in-between to pump

Question 24

Shortening velocity in Isotonic contraction

Answer 24

Speed of shortening is related to the load (force of weight)
with 0 weight there is Vmax, if weight is too heavy no shortening occurs

Question 25

Calcium sources of smooth muscles

Answer 25

1. Plasma membrane Ca(+2) channels
2. Sartoplasmatic reticulum

Question 26

Types of smooth muscles (single unit, multiunit)

Answer 26

single unit smooth muscle: gap junctions, can be activated by stretching: GI, uterus, small diameter blood vessels

multiple unit smooth muscle: no gap j., no activation by stretching: lungs, large arteries