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Physiology > L17, L18, L19, L20 Muscles (not all info! - see drawings) > Flashcards

L17, L18, L19, L20 Muscles (not all info! - see drawings) Flashcards

1
Q

what is isometric contraction?

A

muscle develops tension, but DOES NOT SHORTEN
cannot lift objective
example - pushing palms of hands together

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2
Q

what is isotonic contraction?

A

muscle SHORTENS while pulling a constant LOAD (AFTERLOAD)

weight of load unchanged, muscle tension is constant!

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3
Q

define preload

A

the muscle resting length prior to contraction

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4
Q

what is preload determined by

A

stretch of the muscle

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5
Q

when you increase length, what happens to preload

A

increase

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6
Q

what is the length tension relationship

A

amount of tension a muscle generates depends on how stretched it is before it is stimulated to contract

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7
Q

what are the 3 measurements of tension that can be made as a function of resting length (preload)

A

passive tension
active tension
total tension

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8
Q

what does the speed of shortening depend on?

A

afterload

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9
Q

what is passive tension?

A

tension developed by stretching muscle to different lengths

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10
Q

what is active tension?

A

active force developed when muscle contracts

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11
Q

what is total tension

A

active + passive

tension when muscle is stimulated to contact at different preloads

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12
Q

active tension is proportional to what

A

the number of cross bridges formed

*it is max tension when there is an max overlap of thick and thin filaments = max crossbridging!

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13
Q

what happens to active tension when you increase passive tension?

A

decrease

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14
Q

when are maximal muscle contractions achieved?

A

when muscle fiber is at optimal length

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15
Q

what is the velocity of shortening affected by

A

load

resting muscle length (preload)

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16
Q

what happens to velocity when you increase preload to optimum

A

increase

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17
Q

what happens in a muscle contraction

A

a single AP
release calcium
a single twitch

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18
Q

if a muscle fiber is restimulated after it has completely relaxed, the second twitch is the ___ magnitude as the first twitch

A

same

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19
Q

if a muscle fiber is restimulated before it has completely relaxed, the second twitch is _____ which results in___

A

added to the first twitch

summation

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20
Q

is a muscle fiber is stimulated so rapidly that it does not have an opportunity to relax at all between stimuli, _____ occurs

A

tetanus - max sustained contraction

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21
Q

what happens to relaxation time as stimuli are repeated at rapid interval?

A

shorter and shorter until tetanus = no relaxation time!

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22
Q

what is muscle fatigue

A

loss ability for muscle to generate force

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23
Q

what can cause muscle fatigue?

A 
nerve (nerve fatigue)
muscle cells (metabolic fatigue)
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24
Q

what happens with nervous fatigue

A

after a period of max contraction, nerve signal reduce in frequency and the force generated by contraction diminishes - no pain = muscle “stops listening” and stops moving

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25
Q

an increase in tension reflects accumulation of what

A

calcium in cytosol

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26
Q

what is the major mechanism for adjusting strength of contraction in skeletal muscle?

A

adjust frequency of AP traveling down motor neurons to muscle fibers

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27
Q

what is another way to control muscle contraction besides adjusting frequency of AP?

A

recruitment of motor units and fibers

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28
Q

what is muscle force dependent on

A

number of contracting fibers

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29
Q

what are the similarities between skeletal and cardiac muscle?

A
  • both have sarcomeres with z disks
  • sarcomeres made of thick and thin filaments (iwth tropomyosin and troponin)
  • sliding filament model + crossbridging
  • T tubules
  • excitation contraction coupling (AP –> tension)
30
Q

what are the major differences between skeletal and cardiac muscle?

A
  • sarcoplasmic reticulum is not as well developed in cardiac cells
  • t tubule system runs in both transverse and longitudinal directions
  • cells function as a syncytium
  • cell joined at intercalated disks
  • cells held together by desmosomes
  • cell connected by gap junctions
  • cells are branches to form a network
  • muscle fibers are morphologically different in different areas of the heart
31
Q

where does most of the Ca2+ come from if the sarcoplasmic reticulum isn’t well developed?

A

extracellular

32
Q

what is calcium induced calcium release?

A

a biological process whereby extracellular calcium is able to activate calcium release from intracellular Ca2+ stores (e.g. endoplasmic reticulum or sarcoplasmic reticulum)
occurs in cardiac muscle cells

33
Q

why can the heart never develop tetany?

A

the long refractory period will not allow for it

- still can get treppe and summation though

34
Q

what is the resting length/left ventricular end diastolic volume (preload)?

A

length of muscle fibers at end of diastole just before contraction

35
Q

what is starlings law of the heart?

A

the greater the end diastolic volume (preload), the greater the ventricular pressure that can be developed ==> greater the contraction!

36
Q

cardiac muscles is less ___ than skeletal muscle

A

distensible

when stretched extensively = damage to tissue

37
Q

how do you change the strength of contraction?

A
  1. change EDV (preload)

2. change cytosolic [Ca2+] = cardiac contractility (inotropism)

38
Q

what is contractility?

A

intrinsic ability of myocardial cells to develop force at a given muscle length - correlated directly with [Ca2+] - without changing the muscle length

39
Q

how do you change contractility?

A
  1. neurohumoral factors - NE increases sarcolemma permeability to Ca2+
  2. increasing the frequency of contraction = treppe
40
Q

what does the tension generated by a skeletal muscle depend on?

A
  1. properties of individual muscle fibers
  2. properties of motor units
  3. recruitment of motor units
41
Q

what are the different types of muscle fibers?

A 
slow oxidative (type 1) - red - marathon
fast oxidative-glycolytic (type IIa) - red
fast glycolytic (Type IIb) - white - sprints
42
Q

what does muscle fiber type depend on?

A

the nerve the innervates the fiber

muscles are a mix of fiber types but one type dominates over others

43
Q

how do you increase the strength and speed of contraction?

A

increase the amount of Ca2+
change the length of muscle fibers
change the frequency of stimulation (intra Ca2+)
size of muscle fibers (hypertrophy)
number of muscle fibers in motor unit (hyperplasia)
recruitment of motor units
ADJUST THE FREQUENCY OF AP TRAVELING DOWN A MOTOR NEURON TO A MUSCLE FIBER

44
Q

what systems supply ATP energy for muscle contraction?

A

phosphocreatine
glycogen
glucose, fatty acids, amino acids

45
Q

what is an immediate source of ATP for muscle

A

creatine phosphate

46
Q

what is the main source of ATP when O2 is absent?

A

anaerobic metabolism - glycolysis ==> pyruvate -> lactic acid

47
Q

what is the main source of ATP when O2 is present?

A

aerobic metabolism - oxidative phosphorylation - fueled by glucose, FA, aa from food!

48
Q

when does oxygen debt remain until?

A

until excess lactic acid is metabolized into CO2 and H2O or converted to glucose in liver

49
Q

are there actin and myosin filaments in smooth muscle?

A

yes

50
Q

what layers do smooth layers generally present in?

A

circular layer - squeeze/dilate

longitudinal layer - stretch or shorten

51
Q

how are the actin and myosin filaments arranged in smooth muscle?

A

actin filaments radiate from dense bodies

myosin filaments between actin - look at picture!

52
Q

how are dense bodies in smooth muscle attached to one another?

A

by intracellular protein bridges - serves as Z disks

53
Q

what appearance does smooth muscle take on once it is contracted?

A

globular appearance

54
Q

what muscles are examples of multiunit smooth muscle

A

iris
ciliary m.
vas deferens
piloerector m.

55
Q

are AP common in multiunit smooth muscle?

A

no - fibers are too small

56
Q

how do multiunit smooth muscles contract?

A

ANS stimulation - varicosities - which hold NT ACh and NE = local depolarization (“junctional potential” => spreads over fibers = contraction

57
Q

what muscles are examples of unitary smooth muscle?

A 
Gi tract
bile ducts
bladder
ureter
uterus
blood vessels
58
Q

do AP occur in unitary smooth m.?

A

yes - muscle fibers depolarize simultaneously before AP occurs - nerve impulses spread via gap junctions

59
Q

describe a spike smooth muscle action potential

A

typical- elicited by an external stimulus (electrical stim, hormones, stretch, spontaneously)

60
Q

describe a plateau smooth muscle action potential

A

uterus, ureter, vascular smooth.
repolarization delayed up to 1 sec due to Ca2+ channels

self excitatory - AP elicited without extrinsic stimulation (GI wall)

61
Q

describe a slow wave smooth muscle action potential

A

(pacemaker waves) = low oscillation of RMP - do not reach threshold unless strong enough

if slow wave potential reaches threshold trains of action potential are generated - rhythmical contractions

interstitial cells of Cajal - pacemakers for the electrical and contractile activity of smooth muscle

62
Q

where does Ca2+ come from in smooth muscle contractions?

A

extracellular!

63
Q

what does Ca2+ bind to in smooth muscle?

A

calmodulin

64
Q

describe a phasic contraction

A

twtich like shortening followed by relaxation

65
Q

describe a tonic contraction

A

force is sustained for long periods - ability to maintain force of contraction with decreased numbers of activated crossbridges greatly reducing levels of energy consumption (ATP turnover)

66
Q

what type of contractility or tone does smooth m. exhibit (important)

A

continuous low level

67
Q

arteriole contract ____ throughout life

A

tonically - sustained contraction of a muscle

68
Q

how is the length tension relationship in smooth muscle different from skeletal muscle?

A

smooth m. - can develop tension over a greater range of lengths - allows smooth m. to develop tension even with relatively large increases in organ volume - stomach, bladder etc.

69
Q

what channels are involved in smooth m. that increase cytoplasmic Ca2+ and promote contraction?

A

v-g- Ca2+ channels - opens with AP depolarization
L-g Ca2+ channels - receptor mediated - hormones, NT
IP3-gated SR Ca2+ channels- receptor mediated - hormones, NT
stretch-activated channels
leak channels

70
Q

what processes of smooth m. decreased internal Ca2+ and promote relaxation?

A

Ca ATPase pump - 2
Ca2+/Na+ exchanger
Na+/K+ ATPase pump

71
Q

what is Raynaud’s phenomenon?

A

skin discoloration (upon temp or emotional changes) due to abnormal spasm of vascular smooth muscle in peripheral tissues - diminished blood supply to local tissues

turn white - dimished blood supply
turn blue - prolonged lack of oxygen
turn red - blood vessels reopen = flushing

Physiology (16 decks)

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