10. Physiology of Muscle & NMJ Flashcards
Muscle spindle - Describe structure of muscle spindle and innervation
Spindle - collect 10 special fibre - enclosed nit in CT capsule
called intrafusal fibre - disting main musce
Spindle aranged paralle w/ fibres
2 type intrafusal fibre
1 nucelar bag
2 nuclear chain
innervation nuclear bag fivre
Ia primary afferent
Y efferent
B efferent
Inerv - cont pg 233
What muscle spinde monitor
Reflex control muscle legnth
respond length and rate change
Pattelar tendon reflex
Stretch reflex - monosynaptic SC reflex
1 Tap stretch quad
2 Spindle stretch - stim annulospiral ending nuclear bag and chain
3 AP travel Ia to synapse alpha motor - innervate muscle
4 Stim neuro - afferent contraction of quad - maintan muscle length - overcome stretch
5 Tap finished + muscle contracted - spindle no longer stretch
Ia sensor output decrease - aefferent discharge decrease - muscle return to preexist
Inhbi antagonist
recpirpoca innerv
what is A Y linkage
Increased A efferent discahrge - increased Y efferent discharge
Shortening spindle - as contract
Effect - sensitivity of muscle spindle to change in stretch maintain during contraction
Golgi tendon
Sens organnet collection locate in tendon
feedback inhibtoy loop control rate and force contraction
nerve fibre golgi organ make up Ib / sensory fibre
Stim golgi - if muscle stretch or contract strongly
activates inverse stgrech reflex - inhib internuerone inhib alpha motor neuroes to muscle
Weaken cntract
remove stim golg apparturs - autogeni inhib
not stim passive strech
regulate force contract
prevent damge d/t over vig contract
Physiology of NM tmission
What is structure of nicotinic receptor at NMJ
Nic rec Ligand ion
span post junc membrane
pentaganol array - 5 sub
a b d e
two a - contain ach binding site
clin site for nmbd
How is Ach synthesised and metabolised
Produced Choline - nerve terminal - rxn cataylsed choline aceylase
ach store vsicle - nerve term
after release - broken down acetylcholinsterase
chol recycle - taken up resued
What is an EPP
Post jxn membrane - End plate
Normal RMP -90mV inside
BInd Ach - both A - open and rpid influx Na
alter membrane - potential post jnction - end plate potentaion
If reach -50
Cause depol surr muscle membran - propagated A
What is a miniature EPP
siGNLE VESCILE FUSE - DISC CONT -
SMALL AMT ACH - POST JUCN TO DEPOL .5-1Mv - Mepp _ Not suffic threshold
Normal seq eents - response AP reach term
1 Ca permeability - prejunc - greatly increase
2 Influx Ca - triggers fusion vesicles - - membrane
d.c ACH contents in cleft -
3 Ach bdown achesterase
- some bind prejunction nic rec - pos feedback
sml amt bind a subunut post junc
4 Chanell open Na - cause EPP less negative
5 suffic - recp activated - entra Na suffic decrease ->threshold - 50mV
Causes Depo - initi porpagated AP - surround membrane
Signle AP - release 60 vescile - each 10000 molec ACH
no vescile - per impulse w. repeat stim - decrease
Not ever AP - resuslts exocyotsis
Ca trigger- exo very rapid - 1msec
Bdown Chesterase - rapid terminates pot
Recycline chole
Gap Jxn similar to NMJ?
Connect betwen cytoplasm - adjacent cell permit - rpaid tfer dpol cell to cell
passage ion and other small molecules
Electrical conduction more rapid - than at NMJ
doesnt requre delay -
Gap jxn - myocard cell heart - allow depol thru
functional synitium
Adjacent muscle skell - seperate connective tissue
depol - not travel skeletal to adjacent
Gap jxn - connexcion
6 subunit - thru chnaell membarne
Structure muscle overlap
Z disc - M line H zone I band A band
What is a motor unit
Single anterior horn a motor neuro
axon
all fibers it innervates
smallest amt contraction occur response stim - contract all fibre - fxn unit contraction
Number fibres in unit varies
Fine movemnte - small motor unit
Large muscle back - large no fibers
Outline mech respons muscle contrx in skel muscle
Sliding filamet hypotehsis
Sliding thin and thick filament
formation x ling actin myosin = pull
X link - break small amt shortening - actin reforms cross w/ next - futher shorening
Each cycle shorten muscle 1%
Continue reapeadtly - cause shortening
Sequence - excitation motor neurone -> contraction muscle fiber
Excitation contraction coupling
AP - travels nerve ach - rel synapse = bind to postjxn msucle end plate
Result depo - end plate = end plate potential = depol adjacent muscle membrane
Threshold 55 - reached surround - muscle AP occurs - propagated over whole muscle mebrane
traecls t tubule - activate Volt gated L type Ca (dihydropyridine rec)
2 effect -
1 Ca enter cytoplasm - Ca chanell
2 Charge movement
Charge movement = openng Sarco Ca rel (ryanonide rec)
Cyoplasmic Ca - diffuses to thick and thin
Ca ind to Trop C - thin filaments
Interact Trop 1 + tropomysin = move away expose sites actin where myosin head bind
Actin and myosin form cross link -
Sliding filament - wered hydrolysis - Atp by atpase activity myosin head
Whats the thin filament
Whats the thick
Thin - Actin tropomyosin troponin
Thick - Myosin
How is it different in cardiac muscle
Depol - spread spec muscle cell in conducting sys then spread cell to cell
(muslce- nerve AP to each muscle cell - then endplat)
Role Volt Ca - Sim - Ca enter ECF - rel Ca from Sr
Duration depol = lOng 150-250 (short 5-10msec)
Muscle spindle - Not present (present and important in reg contrcat
Invol control v voluntary
What process causes termination of contraction
Persists until Cyto Ca fall - ca rel trop C - actin no longer avail interact myosin head
Rapid pump Ca - via Ca Mg atpase
back SR
Ca - diffuses to terminal cisternae - adjacnet T tubles - ready another contraction
relax - ATP use process
Smooth muscle
Lacc cross striation= actin myosin not arranged as regulary
Extracell source Ca - excite contract couple
DIfferent biochem event - excite contract couple * calmodulin)
DIfferent location fxn
More sensitive to circ chem mediator
Tend contract response increase tension
plasticity
Describe contract SM v Msk
Entry Ca
Plasticirt
Vary tension - visceral SM at given length
Stretched - contracts tension develop changed w/ time - despite constant length
What is latch bridge mechanism
Some circ SM - myosin remains attached actin despite fall cyto Ca - resul sustain contract
Diff type sm
Mult unit - iris
Visceral - casular gut myometrium
Whats calmodlin
Intracell Ca vind prote
4 ca bind domian
can act 5 diff calmod dep kinase
act my light chain kin = phosphorylation msoin - conseq initiation contracton
NO + SM
Vascular tone - effects Vasc sm
local - highl reactive free rad
short t1/
Prod endo larg - + nitric ox synthase
diff to VSM _ stim GC
CGMP = relax VSM
major determ basal rest tone vsm
also inhib plt aggreg + adhesion
Types of skeltal muscle
What are types fibre
Fast
slow
Slow - omit uncommon - extraocullar muslce -
respond sux diff vs twich
dont produec prop ap
dont response rapdiyl - stim many
innerv - grpp like nerve ending not end plte
ending distrib whole muslce
respond nerbe stim - tonic contraction - rather twitch
Fast fatigable fibre
Type IIb/ fast glycolytic / white muscle
White musle - resp fast twich response but rapidly fatigue
rlax reapdily - 7.5-10msc
fine skill movement (hand / ex oc muscle)
Slow fatigue resistant
Type I fiber / Slow ox fiber / red muscle
Respond slowl dont fatigue easily
100 ms
Muscle back - posture `
Fast fatigue resistant
Type IIa / fast oxid
uncommn human`
Red v white
Red - red pigment myoglobin
Fast - low myoglob, low mitochond, myosin atpse fast , high level glyco enz
Slow - high myog cont high mito content , slow myosin atpase low glyoclytics en
Conseq- fast fatige low ox capacity high glycolytic
= able fxn anaerboically short period
I - high ox acpicty high mito + myo
aerobic
