skeletal muscle physiology I Flashcards
motorneuron=
neurons that innervates muscle fibers
motor unit=
single motorneuron and muscle fibers it innervates
small motor units=
fine activities
large motor units=
gross control
1st event at neuromuscular junction
AP propagated to presynaptic terminal, VOLTAGE-GATED CA2+ CHANNELS OPEN, Ca2+ permeability increases, Ca2+ flows in
2nd event at neuromuscular junction
CA2+ CAUSES RELEASE OF ACH stored in synaptic vesicles
3rd event at neuromuscular junction
Ach diffuses to post-synaptic membrane-called motor end plate
4th event at neuromuscular junction
ACH BINDS TO NICOTINE RECEPTORS, channels opens, Na+ moves in, K+ moves out
5th event at neuromuscular junction
motor end plate depolarizes from -90 mV to -50 mV- THIS IS THE END PLATE POTENTIAL (EPP)
- single vesicle of Ach produces miniature end plate potential (MEPP)
6th event at neuromuscular junction
depolarization spreads from motor end plate to muscle fiber cells
7th event at neuromuscular junction
EPP stops when Ach degraded by ACETYLCHOLINESTERASE (AchE)
botulinum toxin
- produced by Clostridium botulinum
- blocks release of Ach from presynaptic terminals
AChE inhibitors
- prevent degradation of ACh in synaptic cleft
- treat myasthenia gravis -> Ach receptors blocked by antibodies
physical characteristics of skeletal muscle
striated appearance, under voluntary control
skeletal muscle organization
- muscle fiber (muscle cell or myocyte) contains MYOFIBRILS
- groups of muscle fibers= FASCICULUS
muscle cells innervated by…
motorneurons
events between AP in muscle fiber and contraction are called…
excitation-contraction coupling
what are myofibrils?
- basic unit of muscle cells
- surrounded by sarcoplasmic reticulum
- composed of actin, myosin, and titin -> thick and think filaments (myofilaments- repeat into sarcomeres)
what is a sarcomere?
- repeating thick and thin filaments along the myofibril
- occur between adjacent Z lines (disks)
- contractile unit
Light band=
I band
- think filament= actin
- Z disks
dark band=
A band
- thick filaments= myosin
- darkest region at end of A band= overlap -> overlap of actin think filaments with myosin thick filaments -> where force of contraction starts
bare zone=
H zone
- center of sarcomere, no thin filaments
M line=
- dark-staining protein
- links thick filaments
thick filaments=
- myosin: heavy chains and light chains
- 1 pair of heavy chains: form tail
- 2 pairs of light chains: form 2 globular heads -> have actin binding site & ATP binding site
think filaments=
- actin: 2 strands twisted
- tropomyosin: runs along groove of twisted actin -> BLOCKS MYOSIN-BINDING SITE ON ACTIN
- troponin: complex of troponin T, troponin I and troponin C at regular intervals along tropomyosin
troponin T
attaches entire complex to tropomyosin
troponin I
inhibits interaction of actin & myosin by covering binding site
troponin C
Ca binding protein
what do cytoskeletal proteins do
help align thick and thin filaments
- dystrophin
- titin
- nebulin
dystrophin=
anchors myofibril scaffold to the cell membrane
titin=
centers thick filaments in the sarcomere
nebulin=
sets length of thin filaments
muscle cell surrounded by…
sarcolemma
sarcolemma has invaginations=
transverse (T) tubules
- extending into muscle cells -> carry depolarization from motor end plate to cell interior -> contact SR
myofibrils surrounded by…
sarcoplasmic reticulum -> regulating Ca in cytosol
sarcoplasmic reticulum
- stores Ca2+ using the SERCA pump (Ca2+ ATPase)
- Ca2+ bound to CALSEQUESTRIN in SR
- Ca2+ release channel= RYANODINE RECEPTOR
