Skeletal Muscle Physiology. Flashcards
In Muscle characteristics, what does excitable mean?
Responds to stimuli by producing action potentials.
In Muscle characteristics, what does contractile mean?
Can shorten, thicken.
In Muscle characteristics, what does extensible mean?
Can stretch when pulled.
In Muscle characteristics, what does elastic mean?
can return to original shape after contractile or extension.
what are the functions of muscle?
1) movement.
2) posture, facial expression.
3) heat production.
4) protection of viscera- body wall.
A muscle fiber is innervated by at least ____ neuron(s)
one.
how many muscle fibres does one neuron approximately innervate?
about 150.
what is a motor Unit?
a single motor neuron + ALL the muscle fibres it innervates.
Describe the structure of a Neuromuscular Junction:`
- presynaptic cell (neuron) with ACh (nt) in vesicle
- postsynaptic cell (muscle) membrane (sacrolemma) - specialized region with ACh receptors (= motor end plate)
- two membranes separated by a synaptic cleft.
what is rigor mortis?
“stiffness of death”
Your myosin heads are still activated even after death.
ATP production gradually stops after death (because there is no O2, so what happens?
intracellular calcium increases from ECF, SR (there is a leakage) which causes the binding sites to be exposed (cross bridegs form. The mtosin heads cannot be released from actin (becasue there is no new ATP produced. therefore the muscle stays contracted.
What happens when extracellular Ca++ is low? (like durring pregnancy, lactation)
Na++ enters muscle fibre and causes contraction\cramps
what are some conditions\ substances that can cause flaccid paralysis?
Myasthenia gravis, Cucare poisoning, Botulism.
What are the Steps of a muscle contraction at the molecular basis.
1) Excitation of muscle.
2) Excitation-contraction Coupling
3) Contraction
what is the excitation of a muscle fibre?
Sacrolemma is depolarized causing an EPP causing an AP.
AP propagates down T-tubules to deep within fibre.
Explain the excitation-contraction Coupling ?
AP in T-tubules cause release of calcium (coupling agent) from terminal cisternae or Sacroplasmic reticulum via mechanically gated channels.
Ca++ binds to toponin
Troponin-tropomyosin complex moves out of the way of binding sites on actin.
What is a cross bridge formation?
Activated myosin heads attach to binding sites on actin.
Describe the Thin Filament Mechanism.
Sacromeres shorten shorten (Hzone and I band shorten and A band stays the same length)
Myofibrils shorten which makes the muscle shorten
thin (actin) and thick (myosin) myofilaments remain the same length
what is ATP necessary for in relaxation?
1) cross bridge release
2) activation of myosin (ATP — ADP + Pi) + power stroke
3) pump Ca++ into SR
4) fibre Na+/K+-ATPase activity
What was Cucare poisoning used for and what did it do?
It prevents ACh from binding to receptors and was used in surgery.
What is Botulism?
- improper canning (clostridium botulinium)
- prevents exocytosis of ACh
- used t control uncontrolable blinking, crossed eyes
- used in cosmetic surgery to prevent wrinkles (Botox)
What is muscle tension?
the force exerted by a muscle fibre determined by # of cross bridges formed.
what does more tension do to the size of a muscle fibre?
Makes it thicker.
what does an increased number of myofibrils\ fibre do to the size of a muscle fibre?
makes it thicker.
