Synpatic Transmission And EC Coupling Flashcards
What is synaptic transmission?
Site where electrical signal from one excitable cell is communicated to another
Can be electrical or chemical
Describe electrical synaptic transmission
Uncommon in mammals
Best example is between cardiac myocytes using gap junctions
Describe chemical synaptic transmission
Utilizes a NT diffusing across the synaptic cleft and binding to a receptor
Can be excitatory or inhibitory
Presynaptic cell can signal one or many post synaptic cells
Post synaptic cell can receive signals from one or many presynaptic cells
What chemical is used at the neuromuscular junction?
ACh
A presynaptic axon at the neuromuscular junction can innervate how many cells?
As few as 1 or many muscle cells
A post synaptic (muscle) cell at the neuromuscular junction can receive signals from how many cells?
Only one presynaptic axon
At the neuromuscular synapse an AP travels from what to what?
From spinal cord via myelinated motor neuron axon to synapse on one or more muscle fibers
One synapse per fiber
What is the specialized synaptic region of the neuromuscular synaptic transmission?
Motor end plate
After a synapse occurs what happens next in the neuromuscular synaptic transmission?
ACh is released in response to Ca entry
Binds to ACh (nicotinic) receptors on muscle membrane
Opens ion gates initiating an AP
Summarize excitation/contraction
AP travels to motor end plate causing Ca channels to open
Entry of Ca causes ACh vesicles to release contents into synaptic clefts
ACh causes opening of Na channels
Entry of Na causes depolarization and generation of an AP
In skeletal muscle the AP causes DHP receptor to physically alter the state of what?
Underlying ryanodine receptors (RyRs) causing the Ca channels to open
What do ryanodine receptors on skeletal muscle cause?
Ca channels of SR open and Ca diffuses to troponin component of actin
Ca/troponin complex causes tropomyosin to pull of of binding sites of actin
What is the thick/myosin filament comprised of?
A bundle of myosin threads
Two protein strings wind together to form the myosin molecule
Describe the structure of a myosin filament
Each myosin molecule has a heavy chain comprised of a protein chain which coils with its companion and ends in a bulbous hinged appendage
Bulbous end has two light chain molecules associated with it to complete the myosin molecule structure
Bulbous end of heavy chain + light chain form the head of myosin
What are thin filaments comprised of?
Four chains of two types of molecules
Two F actin chains comprised of G-actin molecules are wound together with two tropomyosin chains
When troponin binds with Ca what does this cause?
The tropomyosin to expose the binding sites of actin
Describe the association between actin and myosin in muscle
Actin molecules are attached at their ends and project from both directions towards each other
Myosin molecules are distributed b/w the actin
Myosin heads form potential crossbridges b/w actin and mysoin
Each mysoin is associated with how many actin molecules?
6 actin molecules
What are some binding proteins associated with a sarcomere?
Nebulin, titan and dystrophin
What is nebulin?
A long molecule which assists with aligning actin
What is titan?
A large, long and elastic protein associated with myosin and anchors it within the sarcomere
It also acts to return a stretched sarcomere to its resting length
What is dystrophin?
A large protein that connects the muscle cell cytoskeleton including actin to the ECM
Myosin will remain bound to actin until what occurs?**
Until ADP is released and ATP is bound to myosin
What is peripheral fatigue?
Contraction requires the availability of ATP
Stored sources mainly as phosphocreatine
Derived from glycolysis thus producing lectin acid derived from ox phos in mitochondria (requires constant supply of O2)
